Swan C, Sheikh R
Department of Civil and Environmental Engineering, Imperial College London, London SW7 2BU, UK
Department of Civil and Environmental Engineering, Imperial College London, London SW7 2BU, UK.
Philos Trans A Math Phys Eng Sci. 2015 Jan 28;373(2033). doi: 10.1098/rsta.2014.0114.
Experimental observations are presented of a single surface-piercing column subject to a wide range of surface gravity waves. With the column diameter, D, chosen such that the flow lies within the drag-inertia regime, two types of high-frequency wave scattering are identified. The first is driven by the run-up and wash-down on the surface of the column in the vicinity of the upstream and downstream stagnation points. The second concerns the circulation of fluid around the column, leading to the scattering of a pair of non-concentric wavefronts. The phasing of the wave cycle at which this second mode evolves is dependent upon the time taken for fluid to move around the column. This introduces an additional time-scale, explaining why existing diffraction solutions, based upon a harmonic analysis of the incident waves, cannot describe this scattered component. The interaction between the scattered waves and the next (steep) incident wave can produce a large amplification of the scattered waves, particularly the second type. Evidence is provided to show that these interactions can produce highly localized free-surface effects, including vertical jetting, with important implications for the setting of deck elevations, the occurrence of wave slamming and the development of large run-up velocities.
本文给出了对一根单根透浪柱在多种表面重力波作用下的实验观测结果。选取柱体直径D，使得流动处于拖曳惯性区，识别出了两种高频波散射类型。第一种是由柱体表面上游和下游驻点附近的上爬和下冲驱动的。第二种涉及柱体周围流体的环流，导致一对非同心波前的散射。第二种模式演化时的波周期相位取决于流体绕柱体流动所需的时间。这引入了一个额外的时间尺度，解释了为什么基于入射波谐波分析的现有绕射解无法描述这种散射分量。散射波与下一个（陡峭的）入射波之间的相互作用会使散射波大幅放大，尤其是第二种类型。有证据表明，这些相互作用会产生高度局部化的自由表面效应，包括垂直喷射，这对甲板高程的设定、波浪砰击的发生以及大上爬速度的发展具有重要意义。
