Houdini 17.0 Shelf tools Grains tab

Granular Solid shelf tool

Fills an object loosely with grains and creates constraints to hold it together into one object.

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This tool fills an object loosely with grains and creates constraints to hold it together into one object. It is similar to Dry Sand and Wet Sand. However, instead of filling an object with unconstrained independent grains, all of the grains are constrained to each other to maintain the distance between each particle. It creates actual bonds that either always stay together, or can be torn apart.

The controls in the Explicit Constrains section of the POP Grains node can be used to change the behavior of the grains. The default result is a soft and bouncy object that does not break apart. However, by turning on the Break Constraints checkbox and setting a Break Threshold, this tool can be use to create wet sand objects that break apart when forces are applied, like a sand castle.

This tool can be thought of as a simple FEM solver. It results in solid-like behavior because there are no collisions between particles since they are all right next to each other and constrained. Like FEM, you can use Granular Solid to simulation disintegrating soft bodies. Granular Solid may run faster, but have less realistic, more bouncy results.

Note

This shelf tool puts down a Point Deform SOP in the geometry network, to allow the skin to deform with the grains. It deforms the high resolution mesh according to the animated low resolution mesh.

For more information, see PBD vs FEM.

Using Granular Solid

  1. Select the geometry object to convert to a Granular Solid object.

  2. Click the Granular Solid tool on the Grains tab.

The following are a couple of examples of things you can use the Granular Solid tool for.

For specific parameter information, see the POP Grains help.

Note

Scaling is an issue for sand because the number of grains are based on how many particles are around it. Changing resolutions may change results.

Tips

The following parameters in the Explicit Constraints section of the POP Grains node will allow you to change the behavior of the grains.

To...Do this

Make objects break apart

Enable the Break Constraints checkbox and set a Break Threshold. If the constraints stretch beyond the threshold, the bonds will break apart. The Break Threshold is a percentage of the rest length.

Make the object less bouncy

Increase the Stiffness parameter. This will control how stiff the bonds between particles are.

Grains tab