Blocked by #162 .
Goal
Integrate the shared MPM particle-grid transfer foundation with the state required by a weakly compressible fluid in both 2-D and 3-D.
Scope
Reuse the interpolation kernel, active nodal grid, and conservative transfers produced by Implement 2-D and 3-D MPM particle-grid transfers #162
Carry particle mass, reference volume, current volume or volume ratio, position, and velocity.
Retain old and updated nodal velocities required for PIC/FLIP transfer.
Update the particle velocity gradient and volume ratio from the grid motion.
Avoid duplicating snow-specific deformation and plasticity state.
Acceptance criteria
Particle-to-grid transfer conserves total mass and linear momentum within numerical tolerance.
A uniform velocity field remains uniform after a transfer round trip.
Uniform expansion and compression update the particle volume ratio with the expected sign.
Empty and boundary-adjacent particle sets are safe.
Focused 2-D and 3-D tests pass.
References
Blocked by #162.
Goal
Integrate the shared MPM particle-grid transfer foundation with the state required by a weakly compressible fluid in both 2-D and 3-D.
Scope
Acceptance criteria
References