Suggestion / Idea Changing Medium Parameters for Cloth Physics in ObiCloth: From Air to Water

[josemendez]

Hi,

Thank you for your prompt response. I have noticed the ability to adjust drag and lift coefficients in ObiRope, and this does seem like a promising path.

However, in our pursuit of creating a highly realistic trawler net simulation, we aim to factor in the specific properties of the net’s material and the underwater medium as accurately as possible. Given this, I wanted to ask if there is a recommended method for calculating these drag and lift coefficients to closely mirror real-world conditions?

If this isn’t feasible within the scope of cloth physics in ObiCloth, would it perhaps be more suitable to use a line renderer coupled with custom physics scripting to achieve our desired level of realism? 

Hi!

This isn't related to cloth simulation as much as it is to fluid simulation.

Obi assumes wind direction is the result of accumulating all force areas affecting the cloth. For instance, if you add a ObiAmbientForceZone and a ObiSphericalForceZone, the resulting wind blows in the same direction/magnitude everywhere in space (due to the ambient force) except in a spherical area, where it gets modified due to the spherical force zone.

This is simple to understand and easy to control, but doesn't behave at all like wind -or fluids in general- do in the real world. More specifically, the resulting velocity field is not incompressible and may have divergence. To accurately simulate wind or underwater currents you'd want to have a divergence-free fluid velocity field that takes pressure/density into account, which is far beyond the scope of cloth or rope simulation. This can be achieved using an eulerian (grid based) fluid simulator, either 2D or 3D depending on your needs. Simplest method is probably Stam's stable fluids.

Once you've got a proper fluid simulation for the wind, you just need to extract the wind direction/magnitude at each cloth particle position and write it into the  solver's "wind" data array, which is where particles in the simulation get their wind values from. Drag and lift forces resulting from wind are pretty accurately simulated in ObiCloth.

Note that if you want two-way coupling between the fluid and the cloth, you'd also need to take cloth geometry into account as a boundary condition for the fluid simulation.

kind regards,