Newton-Lightwheel 

This repository contains the scene setup, assets, and tools used for particle-based simulations with Newton. It includes USD scene files, textures, Houdini setups, and Python scripts to help load and run the environment.  

Collisions

The collision geometry in the scene is currently divided into two parts:  

• One part is passed to the Mujoco solver.  
• The other part is used by the MPM solver.   Collision updates are handled separately for these two parts.  

Particles

The USD files stored in this repository contain around 1.5M particles. Both the particle count and shapes can be adjusted in Houdini.  

Assets

All assets (textures, USDA files) are located in the Assets folder. For now, only a preliminary organization has been done.  

Newton

The Newton version currently in use:
https://github.com/LightwheelAI/newton_corl

Houdini

Current Houdini Version to load the Hip file is 20.5.487 and the Hip file are placed in the root directory of this repository:  

• The hda folder contains the required Houdini Digital Assets.  
• The hip files mainly process terrain, particles, and all Newton-related attributes and key values.  

Scene Files

The scene file can be edited in any USD-compatible tool (IsaacSim, Blender, etc.).  

A Python file is also provided for loading the scene. It can be run in the corresponding Newton environment. The loading code is still at an early stage and will be updated further.  

Usage

1. Open the USD scene      - Load the scene file directly in IsaacSim, Blender, or any other USD-supported tool for layout and inspection.  

2. Run with Newton      - Use the provided Python script to load the scene into the Newton environment.      - Example:        bash      uv run mpm_test.py        

3. Edit with Houdini      - Use the .hip files to adjust terrain, particle counts, or Newton-related attributes.      - Export the modified assets (USD/USDA) back into the Assets folder for reuse.  

_newton__ Static Collision Fields

Name	Type	Mapping to Newton
NewtonCollisionAPI	bool	Toggle collision on or off
_newton__contact_ka	float	ShapeConfig.ka
_newton__contact_ke	float	ShapeConfig.ke
_newton__contact_kd	float	ShapeConfig.kd
_newton__contact_kf	float	ShapeConfig.kf
_newton__contact_thickness	float	ShapeConfig.thickness
_newton__material_staticFriction	float	ShapeConfig.mu
_newton__material_dynamicFriction	float	ShapeConfig.mu
_newton__material_restitution	float	ShapeConfig.restitution
_newton__material_density	float	ShapeConfig.density
_newton__collision_group	int	ShapeConfig.collision_group
_newton__collision_isVisible	bool	ShapeConfig.is_visible
_newton__collision_approximation	bool	Toggle Mesh approximation on or off
_newton__collision_approximationMethod	string	Mesh approximation method name (e.g., “coacd”)

_newton__ Particle Attribute Fields

Name	Type	Mapping to Newton
_newton__particle_qd	vec3	Model.particle_qd
_newton__particle_mass	float	Model.particle_mass
_newton__particle_radius	float	Model.particle_radius
_newton__particle_flags	float	Model.particle_flags
_newton__particle_material_friction	float	Model.particle_mu
_newton__particle_material_youngModulus	float	ImplicitMPMOptions.young_modulus
_newton__particle_material_damping	float	ImplicitMPMOptions.damping
_newton__particle_material_poissonRatio	float	ImplicitMPMOptions.poisson_ratio
_newton__particle_material_hardening	float	ImplicitMPMOptions.hardening
_newton__particle_material_yieldPressure	float	ImplicitMPMOptions.yield_pressure
_newton__particle_material_yieldStress	float	ImplicitMPMOptions.yield_stress
_newton__particle_material_tensileYieldRatio	float	ImplicitMPMOptions.tensile_yield_ratio

Future Work

• Lighting and Materials: Explore more realistic lighting models and textures. For presentation purposes, consider offline rendering as well.  
• Performance Optimization: Improve real-time performance. With reduced particle counts and higher-end hardware, the goal is to reach ~20 FPS.  
• Particle-to-Mesh Conversion: Investigate converting mud or snow particles into mesh representations.