Grains

Size & mass

Start with a manageable grain count. Reducing radius adds detail and increases both memory use and simulation work. With a fixed volume, halving the radius can produce roughly eight times as many grains; the exact count depends on the source and packing.

Grain RadiusDefault: 0.05

Radius of the simulated grains. Smaller values create more particles within the same volume, increasing detail, simulation time, and memory use.

Size VariationDefault: 0.0

Randomly varies grain radii around Grain Radius. A value of 0 gives equal-sized grains; 0.25 varies radii by up to 25% smaller or larger.

Mass From SizeDefault: On

Calculate each grain's mass from its volume and Density. Doubling a grain's radius gives it eight times the mass. Works with or without Size Variation. Turn off to give every grain the same Grain Mass

DensityDefault: 1000.0

Material density used to calculate each grain's mass from its spherical volume. At the same density, larger grains have greater mass.

Grain MassDefault: 0.1

Mass assigned to each grain when Mass From Size is disabled. All grains receive the same mass regardless of radius.

Packing

PackingDefault: Hex Close Pack

How particles are arranged when filling the volume

• Hex Close Pack: Arranges grains in staggered layers for a dense, regular packing. Generally creates more particles than Cubic at the same Grain Radius and Separation.
• Cubic: Arranges grains in evenly spaced rows and layers along three perpendicular axes. Leaves more space between grains than Hex Close Pack.

SeparationDefault: 0.0

Extra spacing between grains when filling the source volume. Higher values increase gaps and generally reduce particle count. A value of 0 uses the minimum initial spacing.

Source OffsetDefault: 0.0

Expand or contract the fill boundary in multiples of Grain Radius. Positive values add room for surface grains; negative values erode the source. Zero preserves existing packing. Does not change grain size or spacing. Keep Inside Fill uses this offset boundary. Applies to fresh initialization, not existing caches

JitterDefault: 0.0

Randomly offsets initial grain positions to break up the packing pattern. Higher values increase the offset relative to Grain Radius.

Relax OverlapsDefault: On

Separates overlapping grains created by initial Jitter before the simulation starts.

Keep Inside FillDefault: On

Keep grain centers inside the offset fill volume during initial Jitter and Relax Overlaps. Preserves particle count and grain size. Turn off to allow initial jitter and relaxation to move grain centers outside the fill boundary. Applies on a fresh simulation; does not constrain moving grains

Using the fill boundary

Source Offset moves the fill boundary without changing grain size or spacing. Keep Inside Fill confines grain centers during initial jitter and overlap relaxation; it is not a collider and does not contain grains after release.

Use a watertight mesh with consistent normals. If no grains are generated, reduce Grain Radius or reduce a negative Source Offset. Changes to these settings apply to a fresh simulation, not an existing cache.