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Boundary Conditions Styles

The possible boundary condition styles are defined below. The style can be set by name or number. Unless otherwise specified, the units for (value) are the standard units for the current type of boundary condition and the units for (time) are alt time units.

To get any time-dependence for a boundary condition, you can combine more than one conditions in the same direction and the resulting condition will be a superposition of the applied conditions. See below for some special considerations when applying velocity conditions.

Silent Boundary Conditions

The object of silent boundary conditions is to apply an absorbing edge. The goal is to simulate a small portion of a large object by having stress waves, heat fluxes, and concentration fluxes absorbed by the edges rather the reflect back into the object. Their development in MPM is in a paper by Shen and Chen (2005). These conditions can be shown to work well in small, idealized simulations. They have been less useful on other simulations.

Some considerations about using silent boundary conditions are:

Notes

  1. When applying multiple velocity conditions on the same node, the combinations must either be in the same direction or in orthogonal directions. For example, you can apply any combination of velocities along analysis axes (x, y, or z).
  2. When using skewed velocity conditions, the typical problem will use only a single skewed direction on a node. You can use any number of conditions in that single direction. You should not mix skewed velocity conditions with velocity conditions along one of the skew axes. For example, you should not apply some conditions in the x direction and others in the skewed x-y or x-z direction, because these two directions are not orthogonal. In principle orthogonal skewed directions could be used, but such problems can normally be recast to get the same fixed velocity by fixing the two axes in the skew plane instead.