Hi Christopher, thanks for baptizing the new forum with your question :)
1. I noticed, during a reversed-gravity test, that if IcePhys bonding is enabled ("bonds1"=15), bonds will form between Spheres and Walls, not just between pairs of Spheres. Is there any means of turning off automatic bond creation between spheres and walls on contact? Would changing the material of the walls to something other than ice accomplish this?
This is not directly possible. If you need to have different bonds between different groups of particles handled differently, we can introduce some switching based on either particle's mask, or perhaps based on Material instances of which couples would be handled using MatchMaker (this is a sort-of forgotten framework for handling such things, e.g. when different material combinations required different friction coefficients). If this is what you need, then let me think about the most elegant way to do it. We always want to extend the functionality in ways which are useful for other cases, and don't complicate other things overly.
2(a). Is it possible to set up the Woo 3D View (or the Display pane) such that bonds are explicitly shown on the screen (e.g., by lines) while other contacts are NOT shown? In other words, is it possible to get a visual representation only of bonded contacts?
2(b). Would such bonds-only visualization be possible in ParaView if we exported our data to that program?
Again, not directly possible now. What would be possible and relatively straightforward is combining the following two points:
- enhance Gl1_DemField to have color scale for contacts based on various things (like there is for particles which can be colored according to radius, velocity, mask, displacement etc).
- Make contacts outside of the range of the color scale not appear at all (the underlying code has been there for some time already, I just never really finished that). Since bonds are characterized by different stiffness values, this could work. A model-dependent criterion (like bonded/unbonded) would be less nice, but perhaps doable.
For Paraview, same thing. Since VtkExport exports also stiffnesses, by applying some filters, this result could be achieved.
3(a). What is the precise effect of the damping coefficient "damping", which is defined in (I believe) the "Leapfrog" integrator? There are some circumstances in which it appears to not produce any damping at all. The most notable of these occurs when a particle is in free-fall and lands on a surface: it will rebound (bounce) to the full height from which it was originally dropped, with no inelasticity whatsoever. This occurs despite my "damping" coefficient being set to 0.5.
I enhanced the documentation at https://woodem.org/theory/leapfrog.html#numerical-damping (just took over what I wrote for Yade a few yars back). And I checked and found a bug that you describe, in that that ContactModelSelector did not set Leapfrog.damping for any other contact models than the linear one (so not for ice, either). When you update from git (which includes this commit) it should behave as you had expected.
3(b). Is there a means of introducing hysteretic damping?
Yes, it is called c++. If you give me the equations, I will add them to the ice model.
If you are going to do only quasi-static simulations for ice (which I'd say also includes simulations with massively scaled time, and only the resulting forces matter), use the numerical damping. Otherwise contact-level damping is the way to go.
Hope this helps,