LeaveLimit Command

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

LeaveLimit #1

where #1 is the number of steps with one or more unique particles leaving the grid that are tolerated before an analysis is stopped. If this command is omitted, the default is 1% of the particles. If a particle leaves the grid prior to the limit, the particle will be moved back into the grid and the analysis will continue. Set it to 1 to have simulations 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. 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.
3. Normally particles are keep within the grid by using <a href="moveline.html">velocity boundary conditions</a>, but isolated particles sometimes even pass through such conditions. The LeaveLimit command can help in such calculations.
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.