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老规矩，先贴上教程地址：

User-Defined Constitutive Models in FLAC3D
不想点击上面链接的可以下载下面的附件：

里面感觉很有用的话：

At this point, it is important to understand something about how FLAC3D implements mixed-discretization in hexahedral zones. Each such zone is actually two overlays of five tetrahedra covering the hexahedron volume, called subzones. The constitutive relations are called on each tetrahedra separately. Properties and state variables are stored for the zone as a whole. Normally, state variables are assumed to be based on volume-averaged quantities over the entire zone. The constitutive model can access both the total number of subzones and which subzone is being calculated.
In the [size=; font-size: inherit,inherit]run() function, we use a working value [size=; font-size: inherit,inherit]s->working_[0] to store the averaged shear failure state value in the zone weighted by the subzone volumes (in the subzones, the shear failure state is assumed 1 if shear failed; 0 if not). We update the cohesion to the value of residual cohesion once the volume averaged shear failure value is greater than 0.5. Related variables need to be updated correspondingly.
f2d449-flac3dUDM.pdf (128 K) 下载次数:82
当然，还有手册（http://bbs.yantuchina.com/read.php?tid=316649&fpage=2 ）可以参考，这儿介绍的并没有太详细。但好在简单明了。