Calm Fluid Surfaces

Owned by thomas (Unlicensed)
Last updated: 26 Aug, 2014
3 min read

When a fluid is poured into a glass or any other container you will see an up and down motion for a certain amount of time. A little later, the fluid comes to rest and forms an even surface. RealFlow mimics this behaviour, but it can take some time before the fluid is totally calm. During this time you can observe the fluid sloshing and moving. One method is simply to sit and wait until the fluid has relaxed, but this can be a very time consuming task. It is much better to support this process with RealFlow's “k Speed” daemon. Please bear in mind that this approach is suited for standard particle emitters. Hybrido fluids do not have to be relaxed.

 

A sloshing fluid and its relaxed state created with the method described here.


All scene elements can be added from RealFlow's “Edit” menu:

  • Add > Emitters | Objects | Daemons

  • RealFlow nodes can be moved, scaled, and rotated with the W, R, and E keys.

  • Imported objects from SD files have to be unlocked before they can be transformed with Selected object > Node Params > Node > SD ↔ Curve

  • Viewport perspective is changed with the 1, 2, 3, and 4 keys.

  • Shading modes are toggled with the 7, 8, 9, and 0 keys.


The Relaxation Process

To create a calm and even surface, please follow these steps:

Start the simulation without the influence of the “k Speed” and "Drag Force" daemons.

  • Fill the object until the desired water level has been reached and let the simulation run for a few more frames.
  • Set the emitter's “Speed” parameter to 0.
  • Create an initial state and activate “Reset To Initial State”; reset the scene.
  • Add a “k Speed” daemon.
  • Node Params > k Speed > Limit & Keep > Yes
  • Max speed > 1.0
  • Max speed > right-click > Add key
  • Shift the timeline slider to frame 200 (the fluid disappears).
  • Max speed > 0.01
  • Max speed > right-click > Add key
  • Reset (the fluid reappears).
  • Add a “Drag Force” daemon.
  • Under Drag Force > Drag Strength create two keys with values of 0 (f = 0) and 75 (f = 200).
  • Simulate. At frame 200 the fluid should be calm and relaxed.
  • Create a new initial state for your final simulation as described above.
  • Reset.

An initial state can be saved easily:

  • Make an initial state with Node Params > Initial State > Make Initial State.
  • Set “Use Initial State” to “Yes”.
  • Activate the “Reset To InitialState” option with a click on the triangle next to the “Reset” button.
  • Optional: backup your previous data or apply a new export name for the emitter.
  • Reset the scene to load the initial state at frame 0 (or any other specified frame).
  • Simulate, using the initial state.

 

 

This procedure will help you get an even fluid surface you can use as a starting point for a new simulation. Depending on the number of particles, this process can take a while. We therefore recommend disabling the viewport during simulation (Alt + D) or using the Command Line version:

  • Simulation button context menu > Command line