岩土体大型三维离散元模拟系统的研发与应用

本文分析了当前岩土体离散元法存在的两个主要问题：（1）离散元颗粒与宏观模型间力学关系不明确； （2）离散元法计算量大，计算效率低。并针对这两个问题开展了理论研究和系统研发。在建立离散元颗粒接触关系基础上，提出了利用微宏观力学参数转换公式，构建具有特定力学性质的离散元模型； 提出了离散元颗粒系统的能量计算方法。在一系列理论研究的基础上，自主研发了岩土体大型三维离散元模拟系统MatDEM。其具有良好的前处理和后处理功能，能自动生成各种云图和模拟动画； 采用矩阵运算和GPU（图形处理器）高速计算，显著地提高了离散元计算的速度。在实例中，MatDEM被用于岩体孔隙的水力压裂模拟，在单台计算机上完成了一百万颗粒的动态模拟。结果表明，微裂隙趋于平行最大压应力方向和各向异性软弱方向形成； 能量转化曲线表明，弹性应变能和动能逐步转化为热量，但总能量始终恒定，离散元系统实现了能量守恒计算。

DEVELOPMENT AND APPLICATION OF LARGE-SCALE DISCRETE ELEMENT SIMULATION SYSTEM FOR ROCK AND SOIL

Two major current issues of discrete element method(DEM)in rock and soil fields are proposed：1)mechanical relationship between discrete particles and macro model is not clear; 2)DEM requires huge computation, and it is low in efficiency. Theoretical studies and software development are carried out for the two issues. On the basis of the particle contact model of DEM,conversion formulas are introduced to build discrete element model with specified mechanical properties; a method for energy calculation of discrete element particles is also proposed. Based on these theoretical studies, a three-dimensional discrete element simulation system of rock and soil,MatDEM,has been developed from scratch. The software has good pre-processing and post-processing functions, with which result images and simulation demos can be generated automatically. Furthermore, the speed of DEM calculation is improved significantly using matrix calculation and high-performance GPU(Graphic Processing Unit) computation. MatDEM was used in the numerical simulation of hydraulic fracturing in a rock pore. Dynamic simulation of one million particles was completed in a single computer. The result indicates that micro-cracks tend to form along direction of maximum compressive stress and weak directions of anisotropic rock. Energy conversion curves show that elastic strain energy and kinetic energy were converted to heat during the simulation. However, the total energy always maintained unchanged, which indicates the conservation of energy in the discrete element system.