波浪中航行两船模池壁干扰效应的数值研究

对规则波中顶浪并行航行的两船模,基于频域移动脉动源格林函数建立了有效表达池壁效应的三维数学模型,该模型采用分布源积分方法求解近距航行两船模的波浪作用力和运动响应,并利用镜像原理将水池格林函数表示为开阔水域的格林函数和由镜像点源组成的无穷级数.分析移动脉动源格林函数的远场传播模态及其特性可知,当τ>0.272(τ为斯特劳哈尔数)时各传播波模态均不在点源的上游出现,故此时点源波系的影响范围可由环形—扇形波的半楔角确定,在此基础上计及船模辐射—绕射波的池壁反射作用对自身和另一船模的干扰,依据船型要素、水池宽度和两船相对位置,采用六个几何临界半楔角表征船体的辐射—绕射波,提出了并行航行两船模的池壁效应判别方法.数值研究表明:不同镜像次数下水池格林函数的数值差异主要体现在距船艏较远处,在兼顾计算精度与效率的原则下可选取有限项级数的水池格林函数作为积分内核,而池壁效应对近距航行两船运动响应的影响主要体现在长波区.

Numerical Investigation of the Side Wall Effects for Two Ship Models Advancing Parallel in Waves

A three-dimensional (3-D) Green function method, as the translating-pulsating source in frequency domain as its kernel, is developed to investigate the side wall effects for two ship models ad-vancing parallel in the regular waves of towing tank. Distributed source integration approach is ap-plied to solve the wave exciting forces and free motions of the two models in close proximity. Satis-faction of the impenetrable boundary condition of tank walls is achieved by the mirror image princi-ple, as a result of the tank-wall Green function representation including an infinite series. From the propagation characteristics of a point source in far field, it is obvious that all kinds of wave patterns are not possible to emerge ahead of the source if Strouhal number is larger than 0.272 and the in-fluence scope of propagating waves can then be defined by the half angle of ring-fan wave. Differ-ent from the side wall effects for single ship model, the interference of the reflection waves from the tank walls acting on both ships has to be taken into consideration. According to the ship particulars, tank breadth and relative position of two ships, a discriminant method is proposed for two models by six geometric critical half angles. For the sake of simplifying tank-wall Green function, mirrored im-ages of point source and ship model are discussed to acquire the approximate mirror number. The quantitative differences of tank-wall Green function at different mirror numbers involve the area aft of ship bow. Based on the principles of integral efficiency and accuracy, finite terms of the infinite series can be selected for the tank-wall Green function. Numerical results show that the impact of the side wall effects on the two-ship motion responses is focused on the long-wave tested conditions.