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At present, I'm tinkering with a simple clutter-generation Python script.

Where can I find information on how to best "minimize" energy in a plant that I wish to forward simulate, possibly by "damping" the parameters for MultibodyPlant's contact model?

My desire is to be able to forward simulate clutter falling into a sink (or bin), and effectively have the kinetic energy be dampened out (i.e. no bouncing), in such a way that hopefully doesn't make the integration too stiff. For now, I'm fine if this is a "non-physical" hack.

I have seen the following Doxygen sections:

• Doxygen C++: Contact Modeling in Drake
• Doxygen C++: MultibodyPlant - that's where I got the reference to contact modeling and all.

I see options for changing stiction tolerance (in my mind, I would want less slipping, but decreasing this would cause more assertion failures?), as well as time step (accuracy / stiffness, at the trade-off of computation time). I have not yet come across damping terms that I can tune.

One option I have in mind too is to just use AdvanceTo(t + dt), and in between steps, do some simple heuristics to "remove" energy (e.g. see if there was a direction change, and strip out velocity if there was). My guess is this won't really help computation time if the system is still stiff.

Effectively, this script is just porting a form of Naveen's prior library (which was in the attic, used RigidBodyTree) to use MultibodyPlant:

drake@f2808c7a:attic/manipulation/scene_generation

My goal is to have quick computation (via wall clock time) to generate novel clutter scenes that are "settled" to a certain extent.

I have a simple toy example working (I can spawn and drop objects into a kitchen sink), but have found that in order to spawn objects where their initial conditions do not cause non-physical behavior / numeric instability (e.g. interpenetrating objects), I am injecting too much "energy" into the system (I spawn them within a box in the xy-plane, but I space them out along z s.t. the initial configuration has no penetration).

I am toying with different ways to "minimize" that energy and make the objects settle with as little compute time as possible.

Some things I've tried briefly:

1. Just forward-simulate within non-penetrating initial conditions. This is fine, but (possibly due to settings in the compliant contact model) it can take a while to settle, and/or there's so much energy that objects will bounce out of the sink. On the "take a while" part,
2. Use the Anzu version of the-soon-to-be-published Collision Remover, with "zero-height" of all objects as the starting point, and the original spawning height as the "collision free" state. This works, but can be computationally expensive for a large number of objects (>5), and overall much slower than just using forward simulation to settle the objects.
3. Try to write a naive height-minimizing MathematicalProgram in conjunction using MinimumDistanceConstraint. This is slow and rather brittle, though possible it could use more tuning. Example code here.

Disclaimer: I am a TRI Anzu / Drake Developer, but just ignorant of the more intricate parts of Drake's physical simulation setup :P