水线积分项对运动浮体波浪绕射力的影响

The Effect of the Water Line Term on Wave Diffraction by a Floating Body with Forward Speed

基于常值分布源的时域边界元方法（ＢＥＭ）讨论海洋浮式结构物运动（或有流）时的波浪绕射问题，研究比较了３种水线数值模型对于波浪力的影响作为算例，给出了直立圆柱和半球上的一阶力、二阶平均力（漂力或增阻）和波浪升高的数值结果计算表明：分布源积分方程中的水线应取在自由面（ｚ＝０）上；水线积分项对一阶力的影响可忽略不计；二阶平均力中的水线项是主要部分，它依赖于水线上的波高；波高的计算位置应取在自由面下方５００～１０００分之一吃水处，这时积分方程中的水线项影响很小。

A boundary element method with constant distributed source panels,based on a convolution equation involving a time-dependent Green function,is employed to investigate the water-line(WL)effect on wave diffraction by a 3-D floating body with forward speed.Three WL numerical models for the analysis are compared,and the results for linear exciting forces, mean drifting forces,and wave elevations are presented for the cases of a truncated piercing cylinder and a hemisphere moving in regular waves.The study shows that:(1)The WL term in the source distribution integral equations has little effect on linear exciting forces.(2)The WL term in the mean drifting forces is a dominant part which depends on the wave run-up around the WL;the wave run-up should be at a distance of about the draft/(500-1000)below the free surface while the WL in the source integral equation is at z=0.Under such conditions the effect of the WL in the integral equation on the drift forces can be modelled satisfactorily and could be neglected in practical calculations.