基于LES的跨海桥梁施工期围堰波流力数值模拟

Numerical Simulation of Wave-Current Forces Acting on Cofferdam for Sea-Crossing Bridge Based on Large Eddy Simulation

跨海大桥基础施工可能面临水深、浪大和流急等恶劣海况,波流力甚至可能成为围堰施工的主要控制荷载.为研究跨海桥梁施工期围堰波流力,采用垂向多层σ坐标变换模型追踪三维波流自由液面,添加浸没边界法(IBM)处理不规则结构物界面,建立了基于LES的三维波流与结构物相互作用的数值模型,利用所建立并验证的三维数值模型模拟不同长宽比的矩形围堰与斜向波流的相互作用.分析结果表明:所建立的三维数值模型能够较好地模拟矩形结构波流力;长宽比为1.0时,由于结构的对称性,波流入射角对围堰总波流力影响很小,增幅均在5%以内;随着长宽比的增加,波流入射角对围堰总波流力的影响增大;如长宽比为2.0时,波流沿纵桥向入射时(90°)结构的总波流力约为沿横桥向入射时(0°)总波流力的2.48倍.与纯波情况相比,矩形围堰波流力普遍比纯波力偏大,但入射角对结构纯波力或波流力的影响系数较为接近.

The foundation construction of a sea-crossing bridge may encounter complex sea conditions,such as deep-water,large-wave and rapid-flow conditions.Wave-current forces may even become dominant loads for the cofferdam construction of a sea-crossing bridge.To study wave-current forces acting on cofferdams of seacrossing bridges,a numerical model for simulation of three-dimensional(3D)wave-current interactions with a structure was established using the large eddy simulation method.In this model,the vertical multiple-layerσ-coordinate transformation model was used to track the 3D wave current-induced free surface,and the immersed boundary method(IBM)was added to deal with the irregular structural surface.The proposed 3D numerical model was then validated and applied to simulate oblique wave-current interaction with a rectangular bridge cofferdam under different length-width ratios.The results indicated that the established 3D numerical model could well simulate wave-current forces acting on the rectangular structure.When the length-width ratio equals 1.0,the incident angle has little effect on the total wave-current forces due to structural symmetry,with a growth below 5%.As the length-width ratio increases,however,the incident angle will have greater impact on the total wave-current forces acting on the rectangular cofferdam.At a length-width ratio of 2.0,the total force acting on the structure when wave current is incident along longitudinal direction(90°)are 2.48 times as big as that when it is incident along transverse direction (0°). Wave-current forces acting on rectangular structure are generallybigger than wave forces in the wave only condition;however,influence coefficients of incident angles on wavecurrentforces or wave forces are relatively close.