| Kim E, Skjetne R and Høyland KV (2023), "Quadruple Helix Framework for Sea Ice Monitoring: Next Steps", In ESA’s 2023 Workshop on Coastal and Marine applications of SAR (ESA SP-565). Longyearbyen, Svalbard, Norway, May, 2023. |
| Abstract: The Arctic - one of the most desolate and sparsely populated areas on our planet - plays a crucial role in regulating the world's climate. Despite Arctic’s importance for the Earth’s climate, this area remains severely under-monitored and not well known to the broad public. Few humans are directly involved in monitoring (this is mostly done using remote sensing tools). As urbanization continues, there is limited human engagement, and participation in monitoring of nature and a further disassociation with it. In view of this challenges, we readopted a quadruplex helix framework for monitoring of sea ice. The framework relates sea ice knowledge at different spatial and temporal resolutions to each other (i.e., remote sensing, in-situ scientific measurements, citizen science, and indigenous knowledge) |
BibTeX:
@conference{ekim23A,
author = {Kim, E. and Skjetne, R. and Høyland, K. V.},
title = {Quadruple Helix Framework for Sea Ice Monitoring: Next Steps},
booktitle = {ESA’s 2023 Workshop on Coastal and Marine applications of SAR (ESA SP-565)},
year = {2023},
url = {https://eo4society.esa.int/training_uploads/seasar2023/Seasar2023_Theme_4_Sea_Ice_Retrievals_part1.pdf}
}
|
| Panchi N, Kim E, Skjetne R and Hughes N (2023), "Assist Observations 2017‑2021: Uncertainty, Comparison with Sea Ice Charts, and Ice Concentration from Deep Learning Models", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Melbourne, Australia, June, 2023. Vol. Volume 6: Polar and Arctic Sciences and Technology, pp. V006T07A005. |
| Abstract: The Arctic Ocean is undergoing significant changes, leading to a surge in research and commercial activity in the region. As a result, the number of manual observations of ice conditions, known as ASSIST observations, has dramatically increased in recent years. These observations provide valuable information on the state of the Arctic ice cover and have been used as a source of ‘ground truth’ for other satellite products. However, their manual nature raises concerns about the associated uncertainty. To address these concerns, the present study evaluates the uncertainty of total ice concentrations, partial ice concentrations, ice types, and ice thicknesses reported in ASSIST observations. First, the study compares ASSIST observations from 2017 to 2021 against sea ice charts from the Norwegian Meteorological Institute, the US National Ice Center, and the Arctic and Antarctic Research Institute. Second, as a test case, the study evaluates simulated ASSIST observations conducted on optical images by an ice expert, three non-experts, and a deep learning model. Results from the comparisons indicate a good agreement between ASSIST observations and the sea ice charts, with 80% of comparisons resulting in a difference of less than ±10% in total ice concentration. Analysis of the remaining 20% reveals high underestimation in summer and overestimation in winter compared to sea ice charts. Groupwise comparison of ice types reveals an accuracy of 50% and a good match between the ice thickness reported by ASSIST observations and ice thickness associated with ice types reported by the ice charts, with 70% of comparisons resulting in a difference of ±10 cm. Results from the inter-comparison of simulated ASSIST observation point to an agreement between experts and novices in simple scenes with a single type of ice and disagreement in the case of complex scenes. |
BibTeX:
@proceedings{npan23A,
author = {Panchi, N. and Kim, E. and Skjetne, R. and Hughes, N.},
title = {Assist Observations 2017‑2021: Uncertainty, Comparison with Sea Ice Charts, and Ice Concentration from Deep Learning Models},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2023},
volume = {Volume 6: Polar and Arctic Sciences and Technology},
pages = {V006T07A005},
url = {https://doi.org/10.1115/OMAE2023-101757},
doi = {10.1115/OMAE2023-101757}
}
|
| Najjaran S, Skjetne R and Godø JMK (2023), "Optimal Energy Management for Zero-Emission High-Speed Passenger Vessels", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Melbourne, Australia, June, 2023. Vol. Volume 5: Ocean Eng., pp. V005T06A036. |
| Abstract: To comply with IMO’s regulations on reduced emissions, the maritime industry is investigating various alternatives to achieve zero-emission high-speed passenger vessels (HSPVs). In this work, optimal loadsharing is studied for a given vessel with a zero-emission hybrid driveline with a fuel cell (FC) and a battery. The further aim is to include this as part of a computation model to assess feasibility of zero-emission solutions for passenger transport connections under study along the coast of Norway. A dynamic programming (DP) algorithm is derived to provide the global optimal solution of the loadsharing problem. This will serve as a benchmark for other and more computationally efficient optimization algorithms to be feasible for runtime applications. Here we formulate an alternative optimal loadsharing model based on a linear program (LP) and compare that to the DP. The proposed LP and DP are applied to a numerical model for an existing HSPV operating along a given route. AIS data is used to extract the route information and power load profile of the vessel. The results demonstrate a step towards an overall methodology for assessing the feasibility of a vessel and an onboard propulsion and power system to allow for zero-emission passenger transport. |
BibTeX:
@proceedings{snaj23A,
author = {Najjaran, S. and Skjetne, R. and Godø, J. M. K.},
title = {Optimal Energy Management for Zero-Emission High-Speed Passenger Vessels},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2023},
volume = {Volume 5: Ocean Eng.},
pages = {V005T06A036},
url = {https://doi.org/10.1115/OMAE2023-104731},
doi = {10.1115/OMAE2023-104731}
}
|
| Reddy NP, Skjetne R and Papageorgiou D (2023), "A Decentralized Droop-Based Power Management System for Ship Power Systems Using Hybrid Dynamical Systems Framework", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Melbourne, Australia, June, 2023. Vol. Volume 5: Ocean Eng., pp. V005T06A032. |
| Abstract: In maritime transport, inspired by the automobile sector, autonomy is gaining traction in parallel with decarbonization. One of the numerous challenges in realizing fully autonomous operation in shipping is to design a resilient and fault-tolerant power system that preserves the survivability of ships during worst-case failures in unpredictable maritime weather conditions. In newly built ships, power systems are designed with a high number of sensors and communication equipment to enable remote control and condition monitoring in real time. In such power systems, the traditional concept of a centralized power management system (PMS) is not reliable during communication failures and cyberattacks. To address this issue a decentralized fault-tolerant droop-based PMS that does not rely on communication between energy sources is proposed. The droop curves are further designed for the derating operation of energy sources and energy storage devices. A ship power system exposed to faults represents a hybrid system that consists of interaction between continuous and discrete states. Hybrid dynamical systems theory is used to model the DC power system and implement the proposed PMS. The normal operation of energy sources, energy storage devices, and shiploads are modeled as continuous dynamics. The faults such as derating operation and disconnection of energy sources, energy storage devices, and shiploads are modeled as discrete events. The results demonstrate that the proposed PMS can keep the system parameters such as DC bus voltage within the limits permissible by class rules during the loss of power generation. |
BibTeX:
@proceedings{nred23A,
author = {Reddy, N. P. and Skjetne, R. and Papageorgiou, D.},
title = {A Decentralized Droop-Based Power Management System for Ship Power Systems Using Hybrid Dynamical Systems Framework},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2023},
volume = {Volume 5: Ocean Eng.},
pages = {V005T06A032},
url = {https://doi.org/10.1115/OMAE2023-102570},
doi = {10.1115/OMAE2023-102570}
}
|
| Dugan SA, Utne IB, Skjetne R, Montewka J, Gil M and Wrobel K (2022), "STPA-based hazard analysis of a ship collision avoidance and stability monitoring system", In 10th European STAMP Workshop and Conf.. Gdynia, Poland, Sept., 2022.
[BibTeX] |
BibTeX:
@conference{sdug22A,
author = {Dugan, S. A. and Utne, I. B. and Skjetne, R. and Montewka, J. and Gil, M. and Wrobel, K.},
title = {STPA-based hazard analysis of a ship collision avoidance and stability monitoring system},
booktitle = {10th European STAMP Workshop and Conf.},
year = {2022}
}
|
| Krata P, Hinz T, Marley MH, Dugan SA, Gil M, Montewka J and Skjetne R (2022), "DSA-inspired assessment of autonomous ships stability during turning maneuver", In Proc. Int. Ship Stability Workshop. Gdańsk, Poland, Sept., 2022. |
| Abstract: Assessing the stability of autonomous ships is challenging due to a lack of crew ensuring situational awareness, experience and good seamanship, which have contributed to safety of navigation to date. Therefore, a comprehensive approach towards evaluation of autonomous ship stability in each phase of operation is required. This problem is raised here with respect to the ship turning maneuver. A Direct Stability Assessment (DSA) inspired approach is applied. Therefore, a series of ship motion simulations are carried out to obtain the dynamic angle of heel for sample operational scenarios and numerous irregular wave realizations to enable identification of a stability failure. An up-to-date 6DoF ship dynamics model is utilized. The simulations account for both the maneuverability and stability characteristics of a vessel. A 56-m long training vessel is used as an example. The simulation results are statistically processed to elicit the maximum instantaneous angle of heel corresponding to a 5% probability of exceedance, to be compared to the assumed threshold. However, the required number of simulations ensuring the required statistical significance of the results remains an open question. |
BibTeX:
@conference{pkra22A,
author = {Krata, P. and Hinz, T. and Marley, M. H. and Dugan, S. A. and Gil, M. and Montewka, J. and Skjetne, R.},
title = {DSA-inspired assessment of autonomous ships stability during turning maneuver},
booktitle = {Proc. Int. Ship Stability Workshop},
year = {2022},
url = {https://hdl.handle.net/11250/3058183}
}
|
| Marley M and Skjetne R (2022), "Mitigating Force Oscillations in a Wave Energy Converter Using Control Barrier Functions", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Hamburg, Germany, June, 2022. Vol. Volume 8: Ocean Renewable Energy, pp. V008T09A089. |
| Abstract: Control barrier functions (CBFs) is a novel feedback control strategy for enforcing safety constraints of mechanical systems. An appealing feature of the CBF method is that the safety objective is defined and enforced independent of the underlying control objective. This enables the merging of CBF-based control with any existing nominal control strategy, by imposing the safety objective as input constraints in a convex optimization problem. CBFs are gaining popularity in the robotics community, in particular for motion control of autonomous vehicles. Yet, limited use of CBFs for mechanical devices such as wave energy converters (WECs) are reported in literature. This paper motivates the use of CBF-based control for constraint satisfaction of WECs, using the Bolt Lifesaver point absorber WEC developed by Fred. Olsen Ltd. as a case study. During initial sea trials of Bolt Lifesaver, large force oscillations were observed in the power take-off unit. The source of oscillations was identified as sudden saturation of the actuator force provided by the generator. Mitigating the undesired response using conventional feedback control is non-trivial, since any such control strategy will attempt to cancel inertia forces, resulting in a reduced stability margin of the system. Using higher order CBF theory, we design a robust controller that ensures safe operation of the device, while minimally interfering with the existing control law optimized for power output. The theoretical results are verified by numerical simulations. |
BibTeX:
@proceedings{mmar22A,
author = {Marley, M. and Skjetne, R.},
title = {Mitigating Force Oscillations in a Wave Energy Converter Using Control Barrier Functions},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2022},
volume = {Volume 8: Ocean Renewable Energy},
pages = {V008T09A089},
url = {https://doi.org/10.1115/OMAE2022-82707},
doi = {10.1115/OMAE2022-82707}
}
|
| Reddy NP, Cai Y, Skjetne R and Papageorgiou D (2022), "Voltage Sensor Fault Detection in Li-ion Battery Energy Storage Systems", In IEEE Transportation Electrification Conf. and Expo (ITEC). Anaheim, California, USA, June, 2022. , pp. 1314-1320. |
| Abstract: Safe and optimal operation of battery energy storage systems requires correct measurement of voltage, current, and temperature. Therefore, fast and correct detection of sensor faults is of great importance. In this paper, model-based and non-model-based voltage sensor fault detection methods are developed for a comprehensive comparison. The residual is generated from the difference of measured voltage and estimated voltage. In the model-based method, the voltage is estimated using an extended Kalman filter (EKF). In the non-model-based method, the voltage is predicted using a recurrent neural network (RNN) with long short-term memory (LSTM). For both methods, a scalar generalized likelihood ratio (GLR) detector is developed to detect changes in the sequence of residual signal data and compared with a systematically computed threshold. The parameters threshold (h) and window-size (M) used in the GLR detector, are computed based on the probability of false alarm (P f ) and probability of correct detection (P d ). The GLR detector demonstrates the ability to effectively detect the voltage sensor fault with a maximum delay of 500 ms for the model-based residual and 200 ms for the non-model-based method. |
BibTeX:
@inproceedings{nred22A,
author = {Reddy, N. P. and Cai, Y. and Skjetne, R. and Papageorgiou, D.},
title = {Voltage Sensor Fault Detection in Li-ion Battery Energy Storage Systems},
booktitle = {IEEE Transportation Electrification Conf. and Expo (ITEC)},
year = {2022},
pages = {1314-1320},
url = {https://ieeexplore.ieee.org/document/9813853},
doi = {10.1109/ITEC53557.2022.9813853}
}
|
| Kim E and Skjetne R (2021), "Artificial intelligence for ship speed management during navigation in the Arctic", In Proc. Int. Conf. Port Ocean Eng. Arctic Conditions. Moscow, Russia, June, 2021. Vol. 26, pp. 6. |
| Abstract: Difficult ice conditions are one of the major threats to ships, shipboard crew, and cargoes carried in Arctic waters. Ship-speed choice is influenced by many factors including the navigational conditions (ice, weather, bathymetry, etc.), the purpose of the voyage, personal preferences of the ship master (and/or the ice pilot) as well as onboard regulations (e.g., ice passport, polar water operational manual). Faults and incidents during navigation in ice (i.e., excessive ship speed) almost always results in ship damage. This can be fixed with the help of electronic environments that are sensitive and responsive to the presence of ice. This work describes AI-infused systems that can capture details of ice conditions around the ship and place them in the context of safe ship speed and ice conditions reporting. The focus is on online sensors-to-service solutions that run in the background and rely on shipboard sensors. Apart from just being AI-infused information systems, some solutions could also be applied to provide an early alert to the user if the user is approaching potentially dangerous ice object(s) at elevated speeds. The presented systems are not tested during real ship operations, but we provide illustrative examples for exploration of the solution space based on Arctic data. Ice navigation is about masters taking decisions and keeping ships and their crew safe. AI is to enhance human performance and not to replace human operators. |
BibTeX:
@conference{ekim21A,
author = {Kim, E. and Skjetne, R.},
title = {Artificial intelligence for ship speed management during navigation in the Arctic},
booktitle = {Proc. Int. Conf. Port Ocean Eng. Arctic Conditions},
year = {2021},
volume = {26},
pages = {6},
url = {https://poac.com/Papers/2021/pdf/POAC21-036.pdf}
}
|
| Marley M, Skjetne R, Basso E and Teel AR (2021), "Maneuvering with safety guarantees using control barrier functions", In Proc. IFAC Conf. Contr. Appl. Marine Systems. Oldenburg, Germany, Sept, 2021. , pp. 370-377. |
| Abstract: Control barrier functions (CBFs) ensure safety of controlled dynamical systems, by restricting the control inputs to render desired sets forward invariant. In this paper we propose a dynamic guidance scheme for autonomous vehicles, using CBFs to reactively generate an obstacle-free trajectory. By implementing the safety constraints on a kinematic guidance level, rather than on a lower-level control layer, we do not need to account for uncertainty in the ship dynamics explicitly. Moreover, for ships with well-proven and resilient control systems, this is an appropriate interface level, since it does not require modification of lower-level feedback control. The guidance scheme is applied to maneuvering of underactuated ships, using a virtual vessel with unicycle dynamics to trace out a feasible trajectory. |
BibTeX:
@conference{mmar21B,
author = {Marley, M. and Skjetne, R. and Basso, E. and Teel, A. R.},
title = {Maneuvering with safety guarantees using control barrier functions},
booktitle = {Proc. IFAC Conf. Contr. Appl. Marine Systems},
year = {2021},
pages = {370-377},
note = {IFAC-PapersOnLine, Vol.54, No.16},
url = {https://www.sciencedirect.com/science/article/pii/S2405896321015202},
doi = {10.1016/j.ifacol.2021.10.118}
}
|
| Marley M, Skjetne R and Teel AR (2021), "Synergistic control barrier functions with application to obstacle avoidance for nonholonomic vehicles", In Proc. American Control Conf.. New Orleans, USA, May, 2021. , pp. 243-249. |
| Abstract: Control barrier functions (CBFs) have recently emerged as a means to ensure safety of controlled dynamical systems. CBFs are suitable for obstacle avoidance, where the CBF is often constructed from the distance and relative velocity between the vehicle and the obstacle. For vehicles required to maintain non-zero forward speed, ordinary (non-hybrid) CBFs cannot ensure safety due to vanishing control authority when the vehicle is oriented directly towards the obstacle. In this paper, synergistic CBFs are proposed, which is an intuitive extension of CBFs using ideas from synergistic Lyapunov functions. A synergistic CBF for obstacle avoidance for nonholonomic vehicles is constructed by shifting the orientations with vanishing control authority. This induces a penalty for traversing the obstacle in the counterclockwise or clockwise direction, where a logic variable is used to determine the preferred direction. The performance of the CBF is illustrated by a case study. |
BibTeX:
@conference{mmar21A,
author = {Marley, M. and Skjetne, R. and Teel, A. R.},
title = {Synergistic control barrier functions with application to obstacle avoidance for nonholonomic vehicles},
booktitle = {Proc. American Control Conf.},
year = {2021},
pages = {243-249},
url = {https://ieeexplore.ieee.org/document/9482979},
doi = {10.23919/ACC50511.2021.9482979}
}
|
| Basso EA, Thyri EH, Pettersen KY, Breivik M and Skjetne R (2020), "Safety-Critical Control of Autonomous Surface Vehicles in the Presence of Ocean Currents", In Proc. IEEE Conf. Control Tech. and Appl. (CCTA). Montrèal, Canada, Aug., 2020. , pp. 396-403. |
| Abstract: Autonomous surface vehicles (ASVs) are safety-critical systems that must provide strict safety guarantees such as collision avoidance to enable fully autonomous operations. This paper presents a unified framework for safety-critical control of ASVs for maneuvering, dynamic positioning, and control allocation with safety guarantees in the presence of unknown ocean currents. The framework utilizes control Lyapunov function (CLF)- and control barrier function (CBF)-based quadratic programs (QPs), and is applicable to a general class of nonlinear affine control systems. The stabilization objective is formulated as a maneuvering problem and integral action is introduced in the CLFs to counteract the effect of unknown irrotational ocean currents. Furthermore, ocean current estimates are constructed for robust CBF design, and analytic conditions under which the estimates guarantee safety are derived. Subsequently, robust CBFs are designed to achieve collision avoidance of static obstacles. The paper concludes by verifying the framework in simulation for a double-ended passenger ferry. |
BibTeX:
@conference{ebas20A,
author = {Basso, E. A. and Thyri, E. H. and Pettersen, K. Y. and Breivik, M. and Skjetne, R.},
title = {Safety-Critical Control of Autonomous Surface Vehicles in the Presence of Ocean Currents},
booktitle = {Proc. IEEE Conf. Control Tech. and Appl. (CCTA)},
year = {2020},
pages = {396--403},
url = {https://ieeexplore.ieee.org/document/9206276},
doi = {10.1109/CCTA41146.2020.9206276}
}
|
| Bjørnø van den Berg M, Lu W, Skjetne R, Lubbad R and Løset S (2020), "Quantifying Icebreaker Performance in Ice Management Operations by High-Fidelity Numerical Simulations", In Int. Offshore (Ocean) and Polar Eng. Conf. (ISOPE). Shanghai, China, Oct., 2020. Vol. I, pp. 824-830. |
| Abstract: In the study presented in this paper, the problem of quantifying the performance of icebreaker operations within ice management (IM) has been targeted, using the capabilities of high-fidelity simulations by a discrete element simulation model. An accurate geometric and dynamic model of the icebreaker IB Oden, as well as the characterization of a realistic multi-domain ice environment, has been numerically modeled within the simulator. The simulator includes features to easily vary parameters such as ice thickness, ice concentration, floe size distribution, and ice drift velocity and direction. The protected structure is modeled as a cylindrical structure, acting as a measurement probe of the ice loads, ice actions, ice-ice and ice-hull friction resulting from various simulated operations and scenarios. In overall, this give us the tools we need to numerically model, with high fidelity, complex icebreaker operations on realistic ice conditions in order to quantify the performance of IM strategies under various scenarios. This can give us better insight into which IM strategies that are effective, thereby enabling better planning and online guidance of icebreaker operations. |
BibTeX:
@conference{jbjo20B,
author = {Bjørnø, van den Berg, M. and Lu, W. and Skjetne, R. and Lubbad, R. and Løset, S.},
