| Dirdal JA, Skjetne R, Roháv c J and Fossen TI (2023), "A phase-time-path-difference approach for online wave direction and wave number estimation from measured ship motions in zero and forward speed using a single inertial measurement unit", Ocean Engineering. Vol. 288, pp. 116131. |
| Abstract: This study investigates the potential capability of a relatively new and unexplored signal-based approach for shipboard wave estimation. The approach uses the phase-time-path-differences (PTPDs) from an array of shipboard sensors to uniquely resolve the wave propagation direction and wave number. We derive a kinematic PTPD model accounting for forward vessel speed and assess its theoretical foundation to model the sensor delays on a rigid body. The forward-speed PTPD model is structurally equivalent to the zero-speed model considered in previous works, thus retaining the same observability results provided by a noncollinear array of a minimum of three sensors. Moreover, based on the outlined theory and PTPD model, we propose a methodology to estimate the main wave propagation direction and wave number online by employing a fast Fourier transform (FFT), an unscented Kalman filter (UKF), and a rigid-body measurement transformation based on a single inertial measurement unit (IMU). Provided that the vessel in question can be considered a rigid body, a single IMU is sufficient to obtain the desired wave quantities instead of three IMUs, as initially proposed in our previous work. Additionally, our methodology incorporates a novel frequency threshold to avoid distorted wave components caused by the effect of vessel filtering. The performance of our PTPD method is evaluated on data collected from a wave tank and full-scale experiments involving a vessel with zero and non-zero forward speed. The results show very good agreement with the reference wave values reported from a commercial wave radar and wave buoys operating in proximity to the vessel, indicating that our proposed method is competitive with existing wave measurement technology in terms of accuracy and online performance while being cheap, easy to install, flexible, and robust against environmental influences. |
BibTeX:
@article{jdir23A,
author = {Dirdal, J. A. and Skjetne, R. and Roháv c, J. and Fossen, T. I.},
title = {A phase-time-path-difference approach for online wave direction and wave number estimation from measured ship motions in zero and forward speed using a single inertial measurement unit},
journal = {Ocean Engineering},
year = {2023},
volume = {288},
pages = {116131},
url = {https://www.sciencedirect.com/science/article/pii/S0029801823025155},
doi = {10.1016/j.oceaneng.2023.116131}
}
|
| Dugan S, Skjetne R, Wróbel K, Montewka J, Gil M and Utne IB (2023), "Integration Test Procedures for a Collision Avoidance Decision Support System Using STPA", TransNav. Vol. 17(2), pp. 375-381. Gdynia Maritime University, Faculty of Navigation. |
| Abstract: The transition from conventionally manned to autonomous ships is accompanied by the development of enhanced Decision Support Systems (DSS) for navigators. Such systems need to consider interactions among hardware, software, and humans and their potential effects on system performance, which require rigorous testing to verify the system's safe decision-making ability and operational limits. Testing requirements for verification are aimed at 1) assessing the system's reliability and failure handling performance, and 2) integration testing. This work uses the System-Theoretic Process Analysis (STPA) to develop integration tests for a novel DSS. STPA is a structured methodology to identify hazards from multiple sources, including hardware or software failures, system interactions, and human errors. The objectives of the study are to develop and assess the feasibility of integration test procedures based on STPA. The stability monitoring subsystem from the DSS is analyzed as a case study. The results are used to suggest functional and performance integration test procedures. |
BibTeX:
@article{sdug23A,
author = {Dugan, S. and Skjetne, R. and Wróbel, K. and Montewka, J. and Gil, M. and Utne, I. B.},
title = {Integration Test Procedures for a Collision Avoidance Decision Support System Using STPA},
journal = {TransNav},
publisher = {Gdynia Maritime University, Faculty of Navigation},
year = {2023},
volume = {17},
number = {2},
pages = {375-381},
url = {https://www.transnav.eu/Article_Integration_Test_Procedures_for_Dugan,66,1309.html},
doi = {10.12716/1001.17.02.14}
}
|
| Marley M, Skjetne R, Gil M and Krata P (2023), "Four Degree-of-Freedom Hydrodynamic Maneuvering Model of a Small Azipod-Actuated Ship With Application to Onboard Decision Support Systems", IEEE Access. Vol. 11, pp. 58596-58609. IEEE. |
| Abstract: The main contribution of this paper is a numerical ship motion model of NTNU’s research vessel Gunnerus, capturing the surge, sway, roll, and yaw dynamics when sailing in uniform and steady currents. The model utilizes a crossflow drag formulation for the transverse viscous loads, and it includes a nonlinear formulation for the propulsion and steering loads provided by two azipod thrusters. A wide range of experimental data obtained from sea trials are used for model calibration and validation. The model is intended for development of Decision Support Systems (DSS) that provide the helmsman with recommendations for safe maneuvers. As a demonstration, the model is used to generate input to a previously proposed DSS solution, which uses offline simulations to create a database of the critical navigation area for different encounter scenarios. Additionally, we propose a DSS solution that uses online simulations to predict the future ship trajectory under guidance of a virtual autopilot. The virtual autopilot is designed using a novel hybrid control barrier function formulation to predict the need of evasive maneuvers for collision avoidance. |
BibTeX:
@article{mmar23A,
author = {Marley, M. and Skjetne, R. and Gil, M. and Krata, P.},
title = {Four Degree-of-Freedom Hydrodynamic Maneuvering Model of a Small Azipod-Actuated Ship With Application to Onboard Decision Support Systems},
journal = {IEEE Access},
publisher = {IEEE},
year = {2023},
volume = {11},
pages = {58596-58609},
url = {https://ieeexplore.ieee.org/document/10147119},
doi = {10.1109/ACCESS.2023.3284684}
}
|
| Ren Z, Han X, Yu X, Skjetne R, Leira BJ, Sævik S and Zhu M (2023), "Data-driven simultaneous identification of the 6DOF dynamic model and wave load for a ship in waves", Mech. Syst. and Signal Proc.. Vol. 184, pp. 109422. Elsevier. |
| Abstract: In marine operations, the performance of model-based automatic control design and decision support systems highly relies on the accuracy of the representative mathematical models. Model fidelity can be crucial for safe voyages and offshore operations. This paper proposes a data-driven parametric model identification of a ship with 6 degrees of freedom (6DOF) exposed to waves using sparse regression according to the vessel motion measurements. The features of the complex ship dynamics are extracted and expressed as a linear combination of several functions. Thruster inputs and environmental loads are considered. The hydrodynamic coefficients and wave-induced loads are simultaneously estimated. Unlike earlier studies using a limited number of unknown functions, a library of abundant candidate functions is applied to fully consider the coupling effects among all DOFs. The benefit of the proposed method is that it does not require the exact construction of the library functions. Based on the estimated model, short-term motion prediction is achievable. The algorithm is verified through experiments. The method can be extended to other types of floating structures. |
BibTeX:
@article{zren23A,
author = {Ren, Z. and Han, X. and Yu, X. and Skjetne, R. and Leira, B. J. and Sævik, S. and Zhu, M.},
title = {Data-driven simultaneous identification of the 6DOF dynamic model and wave load for a ship in waves},
journal = {Mech. Syst. and Signal Proc.},
publisher = {Elsevier},
year = {2023},
volume = {184},
pages = {109422},
url = {https://www.sciencedirect.com/science/article/pii/S0888327022005441},
doi = {10.1016/j.ymssp.2022.109422}
}
|
| Bjørnø J, van den Berg M, Lu W, Skjetne R, Lubbad R and Løset S (2022), "Performance quantification of icebreaker operations in ice management by numerical simulations", Cold Regions Sci. and Tech.. Vol. 194, pp. 103435. Elsevier. |
| Abstract: The paper addresses the problem of quantifying and assessing the effectiveness of icebreaker operations in ice management (IM) using a high-fidelity simulator. The numerical model includes an accurate geometric representation of an icebreaker, a cylindrical protected structure, and a synthetic ice environment. A set of key performance indicators (KPIs) are defined and proposed to quantify the effectiveness of IM strategies for protecting the downstream structure. This give better insight into which IM strategies are more effective with respect to different objectives for certain conditions, thereby enabling better planning and guidance of icebreaker operations.
