smoke details

Phoenix Issues
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1

Hi,
I have a smoke sim that look the way I want but it is too fast. if I slow the sim with the time scale. Unfortunately I loose all the details when slown down. The details are generated by the vorticity.
is there any trick to have a slown down sim but keep all the details?

Otherwise, is there a way to create a slow smoke without the time scale?

thanks,
Yannick

2

decreasing the time scale really changes the simulation behavior because it decreases the simulation step.
you can try to use the play speed option in the input panel. decreasing the play speed you will need frames between the ones stored in the cache files, and they are obtained by interpolation. interpolation of the frames is not always problemless, there are two methods available, the linear interpolation works good if the content does not change too much between the frames , that is not satisfied in the most cases, the velocity based interpolation can handle better such situations but can produce weird looking result sometimes. there is a third option that is harder to set up, you can use drag particles with id channel exported, this ensures smooth interpolation, but you will need relatively big particle count and huge disk space for good quality of the rendered smoke.

3

Hi, Yannick,
One other thing you can try is to slow down using resimulation, you can choose between two methods, you should try the “Slow Down” method first:
Chaos Docs.

4

Hi Guys,

Thank you for the suggestions.
Ivaylo, I tried that but that didn’t work. I also loose the details.

Svetlin, I am on Maya, these option don;t seem to be here.

I have attached a frame of the sim that is too fast be I like the details in the smoke.

Here is a preview before and after resim:

I have attached the file also:

The details in the file is good but the speed is too slow. Please have a look and let me know how I can slow it down but keep the details.

Thanks,

Yannick

Smoke 1.jpg
Smoke 1.jpg1089×459 42.4 KB

Smoke details.jpg
Smoke details.jpg701×713 124 KB

Fog_detail.zip (1.2 MB)

5

The resimulation with time controls is not yet ported to maya indeed. Then, the only option left would be to use the time scale, but on a higher resolution, so the details persist.. Are you using multi-pass advection? It has least dissipation, so it’s a must.

6

I will give the multi-pass advection a go and let you know.
Please have alook at my file and let me know if you see anything wrong?

Thanks,

Yannick

7

Hi,

Any tip to do slow smoke?
By default the smoke is really quick, this can be seen in the doc: http://help.chaosgroup.com/phoenix\_maya\_20/simulation.htm

Thanks

Yannick

8

Are you still working on the same setup? The gif’s on the help site represent a burning fire with the temperature channel made not renderable. The smoke rises fast when the temperature is high and/or the scene scale is small. If you do have only smoke without temperature, it will only rise depending on the smoke buoyancy option, which is 0 by default.

9

Hi,
I am trying various option at the moment, I am realizing that the vorticity is the parameter that gives me the nice details, I am after. But it is too fast. Is there a way to slow it down?

Thanks,

Yannick

10

Ah, you mean the vorticity creates swirls that move too fast? If that’s the problem, currently it’s being reworked and hopefully the new version will be in the nightly builds soon. You may try to switch on and off the “x Vel” option, but in general the vorticity has some issues that we’re currently resolving.

11

Thanks Svetlin for the answer.

I guess I will have to find another way to bring some nice details in the smoke.

12

Quick question:

In rendering / Density/opacity, there is a texture slot. Could I have details through a texture? How does it work? Also I have a modulate tick option, what does this do?

Thanks,

Yannick

13

Sure, you could map a texture to the smoke channel and use it instead of the simulated smoke, or you can multiply both using the modulate option. This might not look good on a moving simulation though, as the mapping takes the simulator’s box.

You could also check the displacement option under the rendering panel, but it might also create artifacts in motion: Chaos Docs

14

Is there a sample scene for Maya showing the displacement on smoke?
This might be the solution to my problem.

Edit:
I have tried to plug a 3d texture in the displacement, but I can’t get anything unless I set the type to vector. The texture are regular Maya 3d texture like cloud. I would assume they do not have the right range value to work in vector mode.Am I missing something?

Thanks,

Yannick

15

Yup, when you use displacement, you need to set the Surface to a meaningful channel - in your case - to smoke. This way the gradient and surface displacement modes will work. Please have a look at the help link above, it’s for 3ds max, but the only difference is that in maya there is no Advection mode displacement yet, otherwise it’s the same principle.

16

Hi,
Is a 3d texture the best to connect in the displacement?
is the displacement following the smoke as it moves or is the smoke displaced as it goes through the texture?

Thanks,

Yannick

17

The smoke is displaced as it goes through the texture. The other way around was implemented in earlier versions of Phoenix, but it’s currently dropped as it did not behave well.

In vector mode, you must connect a color texture that has color values between -1 and 1.

In gradient mode and surface mode, you can connect a monochrome texture, and also you need to have the smoke channel selected as an effects channel and to set the surface level to 0.1-0.5, depending on the thickness of your smoke. You can get a preview the surface over which the displacement will be applied if you change the preview mode to Mesh.

You can give the different modes a try and see which one best suits the dynamics of your sim.