title = {Quantifying Icebreaker Performance in Ice Management Operations by High-Fidelity Numerical Simulations},
booktitle = {Int. Offshore (Ocean) and Polar Eng. Conf. (ISOPE)},
year = {2020},
volume = {I},
pages = {824--830},
url = {https://www.onepetro.org/conference-paper/ISOPE-I-20-1271}
}
|
| Bjørnø J, Marley M and Skjetne R (2020), "Guidance Model Representing an Ice Field for Path-Planning in Ice Management", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.., Aug., 2020. Vol. 7 |
| Abstract: In the work presented in this paper, the problem on how to represent a simplified ice field in a guidance model, enabling path and maneuver planning for IM operation, has been studied. The use of B-splines and other basis functions are considered to represent relevant guidance information over the 2D drifting ice field. A weight value is computed and updated at locations that represents broken ice (visited by an icebreaker) versus unbroken ice. The guidance model will ensure that there is a continuous representation of the state of the ice field during the operations. The drifting behavior of the ice field is incorporated into the guidance model. The model will be updated with new (solid) ice that is formed at the beginning of the ice field, and it will continuously be updated in the path where the icebreaker moves. To simulate the maneuvers of the icebreaker, a dynamic model is used, and the ice breaking effect where the ice field is continuously broken into smaller ice floes is included in the model. This representation of an ice field can be used in a path-planning algorithm to determine the icebreaker path in a moving ice environment in order to reduce the ice field into small enough ice floes and reduce the load on the protected structure. |
BibTeX:
@conference{jbjo20A,
author = {Bjørnø, J. and Marley, M. and Skjetne, R.},
title = {Guidance Model Representing an Ice Field for Path-Planning in Ice Management},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2020},
volume = {7},
note = {V007T07A023},
url = {https://doi.org/10.1115/OMAE2020-19117},
doi = {10.1115/OMAE2020-19117}
}
|
| Marley M, Skjetne R, Breivik M and Fleischer C (2020), "A hybrid kinematic controller for resilient obstacle avoidance of autonomous ships", In Proc. Int. Conf. Maritime Autonomous Surface Ship. Ulsan, Republic of Korea, Nov., 2020. Vol. 929, pp. 012022. |
| Abstract: Resilience is an important feature of autonomous systems. To be resilient, a control system must be stable, robust, and safe. This paper explores the use of hybrid feedback controllers to ensure robustness towards uncertainties and disturbances in motion control systems for autonomous ships. Motivated by recent developments in control barrier functions (CBFs) for safe maneuvering of autonomous ships, a CBF-based hybrid kinematic controller for obstacle avoidance is proposed. The controller uses course angle as control input, making it suitable for ships with a limited speed envelope. The performance of the controller is illustrated by simulations, using an underactuated ship as a case study. |
BibTeX:
@conference{mmar20B,
author = {Marley, M. and Skjetne, R. and Breivik, M. and Fleischer, C.},
title = {A hybrid kinematic controller for resilient obstacle avoidance of autonomous ships},
booktitle = {Proc. Int. Conf. Maritime Autonomous Surface Ship},
year = {2020},
volume = {929},
pages = {012022},
note = {IOP Conf. Ser.: Mater. Sci. Eng.},
url = {https://iopscience.iop.org/article/10.1088/1757-899X/929/1/012022},
doi = {10.1088/1757-899X/929/1/012022}
}
|
| Marley M, Skjetne R and Teel AR (2020), "A kinematic hybrid feedback controller on the unit circle suitable for orientation control of ships", In Proc. IEEE Conf. Decision & Control. Jeju Island, Korea (South), Dec., 2020. , pp. 1523-1529. |
| Abstract: This paper presents a hybrid feedback controller suitable for orientation control of ships. A hybrid kinematic controller on the unit circle is constructed from the gradient of a synergistic potential function, which globally asymptotically stabilizes a desired orientation, with yaw rate viewed as control input. While this idea is not new, the potential function is novel and possesses some desired properties. The kinematic controller generates smooth reference signals for the desired velocity and acceleration, except at instances when the controller switches. Continuity of velocity and acceleration is achieved by controlling the yaw rate through a double integrator. Moreover, the velocity and acceleration converge to their desired values exponentially. The resulting closed-loop system is stable, provided the controller gains satisfy mild constraints. This is shown using a hybrid Lyapunov function. |
BibTeX:
@conference{mmar20A,
author = {Marley, M. and Skjetne, R. and Teel, A. R.},
title = {A kinematic hybrid feedback controller on the unit circle suitable for orientation control of ships},
booktitle = {Proc. IEEE Conf. Decision & Control},
year = {2020},
pages = {1523-1529},
url = {https://ieeexplore.ieee.org/document/9304108},
doi = {10.1109/CDC42340.2020.9304108}
}
|
| Park D, Zadeh M and Skjetne R (2020), "DC-DC Converter Control for Peak-Shaving in Shipboard DC Power System via Hybrid Control", In Proc. IEEE Conf. Industrial Electronics and Appl.. Kristiansand, Norway, Nov., 2020. Vol. 15, pp. 681-686. |
| Abstract: For the stable operation of the shipboard hybrid DC power systems, the DC bus voltage should be controlled within the recommended range by the regulations. However, the challenge comes from the load variations, and it makes the main bus voltage fluctuate. This paper proposes a control approach based on hybrid dynamical modeling of the DC-DC converter for the battery interface. In this method, the switching signal of the DC-DC converter is calculated to satisfy the Lyapunov stability criteria, and the reference power of the battery is generated for the peak-shaving of the load changes to stabilize the voltage. The effectiveness of the controller is evaluated with real ship load data which has a transient profile. The performance of the proposed control strategy is presented, and the results show that the proposed method can provide significant advantages in terms of fast and stable control performance, as well as the peak-shaving function by the battery to operate the diesel generators at the best efficiency point. |
BibTeX:
@conference{dpar20A,
author = {Park, D. and Zadeh, M. and Skjetne, R.},
title = {DC-DC Converter Control for Peak-Shaving in Shipboard DC Power System via Hybrid Control},
booktitle = {Proc. IEEE Conf. Industrial Electronics and Appl.},
year = {2020},
volume = {15},
pages = {681-686},
url = {https://ieeexplore.ieee.org/document/9248194},
doi = {10.1109/ICIEA48937.2020.9248194}
}
|
| Thyri EH, Basso EA, Breivik M, Pettersen KY, Skjetne R and Lekkas AM (2020), "Reactive collision avoidance for ASVs based on control barrier functions", In Proc. IEEE Conf. Control Tech. and Appl. (CCTA). Montrèal, Canada, Aug., 2020. , pp. 380-387. |
| Abstract: A reactive collision avoidance method for autonomous surface vehicles based on control barrier functions (CBFs) is proposed. An encounter between the ownship (the vessel that we control) and a target ship is classified, in accordance with the International Regulations for Preventing Collisions at Sea (COLREGs), to be either a head-on, overtake, give-way, stand-on or a safe situation with respect to the ownship. Subsequently, a spatial region is assigned to the target ship based on the classification, and this region is used to define a collision-free set. Based on this, a CBF is formulated to ensure forward invariance of the collision-free set. This CBF can then be applied as an inequality constraint to any guidance, navigation and control system with an optimization-based trajectory tracking or thrust allocation system. The method is verified through simulations and is seen to handle head-on, overtaking and crossing situations with both give-way and stand-on duty in compliance with COLREGs rules 13-15 and 17. |
BibTeX:
@conference{ethy20A,
author = {Thyri, E. H. and Basso, E. A. and Breivik, M. and Pettersen, K. Y. and Skjetne, R. and Lekkas, A. M.},
title = {Reactive collision avoidance for ASVs based on control barrier functions},
booktitle = {Proc. IEEE Conf. Control Tech. and Appl. (CCTA)},
year = {2020},
pages = {380--387},
url = {https://ieeexplore.ieee.org/document/9206340},
doi = {10.1109/CCTA41146.2020.9206340}
}
|
| Reddy NP, Pasdeloup D, Zadeh MK and Skjetne R (2019), "An Intelligent Power and Energy Management System for Fuel Cell/Battery Hybrid Electric Vehicle Using Reinforcement Learning", In IEEE Transportation Electrification Conf. and Expo (ITEC). Detroit, MI, USA, June, 2019. |
| Abstract: Hybrid electric vehicles powered by fuel cells and batteries have attracted significant attention as they have the potential to eliminate emissions from the transport sector. However, fuel cells and batteries have several operational challenges, which require a power and energy management system (PEMS) to achieve optimal performance. Most of the existing PEMS methods are based on either predefined rules or prediction that are not adaptive to real-time driving conditions and may give solutions that are far from the actual optimal solution for a new drive cycle. Therefore, in this paper, an intelligent PEMS using reinforcement learning is presented, that can autonomously learn the optimal policy in real time through interaction with the onboard hybrid power system. This PEMS is implemented and tested on the simulation model of the onboard hybrid power system. The propulsion load is represented by the new European drive cycle. The results indicate that the PEMS algorithm is able to improve the lifetime of batteries and efficiency of the power system through minimizing the variation of the state of charge of battery. |
BibTeX:
@conference{nred19A,
author = {Reddy, N. P. and Pasdeloup, D. and Zadeh, M. K. and Skjetne, R.},
title = {An Intelligent Power and Energy Management System for Fuel Cell/Battery Hybrid Electric Vehicle Using Reinforcement Learning},
booktitle = {IEEE Transportation Electrification Conf. and Expo (ITEC)},
year = {2019},
url = {https://ieeexplore.ieee.org/document/8790451},
doi = {10.1109/ITEC.2019.8790451}
}
|
| Dahl AR, Thorat L and Skjetne R (2018), "Model Predictive Control of Marine Vessel Power System by Use of Structure Preserving Model", In Proc. IFAC Conf. Contr. Appl. Marine Systems. Opatija, Croatia, Sept., 2018. Vol. 51(29), pp. 335-340. |
| Abstract: The paper presents model predictive control (MPC) based on an optimization model drawn from the structure preserving model (SPM) for marine vessel power systems. Three objective functions are proposed to control frequency, transient load and power flow. The objective functions, in addition to a benchmark controller, are applied to a simulated power system. |
BibTeX:
@conference{adah18A,
author = {Dahl, A. R. and Thorat, L. and Skjetne, R.},
title = {Model Predictive Control of Marine Vessel Power System by Use of Structure Preserving Model},
booktitle = {Proc. IFAC Conf. Contr. Appl. Marine Systems},
year = {2018},
volume = {51},
number = {29},
pages = {335--340},
note = {IFAC-PapersOnLine},
url = {http://www.sciencedirect.com/science/article/pii/S2405896318321906},
doi = {10.1016/j.ifacol.2018.09.501}
}
|
| Heyn H-M, Skjetne R and Scibilia F (2018), "Distributed sensing of loads acting against the hull of a stationkeeping vessel in ice", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Madrid, Spain, June, 2018. Vol. 8, pp. 7. |
| Abstract: This paper introduces the concept of distributed motion sensing for stationkeeping vessels in ice infested waters. During the SKT 2017 project, conducted in February and March 2017 in the Bay of Bothnia, five inertial measurement units were installed on the vessel Magne Viking. Four of the sensor units were installed at different positions inside the hull of the vessel, which enabled the system to locally measure ice-induced vibrations in the hull of the vessel. The fifth sensor unit was installed at a central position of the vessel and served as reference sensor for measuring the acting global load on the vessel. Under stationkeeping the global load measured on the ship should be close to zero, because the environmental load is equal to the force from the stationkeeping system. However the remaining four motion sensor units in the hull also measured locally induced vibrations. The study shows that this sensor configuration allows for the detection of changes in the acting load against the vessel. This is demonstrated with motion data obtained during the stationkeeping trials on the vessel Magne Viking. |
| Comment: SKT2017 |
BibTeX:
@conference{mhey18B,
author = {Heyn, H.-M. and Skjetne, R. and Scibilia, F.},
title = {Distributed sensing of loads acting against the hull of a stationkeeping vessel in ice},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2018},
volume = {8},
pages = {7},
note = {Polar and Arctic Sci. and Tech.},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2704665},
doi = {10.1115/OMAE2018-78579}
}
|
| Jiang Z, Ren Z, Gao Z, Sandvik PC, Halse KH and Skjetne R (2018), "Mating Control of a Wind Turbine Tower-Nacelle-Rotor Assembly for a Catamaran Installation Vessel", In Int. Offshore (Ocean) and Polar Eng. Conf. (ISOPE). Sapporo, Hokkaido, Japan, June, 2018. , pp. 584-593. |
| Abstract: The assembly and installation costs of an offshore wind farm can approach 20% of the capital expenditures; therefore, time efficient installation methods are needed for installing offshore wind turbines. This study investigates the feasibility of a novel wind turbine installation concept
using a catamaran. The catamaran is designed to carry wind turbine assemblies on board and to perform installation using lifting grippers. The installation of a rotor-tower-assembly onto a spar foundation is considered with a focus on the mating process of a tower-nacelle-rotor assembly. The spar foundation has been pre-installed at a representative site in the North Sea, and the catamaran has thrusters regulated by a dynamic positioning system. Numerical modelling of various components of the concept are introduced. Time-domain simulations of the system are performed in irregular waves, and the relative motion and velocity between the tower bottom and the spar top are analysed during the mating process. It was found that the active heave compensator can effectively reduce the relative heave velocity and the risks of structural damage during the mating process. |
BibTeX:
@conference{zjia18A,
author = {Jiang, Z. and Ren, Z. and Gao, Z. and Sandvik, P. C. and Halse, K. H. and Skjetne, R.},
title = {Mating Control of a Wind Turbine Tower-Nacelle-Rotor Assembly for a Catamaran Installation Vessel},
booktitle = {Int. Offshore (Ocean) and Polar Eng. Conf. (ISOPE)},
year = {2018},
pages = {584--593},
url = {https://www.onepetro.org/conference-paper/ISOPE-I-18-120}
}
|
| Ren Z, Jiang Z, Skjetne R and Gao Z (2018), "Single Blade Installation Using Active Control of Three Tugger Lines", In Int. Offshore (Ocean) and Polar Eng. Conf. (ISOPE). Sapporo, Hokkaido, Japan, June, 2018. , pp. 594-601. |
| Abstract: Single blade installation using jack-up vessels is a commonly used blade installation setup for offshore wind turbines. During this operation, each blade is lifted by the main crane from the deck, moved, and then bolted to the rotor hub at the top of the turbine tower. Tugger lines from the crane boom are connected to the suspended blade to reduce the blade’s pendulum motions. Lately, much research has been conducted to reduce the blade motion by actively controlling the tension force in the tugger lines. Since the tugger lines can only provide positive tension, pretension is needed before the mating process. In this paper, an active PID control strategy with a three-tugger-line configuration is proposed to reduce the blade motion by controlling the tugger line forces acting on the blade. The placement of the additional 3rd line is discussed. The control allocation is achieved by convex programming with an auto-generation solver using CVXGEN. Simulations under turbulent wind conditions are conducted to verify the active control scheme in HAWC2. The results show that the active control scheme effectively reduces the translational motion of the blade root relative to the hub in the mean wind direction. |
BibTeX:
@conference{zren18C,
author = {Ren, Z. and Jiang, Z. and Skjetne, R. and Gao, Z.},
title = {Single Blade Installation Using Active Control of Three Tugger Lines},
booktitle = {Int. Offshore (Ocean) and Polar Eng. Conf. (ISOPE)},
year = {2018},
pages = {594--601},
url = {https://www.onepetro.org/conference-paper/ISOPE-I-18-229}
}
|
| Ruud S and Skjetne R (2018), "Ice management and design philosophy", In Int. Marine Design Conf. (IMDC). Helsinki, Finland, June, 2018. Vol. 2, pp. 819-830. #crc#. |
| Abstract: Ice management (IM) is defined as all activities carried out with the objective of mitigating hazardous situations by reducing or avoiding actions from any kind of ice feature to a protected unit (e.g. a drilling vessel) and includes several types of barriers. IM barriers are ranging from ice observation, ice prediction, ice alerting, ice fighting with icebreakers, and disconnection procedures of the protected unit. The design decisions of the IM barrier systems can be based on qualitative or quantitative performance models. Qualitative descriptions of independent and dependent barriers are first defined and exemplified with qualitative decision criteria. Quali-tative concepts for barrier performance of ice prediction are defined and illustrated in event trees. National barrier regulations (e.g. PSA) contain requirements to model quantitatively the barrier performances. Quantification of the IM performance, which are defined by probabilities of barrier functions, is a major challenge due to lack of data and existing uncertainties. Finally, the paper presents a brief plan for demonstration of the performance models in the design phase with experience data collection supporting the safe learning principle. |
| Comment: Volume 2, Arctic Design |
BibTeX:
@incollection{sruu18A,
author = {Ruud, S. and Skjetne, R.},
editor = {Kujala and Lu},
title = {Ice management and design philosophy},
booktitle = {Int. Marine Design Conf. (IMDC)},
publisher = {#crc#},
year = {2018},
volume = {2},
pages = {819--830},
url = {https://www.taylorfrancis.com/books/e/9780429803253/chapters/10.1201%2F9780429440519-20}
}
|
| Thorat L and Skjetne R (2018), "Optimal online configuration and load-sharing in a redundant electric power system for an offshore vessel using mixed-integer linear programming", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Madrid, Spain, June, 2018. Vol. 1, pp. 10. |
| Abstract: This paper proposes several schemes for optimal online configuration and load sharing for a shipboard power system of a typical offshore vessel, having a number of varying capacity gensets. Different methods are presented for optimal online scheduling and minimization of specific fuel oil consumption using mixed integer linear programming. The simulations for optimization of specific fuel oil consumption for three different scheduling methods demonstrate their properties. |
BibTeX:
@conference{ltho18A,
author = {Thorat, L. and Skjetne, R.},
title = {Optimal online configuration and load-sharing in a redundant electric power system for an offshore vessel using mixed-integer linear programming},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2018},
volume = {1},
pages = {10},
note = {Offshore Technology},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2703564},
doi = {10.1115/OMAE2018-77955}
}
|
| Ueland ES, Skjetne R and Vilsen SA (2018), "Force Actuated Real-Time Hybrid Model Testing of a Moored Vessel: A Case Study Investigating Force Errors", In Proc. IFAC Conf. Contr. Appl. Marine Systems. Opatija, Croatia, Sept., 2018. Vol. 51(29), pp. 74-79. |
| Abstract: This paper presents a study where real-time hybrid testing is used to emulate a moored barge. The barge is modelled physically while the mooring forces are simulated numerically and actuated onto the physical substructure. Assuming no errors in modelling of the numerical substructure, we investigate what separates the instantaneous forces acting on the physical substructure, from the forces that would be acting on it in the ideal, non-substructured case that we are trying to replicate. Four different types of errors are identified, discussed, and partly quantified. |
BibTeX:
@conference{euel18A,
author = {Ueland, E. S. and Skjetne, R. and Vilsen, S. A.},
title = {Force Actuated Real-Time Hybrid Model Testing of a Moored Vessel: A Case Study Investigating Force Errors},
booktitle = {Proc. IFAC Conf. Contr. Appl. Marine Systems},
year = {2018},
volume = {51},
number = {29},
pages = {74--79},
note = {IFAC-PapersOnLine},
url = {http://www.sciencedirect.com/science/article/pii/S240589631832161X},
doi = {10.1016/j.ifacol.2018.09.472}
}
|
| Wu Z, Thorat L and Skjetne R (2018), "Comparison of fuel consumption on a hybrid marine power plant with low-power versus high-power engines", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Madrid, Spain, June, 2018. Vol. 1, pp. 10. |
| Abstract: In this paper, we are comparing fuel consumption on a case study hybrid marine power plant with diesel gensets and batteries. Optimization methods are used to find an optimal operating point for the gensets, under different power demands, with regards
to fuel consumption andNOx emissions. Three different power system example configurations for an offshore construction vessel are explored in this study, and the simulations are carried out to compare the resulting fuel consumption and NOx emissions for these power system configurations. |
BibTeX:
@conference{zwu18A,
author = {Wu, Z. and Thorat, L. and Skjetne, R.},
title = {Comparison of fuel consumption on a hybrid marine power plant with low-power versus high-power engines},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2018},
volume = {1},
pages = {10},
note = {Offshore Technology},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleID=2703565},
doi = {10.1115/OMAE2018-77959}
}
|
| Bjørnø J, Heyn H-M, Skjetne R, Dahl AR and Frederich P (2017), "Modeling, parameter identification and thruster-assisted position mooring of C/S Inocean Cat I Drillship", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Trondheim, Norway, June, 2017. Vol. 7B, pp. 10. |
| Abstract: A thruster-assisted position mooring (TAPM) system includes different control functions for stationkeeping and motion damping for a moored offshore vessel with assist from thrusters. It consists of a conventional mooring system and a dynamic positioning (DP) system. The thrusters are used to provide damping and some restoring to the vessel motion and compensate if line breakage occurs. The mooring system absorbs the main loads to keep the vessel in place. This paper presents a complete modeling, parameter identification, and control design for a 1:90 scaled TAPM model vessel. The numerical values for the different model parameters are identified from towing tests.
