newton.solvers.SolverImplicitMPM#

class newton.solvers.SolverImplicitMPM(model, options)[source]#

Bases: SolverBase

Implicit MPM solver.

This solver implements an implicit MPM algorithm for granular materials, roughly following [1] but with a GPU-friendly rheology solver.

This variant of MPM is mostly interesting for very stiff materials, especially in the fully inelastic limit, but is not as versatile as more traditional explicit approaches.

[1] https://doi.org/10.1145/2897824.2925877

Parameters:

  • model (Model | ImplicitMPMModel) – The model to solve.

  • options (ImplicitMPMOptions) – The solver options.

Returns:

The solver.

Model#

alias of ImplicitMPMModel

Options#

alias of ImplicitMPMOptions

__init__(model, options)#
collect_collider_impulses(state)#

Collect current collider impulses and their application positions.

Returns a tuple of 3 arrays:

  • Impulse values in world units.

  • Collider positions in world units.

  • Collider ids.

enrich_state(state)#

Allocate additional per-particle and per-step fields used by the solver.

Adds velocity gradient, elastic and plastic deformation storage, and per-particle rendering transforms. Initializes grid-attached fields to None so they can be created on demand during stepping.

notify_model_changed(flags)#
project_outside(state_in, state_out, dt, max_dist=None)#

Project particles outside of colliders, and adjust their velocity and velocity gradients

Parameters:

  • state_in (State) – The input state.

  • state_out (State) – The output state. Only particle_q, particle_qd, and particle_qd_grad are written.

  • dt (float) – The time step, for extrapolating the collider end-of-step positions from its current position and velocity.

  • max_dist (float | None) – Maximum distance for closest-point queries. If None, the default is the voxel size times sqrt(3).

sample_render_grains(state, grains_per_particle)#

Generate per-particle point samples used for high-resolution rendering.

Parameters:

  • state (State) – Current Newton state providing particle positions.

  • grains_per_particle (int) – Number of grains to sample per particle.

Returns:

A wp.array with shape (num_particles, grains_per_particle) of type wp.vec3 containing grain positions.

step(state_in, state_out, control, contacts, dt)#
update_particle_frames(state_prev, state, dt, min_stretch=0.25, max_stretch=2.0)#

Update per-particle deformation frames for rendering and projection.

Integrates the particle deformation gradient using the velocity gradient and clamps its principal stretches to the provided bounds for robustness.

update_render_grains(state_prev, state, grains, dt)#

Advect grain samples with the grid velocity and keep them inside the deformed particle.

Parameters:

  • state_prev (State) – Previous state (t_n).

  • state (State) – Current state (t_{n+1}).

  • grains (array) – 2D array of grain positions per particle to be updated in place. See sample_render_grains.

  • dt (float) – Time step duration.