Animated mesh emitter with wispy curly edges

[elyptic]

Hi all,

I've spent the last few weeks trying to come up with a reasonably good looking solution to this dry ice / fog effect. My results have varied between decent and awful. Initially I was using just the Smoke sim, but found the edges to be very puffy and consistent, trying both the Clouds and Cold Smoke presets. So then I checked out the ink in water sample, and while the effect was much wispier, it flew pretty far out of control over time and I've been trying to tame that. The problem I'm finding is the documentation doesn't help much, it's so basic.

The point of it is to arrive at something like in this clip, at 2:42 and on. It's doing the very same thing we're trying to achieve, with a translucent figure emitting a curly smoke/mist with some soft turbulence and floating in air.

https://www.youtube.com/watch?v=VSDqDOLupNc

Before I get into all the other tests I've done, does someone have a good idea of at least where to start getting this kind of effect? The simulations take hours to do, rendering is equally painful even on just one animated mesh and a basic scene. Right now I'm using 25K particles and a point particle shader into a grid of 3cm cells, with a turbulence as well. The turbulence preview is boggling, I figured I want it in a 10cm area but it's a straight line.

I was trying to post a screenshot of the interface and my render but 3dsmax 2014 is completely unresponsive after stopping the simulation. I guess I'll kill it and launch my last save. Here is the last image I rendered before the interface went to hell.

Thanks,
Chris

Anyways any ideas about doing this effect?

[Svetlin.Nikolov]

Hey,

I'd suggest turbulence and smoke simulation with smoke dissipation and a spiky opacity curve for rendering the smoke so you'll get these thin veils of smoke. Using particles, it would look good as well, but you need a very high amount in order to not have it look grainy, or you could use the count multiplier of the particle shader to render more particles than you actually simulated. With a particle sim, the alternative to smoke dissipation would be to use Drag particles emitted from a source and enable the lifespan of the particles so that they disappear over time. You wouldn't need too much of a grid resolution with drag particles, so you should have a very fast sim this way. You should also make sure you use PCG conservation with quality of 50 or more and Multi-Pass advection.

Can you tell me more about the grid resolution and the setting you use to simulate? It should definitely not take that long to simulate and it should not be so hard to preview as well. Do you have Auto reduction enabled in the preview? Are you using GPU preview? Regarding the rendering, you should make sure you use the Phoenix light cache in the Particle Shader and you have as high Speedup as possible without artifacts appearing. If you could share the settings you are using, it would be very helpful so we can figure out what needs to be changed.

Cheers!

[elyptic]

The Grid resolution was initially very small (1cm) when I was doing pure Smoke, but I decreased the res to something aroun 10cm when I started using particles as a solution. I'll gladly scrap everything and start from scratch as it's pretty much what I've been doing all along anyways.

It sounds like your recommendations are where I started, with dissipation at 0.75 because the entire scene would fill up without it. I hacked at the opacity curve as much as I could to this out the edges, but then the mesh would be invisible and have these awful lego blocks on the leading face of the mesh.

Particles seem to be the only way to get the mesh to emit smoke evenly out of the front as well as curl the drag nicely.

For the previews, I have the PhoenixFD GPU Preview in one extended viewport, the option is still greyed out in the panel, so I can't select GPU "Enable in viewport" I guess it's a 3dsmax 2014 thing. I only get to see a rough preview when the grid is selected. Auto reduction is enabled, it was at 5 last I checked. I also have 'save images during sim' turned off trying to save time.

I'd attach the scene but it tells me both a .max and a .rar are invalid files..

System specs:
AMD FX8350 8 cores@4Ghz
32GB DDR 1600
nVidia GTX 970

[Svetlin.Nikolov]

Ah, yes - 3ds Max cannot do the viewport GPU preview with 2014 and older. I'm quite interested in what would cause the "lego" look as well.