State-of-the-art TAPM control algorithms have been tested on the vessel in the Marine Control Laboratory (MC-Lab), to see the behavior resulting from the different control algorithms. The presented experiments focus on the setpoint chasing algorithm, where the position setpoint slowly moves to the equilibrium position where the environmental loads are balanced by the mooring loads. This avoids conflicts between the mooring system and the control actions. If the environmental loads are too large so that the setpoint exceeds a user-defined safety radius, the setpoint is set to this radius and thruster forces grow to support the mooring system in counteracting the environmental loads to avoid line breakage. The experiments show that the vessel and setpoint chasing control algorithm behaves as expected, minimizing thruster usage and maximizing utilization of mooring system. |
BibTeX:
@conference{jbjo17A,
author = {Bjørnø, J. and Heyn, H.-M. and Skjetne, R. and Dahl, A. R. and Frederich, P.},
title = {Modeling, parameter identification and thruster-assisted position mooring of C/S Inocean Cat I Drillship},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2017},
volume = {7B},
pages = {10},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2655776},
doi = {10.1115/OMAE2017-61896}
}
|
| Dahl AR, Skjetne R and Johansen TA (2017), "A structure preserving power system frequency model for dynamic positioning vessels", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Trondheim, Norway, June, 2017. Vol. 1, pp. 10. |
| Abstract: This paper adapts a structure preserving model to on-board power plants. The model, originally developed for land-based power systems, is expanded for the larger frequency range allowable to on-board plants. State-space equations are developed from first principles and transformed to a form suitable for analysis and computer implementation. Recommendations for parameter selection are given. An example plant scenario is simulated both in the proposed framework and in a higher fidelity model for comparison. |
BibTeX:
@conference{adah17A,
author = {Dahl, A. R. and Skjetne, R. and Johansen, T. A.},
title = {A structure preserving power system frequency model for dynamic positioning vessels},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2017},
volume = {1},
pages = {10},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2655325},
doi = {10.1115/OMAE2017-61901}
}
|
| Heyn H-M, Udjus G and Skjetne R (2017), "Distributed motion sensing on ships", In Proc. MTS/IEEE OCEANS. Anchorage, Alaska, Sept., 2017. |
| Abstract: A current trend is autonomous transport of goods and people in the air, at land, and at sea. For safe and reliable operations, autonomous systems require sensors that replace, or even exceed, the senses of a human operator. A system of spatially distributed inertial measurement units (IMUs) along the hull of a vessel, which allows sensing of local accelerations of a vessel or structure at sea is proposed. In contrast to classic motion sensors on ships, the sensors are not placed in a central location of the ship, but are instead mounted on the inside of hull of the vessel. This enables the system to measure local hull vibrations, which are induced by external forces or pressure gradients. The measurements can be processed to allow a spatial awareness of environmental loads or force fields acting on the vessel. After a discussion of the fundamentals of local motion sensing on a marine vessel, this paper presents two applications for distributed motion sensing. The first application is the measurement and classification of ice-induced vibrations in the hull of an Oden-class icebreaker during transit and stationkeeping in ice-infested waters. At four locations on the vessel, the local vibrations were measured and probability distribution function fitted to the motion data. It is shown, depending on the ice-conditions, that the stochastic properties of the signal change. In a second application, a model scale ship is equipped with an array of four motion sensors along the hull of the vessel and one virtual sensor in the center of gravity as a reference measurement. By this configuration, it is demonstrated how to detect local pressure zones along the hull caused by incoming waves. |
BibTeX:
@conference{hhey17B,
author = {Heyn, H.-M. and Udjus, G. and Skjetne, R.},
title = {Distributed motion sensing on ships},
booktitle = {Proc. MTS/IEEE OCEANS},
year = {2017},
url = {http://ieeexplore.ieee.org/document/8232153}
}
|
| Heyn H-M, Knoche M, Zhang Q and Skjetne R (2017), "A system for automated vision-based sea-ice concentration detection and floe-size distribution indication from an icebreaker", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Trondheim, Norway, June, 2017. Vol. 8, pp. 10. |
| Abstract: This paper presents a ship-mounted multi-lens camera system for sea-ice monitoring and algorithms to automatically evaluate the sea-ice concentration and to indicate the floe-sizes in a radius of 100 meter around the vessel. During the SWEDARCTIC Arctic Ocean 2016 expedition, 11 camera lenses recorded the sea-ice conditions around the Swedish icebreaker Oden. As an example of the possible use of this image system, the images of six lenses are combined into one 360° panoramic image. To distinguish between water and sea-ice in the images, and thus to evaluate the sea-ice concentration around the vessel, a direct thresholding, the k-means, and a novel adaptive thresholding method are applied. Moreover, an edge detector gives the number of pixels that either form the boundary between sea-ice and water or are part of a visible ice fracture. The ratio between these edge pixels and the total number of pixels containing sea-ice gives an indication of the floe size distribution (FSD) in the image. |
BibTeX:
@conference{hhey17A,
author = {Heyn, H.-M. and Knoche, M. and Zhang, Q. and Skjetne, R.},
title = {A system for automated vision-based sea-ice concentration detection and floe-size distribution indication from an icebreaker},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2017},
volume = {8},
pages = {10},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2655827},
doi = {10.1115/OMAE2017-61822}
}
|
| Norgren P and Skjetne R (2017), "A particle filter SLAM approach to online iceberg drift estimation from an AUV", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Trondheim, Norway, June, 2017. Vol. 8 , pp. 11. |
| Abstract: Using autonomous underwater vehicles (AUVs) for mapping the underwater topography of sea-ice and icebergs, or detecting keels of ice ridges, is foreseen as an enabling technology in future Arctic offshore operations. This paper presents a method for online iceberg drift estimation using a Simultaneous Localization and Mapping (SLAM) approach using an AUV with a multibeam echosounder (MBE) during such survey/monitoring operations. Iceberg drift is affected by wind, current, and Coriolis forces. This can be hard to predict, making automated mapping of icebergs difficult. The method proposed in this paper estimates the iceberg’s pose using a particle filter, where each particle uses extended information filters to estimate the topography
of the iceberg. A grid map is used to store the iceberg topography, and distributed particle mapping is used to avoid expensive copy operations during particle resampling. The proposed method is verified through a simulation study, using a 6 DOF AUV model, an MBE sensor model, and an iceberg topography taken from the PERD iceberg sightings database. The method is able to provide a georeferenced iceberg position, thus, estimating the iceberg’s drift trajectory. A topography estimate of the iceberg, corrected for iceberg drift, is also generated. Furthermore, the algorithm estimates the iceberg drift velocity, as well as the relative iceberg-AUV pose, for use in future iceberg mapping guidance algorithms. The simulation study illustrates the performance of the method, and a short execution time analysis is presented to illustrate the method’s real-time potential. |
BibTeX:
@conference{pnor17A,
author = {Norgren, P. and Skjetne, R.},
title = {A particle filter SLAM approach to online iceberg drift estimation from an AUV},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2017},
volume = {8 },
pages = {11},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2655826},
doi = {10.1115/OMAE2017-61639}
}
|
| Ren Z, Skjetne R and Gao Z (2017), "Modeling and control of crane overload protection during marine lifting operation based on model predictive control", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Trondheim, Norway, June, 2017. Vol. 9, pp. 9. |
| Abstract: This paper deals with a nonlinear model predictive control (NMPC) scheme for a winch servo motor to overcome the sudden peak tension in the lifting wire caused by a lumped-mass payload at the beginning of a lifting off or a lowering operation. The crane-wire-payload system is modeled in 3 degrees of freedom with the Newton-Euler approach. Direct multiple shooting and real-time iteration (RTI) scheme are employed to provide feedback control input to the winch servo. Simulations are implemented with MATLAB and CaSADi toolkit. By well tuning the weighting matrices, the NMPC controller can reduce the snatch loads in the lifting wire and the winch loads simultaneously. A comparative study with a PID controller is conducted to verify its performance. |
BibTeX:
@conference{zren17A,
author = {Ren, Z. and Skjetne, R. and Gao, Z.},
title = {Modeling and control of crane overload protection during marine lifting operation based on model predictive control},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2017},
volume = {9},
pages = {9},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2655967},
doi = {10.1115/OMAE2017-62003}
}
|
| Skjetne R, Sørensen MEN, Breivik M, Værnø SAT, Brodtkorb AH, Sørensen AJ, Kjerstad ØK, Calabrò V and Vinje BO (2017), "AMOS DP Research Cruise 2016: Academic full-scale testing of experimental dynamic positioning control algorithms onboard R/V Gunnerus", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Trondheim, Norway, June, 2017. Vol. 1, pp. 10. |
| Abstract: In order to validate relevant dynamic positioning (DP) control algorithms in a realistic environment, a full-scale DP test campaign, the AMOS DP Research Cruise 2016 (ADPRC’16), was organized in a collaboration between the NTNU Centre for
Autonomous Marine Operations and Systems (NTNU AMOS) and the company Kongsberg Maritime onboard the research vessel (R/V) Gunnerus. To the authors’ best knowledge, closed-loop DP feedback control algorithms have never been tested full-scale on a ship in an academic research experiment before. However, we have now achieved this by coding our algorithms into a testmodule of the DP system, as prepared by Kongsberg Maritime. Among the tested algorithms is an output feedback control law with both good transient and steady-state performance. In another experiment, different adaptive backstepping control laws for DP were tested to compare and contrast their performance and properties. A hybrid state observer with a performance monitoring function proposed to switch between two observers, choosing the best one at any time instant, was also part of the test scope. For this, necessary measurements (including acceleration measurements) were logged to be able to rerun and validate the observer algorithms in post-processing. Finally, several experiments were done to test a pseudo-derivative feedback control law for DP. The feedback mechanism was tested with and without a feedforward disturbance rejection term, called acceleration feedforward. This paper reports the experimental setup, test program, and an overview of results from the ADPRC’16 campaign. |
BibTeX:
@conference{rskj17A,
author = {Skjetne, R. and Sørensen, M. E. N. and Breivik, M. and Værnø, S. A. T. and Brodtkorb, A. H. and Sørensen, A. J. and Kjerstad, Ø. K. and Calabrò, V. and Vinje, B. O.},
title = {AMOS DP Research Cruise 2016: Academic full-scale testing of experimental dynamic positioning control algorithms onboard R/V Gunnerus},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2017},
volume = {1},
pages = {10},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2655328},
doi = {10.1115/OMAE2017-62045}
}
|
| Thorat L and Skjetne R (2017), "Load-dependent start-stop of gensets modeled as a hybrid dynamical system", In Proc. IFAC World Congress Automatic Control. Toulouse, France, July, 2017. Vol. 50, pp. 9321-9328. |
| Abstract: Shipboard power systems consist of components such as gensets and loads that have continuous dynamic behaviour, and these can be represented by differential equations. Other components, such as breakers, exhibit discrete dynamic behaviour and can be represented by discrete equations. In this paper, a hybrid dynamical system framework is used to develop a mathematical model of a shipboard electrical power system. The continuous nonlinear swing dynamics of diesel generators are considered as continuous flow dynamics and logical connection in/out of generators is considered as discrete jump dynamics to model shipboard electrical power system as a hybrid dynamical system. A load-dependent start/stop table defines the logical rules to connect/disconnect next genset in sequence, extending the plant with additional discrete functions. |
BibTeX:
@conference{ltho17A,
author = {Thorat, L. and Skjetne, R.},
title = {Load-dependent start-stop of gensets modeled as a hybrid dynamical system},
booktitle = {Proc. IFAC World Congress Automatic Control},
year = {2017},
volume = {50},
pages = {9321--9328},
url = {http://www.sciencedirect.com/science/article/pii/S2405896317316762},
doi = {10.1016/j.ifacol.2017.08.1180}
}
|
| Ueland ES and Skjetne R (2017), "Effect of time delays and sampling in force actuated real-time hybrid testing; A case study", In Proc. MTS/IEEE OCEANS. Anchorage, Alaska, Sept., 2017. |
| Abstract: This paper presents a study where real-time hybrid testing is applied on a double mass-damper-spring system. Simulations show how delays and sampling terms affect the system both when it is subjected to excitations forces and in free decay. In particular, it is shown how the stiffness of the actuator combined with time delays can have a profound effect on the real-time hybrid test case. Further, using the test case, first order Taylor expansions are used to show how linear stiffnesses combined with delays can be approximated as linear damping terms, while linear damping terms can be approximated as added mass terms. These approximations are useful in providing intuitive insight into how delays will affect the real-time hybrid test system. |
BibTeX:
@conference{euel17B,
author = {Ueland, E. S. and Skjetne, R.},
title = {Effect of time delays and sampling in force actuated real-time hybrid testing; A case study},
booktitle = {Proc. MTS/IEEE OCEANS},
year = {2017},
url = {http://ieeexplore.ieee.org/document/8232196}
}
|
| Ueland ES, Skjetne R and Dahl AR (2017), "Marine autonomous exploration using a lidar and SLAM", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Trondheim, Norway, June, 2017. Vol. 6, pp. 10. |
| Abstract: This paper presents the implementation of a 2D-lidar to a model-scale surface vessel, and the design of a control system that makes the vessel able to perform autonomous exploration of a small-scale marine environment by the use of the lidar and SLAM. This includes a presentation and discussion of experimental results. The completion of this system has involved the development of a suitable control system that merges exploration strategies, path planners, a motion controller, and a strategy for generating controller setpoints. The system was implemented on the Robot Operating System platform, which made it possible to utilize open-source algorithms for state of the art SLAM. |
BibTeX:
@conference{euel17A,
author = {Ueland, E. S. and Skjetne, R. and Dahl, A. R.},
title = {Marine autonomous exploration using a lidar and SLAM},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2017},
volume = {6},
pages = {10},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2655682},
doi = {10.1115/OMAE2017-61880}
}
|
| Xu J, Ren Z, Li Y, Skjetne R and Halse KH (2017), "Dynamic simulation and control of an active roll reduction system using free-flooding tanks with vacuum pumps", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Trondheim, Norway, June, 2017. Vol. 1, pp. 10. |
| Abstract: Ship roll motion is often the critical factor for offshore operations due to its lack of damping mechanism. This paper demonstrates a dynamic simulation scheme of an active roll reduction system using free-flooding tanks controlled by vacuum pumps. The two tanks in the system are installed on each sides of a catamaran. The tank hatches are opened to the sea and the air chambers of both tanks are connected by an air duct. Vacuum pumps and air valve with active stabilization controller provides desired filling level for the tank. The ship is a dynamic model with single degree of freedom in roll. The hydrodynamic behavior of the ship is calculated using potential theory by SHIPX. The air chamber above is modelled as isothermal process of ideal gas. The behavior of the liquid flow in the tank is simulated by incompressible RANS solver using Volume of Fluid (VOF) model, then summarized as response function for the ship model. A simplified control plant model for the vacuum pumps is proposed where insignificant higher order behaviors are regarded as biases and noises. The stability is proved by Lapunov direct method. The performance of the entire system is evaluated in terms of roll reduction capability and power cost. The system is more suitable for roll reduction in low-speed or resting conditions. |
BibTeX:
@conference{jxu17A,
author = {Xu, J. and Ren, Z. and Li, Y. and Skjetne, R. and Halse, K. H.},
title = {Dynamic simulation and control of an active roll reduction system using free-flooding tanks with vacuum pumps},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2017},
volume = {1},
pages = {10},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2655263},
doi = {10.1115/OMAE2017-61292}
}
|
| Brodtkorb AH, Vernø SAT, Teel AR, Sørensen A and Skjetne R (2016), "Hybrid observer for improved transient performance of a marine vessel in dynamic positioning", In Proc. IFAC Symp. Nonlinear Control Systems Design. Monterey, USA, Aug., 2016. Vol. 49(18), pp. 345-350. |
| Abstract: Dynamic positioning (DP) systems are used on marine vessels for automatic stationkeeping and tracking operations solely by use of thrusters. Observers are key components of DP systems, and two main types are proposed in this paper. The model-based type is used in steady state conditions since it is especially good at filtering out first order wave induced
motions and predicting states in the case of signal loss, and the signal-based type typically has superior performance during transients. In this paper a hybrid observer including a signal-based part and a model-based part with a performance monitoring function is proposed. The observer part that provides the best estimate of the vessel position and heading is used in closed-loop control, thereby allowing for improved transient response while maintaining good steady state performance. The contributions of this paper include the design of a hybrid signal-based and model-based observer with performance monitoring, stability analysis of the vessel with hybrid estimates in output feedback control, and simulations of a platform supply vessel during a setpoint and heading change. |
BibTeX:
@conference{abro16A,
author = {Brodtkorb, A. H. and Vernø, S. A. T. and Teel, A. R. and Sørensen, A. and Skjetne, R.},
title = {Hybrid observer for improved transient performance of a marine vessel in dynamic positioning},
booktitle = {Proc. IFAC Symp. Nonlinear Control Systems Design},
year = {2016},
volume = {49},
number = {18},
pages = {345--350},
note = {IFAC-PapersOnLine},
url = {http://www.sciencedirect.com/science/article/pii/S2405896316317682},
doi = {10.1016/j.ifacol.2016.10.189}
}
|
| Heyn H-M and Skjetne R (2016), "A system for measuring ice-induced accelerations and identifying ice actions on the CCGS Amundsen and a Swedish Atle-class icebreaker", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Busan, Korea, June, 2016. Vol. 8, pp. 1-9. |
| Abstract: When ships operate in the Arctic, sea-ice induce an additional environmental load on the vessel. The ice load can vary significantly depending on the dominating ice-breaking failure mode.