The results from a selection of the simulations performed with nearly 100% ice concentration are presented. This will illustrate the methodology using the different KPIs to quantify the effectiveness and highlight differences between the different IM strategies. From the simulations we see that all patterns have strengths and weaknesses; some KPIs are consistent while others are changing with the ice drift velocity. |
BibTeX:
@article{jbjo22A,
author = {Bjørnø, J. and van den Berg, M. and Lu, W. and Skjetne, R. and Lubbad, R. and Løset, S.},
title = {Performance quantification of icebreaker operations in ice management by numerical simulations},
journal = {Cold Regions Sci. and Tech.},
publisher = {Elsevier},
year = {2022},
volume = {194},
pages = {103435},
url = {https://www.sciencedirect.com/science/article/pii/S0165232X21002160},
doi = {10.1016/j.coldregions.2021.103435}
}
|
| Dirdal JA, Skjetne R, Roháv c J and Fossen TI (2022), "Online wave direction and wave number estimation from surface vessel motions using distributed inertial measurement arrays and phase-time-path-differences", Ocean Engineering. Vol. 249, pp. 110760. |
| Abstract: A common approach for finding the direction of ocean waves is to use the phase-time-path-differences (PTPDs) between a static array of various types of sensors mounted on either the sea surface or seabed. However, some practical drawbacks of such arrays are that they tend to be expensive, difficult to install, and fixed in location. We show that the PTPD approach can be generalized to a portable shipboard array of spatially distributed sensors rendering it more practical. In this respect, we derive a nonlinear PTPD model for shipboard sensor arrays and prove that the wave direction and wave number can be resolved from a minimum of three noncollinear sensors using observability analysis. Moreover, based on our PTPD model, we propose an unscented Kalman filter algorithm for online estimation of the wave direction and wave number, which offers a convenient framework for adding multiple measurements and incorporating uncertainties. Our experimental results from model basin testing with a model ship equipped with several inertial measurement units (IMUs) confirm that the wave direction and wave number can be estimated from the wave-induced motions of a surface vessel with a minimum of three noncollinear IMUs. In this study, we consider parameter estimation for regular waves and assume a dynamically positioned surface vessel with small roll and pitch angles. |
BibTeX:
@article{jdir22A,
author = {Dirdal, J. A. and Skjetne, R. and Roháv c, J. and Fossen, T. I.},
title = {Online wave direction and wave number estimation from surface vessel motions using distributed inertial measurement arrays and phase-time-path-differences},
journal = {Ocean Engineering},
year = {2022},
volume = {249},
pages = {110760},
url = {https://www.sciencedirect.com/science/article/pii/S0029801822002098},
doi = {10.1016/j.oceaneng.2022.110760}
}
|
| Heyn H-M and Skjetne R (2022), "Fast onboard detection of ice drift changes under stationkeeping in ice", Cold Regions Sci. and Tech.. Vol. 196, pp. 103483. |
| Abstract: Early detection of ice drift changes is essential for safe stationkeeping in ice-infested waters. This paper presents a conceptual system allowing onboard detection of ice drift changes in managed and unmanaged ice using distributed accelerometers installed in the hull of a stationkeeping vessel. With methods from statistical signal processing, specifically probability of exceedance analysis, a relation between the measured signals' entropy and the location along the hull where the ice action occurs is found. With field data from a stationkeeping operation in the Bay of Bothnia this relation is validated. The main contribution of this paper is a concept for ice drift estimation which only requires distributed vibration measurements along the hull and the ship's heading information. |
BibTeX:
@article{mhey22A,
author = {Heyn, H.-M. and Skjetne, R.},
title = {Fast onboard detection of ice drift changes under stationkeeping in ice},
journal = {Cold Regions Sci. and Tech.},
year = {2022},
volume = {196},
pages = {103483},
url = {https://www.sciencedirect.com/science/article/pii/S0165232X22000027},
doi = {10.1016/j.coldregions.2022.103483}
}
|
| Zhou H, Ren Z, Marley M and Skjetne R (2022), "A Guidance and Maneuvering Control System Design With Anti-Collision Using Stream Functions With Vortex Flows for Autonomous Marine Vessels", IEEE Trans. Ctrl. Sys. Tech.. Vol. 30(6), pp. 2630-2645. IEEE. |
| Abstract: Autonomous marine vessels are expected to avoid intervessel collisions and comply with the international regulations for safe voyages. This article presents a stepwise path planning method using stream functions. The dynamic flow of fluids is used as a guidance model, where the collision avoidance in static environments is achieved by applying the circular theorem in the sink flow. We extend this method to dynamic environments by adding vortex flows in the flow field. The stream function is recursively updated to enable “on the fly” waypoint decisions. The vessel avoids collisions and also complies with several rules of the convention on the International Regulations for Preventing Collisions at Sea. The method is conceptually and computationally simple and convenient to tune and yet versatile to handle complex and dense marine traffic with multiple dynamic obstacles. The ship dynamics are taken into account, by using Bézier curves to generate a sufficiently smooth path with feasible curvature. Numerical simulations are conducted to verify the proposed method. |
BibTeX:
@article{hzho22A,
author = {Zhou, H. and Ren, Z. and Marley, M. and Skjetne, R.},
title = {A Guidance and Maneuvering Control System Design With Anti-Collision Using Stream Functions With Vortex Flows for Autonomous Marine Vessels},
journal = {IEEE Trans. Ctrl. Sys. Tech.},
publisher = {IEEE},
year = {2022},
volume = {30},
number = {6},
pages = {2630-2645},
url = {https://ieeexplore.ieee.org/document/9756206},
doi = {10.1109/TCST.2022.3161844}
}
|
| Thorat L, Skjetne R and Osen OL (2021), "Genset Scheduling in a Redundant Electric Power System for an Offshore Vessel Using Mixed Integer Linear Programming", J. Offshore Mechanics and Arctic Eng.. Vol. 143(6), pp. 10. ASME. |
| Abstract: This paper proposes several schemes for optimal scheduling of power producers in a shipboard power system for a typical offshore supply vessel, having a multiple number of possibly varying capacity gensets. The proposed scheduling methods are illustrated using four alternative power system configurations, ranging from a few large gensets to many gensets of smaller ratings. Mixed integer linear programming is used to formulate the optimization problems. Three formulations are presented: one for minimizing online capacity without further objectives, one that includes a redundancy constraint for loosing a group of gensets (to account for a worst-case failure scenario), and one to also balance running hours and minimizing connect/disconnect of the gensets. These different objectives can be combined and weighted based on importance, with or without redundancy constraints. Simulations are carried out to demonstrate the properties of the three different scheduling methods. The first method, minimizing online capacity only, is also used to illustrate the differences between the four genset configurations. This shows, for instance, that using more small gensets ensures generally a lower online available power (the connected capacity matches better the prevailing load) and near optimal loading of each genset around 80% (assuming equal loadsharing), at the same time as resilience to genset failures is preserved. |
BibTeX:
@article{ltho21A,
author = {Thorat, L. and Skjetne, R. and Osen, O. L.},
title = {Genset Scheduling in a Redundant Electric Power System for an Offshore Vessel Using Mixed Integer Linear Programming},
journal = {J. Offshore Mechanics and Arctic Eng.},
publisher = {ASME},
year = {2021},
volume = {143},
number = {6},
pages = {10},
note = {061401},
url = {https://asmedigitalcollection.asme.org/offshoremechanics/article-abstract/143/6/061401/1105193/Genset-Scheduling-in-a-Redundant-Electric-Power},
doi = {10.1115/1.4050643}
}
|
| Ueland E, Sauder T and Skjetne R (2021), "Force Tracking Using Actuated Winches With Position-Controlled Motors for Use in Hydrodynamical Model Testing", IEEE Access. Vol. 9, pp. 77938-77953. IEEE. |
| Abstract: In this paper, we consider the problem of accurate force control using actuated winches, intended for use in real-time hybrid hydrodynamic model testing. The paper is also relevant to other cable-driven parallel robot applications that use force control in an inner control loop. For this problem, conventional strategies typically use actuated winches with torque-controlled servomotors directly connected to the cabled drum. In contrast, we propose using actuated winches with position-controlled servomotors that connect to the cabled drum via a clockspring. The servomotors are position controlled at drive-level and are rapid, accurate, robust, and simple to install. We show how this, combined with an accurate estimate of the clockspring deflection and stiffness, can yield fast and precise force tracking on moving objects. This includes proposing associated feedforward force-controllers that compensates for damping, angle-dependent force variations, delays, and non-constant clockspring characteristics. Extensive experimental testing on a 1 degree of freedom actuated mass-spring system supports the work. |
BibTeX:
@article{euel21C,
author = {Ueland, E. and Sauder, T. and Skjetne, R.},
title = {Force Tracking Using Actuated Winches With Position-Controlled Motors for Use in Hydrodynamical Model Testing},
journal = {IEEE Access},
publisher = {IEEE},
year = {2021},
volume = {9},
pages = {77938-77953},
url = {https://ieeexplore.ieee.org/document/9440403},
doi = {10.1109/ACCESS.2021.3083539}
}
|
| Ueland E, Sauder T and Skjetne R (2021), "Optimal Actuator Placement for Real-Time Hybrid Model Testing Using Cable-Driven Parallel Robots", J. Mar. Sci. Eng.. Vol. 9(2) MDPI. |
| Abstract: In real-time hybrid model testing, complex ocean structures are emulated by fusing numerical modelling with traditional hydrodynamic model testing. This is done by partitioning the ocean structure under consideration into a numerical and a physical substructure, coupled in real time via a measurement and control interface. The numerically computed load vector is applied to the physical substructure by means of multiple actuated winches so that the resulting experimental platform becomes a type of cable-driven parallel robot. In this context, the placement of the actuated winches is important to ensure that the loads can be accurately and robustly transferred to the physical substructure. This paper addresses this problem by proposing a performance measure and an associated actuator placement procedure that enables accurate force tracking and ensures that the numerically calculated loads can be actuated throughout the testing campaign. To clarify the application of the proposed procedure, it is applied to the design of a test setup for a moored barge. Overall, the paper represents a guideline for robust and beneficial actuator placement for real-time hybrid model testing using cable-driven parallel robots for load-actuation. |
BibTeX:
@article{euel21B,
author = {Ueland, E. and Sauder, T. and Skjetne, R.},
title = {Optimal Actuator Placement for Real-Time Hybrid Model Testing Using Cable-Driven Parallel Robots},
journal = {J. Mar. Sci. Eng.},
publisher = {MDPI},
year = {2021},
volume = {9},
number = {2},
url = {https://www.mdpi.com/2077-1312/9/2/191},
doi = {10.3390/jmse9020191}
}
|
| Ueland E, Sauder T and Skjetne R (2021), "Optimal Force Allocation for Overconstrained Cable-Driven Parallel Robots: Continuously Differentiable Solutions with Assessment of Computational Efficiency", IEEE Trans. Robotics. Vol. 37(2), pp. 659-666. IEEE. |
| Abstract: In this article, we present a novel method for force allocation for overconstrained cable-driven parallel robot setups that guarantees continuously differentiable cable forces and allows for small penalized errors in the resulting wrench. For the latter, we also provide a bound on the error under some assumptions. We study real-time feasibility by performing numerical simulations on a large set of configurations. |
| Comment: First online publication: 01 October 2020 |
BibTeX:
@article{euel21A,
author = {Ueland, E. and Sauder, T. and Skjetne, R.},
title = {Optimal Force Allocation for Overconstrained Cable-Driven Parallel Robots: Continuously Differentiable Solutions with Assessment of Computational Efficiency},
journal = {IEEE Trans. Robotics},
