海洋地震工程流固耦合问题统一计算框架——————不规则界面情形

海底地震动场及海洋声场的模拟中,需要考虑复杂海床介质及海底地形的影响,涉及到海水、饱和海床、弹性基岩之间的相互耦合.传统的方法分别采用声波方程描述理想流体、Biot方程描述饱和海床、弹性波方程描述基岩,分别进行空间离散和界面耦合, 十分不便.本文基于理想流体、固体分别为饱和多孔介质的特殊情形(孔隙率分别为1和0),由饱和多孔介质的Biot方程可退化得到理想流体的声波方程和固体的弹性波方程.然后, 以饱和多孔介质方程为基础, 经集中质量有限元离散,严格考虑不同孔隙率的饱和多孔介质在不规则界面的耦合条件,通过求解法向和切向界面力的途径,建立了不同孔隙率的饱和多孔介质耦合情形的求解方法,将流体、固体、饱和多孔介质间的耦合问题纳入到统一计算框架,并编制了相应的三维并行分析程序.考虑海水--弹性基岩、海水--饱和海床--弹性基岩体系中凹陷地形情形,采用本文提出的统一计算框架, 结合透射边界条件,分析了P波入射时的动力反应, 并通过结果是否满足界面条件,验证了该统一计算框架的有效性以及并行计算的可行性. 

A UNIFIED COMPUTATIONAL FRAMEWORK FOR FLUID-SOLID COUPLING IN MARINE EARTHQUAKE ENGINEERING: IRREGULAR INTERFACE CASE1)

The simulation of seismic wavefield at seafloor and ocean acoustic field, the influence of complex seabed media and seabed topography needs to be considered, involving the coupling between seawater, saturated seabed, elastic bedrock and structure. That means, we target simulation where several types of equations are involved such as fluid, solid and saturated porous media equation. The conventional method for this fluid-solid-saturated porous media interaction problem is to use exsisting solvers of different equations and coupling method, which needs data mapping, communication and coupling algorithm between different solvers. Here, we present an alternative method, in which the coulping between different solvers is avoided. In fact, when porosity equals to one and zero,the saturated porous media is reduced to fluid and solid respectively, so we can use the porous media equation to describe the ideal fluid and solid, and the coupling between porous media,solid and fluid turns to the coupling between porous media with different porosity. Based on this idea, firstly the Biot's equations are approximated by Galerkin scheme and the explicit lumped-mass FEM is chosen, that are well suited to parallel computation. Then considering the conditions of coupling on the irregular interface between porous media with different porosity,by solving the normal and tangential interface forces, the coupled algorithm is derived, which is proved to be suitable for the coupling between fluid,solid and saturated porous media. Thus, the coupling problem between fluid, solid and saturated porous media can be brought into a unified framework, in which only the solver of saturated porous media is used. The three-dimensional parallel code for this proposed method is programed. Considering the situation of sag terrain in water-bedrock, water-saturated seabed-bedrock system, the unified framework proposed in this paper is combined with the transmission boundary conditions to analyze the dynamic response of P wave incident, and the unified framework are verified by the results meeting the interface conditions.