In this work a sensor system for measuring ice induced accelerations on the Canadian icebreaker CCGS Amundsen and a Swedish Atle-class icebreaker is presented. The sensor system consists of low-cost inertial measurement units. Ship-ice interaction data has been collected during expeditions along the coast of Labrador in Canada and in the Greenland Sea north of the Norwegian Svalbard archipelago. Depending on the failure mechanism of the interacting ice, vibrations at different frequencies are induced into the icebreaker ship. A time-frequency decomposition based on the Wigner-Ville distribution has been modified such that it is applicable to analysis of ice-load induced acceleration signals. Based on the frequency pattern of the induced vibrations, this novel method allows for evaluation of the intensity of the ice-loads and identification of the dominating ice failure mechanism, which is demonstrated for several ship-ice interaction events. The presented novel time-frequency decomposition for ice induced accelerations is a powerful tool for the identification of the threat imposed by sea-ice to a structure. In further work the time-frequency decomposition will be used as feedback in ice-capable control and monitoring systems for Arctic offshore operations. |
| Comment: OMAE2016-54738 |
BibTeX:
@conference{hhey16A,
author = {Heyn, H.-M. and Skjetne, R.},
title = {A system for measuring ice-induced accelerations and identifying ice actions on the CCGS Amundsen and a Swedish Atle-class icebreaker},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2016},
volume = {8},
pages = {1--9},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2571116},
doi = {10.1115/OMAE2016-54738}
}
|
| Kjerstad ØK, Værnø SAT and Skjetne R (2016), "A Robust Dynamic Positioning Tracking Control Law Mitigating Integral Windup", In Proc. IFAC Conf. Contr. Appl. Marine Systems. Trondheim, Norway, Sept., 2016. Vol. 49(23), pp. 239 - 244. |
| Abstract: This paper deals with the design of a tracking control law for dynamic positioning of marine vessels subject to disturbances. It shows that the integral windup problem can be mitigated by removing the position setpoint in the proportional error term and injecting the velocity setpoint in the integral state. This creates an internal reference point in the control law for the vessel to follow. Control of the transient convergence trajectories is achieved without compromising stability by constraining the internal convergence velocity. The proposed control law provides the same functionality as a conventional tracking control law in combination with a reference filter, but with lower complexity and fewer tuning parameters. A closed-loop simulation case study verifies the theoretical findings and show feasible and robust performance. |
BibTeX:
@conference{okje16A,
author = {Kjerstad, Ø. K. and Værnø, S. A. T. and Skjetne, R.},
title = {A Robust Dynamic Positioning Tracking Control Law Mitigating Integral Windup},
booktitle = {Proc. IFAC Conf. Contr. Appl. Marine Systems},
year = {2016},
volume = {49},
number = {23},
pages = {239 -- 244},
note = {IFAC-PapersOnLine},
url = {http://www.sciencedirect.com/science/article/pii/S240589631631936X},
doi = {10.1016/j.ifacol.2016.10.349}
}
|
| Lu W, Zhang Q, Lubbad R, Løset S and Skjetne R (2016), "A Shipborne Measurement System to Acquire Sea Ice Thickness and Concentration at Engineering Scale", In Proc. Arctic Tech. Conf.. St. John’s, Canada, Oct., 2016. |
| Abstract: Sea ice concentration and thickness are important parameters for the calculations of ice actions and their effects on Arctic offshore structures and for the evaluation of icebreaker performance. Various methods exist nowadays to monitor these parameters, ranging from geophysical scale to local scale. During the Oden Arctic Technology Research Cruise 2015 (OATRC’ 15), we installed both Ice Concentration and Ice Thickness cameras and developed corresponding algorithms to achieve real time quantification of ice concentration and visual estimation of ice thickness information. For the ice concentration analysis, we utilized both the global Otsu method to categorize an image into two regions (black water and white ice); and the K-means method to identify more regions based on the gray scale from the image. With the methods, we conducted a case study by analyzing the ice concentration in a selected time window. In the case study, we include both dry ice (in white color) and wet ice (in gray color, generally composed of ice rubbles, young ice, and melt ponds) as ice region for the K-means method. The K-means method yields higher ice concentration values in comparison to the global Otsu method, in which, melt ponds/young ice was frequently mistaken as open water. It turns out that the K-means method enables more flexibility to cope with the complicated ice environment by separating the image into more regions that can be included as ice in an ice concentration analysis. For the ice thickness camera, the intention was to capture the events while a broken ice piece is tilted, next to the ship side, and expose its thickness region to the camera. In this paper, we developed an automatic tracking algorithm to sift these events out from all the images taken by the Ice Thickness acquisition system. After projecting a grid with physical length onto the image, the ice thickness information can be visually quantified. We compared the ice thickness obtained from the Ice Thickness camera and that obtained by an Electro-Magnetic inductive device in a selected time window. The results agree well with each other. Considering the advantages and disadvantages of each method, this demonstrates the benefits of combining redundant approaches for obtaining the ice thickness information with a higher degree of confidence. |
BibTeX:
@conference{wlu16B,
author = {Lu, W. and Zhang, Q. and Lubbad, R. and Løset, S. and Skjetne, R.},
title = {A Shipborne Measurement System to Acquire Sea Ice Thickness and Concentration at Engineering Scale},
booktitle = {Proc. Arctic Tech. Conf.},
year = {2016},
url = {https://www.onepetro.org/conference-paper/OTC-27361-MS},
doi = {10.4043/27361-MS}
}
|
| Lu W, Lubbad R, Løset S and Skjetne R (2016), "Parallel Channel Tests during Ice Management Operations in the Arctic Ocean", In Proc. Arctic Tech. Conf.. St. John’s, Canada, Oct., 2016. |
| Abstract: During ice management operations, creating narrow parallel channels with icebreakers can effectively reduce ice floe sizes for the protected vessel/structure. Yet too narrow channel spacing requirement shall lead to excessive or even unpractical ice management operations. Empirical experience shows an almost 1:1 relationship between ‘downstream floe size’ and ‘parallel channel spacing’ while designing an ice management operation. However, before this paper, there exists no dedicated parallel channel tests with strictly controlled channel spacing and sufficient instrumentation to quantify such relationship. In this paper, we report two parallel channel tests, which have been conducted in September 2015 during an expedition to the Arctic Ocean with icebreakers, Oden and Frej. During the test, helicopter images and an onboard camera were utilised to document the parallel channel fracturing events. With the collected data, we strive to quantify if there is a prominent relationship between parallel channel spacing and the corresponding managed ice floe size. In order to analyse the floe size distribution and its relationship with channel spacing from helicopter images, we developed an image segmentation method that
propagates visually identifiable seeding cracks in the image. In addition, onboard camera images were utilised to yield the frequency of parallel channel fracturing events. Given the ice conditions and Oden’s specific structural form, with all the different channel spacing tested, it turned out that a channel spacing over 200 m would already prohibit the development of parallel channel fracturing events. Most of the observed events take place when the spacing is smaller than around 100 m. In addition, as was expected, more frequent fractures are taking place with narrower channel spacing, e.g., distances smaller than 30 m. The relationship between managed ice floe size and channel spacing are studied. It is found that almost all (100%) of the produced downstream floe sizes are smaller than twice the channel spacing; 90% of them are smaller than 1.5 times of the spacing; and the majority of them (from 46% to 80%, depending on the spacing distance) are smaller than 1 time of the channel spacing. With such quantified relationships, we can practically estimate the size of the managed ice floes based on known/expected channel spacing. |
BibTeX:
@conference{wlu16A,
author = {Lu, W. and Lubbad, R. and Løset, S. and Skjetne, R.},
title = {Parallel Channel Tests during Ice Management Operations in the Arctic Ocean},
booktitle = {Proc. Arctic Tech. Conf.},
year = {2016},
url = {https://www.onepetro.org/conference-paper/OTC-27344-MS},
doi = {10.4043/27344-MS}
}
|
| Ludvigsen M, Albrektsen SM, Cisek K, Johansen TA, Norgren P, Skjetne R, Zolich AP, Dias PS, Ferreira S, Sousa JB, Fossum TO, Sture Ø, Krogstad TR, Midtgaard Ø, Hovstein VE and Vagsholm E (2016), "Network of heterogeneous autonomous vehicles for marine research and management", In Proc. MTS/IEEE OCEANS. Monterey, CA, USA, Sept., 2016. , pp. 1-7. |
| Abstract: In April 2016, NTNU, FFI, Kongsberg Seatex, LSTS and Maritime Robotics set up an experiment to explore their capability to combine the research vessel Gunnerus, the AUV Hugin, the UAV X8 and the USV Mariner in a network of heterogeneous unmanned vehicles. Communication, manoeuvring, onboard processing and operational complexity are essential components in such networks. To provide communication the MBR broadband radio system was implemented. To show the capabilities of the system proposed, a scenario with seabed mapping and target recognition was defined. The experiment made it apparent that these networks has the potential of significantly saving cost for data collection in marine research and management by reducing ship time. To fully unlock the potential of networks of heterogeneous unmanned vehicles, the missions of each vehicle need to be more integrated. |
BibTeX:
@conference{mlu16A,
author = {Ludvigsen, M. and Albrektsen, S. M. and Cisek, K. and Johansen, T. A. and Norgren, P. and Skjetne, R. and Zolich, A. P. and Dias, P. S. and Ferreira, S. and Sousa, J. B. and Fossum, T. O. and Sture, Ø. and Krogstad, T. R. and Midtgaard, Ø. and Hovstein, V. E. and Vagsholm, E. },
title = {Network of heterogeneous autonomous vehicles for marine research and management},
booktitle = {Proc. MTS/IEEE OCEANS},
year = {2016},
pages = {1--7},
url = {http://ieeexplore.ieee.org/document/7761494/},
doi = {10.1109/OCEANS.2016.7761494}
}
|
| Værnø SAT, Brodtkorb AH, Skjetne R and Sørensen AJ (2016), "An Output Feedback Controller with Improved Transient Response of Marine Vessels in Dynamic Positioning", In Proc. IFAC Conf. Contr. Appl. Marine Systems. Trondheim, Norway, Sept., 2016. Vol. 49(23), pp. 133 - 138. |
| Abstract: An output feedback controller for dynamic positioning (DP) of marine surface vessels is developed. The proposed algorithm has good performance during transients as well as good steady state performance. The method achieves this by a flexible injection gain in the bias estimation dynamics in the observer. In addition, the traditional integral action is replaced
by a filtered bias estimate from the observer. Both these elements combined provide good DP performance in transients, as well as calm behavior in steady state. A simulation study is performed showing the benefit of the proposed output feedback controller, and a stability analysis is performed to show uniform asymptotic stability. |
BibTeX:
@conference{svar16A,
author = {Værnø, S. A. T. and Brodtkorb, A. H. and Skjetne, R. and Sørensen, A. J.},
title = {An Output Feedback Controller with Improved Transient Response of Marine Vessels in Dynamic Positioning},
booktitle = {Proc. IFAC Conf. Contr. Appl. Marine Systems},
year = {2016},
volume = {49},
number = {23},
pages = {133 -- 138},
note = {IFAC-PapersOnLine},
url = {http://www.sciencedirect.com/science/article/pii/S2405896316319206},
doi = {10.1016/j.ifacol.2016.10.333}
}
|
| Ren Z and Skjetne R (2016), "An On-site Current Profile Estimation Algorithm for a Moored Floating Structure", In Proc. IFAC Conf. Contr. Appl. Marine Systems. Trondheim, Norway, Sept., 2016. Vol. 49(23), pp. 153 - 158. |
| Abstract: The current speed influences the safety of subsea and marine operations. This paper proposes an algorithm to estimate the depth-dependent current profile though data from existing commercial sensors, that is the mooring line tension measurements and riser end angle measurements. This will aid prediction of the weather window to enhance the safety during the subsea operations. The influence of various current profile types and the vessel’s motion are discussed. A governing equation is proposed for the algorithm. A simulation is conducted to verify the algorithm. |
BibTeX:
@conference{zren16B,
author = {Ren, Z. and Skjetne, R.},
title = {An On-site Current Profile Estimation Algorithm for a Moored Floating Structure},
booktitle = {Proc. IFAC Conf. Contr. Appl. Marine Systems},
year = {2016},
volume = {49},
number = {23},
pages = {153 -- 158},
note = {IFAC-PapersOnLine},
url = {http://www.sciencedirect.com/science/article/pii/S2405896316319231},
doi = {10.1016/j.ifacol.2016.10.336}
}
|
| Ren Z and Skjetne R (2016), "A Tension-based Position Estimation Solution of a Moored Structure and its Uncertain Anchor Positions", In Proc. IFAC Conf. Contr. Appl. Marine Systems. Trondheim, Norway, Sept., 2016. Vol. 49(23), pp. 251 - 257. |
| Abstract: Thruster-assisted position mooring (TAPM) is an attractive stationkeeping solution for longterm operation. Due to the complex environmental loads and system structure, increasing attention has been paid to improve the redundancy and reliability. This paper summaries the key research results when introducing the simultaneous localization and mapping algorithm to moored structures, which can provide an additional position reference system with uncertain anchor positions. It is especially cost-efficient for some applications alleviating the need for special sensors, such as, hydroacoustic sensors. The line-of-sight range mapping from tension measurements is discussed. Fairleads, the turret dynamics, and loading effects are considered to provide a more realistic and robust solution. A sensor network scheme and a state-space model are proposed, and an extended Kalman filter (EKF) is employed to estimate the uncertain anchor position. |
BibTeX:
@conference{zren16A,
author = {Ren, Z. and Skjetne, R.},
title = {A Tension-based Position Estimation Solution of a Moored Structure and its Uncertain Anchor Positions},
booktitle = {Proc. IFAC Conf. Contr. Appl. Marine Systems},
year = {2016},
volume = {49},
number = {23},
pages = {251 -- 257},
note = {IFAC-PapersOnLine},
url = {http://www.sciencedirect.com/science/article/pii/S2405896316319383},
doi = {10.1016/j.ifacol.2016.10.351}
}
|
| Bø TI, Johansen TA, Dahl AR, Miyazaki MR, Pedersen E, Rokseth B, Skjetne R, Sørensen AJ, Thorat L, Utne IB, Yum KK and Mathiesen E (2015), "Real-Time Marine Vessel and Power Plant Simulation", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. St. John's, Newfoundland, Canada, May 31 -- June 5, 2015. Vol. 1 |
| Abstract: In this paper, we present a system simulator of a marine vessel and power plant which contains the mechanical system with diesel engines, propellers, steering gear, and thrusters; the electrical system with generators, switchboards, breakers, and motors; and the plant level controllers with dynamic position- ing controller, thrust control, and power management system. Interconnections are possible to simulate by using a multi do- main simulator. This is important when evaluating system per- formance and fault handling. The simulator is implemented in Simulink and is modular, configurable and scalable. It can be extended to run on National Instruments’ cRIO embedded con- trol and acquisition system, for real-time simulation. |
BibTeX:
@conference{tbo15A,
author = {Bø, T. I. and Johansen, T. A. and Dahl, A. R. and Miyazaki, M. R. and Pedersen, E. and Rokseth, B. and Skjetne, R. and Sørensen, A. J. and Thorat, L. and Utne, I. B. and Yum, K. K. and Mathiesen, E.},
title = {Real-Time Marine Vessel and Power Plant Simulation},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2015},
volume = {1},
url = {http://proceedings.asmedigitalcollection.asme.org/mobile/proceeding.aspx?articleID=2465402},
doi = {10.1115/OMAE2015-41479}
}
|
| Candeloro M, Valle E, Miyazaki MR, Skjetne R, Ludvigsen M and Sørensen AJ (2015), "HMD as a new Tool for Telepresence in Underwater Operations and Closed-Loop Control of ROVs", In Proc. MTS/IEEE OCEANS. Washington DC, USA, Oct., 2015. |
| Abstract: With the recent development of computer graphics and video-gaming, 360 deg cameras and related technologies, Head Mounted Displays (HMDs) are becoming a popular tool to improve the users experience and efficiency. This trend is also connected to the computer technology improvements of the latest years and its price decrease: HMDs are now more performing and, at the same time, commercially accessible to the masses.
