基于SPH方法的开孔沉箱比尺效应研究

SPH study on scale effect of perforated caisson

由于在前壁上设置了尺寸较小的孔,开孔沉箱受流体黏性力作用显著,依照弗劳德数相似准则设计模型存在比尺效应。为揭示比尺效应,建立了模拟波浪与开孔沉箱相互作用的光滑粒子流体动力学(SPH)模型。其中流体运动由连续性方程和Navier-Stokes方程控制,固壁边界由改进的动力边界粒子施加。模型收敛性通过分析不同粒子分辨率下的波浪反射系数得到,模型精度通过比较计算与理论波浪反射系数证明。使用经过验证的SPH模型,计算并比较了不同几何比尺和开孔率下开孔沉箱附近的涡量场、箱体外侧的波面时程曲线和波浪反射系数。结果表明,随着模型几何比尺的减小,开孔沉箱受到偏大的流体黏性力,致使更多波能在湍流运动中耗散,进而减小了波浪反射系数并降低了箱体外侧的波面高度。

A perforated caisson is subjected to significant viscous force by fluid due to the relatively small slots on its front wall.Thus,the model design based on the Froude similarity encounters the scale effect.To reveal the scale effect,a smoothed particle hydrodynamics(SPH)model for simulating wave interactions with perforated caissons is built.In the SPH model,the fluid motion is governed by the continuity equation and Navier-Stokes equations,and the solid boundary is implemented using modified dynamic boundary particles.Wave reflection coefficients under different particle resolutions are analyzed to obtain the numerical convergence,and the numerical and theoretical wave reflection coefficients are compared to demonstrate the numerical accuracy.The validated SPH model is then used to calculate and compare the vorticity fields near the perforated caisson,the wave elevation curves in front of the caisson and the wave reflection coefficients under different length scales and porosities.The results show that with the decrease of the model length scale,more wave energy is dissipated in turbulent motion because the perforated caisson is subjected to greater viscous force by fluid.Correspondingly,both the wave reflection coefficient and the wave height in front of the caisson decrease.