publisher = {IEEE},
year = {2021},
volume = {37},
number = {2},
pages = {659--666},
url = {https://ieeexplore.ieee.org/document/9210755},
doi = {10.1109/TRO.2020.3020747}
}
|
| Ren Z, Han X, Verma AS, Dirdal JA and Skjetne R (2021), "Sea state estimation based on vessel motion responses: Improved smoothness and robustness using Bézier surface and L1 optimization", Marine Structures. Vol. 76, pp. 102904. Elsevier. |
| Abstract: Floating structures oscillate in waves, where these wave-induced motions may be critical for various marine operations. An important consideration is thereby given to the sea states at the planning and operating stages for an offshore project. The most important information extracted from a sea state is the directional wave spectrum, indicating wave direction, significant wave height, and wave spectrum peak period. Among several available methods of measuring and estimating the directional wave spectrum, the wave buoy analogy technique based on vessel motion responses is an in situ and almost real-time solution without extra costs of devices. If the forms of the wave spectra are not predefined in the estimation, the method is called a nonparametric approach. Its most remarkable advantage is the flexible form, but the smoothness should be regulated. After the discrete Fourier transform has been applied to the measured vessel motions, smoothing is necessary. However, this process results in disturbed vessel cross-spectra and a lowpass characteristic of the windowing function. This paper presents a nonparametric approach for directional wave spectrum estimation based on vessel motion responses. It introduces novel smoothness constraints using Bézier surface and includes a more robust estimate using L1 optimization. Both techniques are applied to the wave buoy analogy for the first time. Numerical simulations are conducted to verify the proposed algorithm. |
BibTeX:
@article{zren21B,
author = {Ren, Z. and Han, X. and Verma, A. S. and Dirdal, J. A. and Skjetne, R.},
title = {Sea state estimation based on vessel motion responses: Improved smoothness and robustness using Bézier surface and L1 optimization},
journal = {Marine Structures},
publisher = {Elsevier},
year = {2021},
volume = {76},
pages = {102904},
url = {https://www.sciencedirect.com/science/article/pii/S0951833920301969},
doi = {10.1016/j.marstruc.2020.102904}
}
|
| Ren Z, Skjetne R, Verma AS, Jiang Z, Gao Z and Halse KH (2021), "Active heave compensation of floating wind turbine installation using a catamaran construction vessel", Marine Structures. Vol. 75, pp. 102904. Elsevier. |
| Abstract: The application of floating wind turbines is limited by the high cost that increases with the water depth. Offshore installation and maintenance continue to consume a high percentage of the project budget. To improve the installation efficiency of the floating offshore wind turbine, a novel concept is proposed by the SFI MOVE project. Several wind turbine superstructure components are preassembled onshore and carried to the installation site by a catamaran construction vessel. Each assembly can then be installed using only one lift, and the concept is less sensitive to weather conditions. In this paper, a control algorithm of the proposed hydraulic active heave compensator system is developed using singular perturbation theory to cancel the relative motion between the spar top and gripped preassembly bottom. Closed-loop stability is proven, and the simulation results show that the installation efficiency is improved with an increase in the acceptable weather conditions. |
BibTeX:
@article{zren21A,
author = {Ren, Z. and Skjetne, R. and Verma, A. S. and Jiang, Z. and Gao, Z. and Halse, K. H.},
title = {Active heave compensation of floating wind turbine installation using a catamaran construction vessel},
journal = {Marine Structures},
publisher = {Elsevier},
year = {2021},
volume = {75},
pages = {102904},
url = {https://www.sciencedirect.com/science/article/pii/S0951833920301611},
doi = {10.1016/j.marstruc.2020.102868}
}
|
| Borisov OI, Dahl AR, Pyrkin AA, Gromova FB and Skjetne R (2020), "Consecutive Compensator in Station-Keeping of a Surface Vessel", Mechatronics, Automation, Control. Vol. 21(10), pp. 566-574. |
| Abstract: This paper addresses the problem of station-keeping of a surface vessel by means of the consecutive compensator approach. The horizontal motion of the vessel is described by a dynamic model. The model is set up in vessel parallel coordinates, with three degrees of freedom: longitudinal, transverse and rotational motion. It is assumed that the vessel is fully actuated, i.e. there is a sufficient number and type of actuators and a thrust allocation system to ensure full manoeuvrability. Thus, the control can be designed with the assumption of three independent inputs and three output signals. The longitudinal motion can be considered separately, but a cross-coupling exists between the transverse and rotational kinetics. There is uncertainty both in parameters and signals, due to the vessel mass, inertia, and damping, as well as the unmeasured derivatives. The proposed control ensures station-keeping when the vessel is subjected to external disturbances. The consecutive compensator, which is based on high-gain feedback, provides robustness. Stability analysis is presented considering the cross-terms as limited disturbances. This allows proof of exponential stability. Experimental results are included from the Marine Cybernetics Laboratory (MC lab) at the Centre for Autonomous Marine Operations and Systems (A MOS) at the Norwegian University of Science and Technology (Norges teknisk-naturvitenskapelige universitet, NTNU ). Two scenarios are investigated: the scaled vessel is subjected to external disturbance, and the vessel executes the " four corner test". The experiments illustrate the applicability of the method. |
BibTeX:
@article{obor20A,
author = {Borisov, O. I. and Dahl, A. R. and Pyrkin, A. A. and Gromova, F. B. and Skjetne R.},
title = {Consecutive Compensator in Station-Keeping of a Surface Vessel},
journal = {Mechatronics, Automation, Control},
year = {2020},
volume = {21},
number = {10},
pages = {566--574},
url = {https://mech.novtex.ru/jour/article/view/887},
doi = {10.17587/mau.21.566-574}
}
|
| Heyn H-M, Blanke M and Skjetne R (2020), "Ice condition assessment using onboard accelerometers and statistical change detection", IEEE J. Oceanic Engineering. Vol. 45(3), pp. 898-914. IEEE. |
| Abstract: The presence of sea ice is the predominant risk for ship operations in the Arctic, and monitoring of ice condition around a vessel is crucial during all times of operation. This paper presents a system for online onboard assessment of ice condition. It is demonstrated that ice-induced accelerations in the bow section of the hull follow a bivariate t-distribution and parameters of the distribution have a one-to-one relation to ice condition. This paper suggests a methodology to monitor the ice condition in real time through estimation of parameters that characterize the distribution of hull accelerations. It is shown how a Kullback–Leibler divergence measure can classify ice condition among a set of pretrained conditions. An absolute measure of ice load is suggested as an alternative for situations when pretraining data are not available. The alternative algorithm quantifies the condition through the entropy of measured accelerations. This paper presents a computationally easy methodology and tests against data collected during Arctic transit of an icebreaker. Furthermore, the classification results are compared with the results from two standard methods from machine learning, decision tree and a support vector machine approaches. The results show that the statistical methods provide robust assessment of the prevailing ice conditions, independent of visual and weather conditions. Also, the comparison shows that the statistical classification methods, designed by process knowledge, provide steadier and more reliable results. |
BibTeX:
@article{mhey20A,
author = {Heyn, H.-M. and Blanke, M. and Skjetne, R.},
title = {Ice condition assessment using onboard accelerometers and statistical change detection},
journal = {IEEE J. Oceanic Engineering},
publisher = {IEEE},
year = {2020},
volume = {45},
number = {3},
pages = {898--914},
url = {https://ieeexplore.ieee.org/document/8661747},
doi = {10.1109/JOE.2019.2899473}
}
|
| Ren Z, Skjetne R, Jiang Z and Gao Z (2020), "Active Single-Blade Installation Using Tugger Line Tension Control and Optimal Control Allocation", Int. J. Offshore & Polar Eng.. Vol. 30(2), pp. 220-227. ISOPE. |
| Abstract: The single-blade installation is a common method for the installation of wind turbine blades. In an offshore installation, a jackup vessel is often involved, and a crane is used to lift, move, and bolt each blade onto the rotor hub at the tower top. To reduce the blade pendular motions, tugger lines are connected to the suspended blade. Active control of the tension force on the tugger lines has been recently investigated to reduce the blade motion. In this situation, a pre-tension is needed during the mating process, as only positive tension can be provided by the tugger lines. To further improve the effectiveness of active force control, we propose an active control strategy with a three-tugger-line configuration in this work. The placement of the third tugger line is examined. The proportional–integral–derivative (PID) control strategy is adopted, and allocation is achieved by convex programming. Aeroelastic simulations are carried out to verify the active control scheme under turbulent wind conditions. The results show that the proposed active control scheme is an effective means of reducing the translational motion of the blade root relative to the hub in the mean wind direction. |
BibTeX:
@article{zren20A,
author = {Ren, Z. and Skjetne, R. and Jiang, Z. and Gao, Z.},
title = {Active Single-Blade Installation Using Tugger Line Tension Control and Optimal Control Allocation},
journal = {Int. J. Offshore & Polar Eng.},
publisher = {ISOPE},
year = {2020},
volume = {30},
number = {2},
pages = {220--227},
url = {http://www.isope.org/ijope-volume-30-issue-2-june-2020},
doi = {10.17736/ijope.2020.jc759}
}
|
| Skjetne R and Ren Z (2020), "A survey on modeling and control of thruster-assisted position mooring systems", Marine Structures. Vol. 74, pp. 102830. Elsevier. |
| Abstract: This review presents a systematic summary of the state-of-the-art development of technological solutions, modeling, and control strategies of thruster-assisted position mooring (TAPM) systems. The survey serves as a starting point for exploring automatic control and real-time monitoring solutions proposed for TAPM systems. A brief historical background of the mooring systems is given. The kinematics and a simplified kinetic control-design model of a TAPM system are derived in accordance with established control methods, including a quasistatic linearized model for the restoring and damping forces based on low-frequency horizontal motions of the vessel. In addition, another two mooring line models, i.e., the catenary equation and the finite element method model, are presented for the purpose of higher-fidelity simulations. The basic TAPM control strategies are reviewed, including heading control, surge-sway damping, roll–pitch damping (for semisubmersibles), and line break detection and compensation. Details on the concepts of setpoint chasing for optimal positioning of a vessel at the equilibrium position are discussed based on balancing the mooring forces with the environmental loads and avoiding mooring line failure modes. One method for setpoint chasing is the use of a structural reliability index, accounting for both mean mooring line tensions and dynamic effects. Another method is the use of a lowpass filter on the position of the vessel itself, to provide a reference position. The most advanced method seems to be the use of a fault-tolerant control framework that, in addition to direct fault detection and isolation in the mooring system, incorporates minimization of either the low-frequency tensions in the mooring lines or minimization of the reliability indices for the mooring lines to select the optimal directions for the setpoint to move. A hybrid (or supervisory switching) control method is also presented, where a best-fit control law and observer law are automatically selected among a bank of control and observer algorithms based on the supervision of the sea-state and automatic switching logic. |
BibTeX:
@article{rskj20A,
author = {Skjetne, R. and Ren, Z.},
title = {A survey on modeling and control of thruster-assisted position mooring systems},
journal = {Marine Structures},
publisher = {Elsevier},
year = {2020},
volume = {74},
pages = {102830},
url = {http://www.sciencedirect.com/science/article/pii/S0951833920301222},
doi = {10.1016/j.marstruc.2020.102830}
}
|
| Sørensen MEN, Breivik M and Skjetne R (2020), "Comparing Combinations of Linear and Nonlinear Feedback Terms for Ship Motion Control", IEEE Access. Vol. 8, pp. 193813-193826. IEEE. |
| Abstract: In this paper, combinations of linear and nonlinear feedback terms are investigated for 3 degrees-of-freedom pose and velocity control of ships. Nonlinear control algorithms that are found in the literature often have linear feedback terms, which result in nice globally exponential stability properties when assuming no actuator constraints. However, considering that all actuators have saturation constraints, such stability properties are not feasible in practice. Applying nonlinear feedback terms can be a step to handle such constraints. As a result, this paper explores nonlinear feedback terms for both the kinematic and kinetic control loops. Specifically, three controllers based on a cascaded backstepping control design are implemented and compared through simulations and model-scale experiments in an ocean basin. Stability properties and tuning rules for all the controllers are also provided. Interestingly, the use of nonlinear feedback terms gives the ability to constrain the feedback control inputs globally while simultaneously being able to change the convergence rates locally. The price to be paid is the introduction of additional tuning parameters. The three controller types are compared using performance metrics which consider both control accuracy and energy use. |
BibTeX:
@article{msor20A,
author = {Sørensen, M. E. N. and Breivik, M. and Skjetne, R.},
title = {Comparing Combinations of Linear and Nonlinear Feedback Terms for Ship Motion Control},
journal = {IEEE Access},
publisher = {IEEE},
year = {2020},
volume = {8},
pages = {193813-193826},
url = {https://ieeexplore.ieee.org/document/9241400},
doi = {10.1109/ACCESS.2020.3033409}
}
|
| Kim E, Dahiya GS, Løset S and Skjetne R (2019), "Can a computer see what an ice expert sees? Multilabel ice objects classification with convolutional neural networks", #RIE#. Vol. 4, pp. 13. Elsevier. |
| Abstract: Computer-aided scene analysis has drawn much attention, especially in autonomous navigation and advanced navigation assistance systems for surface vessels. In ice-infested waters, multilabel ice object classification and segmentation form the core of these systems, which are required for path-planning and collision avoidance algorithms. This study focuses on the interpretation of ice conditions from close-range optical imagery. It presents a model for multilabel ice object classification that builds on state-of-the-art open source libraries and deep learning platforms. This work explores the generalization ability of open source models to differentiate between nine categories of surface ice features: level ice, deformed ice, broken ice, icebergs, floebergs, floebits, ice floes, pancake ice, and brash ice. The results demonstrate the ability of the models to classify these nine categories from optical close-range images, which were gathered online and during a research cruise to the Fram Strait on the RV Lance in 2012. We tested a variety of classification algorithms on the collected ice imagery and compared the results against randomly selected test cases representing different ice features with different degrees of local texture distortion. In doing so, we can evaluate the effectiveness of the classification of different classes and compare different levels of information presented for the classification. In addition, we provide a model implementation: a GitHub repository, ICEXPERT, that is suitable for ice object classification from close-range ice imagery. |
BibTeX:
@article{ekim19A,
author = {Kim, E. and Dahiya, G. S. and Løset, S. and Skjetne, R.},
title = {Can a computer see what an ice expert sees? Multilabel ice objects classification with convolutional neural networks},
journal = {#RIE#},
publisher = {Elsevier},
year = {2019},
volume = {4},
pages = {13},
url = {https://www.sciencedirect.com/science/article/pii/S2590123019300362},
doi = {10.1016/j.rineng.2019.100036}
}
|
| Reddy NP, Zadeh MK, Thieme CA, Skjetne R, Sørensen AJ, Aanondsen SA, Breivik M and Eide E (2019), "Zero-emission autonomous ferries for urban water transport", IEEE Electrification Magazine. Vol. 7(4), pp. 32-45. IEEE. |
| Abstract: Because water is an integral part of day-to-day life for humans, civilizations have generally flourished either in coastal areas or near river basins. Today, about 40% of the world?s population lives near a coast and many of the biggest cities are located near the sea or along rivers. In Norway, a high percentage of people live in coastal areas. There are many waterways, such as canals and fjords, in these coastal areas. Constructing bridges over these water channels is expensive and may hinder marine traffic. Therefore, in the coastal cities, urban ferries are much more than tourist attractions. They are an integral part of the city?s multimodal transportation system and essential for easing road traffic and congestion. |
BibTeX:
@article{nred19B,
author = {Reddy, N. P. and Zadeh, M. K. and Thieme, C. A. and Skjetne, R. and Sørensen, A. J. and Aanondsen, S. A. and Breivik, M. and Eide, E.},
title = {Zero-emission autonomous ferries for urban water transport},
journal = {IEEE Electrification Magazine},
publisher = {IEEE},
year = {2019},
volume = {7},
number = {4},
pages = {32--45},
url = {https://ieeexplore.ieee.org/document/8917843},
doi = {10.1109/MELE.2019.2943954}
}
|
| Ren Z, Skjetne R, Jiang Z, Gao Z and Verma AS (2019), "Integrated GNSS/IMU Hub Motion Estimator for Offshore Wind Turbine Blade Installation", Mech. Syst. and Signal Proc.. Vol. 123, pp. 222-243. Elsevier. |
| Abstract: Offshore wind turbines (OWTs) have become increasingly popular for their ability to harvest clean offshore wind energy. Bottom-fixed foundations are the most used foundation type. Because of its large diameter, the foundation is sensitive to wave loads. For typical manually assisted blade-mating operations, the decision to perform the mating operation is based on the relative distance and velocity between the blade root center and the hub, and in accordance with the weather window. Hence, monitoring the hub real-time position and velocity is necessary, whether the blade installation is conducted manually or automatically. In this study, we design a hub motion estimation algorithm for the OWT with a bottom-fixed foundation using sensor fusion of a global navigation satellite system (GNSS) and an inertial measurement unit (IMU). Two schemes are proposed based on a moving horizon estimator, a multirate Kalman filter, an online smoother, and a predictor. The moving horizon estimator mitigates the slow GNSS sampling rate relative to the hub dynamics. The multirate Kalman filter estimates the position, velocity, and accelerometer bias with a constant GNSS measurement delay. The online smoothing algorithm filters the delayed estimated trajectory to remove sudden step changes. The predictor compensates the delayed estimate, resulting in real-time monitoring. HAWC2 and MATLAB are used to verify the performance of the estimation algorithms, showing that a sufficiently accurate real-time position and velocity estimate with a high sampling rate is achieved. A sensitivity study compares the accuracy of different algorithms applied in various conditions. By combining both proposed algorithms, a sufficiently accurate estimation can be achieved for a wider scope of practical applications. |
BibTeX:
@article{zren19B,
author = {Ren, Z. and Skjetne, R. and Jiang, Z. and Gao, Z. and Verma, A. S.},
title = {Integrated GNSS/IMU Hub Motion Estimator for Offshore Wind Turbine Blade Installation},
journal = {Mech. Syst. and Signal Proc.},
publisher = {Elsevier},
year = {2019},
volume = {123},
pages = {222--243},
url = {http://www.sciencedirect.com/science/article/pii/S088832701930007X},
doi = {10.1016/j.ymssp.2019.01.008}
}
|
| Ren Z, Skjetne R and Gao Z (2019), "A Crane Overload Protection Controller for Blade Lifting Operation Based on Model Predictive Control", Energies. Vol. 12(1) MDPI. |
| Abstract: Lifting is a frequently used offshore operation. In this paper, a nonlinear model predictive control (NMPC) scheme is proposed to overcome the sudden peak tension and snap loads in the lifting wires caused by lifting speed changes in a wind turbine blade lifting operation. The objectives are to improve installation efficiency and ensure operational safety. A simplified three-dimensional crane-wire-blade model is adopted to design the optimal control algorithm. A crane winch servo motor is controlled by the NMPC controller. The direct multiple shooting approach is applied to solve the nonlinear programming problem. High-fidelity simulations of the lifting operations are implemented based on a turbulent wind field with the MarIn and CaSADi toolkit in MATLAB. By well-tuned weighting matrices, the NMPC controller is capable of preventing snap loads and axial peak tension, while ensuring efficient lifting operation. The performance is verified through a sensitivity study, compared with a typical PD controller. |
BibTeX:
@article{zren19A,
author = {Ren, Z. and Skjetne, R. and Gao, Z.},
title = {A Crane Overload Protection Controller for Blade Lifting Operation Based on Model Predictive Control},
journal = {Energies},
publisher = {MDPI},
year = {2019},
volume = {12},
number = {1},
url = {https://www.mdpi.com/1996-1073/12/1/50},
doi = {10.3390/en12010050}
}
|
| Værnø SA, Brodtkorb AH and Skjetne R (2019), "Compensation of bias loads in dynamic positioning of marine surface vessels", Ocean Engineering. Vol. 178, pp. 484-492. Elsevier. |
| Abstract: This paper investigates different methods for compensating the mean and slowly varying environmental loads, and unmodeled dynamics (bias loads) in dynamic positioning of marine vessels. Four different methods are compared; using the bias estimate from an observer tuned to estimate position and velocity well, using a wave-filtered version of this bias load, using the estimate from a separate observer tuned to work well for estimating the bias loads, and finally traditional integral action on the tracking errors. The results show that the bias from the bias observer is the best solution, both in transients and steady state. Standard integral action matches the steady state performance, but is slower in transients. The estimate from the observer used for position and velocity is fast in transients, but too oscillatory in the bias state. The wave-filtered version of this has less oscillations, but falls short compared to the other methods due to added phase lag from the extra wave filter. Using a bias estimate from an observer has benefits over typical integral action, such as the possibility of offline or open-loop tuning and avoiding integral windup issues. For the comparison study, a 6 DOF simulation model of a supply vessel is used. |
BibTeX:
@article{svar19B,
author = {Værnø, S. A. and Brodtkorb, A. H. and Skjetne, R.},
title = {Compensation of bias loads in dynamic positioning of marine surface vessels},
journal = {Ocean Engineering},
publisher = {Elsevier},
year = {2019},
volume = {178},
pages = {484--492},
url = {https://www.sciencedirect.com/science/article/pii/S0029801818310928},
doi = {10.1016/j.oceaneng.2019.03.010}
}
|
| Værnø SA, Skjetne R, Kjerstad ØK and Calabrò V (2019), "Comparison of control design models and observers for dynamic positioning of surface vessels", Contr. Eng. Practice. Vol. 85, pp. 235-245. Elsevier. |
| Abstract: This paper investigates some fundamental aspects of control system design for dynamic positioning of marine surface vessels. Different control design models are compared. The impact of applying linear and nonlinear models to describe the hydrodynamic damping loads are investigated, and common observer algorithms for DP are compared. The comparison includes a linear time-varying Kalman filter, an extended Kalman filter, and an unscented Kalman filter. To make the comparisons rigorous, optimization is employed to find optimal observer gains, and high-fidelity simulation data and full-scale experimental data are used to test the performance under operations/conditions with significant transient effects. |
BibTeX:
@article{svar19A,
author = {Værnø, S. A. and Skjetne, R. and Kjerstad, Ø. K. and Calabrò, V.},
title = {Comparison of control design models and observers for dynamic positioning of surface vessels},
journal = {Contr. Eng. Practice},
publisher = {Elsevier},
year = {2019},
volume = {85},
pages = {235--245},
url = {http://www.sciencedirect.com/science/article/pii/S0967066119300085},
doi = {10.1016/j.conengprac.2019.01.015}