In this paper a HMD is used to improve the telepresence experience, to increase the situational awareness during underwater operations, and to actively control a Remotely Operated Vehicle (ROV). Although HMDs are already used to actively control the point of view of the operator by moving the camera system of vehicles, in this paper they are used to control the vehicle itself, providing a hand-free Human-Machine Interface (HMI). In this way the operator has the possibility of controlling other devices (e.g. a manipulator attached to the ROV) while moving the ROV, highly increasing the efficiency of the underwater operations. Three control methods inspired by previous work developed for the classical joystick interface are presented, full-scale experiments and conclusions on the usability of the proposed solution for real off-shore operations are discussed. |
BibTeX:
@conference{mcan15A,
author = {Candeloro, M. and Valle, E. and Miyazaki, M. R. and Skjetne, R. and Ludvigsen, M. and Sørensen, A. J.},
title = {HMD as a new Tool for Telepresence in Underwater Operations and Closed-Loop Control of ROVs},
booktitle = {Proc. MTS/IEEE OCEANS},
year = {2015},
url = {https://ieeexplore.ieee.org/document/7404466},
doi = {10.23919/OCEANS.2015.7404466}
}
|
| Heyn H-H and Skjetne R (2015), "Estimation of Forces caused by Ship-Ice Interaction using on-board Sensor Measurements", In Proc. Int. Conf. Port Ocean Eng. Arctic Conditions. Trondheim, Norway, June, 2015. Vol. 23 |
| Abstract: The main objective of this paper is to describe a method to estimate severity of the forces caused by ship-ice interaction using only sensors regularly available on a position-moored vessel. Commonly available sensors are contained in an inertial navigation system (INS), consisting of a position reference system (GNSS), a heading reference system (e.g. a gyrocompass) and an inertial measurement unit (IMU). The data recorded by these sensors contains information about the ship-ice interaction, which can be extracted using suitable filter techniques. This paper will give an overview of existing filter techniques, which can be applied for spectral analysis of ice-load measurements. Furthermore, first results from a ship-ice interaction simulator will be presented which verify the usability of INS sensor data for ice load identification. |
BibTeX:
@conference{hhey15B,
author = {Heyn, H.-H. and Skjetne, R.},
title = {Estimation of Forces caused by Ship-Ice Interaction using on-board Sensor Measurements},
booktitle = {Proc. Int. Conf. Port Ocean Eng. Arctic Conditions},
year = {2015},
volume = {23},
url = {http://www.poac.com/Papers/2015/pdf/poac15Final00132.pdf}
}
|
| Kjerstad ØK, Metrikin I and Skjetne R (2015), "Description and Numerical Simulations of Dynamic Positioning In Reversing Managed Ice", In Proc. Int. Conf. Port Ocean Eng. Arctic Conditions. Trondheim, Norway, June, 2015. Vol. 23 |
| Abstract: This paper discusses and describes the design of dynamic positioning control systems for drifting managed sea ice environments. Compared to open water conditions, the presence of ice imposes complex dynamics on the motions of the vessel, which must be accounted for in the control algorithms. Foremost this relates to estimating and tracking variations of the global loads with sufficient precision, and, if possible, automatically vaning the vessel into the ice drift direction. In this paper, several approaches and design possibilities for this is explored, and two distinctly different designs are proposed. These are compared in a high-fidelity numerical tool which simulates the ship-ice interaction in managed ice. The case investigated is an 180 degree elliptic ice drift reversal with severe curvature, where the ice drift velocity decreases until the ellipse pivot point is reached, and then it increases again. Both proposed systems demonstrate positioning and vaning capabilities in moderate and severe ice conditions, but with different performance. These differences are discussed in the paper. Additionally, the study showcases the importance of using high-fidelity numerical models as a control system development tool. |
BibTeX:
@conference{okje15B,
author = {Kjerstad, Ø. K. and Metrikin, I. and Skjetne, R.},
title = {Description and Numerical Simulations of Dynamic Positioning In Reversing Managed Ice},
booktitle = {Proc. Int. Conf. Port Ocean Eng. Arctic Conditions},
year = {2015},
volume = {23},
url = {http://www.poac.com/Papers/2015/pdf/poac15Final00223.pdf}
}
|
| Lubbad R, Løset S and Skjetne R (2015), "Numerical Simulations Verifying Arctic Offshore Field Activities", In Proc. Int. Conf. Port Ocean Eng. Arctic Conditions. Trondheim, Norway, June, 2015. Vol. 23 |
| Abstract: A main challenge for offshore structures and marine operations in the Arctic is the presence of sea ice. Drillships and floating production units (FPUs) running operations in the Arctic typically require protection by using ice management, e.g. icebreakers battling large ice floes followed by icebreakers downstream that cut the ice into smaller pieces in front of the drillship or FPU. The essence of such operations is to reduce the ice actions on the protected units by manipulating the ice conditions. As offshore activities in the Arctic constitute a relatively new field with only a handful of relevant operations to draw experience from, and since full-scale trials are extremely expensive, there is an expressed need for more detailed and cost-efficient analysis of concepts based on numerical simulations. However, until recently simulation tools of sufficient quality to perform such numerical analysis have not existed. The only verification available has been through a limited set of experiments in ice model basins. Today, this has changed through the efforts at NTNU hosting the SFI SAMCoT, laying the foundation of a versatile and highly accurate high-fidelity numerical simulator of offshore structures in drifting sea-ice conditions. The paper presents this numerical simulator, which simulates the interaction between floe-ice including ridges and floating structures. This technology has a considerable potential for applications, such as simulation-based verification of structural designs and Arctic offshore operations. We will then discuss how this can be fitted into a new framework for third party verification of new concepts for Arctic offshore activities that will benefit solution suppliers, contractors, end clients, and the public. |
BibTeX:
@conference{rlub15A,
author = {Lubbad, R. and Løset, S. and Skjetne, R.},
title = {Numerical Simulations Verifying Arctic Offshore Field Activities},
booktitle = {Proc. Int. Conf. Port Ocean Eng. Arctic Conditions},
year = {2015},
volume = {23},
url = {http://www.poac.com/Papers/2015/pdf/poac15Final00254.pdf}
}
|
| Norgren P and Skjetne R (2015), "Iceberg Detection and Edge-Following using AUV with Multibeam Sonar", In Proc. Int. Conf. Port Ocean Eng. Arctic Conditions. Trondheim, Norway, June, 2015. Vol. 23 |
| Abstract: Detailed information about the subsurface section of an iceberg is of high value to researchers and offshore operators, and can be used to create hydrodynamic models of icebergs, calculate impact loads, and to forecast iceberg drift. However, since the iceberg will translate and rotate when affected by water currents, mapping the underwater geometry of an iceberg is non-trivial. This paper will describe an algorithm for automatic detection and mapping of drifting icebergs using autonomous underwater vehicles (AUVs). Using an upwards-looking multibeam echosounder (MBE), the AUV monitors a given area in detection mode. When exceeding a specified ice draft threshold, the AUV will enter mapping mode. The AUV will search for the edge of the iceberg, and follow the edge once detected. Through this paper, the detection procedure based on measurements from a MBE is presented, and the algorithm for mapping the iceberg while the iceberg is drifting is outlined. The results will be presented in a simulation study, which will show the effectiveness of the mapping procedure for a simulated iceberg drifting with constant, linear speed. The AUV will perform a complete circumnavigation of the iceberg, before completing the mapping procedure, and continuing its pre-defined mission. |
BibTeX:
@conference{pnor15A,
author = {Norgren, P. and Skjetne, R.},
title = {Iceberg Detection and Edge-Following using AUV with Multibeam Sonar},
booktitle = {Proc. Int. Conf. Port Ocean Eng. Arctic Conditions},
year = {2015},
volume = {23},
url = {http://www.poac.com/Papers/2015/pdf/poac15Final00115.pdf}
}
|
| Norgren P and Skjetne R (2015), "Line-of-sight iceberg edge-following using an AUV equipped with multibeam sonar", In Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts. Copenhagen, Denmark, Aug., 2015. Vol. 48, pp. 81-88. |
| Abstract: Obtaining 3D information about ice features, like icebergs, are of interest to researchers and o shore operators moving into the Arctic. Icebergs are affected by wind, and
ocean currents, and can have unpredictable drift patterns, causing challenges when it comes to mapping objectives. Autonomous underwater vehicles (AUVs) equipped with multibeam echosounders are suitable for obtaining measurements of the underwater geometry of icebergs, but advances in autonomy are needed to map drifting icebergs reliably. This paper details a guidance algorithm for detecting and circumnavigating an iceberg - following the iceberg edge. The guidance scheme is implemented as a state machine, starting in an iceberg detection-mode. Once an iceberg is detected, the AUV will enter a mapping-mode. An edge detection algorithm will determine the position of the edge, and a line-of-sight approach will be used for edge-following. A six degree-of-freedom AUV simulator is used to perform a simulation study, to show how AUV dynamics affect the results. The simulation study presented shows the algorithm's effectiveness, both when the iceberg is assumed stationary, and when the iceberg is drifting and rotating with constant velocity. |
BibTeX:
@conference{pnor15B,
author = {Norgren, P. and Skjetne, R.},
title = {Line-of-sight iceberg edge-following using an AUV equipped with multibeam sonar},
booktitle = {Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts},
year = {2015},
volume = {48},
pages = {81--88},
note = {IFAC-PapersOnLine},
url = {http://www.sciencedirect.com/science/article/pii/S2405896315021539},
doi = {10.1016/j.ifacol.2015.10.262}
}
|
| Ren Z, Skjetne R and Hassani V (2015), "Supervisory Control of Line Breakage for Thruster-Assisted Position Mooring System", In Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts. Copenhagen, Denmark, Aug., 2015. Vol. 48, pp. 235-240. |
| Abstract: Thruster-assisted position mooring (TAPM) is an energy-effcient and reliable stationkeeping method for deep water structures. Mooring line breakage can significantly influence the control system, and ultimately reduce the reliability and safety during operation and production. Therefore, line break detection is a crucial issue for TAPM systems. Tension measurement units are useful tools to detect line failures. However, these units increase the building cost of the system, and in a large portion of existing units in operation line tension sensors are not installed. This paper presents a fault-tolerant control scheme based on estimator-based supervisory control methodology to detect and isolate a line failure with only position measurements. After detecting a line break, a supervisor switches automatically a new controller into the feedback loop to keep the vessel within the safety region. Numerical simulations are conducted to verify the performance of the proposed technique, for a turret-based mooring system. |
BibTeX:
@conference{zren15A,
author = {Ren, Z. and Skjetne, R. and Hassani, V.},
title = {Supervisory Control of Line Breakage for Thruster-Assisted Position Mooring System},
booktitle = {Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts},
year = {2015},
volume = {48},
pages = {235--240},
note = {IFAC-PapersOnLine},
url = {http://www.sciencedirect.com/science/article/pii/S2405896315021771},
doi = {10.1016/j.ifacol.2015.10.286}
}
|
| Ren Z, Skjetne R and Kjerstad ØK (2015), "A Tension-based Position Estimation Approach for Moored Marine Vessels", In Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts. Copenhagen, Denmark, Aug., 2015. Vol. 48, pp. 248-253. |
| Abstract: This paper presents a novel idea on a tension-based localization approach as a redundancy measure to handle the situation when the position reference (posref) signals are not available or significant GNSS drifts occur, such as sudden ionospheric disturbances, for thruster-assisted moored vessels. The only information needed is the tension measurements from tension cells. This method can improve the redundancy and safety of offshore operation, by detecting and verifying posref failure modes. It can even take over the posref function if one no longer trust the main posref measurements. Based on a residual signal, a fault detection and estimation approach is introduced and verified through simulations. |
BibTeX:
@conference{zren15B,
author = {Ren, Z. and Skjetne, R. and Kjerstad, Ø. K.},
title = {A Tension-based Position Estimation Approach for Moored Marine Vessels},
booktitle = {Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts},
year = {2015},
volume = {48},
pages = {248--253},
note = {IFAC-PapersOnLine},
url = {http://www.sciencedirect.com/science/article/pii/S2405896315021795},
doi = {10.1016/j.ifacol.2015.10.288}
}
|
| Skjetne R (2015), "Determining ice loads for OSVs", Keynote lecture. Nov. 30 - Dec. 01, 2015. |
| Abstract: Standardized load formulas from ISO are based on empirical formulations and are valid only for single ice features and a single limiting load mechanism. Numerical tools giving more realistic and accurate loads on structures are entering the market. This is necessary in order to ensure sufficiently rich and detailed analysis of structures and operations in Arctic sea-ice. Independent verification of Arctic activities is one way to ensure a distribution of responsibilities and a sound "concept review" that can ensure necessary safety. Effective stationkeeping was discussed, including ice management and ice intelligence activities, to ensure DP in ice. In particular, methods for updating the DP control systems to handle ice loads have been studied deeply, and new ice-adapted systems are believed to be issued soon if the market continues to request it. |
BibTeX:
@misc{rskj15A,
author = {Skjetne, R.},
title = {Determining ice loads for OSVs},
howpublished = {Keynote lecture},
year = {2015},
note = {6th Annual seminar on Design and Operation of OSVs for Ice and Cold Climates},
url = {https://www.researchgate.net/publication/285583786_Determining_ice_loads_for_OSVs},
doi = {10.13140/RG.2.1.2537.6086}
}
|
| Skjetne R and Bø TI (2015), "Design and Verification of Control Systems for Safe and Energy-efficient Vessels with Hybrid Power Plants", Plenary. Feb. 11-12, 2015. |
BibTeX:
@misc{rskj15B,
author = {Skjetne, R. and Bø, T. I.},
title = {Design and Verification of Control Systems for Safe and Energy-efficient Vessels with Hybrid Power Plants},
howpublished = {Plenary},
year = {2015},
note = {DP og forankring av offshore installasjoner 2015},
url = {https://www.researchgate.net/publication/285584324_Design_and_Verification_of_Control_Systems_for_Safe_and_Energy-efficient_Vessels_with_Hybrid_Power_Plants},
doi = {10.13140/RG.2.1.4864.1365}
}
|
| Tutturen SA and Skjetne R (2015), "Hybrid Control to Improve Transient Response of Integral Action in Dynamic Positioning of Marine Vessels", In Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts. Copenhagen, Denmark, Aug., 2015. Vol. 48, pp. 166-171. |
| Abstract: A hybrid control approach for integral action in the PID control law for dynamically positioned marine vessels is considered. The proposed method is essentially a resetting of the integration gain when the control performance deteriorates. The method allows for a flexible tuning, and could be useful when there are long periods of normal operating conditions, but abnormal events may occur. In that case the hybrid controller will have a low tuning in the normal regime and switch to a more aggressive tuning in the abnormal regime. Stability of the
hybrid system is investigated, and a simulation case is performed. |
BibTeX:
@conference{stut15A,
author = {Tutturen, S. A. and Skjetne, R.},
title = {Hybrid Control to Improve Transient Response of Integral Action in Dynamic Positioning of Marine Vessels},
booktitle = {Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts},
year = {2015},
volume = {48},
pages = {166--171},
note = {IFAC-PapersOnLine},
url = {http://www.sciencedirect.com/science/article/pii/S2405896315021667},
doi = {10.1016/j.ifacol.2015.10.275}
}
|
| Skjetne R (2014), "Arctic DP: The Arctic Offshore Project on Stationkeeping in Ice", Keynote lecture. Oct. 28-29, 2014. |
| Abstract: In this keynote lecture we discuss the challenges and results from the project Arctic DP: «Safe and green dynamic positioning operations of offshore vessels in an Arctic environment» that was awarded by the Research Council of Norway in 2010 to our research group and industry partners Kongsberg Maritime, Statoil, and DNV GL. In particular we are looking into new control strategies for dynamic positioning systems to compensate loads from drifting sea-ice in an Arctic stationkeeping operation. In addition we are looking into the Ice Management system and methods to provide better local surveillance of sea-ice and icebergs in Arctic offshore operations by using UAVs and AUVs as mobile sensor platforms in combination with shipboard sensors, and image processing algorithms to extract useful information from sea-ice images. Such sensory information of the Arctic ice environment can then potentially be used in future Ice Management decision support systems and in feedforward control algorithms to better guide and control the DP vessel. |
BibTeX:
@misc{rskj14A,
author = {Skjetne, R.},
title = {Arctic DP: The Arctic Offshore Project on Stationkeeping in Ice},
howpublished = {Keynote lecture},
year = {2014},
url = {https://www.researchgate.net/publication/267512220_Arctic_DP_The_Arctic_Offshore_Project_on_Stationkeeping_in_Ice_IBC_Ice_Class_Vessels_2014},
doi = {10.13140/2.1.2843.1360}
}
|
| Norgren P, Lubbad R and Skjetne R (2014), "Unmanned underwater vehicles in Arctic operations", In Proc. IAHR Int. Symp. on Ice. Singapore, Aug. 11-15, 2014. , pp. 89-101. |
| Abstract: Unmanned underwater vehicle technology has matured to a point where it is possible to use these types of vehicles for deep water, and long endurance missions. The Arctic seafloor remains one of the last unexplored areas on Earth, but unmanned underwater vehicles are starting to change this. From the first deployment of autonomous underwater vehicles in the Arctic in 1972, these vehicles have been used in more complex and longer missions. This paper presents a survey of autonomous underwater vehicles used in Arctic operations. The paper highlights the applications of such vehicles in the Arctic and discusses the motivation behind their development. Through this paper, it will be made clear that special equipment, planning, and considerations must be made for an operation in the Arctic to be successful. Much experience has been gathered through the different expeditions that have taken place in the last two decades, and a summary of the different experiences will be discussed. Specifically, experiences from autonomous underwater vehicles operating under ice, navigation and communication in the Arctic, and operations from ships are discussed. Furthermore, some of the authors own experience from deploying a remotely operated vehicle from the icebreaker Oden north-east of Greenland in 2013 will be presented. |
BibTeX:
@conference{pnor14A,
author = {Norgren, P. and Lubbad, R. and Skjetne, R.},
title = {Unmanned underwater vehicles in Arctic operations},
booktitle = {Proc. IAHR Int. Symp. on Ice},
year = {2014},
pages = {89--101},
url = {https://www.researchgate.net/publication/330703330_Unmanned_underwater_vehicles_in_Arctic_operations}
}
|
| Orsten A, Norgren P and Skjetne R (2014), "LOS guidance for towing an iceberg along a straight-line path", In Proc. IAHR Int. Symp. on Ice. Singapore, Aug. 11-15, 2014. , pp. 526-534. |
| Abstract: Motivated by the need to develop a reliable and safe way of towing icebergs, this paper investigates the use of a feedback-based guidance algorithm for steering the iceberg along a pre-defined safe track. A simplified, linear iceberg model is developed in 2 degrees of freedom (DOF) to capture the horizontal motion, including the effect of constant and irrotational ocean currents. Previously, a Line-of-Sight (LOS) algorithm has been implemented for steering a ship along a pre-defined path. The algorithm has been modified to include the effect of an ocean current, using integral action. In this paper, the current-modified LOS algorithm is augmented in order to apply it to the 2-DOF horizontal iceberg model. The output of the iceberg LOS algorithm is the desired towline angle. Guidance of the model is achieved through a tow force T with a direction that should conform to the desired towline angle.
