Fast moving object issues

[BenOC]

Hi

I've got a animated object that moves very fast through my scene. It jumps a fair distance per frame and I'm having some issues trying to keep the smoke residing in the initial position while continuing to emit as the object gets further away.

Imagine a football being kicked and traveling through the air fast as the camera remains in the same position but following the trajectory of the ball object.

Image attached with my settings.

I was hoping that someone could tell me some settings or a link to a tutorial that covers a similar scenario.

Thanks for any guidance with this.

Cheers

[Svetlin.Nikolov]

Hey,

There is just one rule when it comes to fast moving geometry or fluid - use more steps per frame. Since your steps are already high enough and if you still are not getting the desired result, think about approaching the setup differently - can't you attach the simulator to the moving object instead?

Cheers!

[BenOC]

Excellent, thanks Svetlin!

I changed the emitter to a slightly simpler object and positioned constrained it to the animated object so it didn't rotate with it (this was causing some unwanted results).

The sim time is a bit of a killer though, but hey it's working, so I'm very happy.

1 more question, is it 'Inscribed' I should be using for the PFD Properties on the ground plane so the smoke doesn't float above it?

Thanks for your help help!

[Svetlin.Nikolov]

Yup, inscribed, and also it would be best if the plane is shelled. Also, if you attached the sim to the moving object, maybe it would allow you to reduce the number of steps per frame now?

[BenOC]

Inscribed it is, I'll make sure the to put a shell mod on the plane object. By attached do you mean linked? I have it constrained which is almost the same ( I thought?).

[Svetlin.Nikolov]

Anything works, as long as it moves together with the geometry

[BenOC]

I now have a box for the ground plane, I have set the Voxel Mode Override to Inscribed but the smoke still floats above the ground? I am unsure what I am doing wrong?

I've attached the file.

Cheers

[BenOC]

Here is what it looks like:

[BenOC]

The only work around I have come up with is to set the ground box as excluded and create another collision box underneath this and do several sim tests to get the right height. But I would expect that setting the object to inscribe would work and I must be missing something?.

[Svetlin.Nikolov]

Oh, this is not the voxel mode - it would have been a matter of less than one voxel above or below.

Does that also show up in the render? Don't base your conclusions on the viewport previews - they are there to help, but rendering is what matters after all.

[Svetlin.Nikolov]

Looking at the scene now, looks like something with the adaptive grid maybe...

[BenOC]

Yes it seems to be happening in the render for some reason?

[BenOC]

Here is the same sim paused at the same time with the ground box set to Exculde in the Scene Interaction rollout and a box several cm underneath it acting as the collision object:

[Svetlin.Nikolov]

Yess, exactly - either exclude the ground box, or make it non-Solid from it's right click Phoenix properties, and also set the adaptive grid extra margin to 10.

As the grid is moving together with the ball, seems like the adaptive grid first moves, clips the end of the smoke, and just then expands... Please try these settings as a workaround and ping me if it does not look okay.

[BenOC]

Thanks very much for your help it is greatly appreciated!

One more question: what would be the best matte settings for objects that interact with the smoke but are not rendered with it.

I think the attached picture illustrates what I am trying to achieve but not managing to do. The smoke in the render should be over the parts of the matte object but disappears totally.

Currently I have the objects Vray properties Matte object set to -1.0 . If I set this to 1.0 then the object is white in the alpha, I believe I just want to see the object as black with varying degrees of white transparency where the smoke wraps around the mesh.