}
|
| Brodtkorb AH, Værnø SAT, Teel AR, Sørensen AJ and Skjetne R (2018), "Hybrid controller concept for dynamic positioning of marine vessels with experimental results", Automatica. Vol. 93, pp. 489-497. IFAC. |
| Abstract: The next generation marine control systems will, as a step towards increased autonomy, have more automatic functionality in order to cope with a set of complex operations in unknown, challenging and varying environments while maintaining safety and keeping operational costs low. In this paper a hybrid control strategy for stationkeeping and maneuvering of marine vessels is proposed. The hybrid concept allows a structured way to develop a control system with a bank of controllers and observers improving dynamic positioning (DP) performance in stationary dynamics, changing dynamics including enhancing transient performance, and giving robustness to measurement errors. DP systems are used on marine vessels for automatic stationkeeping and tracking operations solely by use of the thrusters. In this paper a novel method improving the transient response of a vessel in DP is developed. The performance of the hybrid control system, including two observer candidates and one controller candidate, is demonstrated in model-scale experiments and on full-scale field data. The hybrid system has global stability properties. |
BibTeX:
@article{abro18A,
author = {Brodtkorb, A. H. and Værnø, S. A. T. and Teel, A. R. and Sørensen, A. J. and Skjetne, R.},
title = {Hybrid controller concept for dynamic positioning of marine vessels with experimental results},
journal = {Automatica},
publisher = {IFAC},
year = {2018},
volume = {93},
pages = {489--497},
url = {https://www.sciencedirect.com/science/article/pii/S0005109818301341},
doi = {10.1016/j.automatica.2018.03.047}
}
|
| Heyn H-M and Skjetne R (2018), "Time-frequency analysis of acceleration data from ship-ice interaction events", Cold Regions Sci. and Tech.. Vol. 156, pp. 61-74. Elsevier. |
| Abstract: During operations with ships in ice-infested waters, vibrations of the hull occur due to ship-ice interaction. The acting ice load and the induced vibrations depend on the ice regime and ice breaking mechanism. Especially crushing of ice against the hull causes high loads against the vessel. The objective of this study is to analyse the frequency components of ice-induced vibrations, measured with accelerometers placed in the bow section of the ship's hull. The Wigner-Ville distribution, which provides a time-frequency representation, is applied on acceleration data collected on the icebreaker Frej during transit in ice-infested Arctic waters. The resulting time-frequency representations show that the excited frequencies depend on the dominant ice breaking mechanism, on the encounter velocity, and on the position of where the ice interaction against the hull occurs. Furthermore, the natural frequencies of the ship's hull change slightly, depending on the conditions on the sea-ice around the vessel. It is concluded that a system of distributed accelerometers on a ship can provide information about the acting ice breaking mechanism, the ice conditions around the vessel, and about the location along the hull, where the ship-ice interaction occurs. This can be used as an additional tool in monitoring systems during operations in ice-infested waters. |
BibTeX:
@article{mhey18A,
author = {Heyn, H.-M. and Skjetne, R.},
title = {Time-frequency analysis of acceleration data from ship-ice interaction events},
journal = {Cold Regions Sci. and Tech.},
publisher = {Elsevier},
year = {2018},
volume = {156},
pages = {61--74},
note = {OATRC2015},
url = {https://www.sciencedirect.com/science/article/pii/S0165232X17300368},
doi = {10.1016/j.coldregions.2018.01.019}
}
|
| Kjerstad ØK, Lu W, Skjetne R and Løset S (2018), "A method for real-time estimation of full-scale global ice loads on floating structures", Cold Regions Sci. and Tech.. Vol. 156, pp. 44-60. Elsevier. |
| Abstract: This paper proposes an algorithm that uses conventional measurements found on-board ships coupled with additional Inertial Measurement Units to estimate the motions and global loads acting on them. The work is motivated by the scarce availability of full-scale load data for sea-ice operations and by the invasive instrumentation of strain gauges used to obtain global loads of all degrees of freedom. Full-scale data are key to a number of design, operational, and research aspects related to sea-ice operations. The proposed algorithm is based on four Inertial Measurement Units (IMUs) that together with position and heading measurements are used to make estimates of dynamic linear and rotational acceleration (acceleration resulting in motion). We show how to use models updated with propulsion and wind measurements to estimate propulsion, hydrodynamic, wind, and ice loads through a setup catering to real-time implementation. A case study with the Swedish icebreaker Oden is presented and discussed. The algorithm effectively yields reasonable ice load history estimations and presents great potential in its further application to real-time global ice load estimations. |
BibTeX:
@article{okje18B,
author = {Kjerstad, Ø. K. and Lu, W. and Skjetne, R. and Løset, S.},
title = {A method for real-time estimation of full-scale global ice loads on floating structures},
journal = {Cold Regions Sci. and Tech.},
publisher = {Elsevier},
year = {2018},
volume = {156},
pages = {44--60},
note = {OATRC2015},
url = {https://www.sciencedirect.com/science/article/pii/S0165232X17306018},
doi = {10.1016/j.coldregions.2018.03.012}
}
|
| Kjerstad ØK, Løset S, Skjetne R and Skarbø R (2018), "An Ice-Drift Estimation Algorithm Using Radar and Ship Motion Measurements", IEEE Trans. Geoscience Remote Sensing. Vol. 56(6), pp. 3007-3019. IEEE. |
| Abstract: This paper presents a novel automatic real-time remote sensing algorithm that uses radar images and global positioning satellite system measurements to estimate the ice-drift velocity vector in a region around a free-floating and potentially moving vessel. It is motivated by the low image frequency of satellite systems together with the inconvenience of deploying and retrieving ice trackers (beacons) on the ice. The algorithm combines radar image processing with two Kalman filters to produce the estimated local drift vector decoupled from the ship motion. The proposed design is verified using a full-scale data set from an ice management operation north of Svalbard in 2015. It is found that the performance of the algorithm is comparable with that of trackers on the ice. |
BibTeX:
@article{okje18A,
author = {Kjerstad, Ø. K. and Løset, S. and Skjetne, R. and Skarbø, R.},
title = {An Ice-Drift Estimation Algorithm Using Radar and Ship Motion Measurements},
journal = {IEEE Trans. Geoscience Remote Sensing},
publisher = {IEEE},
year = {2018},
volume = {56},
number = {6},
pages = {3007--3019},
url = {https://ieeexplore.ieee.org/document/8352786/},
doi = {10.1109/TGRS.2017.2787996}
}
|
| Norgren P and Skjetne R (2018), "A multibeam-based SLAM algorithm for iceberg mapping using AUVs", IEEE Access. Vol. 6(1), pp. 26318-26337. IEEE. |
| Abstract: Using autonomous underwater vehicles (AUVs) for mapping underwater topography of sea-ice and icebergs, or detecting keels of ice ridges, is foreseen as enabling technology in future Arctic marine operations. Wind, current, and Coriolis forces affect an iceberg’s trajectory, making automated mapping difficult. This paper presents a method aiming at enabling autonomous iceberg mapping using AUVs equipped with a multibeam echosounder by estimating the position and orientation of the iceberg. The method is based on a bathymetric simultaneous localization and mapping (SLAM) algorithm, namely the bathymetric distributed particle filter SLAM (BPSLAM) algorithm. The proposed method estimates the AUV’s pose in an iceberg-fixed coordinate system. The relative states can be used for both guiding the vehicle to achieve complete coverage, as well as estimation of a consistent iceberg topography. The algorithm also provides an estimate of the iceberg’s drift velocity – an important parameter for the AUV trajectory planning as well as any related ice management (IM) operations. Two new weighting algorithms for the BPSLAM method are proposed, enabling batch processing of multibeam echosounder (MBE) measurements to ensure real-time operation without discarding information. The proposed method is demonstrated using a real iceberg topography taken from the PERD iceberg sightings database, with simulated AUV and MBE range measurements. The algorithm is also evaluated on a real world bathymetric dataset, collected using the HUGIN HUS AUV. |
| Comment: Simultaneous localization and mapping, Ice, Arctic, Biological system modeling, Real-time systems, Sea measurements |
BibTeX:
@article{pnor18A,
author = {Norgren, P. and Skjetne, R.},
title = {A multibeam-based SLAM algorithm for iceberg mapping using AUVs},
journal = {IEEE Access},
publisher = {IEEE},
year = {2018},
volume = {6},
number = {1},
pages = {26318--26337},
url = {https://ieeexplore.ieee.org/document/8351915},
doi = {10.1109/ACCESS.2018.2830819}
}
|
| Ren Z, Jiang Z, Gao Z and Skjetne R (2018), "Active tugger line force control for single blade installation", Wind Energy. Vol. 21(12), pp. 1344-1358. Wiley. |
| Abstract: Single blade installation is one of the methods for installing large wind turbine blades at an offshore site. During this installation, each blade is lifted by the main crane from the deck of an installation vessel or a transportation barge with blade root approaching the hub. The blade root is then bolted to the hub. The final mating phase is critical and requires high precision. Tugger lines from the crane boom are connected to the suspended blade to reduce pendulum motions. The entire process is typically completed without active tugger line force control. Due to wind‐induced blade loads, strict requirement on installation precision, and the limitations imposed by the lifting equipment, the single blade installation operations are subject to weather constraints. Therefore, developing techniques to reduce the blade motions and consequently shorten the installation time is desired. In this paper, an active control scheme is proposed to control the tugger line forces acting on a blade during the final installation stage before mating. A simplified three degree‐of‐freedom blade installation model is developed for the control design. An extended Kalman filter is used to estimate the blade motions and wind velocities. Feedback linearization and pole placement techniques are applied for the design of the controller. Simulations under turbulent wind conditions are conducted to verify the active control scheme, which effectively reduces the blade root motions in the wind direction. |
BibTeX:
@article{zren18B,
author = {Ren, Z. and Jiang, Z. and Gao, Z. and Skjetne, R.},
title = {Active tugger line force control for single blade installation},
journal = {Wind Energy},
publisher = {Wiley},
year = {2018},
volume = {21},
number = {12},
pages = {1344--1358},
url = {https://onlinelibrary.wiley.com/doi/full/10.1002/we.2258},
doi = {10.1002/we.2258}
}
|
| Ren Z, Jiang Z, Skjetne R and Gao Z (2018), "Development and application of a simulator for offshore wind turbine blades installation", Ocean Engineering. Vol. 166, pp. 380-395. Elsevier. |
| Abstract: In an offshore environment, offshore wind energy resources are more available and stable, but the investment cost is much higher than that of onshore wind. The installation cost is a crucial factor of the investment. With the increasing number of planned and approved offshore wind farms, offshore wind turbine installation and relevant operations have received tremendous attention. Therefore, expediting the turbine-structure mating operations through a higher level of automation in offshore wind turbine installations may provide important economic benefits. To achieve a higher automation level and reduce the weather waiting time during the installation of offshore wind turbines, a flexible simulation-verification framework with high fidelity is needed. However, state-of-the-art wind turbine numerical analysis code is neither convenient nor open enough for applications concerning the design and verification of control algorithms. MATLAB/Simulink is among the most widely utilized numerical platforms by control engineers and researchers. This paper describes the development of a modularized blade installation simulation toolbox for the purpose of control design in MATLAB/Simulink. The toolbox can be used to simulate several blade installation configurations, both onshore and offshore. The paper presents the key features and equations of the different modules, exemplified by a single blade installation operation. Code-to-code verification results are presented and discussed with both quasi-steady wind and three-dimensional turbulent wind field. |