Simulation studies, showing the performance of the LOS algorithm, are performed in the presence of both a constant, and a slowly-varying ocean current. A towing vessel reference model is proposed in order to obtain a better resemblance between the change of the towline angle and the movements of the towing vessel. The simulation studies all show that the iceberg trajectories converge to and move along the desired path, and that the vessel reference model provides feasible trajectories for the towing vessel. |
BibTeX:
@conference{aors14A,
author = {Orsten, A. and Norgren, P. and Skjetne, R.},
title = {LOS guidance for towing an iceberg along a straight-line path},
booktitle = {Proc. IAHR Int. Symp. on Ice},
year = {2014},
pages = {526--534},
url = {https://www.researchgate.net/publication/330703161_LOS_guidance_for_towing_an_iceberg_along_a_straight-line_path}
}
|
| Veksler A, Johansen TA, Skjetne R and Mathiesen E (2014), "Reducing power transients in diesel-electric dynamically positioned ships using re-positioning", In Proc. Annual Conf. IEEE Industrial Electronics Society. Dallas, TX, USA, Oct-Nov, 2014. Vol. 40 |
| Abstract: A thrust allocation method with a functionality to assist power management systems by using the hull of the ship as a store of potential energy in the field of environmental forces has been recently proposed and demonstrated to work in simulation. This functionality allows the thrust allocation algorithm to decrease the power consumption in the thrusters when a sharp increase in power consumption is demanded elsewhere on the ship. This way, the high-frequency part of the load variations on the power plant can be reduced, at the expense of minor (typically less than 1 meter) variations in the position of the vessel. The advantages from reduced variations in load include reduced wear-and-tear of the power plant, more stable frequency on the electric grid, reduced risk of blackout due to underfrequency, and more reliable synchronization when connecting additional generators or connecting bus segments. In the present work, this functionality is improved further by continuously monitoring the environmental forces and modifying the setpoint of the dynamic positioning algorithm to place the vessel a short distance (e.g. 20 cm) in the direction of steepest increase of the environmental force potential, thus maximizing the available potential energy. The increased potential energy creates additional capacity for assisting the power plant, which is shown in simulation to be significant. |
BibTeX:
@conference{avek14A,
author = {Veksler, A. and Johansen, T. A. and Skjetne, R. and Mathiesen, E.},
title = {Reducing power transients in diesel-electric dynamically positioned ships using re-positioning},
booktitle = {Proc. Annual Conf. IEEE Industrial Electronics Society},
year = {2014},
volume = {40},
url = {https://ieeexplore.ieee.org/document/7048510},
doi = {10.1109/IECON.2014.7048510}
}
|
| Chabaud V, Steen S and Skjetne R (2013), "Real-Time Hybrid Testing for Marine Structures: Challenges and Strategies", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Nantes, France, June, 2013. Vol. 5 |
| Abstract: Within the field of hydrodynamics, it is fairly easy to find examples of model tests whose performance is impaired by only a subpart of the whole system, which may not be the one of interest.Real-time hybrid testing (RTHT) overcomes this issue by performing scale model testing only on a subpart of the whole structure, the remainder being simulated numerically. The loads acting on the virtual substructure are calculated from onlinemeasured motions of the physical substructure and actuated back on the latter in real-time. RTHT involves data measurement, filtering, force estimation, motion observing and force actuation. The main challenge is to fit all of those items into one time step. A simple case study is suggested. It consists in a linearized one degree of freedom floating wind turbine, whose floating substructure is physically tested while wind loads are numerically simulated and actuated. Design rules to build the corresponding RTHT set up are then presented. |
BibTeX:
@conference{cval13A,
author = {Chabaud, V. and Steen, S. and Skjetne, R.},
title = {Real-Time Hybrid Testing for Marine Structures: Challenges and Strategies},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2013},
volume = {5},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1786426},
doi = {10.1115/OMAE2013-10277}
}
|
| Jørgensen U and Skjetne R (2013), "Real-time 3D Reconstruction of Underwater Sea-ice Topography by Observations from a Mobile Robot in the Arctic", In Proc. IFAC Conf. Contr. Appl. Marine Systems. Osaka, Japan, Sept., 2013. Vol. 9, pp. 310-315. |
| Abstract: In this paper we present an online estimation design for a drifting three dimensional ice topography. Representing the topography by a 2D truncated Fourier series model based on a set of nodes distributed over the area of interest, an observer is proposed to estimate the unknown coefficients of the model. The measurements are assumed provided by an underwater robot equipped with an upwardlooking multi-beam echo sounder or similar. An observer is defined for each node to filter the ice draft measurements and handle the on-off switching when the underwater mobile sensor moves in and out of range. The effectiveness of the estimation algorithm is simulated based on an extensive data set with a highly varying seabed topography, emulating in our case a typical ice topography. |
BibTeX:
@conference{ujor13B,
author = {Jørgensen, U. and Skjetne, R.},
title = {Real-time 3D Reconstruction of Underwater Sea-ice Topography by Observations from a Mobile Robot in the Arctic},
booktitle = {Proc. IFAC Conf. Contr. Appl. Marine Systems},
year = {2013},
volume = {9},
pages = {310-315},
note = {IFAC-PapersOnLine},
url = {http://www.sciencedirect.com/science/article/pii/S1474667016461768},
doi = {10.3182/20130918-4-JP-3022.00054}
}
|
| Jørgensen U and Skjetne R (2013), "Dynamic estimation of drifting ice topography over a 2D area using mobile underwater measurements", In Proc. Int. Conf. Port Ocean Eng. Arctic Conditions. Espoo, Finland, June, 2013. |
| Abstract: We present an estimation design for monitoring a drifting underwater ice topography, for realtime acquisition of high resolution ice thickness data in a local operations area. Additionally, the feature of detection and tracking of significant ice features such as ridges, growlers, bergy bits, and icebergs frozen into the sea ice comes for free from the setup. For continuous underwater monitoring of the drifting sea-ice we are challenged by two obstacles: 1) the ice topography is a dynamic landscape, and 2) we need to communicate the measurement data in real time through a limited hydroacoustic communication channel. Representing the topography by a truncated 2D Fourier series and a spatially discretized set of measurement nodes distributed over the surveillance area, a steepest descent method is proposed to make the underwater ice topography estimate converge to the real topography. Since only a small number of Fourier coefficients is needed to represent the topography sufficiently well, it becomes possible to transmit the estimated topography in real time through the hydroacoustic communication channel and to online reconstruct and present it in a surface-based operation center. Since the nodes in the observation grid will only be measured while the mobile sensor is in range, a nonlinear observer is proposed to filter the measurements and update them dynamically in dead-reckoning when measurements are not available. The effectiveness of the estimation algorithm is simulated based on an extensive and highly varying bottom topography, emulating in our case a typical ice topography. |
BibTeX:
@conference{ujor13A,
author = {Jørgensen, U. and Skjetne, R.},
title = {Dynamic estimation of drifting ice topography over a 2D area using mobile underwater measurements},
booktitle = {Proc. Int. Conf. Port Ocean Eng. Arctic Conditions},
year = {2013},
url = {http://www.poac.com/Papers/2013/pdf/POAC13_043.pdf}
}
|
| Kjerstad ØK, Skjetne R and Berge BO (2013), "Constrained nullspace-based thrust allocation for heading prioritized stationkeeping of offshore vessels in ice", In Proc. Int. Conf. Port Ocean Eng. Arctic Conditions. Espoo, Finland, June, 2013. |
| Abstract: The positioning capability is a crucial property for safe and reliable operations of a dynamically positioned (DP) offshore vessel. The limiting factor in such is the vessel's thruster configuration and the maximum resultant forces and turning moment this can produce in all directions. Based on the vessel's position and velocity deviations, the DP control law computes a desired resultant load set as correction. This is distributed by the DP thrust allocation algorithm to individual thruster forces based on rated power, thruster type (force direction capability), and hull position. In this paper, a novel and computationally light constrained thrust allocation algorithm which offers eased thruster weighting and prioritization between the degrees of freedom (surge, sway, and yaw), is developed. It is motivated by the importance of maintaining the heading directly against the ice drift, such that the projection of the vessel in the ice is minimized. Thus, first the yaw moment is allocated to the thrusters with a given fraction of the capability at its disposal. Then, the total remainder is distributed to surge and then sway. If the loads on the vessel are beyond the capability of the thrusters, then sway is affected first, then surge, and last yaw. Due to its simplicity, this method provides a convenient tool to evaluate and compare ice loads from model testing with the thrust capability of the DP vessel. In order to enable a DP-ice capability analysis, the quantification of loss of capability is investigated. This introduces three descriptive measures of the ice loads of a given ice condition; peak load, significant load, and mean load. As a case study, a towing tank dataset of an experimental intervention vessel (the CIVArctic vessel) in broken ice is investigated and discussed. |
BibTeX:
@conference{okje13A,
author = {Kjerstad, Ø. K. and Skjetne, R. and Berge, B. O.},
title = {Constrained nullspace-based thrust allocation for heading prioritized stationkeeping of offshore vessels in ice},
booktitle = {Proc. Int. Conf. Port Ocean Eng. Arctic Conditions},
year = {2013},
url = {http://www.poac.com/Papers/2013/pdf/POAC13_064.pdf}
}
|
| Skjetne R and Kjerstad ØK (2013), "Recursive nullspace-based control allocation with strict prioritization for marine craft", In Proc. IFAC Conf. Contr. Appl. Marine Systems. Osaka, Japan, Sept., 2013. Vol. 9, pp. 49-54. |
| Abstract: In control allocation it is often important to prioritize among the directions to produce control effort, especially in cases of limited capacity. Motivated by a requirement for strict prioritization among the control directions, a recursive nullspace-based allocation design based on direct use of the generalized pseudoinverses and nullspace matrices is proposed. The allocation design divides the overall problem into r subproblems according to a prioritization sequence, and a recursive method is proposed to solve the allocation subproblem in each step. By hiding the allocated controls from subsequent steps in the nullspace corresponding to the present step, the influence of lower priority control actions onto higher priority directions are nullified to achieve the specified prioritization. The method is verified by analyzing the thruster capacity of an Arctic intervention vessel based on experimental ice towing data. |
BibTeX:
@conference{rskj13A,
author = {Skjetne, R. and Kjerstad, Ø. K.},
title = {Recursive nullspace-based control allocation with strict prioritization for marine craft},
booktitle = {Proc. IFAC Conf. Contr. Appl. Marine Systems},
year = {2013},
volume = {9},
pages = {49-54},
note = {IFAC Proceedings Volumes},
url = {http://www.sciencedirect.com/science/article/pii/S147466701646132X},
doi = {10.3182/20130918-4-JP-3022.00052}
}
|
| Su B, Kjerstad ØK, Skjetne R and Berg TE (2013), "Ice-going capability assessment and DP-Ice Capability Plot for a double acting intervention vessel in level ice", In Proc. Int. Conf. Port Ocean Eng. Arctic Conditions. Espoo, Finland, June, 2013. |
| Abstract: In this paper a numerical model and experimental data are applied to investigate and analyze the level ice performance of a double acting intervention vessel. This includes both ice-breaking capability and maneuverability aspects where h-v curves, breaking pattern, and turning circles are evaluated and discussed. As part of the study a static dynamic positioning capability analysis is carried out to evaluate the vessel's stationkeeping performance in ice. The analysis is based on a heading prioritized thrust allocation algorithm and the simulated ice loads acquired by numerical towing experiments. The preliminary results include, what we call, DP-Ice Capability Plots, which are parameterized by ice thickness and drift speed. |
BibTeX:
@conference{bsu13A,
author = {Su, B. and Kjerstad, Ø. K. and Skjetne, R. and Berg, T. E.},
title = {Ice-going capability assessment and DP-Ice Capability Plot for a double acting intervention vessel in level ice},
booktitle = {Proc. Int. Conf. Port Ocean Eng. Arctic Conditions},
year = {2013},
url = {http://www.poac.com/Papers/2013/pdf/POAC13_095.pdf}
}
|
| Veksler A, Johansen TA, Mathiesen E and Skjetne R (2013), "Governor principle for increased safety and economy on vessels with diesel-electric propulsion", In Proc. European Control Conf.. Zürich, Switzerland, July, 2013. , pp. 2579-2584. |
| Abstract: In this paper, a governor principle for marine dieselelectric power plants with a normal and an emergency mode is proposed. In the normal mode, the governor is tuned such that the variations in the electric frequency are weighed against operational costs such as specific fuel consumption, pollutant emissions and wear-and-tear of the diesel engine due to thermal variations. In emergency mode, the governor disregards the operational costs and attempts to keep the frequency as steady as possible. This leads to larger margins to the underfrequency condition and therefore reduces the risk of blackout. It also allows for a more reliable synchronization of additional generating sets to the electric grid. Because the emergency mode is entered under abnormal conditions only, the overall increase in operational costs resulting from this addition is negligible. The governor is implemented as a receding horizon controller. |
BibTeX:
@conference{avek13A,
author = {Veksler, A. and Johansen, T. A. and Mathiesen, E. and Skjetne, R.},
title = {Governor principle for increased safety and economy on vessels with diesel-electric propulsion},
booktitle = {Proc. European Control Conf.},
year = {2013},
pages = {2579-2584},
url = {https://ieeexplore.ieee.org/document/6669837},
doi = {10.23919/ECC.2013.6669837}
}
|
| Zhang Q, Skjetne R and Su B (2013), "Automatic image segmentation for boundary detection of apparently connected sea-ice floes", In Proc. Int. Conf. Port Ocean Eng. Arctic Conditions. Espoo, Finland, June, 2013. |
| Abstract: Ice concentration, ice types, and floe size distribution are three important factors in the analysis of ice-structure interaction in a broken ice field. The use of cameras as sensors for offshore operations in ice-covered regions is relevant for identification of the ice conditions and ice parameters, as part of a sea-ice monitoring system. In particular, this can be used for estimation of ice forces that are critical to Dynamic Positioning (DP) operations in Arctic waters. For the actual ice image, the apparent connection between ice floes should be identified, as it challenges the boundary detection algorithms and seriously affects ice floe size analysis. To solve this problem, a method of connected ice floes segmentation based on the watershed transform is presented in this paper. After ice image preprocessing, all the ice floes in the image are first identified by the Otsu threshold algorithm, and the greyscale image is converted into a binary image. Then, the seed points for the individual ice floes are located, and the watershed algorithm is carried out to segment the image. Finally, a chain code is used for concave spot localization, and then over-segmentation lines are removed. Experimental results are presented and a discussion of the method is given. |
BibTeX:
@conference{qzha13A,
author = {Zhang, Q. and Skjetne, R. and Su, B.},
title = {Automatic image segmentation for boundary detection of apparently connected sea-ice floes},
booktitle = {Proc. Int. Conf. Port Ocean Eng. Arctic Conditions},
year = {2013},
url = {http://www.poac.com/Papers/2013/pdf/POAC13_035.pdf}
}
|
| Jørgensen U and Skjetne R (2012), "Generating Safe and Equally Long Trajectories for Multiple Unmanned Vessels", In Proc. Mediterranean Conf. Contr. and Automation. Barcelona, Spain, July, 2012. Vol. 20 |
| Abstract: In this paper a path planning method for multiple unmanned agents is presented. The proposed algorithm utilizes Dubins paths such that the final paths will be feasible for
agents with a given turning constraint. The algorithm further ensures that the agents will avoid collisions. For cases where it is important to arrive simultaneously, this is achieved by assuming that the vehicles are operating with constant speeds and then create equally long paths. The main challenge is, however, to ensure that the algorithm is computationally efficient, as it is intended for small sized unmanned vehicles where decisions have to be taken in a short time and calculated with restricted computational units. The proposed algorithm is tested with a case study that illustrates the findings. |
BibTeX:
@conference{ujor12B,
author = {Jørgensen, U. and Skjetne, R.},
title = {Generating Safe and Equally Long Trajectories for Multiple Unmanned Vessels},
booktitle = {Proc. Mediterranean Conf. Contr. and Automation},
year = {2012},
volume = {20},
url = {https://ieeexplore.ieee.org/document/6265862},
doi = {10.1109/MED.2012.6265862}
}
|
| Jørgensen U and Skjetne R (2012), "Dynamic Estimation of Drifting Ice Topography Using Underwater Mobile Measurements", In Proc. American Control Conf.. Montreal, Canada, June, 2012. , pp. 301-306. |
| Abstract: In this paper we present an estimation design for a drifting two dimensional ice topography. Under the assumption that the topography can be accurately represented by a truncated Fourier series, and given a set of measurements distributed discretely along the topography, the steepest descent method is proposed to solve the problem. The chosen method
allows different weighting on the various measurements and coefficients such that the weight on possible faulty measurements can be reduced, while important coefficients can be prioritized. In cases where measurements of the ice topography are available only periodically, an observer is proposed such that non-measured nodes can be dynamically updated. In both cases the effectiveness of the estimation algorithm is simulated in a constructed ideal scenario, as well as a scenario where a set of real ice measurements are taken from the underside of an ice sheet off the cost of Greenland. |
BibTeX:
@conference{ujor12A,
author = {Jørgensen, U. and Skjetne, R.},
title = {Dynamic Estimation of Drifting Ice Topography Using Underwater Mobile Measurements},
booktitle = {Proc. American Control Conf.},
year = {2012},
pages = {301--306},
url = {https://ieeexplore.ieee.org/document/6315459},
doi = {10.1109/ACC.2012.6315459}
}
|
| Kjerstad ØK and Skjetne R (2012), "Observer design with disturbance rejection by acceleration feedforward", In Proc. IFAC Symp. Robust Control Design. Aalborg, Denmark, June, 2012. Vol. 7 |
| Abstract: This paper addresses observer design of mechanical systems subject to unknown external disturbances and unmodeled dynamics. For fast-acting disturbance forces, realistic and accurate physical models do not always exist, such as for dynamic positioning of marine vessels in ice-infested waters. To accommodate such forces and provide disturbance rejection, a delayed acceleration measurement is used to form an acceleration feedforward which captures the perturbations and enhances the observer phase margins. Through the acceleration measurement, an inherent sensor bias is introduced, creating a pseudo-force in the system. This is tracked and compensates by a bias estimate. The theoretical foundation is exemplified by the derivation of a DP observer and a simulation study featuring an inverted pendulum. |
BibTeX:
@conference{okje12A,
author = {Kjerstad, Ø. K. and Skjetne, R.},
title = {Observer design with disturbance rejection by acceleration feedforward},
booktitle = {Proc. IFAC Symp. Robust Control Design},
year = {2012},
volume = {7},
note = {IFAC-PapersOnLine},
url = {http://www.sciencedirect.com/science/article/pii/S1474667015377430},
doi = {10.3182/20120620-3-DK-2025.00157}
}
|
| Kjerstad ØK and Skjetne R (2012), "Feedforward linearization and disturbance rejection of mechanical systems using acceleration measurements", In Proc. IFAC Symp. Robust Control Design. Aalborg, Denmark, June, 2012. Vol. 7 |
