Houdini 13.0 Nodes

interface version 1

Computes per-particle vorticity values for FLIP fluids.

“Vorticity is a (...) field that describes the local spinning motion of a fluid near some point, as would be seen by an observer located at that point and traveling along with the fluid.” (wikipedia)

Computing vorticity (especially a smoothed variant, see below) can be useful in various ways, for example to add additional small render-time displacement details to fluid surface areas with high vorticity.

Vorticities are represented as per-point scalar (float) values.

Credits

Special thanks for Ian Farnsworth for the original idea and implementation details. For more information, see his flip tricks post on fx-td.com.

Usage

Connect this operator to the Volume Velocity input of a FLIP Solver.

  • The operator, connected to the FLIP Solver's Volume Velocity input.

Parameters

Activation

Controls whether the computation is to be performed.

Parameters
Vorticity Attribute

Name of the per-point attribute to store vorticity values.

These values always represent the currently evaluated fluid vorticities (as opposed to smoothed values, see below).

Compute Smoothed Vorticity

Maintain a time-smoothed variant of vorticity values.

These gradually fade out over time, and provide more pleasing results for visual purposes (e.g. driving render-time micro-displacements).

Smoothed Attribute

Name of the attribute to store smoothed vorticity values.

Fading Rate

How fast the smoothed values to be scaled towards zero. Higher values means faster (e.g. 0.9 means 90% value loss for each time unit).

Bindings
Geometry

Name of the simulation geometry (particles) data.

Curl Field

Name of the intermediate vector volume field where the computed Gas Analysis curl vectors are stored.

Vorticity Field

Name of the intermediate scalar volume field for storing the computed vorticity values.

To Do

  • Check/make sure Fading Rate is global-DOP-substep-proof.

  • Add a pretty picture :D

Release Notes

interface version 1 —

2014-05-17

First version.