On estimation method of diffraction forces on cylindrical structures in multi-directional waves

实验和理论研究了多向不规则波场中圆柱结构的非线性波衍射和作用在圆柱上的波力。本文介绍了圆柱上衍射力的估计方法。为了讨论波场及其对圆柱体的诱导力的作用机理，在规则波列和双交叉波的情况下进行了大量的实验。根据项目工作可以得出以下结论：(1) MacCamy和Fuchs的理论给出了规则波场情况下圆柱上的衍射波力的合理估计。但是，对于在单向不规则波中圆柱上的衍射波力的估计，理论是不充分的。在多向波场中，该理论对衍射波力的估计精度较低。(2)铺展参数总体上影响衍射波力。随着扩散参数的增大，主方向上的波力并不总是增大。此外，由于波浪的折射作用，在斜坡上构造的圆柱体所受的波浪力与在恒定水深下的波浪力表现出不同的特征。(3)在弱定向波场中，圆柱阵中作用在圆柱上的波浪力主要受圆柱间距和入射波周期的影响，而不受传播参数的影响。当入射波的定向传播变得明显时，来自各个圆柱体的绕射波之间相互作用的影响就变得不那么显著了。(4)随着阵列柱间距的减小，柱间区域的波高增大。这增大了圆柱表面的波压。柱面阵列外的波高似乎与柱面间距无关，但这取决于入射波的方向性，因此当方向性扩散增加时，波高就会变大。这可能导致在多向波场中圆柱表面产生较大的波压。(5)除本项目未讨论的脉冲破波力外，可以判断，在估算圆柱结构的设计波力时，应适当考虑定向传播的影响。(6)为了更详细地讨论非线性波衍射和波力，可能需要进行时域分析。此外，多向波中的速度场应考虑波高分布。这些被认为是今后研究这个问题所必需的。少

Nonlinear wave diffraction due to cylindrical structures in a multidirectional irregular wave field and the wave forces acting on the cylinder are investigated experimentally and theoretically. An estimation technique for the diffraction forces on the cylinders is introduced in this work. To discuss the mechanism of both the wave field and its induced forces on the cylinders, extensive experiments have been conducted in case of a regular wave train and two-crossing waves. The followings can be concluded based on the project work.(1) The theory obtained by MacCamy and Fuchs gives reasonable estimate of the diffraction wave force on a cylinder in case of regular wave field. However, the theory is inadequate in estimating the diffraction wave force on a cylinder in unidirectional irregular wave. In the multidirectional wave field, the estimation of the diffraction wave forces by the theory has low accuracy.(2) The spreading parameter affects the diffraction wave force in general. The wave … More force in the principal direction does not always increase with increasing the spreading parameter. Moreover, it is found that the wave force on a cylinder constructed on a slope shows different characteristics from that in a constant water depth because of wave refraction.(3) Wave forces acting on a cylinder in an array of two cylinders are influenced by the spacing between the cylinders and the incident wave period rather than the spreading parameter in case of weakly directional wave field. As the directional spreading of the incident waves becomes appreciable, the effect of the interaction between diffracted waves from individual cylinders becomes less significant.(4) As the spacing between the cylinders in an array becomes smaller, the wave height in the area between the cylinders increases. This enlarges the wave pressure on the cylinder surface. The wave height outside the cylinder array seems to be independent of the cylinder's spacing, however, this depends on the directionality of incident waves such that it becomes larger when increasing the directional spreading. This may result in larger wave pressures on the cylinder surface in a multidirectional wave field.(5) Except for the impulsive wave breaking force, which is not discussed in this project, it can be judged that the effect of the directional spreading should be properly considered in estimating the design wave force on cylindrical siructures.(6) For more detailed discussions of the nonlinear wave diffraction and wave forces, the time domain analysis may be necessary. Moreover, the velocity field in a multidirectional wave should be investigated with respect to the wave height distribution. These deemed necessary for future investigations of this problem. Less