MPM Sand Parameters

The need to simulate granular materials like sand and grains an important part nowadays in the Visual Effects industry. In the past one could get away by using simple particle simulations with a combination of rigid body simulations. However, advances in computer science and ongoing improvements in the Material Point Method allows us to create plausible real world simulations of granular flow effects.

Stiffness - defines the overall “rigidness” or stiffness of the sand simulation. Keep in mind, all MPM simulation values are dependent on the Cell Size value of the simulation. Reducing Cell Size, for example, increases the effect of stiffness by a large amount! So when reducing Cell Size, make sure to adjust stiffness accordingly. A proper balance between Cell Size and Stiffness prevents explosive behavior or other simulation artefacts. Increasing the amount of simulation sub-step in the solver also helps a great deal!

DChannel - sets the data channel to be used for procedurally setting the Stiffness value per particle.

Friction Angle - defines the friction angle of the grain/sand simulation. Ordinary sand has a friction angle of 30 Degrees. However, you may set this value to whatever you find visually pleasing.

DChannel - sets the data channel to be used for procedurally setting the Friction Angle value per particle.

Cohesion defines the stickiness or wetness in a sand simulation. The wetter the sand the more it will behave like a high viscosity fluid.

Cohesion - sets the “wetness” or humidity of the sand or grain simulation. The larger this value the more bouncy and fluid like the grain simulation becomes.

DChannel - sets the data channel to be used for procedurally setting the Cohesion value per particle.

Air Humidity - sets the amount of humidity in the air. All grains exposed to air will acquire this amount of humidity/wetness.

Dry Rate - a multiplier that specifies how fast the sand or grain simulation loses its wetness. Higher values will dry out the material much faster.

Dry Min - sets the minimum humidity/wetness a sand or grain simulation will always retain as it is drying out.

Wet Rate - a multiplier to control the speed at which any humidity is absorbed by the sand or grain simulation

Wet Max - defines the maximum wetness or humidity a sand or grain simulation can hold.

Cluster Deform - defines a threshold for the wetness (Cohesion) when this threshold is reached the cluster deformation will kick in. Important: clusters need to be present and active! A value of 1.0 represents the maximum Cohesion a sand or grain simulation can have.

Cluster Leave - defines a threshold for the wetness (Cohesion) when this threshold is reached the cluster leave condition will kick in and particles will be removed from the cluster. Important: clusters need to be present and active! A value of 1.0 represents the maximum Cohesion a sand or grain simulation can have.

Cluster ReCluster - defines a threshold for the wetness (Cohesion) when this threshold is reached the cluster ReCluster condition will kick in and clusters will be subdivided. Important: clusters need to be present and active! A value of 1.0 represents the maximum Cohesion a sand or grain simulation can have.

Opposite Pressure - defines the counter force to be used when the material is compressed. This is a  multiplier for Stiffness.

Shearing Force - sets a force to counter act shearing within the material. This is a multiplier for Stiffness.