Houdini 20.5 MPM

MPM Configure Metal Tearing

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There are several MPM Configure examples available through the tab menu. These are similar to shelf tools that put down networks of nodes for learning purposes. The MPM Configure Metal Tearing example illustrates the use of the Metal material type. It puts down a simple network of nodes to simulate a sphere collider ripping through a metal sheet.

Important nodes

metal_sheet

This is the MPM Source that uses the Metal material preset. However, the Type is set to Surface instead of the default Volume. This scatters points on the surface of the input geometry. It also has Relax Iterations of 250 to make sure there is a uniform distribution across the surface that fills as many holes as possible to create a good representation of the surface.

frame, distance_to_frame, and pin_frame

These nodes highlight the frame of the metal sheet, use a Ray SOP to detect the distance between the frame and sheet, and based on that distance, pin to animation all of the points that are near the edge.

sphere_collider

This is the MPM Collider, which uses the Animated (Rigid) collider type. It allows for very precise collisions as, for each substep, it interpolates the transforms of a single VDB which is both lighter in memory and more accurate than Animated (Deforming) colliders.

mpmcontainer

This setup uses a default MPM Container, which defines the resolution of the simulation using the Particle Separation parameter.

mpmsolver

This setup uses a default MPM Solver, which does the work of solving the scene. The Material Condition is decreased slightly to increase the number of substeps based on the stiffness of the material which fixes some instability in this case.

Learning from this example

To...Do this

Fix instability in the behavior of the material

In some cases, there could be some instability in the simulation where the material requires more substeps than what you're providing, which could result in points that merge or collapse onto each other. The quickest way to solve this is to slightly decrease the Material Condition on the MPM Solver. This reduces the timestep of the solvers which keeps the material stable. In this example, the value was decreased from 0.9 to 0.6. It is also possible to raise the Substeps Min/Max directly but this will not dynamically adapt to changes in material or resolution.

MPM

Getting Started

MPM Configure Examples

Next Steps

Advanced