Maya Real World Dynamics Problem

#4

guys instead of typing I have made video to my question in this thread…
here is the link

http://www.youtube.com/watch?v=t06l05k0xWI
(the sound is a little low, sorry for that…)

Hope the video will add more clarity to what I posted above…!!

#5

I will try to scale down the whole set, avoid transform scale & work with default unit.
Fluid will work best with standard unit size.

In production I have scale down the mammoth size Sets to ant size & worked with standard size fluid. Sim it & cache it , later you can scale back to mammoth size to suit ur need. so if you work in bigger scale…increasing resolution will slow down the speed & you wont be able to go hires much to get finer details. hope it hepls !

Thanks,

  • Vik
#6

Alright…
So caching fluids and then scaling it to a bigger size, right (with transform scale)?

Will give it a shot…!!

#7

Yes , you can scale up with transform after cache :wink:

#8

JUST great, problem solved… VIK, you are great :beer: .

Here is a video to prove the solution Vik suggested :smiley: .

http://www.youtube.com/watch?feature=player_detailpage&v=b1Qd3uFKvWg

(no sound because my mic screwed up :sad:, so added Jake Lonergan instead :thumbsup: … )

#9

Normally when you want the same look but at a different scale then scaling up the fluid using its transform is the way to go… just avoid non-proportional scaling as this will make the apparent transparency different viewing down different axis. The size attribute on the fluid is more for extending the bounds of the fluid container… when you want to reveal more of the fluid.

However one thing to be aware of is that the default emitter for the fluid (omni) uses a worldspace distance and also the dropoff is in worldspace. Thus it appears to emit less when you scale the fluid big. To compensate lower the emitter fluid dropoff and increase the maxDistance(this is the radius of emission for the omni emitter). If you use a volume fluid emitter you don’t need to compensate because the size of the volume will also get scaled up and the dropoff by default is relative to the size of the volume emitter (normalized dropoff attribute) where the emission fades to zero at the volume bounds.

#10

Great.

But Duncan, caching and then scaling? Isn’t it safer?
So I heard that scaling fluids to a huge grid gives so many artifacts

Sorry Duncan, I am drifting a little from the topic here, but here goes;

someone told me that to get a smooth looking smoke use particles. I did it, but I get streaks instead of smooth smoke… I mean my particles are emitting forwards and in the beginning I am getting these weird streaks before the fluid merges seamlessly :frowning:

Any tip to achieve a fast moving fluid like this (YouTube link below), which becomes slow gradually like a exhaust from a motor bike or car with bad engine?
I tried using Volume axis field with 500 as its magnitude, but it I get one straight line of fluid and not spreading, the Diffusion is not happening.

Getting a good sim is really tough

http://www.youtube.com/watch?feature=player_detailpage&v=rnwj4Mq_RlU

#11

I don’t know if this will work but…
Maybe your container is oriented with y axis up (the default orientation) and you are pushing the fluid sideways with the volume axis field. Instead of that, to emit the smoke side ways (like in the youtube like you provided) rotate the container so its y axis is pointing in the x axis of the world. Create a cylindrical emitter, add emitter turbulence and change its speed method to add or replace and increase its along axis value. Add some damp in the fluid container and and maybe put the gradient force value under content details > density> gradient force to a negative number like -5 or -10 which should create a little bit of a repelling force.
Maybe not increasing the bouyancy is a good idea. Keep it at default value so the fluid can slowdown and have some time to spread. The speed should come from the emitter (speed method to add or replace) or by an applied volume axis field.
Add swirl and try increasing your solver quality which will make it more incompressible but default value of 20 might work.

If you wanna use particle then don’t let them shoot into the container too far or they will leave a streaking effect behind as they emit fluid. Have particles be in one place and where they quickly die and get born and then emit fluids from them. But remember to rotate the container sideways.

Also try using temperature turbulence which should get the fluid turbulent enough to spread out like you want.

I’m not testing fluids while I’m writing this so not sure if these solutions will have any effect but I hope it helps. :slight_smile:

#12

Yes i always rotate my container to where I want to emit.

