Hey guys, been away for a few days.
Thanks for sharing a bit more about your pipeline needs. We don't force anybody to use a specific pipeline or workflow but just have a recommended method which is passing alembics between passes.
So there's actually nothing stopping you from simulating everything in one file. As computers get more powerful and our software gets faster I'd imagine this would be the way forward, but for now we do recommend splitting out muscles from fat/skin just so that your iteration loop is quicker.
With your sliding fat, is the character moving quite quickly? How many substeps are you running?
It may be that the fat is simply lagging behind everything else and the collisions can't push the fat back to where it's supposed to be because of the amount of force running through it. Substeps can help resolve collisions for fast moving animations.
Like Tristan said, inertial damping might also help you, although this attribute is most effective on muscle bodies. And not quite a silver bullet for large surface tissues. You could also try dropping the mass density on the material for the fat. On Mr. Ink I have it right down to 106 (one tenth of default) At this point you're getting away from real world physical properties though. But it will probably help you with the lagging thing.
In answer to your question about adding sliding attachments. Generally I try to let collisions/surface-tension/pressure do the bulk of the work. And I only add selective sliding attachments in areas that are persistently troublesome, like wide thin muscles such as the lats.
Just to clear up any confusion around what Ziva does or does not do with turning off collisions. By default, collisions are always on when you make a tissue, cloth or bone. Also by default, collisions are turned off globally on the zSolver, so they need to be turned on there if you want to use them. (I can see you've done that. I'm just writing for total clarity 😃 )
The ONLY alteration we make to default is that we turn collision volume OFF on bones/cloth/tissue if they are not closed volumes when they're created. Like this for example:
Ziva needs at least one of the bodies to be a closed volume for collisions to resolve. So for example, these objects will never collide in Ziva at the time of writing: