Analysis Command

Decide the type of analysis that will be done.

Analysis Command

Both MPM and FEA calculations can do 2D or axisymmetric calculations. MPM can additionally do 3D calculations. You pick the type of analysis to run with an analysis command. In scripted commands, the format is

Analysis (number or name)

In XML files it is

<Analysis>(number)</Analysis>

The possible analysis types, by number or name, to use in above commands, are:

• 0 = "Plane Strain" for a 2D plane strain FEA analysis
• 1 = "Plane stress" for a 2D plane stress FEA analysis
• 2 = "Axisymmetric" for an Axisymmetric FEA analysis
• 10 = "Plane Strain MPM" for 2D plane strain dynamic MPM analysis
• 11 = "Plane Stress MPM" or 2D plane stress dynamic MPM analysis
• 12 = "3D MPM" or 3D dynamic MPM analysis
• 13 = "Axisymmetric MPM" for axisymmetric dynamic MPM analysis

When using analysis name in scripts, it must exactly match the quoted text above (case insensitive). When writing XML files, the entry must be by number only.

Tracking Velocity Gradient

A option in development in OSParticulas is to track particle velocity gradient. The hope that this approach can improve convergence or more accurately following rotation motion. For scripted input files, simply add "+PS" to the option name (and must be by name and not number). Here "+PS" suggests "Particle Spin" but the new mode tracks all component components of the velocity gradient. The new MPM options are:L

• "Plane Strain MPM+PS" for 2D plane strain dynamic MPM analysis with velocity gradient tracking.
• "Plane Stress MPM+PS" or 2D plane stress dynamic MPM analysis with velocity gradient tracking.
• "3D MPM+PS" or 3D dynamic MPM analysis with velocity gradient tracking.
• "Axisymmetric MPM+PS" for axisymmetric dynamic MPM analysis with velocity gradient tracking.

In XML files, pick the MPM method number from above and then add the following command to the <MPMHeader>

<TrackParticleSpin/>

When used in standard FLIP MPM, a revised extrapolation to the grid follows methods first presented by Wallstedt and Guilkey. The method used to track velocity gradients, however is different. The best approach to FLIP analysis with velocity gradient tracking is under evaluation.

Another paper relevant to velocity gradient tracking is the APIC method. APIC is equivalent to using the PeriodicXPIC Custom Task with FMPMOrder 1 (i.e., PIC style) every time step combined with with Classic or B2Spline grid-based shape functions (the APIC paper is not clear which they used, but it was probably B2Spline). Like all PIC-style methods, APIC can dissipate much energy in certain problems. Using higher FMPMOrder while tracking velocity gradient extends APIC to reduce dissipation using approximate full mass matrix methods. Switching to other available shape function types extends APIC to methods that work better with large deformations. These extensions to APIC are under evaulation.

Notes

• The first three (0,1,2) are for FEA calculations only, while the rest (10,11,12,13) are for MPM calculations only.
• In axisymmetric analyses, the x, y, z, directions become R, Z, and θ directions. If any commands do not mention use of R and Z, they may still work or you can use x and y to mean the same thing. When visualizing results, most labels are changed to reflect R, Z, and θ coordinates. The implementation of axisymmetric MPM is described in a paper by Nairn and Guilkey.
• A feature in development can generalize MPM plane stress or plane strain to allow non-zero, out-of-plane strain or stress, respectively. The only way to set out-of-plane stress or strain is to use a PropertyRamp Custom Task.
• One (and only one) Analysis command is required in every input file and it should be near the beginning, because many other commands depend on whether or not the commands are for FEA or for MPM analysis.