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Swirl Pyro Equivalent


ejr32123

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Hey,

I have been struggling to get a nice swirling motion in slower moving pyro smoke simulations. In Maya fluids I had an option called swirl witch worked beautifully. I found an old post addressing this issue, but it seems to have died before arriving at a good solution: http://forums.odforce.net/topic/23132-smoke-swirl-vorticity-with-smoke-solver/

Here is a simulation I did in Maya using the swirl attribute. https://youtu.be/Ifd6FJ2oHIc 

In houdini I have been using disturbance but I don't seem to get the results I want. Disturbance doesn't really seem to add swirl but more turbulent detail. For example, look at this sim I found on vimeo. You can see the disturbance start overpower the simulation towards the end, it doesn't really add a swirling motion. https://vimeo.com/220668349

What is a good Idea to get nice swirls?

Thanks

 

 

 

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Look at the "Confinement" parameter in the Shape tab of the Pyro solver, is based on the Gas Vortex Confinement dop. is a starting point.

in other hand, you can create some vorticles forces advecting particles. look at this thread plenty of pyro info and some examples i guess

 

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Take a look at this file.

SeedVorticles.hipnc

as i mention before, you can inject some particles that will be use as a vortex seed (Vorticles = Vortex-Particles).

The process will be:

  • Create a source to apply the vortex forces
  • Apply Forces
  • Update the Velocity field
  • Advect the vorticles to move accordingly to velocity field

So houdini comes with a Microsolver called "Gas vorticle Geometry", this MS create a bunch of points on a fixed volume that match your fluid object, each with a magnitude and radius, Then "Gas vorticles forces" applies a Paddlewheel-like force to each point and updates the velocity field based on a Confinement Strength. 

Finally in the advection step "Gas advect" MS, moves the points according to the velocity field to track the fluid movement and preserve the position of each vortex.

 

btw there is a shelf tool under "Container Tools" tab called Seed vorticles that make all setup for you. ( i never seen that before :D )

its not the best explanation but i hope you find it usefull.

Cheers!

 

 

Edited by Martin47
wrong file
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1 hour ago, Martin47 said:

Take a look at this file.

SeedVorticles.hipnc

as i mention before, you can inject some particles that will be use as a vortex seed (Vorticles = Vortex-Particles).

The process will be:

  • Create a source to apply the vortex forces
  • Apply Forces
  • Update the Velocity field
  • Advect the vorticles to move accordingly to velocity field

So houdini comes with a Microsolver called "Gas vorticle Geometry", this MS create a bunch of points on a fixed volume that match your fluid object, each with a magnitude and radius, Then "Gas vorticles forces" applies a Paddlewheel-like force to each point and updates the velocity field based on a Confinement Strength. 

Finally in the advection step "Gas advect" MS, moves the points according to the velocity field to track the fluid movement and preserve the position of each vortex.

 

btw there is a shelf tool under "Container Tools" tab called Seed vorticles that make all setup for you. ( i never seen that before :D )

its not the best explanation but i hope you find it usefull.

Cheers!

 

 

MVP : ) thanks

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I don't think that you will have the exact same thing as Maya Fluid swirl parameter , by default. If i remember correctly from my maya days :) , swirl just

- take the velocity grid 

- analyse it to isolate area of high curl

- multiply velocity vector of the grid by the input set in swirl in the isolated area.

In houdini we do add swirl with all method mention above, aka confinment microsolver and vorticles but i think you will not be able to replicate the exact same thing as swirl.

I have set a dumb scene with all methods and you are right it does add at some point curl noise to the vel grid. it is not just a dumb multiplicator.

You could try to play with all methods, i find vorticles to slow down sims a little bit. I agree with bunker from what i have see the closest thing to maya swirl would be to start from vortex boost confinment.

But a simplify version of it where you just compute curl with gaz analysis isolate the area you want and then use this as a mask to multiply your initial grid would be sufficient to replicate maya swirl.

Cheers 

E

 

 

 

confinment_test.hiplc

Edited by sebkaine
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i reopen maya and check inside houdini microsolver.

if you look inside gaz vortex confinement solver you see that the logic is extremelly close to what i describe for maya.

i think i would start from that instead of vortex boost if i was trying to replicate it.

confinment in houdini is close to what you get in maya with high details solved on and a decent rez, you get those extra swirl.

but replicate the maya swirl behavior when high density grid is off would need some custom work.

i find that confinement when you use high rez introduce a lot of parasite motion. 

one way is to use the exact same logic but as a post process to displace your sim.

basically you compute the confinement but you don't add it to the velocity in the grid, you use it to advect your density along the confinment vector, like a sort of displacement.

this logic of advecting extra detail is also there when you use uprez node on the shelf, but it is a 2 step process.

i recommand to watch those 2 videos to better understand pyro, they are great

https://vimeo.com/42988999

https://vimeo.com/119694897

 

Edited by sebkaine
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  • 1 month later...

does seed vorticles work with resizing containers? I tried adding the vorticle field to the extra fields to resize in gas resize fluid dynamic node and it didnt work. Do i just need to make the container initially big enough?

 

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I dont understand how you get such nice movement with pyro using disturbance or turbulence. I have tried all the micro solvers and they produce weird results too. Obviously I exaggerated the motion,but you can see none of them really seem to create a swirling motion like maya fluids. First photo is the patter disturbance creates, the second is turbulence and third is gas vortex equalizer. It seems easy (sometimes) to tell what software was used to create a simulation based off its look. Maya fluids has its look, fume has its look and now I notice pyros look. Look at all these sims, they don't have swirling motion like maya fluids, they have turbulent patterns instead. Either that or really small swirl from gas confinement. take a look at this album, you can tell what I am talking about by the pattern seen in these simulations. https://vimeo.com/album/5305665

It seems really hard to get motion like this: https://vimeo.com/141476011 only using disturbance any turbulance. 

 

disturbance.png

turbulence.png

vortex equalizer.png

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  • 2 weeks later...

still working on a good solution, but here is something else that I tried that works a bit better. I added gas vortex confinement,but kept the values low (around 1 - 2). I plugged that into a gas repeat solver. That seems to work much better than using confinement and turning up the scale. Also added more sub steps on the dopnet. That seems to just create a lot of small swirl. This isn't perfect buts its getting away from disturbance patterns

https://drive.google.com/file/d/1UNp13Arv7sv7XiWhF82A5OTH_CWhTME1/view?usp=sharing

Edited by ejr32123
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  • 6 months later...

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