BibTeX:
@article{zren18A,
author = {Ren, Z. and Jiang, Z. and Skjetne, R. and Gao, Z.},
title = {Development and application of a simulator for offshore wind turbine blades installation},
journal = {Ocean Engineering},
publisher = {Elsevier},
year = {2018},
volume = {166},
pages = {380--395},
url = {https://www.sciencedirect.com/science/article/pii/S0029801818307224},
doi = {10.1016/j.oceaneng.2018.05.011}
}
|
| Xu J, Ren Z, Li Y, Skjetne R and Halse KH (2018), "Dynamic Simulation and Control of an Active Roll Reduction System Using Free-Flooding Tanks With Vacuum Pumps", J. Offshore Mechanics and Arctic Eng.. Vol. 140(6), pp. 9. ASME. |
| Abstract: Ship roll motion is critical 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. A tank is installed on each side of a catamaran. Both 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 stabilized the wave-induced roll motion by controlling the water levels in the tanks through a feedback controller. The catamaran is a dynamic model with single degree-of-freedom (DOF) in roll, and its hydrodynamic behavior is calculated using potential theory by SHIPX. The air chambers are modeled as isothermal processes of ideal gas. The behavior of the liquid flow in a tank is simulated by incompressible Reynolds-averaged Navier–Stokes solver with the volume of fluid model, then summarized as a response function for the vessel model. A simplified control plant model for the vacuum pumps is proposed where higher order behaviors are neglected and the external wave-induced load is unknown. A parameter-dependent observer and a backstepping controller are adopted to estimate the external load and to reduce the roll motion. The system stability is proved by Lyapunov's 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:
@article{jxu18A,
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},
journal = {J. Offshore Mechanics and Arctic Eng.},
publisher = {ASME},
year = {2018},
volume = {140},
number = {6},
pages = {9},
url = {http://offshoremechanics.asmedigitalcollection.asme.org/article.aspx?articleid=2681698},
doi = {10.1115/1.4040235}
}
|
| Sørensen AJ, Skjetne R, Bø T, Miyazaki MR, Johansen TA, Utne IB and Pedersen E (2017), "Toward Safer, Smarter, and Greener Ships: Using Hybrid Marine Power Plants", IEEE Electrification Magazine., Sept, 2017. Vol. 5(3), pp. 68-73. |
| Abstract: Electrical power plants with dieselgenerator sets segregated (i.e., the diesel generator sets are divided into different power buses and physical stations on ships and rigs) on several power buses have become the preferred solution for ships with various operational profiles and corresponding power demands. Examples of such ships are dynamically positioned (DP) vessels with electric power plants in the range of 10-80 MW used in the offshore oil and gas industry for service, drilling, intervention, and production operations (Figure 1). The operations are characterized as safety critical and take place year-round, with large variations in the environmental loads acting on the ship, e.g., wind, waves, ocean currents, and sea ice. Electrical power plants have also become the preferred solution for cruise ships, ferries, navy ships, liquefied natural gas tankers, and icebreakers. The electric energy production may be powered by a hybrid marine power plant consisting of diesel or gas engines and integrated energy storage devices (ESDs) such as banks of batteries. Proper design and control systems can deliver significant fuel savings to make the ships greener and safer. |
BibTeX:
@article{asor17A,
author = {Sørensen, A. J. and Skjetne, R. and Bø, T. and Miyazaki, M. R. and Johansen, T. A. and Utne, I. B. and Pedersen, E.},
title = {Toward Safer, Smarter, and Greener Ships: Using Hybrid Marine Power Plants},
journal = {IEEE Electrification Magazine},
year = {2017},
volume = {5},
number = {3},
pages = {68-73},
url = {http://ieeexplore.ieee.org/document/8025702},
doi = {10.1109/MELE.2017.2718861}
}
|
| Værnø SA, Brodtkorb AH, Skjetne R and Calabrò V (2017), "Time-Varying Model-Based Observer for Marine Surface Vessels in Dynamic Positioning", IEEE Access. Vol. 5, pp. 14787-14796. IEEE. |
| Abstract: This paper deals with the problem of transient events in model-based observers for dynamic positioning of marine surface vessels. Traditionally, model-based observers experience a deterioration of performance during transients, and there is a give or take relationship between transient and steady state performance. To remedy this problem, we propose to use time-varying gains for a model-based observer. The gains are aggressive during transients to improve transient performance, and relaxed in steady state to lower the oscillations of the estimates. The proposed observer is analyzed with regard to stability. Its performance is verified in both a high-fidelity simulation model, and on experimental data with the research vessel (R/V) Gunnerus. In addition, a partial closed-loop validation with R/V Gunnerus has been performed. |
BibTeX:
@article{svar17B,
author = {Værnø, S. A. and Brodtkorb, A. H. and Skjetne, R. and Calabrò, V.},
title = {Time-Varying Model-Based Observer for Marine Surface Vessels in Dynamic Positioning},
journal = {IEEE Access},
publisher = {IEEE},
year = {2017},
volume = {5},
pages = {14787--14796},
url = {http://ieeexplore.ieee.org/document/7993007},
doi = {10.1109/ACCESS.2017.2731998}
}
|
| Kjerstad ØK and Skjetne R (2016), "Disturbance rejection by acceleration feedforward for marine surface vessels", IEEE Access. Vol. 4, pp. 2656-2669. IEEE. |
| Abstract: Acceleration signals have a powerful disturbance rejection potential in rigid body motion control as they carry a measure proportional to the resulting force. Yet, they are seldom used, since measuring, decoupling, and utilizing the dynamic acceleration in the control design is not trivial. This paper discusses these topics and presents a solution for marine vessels building on conventional methods together with a novel control law design where the dynamic acceleration signals are used to form a dynamic reference-less disturbance feedforward compensation. This replaces conventional integral action and enables unmeasured external loads and unmodel dynamics to be counteracted with low time lag. A case study shows feasibility of the proposed design using experimental data and closed-loop high fidelity simulations of dynamic positioning in a harsh cold climate environment with service. |
BibTeX:
@article{okje16B,
author = {Kjerstad, Ø. K. and Skjetne, R.},
title = {Disturbance rejection by acceleration feedforward for marine surface vessels},
journal = {IEEE Access},
publisher = {IEEE},
year = {2016},
volume = {4},
pages = {2656--2669},
url = {http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=7454698&tag=1},
doi = {10.1109/ACCESS.2016.2553719}
}
|
| Veksler A, Johansen TA, Skjetne R and Mathiesen E (2016), "Thrust Allocation With Dynamic Power Consumption Modulation for Diesel-Electric Ships", IEEE Trans. Ctrl. Sys. Tech.. Vol. 24(2), pp. 578-593. |
| Abstract: Modern ships and offshore units built for dynamic positioning (DP) are often powered by an electric power plant consisting of two or more diesel-electric generators. Actuation in any desired direction is achieved by placing electrical thrusters at suitable points on the hull. Usually, such ships also have other large electrical loads. Operations in the naturally unpredictable marine environment often necessitate large variations in power consumption, both by the thrusters and by the other consumers. This wears down the power plant and increases the fuel consumption and pollution. This paper introduces a thrust allocation algorithm that facilitates more stable loading on the power plant. This algorithm modulates the power consumption by coordinating the thrusters to introduce load variations that counteract the load variations from the other consumers on the ship. To reduce load variations without increasing the overall power consumption, it is necessary to deviate from the thrust command given by the DP system. The resulting deviations in the position and velocity of the vessel are tightly controlled, and the results show that small deviations are sufficient to fulfill the objective of reducing the load variations. The effectiveness of the proposed algorithm has been demonstrated on a simulated vessel with a diesel-electric power plant. A model for the simulation of a marine power plant for control design purposes has been developed. |
BibTeX:
@article{avek16A,
author = {Veksler, A. and Johansen, T. A. and Skjetne, R. and Mathiesen, E.},
title = {Thrust Allocation With Dynamic Power Consumption Modulation for Diesel-Electric Ships},
journal = {IEEE Trans. Ctrl. Sys. Tech.},
year = {2016},
volume = {24},
number = {2},
pages = {578--593},
url = {http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=7217809},
doi = {10.1109/TCST.2015.2446940}
}
|
| Bø TI, Dahl AR, Johansen TA, Mathiesen E, Miyazaki MR, Pedersen E, Skjetne R, Sørensen AJ, Thorat L and Yum KK (2015), "Marine Vessel and Power Plant System Simulator", IEEE Access. Vol. 3, pp. 2065-2079. Inst. Electrical and Electronics Engineers. |
| Abstract: Modern marine electric propulsion vessels have many systems. These interactions and integration aspects are essential when studying a system and subsystem behavior. This is especially important when considering fault scenarios,s harsh weather, and complex marine operations. However, many simulators, including a selection presented here, study the positioning system and the power system separately. This paper proposes a simulator combining the two systems, as an extension to the marine systems simulator MATLAB/Simulink library. The intended use cases and the according design choices are presented. New subsystem models include a power-based electrical bus model and a simplified diesel engine model. Both are validated through the simulation against established models. In addition, established models for generators, electrical storage devices, thrusters, and a mean-value diesel engine model are summarized with rich references. Three case studies illustrate the multi-domain use of the simulator: 1) a semi-submersible drilling rig performing station keeping under environmental disturbances; 2) the same vessel subject to an electrical bus reconfiguration; and 3) a supply vessel with a hybrid power plant. |
BibTeX:
@article{tbo15B,
author = {Bø, T. I. and Dahl, A. R. and Johansen, T. A. and Mathiesen, E. and Miyazaki, M. R. and Pedersen, E. and Skjetne, R. and Sørensen, A. J. and Thorat, L. and Yum, K. K.},
title = {Marine Vessel and Power Plant System Simulator},
journal = {IEEE Access},
publisher = {Inst. Electrical and Electronics Engineers},
year = {2015},
volume = {3},
pages = {2065--2079},
url = {http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=7312888},
doi = {10.1109/ACCESS.2015.2496122}
}
|
| Jørgensen U and Skjetne R (2015), "Online reconstruction of drifting underwater ice topography: The 2D case", Asian J. of Control. Vol. 17(5), pp. 1509-1521. Wiley. |
| Abstract: An online estimation design for a drifting two dimensional ice topography is presented. Under the assumption that the topography can be accurately represented by a truncated Fourier series, and given a moving window of measurements along the topography, an observer design is proposed to estimate the parameters of the model. The chosen method ensures an online cutoff of higher wave numbers in the spectrum representing the topography such that sufficient data compression is achieved for transmitting the model parameters through a limited hydroacoustic communication channel. This allows online reconstruction of the underwater drifting ice topography at a remote operation center. The observer is shown to be uniformly globally exponentially stable under a persistency of excitation condition. For comparison, a design based on B-spline basis functions is also presented. The effectiveness of the estimation algorithm is verified on a set of real ice draft measurements taken from the underside of an ice sheet off the coast of Greenland. |
BibTeX:
@article{ujor15A,
author = {Jørgensen, U. and Skjetne, R.},
title = {Online reconstruction of drifting underwater ice topography: The 2D case},
journal = {Asian J. of Control},
publisher = {Wiley},
year = {2015},
volume = {17},
number = {5},
pages = {1509--1521},
url = {http://dx.doi.org/10.1002/asjc.1088},
doi = {10.1002/asjc.1088}
}
|
| Kjerstad ØK, Metrikin I, Løset S and Skjetne R (2015), "Experimental and phenomenological investigation of dynamic positioning in managed ice", Cold Regions Sci. and Tech.. Vol. 111, pp. 67-79. Elsevier. |
