渗透海床三维波生流的演化研究

Wave and wave induced currents are one of the major factors that drive the sand transport and the seabed evolution in coastal regions. Most of the related researches are based on the assumption of impermeable seabed, thus there exists apparent shortcomings in permeable seabeds conditions. To solve this problem, the combination method of theoretical analysis, numerical simulations and physical laboratory tests is applied to study three dimensional wave motion and wave induced currents. Three dimensional Boussinesq equations are derived to describe wave motion over the permeable seabeds, and the corresponding three dimensional numerical models for wave and wave induced currents are established. The numerical simulations and experimental tests are carried out on wave evolution over a permeable bottom, and the information of wave height and wave velocity is used to calculate wave radiation stress, the effects of the characterized permeable parameters to the three dimensional wave velocity and radiation stress are analyzed, and the relationships between wave velocity & wave radiation stress and the permeable parameters(three-dimensional length, porous rate and medium diameter) are established. The numerical simulations and experimental tests on wave induced current over permeable bottom are conducted, the three dimensional current information is analyzed to study the effect of the characterized permeable parameters on wave induced currents, and the relationship between them is established. Through the present study, the effect of the seabed permeable or impermeable on wave induced currents are quantitatively described, and the mechanics of permeable characteristics on wave induced current will be faithfully discoved, and this can provide scientific foundations for both the research on longshore sand transport & seabed evolution and the engineer practice.

波浪和波生流是沿岸输沙和海床演变的主要驱动力之一，当前波生流的研究主要假定海床不渗透，在渗透性海床条件下这一研究存在明显不足。本项目通过理论分析、数值模拟和模型实验相结合的方式开展渗透性海床三维波浪运动及波生流的水动力研究。建立适于描述渗透海床波浪运动的三维Boussinesq水波方程，进而发展波浪和波生流计算模型。实验与数值模拟渗透海床上的波浪演化，利用波高和速度信息计算辐射应力，研究海床渗透对波浪速度场和辐射应力三维结构特征的影响，建立其与渗透性特征参数（尺度、孔隙率和中值粒径）之间的依赖关系；开展波生流的模型实验与数模计算，分析波生流的三维流场信息，研究渗透对波生流三维结构特征的影响，建立其与渗透性特征参数的依赖关系。通过以上研究，定量描述渗透海床与非渗透海床对波生流的影响差异，从而全面揭示渗透海床三维波浪和波生流的运动规律，为沿岸输沙和海床演变研究与工程实践提供科学依据。

渗透海床上波浪水动力特性的研究与传统不渗透海床水动力特性之间存在较大的不同。本项目进行了有无渗透两种情况下的多层Boussinesq基础方程的理论推导、数值模型开发、数值模拟以及渗透地形上的波浪演化以及三维渗透地形上的波生流等实验研究工作。首先推导了多层Boussinesq水波方程（Liu等，2018），该方程是水波理论的原创性成果，是Boussinesq水波理论适用深水情况的重大突破。继而在这个多层水波方程基础上，通过引入线性阻力和非线性阻力，形成了适合多层渗透的Boussinesq水波方程，以及考虑多层流体分层情况下的Boussinesq内波方程。三种情况下的Boussinesq水波方程同出一脉，新推导的适合多层渗透情况的Boussinesq水波理论可以给出精确的衰减和波浪色散特性，从理论方面建立起渗透参数特征对衰减特性影响的理论关系表达式。建立了水平二维和准三维Boussinesq水波计算模型，数值模拟了一系列基础性水波演化的研究工作。系统推导的这些方程为水波在渗透地形上的演化、超水深波浪传播、分层传播奠定了理论和计算模型基础，因此具有较为重要的科学研究价值和实践应用价值。