孤立波對泥質海床上直立式圓柱作用的數值研究

Abstract

本文進行泥床海域孤立波作用下直立圓柱周圍的水動力特性研究。基於開源數值模擬軟體OpenFOAM，建立三維數值波浪水槽，水槽中同時存在空氣、水、泥三種黏性流體以及圓柱結構物。研究表明，泥面的變化雖然是孤立波傳播導致的，但其起伏運動與水面不太相同，有其特殊性：在孤立波通過整個泥床的過程中，圓柱迎流側泥面先上升再下降形成低谷區，隨著時間推進低谷區逐漸以圓弧狀包圍在圓柱周圍，而圓柱兩側泥面則持續爬升，圓柱背流側泥面則形成逐漸變大的近似橢圓形低谷區。研究發現，圓柱周圍泥水交界面以上一定範圍內出現了回流的現象，而水面高度的變化是導致壓力梯度變化的主要因素，逆壓梯度則是導致回流出現的主要因素。研究還發現，泥床的存在雖然會使孤立波波高衰減、直立圓柱上的波浪溯升降低，但是卻使得作用於圓柱的總水平波浪力增大。這些研究結果，在一定程度上，可為離岸風力發電及其他海洋工程的規劃設計提供參考。

In this paper, the hydrodynamic characteristics around a vertical cylinder under solitary wave action in mud-bed sea area are studied. Based on the open source software OpenFOAM, a three-dimensional numerical wave water tank is established, in which there are three kinds of viscous fluids including air, water, and mud and a cylindrical structure. Investigations have shown that although the variation of the mud surface elevation is caused by the propagation of solitary waves, its undulating motion is not the same as that of the water surface. There are some special phenomena: in the process of solitary wave passing through the entire mud bed, the mud surface on the upwind side of the cylinder rises first and then falls to forms a trough area. As time progresses, the trough area gradually surrounds the cylinder in an arc shape, and the mud surface on both sides of the cylinder continues to climb, and the mud surface on the downwind side of the cylinder forms an approximately elliptical trough area that gradually becomes larger. The study found that there is reverse flow in a certain range above the mud-water interface around the cylinder. Furthermore, the change of water surface elevation is the main factor leading to the change of pressure gradient, and the reverse pressure gradient is the principal reason that causes the emergence of reverse flow. The study also found that the presence of the mud bed can attenuate the solitary wave height and reduce the wave run-up around the cylinder, but it increases the total horizontal wave forces acting on the cylinder. These research results, to a certain extent, can provide references for the planning and design of offshore wind power projects and other offshore structures.