contact joints
 

Hello,
I have a number of questions with the aim to simulate a kind of contact joints between elastic bodies. By contact joints I mean this: when two not-neighbour-cells approach closer than some epsilon, their degree of freedom along their position difference is removed as long as the net acceleration would reduce their distance.

The simplest question first. How do I change the parameters of a boundary condition at runtime? Let's say I have a patch with fixedValue U=1.23. The solver needs to change this to fixedValue U=0.0 if a certain condition is met at some point. Maybe the Wiki has some demonstrations how to do this?

The next task would be to modify a zeroGradient patch to a fixedValue patch at some point at runtime. With a few more thoughts this should allow me to simulate a rubber cube bouncing off a static plane.

Now, how can contacts between two moving elastic bodies be described? Or self-contacts of a single body that is bent such that it bounces off itself, whatever you think is easier to explain?
This requires a boundary condition which sets the components v1*n and v2*n identical for the two velocities v1 and v2 of the contact cells c1 and c2 along the normal n. To my knowledge the boundary conditions don't constrain relations between two patches (except for cyclic boundaries). Any hints, how to constrain the relative velocity between two patches?

Thanks
Paul