Houdini 21.0 Nodes Geometry nodes

MPM Deform Pieces geometry node

Transfers the dynamics of the MPM simulation onto the renderable geometry.

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Since 21.0

Overview

The MPM Deform Pieces transfers the dynamics of the MPM simulation onto the renderable geometry. The renderable geometry must first be fractured using the MPM Post-Fracture once you are satisfied with the dynamics of the MPM simulation.

Note

In comparison with the RBD workflow, this might feel a little bit backward. With MPM, first you get the simulation that you like, then you use the last frame of the simulation to fracture the renderable geometry, and lastly you retarget the dynamics of the MPM simulation onto the fractured geometry.

This has the benefit of allowing the geometry to dynamically fracture where it needs to instead of blindly predefining where things can break. On the other hand, you need to refracture the renderable geometry each time the MPM simulation changes.

For more information, see the Destruction help page in the MPM Chapter.

Warning

The deformation gradient F needs to be cached for the destruction workflow. It is not by default. You must turn on the Deformation Gradient (F) checkbox on the Output tab of the MPM Solver.

Inputs

Named Pieces to Deform

The output of the MPM Post-Fracture or any named geometry. This could be packed fragments if Piece (Transform) is selected as the Retargeting Type.

MPM Particles

The output of the MPM Solver.

Parameters

Start Frame

Manually define the start frame of the MPM simulation. The start frame usually comes as a detail attribute on the MPM particles.

End Frame

Manually define the end frame of the MPM simulation. The end frame usually comes as a detail attribute on the named pieces to deform.

Retargeting Type

Defines how the MPM dynamics will be applied to the fractured geometry.

Point + Piece

The fractured geometry will be both transformed per piece and deformed per point. The Stretch Ratio Tolerance will define when to smoothly transition from the deformation to the transformation to prevent too much deformation to occur.

Piece (Transform)

Transform each piece of the fractured geometry with a single transformation extracted from the MPM points. Packed fragments can be processed directly in this mode.

Point (Deform)

Deform each point of the fractured geometry with its nearest MPM point at rest.

Rigid Transformations

Make the pieces' transformations orthogonal which removes the shear and scale components from the 3×3 transform matrix.

Convert to PolySoup

Converts the deformed polygon mesh into a polysoup to reduce disk and memory footprint. This parameter is ignored when packed primitives are used in Piece (Transform) mode.

Compute Point Velocity

Compute the point velocity on the deformed fractured geometry.

Stretch Ratio Tolerance

When in Point + Piece mode, it defines the amount of piece deformation that will trigger a smooth transition from the deformation to the transformation.  Very high values will be equivalent to using the Point (Deform) type while a value of 0 will be equivalent to using the Piece (Transform) type.

When in Piece (Transform) or Point (Deform) mode, this parameter can still be used to define the threshold for piece deletion in the Delete Stretched Pieces tab.

Close Gaps

Close Gaps

Allows per point corrections to close cracks that appear when a piece is transitioning from deforming to transforming. This is especially useful when simulating plastically deformable material like metal where things can stretch a fair bit before actually tearing.

Tolerance

The maximum distance to fix the gaps between pieces. This distance threshold is relative to the particle separation to make it scene scale agnostic. The distance is the difference between the point position in Piece (Transform) vs Point (Deform) mode.

Transition Width

This is the width of the transition region between full correction and no correction.

For example a Tolerance of 1.0 and Transition Width of 1.0 means that the gaps of distance 0.5 are fully closed while the gaps of distance 1.5 are untouched. The gaps between 0.5 and 1.5 are partially corrected following a smooth transition.

Attribute Transfer

Attribute List

The list of point attributes to transfer from the MPM particles.

Kernel Radius

Scales the transfer kernel radius as a multiplier of the particle separation.

Max Sample Count

Maximum number of points to interpolate from.

See also

Geometry nodes