If you could attach the scene it would be great - a zip would pass through the forum's defences Otherwise you could drop it to Support (@chaosgroup.com).

Cheers!

[elyptic]

OK cool here's the Zip then You'll see what I mean by the lego chest, all voxelated and blocky. Just about the opposite of wispy curly smoke!

[Svetlin.Nikolov]

Some first observations - so the grid artifacts are due to the very low resolution - if you go with the smoke approach as opposed to the particle approach, you'd need drastically more voxels in the grid - 50M or more. You'd also improve the appearance of the smoke if you switch to Spherical sampler in the rendering options. The particular blocky look of the smoke is due to the surface force mode of the source - the smoke is created only over the surface of the mesh, and it's the thickest there, so the first voxels are visible when the resolution is low. You could go with brush mode instead, or inject with a very low strength, which will create smoke inside the model, and then if you don't want it to render, you can use the render cutter and inverse it (seems like there is a problem with the geometry there - the mesh needs to be closed and without any holes, overlapping triangles or inverted normals).

Some more things you should try with the smoke sim is to use Multipass advection and PCG conservation if you want more detail and a more natural motion of the smoke, and you could also substitute the randomization with vorticity in order not to have the smoke look like it's boiling.

If you go with Drag particles, the same tips about the dynamics apply - the drag particles are carried by the smoke/fire simulation's velocity, even when there is no smoke or fire simulated. Will try to reproduce the viewport problems now...

Cheers!

[elyptic]

The problem is my system will be out of memory, even at 32GB, before we can push the res up that far. Phoenix crashes out even when I'm at 1cm grid size, depending how high I keep the smoke dissipation.

Another thought I had was to combine a point particles shader with the smoke sim, but it only seems to want to render one or the other. When I add the Point, my smoke is no longer rendered. Is that normal?

[Svetlin.Nikolov]

Would it be possible to send a scene over that can reproduce the crash? This should absolutely not happen and should be fixed - even if you run out of memory, this should be handled and you should get a message, but not a crash. And also, you have plenty of memory - 32 gigs are more than enough for small and medium scale sims. If you are going over 200-300 million cells, then you might start running out of RAM. 1cm with the scene you sent is pretty low res - it does not even come near to filling the memory, so there must be some other problem that causes a crash.

Also, which version are you using? Is it the official build or a nightly? If you don't see Phoenix nightlies at nightlies.chaosgroup.com, you can ask the Support for permissions for the Phoenix 3 ones and try it out to see if the crashes and slowdowns are still there. If we are able to reproduce the issues here, the fixes will be in the new nightlies in several days.

Regarding smoke and particle rendering, they should render together with no problem as well - if this can be reproduced with a simple scene, it'd be very helpful so we can see what's going on. Btw, is the render from your first post smoke and particles combined?

[elyptic]

I'm going to post a couple of screenshots to show you what's happening.

1: Idle after simulation. My smoke is visible in the GPU viewport (white to red, opacity ~0.65). Memory footprint pretty small, about 2.6GB. Rendering particle shader at 0% opacity, should show the cloud but it doesn't. Base mesh material visible (falloff etc).



2. Change particle shader to alpha .01, shadows .01, re-render. It's pretty furry looking now but the particles are obvious. This doesn't look like 1% opacity though. Smoke not visible. Render takes 17m.



3. Delete particle shader, re-render. Check smoke opacity etc., should be a red cloud, but nothing in the render except base material. Renders in seconds.



4. Change Particles from Drag to Foam, start simulation. RAM usage jumps to 18GB+, still only at 1cm cell size.

[georgi.zhekov]

Hello,

Can you upload the version of the file that reproduces your problems?

With the file you have provided everything seems to be working correctly in here.

Thank you,

[elyptic]

Well I've discovered that I don't even need a particle shader at all, and it cut my render times by about 800%. I thought the foam shader was necessary to drag the swirly edges out but I was wrong, so I'm now experimenting with trading off other items.