Houdini 21.0 Fluids

FLIP Configure Beach Tank

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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 Beach Tank 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 Beach Tank tool shows how to

The tool creates a network for the simulation of beach waves from an ocean spectrum. The spectrum is connected to the solver’s fourth input to create a custom boundary flow. The beach collision object clips intersecting particles to create a typical shoreline with shallow and deeper zones.

Main nodes

Node name Function

file1

File SOP. This node loads the beach.geo file. A downstream extrudevolume1 node, turns the surface into a solid 3D model. The bound1 node calculates the bounding box from the resulting geometry. This bounding box finally defines the simulation domain.

fliptank1

FLIP Container SOP. This node creates a domain where fluid simulation happens. At the domain’s boundaries, particles are sourced and deleted to maintain an equilibrium. You can connect an object to the node’s input. This object will then serve as a custom-shaped domain. The FLIP Container is also the place where you turn on physical properties like Surface Tension or Viscosity. You can also define custom attributes such as temperature or density. If you want to increase the number of particles, decrease Particle Separation.

flipcollide1

FLIP Collide SOP. You need this node to convert geometry or volumes into collision objects for the FLIP fluid. The collision object has to be solid and closed for this setup to work correctly. Collision objects are always connected to the node’s fourth input.

oceanspectrum1

Ocean Spectrum SOP. This node creates volumes containing the ocean wave information. The wave pattern is based on parameters like Direction, Speed and Scale. You can also choose from two Spectrum Type options. The default is TMA, also known as Encino waves. The Philips mode is widely known as Tessendorf waves.

oceanevaluate

Ocean Evaluate SOP. The node used the information from the oceanspectrum1 operator to transform geometry. Under the Volumes tab you can find several expressions to drive the parameters. Velocity is mandatory, because it applies velocity to the waves and finally to the particles. The Hydrostatic Pressure option is referenced to the filpsolver1 node’s boundary Type. The Pressure mode is selected by default. The wave setup is connected to the flipsolver1 node’s fourth input.

flipsolver1

FLIP Solver SOP. This node is the center piece of the network and brings everything together to simulate the fluid’s behavior. The Waterline tab is of particular interest: the Waterline has to be turned off, because the particles are created through the solver’s fourth input (Boundary Flow). Boundary Conditions are also relevant in this setup, because the fluid interacts with FLIP Container’s walls.

particlefluidsurface1

Particle Fluid Surface SOP. Turn on the node’s Display/Render flag to invoke the creation of a polygon mesh, representing the fluid.

Tips

To...Do this

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.

Use viscosity and/or surface tension

In the fliptank1 node, turn on Surface Tension and Viscosity. Expand the sub-panels and enter new values for Surface Tension and Viscosity.

Display particles instead of spheres

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

Preview the waves

  1. Select the oceanevaluate1 node and turn on its Display/Render flag.

  2. Open the Geometry tab.

  3. Turn on Preview Grid.

  4. Change the parameters of the oceanspectrum1 node.

Change the waves' properties

Play with the parameters of the Wind tab, esp. Spectrum Type and Speed. Under the Amplitude tab you can eliminate smaller waves and ripples by increasing Min Wavelength.

Imrpove the quality of the collision geometry

The FLIP Collide node converts connected geometry into a volume. Quality and resolution can only be changed through the FLIP Container’s Particle Separation parameter. Doing this also affects the number fluid particles.

Display particle surface with velocities

  1. Select the particlefluidsurface1 node.

  2. Open the Surfacing tab.

  3. In the Output section, go to Visualize and choose Velocity from the menu.

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