Hello!
I was wondering if anyone could shed light on your workflows when it comes to RBD sims, and how do you go about implementing small changes to the sim while preserving the overall motion


- I am having a tough time adjusting my RBD where the client is happy with the end part but wants to change the velocity/spread at the start of the simulation - whatever way I try to implement this it inheritely changes the end of the simulation.

Trying to take the end part from the original and mix it with a new sim also creates some unlogical/clipping motion. It's a small object sim so any small change to the motion of the pieces makes the simulation look completely different.

If anyone has any advice or useful tutorials that got you started I'd appreciate any help!

You could try something as simple as a ShapeBlend between the two simulations. If we're talking about packed primitives, you just have points. Cache both options and shape blend half-way between them so when it settles, the points from first simulation are used at the start, and the points from the second simulation are used in the end.

I've tried a similar thing, but as I mentioned in the first post, when it blends between the two simulations you get a lot of clipping pieces and weird movement. All the pieces are very thin and wide so the clipping is really apparent even with small changes to the sim :/

You could try to take a frame between the first an second part, and use that as an initial frame to 'reverse'-sim to a different start position (reverse the initial v and w, as we want to match the movement at the start).
You can then just reverse this sim, and switch to the original sim at the previously chosen frame.

Any shaping you do on this extra sim (e.g. noises on velocities), blend them in (as this will practically function as our 'smoothness' for the blend to the original sim).

You can also take a look at the rbd-guide node to better art direct the start position.
https://www.sidefx.com/docs/houdini/nodes/dop/rbdguide.html [www.sidefx.com]

It might be a bit abstract as written, so i've attached a simple example.
Depending on your scene, this technique might still be very tricky. But hopefully it helps!