Hybrido Object Interaction

Owned by thomas (Unlicensed)
Last updated: 15 Nov, 2016 by Alex Ribao
3 min read

Hybrido fluids are able to interact with polygon objects and the first task is to classify an object's shape. In general we can differentiate three possible cases:

  1. Closed object. Fluid interacts with the outer surface.
  2. Closed object. Fluid interacts with the inner surface.
  3. Open, single sided object.

 

 

1. Outer surface | 2. Inner surface | 3. Open, single sided

 

Volume Modes

For the simulation it is necessary to tell Hybrido of which type the object is. In many cases, the differentiation from above is made automatically, but it does not hurt to check if this is done correctly under Selected object > Node Params > Volume > Volume mode

 

 

Now let's assign these options to the objects from the illustrations above. Object

  • #1 is "Solid inside"
  • #2 is "Solid outside"
  • #3 is "Shell".

"Shell" is of particular importance, because this mode creates an imaginary layer around the object to make it watertight. This also means that the fluid will never touch the object's surface.

The thickness of this layer is calculated as Cell size * 3.

Cell size

The "Volume" tab also contains a "Cell size" parameter for controlling the quality of the Hybrido-object interaction. The value is measured in metres and with higher settings, the gap between fluid and object will be bigger. But, there is another "Cell size" parameter for the Hybrido domain and this value is higher-ranking. An example: Let's assume the domain's "Cell size" is 0.15. In this case, the smallest object "Cell size" should be 0.15 as well.

Also take a look at "Adjusting "Cell size" and "Surface offset"" below.

 

Cell size = 1.0 | Cell size = 0.1

 

Leaking Objects

It might happen that some particles go through an object, regardless of the adjusted "Volume mode" or "Cell size". There are several ways to avoid this behaviour:

  • Add a → "k Volume" daemon. This daemon has a "Shape" option. Select "Objects" and choose the body to delete the leaking particles.
  • Slightly increase or decrease the object's Volume > Surface offset parameter to virtually inflate or shrink the object (see "Adjusting "Cell size" and "Surface offset"" below).

 

If all these measures do not help then it is necessary to change the Hybrido core fluid solver's substeps:

  • In simulations, time is subdivided into more or less small steps. The more substeps, the better the simulation.
  • Hybrido uses a very small number of substeps. With fast particles or moving objects it is very likely that the fluid literally cannot "see" the object.
  • Go to RealFlow's → "Simulation Options: Hybrido" and increase Liquid - Hybrido Solver > MAX substeps to 3 - 5.


Here is where to find the "Simulation Options" window:



Adjusting "Cell size" and "Surface offset"

It is possible to directly observe the impact of your "Cell size" and "Surface offset" settings an object's Node Params > Display Volume > Isosurface > Yes.

What you get is a purple mesh, representing the current adjustments. Now, change "Cell size" and "Surface offset" to get an optimal representation of the base object.

Use the 7 key for a bounding box view, or the 8 key to see the object's wireframe.

 

Base object | Cell size = 0.5 | Cell size = 0.25 | Cell size = 0.05