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About minimal mode ¶
The 
Vellum Solver has a Minimal mode that has reduced functionality compared to the Full mode. It supports VDB collisions and a limited feature set, but is faster and well suited for grain and fluid simulations. It has been optimized for fast Substeps, and is particularly useful for large grain and fluid simulations.
When you choose Minimal mode, the Substeps are increased and Constraint Iterartions are decreased. Smoothing Iterations is also turned off, since it’s not really relevant for grains and fluids. There are also fewer Collision Passes and Polish Passes because with the increased substeps and VDBs, there’s a well defined outside and inside so things can be pushed out of the VDB unlike regular polygonal collisions.
Spatial Sort Interval is also turned on by default, which resorts the particles at the specified interval of frames so that everything that is close in space is also close in memory. Vellum fluids and grains perform many calculations involving nearby points, which change as they spread out. Generally performance is greatly improved by ensuring that points that are near other in 3D space are also near each other in memory.
Note
Minimal mode works for other types of geometry and useful for effects you would send into Vellum Brush. For example, you could use it for quickly setting softbodies into a container or draping a piece of cloth over an object. In these cases, Minimal mode will be fast and generally give good collisions.
Fluids ¶
Vellum Fluid simulations can take VDB collisions into account when solving for viscosity and surface tension, giving improved wetting effects when used with this style of collision.
There are parameters available on the Vellum Solver (in the Fluid section of the Advanced tab) that give you options for wetting effects with external collision geometry, such as controls for Viscosity, Surface Tension, and Adhesion. These let you create effects like having water stick, pool, and run off surfaces, such as sweat dripping down a face or body.
Grains ¶
Vellum Grain simulations can take VDB collisions into account when solving for friction and stickiness, giving improved sticking and sliding effects when used with this style of collision.
When using Vellum Grains, there are Friction and Sticky parameters on the 
VDB Collider that let you control how grains stick to the external collision geometry. It is important to note that Sticky is a multiplier for Adhesion, so in order to have adhesion effects its value must be changed to a number higher than 0. The default is not to have grains and fluids stick to external collision geometry, so this must be turned on manually.
Limitations ¶
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External collision geometry must be prepared with a VDB Collider SOP.
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Changing constraint topology in not supported. For example, breaking constraints or adding/deleting new constraints. However, emitting grains or fluid is supported.
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Attach to geometry constraints and animated pins are not supported.
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The built-in Wind forces only work on grains and fluid.
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You can still do general POP Forces and Geometry Wrangles within the DOPnet dive target, but in Minimal mode they only solve per-frame for speed.
Note
For splashes, FLIP will produce better results than Vellum Fluid.