LeaveLimit Command

The LeaveLimit command determines how an MPM analysis responds when a particle leaves the grid:

Use LeaveLimit

In scripted files, the command is

LeaveLimit (maxNum)

In XML input files, the command, which must be within the <MPMHeader> element, is

<LeaveLimit>(maxNum)</LeaveLimit>

where |(maxNum)| is the number of particles leaving the grid that are tolerated before an analysis is stopped. If (maxNum) is positive, a particle that leaves the grid will be moved back into the grid. If (maxNum) is negative, particles that leave the grid will be deleted from the simulation. If |(maxNum)| particles leave the grid, the simulation will stop.

If this command is omitted, the default is positive and set to 1% of the particles. Setting (maxNum) to 1 will cause a simulation to stop if any particle leaves the grid.

Notes

1. Particles that are forced back into the grid might lead to nonphysical or erroneous results. Analyses that have many particles leaving the grid should be highly suspect.
2. Particles that are deleted are moved to the lower-left corner of the grid. That corner element needs to be empty and away from other particles.
3. This command is must useful when the particle leaving the grid itself is already a numerical artifact and therefore forcing it back in may not be making things any worse. A common numerical artifact is an isolated particle that picks up a nonphysical acceleration propelling it off the grid. This command can trap those problem particles and keep the analysis running for the bulk of the remaining particles.
4. If the LeaveLimit is greater than 1 and the analysis eventually finishes, the output file will include a warning when the first particle left left the grid and a count of the number of steps that had at least one new particle leaving the grid.