Numerical Calculation of Wave Pattern and Wake Wash for High-Speed Displacement Ships
|School||Wuhan University of Technology|
|Keywords||Panel Method Wave Pattern Analysis Fourier Transform Equivalent Singularity Distribution Wake Waves|
With the rapid progress of industrial technology,high-speed vessels developed dynamically over the last decades.The speeding up of waterway transportation is one of the main tendencies of modern transportation.However,a common problem of the domestic high-speed ships is the higher wake waves.Severe wake waves would threaten the safety of the smaller ships,and do great harm to the environment. Researches on the wave-making and wake-wave propagation of high-speed ships are theoretically challenging and have attracted attention of marine engineers.A combined near/far-field method is used to calculate the wake wave of high-speed displacement vessels in the far-field.The first-order Rankine-source panel method is employed in the near-field calculations.The hull surface and part of free surface are discretized by quadrilateral panels.Under corresponding boundary conditions,the source strengths are solved and then the linear Kelvin wave pattern obtained through the velocity potential determined by the source strengths solved.Raised panels above the free surface combined with collocation-point shifting up-stream are used to satisfy the radiation condition numerically.At a certain distance away from the hull,the ship waves can be regarded as harmonic waves,so the far-field wake waves can be then determined numerically by one-variable function called wave amplitude spectrum.The wave amplitude spectrums could be determined through wave pattern analysis for the corresponding calculated near-field waves,and far-field wake waves are then obtained numerically.Wigley hulls are selected as computational examples.The far-field wave patterns in deep water and shallow water are computed respectively.In the deep water case, the wave amplitude spectrums are computed through Fourier transform method.The theoretical formulas for transverse-cut method and longitudinal-cut method are derived and comparisons of calculated results between these two methods are made. The principle and numerical treatment of the equivalent-singularity-distribution method are introduced and applied to the shallow water case.The factors that may affect the accuracy are discussed.Because there are no experimental data available,the correctness of the calculation method and numerical treatment for the far-field waves has been checked by the comparisons between the wave heights computed by the wave amplitude spectrums and that calculated by the panel method.The results are reasonable.