Houdini 21.0 Fluids

FLIP Configure FLIP!

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Houdini’s SOP FLIP fluids provide several ready-to-use tools to illustrate some of most common workflows. To access the tools, create a Geometry SOP and double-click it to dive into the node. There, press the ⇥ Tab key to invoke the TAB menu. Enter flip configure and choose FLIP Configure FLIP! from the list. Houdini creates a complete network and you can immediately start the simulation by clicking the icon in the playbar.

The FLIP Configure FLIP! tool shows how to

The tool creates a gradually melting Rubber Toy SOP test geometry with variable viscosity. The toy’s texture information is transferred to the particles and the particle fluid surface.

Main nodes

Node name Function
testgeometry_rubbertoy Test Geometry: Rubber Toy SOP. This node is a ready-to-use object that comes with texture map, material definition, and proper UVs.

fliptank1

FLIP Container SOP. To use point variable viscosity, the node’s Varying Viscosity parameter is turned on. The custom Cd Point Attribute Name is required to transfer colors from the rubber toy’s map to the fluid particles. The Cd attribute is also used in the particlefluidsurface1 node’s Transfer Attributes parameter.

setcolor

Attribute from Map SOP. This node loads the Texture Map and converts the map’s colors into a Cd point attribute.

setviscosity

Attribute Wrangle SOP. The simulation’s viscosity values are defined through a short VEXpression. The expression says that all particles with a Y position greater than 0.3 units have a viscosity of 100000. If a particle’s position falls below this threshold, viscosity is set to 100.

flipsolver1

FLIP Solver SOP. This node is the center piece of the network and brings everything together to simulate the fluid’s behavior. In the Collision tab, a Ground Plane is active. To finally see the texture map colors in the simulation, the node’s Color by Speed option is turned off. Look for this checkbox in the Visualization tab.

Tips

To...Do this

Change the geometry

Create or load an object and connect it to the subdivide1 node. The original testgeometry_rubbertoy operator will be disconnected. If the result of the subdivision process isn’t satisfying, connect the object to the subdivide node.

Change the texture

Select the setcolor node and go to the Texture Map parameter. Click the icon to open a new map file. If you want to apply a material and map the texture onto the object, please read the appropriate chapters in the Materials guide.

Create more particles

In the fliptank1 node you can find the Particle Separation parameter. Decrease the default value to get more particles. Note that small values increase simulation time and memory usage.

Change the viscosity values

Select the setviscosity node and edit the code in VEXPression field. The f@viscosity variable defines the viscosity values. Higher values make the fluid more viscous, lower settings can be used for a more liquid fluid.

Display particles instead of spheres

Go to the flipsolver1 node’s Visualization tab and turn off Points as Spheres.

Show the particle fluid surface

Turn on the particlefluidsurface1 node’s Display/Render flag. This is the rightmost segment of the operator’s icon. When active, the segment turns blue.

Fluids

For beginners

SOP WORKFLOW

Particle Fluids (SOP)

Viscous fluids (SOP)

Optimization (SOP)

FLIP Configure tools (SOP)

DOP WORKFLOW

Particle Fluids (DOP)

Viscous Fluids (DOP)

Oceans (DOP)

Optimization