| Abstract: In this paper a time-delayed acceleration measurement is used to linearize a second order nonlinear system. A theoretical foundation is developed, and a control strategy is presented which handles the challenges related to classical linearization. Utilizing the acceleration measurement to directly cancel the nonlinearities constitute a feedforward approach which increases robustness with respect to unmodeled dynamics and model uncertainties. Due to the time-delay, one or more perturbation terms dependent on a previous state of the system appears. This work outlines a stability criterion which these terms must satisfy in order for the linearization to be valid, where it is shown that the performance of the scheme is dependent on
the measurement time-delay. The proposed method proves feasible when compared to two other nonlinear control strategies, including a conventional linearization control law and a sliding mode control law. In comparison, the feedforward linearization features robust performance without aggressive control input. |
BibTeX:
@conference{okje12B,
author = {Kjerstad, Ø. K. and Skjetne, R.},
title = {Feedforward linearization and disturbance rejection of mechanical systems using acceleration measurements},
booktitle = {Proc. IFAC Symp. Robust Control Design},
year = {2012},
volume = {7},
note = {IFAC-PapersOnLine},
url = {http://www.sciencedirect.com/science/article/pii/S1474667015376576},
doi = {10.3182/20120620-3-DK-2025.00146}
}
|
| Scibilia F and Skjetne R (2012), "Constrained Control Allocation for Vessels with Azimuth Thrusters", In Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts. Arenzano, Italy, Sept, 2012. Vol. 9 |
| Abstract: Control allocation may produce particular thruster configurations which cause poor maneuverability and temporary loss of controllability in certain directions. The paper presents a new approach for dealing with these singular configurations, which allows to formulate the control allocation problem into optimization problems easy to set up. The approach is validated with numerical simulations on experimental model test data. |
BibTeX:
@conference{fsci12C,
author = {Scibilia, F. and Skjetne, R.},
title = {Constrained Control Allocation for Vessels with Azimuth Thrusters},
booktitle = {Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts},
year = {2012},
volume = {9},
note = {IFAC-PapersOnLine},
url = {http://www.sciencedirect.com/science/article/pii/S147466701631196X},
doi = {10.3182/20120919-3-IT-2046.00002}
}
|
| Scibilia F, Jørgensen U and Skjetne R (2012), "AUV Guidance System for Subsurface Ice Intelligence", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Rio de Janeiro, Brazil, July, 2012. Vol. 31 |
| Abstract: This paper considers an AUV guidance system for subsurface ice intelligence. A topologically organized neural network model is used to represent the operating environment. The dynamics of each neuron, characterized by a shunting equation, are used to represent the local environmental information. Targeted areas have the highest values. The AUV moves from areas with low dynamics to areas with higher dynamics like in a potential field navigation. The kinematic constraints of the AUV are taken into account by using Dubins theory to generate feasible paths. |
BibTeX:
@conference{fsci12B,
author = {Scibilia, F. and Jørgensen, U. and Skjetne, R.},
title = {AUV Guidance System for Subsurface Ice Intelligence},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2012},
volume = {31},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1733063},
doi = {10.1115/OMAE2012-83811}
}
|
| Scibilia F, Jørgensen U and Skjetne R (2012), "AUV Guidance System for Dynamic Trajectory Generation", In Proc. IFAC Workshop on Navigation, Guidance and Control of Underwater Vehicles. Porto, Portugal, April, 2012. |
| Abstract: This paper considers an AUV guidance system for collision-free transit and complete area coverage. A topologically organized neural network model is used to represent the operating environment. The activity of each neuron, characterized by a shunting equation, is used to represent the local environmental information. Targeted areas have the highest values. The AUV moves from areas with low activity to areas with higher activity like in a potential field navigation. The kinetic constraints of the AUV are taken into account by using Dubins theory to generate feasible paths. |
BibTeX:
@conference{fsci12A,
author = {Scibilia, F. and Jørgensen, U. and Skjetne, R.},
title = {AUV Guidance System for Dynamic Trajectory Generation},
booktitle = {Proc. IFAC Workshop on Navigation, Guidance and Control of Underwater Vehicles},
year = {2012},
note = {IFAC Proceedings Volumes},
url = {http://www.sciencedirect.com/science/article/pii/S1474667016306024},
doi = {10.3182/20120410-3-PT-4028.00033}
}
|
| Veksler A, Johansen TA and Skjetne R (2012), "Transient power control in dynamic positioning - governor feedforward and dynamic thrust allocation", In Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts. Arenzano, Italy, Sept, 2012. Vol. 9 |
| Abstract: A thrust allocation algorithm with capability to assist the power management system on a vessel with diesel-electric propulsion has recently been proposed. In the work presented here, the results show that the use of this thrust allocation algorithm produces a significant improvement in the stability of the electric bus frequency in the presence of large power load variations, as long as those load variations are small compared to the kinetic energy of the vessel at low speed. Further reduction in the frequency variations are achieved through use of a feedforward signal to the diesel engine governors, which enables them to react to surges in power consumption before they affect the frequency on the electric bus. |
BibTeX:
@conference{avek12B,
author = {Veksler, A. and Johansen, T. A. and Skjetne, R.},
title = {Transient power control in dynamic positioning - governor feedforward and dynamic thrust allocation},
booktitle = {Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts},
year = {2012},
volume = {9},
note = {IFAC-PapersOnLine},
url = {http://www.sciencedirect.com/science/article/pii/S1474667016312216},
doi = {10.3182/20120919-3-IT-2046.00027}
}
|
| Veksler A, Johansen TA and Skjetne R (2012), "Thrust allocation with power management functionality on dynamically positioned vessels", In Proc. American Control Conf.. Montreal, Canada, June, 2012. , pp. 1468-1475. |
| Abstract: A thrust allocation method with capabilities to assist the power management system on dynamically positioned ships is proposed in this paper. Its main benefits are reduction in frequency and/or load variations on the electric network, and a formulation of thruster bias which can be released when required by the power management system. To reduce load variations without increasing overall power consumption it is necessary to deviate from the thrust command given by the dynamic positioning system or joystick. The resulting deviation in position and velocity of the vessel is tightly controlled, and results show that small deviations are sufficient to fulfill the objective. For simplicity, the study has been limited to thrusters with fixed direction, having in mind that generalizations are fairly straightforward. |
BibTeX:
@conference{avek12A,
author = {Veksler, A. and Johansen, T. A. and Skjetne, R.},
title = {Thrust allocation with power management functionality on dynamically positioned vessels},
booktitle = {Proc. American Control Conf.},
year = {2012},
pages = {1468-1475},
url = {https://ieeexplore.ieee.org/document/6315084},
doi = {10.1109/ACC.2012.6315084}
}
|
| Zhang Q, Skjetne R, Løset S and Marchenko A (2012), "Digital image processing for sea ice observations in support to Arctic DP operations", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Rio de Janeiro, Brazil, July, 2012. Vol. 31 |
| Abstract: Various types of remotely sensed data and imaging technology will aid the development of sea ice observation to support estimation of ice forces that are critical to Dynamic Positioning (DP) operations in Arctic waters. The use of cameras as sensors on mobile sensor platforms such as unmanned aerial vehicles in Arctic DP operations will be explored for measurements of ice statistics and ice properties. Several image processing algorithms are adopted to analyze ice concentration, ice floe boundaries, and ice types. The resulting image processing methods for ice observation, including a discussion of possibilities, limitations, and further improvements, are presented in this paper. |
BibTeX:
@conference{qzha12B,
author = {Zhang, Q. and Skjetne, R. and Løset, S. and Marchenko, A.},
title = {Digital image processing for sea ice observations in support to Arctic DP operations},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2012},
volume = {31},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1733066},
doi = {10.1115/OMAE2012-83860}
}
|
| Zhang Q, van der Werff S, Metrikin I, Løset S and Skjetne R (2012), "Image processing for the analysis of an evolving broken-ice field in model testing", In Proc. Int. Conf. Ocean, Offshore & Arctic Eng.. Rio de Janeiro, Brazil, July, 2012. Vol. 31, pp. 597-606. |
| Abstract: Dynamic positioning (DP) experiments in model ice were carried out in the ice tank at the Hamburg Ship Model Basin (HSVA) in the summer of 2011. In these experiments the behavior of two different ships in a broken-ice field were studied. One of the main parameters characterizing a broken-ice field is the ice concentration, defined as the fraction of the total water area covered by ice. In this paper, image processing techniques are applied to derive the ice concentration in the model basin. Several points in time are analyzed in order to describe the evolution of the ice field. The applied techniques include methods for identifying individual ice floes and calculating the ice concentration in the vicinity of the model ship. Ice floe boundaries are then obtained, and the ice floe size distribution and shape factor may further be extracted from the images. The image processing methods applied in this work are object extraction and edge detection algorithms, which are further customized to ice identification. The obtained results can be used for relating the ice field characteristics to the model test results, such as the vessel’s displacements and the corresponding ice forces. |
BibTeX:
@conference{qzha12A,
author = {Zhang, Q. and van der Werff, S. and Metrikin, I. and Løset, S. and Skjetne, R.},
title = {Image processing for the analysis of an evolving broken-ice field in model testing},
booktitle = {Proc. Int. Conf. Ocean, Offshore & Arctic Eng.},
year = {2012},
volume = {31},
pages = {597-606},
url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1733072},
doi = {10.1115/OMAE2012-84117}
}
|
| Zhao B, Blanke M and Skjetne R (2012), "Fault Tolerant ROV Navigation System Based on Particle Filter using Hydro-acoustic Position and Doppler Velocity Measurements", In Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts. Arenzano, Italy, Sept, 2012. Vol. 9 |
| Abstract: This paper presents a fault tolerant navigation system for a remotely operated vehicle (ROV). The navigation system uses hydro-acoustic position reference (HPR) and Doppler velocity log (DVL) measurements to achieve an integrated navigation. The fault tolerant functionality is based on a modified particle filter. This particle filter is able to run in an
asynchronous manner to accommodate the measurement drop out problem, and it overcomes the measurement outliers by switching observation models. Simulations with experimental data show that this fault tolerant navigation system can accurately estimate the ROV kinematic states, even when sensor failures appear frequently. |
BibTeX:
@conference{bzha12B,
author = {Zhao, B. and Blanke, M. and Skjetne, R.},
title = {Fault Tolerant ROV Navigation System Based on Particle Filter using Hydro-acoustic Position and Doppler Velocity Measurements},
booktitle = {Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts},
year = {2012},
volume = {9},
note = {IFAC-PapersOnLine},
url = {http://www.sciencedirect.com/science/article/pii/S1474667016312423},
doi = {10.3182/20120919-3-IT-2046.00048}
}
|
| Zhao B, Blanke M and Skjetne R (2012), "Particle Filter ROV Navigation using Hydroacoustic Position and Speed Log Measurements", In Proc. American Control Conf.. Montreal, Canada, June, 2012. , pp. 6209-6215. |
| Abstract: An integrated navigation system design is presented for an underwater remotely operated vehicle (ROV). The available navigation information is an acoustic position measurement and a Doppler log speed measurement. Both measurements are studied in detail and modeled statistically. A kinematic model is assigned to the ROV with its driving noise from a Gaussian mixture, and a particle filter is suggested to estimate ROV position and velocity. The advantages of using a particle filter in this ROV navigation scheme are: 1) to make full use of all available information to improve the estimation performance, such as the speed measurement that is a nonlinear function of the states; 2) the particle filter makes good use of a Gaussian mixture as the driving noise, which makes the ROV kinematic model more realistic in both high and low frequency ranges; 3) a good estimate of the ROV velocity vector is achieved. The algorithm of the particle filter is presented and verified through a simulation based on real data. This shows that the estimation performance of the particle filter is clearly better than that of
a Kalman filter. |
BibTeX:
@conference{bzha12A,
author = {Zhao, B. and Blanke, M. and Skjetne, R.},
title = {Particle Filter ROV Navigation using Hydroacoustic Position and Speed Log Measurements},
booktitle = {Proc. American Control Conf.},
year = {2012},
pages = {6209-6215},
url = {https://ieeexplore.ieee.org/document/6315511},
doi = {10.1109/ACC.2012.6315511}
}
|
| Haugen J, Imsland L, Løset S and Skjetne R (2011), "Ice Observer System for Ice Management Operations", In Int. Offshore (Ocean) and Polar Eng. Conf. (ISOPE). Maui, Hawaii, June, 2011. Vol. 21, pp. 1120-1127. |
| Abstract: This article describes the structure of an ice observer system, which is intended to aid decisions regarding risk assessment of the ice environment, as well as control performance of dynamic positioning systems, in offshore operations. An ice observer system collects, analyses and employs ice intelligence during operations in ice. Furthermore, Unmanned Aerial Vehicles (UAVs) are presented as a viable sensor platform for close and far field ice monitoring. |
BibTeX:
@conference{jhau11A,
author = {Haugen, J. and Imsland, L. and Løset, S. and Skjetne, R.},
title = {Ice Observer System for Ice Management Operations},
booktitle = {Int. Offshore (Ocean) and Polar Eng. Conf. (ISOPE)},
year = {2011},
volume = {21},
pages = {1120-1127},
url = {http://www.isope.org/publications/proceedings/ISOPE/ISOPE%202011/data/papers/11TPC-670Haugen.pdf#page=1}
}
|
| Kjerstad ØK, Skjetne R and Jenssen NA (2011), "Disturbance rejection in dynamic systems by use of acceleration feedforward: Application to dynamic positioning", In Proc. IFAC World Congress Automatic Control. Milano, Italy, Aug.-Sept., 2011. Vol. 18 |
| Abstract: This paper addresses environmental disturbance rejection in dynamic systems by means of acceleration feedforward. A feedforward structure calculates the environmental force and magnitude by comparing the ltered acceleration measurement with the acceleration due to actuation and known forces. Direct compensation of the environment by feedforward
will alleviate the position and velocity feedback terms. The presented scheme compensates environmental disturbances a ecting the system in addition to model uncertainties. First, the design is used for a mechanical system and illustrated for an inverted pendulum. Then, the main application, being a dynamic positioning system a ected by ice forces in an Arctic operation, is controlled by acceleration feedforward to give enhanced performance. |
BibTeX:
@conference{okje11A,
author = {Kjerstad, Ø. K. and Skjetne, R. and Jenssen, N. A.},
title = {Disturbance rejection in dynamic systems by use of acceleration feedforward: Application to dynamic positioning},
booktitle = {Proc. IFAC World Congress Automatic Control},
year = {2011},
volume = {18},
note = {IFAC Proceedings Volumes},
url = {http://www.sciencedirect.com/science/article/pii/S1474667016439923},
doi = {10.3182/20110828-6-IT-1002.03454}
}
|
| Skjetne R, Jørgensen U and Teel AR (2011), "Line-of-sight path-following along regularly parametrized curves solved as a generic maneuvering problem", In Proc. IEEE Conf. Decision & Control. Orlando, USA, Dec., 2011. , pp. 2467-2474. |
| Abstract: In the traditional maneuvering problem, the objective has been to solve a geometric task and a dynamic task, where the former is to converge to and follow a 1-dimensional manifold, a path, in the output space of the system, and the latter is to satisfy a desired dynamic behavior along the path. In this paper the objective is to generalize this problem statement, by rather stabilizing more general manifolds of higher dimension. With the system output constrained to the desired manifold, the dynamic task becomes to satisfy a
dynamic assignment that ensures that the underlying control objective is solved with sufficient performance. In order to exemplify the theory, a case study is performed where a line-of-sight (LOS) algorithm is used to steer a simplified vessel to and along a desired parametrized path. In this case the desired manifold, which is of dimension 3, is defined as the set in which the LOS method is effectuated. The LOS algorithm then ensures, as the dynamic task, that the vessel steers correctly towards and along the path. A simulation study is provided to illustrate the effectiveness and properties of the resulting dynamic control law. |
BibTeX:
@conference{rskj11A,
author = {Skjetne, R. and Jørgensen, U. and Teel, A. R.},
title = {Line-of-sight path-following along regularly parametrized curves solved as a generic maneuvering problem},
booktitle = {Proc. IEEE Conf. Decision & Control},
year = {2011},
pages = {2467-2474},
url = {https://ieeexplore.ieee.org/document/6161364},
doi = {10.1109/CDC.2011.6161364}
}
|
| Thorvaldsen CFL and Skjetne R (2011), "Formation control of fully-actuated marine vessels using group agreement protocols", In Proc. IEEE Conf. Decision & Control. Orlando, USA, Dec., 2011. , pp. 4132-4139. |
| Abstract: This paper addresses the problem of getting fullyactuated marine surface vessels to establish a formation before executing its mission, which here is to traverse a predetermined path. Whereas existing designs typically solve the problem by establishing the formation on the path, the proposed design in this paper allows the vessels to coordinate at an arbitrary location prior to a collective movement to the path. Protocols for group agreement form the basis of the proposed solution, while ideas from maneuvering control theory are incorporated to yield the desired path-following behavior. To demonstrate the design, a simulation is shown, where the formation’s capability of handling a severe single vessel failure is illustrated. |
BibTeX:
@conference{ctho11A,
author = {Thorvaldsen, C. F. L. and Skjetne, R.},
title = {Formation control of fully-actuated marine vessels using group agreement protocols},
booktitle = {Proc. IEEE Conf. Decision & Control},
year = {2011},
pages = {4132-4139},
url = {https://ieeexplore.ieee.org/document/6160426},
doi = {10.1109/CDC.2011.6160426}
}
|
| Ihle I-AF, Skjetne R and Fossen TI (2005), "Output feedback control for maneuvering systems using observer backstepping", In Proc. Mediterranean Conf. Contr. and Automation. Cyprus, June, 2005. Vol. 13, pp. 1512-1517. |
| Abstract: An output feedback design for maneuvering systems is proposed by using an observer backstepping approach which applies damping terms to counteract disturbances to the controller. By using available exponential observers, stability of the interconnected observer-controller system is obtained. The design is fairly general, and equally applicable for maneuvering systems where an exponentially stable observer is available. As a case study, an output-feedback control design is performed for maneuvering a vessel where only position measurements are available. The resulting design can be viewed as a Guidance-Navigation-Control system for a marine vessel. Simulation of the case study verifies the theoretical results. |
BibTeX:
@conference{iihl05A,
author = {Ihle, I.-A. F. and Skjetne, R. and Fossen, T. I.},
title = {Output feedback control for maneuvering systems using observer backstepping},
booktitle = {Proc. Mediterranean Conf. Contr. and Automation},
year = {2005},
volume = {13},
pages = {1512-1517},
url = {https://ieeexplore.ieee.org/document/1469806},
doi = {10.1109/.2005.1469806}
}
|
| Skjetne R and Egeland O (2005), "Hardware-In-the-Loop Simulation for Testing of DP Vessels", In Proc. Int. Conf. Technology & Operation of Offshore Support Vessels. Singapore, Sept., 2005. |
| Abstract: Digital control systems are important for the performance and safety of modern ships, and the current trend is that many new innovations for ships are related to computer-based control systems. Controllers are becoming more complicated, and the different control systems are becoming closely integrated. Consequently, there is a need for new testing methods and test technology that facilitate verification and validation of maritime control systems.
