Smoke - random Grid clipping.

[patrickfmirage]

Hello. I would sincerely appreciate advice on this. I have done a setup which I like but am not sure if what I have done is correct in terms of a decent Phoenix workflow. I'm still learning PSD.

The idea is simple. Smoke exhaling from a characters nostrils while walking. Breathing in and out. I've animated both 'Discharge' and 'Smoke' to emulate breathing. There is also 'Smoke Dissipation'.

The issue I have is the container expands and contracts and sometimes jerks its scale randomly and clips the smoke. I did try setting the ' Expand and don't contract' but the cache files are immense as the volume grows.

I also played with higher Steps per frame and adaptive grid but that had varying results but none worked.

Lastly, I tried leaving the grid in it's initial position where it was created but as I have animated the discharge between 0 and 3, at 0, it doesn't follow like a standard sim. The solution was to animate the grids position to follow a rough position where the emitter is.

I have attached frames, before and after and can share a small scene file if requested. I wasn't sure how to post one here or if that breaks forum rules.

Cheers

[georgi.zhekov]

Hey,

The expand and don't shrink option should help with the clipping. You can find more about the Adaptive grid options here - https://docs.chaosgroup.com/display/...GridAdaptation

Can you share a playblast how this looks in motion?

If using the expand and don't shrink option makes the grid too large you could use the Manual adaptation limits to limit how far the grid will expand.

Then if the smoke at the edges is too dense and sharp you could use the border fade option in the Rendering rollout of the simulator to fade the edge.

Feel free to attach files to the post - no problem. They just need to be in a zip format so that the forum can accept them. If the files are too large you can use any file sharing platform that you like.

Cheers!

[patrickfmirage]

Hi Georgi. Thanks for looking at this for me too! I have attached a playblast and scene file. I will read more about how the Grid adaptation actually works. the playblast might not demonstrate the randomness of expanding and contracting but it does show a sudden jump which clips the smoke. Is the border fade option a render time feature which translates into a VDB or only for V-ray? Though that is a great idea, it was more the randomness of the volume that was tricky to deal with.
Cheers

[Svetlin.Nikolov]

Hey, looks like you just need a lower Threshold in the afaptive grid settings

[patrickfmirage]

OK Thanks. I presume that is without needing to use the Expand but don't shrink option? Is there a precise method to determine the value or is it tweak until there's a sweet spot. Apologies for the question as I found the docs explains the concept but I am still learning.

[georgi.zhekov]

If you disable the GPU preview, enable the Smoke voxel preview and disable the Auto range checkbox in the Preview rollout - you can play around with the Smoke channel preview range spinners to check the smoke value at the borders.
But this will take some fiddling as well. As a starting point you can just try 0.01 for the Adaptive threshold and lower it to 0.001 if needed.

[patrickfmirage]

Thank you Georgi. I very much appreciate your advice and I shall try this.

[Joelaff]

A little Extra Margin helps too.