MPM Grid Generation

MPM calculations use a background grid. It can be created with commands on this page.

Grid Generation in Scripted Files

For 2D analysis, the entire grid in generate with the following commands:

GridHoriz (nx),<(symx)>,<(symxdir)>
GridVert (ny),<(symy)>,<(symydir)>
GridThickness (thick)
GridRect (xmin),(xmax),(ymin),(ymax)

For 2D analysis, the entire grid in generate with the following commands:

GridHoriz (nx),<(symx)>,<(symxdir)>
GridVert (ny),<(symy)>,<(symydir)>
GridDepth (nz),<(symz)>,<(symzdir)>
GridRect (xmin),(xmax),(ymin),(ymax),(zmin),(zmax)

where

• (nx), (ny), (nz) number of elements in the x, y, and z directions. For axisymmetric calculations (nx) (ny) are the number of elements in the R and Z directions.
• (symx) and (symxdir) (and the analogous ones for y and z) are used to define symmetry planes in the model. Note that symmetry are not allowed in the R direction (i.e., x direction) of axisymmetric calculations.
• (thick) is the grid thickness in 2D planar calculations (see below for details on grid thickness)
• (xmin),(xmax),(ymin),(ymax),(zmin),(zmax) are ranges for the grid only each axis ((zmin) and (zmax) are only used for 3D calculations).

Grid Generation in XML Files

The entire grid is generated within the <Mesh> block. For 2D analyses, use the following commands are:

<Mesh output='file'>
  <Grid units='mm' xmin='(xmin)' xmax='(xmax)' ymin='(ymin)' ymax='(ymax)' thickness='(thick)'>
    <Horiz nx='(nx)'/>
    <Vert ny='(ny)'/>
  </Grid>
</Mesh>

Axisymmetric calculations use x and y limits for R and Z limits. For 3D analyses, use the following commands:

<Mesh output='file'>
  <Grid units='mm' xmin='(xmin)' xmax='(xmax)' ymin='(ymin)' ymax='(ymax)' zmin='(zmin)' zmax='(zmax)'>
    <Horiz nx='(nx)'/>
    <Vert ny='(ny)'/>
    <Depth nz='(nz)'/>
  </Grid>
</Mesh>

Notes

The GridThickness in planar 2D calculations defines the thickness of the grid. It is not needed for axisymmetric calculations. In planar calculations, the thickness is required when doing multimaterial contact that includes the optional volume check or when using traction, concentration flux or heat flux boundary conditions. If omitted, the thickness will be assumed to be 1 mm and if that is not correct, the volume screening or boundary conditions will be wrong. The GridThickness is optional in single-material mode because thickness can be set when defining material point regions and when defining cracks. If used, however, all material points and cracks will default to this grid thickness. You can enter different values, although it is not recommended (and may change the physics in multimaterial simulations). A warning is printed in the output if a crack thickness does not match the grid thickness. Currently no warning is given if material points have a different thickness. The thickness must be set before using GridRect to set the size of the background grid. The GridThickness command is only allowed for MPM analyses.

When using a GIMP method (uGIMP, lCPDI, or qCPDI), a particle is considered to have left the grid if it moves into any element on the edge of the analysis. Thus, the use of a GIMP method will cause this command to automatically add an extra boundary of elements.