| Abstract: This paper investigates the dynamic positioning of offshore vessels in managed ice conditions using a model-scale dataset from the large ice tank of the Hamburg Ship Model Basin. Experimental data obtained from the European research and development project DYPIC (DYnamic Positioning in ICe) are analyzed to determine the governing signal characteristics of ice loads acting on a drillship model in various managed ice conditions. The results indicate that the mean load level is strongly dependent on the oblique angle but independent of the relative velocity between the vessel and the ice (when it is below 0.51 m/s in full-scale). Furthermore, it is found that the managed ice cover characteristics (namely, the ice concentration, ice thickness, and floe size distribution) impact both the mean load level and the signal variation, leading to significant and rapid transients in the global load signal. These findings are investigated from a phenomenological perspective, and it is argued that ice floe contact networks and accumulated ice mass are responsible for the observed signal dynamics. Finally, both load signal and phenomenological analyses are used to discuss the implications of managed ice on conventional dynamic positioning control systems. It is shown that several core elements of the system are affected and require attention. Improved design considerations are proposed, but further work is required to implement and test the new concepts. |
BibTeX:
@article{okje15A,
author = {Kjerstad, Ø. K. and Metrikin, I. and Løset, S. and Skjetne, R.},
title = {Experimental and phenomenological investigation of dynamic positioning in managed ice},
journal = {Cold Regions Sci. and Tech.},
publisher = {Elsevier},
year = {2015},
volume = {111},
pages = {67--79},
url = {http://www.sciencedirect.com/science/article/pii/S0165232X14002237},
doi = {10.1016/j.coldregions.2014.11.015}
}
|
| Zhang Q, Skjetne R, Metrikin I and Løset S (2015), "Image Processing for Ice Floe Analyses in Broken-ice Model Testing", Cold Regions Sci. and Tech.. Vol. 111, pp. 27–38. Elsevier. |
| Abstract: The ice floe shape and size distribution are important ice parameters in ice-structure analyses. Before performing an analysis at full scale, the dynamic positioning (DP) experiments in model ice at the Hamburg Ship Model Basin (HSVA) allow for the testing of relevant image processing algorithms. A complete overview image of the ice floe distribution in the ice tank was generated from the experiments. An image processing method based on a gradient vector flow (GVF) snake and a distance transform is proposed to identify individual ice floes. Ice floe characteristics such as position, area, and size distribution are obtained. A model of the managed ice field's configuration, including identification of overlapping floes, is also proposed for further studies in ice-force numerical simulations. Finally, the proposed algorithm is applied to an ice surveillance video to further illustrate its applicability to ice management. |
BibTeX:
@article{qzha15B,
author = {Zhang, Q. and Skjetne, R. and Metrikin, I. and Løset, S.},
title = {Image Processing for Ice Floe Analyses in Broken-ice Model Testing},
journal = {Cold Regions Sci. and Tech.},
publisher = {Elsevier},
year = {2015},
volume = {111},
pages = {27–38},
url = {http://www.sciencedirect.com/science/article/pii/S0165232X14002201},
doi = {10.1016/j.coldregions.2014.12.004}
}
|
| Zhang Q and Skjetne R (2015), "Image Processing for Identification of Sea-Ice Floes and the Floe Size Distributions", IEEE Trans. Geoscience Remote Sensing., May, 2015. Vol. 53(5), pp. 2913-2924. |
| Abstract: An unmanned aerial vehicle was used as a mobile sensor platform to collect sea-ice features at Ny-Ålesund in early May 2011, and several image processing algorithms have been applied to samples of sea-ice images to extract useful information about sea ice. The sea-ice statistics given by the floe size distribution, being an important parameter for climate and wave- and structure-ice analysis, is challenging to calculate due to difficulties in ice floe identification, particularly the separation of seemingly connected ice floes. In this paper, the gradient vector flow (GVF) snake algorithm is applied to solve this problem. To evolve the GVF snake algorithm automatically, an initialization based on the distance transform is proposed to detect individual ice floes, and the morphological cleaning is afterward applied to smoothen the shape of each identified ice floe. Based on the identification result, the image is separated into four different layers: ice floes, brash pieces, slush, and water. This makes it further possible to present a color map of the ice floes and brash pieces based on sizes, and the corresponding ice floe size distribution histogram. The proposed algorithm yields an acceptable identification result, and its effectiveness is demonstrated in a case study. A discussion on the methods and results concludes the paper. |
BibTeX:
@article{qzha15A,
author = {Zhang, Q. and Skjetne, R.},
title = {Image Processing for Identification of Sea-Ice Floes and the Floe Size Distributions},
journal = {IEEE Trans. Geoscience Remote Sensing},
year = {2015},
volume = {53},
number = {5},
pages = {2913--2924},
url = {http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6971211},
doi = {10.1109/TGRS.2014.2366640}
}
|
| Kjerstad ØK and Skjetne R (2014), "Modeling and Control for Dynamic Positioned Marine Vessels in Drifting Managed Sea Ice", Modeling, Identification and Control. Vol. 35(4), pp. 249-262. Norwegian Soc. Automatic Control. |
| Abstract: This paper presents a development framework for dynamic positioning control systems for marine vessels in managed ice. Due to the complexity of the vessel-ice and ice-ice interactions a configurable high fidelity numerical model simulating the vessel, the ice floes, the water, and the boundaries is applied. The numerical model is validated using experimental data and coupled with a control application incorporating sensor models, control systems, actuator models, and other external dynamics to form a closed loop development platform. The ice drift reversal is simulated by moving the positioning reference frame in an elliptic trajectory, rather than moving each individual ice floe. A control plant model is argued, and a control system for managed ice is proposed based on conventional open water design methods. A case study shows that dynamic positioning in managed ice is feasible for some moderate ice conditions. |
BibTeX:
@article{okje14A,
author = {Kjerstad, Ø. K. and Skjetne, R.},
title = {Modeling and Control for Dynamic Positioned Marine Vessels in Drifting Managed Sea Ice},
journal = {Modeling, Identification and Control},
publisher = {Norwegian Soc. Automatic Control},
year = {2014},
volume = {35},
number = {4},
pages = {249--262},
url = {http://www.mic-journal.no/ABS/MIC-2014-4-3.asp},
doi = {10.4173/mic.2014.4.3}
}
|
| Norgren P and Skjetne R (2014), "Using Autonomous Underwater Vehicles as Sensor Platforms for Ice-Monitoring", Modeling, Identification and Control. Vol. 35(4), pp. 263-277. Norwegian Soc. Automatic Control. |
| Abstract: Due to the receding sea-ice extent in the Arctic, and the potentially large undiscovered petroleum resources present north of the Arctic circle, offshore activities in ice-infested waters are increasing. Due to the presence of drifting sea-ice and icebergs, ice management (IM) becomes an important part of the offshore operation, and an important part of an IM system is the ability to reliably monitor the ice conditions. An autonomous underwater vehicle (AUV) has a unique capability of high underwater spatial and temporal coverage, making it suitable for monitoring applications. Since the first Arctic AUV deployment in 1972, AUV technology has matured and has been used in complex under-ice operations. This paper motivates the use of AUVs as an ice-monitoring sensor platform. It discusses relevant sensor capabilities and challenges related to communication and navigation. This paper also presents experiences from a field campaign that took place in Ny-Aalesund at Svalbard in January 2014, where a REMUS 100 AUV was used for sea-floor mapping and collection of oceanographic parameters. Based on this, we discuss the experiences related to using AUVs for ice-monitoring. We conclude that AUVs are highly applicable for ice-monitoring, but further research is needed. |
BibTeX:
@article{pnor14B,
author = {Norgren, P. and Skjetne, R.},
title = {Using Autonomous Underwater Vehicles as Sensor Platforms for Ice-Monitoring},
journal = {Modeling, Identification and Control},
publisher = {Norwegian Soc. Automatic Control},
year = {2014},
volume = {35},
number = {4},
pages = {263--277},
url = {http://www.mic-journal.no/ABS/MIC-2014-4-4.asp},
doi = {10.4173/mic.2014.4.4}
}
|
| Ruud S and Skjetne R (2014), "Verification and Examination Management of Complex Systems", Modeling, Identification and Control. Vol. 35(4), pp. 333-346. Norwegian Soc. Automatic Control. |
| Abstract: As ship systems become more complex, with an increasing number of safety-critical functions, many interconnected subsystems, tight integration to other systems, and a large amount of potential failure modes, several industry parties have identified the need for improved methods for managing the verification and examination efforts of such complex systems. Such needs are even more prominent now that the marine and offshore industries are targeting more activities and operations in the Arctic environment. In this paper, a set of requirements and a method for verification and examination management are proposed for allocating examination efforts to selected subsystems. The method is based on a definition of a verification risk function for a given system topology and given requirements. The marginal verification risks for the subsystems may then be evaluated, so that examination efforts for the subsystem can be allocated. Two cases of requirements and systems are used to demonstrate the proposed method. The method establishes a systematic relationship between the verification loss, the logic system topology, verification method performance, examination stop criterion, the required examination effort, and a proposed sequence of examinations to reach the examination stop criterion. |
BibTeX:
@article{sruu14A,
author = {Ruud, S. and Skjetne, R.},
title = {Verification and Examination Management of Complex Systems},
journal = {Modeling, Identification and Control},
publisher = {Norwegian Soc. Automatic Control},
year = {2014},
volume = {35},
number = {4},
pages = {333--346},
url = {http://www.mic-journal.no/ABS/MIC-2014-4-9.asp},
doi = {10.4173/mic.2014.4.9}
}
|
| Skjetne R, Imsland L and Løset S (2014), "The Arctic DP Research Project: Effective Stationkeeping in Ice", Modeling, Identification and Control. Vol. 35(4), pp. 191-210. Norwegian Soc. Automatic Control. |
| Abstract: Stress on the environment from a potentially growing energy use is set to rise. Without doubt the energy resources in Arctic regions will be developed. An important goal will be to exploit the resources offered by for instance the Barents Sea as a new European energy province, and to do this in accordance with the principles of sustainable development that have successfully been used e.g. in the North Sea. The special edition of MIC on Arctic DP presents a set of articles that summarize to an extent the activities of the research project Arctic DP: Safe and green dynamic positioning operations of offshore vessels in an Arctic environment. This project was awarded in 2010 by the Research Council of Norway (RCN) as a competence-building project (KMB project) to NTNU and its partners Kongsberg Maritime, DNV GL, and Statoil. The objective was to target some of the challenges related to safe Arctic offshore operations by dynamic positioning. In this first article of the Arctic DP special edition we discuss the background for and establishment of the project, its planning and execution, and project closure. An overview is given for the scientific and engineering research performed in the project, with an account of what we have considered as Effective stationkeeping in ice by dynamic positioning. The corresponding research activities conducted under this main theme is summarized. |
BibTeX:
@article{rskj14B,
author = {Skjetne, R. and Imsland, L. and Løset, S.},
title = {The Arctic DP Research Project: Effective Stationkeeping in Ice},
journal = {Modeling, Identification and Control},
publisher = {Norwegian Soc. Automatic Control},
year = {2014},
volume = {35},
number = {4},
pages = {191--210},
url = {http://www.mic-journal.no/ABS/MIC-2014-4-1.asp},
doi = {10.4173/mic.2014.4.1}
}
|
