08-29-2019, 01:36 AM
Hi Mike,
I took a peek at your scene file. Firstly, anytime you want to deactivate particles from the cloth solver, you need to add a Particle Switch operator set to "deactivate". This will prevent the overstretch you're seeing between cloth particles and bound particles.
Secondly, you'll want to set the timing of your Surface Test to "entry" so that particles are not continually being filtered to the Object Bind event anytime they get close enough to a part of the surface with the matching mat ID.
Most of your cloth issues could be solved by simply subdividing the cloth mesh prior to running the sim. Due to the vertex-based nature of the collision solver right now, the higher density the mesh, the better. The easiest way to subdivide the mesh is to just add a Subdivide operator prior to cloth conversion in the flow. Or of course you could also subdivide the scene mesh using a regular modifier. Also setting a collision radius in your collision operator will help. You had set it to "shape radius" but since your particles don't have a shape, that is effectively zero. You'll want to set it to "absolute" in your case. Too big and the particles will balloon out from the surface, but too small and interpenetrations are more likely to occur in edge cases. In your scene, an absolute value of 0.5 seemed to be pretty good.
Also the Bind Solver substeps are what you want to increase to increase the accuracy of the stretch solver. Default settings are tailored to grain sims. For cloth you'll want to set to 50 or so, depending on sim steps (maybe at 1/8 sim steps 25 bind solver steps would be fine).
In your Collision operator you may also want to set the particle interaction to "collide with front faces" instead of "both", so that if particles end up inside your collision mesh, they are allowed to escape.
Finally, for something like a thin cloth mesh you don't want to set volume constraints on the cloth. That's more for closed-surface softbodies, in order to maintain the inner volume.
I did notice some strange collision inaccuracies in your sim which I will have to dig deeper to see if they're a bug or not. Your file is a bit of a worst-case-scenario since there are lots of interpenetrations in your collision geometry which can result in all kinds of weird collision behavior, but obviously it's nearly impossible to get rid of such things in real productions and so it's a fault of my cloth solver that they are not handled properly, rather than a fault of your setup. In the future I hope to continue to improve the cloth solver for these types of cases (high fidelity character cloth), so stay tuned.
I took a peek at your scene file. Firstly, anytime you want to deactivate particles from the cloth solver, you need to add a Particle Switch operator set to "deactivate". This will prevent the overstretch you're seeing between cloth particles and bound particles.
Secondly, you'll want to set the timing of your Surface Test to "entry" so that particles are not continually being filtered to the Object Bind event anytime they get close enough to a part of the surface with the matching mat ID.
Most of your cloth issues could be solved by simply subdividing the cloth mesh prior to running the sim. Due to the vertex-based nature of the collision solver right now, the higher density the mesh, the better. The easiest way to subdivide the mesh is to just add a Subdivide operator prior to cloth conversion in the flow. Or of course you could also subdivide the scene mesh using a regular modifier. Also setting a collision radius in your collision operator will help. You had set it to "shape radius" but since your particles don't have a shape, that is effectively zero. You'll want to set it to "absolute" in your case. Too big and the particles will balloon out from the surface, but too small and interpenetrations are more likely to occur in edge cases. In your scene, an absolute value of 0.5 seemed to be pretty good.
Also the Bind Solver substeps are what you want to increase to increase the accuracy of the stretch solver. Default settings are tailored to grain sims. For cloth you'll want to set to 50 or so, depending on sim steps (maybe at 1/8 sim steps 25 bind solver steps would be fine).
In your Collision operator you may also want to set the particle interaction to "collide with front faces" instead of "both", so that if particles end up inside your collision mesh, they are allowed to escape.
Finally, for something like a thin cloth mesh you don't want to set volume constraints on the cloth. That's more for closed-surface softbodies, in order to maintain the inner volume.
I did notice some strange collision inaccuracies in your sim which I will have to dig deeper to see if they're a bug or not. Your file is a bit of a worst-case-scenario since there are lots of interpenetrations in your collision geometry which can result in all kinds of weird collision behavior, but obviously it's nearly impossible to get rid of such things in real productions and so it's a fault of my cloth solver that they are not handled properly, rather than a fault of your setup. In the future I hope to continue to improve the cloth solver for these types of cases (high fidelity character cloth), so stay tuned.