design-fluid-scenes

Design fluid scenes

1. Choose phase: smoke for a MAC-grid gas or phase: liquid for APIC/FLIP particles.
2. Represent liquid initial volume with size and particle_spacing [m]; describe smoke sources with timed emitters.
3. Use motion: static rigid bodies or container objects for floors, walls, and obstacles.
4. Leave clearance of at least one particle spacing between fluid particles and container boundaries; use more clearance for fast rigid impacts.
5. Use solver: auto; smoke routes to smoke and liquid routes to apic.
6. Use uniform or radial fields for wind, attraction, repulsion, and other bulk effects.
7. Estimate initial particles as volume / spacing^3; add emitter cross-section samples multiplied by active simulation substeps. For APIC adaptive resampling, also reserve roughly five particles per liquid grid cell. Capacity must cover the largest of these estimates.
8. Prefer a short low-resolution validation run before a final render.

Specify liquid density, viscosity, surface tension, and flip_ratio, or smoke buoyancy and dissipation, directly in the scene IR.

Start smoke at 20--30 FPS and liquid at 20--25 FPS. Higher FLIP ratios preserve splash energy but need more boundary clearance; viscosity damps motion; smaller spacing increases particle count cubically. For pressure_nonconvergence, fix clearance and spacing before raising iterations. For capacity failures, increase spacing or shorten/narrow emission rather than continually raising capacity.