| Su B, Skjetne R and Berg TE (2014), "Experimental and Numerical Investigation of a Double-Acting Offshore Vessel Performance in Level Ice", Modeling, Identification and Control. Vol. 35(4), pp. 317-332. Norwegian Soc. Automatic Control. |
| Abstract: In this paper a numerical model and experimental data are used to investigate the level ice performance of a double-acting intervention vessel. The icebreaking capability and maneuverability in level ice are analyzed by evaluating the behavior of the vessel when it is running both ahead and astern. The paper also presents the implementation of a random crack size model for more realistic icebreaking behavior, giving more consistent evaluation of the vessel's performance in various ice conditions. The numerical simulations are firstly conducted in model-scale for a direct comparison with the experimental results. The scaling of ship speed and ice resistance is then discussed by comparing the simulation results in both full-scale and model-scale. The effect on the vessel's performance of the different properties of scaled model ice and full-scale sea ice is also assessed. |
BibTeX:
@article{bsu14B,
author = {Su, B. and Skjetne, R. and Berg, T. E.},
title = {Experimental and Numerical Investigation of a Double-Acting Offshore Vessel Performance in Level Ice},
journal = {Modeling, Identification and Control},
publisher = {Norwegian Soc. Automatic Control},
year = {2014},
volume = {35},
number = {4},
pages = {317--332},
url = {http://www.mic-journal.no/ABS/MIC-2014-4-8.asp},
doi = {10.4173/mic.2014.4.8}
}
|
| Su B, Skjetne R and Berg TE (2014), "Numerical assessment of a double-acting offshore vessel's performance in level ice with experimental comparison ", Cold Regions Sci. and Tech.. Vol. 106-107(0), pp. 96-109. Elsevier. |
| Abstract: In this paper a numerical model is used to investigate the level ice performance of a double-acting intervention vessel, and the results are compared with a limited set of experimental data. The icebreaking capability and maneuverability in level ice are analyzed by evaluating the behavior of the vessel when it is running both ahead and astern. The simulated icebreaking patterns, h–v curves, and turning circles in different modes of operation are discussed and compared partly with the corresponding ice model tests. The simulation results can supplement the experimental data by providing more information about the vessel's maneuverability in level ice and identifying the physical foundation for the exhibited performance of the vessel. The paper also presents the implementation of a random crack size model for more realistic icebreaking behavior, giving more consistent evaluation of the ship's performance in various ice conditions. |
BibTeX:
@article{bsu14A,
author = {Su, B. and Skjetne, R. and Berg, T. E.},
title = {Numerical assessment of a double-acting offshore vessel's performance in level ice with experimental comparison },
journal = {Cold Regions Sci. and Tech.},
publisher = {Elsevier},
year = {2014},
volume = {106-107},
number = {0},
pages = {96-109},
url = {http://www.sciencedirect.com/science/article/pii/S0165232X14001220},
doi = {10.1016/j.coldregions.2014.06.012}
}
|
| Zhang Q and Skjetne R (2014), "Image Techniques for Identifying Sea-Ice Parameters", Modeling, Identification and Control. Vol. 35(4), pp. 293-301. Norwegian Soc. Automatic Control. |
| Abstract: The estimation of ice forces are critical to Dynamic Positioning (DP) operations in Arctic waters. Ice conditions are important for the analysis of ice-structure interaction in an ice field. To monitor sea-ice conditions, cameras are used as field observation sensors on mobile sensor platforms in Arctic. Various image processing techniques, such as Otsu thresholding, k-means clustering, distance transform, Gradient Vector Flow (GVF) Snake, mathematical morphology, are then applied to obtain ice concentration, ice types, and floe size distribution from sea-ice images to ensure safe operations of structures in ice covered regions. Those techniques yield acceptable results, and their effectiveness are demonstrated in case studies. |
BibTeX:
@article{qzha14A,
author = {Zhang, Q. and Skjetne, R.},
title = {Image Techniques for Identifying Sea-Ice Parameters},
journal = {Modeling, Identification and Control},
publisher = {Norwegian Soc. Automatic Control},
year = {2014},
volume = {35},
number = {4},
pages = {293--301},
url = {http://www.mic-journal.no/ABS/MIC-2014-4-6.asp},
doi = {10.4173/mic.2014.4.6}
}
|
| Zhao B and Skjetne R (2014), "A Unified Framework for Fault Detection and Diagnosis Using Particle Filter", Modeling, Identification and Control. Vol. 35(4), pp. 303-315. Norwegian Soc. Automatic Control. |
| Abstract: In this paper, a particle filter (PF) based fault detection and diagnosis framework is proposed. A system with possible faults is modeled as a group of hidden Markov models representing the system in fault-free mode and different failure modes, and a first order Markov chain is modeling the system mode transitions. A modified particle filter algorithm is developed to estimate the system states and mode. By doing this, system faults are detected when estimating the system mode, and the size of the fault is diagnosed by estimating the system state. A new resampling method is also developed for running the modified PF efficiently. Two introductory examples and a case study are given in detail. The introduction examples demonstrate the manner to model a system with possible faults into hidden Markov model and Markov chain. The case study considers a numerical model with common measurement failure modes. It focuses on the verification of the proposed fault diagnosis and detection algorithm and shows the behavior of the particle filter. |
BibTeX:
@article{bzha14B,
author = {Zhao, B. and Skjetne, R.},
title = {A Unified Framework for Fault Detection and Diagnosis Using Particle Filter},
journal = {Modeling, Identification and Control},
publisher = {Norwegian Soc. Automatic Control},
year = {2014},
volume = {35},
number = {4},
pages = {303--315},
url = {http://www.mic-journal.no/ABS/MIC-2014-4-7.asp},
doi = {10.4173/mic.2014.4.7}
}
|
| Zhao B, Blanke M and Skjetne R (2014), "Particle Filter for Fault Diagnosis and Robust Navigation of Underwater Robot", IEEE Trans. Ctrl. Sys. Tech.. Vol. 22(6), pp. 2399-2407. |
| Abstract: A particle filter (PF)-based robust navigation with fault diagnosis (FD) is designed for an underwater robot, where 10 failure modes of sensors and thrusters are considered. The nominal underwater robot and its anomaly are described by a switching-mode hidden Markov model. By extensively running a PF on the model, the FD and robust navigation are achieved. Closed-loop full-scale experimental results show that the proposed method is robust, can diagnose faults effectively, and can provide good state estimation even in cases where multiple faults occur. Comparing with other methods, the proposed method can diagnose all faults within a single structure, it can diagnose simultaneous faults, and it is easily implemented. |
BibTeX:
@article{bzha14A,
author = {Zhao, B. and Blanke, M. and and Skjetne, R.},
title = {Particle Filter for Fault Diagnosis and Robust Navigation of Underwater Robot},
journal = {IEEE Trans. Ctrl. Sys. Tech.},
year = {2014},
volume = {22},
number = {6},
pages = {2399-2407},
url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6736066},
doi = {10.1109/TCST.2014.2300815}
}
|
| Skjetne R and Egeland O (2006), "Hardware-in-the-loop testing of marine control systems", Modeling, Identification and Control. Vol. 27(4), pp. 239-258. |
| 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:
@article{rskj06A,
author = {Skjetne, R. and Egeland, O.},
title = {Hardware-in-the-loop testing of marine control systems},
journal = {Modeling, Identification and Control},
year = {2006},
volume = {27},
number = {4},
pages = {239--258},
url = {http://www.mic-journal.no/ABS/MIC-2006-4-3.asp},
doi = {10.4173/mic.2006.4.3}
}
|
| Skjetne R, Fossen TI and Kokotović PV (2005), "Adaptive Maneuvering, with Experiments, for a Model Ship in a Marine Control Laboratory", Automatica. Vol. 41(2), pp. 289-298. |
| Abstract: The maneuvering problem involves two tasks. The first, called the geometric task, is to force the system output to converge to a desired path continuously parametrized by a scalar θ. The second task, called the dynamic task, is to satisfy a desired dynamic behavior along the path. In this paper, this dynamic behavior is further specified as a speed assignment for (t). While the main concern is to satisfy the geometric task, the dynamic task ensures that the system output follows the path with the desired speed. An adaptive recursive design technique is developed for a parametrically uncertain nonlinear plant describing the dynamics of a ship. First the geometric part of the problem is solved. Then an update law is constructed that bridges the geometric design with the dynamic task. The design procedure is performed and tested by several experiments for a model ship in a marine control laboratory. |
BibTeX:
@article{rskj05A,
author = {Skjetne, R. and Fossen, T. I. and Kokotović, P. V.},
title = {Adaptive Maneuvering, with Experiments, for a Model Ship in a Marine Control Laboratory},
journal = {Automatica},
year = {2005},
volume = {41},
number = {2},
pages = {289--298},
url = {http://www.sciencedirect.com/science/article/pii/S0005109804003024},
doi = {10.1016/j.automatica.2004.10.006}
}
|
| Skjetne R, Smogeli ØN and Fossen TI (2004), "A Nonlinear Ship Maneuvering Model: Identification and adaptive control with experiments for a model ship", Modeling, Identification and Control. Vol. 25(1), pp. 3-27. |
| Abstract: Complete nonlinear dynamic maneuvering models of ships, with numerical values, are hard to find in the literature. This paper presents a modeling, identification, and control design where the objective is to maneuver a ship along desired paths at different velocities. Material from a variety of references have been used 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 small ship in a marine control laboratory. |
BibTeX:
@article{rskj04F,
author = {Skjetne, R. and Smogeli, Ø. N. and Fossen, T. I.},
title = {A Nonlinear Ship Maneuvering Model: Identification and adaptive control with experiments for a model ship},
journal = {Modeling, Identification and Control},
year = {2004},
volume = {25},
number = {1},
pages = {3--27},
url = {http://www.mic-journal.no/ABS/MIC-2004-1-1.asp},
doi = {10.4173/mic.2004.1.1}
}
|
| Skjetne R, Fossen TI and Kokotović PV (2004), "Robust Output Maneuvering for a Class of Nonlinear Systems", Automatica. Vol. 40(3), pp. 373-383. |
| Abstract: The output maneuvering problem involves two tasks. The first, called the geometric task, is to force the system output to converge to a desired path parametrized by a continuous scalar variable theta. The second task, called the dynamic task, is to satisfy a desired dynamic behavior along the path. This dynamic behavior is further specied via a time, speed, or acceleration assignment. While the main concern is to satisfy the geometric task, the dynamic task ensures that the system output follows the path with the desired speed. A robust recursive design technique is developed for uncertain nonlinear plants in vectorial strict feedback form. First the geometric part of the problem is solved. Then an update law is constructed that bridges the geometric design with the speed assignment. The design procedure is illustrated through several examples. |
BibTeX:
@article{rskj04A,
author = {Skjetne, R. and Fossen, T. I. and Kokotović, P. V.},
title = {Robust Output Maneuvering for a Class of Nonlinear Systems},
journal = {Automatica},
year = {2004},
volume = {40},
number = {3},
pages = {373--383},
url = {http://www.sciencedirect.com/science/article/pii/S0005109803003467},
doi = {10.1016/j.automatica.2003.10.010}
}
|
| Skjetne R (2003), "Ship Maneuvering: The past, the present and the future", Sea Technology. Vol. 44(3), pp. 33-37. |
| Abstract: In the past, ship steering systems were based on controlling the ship heading to a desired heading by the measurement of a gyrocompass. As new measurements are available as well as the knowledge of advanced nonlinear control techniques, it is today possible to perform much more complicated maneuvers by automatic control. This has and will continue to increase the functionality and reliability of commercially available automatic ship navigation systems. Maneuvering a ship along a desired path is the present challenge. |
BibTeX:
@article{rskj03B,
author = {Skjetne, R.},
title = {Ship Maneuvering: The past, the present and the future},
journal = {Sea Technology},
year = {2003},
volume = {44},
number = {3},
pages = {33--37},
url = {https://www.researchgate.net/publication/237063048_Ship_Maneuvering_The_past_the_present_and_the_future/file/9c96051f05e2edd300.pdf}
}
|