Displacement, also known as ocean statistical spectrum, is a layer of small waves and ripples that is added to a → HyFLIP fluid surface to enhance realism. The displacement itself is invisible and can only be seen in conjunction with a mesh.

Create a → basic HyFLIP scene, for example with the “Open Domain” tool.
Add some turbulence by moving an → animated object through the fluid.
Simulate.

Here a → "Waterline" emitter has been added. The particles have been snapped to the mesh with the → "Snap Foam Particles" tool. Furthermore, the amount of waterline particles has been increased with the → "MultiPoint" option:

A Maxwell Render snapshot of the tutorial's result.

The Base Mesh

Before we proceed, it is important to set the (already simulated) domain to → “cache”:

Click on the domain node's small green rocket.
The yellow colour indicates the cache mode.
Move the domain's viewport icon (plane with four boxes - here in red) to the upper third of the fluid as shown below.

Add a mesh – all settings are made under “Node Params”:

Mesh shelf > Hybrido mesh VDB
Boundaries > Open Boundaries > Yes
The last action will remove all polygons outside and below the domain's viewport plane.

Displacement > Use displacement > Yes

The Ocean Statistical Spectrum

Open the domain node's → “Ocean Statistical Spectrum”. There you will see a long parameter list, but just a few a really relevant for your daily work. The result can only be seen when you create a mesh. Here are the most important settings:

Calculate displacement

Set this option to “Always”:

RealFlow will calculate a displacement map immediately using the default values.
Whenever you change a value, the displacement is recalculated for the current frame.

Vertical scale

This parameter mainly depends on “@ dimension”, but you should start with the default settings. If the surface is flat increase the value.

@ dimension

If the level of detail is low, disable “Auto dimension” and increase this parameter. A good start is a value is around 2-3x the size of the domain's viewport plane (10 m by default).

@ wind speed

This parameter removes spiky patterns, smoothes the surfaces, and creates the typical wavy look. A value between 20 and 30 m/s works best.

Seed

Enter any positive integer to change the waves' initial distribution.

Choppiness

Create sharp wave crests; start with values between 0.8 and 1.2.

The Displacement Mesh

Go to a frame with enough detail, splashy structures, and turbulence. Then select the mesh and click on

Mesh shelf > Build mesh to create a single mesh from the current frame.

A possible result could look like in this image:

In order to proceed and refine your settings, change the HyFLIP domain's “Ocean Statistical Spectrum” parameters and create test meshes until you are satisfied. Please also consider the → “Displacement” section's attenuation options, to remove the spectrum waves from splashy structures or areas with high vorticity:

The Mesh Range

In the final step, the entire simulation range is meshed. Currently, the displacement has been created for a single frame:

Reset the scene and simulate.
The domain's “cache” mode prevents the fluid from being re-simulated, and only the displacement is calculated.
The mesh is created simultaneously.

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