RKH - Displacement & Attenuation

A Hybrido simulation can contain an additional structure, called “ocean statistical spectrum” (OSS) or “displacement”. This layer is used to add smaller waves and ripples to the fluid's surface. The OSS is mainly used in simulations of oceans or lakes.

When the fluid's OSS is baked to the mesh you will often observe distortion effects, because some parameters, e.g. “Choppiness” have strong influence on the vertices' positions and finally on the mesh's global geometry.

Attenuation

When the mesh's geometry is attenuated then you control how the statistical spectrum is fading in certain areas of the core fluid. To do this, the Hybrido mesh engine provides a wide variety of attenuation parameters: splashity, vorticity, height, and speed. With “Speed Attenuation”, for example, it is possible to fade and finally remove the displacement patterns in fast moving areas of the core fluid. “Splash Attenuation” removes the displacement waves gradually in areas which behave more like splashes. This prevents the splashes from polygon intersections and distortions.

Normalization

In a technical sense, normalization means that the values of a channel will be recalculated in a way that they range between 0 and 1. But why? In a simulation with 200 frames and several millions of particles it is very difficult to spot the minimum and maximum values. The normalization process is required to make a simulation's values manageable for the user, because everything happens between 0 and 1, instead of a widely spread range of values.

In conjunction with attenuation you have to differentiate between normalized and not-normalized properties:

• “Splashity” and “Vorticity” are normalized and range between 0 and 1. With normalized values you can define where the attenuation process ends, but it will always start at 0.
•  “Speed” and “Height” are not normalized and use real values – metres per second [m/s] for speed, and metres [m] for height. These parameters provide minimum and maximum values allowing you to define where the attenuation process starts and ends.

In the first diagram a typical distribution of values from a simulation is shown. The smallest value is 0.1 and the highest one is 9.8. After the normalization process, the range goes from 0 to 1:

Minimum and Maximum Values

“Height Attenuation” and “Speed Attenuation” offer the definition of ranges, e.g. from 1.0 to 2.5. Now, vertices with values smaller than 1.0 will not be attenuated, while vertices with values greater than 2.5 will receive full attenuation. Within this range, attenuation is applied gradually (first diagram).

Finally, an attenuation factor can applied. With a value of, let's say 3, the displacement will vanish much faster – indicated by the steeper curve (second diagram):