Collisions

Biohydrodynamics Toolbox    

Collisions

Collisions between moving bodies are managed by BhT. In the DAT-File, you can specify that you wish collisions to be taken into account in the computations. This is done by setting the field collisions to yes. Nonetheless it will significantly slows down the computations. If one is sure that the immersed bodies will not collide in their courses, the field collisions can be switched to no (or merely omitted in the DAT-File since no is the default value for this field).

If collisions is set to no and bodies still collide, the computations will crash.

Collisions parameters

When collisions are allowed, both fields alpha and epsilon have to be added and properly set in the DAT-File. Collisions are managed by adding a repulsive potential, somehow similar to an electrostatic potential whose charge would be localized along the fluid's boundaries. The related potential energy between two solids of respective boundaries  and , is given by

The related repulsive force should prevent the bodies from overlapping each other. This force is almost null when the bodies are far enough one from the others, increases when they get close and blows up when the bodies touch each other. If the force is too strong, it may significantly perturb the natural movement of the bodies. However, if it is not strong enough, due to inertia of the bodies, two bodies should still collide, overlappe and make the computations crash. Several attempts are commonly required to correctly set alpha and epsilon. Try alpha = 4 and epsilon = 0.01 as starting values.

See also

Writing a DAT-File

Where do the equations of motion used by BhT come from?

2008 - A. Munnier and B. Pincon (Insitut Elie Cartan and INRIA Lorraine, Projet CORIDA, Nancy, France).