lyhust306@gmail.com

waves


Welcome to Yan Li's homepage

“It is the time you have wasted for your rose that makes your rose so important.”

“And now here is my secret, a very simple secret: It is only with the heart that one can see rightly; what is essential is invisible to the eye.”

--Antoine de Saint-Exupéry
The Little Prince

Publications

My publications page

Ship waves on uniform shear current at finite depth: Wave resistance and critical velocity

25 March 2016 | Yan Li & Simen Å Ellingsen | Journal of Fluid Mechanics, Vol.791

pdf © Cambridge University Press

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on the cover of J. Fluid Mech. vol 791.

Abstract: We present a comprehensive theory for linear gravity-driven ship waves in the presence of a shear current with uniform vorticity, including the effects of finite water depth. The wave resistance in the presence of shear current is calculated for the first time, containing in general a non-zero lateral component. While formally apparently a straightforward extension of existing deep water theory, the introduction of finite water depth is physically non-trivial, since the surface waves are now affected by a subtle interplay of the effects of the current and the sea bed. This becomes particularly pronounced when considering the phenomenon of critical velocity, the velocity at which transversely propagating waves become unable to keep up with the moving source. The phenomenon is well known for shallow water, and was recently shown to exist also in deep water in the presence of a shear current (Ellingsen, J. Fluid Mech., vol. 742, 2014, R2)....

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Multiple resonances of a moving oscillating surface disturbance on a shear current

10 December 2016 | Yan Li & Simen Å Ellingsen | Journal of Fluid Mechanics, Vol.808

pdf © Cambridge University Press

jfmpaper2

Abstract:We consider waves radiated by a disturbance of oscillating strength moving at constant velocity along the free surface of a shear flow, which, when undisturbed, has uniform horizontal vorticity of magnitude S. When no current is present the problem is a classical one and much studied, and in deep water a resonance is known to occur when τ=|V|ω/g; equals the critical value 1/4 (V : velocity of disturbance, ω: oscillation frequency, g: gravitational acceleration). We show that the presence of a subsurface shear current can change this picture radically....

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Wave-interference effects on far-field ship waves in the presence of a shear current

November 2017 | Yan Li | Journal of Ship Resesrch (accepted) | pdf

jsrpaper3

Abstract: Wave-interference effects, in the presence of a shear current of uniform vorticity, are analyzed for the first time. An interesting similarity is found between the analysis of wave interferences when a linear shear current is present and that in finite depth water. In particular, wave{interference regimes exist in both analysis. The consideration of wave interferences in the presence of a shear current, for a 2-point wavemaker model of monohull ships, is shown to have interesting and non-trivial effects on ship waves, as also found in the analysis of wave interferences in finite water depth. The effect of shear on the far-field waves created by a 2-point wavemaker model of a monohull ship greatly depends on....

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Transient wave resistance upon a real shear current

14 September 2017 (in press) | Yan Li, Benjamin. K. Smeltzer & Simen Å Ellingsen | pdf

European Journal of Mechanics B/Fluids (in press)

ejfmBpaper4

Abstract: We study the waves and wave-making forces acting on ships travelling on currents which vary as a function of depth. Our concern is realism; we consider a real current profile from the Columbia River, and model ships with dimensions and Froude numbers typical of three classes of vessels operating in these waters. To this end we employ the most general theory of waves from free-surface sources on shear current to date, which we derive and present here. Expressions are derived for ship waves which satisfy an arbitrary dispersion relation and are generated by a wave source acting on the free surface, with the source's shape and time-dependence is also being arbitrary. Practical calculation procedures for numerically calculating dispersion on a shear current which may vary arbitrarily with depth both in direction and magnitude, are indicated.

For ships travelling at an oblique angle to a shear-current, the ship wave pattern is asymmetrical, and wave-making radiation forces have a lateral component in addition to the conventional wave resistance, the sternward component. No corresponding lateral force exists in the absence of shear. We consider the dependence of wave resistance and lateral force for upstream, downstream and cross-stream motion on the Columbia River current, both in steady motion and during two different manoeuvres: a ship suddenly set in motion, and a ship turning through 360?. We find that for smaller ships (tugboats, fishing-boats) the wave resistance can differ drastically from that in quiescent water, and depends strongly on Froude number and direction of motion. For Froude numbers typical of such boats, wave resistance can vary by a factor 3 between upstream and downstream motion, and the strong Froude number dependence is made more complicated by interference effects.....

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More papers


Education

August 2014 - September 2017

PhD (2017), Norwegian University of Science and Technology (NTNU), Department of Energy & Process Engineering,
Doctoral thesis: "Surface water waves on depth dependent flows".

Septermber 2011 - March 2014

M.Sc.(2014), Shanghai Jiao Tong University (SJTU). School of Naval Architecture, Ocean & Engineering,
Master thesis: "Investigation on hydrodynamic performance and vortex-induced motion of a jacket-combined deep-draft semi-submersible (JCDDS) concept for the South China Sea".

Septermber 2007 - July 2011

B.Eng.(2011), Huazhong University of Science and Technology (HUST), Department of Naval Architecture & Ocean Engineering,
The project of Bachelor thesis: "Overall and structural design of a bulk carrier for the Bohai Sea."


Project

September 2017 - present

  • Fluid dynamics: wave-current interactions;
  • Travelling surface pressure propagator;
  • Surface water waves;

August 2014 - September 2017 (3 years)

  • Fluid dynamics: wave-current interactions;

August 2014 - March 2014 (2.5 years)

  • Hydrodynamic and VIM performance of a Jacket combined deep-draft semi-submersible (JCDDS);
  • Subsurface tunnel project for the Hongkong-Zhuhai-Macau Bridge;
  • Nonlinear analysis of the steel catenary riser and the lazy-wave catenary riser using a lump-mass method;
  • “Hydrodynamic Response of the deep-draft semi-submersible (DDS) and effects of the heave plate in different drafts” project;
  • Design of the Mooring system of a drilling-well barge with a moon pool;