Hardware-in-the-Loop (HIL) testing is proposed as such a methodology for verification and validation of marine control systems. Formalizing HIL testing as a methodology necessitates the development of a vocabulary and set of definitions. This paper treats these issues by constructing a framework of concepts and definitions suitable for development of industrial HIL test applications. |
BibTeX:
@conference{rskj05D,
author = {Skjetne, R. and Egeland, O.},
title = {Hardware-In-the-Loop Simulation for Testing of DP Vessels},
booktitle = {Proc. Int. Conf. Technology & Operation of Offshore Support Vessels},
year = {2005},
url = {https://www.researchgate.net/publication/237063043_Hardware-In-the-Loop_Simulation_for_Testing_of_DP_Vessels}
}
|
| Skjetne R and Egeland O (2005), "Hardware-in-the-loop testing of marine control systems", In Proc. Int. Conf. Simulation and Modeling. Trondheim, Norway, Oct., 2005. Vol. 46, pp. 305-314. |
| Abstract: Hardware-in-the-Loop (HIL) testing is proposed as a new methodology for verification and certification of marine control systems. Formalizing such testing necessitates the development of a vocabulary and set of definitions. This paper treats these issues by constructing a framework suitable for industrial HIL test applications and certification of marine systems. |
BibTeX:
@conference{rskj05C,
author = {Skjetne, R. and Egeland, O.},
title = {Hardware-in-the-loop testing of marine control systems},
booktitle = {Proc. Int. Conf. Simulation and Modeling},
year = {2005},
volume = {46},
pages = {305-314},
url = {https://www.researchgate.net/publication/330703311_Hardware-in-the-loop_testing_of_marine_control_systems}
}
|
| Ihle I-AF, Skjetne R and Fossen TI (2004), "Nonlinear formation Control of Marine Craft with Experimental Results", In Proc. IEEE Conf. Decision & Control. Paradise Island, Bahamas, Dec., 2004. Vol. 1, pp. 680-685. |
| Abstract: Decentralized formation control schemes for a fleet of vessels with a small amount of intervessel communication are proposed and investigated. The control objective for each vessel is to maintain its position in the formation relative to a Formation Reference Point, which follows a predefined path. This is done by constructing an individual parametrized path for each vessel so that when the parametrization variables are synchronized, the vessels are in formation. To obtain this, an individual maneuvering problem is solved for each vessel, with an extension of a synchronization feedback function in the dynamic control laws to ensure that the vessels stay assembled in the desired formation. This setup assures that all vessels will have the same priority, i.e. no leader. Performance and theoretical results are validated by experiments for a scaled model ship and a computer simulated ship in a marine control laboratory. |
BibTeX:
@conference{iihl04A,
author = {Ihle, I.-A. F. and Skjetne, R. and Fossen, T. I.},
title = {Nonlinear formation Control of Marine Craft with Experimental Results},
booktitle = {Proc. IEEE Conf. Decision & Control},
year = {2004},
volume = {1},
pages = {680-685},
url = {https://ieeexplore.ieee.org/document/1428723},
doi = {10.1109/CDC.2004.1428723}
}
|
| Skjetne R, Smogeli Ø and Fossen TI (2004), "Modeling, Identification, and Adaptive Maneuvering of CyberShip II: A complete design with experiments", In Proc. IFAC Conf. Contr. Appl. Marine Systems. Ancona, Italy, July, 2004. , pp. 203-208. |
| Abstract: Good nonlinear maneuvering models with numerical values for control of ships are hard to find. This paper presents a complete modeling, identification, and control design for maneuvering a ship along desired paths at different velocities. Material from a variety of references have been applied to describe the ship model, its difficulties, limitations, and possible simplifications for the purpose of automatic control design. The numerical values of the parameters in the model is identified in towing tests and adaptive maneuvering experiments for a scaled model ship in a marine control laboratory. |
BibTeX:
@conference{rskj04E,
author = {Skjetne, R. and Smogeli, Ø. and Fossen, T. I.},
title = {Modeling, Identification, and Adaptive Maneuvering of CyberShip II: A complete design with experiments},
booktitle = {Proc. IFAC Conf. Contr. Appl. Marine Systems},
year = {2004},
pages = {203--208},
url = {http://www.sciencedirect.com/science/article/pii/S1474667017317329},
doi = {10.1016/S1474-6670(17)31732-9}
}
|
| Skjetne R and Teel AR (2004), "Maneuvering Dynamical Systems by Sliding-Mode Control", In Proc. American Control Conf.. Boston, USA, June, 2004. Vol. 2, pp. 1277-1282. |
| Abstract: Solving a tracking task as a Maneuvering Problem for dynamical systems has shown to be a flexible design methodology, having many advantages over pure trajectory tracking and path following designs. In this paper we give a constructive design for solving the Maneuvering Problem by sliding-mode control. A motivational example with a simulation is used to illustrate the achieved performance. |
BibTeX:
@conference{rskj04D,
author = {Skjetne, R. and Teel, A. R.},
title = {Maneuvering Dynamical Systems by Sliding-Mode Control},
booktitle = {Proc. American Control Conf.},
year = {2004},
volume = {2},
pages = {1277-1282},
url = {https://ieeexplore.ieee.org/document/1386749},
doi = {10.23919/ACC.2004.1386749}
}
|
| Skjetne R and Fossen TI (2004), "On Integral Control in Backstepping: Analysis of Different Techniques", In Proc. American Control Conf.. Boston, USA, June, 2004. |
| Abstract: Including integral action in a nonlinear backstepping design is the topic of this paper. Two methods for adding integral feedback are proposed and analyzed. These are compared to the more traditional methods: 1) adaptive backstepping, and 2) plant augmentation that adds an extra relative degree and thus gives one extra step of backstepping. A test plant is used to compare the different control laws. Based on the theoretical analysis and the simulations, some interesting conclusions are made for each integral control strategy. |
BibTeX:
@conference{rskj04C,
author = {Skjetne, R. and Fossen, T. I.},
title = {On Integral Control in Backstepping: Analysis of Different Techniques},
booktitle = {Proc. American Control Conf.},
year = {2004},
url = {https://ieeexplore.ieee.org/document/1386858},
doi = {10.23919/ACC.2004.1386858}
}
|
| Fossen TI, Breivik M and Skjetne R (2003), "Line-of-Sight Path Following of Underactuated Marine Craft", In Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts. Girona, Spain, Sept., 2003. , pp. 244-249. |
| Abstract: A 3 degrees of freedom (surge, sway, and yaw) nonlinear controller for path following of marine craft using only two controls is derived using nonlinear control theory. Path following is achieved by a geometric assignment based on a line-of-sight projection algorithm for minimization of the cross-track error to the path. The desired speed along the path can be specified independently. The control laws in surge and yaw are derived using backstepping. This results in a dynamic feedback controller where the dynamics of the uncontrolled sway mode enters the yaw control law. UGAS is proven for the tracking error dynamics in surge and yaw while the controller dynamics is bounded. A case study involving an experiment with a model ship is included to demonstrate the performance of the controller and guidance systems. |
BibTeX:
@conference{tfos03A,
author = {Fossen, T. I. and Breivik, M. and Skjetne, R.},
title = {Line-of-Sight Path Following of Underactuated Marine Craft},
booktitle = {Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts},
year = {2003},
pages = {244--249},
url = {http://www.sciencedirect.com/science/article/pii/S1474667017378096},
doi = {10.1016/S1474-6670(17)37809-6}
}
|
| Johansen V, Skjetne R and Sørensen AJ (2003), "Maneuvering of Towed Interconnected Marine Systems", In Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts. Girona, Spain, Sept., 2003. , pp. 253-258. |
| Abstract: Recent developments in maneuvering control of marine surface vessels have shown promising results. In this paper maneuvering of a towed body is addressed. The body may be actuated by a connection to a towing vessel and/or by local control forces. Actuation by connection forces are performed by tracking the towing vessel along a desired position reference. The desired position for the towing vessel is calculated from a desired force acting on the towed body and utilization of the connection's characteristics. Bandwidth limitations are discussed, and a combined solution with local actuation is proposed. |
BibTeX:
@conference{vjoh03A,
author = {Johansen, V. and Skjetne, R. and Sørensen, A. J.},
title = {Maneuvering of Towed Interconnected Marine Systems},
booktitle = {Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts},
year = {2003},
pages = {253--258},
url = {http://www.sciencedirect.com/science/article/pii/S1474667017378163},
doi = {10.1016/S1474-6670(17)37816-3}
}
|
| Skjetne R, Ihle I-AF and Fossen TI (2003), "Formation Control by Synchronizing Multiple Maneuvering Systems", In Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts. Girona, Spain, Sept., 2003. , pp. 280-285. |
| Abstract: This paper investigates formation control of a fleet of vessels with a small amount of intervessel communication. The control objective for each vessel is to maintain its position in the formation. This is obtained by constructing individual parametrized paths for each vessel so that when the parametrization variables are synchronized, the vessels are in formation. Then, vectorial backstepping is used to solve an individual maneuvering problem for each vessel with the extension of a synchronization term in the resulting dynamic controllers to ensure that the vessels keep assembled in the desired formation. |
BibTeX:
@conference{rskj03C,
author = {Skjetne, R. and Ihle, I.-A. F. and Fossen, T. I.},
title = {Formation Control by Synchronizing Multiple Maneuvering Systems},
booktitle = {Proc. IFAC Conf. Manoeuvering and Contr. of Marine Crafts},
year = {2003},
pages = {280--285},
url = {http://www.sciencedirect.com/science/article/pii/S147466701737814X},
doi = {10.1016/S1474-6670(17)37814-X}
}
|
| Fossen TI, Lindegaard KP and Skjetne R (2002), "Inertia shaping techniques for marine vessels using acceleration feedback", In Proc. 15th IFAC World Congress Automatic Control. Barcelona, Spain, July, 2002. |
| Abstract: The concept of energy based Lyapunov control is extended to marine vessels with a nonsymmetric system inertia matrix. Acceleration feedback is used as the main tool to symmetrize the nonsymmetric part of the system inertia matrix. The main reason for a nonsymmetric mass distribution is hydrodynamic added mass which depend on the forward speed of the vessel and the frequency of the incoming waves. This is a well known phenomenon for marine vessels moving at positive speed in waves while low-speed applications like dynamic positioning systems are fairly well described with a symmetric system inertia matrix. The main contribution of the paper is a new Lyapunov-based design technique incorporating acceleration feedback to shape the kinetic energy of the system. Acceleration feedback is implemented in conjuncture with a nonlinear PID-controller derived from vectorial backstepping. The result is a uniformly globally asymptotically stable (UGAS) closed-loop control system applicable to marine vessels with nonsymmetric system inertia matrices. Typical applications are ships in maneuvering situations, vessels in transit and high speed craft where nonsymmetric added mass effects must be compensated for. |
BibTeX:
@conference{tfos02B,
author = {Fossen, T. I. and Lindegaard, K. -P. and Skjetne, R.},
title = {Inertia shaping techniques for marine vessels using acceleration feedback},
booktitle = {Proc. 15th IFAC World Congress Automatic Control},
year = {2002},
note = {IFAC Proceedings Volumes},
url = {http://www.sciencedirect.com/science/article/pii/S1474667015397032},
doi = {10.3182/20020721-6-ES-1901.01282}
}
|
| Skjetne R, Teel AR and Kokotović PV (2002), "Stabilization of Sets Parametrized by a Single Variable: Application to Ship Maneuvering", In Proc. 15th Int. Symp. Mathematical Theory of Networks and Systems. Notre Dame, IN, USA, August, 2002. |
| Abstract: We consider the problem of stabilizing sets parametrized by a single variable. Our approach is based on the solution to the maneuvering problem. In this problem, the state of the system is driven to a path that coincides with the set, and the particular location on the path is determined dynamically from the value of the state. Within this control structure, we induce a separation of time scales between the task of selecting the point on the path closest to the state, and the task of driving the state towards the path. In addition to uniform global convergence to the path, which is achieved without a separation of time scales, the separation of time scales allows us to achieve near forward invariance of the path from a large range of initial conditions. This idea is first illustrated on a simple double integrator with the path corresponding to the unit circle, and then it is discussed for systems in strict feedback form. Finally, the theory is applied to the problem of maneuvering a ship into a harbour. |
BibTeX:
@conference{rskj02E,
author = {Skjetne, R. and Teel, A. R. and Kokotović, P. V.},
title = {Stabilization of Sets Parametrized by a Single Variable: Application to Ship Maneuvering},
booktitle = {Proc. 15th Int. Symp. Mathematical Theory of Networks and Systems},
year = {2002},
url = {http://www3.nd.edu/ mtns/papers/4722_3.pdf}
}
|
| Skjetne R, Moi S and Fossen TI (2002), "Nonlinear Formation Control of Marine Craft", In Proc. 41st IEEE Conf. Decision & Control. Las Vegas, Nevada, USA, Dec. 10-13, 2002. , pp. 1699-1704. |
| Abstract: This paper investigates formation control of a fleet of ships. The control objective for each ship is to maintain its position in the formation while a (virtual) Formation Reference Point (FRP) tracks a predefined path. This is obtained by using vectorial backstepping to solve two subproblems; a geometric task, and a dynamic task. The former guarantees that the FRP, and thus the formation, tracks the path, while the latter ensures accurate speed control along the path. A dynamic guidance system with feedback from the states of all ships ensures that all ships have the same priority (no leader) when moving along the path. Lyapunov stability is proven and robustness to input saturation is demonstrated using computer simulations. |
BibTeX:
@conference{rskj02D,
author = {Skjetne, R. and Moi, S. and Fossen, T. I.},
title = {Nonlinear Formation Control of Marine Craft},
booktitle = {Proc. 41st IEEE Conf. Decision & Control},
year = {2002},
pages = {1699--1704},
url = {https://ieeexplore.ieee.org/document/1184765},
doi = {10.1109/CDC.2002.1184765}
}
|
| Skjetne R, Teel AR and Kokotović PV (2002), "Nonlinear maneuvering with gradient optimization", In Proc. 41st IEEE Conf. Decision & Control. Las Vegas, USA, Dec. 10-13, 2002. , pp. 3926-3931. |
| Abstract: The maneuvering problem involves two tasks. The first, called the geometric task, is to force the system states to converge to a desired parametrized path. The second task, called the dynamic task, is to satisfy a desired dynamic behavior along the path. The desired geometric path is viewed as a target set which is parametrized by a scalar variable. The proposed dynamic controller consists of a stabilization algorithm that drives the state x(t) to a point on the path, and a smooth dynamic optimization algorithm that selects the point in the target set that minimizes the weighted distance of x to the target set. Choosing a gain large in the optimization algorithm, induces a two-time scale behavior of the closed-loop plant. In the fast time-scale the path variable rapidly converges to the minimizer, and in the slow time-scale x(t) converges to the path. Two motivational examples illustrate the design and the achieved performance of the closed-loop. |
BibTeX:
@conference{rskj02C,
author = {Skjetne, R. and Teel, A. R. and Kokotović, P. V.},
title = {Nonlinear maneuvering with gradient optimization},
booktitle = {Proc. 41st IEEE Conf. Decision & Control},
year = {2002},
pages = {3926--3931},
url = {https://ieeexplore.ieee.org/document/1184979},
doi = {10.1109/CDC.2002.1184979}
}
|
| Skjetne R, Fossen TI and Kokotović P (2002), "Output Maneuvering for a Class of Nonlinear Systems", In Proc. 15th IFAC World Congress Automatic Control. Barcelona, Spain, July, 2002. |
| Abstract: The output maneuvering problem involves two tasks. The first, which is the geometric task, is to force the output to converge to a desired path parametrized by a continuous scalar variable theta. The second task is to satisfy a desired speed assignment along the path. The main concern is to satisfy the geometric task. However, the speed assignment will ensure that the output follows the path with sufficient speed. A recursive control design technique is developed for nonlinear plants in vectorial strict feedback form of any relative degree. First the geometric part of the problem is solved. Then an update law is constructed that bridges the geometric design with the speed assignment. An extra degree of freedom is provided for an operator to specify the speed of theta. A computer simulation with a marine vessel is performed to illustrate the design. |
BibTeX:
@conference{rskj02A,
author = {Skjetne, R. and Fossen, T. I. and Kokotović, P.},
title = {Output Maneuvering for a Class of Nonlinear Systems},
booktitle = {Proc. 15th IFAC World Congress Automatic Control},
year = {2002},
note = {IFAC Proceedings Volumes},
url = {http://www.sciencedirect.com/science/article/pii/S1474667015386663},
doi = {10.3182/20020721-6-ES-1901.00245}
}
|
| Skjetne R and Fossen TI (2001), "Nonlinear maneuvering and control of ships", In Proc. MTS/IEEE OCEANS. Honolulu, Hawaii, Nov., 2001. , pp. 1808-1815. |
| Abstract: We address the problem of maneuvering ships onto curves or paths in the plane. To do this, we introduce the Serret-Frenet equations and show how these fit the scope for control design with 3 degrees-of-freedom (DOF) hydrodynamic ship models in the loop. The Davidson & Schiff linear parametrically varying (LPV) ship model is used in the design, and we show how we canmanipulate this by introducing acceleration feedback and by moving the body-frame freely. This simplifies the control design in such a way that we do not have to deal with zero-dynamics. Instead we use a 3-step backstepping design and theory for interconnecting subsystems. Real data from a 175m container ship is used in a computer simulation to validate the design. |
BibTeX:
@conference{rskj01B,
author = {Skjetne, R. and Fossen, T. I.},
title = {Nonlinear maneuvering and control of ships},
booktitle = {Proc. MTS/IEEE OCEANS},
year = {2001},
pages = {1808--1815},
url = {https://ieeexplore.ieee.org/document/968121},
doi = {10.1109/OCEANS.2001.968121}
}
|
| Skjetne R and Shim H (2001), "A systematic nonlinear observer design for a class of Euler-Lagrange systems.", In Proc. Mediterranean Conf. Contr. and Automation. Dubrovnik, Croatia, June, 2001. |
| Abstract: Dynamical output feedback control of Euler-Lagrange systems is still a topic of high interest. In this paper we propose a new type of nonlinear observers that for a class of Euler-Lagrange systems will render the origin of the observer error dynamics uniformly globally exponentially stable. We also show how the error convergence rate can be assignable. A state-feedback control law is given that will exponentially stabilize the plant, and under certainty equivalence it will in conjunction with the observer asymptotically stabilize the overall closed loop. The practical problem of dynamical positioning of surface vessels is considered to show how the observer is designed in a special case. |
BibTeX:
@conference{rskj01A,
author = {Skjetne, R. and Shim, H.},
title = {A systematic nonlinear observer design for a class of Euler-Lagrange systems.},
booktitle = {Proc. Mediterranean Conf. Contr. and Automation},
year = {2001},
url = {https://www.researchgate.net/publication/228776463_A_systematic_nonlinear_observer_design_for_a_class_of_Euler-Lagrange_systems/file/5046351768d47541d6.pdf}
}
|