I will try using cylinder emitter :slight_smile: . Thanks …
I didn’t not understand what you wrote about particles though…!! :surprised

#13

I assumed you are emitting particles inside the container and using them to emit the fluid. I just wanted to say that use a particle volume emitter without any speed (no around axis, no along axis, etc) so the particles stay in the place they are born. Give them a low lifespan so they get born and die quickly but they stay in the same place. And use them to emit fluids instead of the particles that are moving forward because moving particles that are emitting fluid will naturally leave a fluid trail behind unless the dissipation is high.

#14

Thnx for elaborating Parv, appreciate it.

Actually I was going for a look like this http://www.youtube.com/watch?feature=player_detailpage&v=2sU7VJ3Oqp0

When I talked to him, he said the fluid is emitted from particles.
Kinda confused now, if the particles don’t move forwards how will they give a lush fluid effect, isn’t it like emitting from a fluid emitter then?

#15

By all means use particles but for an effect like that don’t have the particles linger too long. Have them die off quickly.
I did a test using the nParticles with low lifespan and I was able to achieve a similar effect: http://vimeo.com/37482697

Here the particles are emitting density and temperature with temperature having a high dissipation and incandescence is mapped to temperature. There is also some inherit velocity being used under the fluid emitter speed method (which was set to add).

This can be made using a simple emitter or a surface emitter but shooting particles in a container for long is usually suited for effects like flame throwers, explosions, water falls etc… Again, there is no rule so approach the effect however you like.:slight_smile:

But by utilizing use per point emission rates check box under the fluid emitter node you can have a particle with any amount of lifespan and decide at what point during its life it emits fluid. However that wasn’t so necessary in this case.

#16

that was neat test Parv.

This might sound stupid, But why do people use particle to emit fluids?! I mean, any specific reason?!

#17

Check these two fluid water falls out. One is done using particle emission and other is using liquid simulation feature and no particles.

With particles:http://area.autodesk.com/blogs/duncan/waterfall_using_fluids_and_nparticles

No particles: http://vimeo.com/33100900

Waterfalls, flame throwers, tornadoes, dust hits, etc can be done using particle emission but its not always necessary. I guess it depends o the look you are going for but emitting from particles does give a more natural and random look. Again, it depends on the effect. You probably will not use it on something as calm as a candle flame.

Particle emission also extends the range of effects you can produce with fluids like if you want the fluid to take the shape of an object then you can use particle goal to attract some particles to that object and use those particles to emit fluid. With a high enough dissipation and other tweaks you can make it look like the fluid flows into the shape of an object.

Particle emission is just another technique that you have in your tool box that can help you with your fluid sims. Check this link out which shows some new features of Maya 2011. There you will find example of fluid emission with particles. Definitely worth looking at.

http://area.autodesk.com/blogs/duncan/some_fun_stuff_in_maya2011

:slight_smile:

#18

Great.

Thank You so much Parv

#19

There was a bug with cached playback of scaled up fluids with “keep voxels square” set off. As well there could be problems with rendering for extreme scales. However both of these problems would still exist if you cached first.

Typically the problem that confuses people is that the emission max distance and dropoff (for emitter types other than “volume”) is defined in world space, so these values need to be adjusted when scaling the fluid up. There might be other issues at really extreme scales, but I’m not aware of them.

For fast moving fluids in your example I would use a stationary volume emitter that emits both density and speed, using the “replace” speed emission. This will avoid a buildup of velocity over time. An auto resize fluid might be useful, but make sure the boundaries are all none and set the auto resize margin to 1 or 2 so it can expand quickly. Also substeps of 2 or more will help… the higher the resolution the more substeps needed for high speed. Also enable emit in substeps( this works well for a stationary emitter, but for fast moving emitters turn this off and use motion streak instead ).

Duncan

#20

For a fast moving fluid, here is an example scene that roughly matches that gunshot reference.

#21

Thanks for the info and scene file Duncan! : )

#22

I will try that out Duncan…

THANX A TON as always…!! :bowdown:

#23

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