Goal
Implement the weakly compressible fluid pressure and stress model required by the CPU MPM fluid solver in both 2-D and 3-D.
Scope
- Derive particle density from mass and current volume.
- Compute pressure with the existing equation-of-state helper in Core/Utils/PhysicsHelpers.hpp.
- Expose target density, speed of sound, EOS exponent, and negative-pressure scale with validated defaults.
- Convert scalar pressure into the isotropic Cauchy stress used by MPM grid forces.
- Keep the implementation fluid-specific; do not add a generic material-model hierarchy.
Acceptance criteria
- Pressure is zero at the target density within numerical tolerance.
- Compression produces positive pressure and expansion follows the configured negative-pressure scale.
- Invalid density, volume, or EOS parameters cannot silently produce non-finite state.
- Focused tests cover equivalent 2-D and 3-D behavior.
- The implementation reuses the existing EOS helper instead of duplicating it.
References
Goal
Implement the weakly compressible fluid pressure and stress model required by the CPU MPM fluid solver in both 2-D and 3-D.
Scope
Acceptance criteria
References