The Stability Analysis Of Rubble Mound Breakwater By Distinct Element Method

At present, the stability analysis of rubble mound breakwater is mainly based on experimental results being short of theory basis, which may be because rubble mound breakwater is distinct medium, and the stability of bricks is not only affected by the extrinsic forces such as wave forces, but also affected by the shape of the blocks, the restriction among themselves etc. Distinct Element Method(DEM) is a new numerical analysis method for distinct medium, and it can be used to analyze the process and mechanism of losing stability of rubble mound breakwater.The 2DEM program is fulfilled based on the fundamental principle of 2 dimensional rigid DEM, correlative parameters are also analyzed in this dissertation. This program is used to analyze the dynamic and static stability of rubble mound breakwater in the end.In the model of 2 dimensional rigid DEM, the elements of blocks are protruding polygons. The grids are generated randomly, and the elements' parameters, such as shape, size, location, porosity can be controlled. Considering two kinds of exterior loads: concentrated loads acting on the cancroids of the blocks and distributing loads acting on the surface. The transit displacement, velocity, acceleration, the forces between blocks under static or dynamic loads are solved by dynamic relaxation (an explicit numerical method), and the quantities are outputted using AutoCAD. Based on the velocity and displacement of blocks, the stability criterion of blocks is established. The definition of safety factor is also given by the displacement, velocity, and coefficient of friction.The DEM is used to analyze the dynamic response of rubble mound breakwater for the first time. The process from stability to instability of rubble mound breakwater under wave attack can be simulated vividly. The coefficient of friction will decrease after the sand comes into the breakwater, which leads to the reduction of safety factor, and the process of large distortion of the breakwater can also be simulated. The results show that the lager the wave force and the smaller the safety factor, the less instability of the breakwater. The results also show that the damage mainly concentrates on the two sides of the breakwater around free-surface and the whole damage is the cumulate result of partial damage, which corresponds to the actual damage process of breakwater under wave attack.The program is verified by an example. By analyzing the example, the effects of the values of timestep, rigid coefficient, damping coefficient are discussed, and the methods to determine the parameters are also given. This dissertation may be the foundation for in-depth research.