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 BaiLong02-20-2009, 04:35 PMHey, I'm a complete newbie to particles and dynamics and want to blow up dust from the ground, when a helicopter is landing. I couldn't find a thread or online tutorial fitting my needs. So if you know one, please just redirect me. Sorry, I don't have any reference material to make it more visual but maybe someone can post a link... :) Otherwise I could need some help with this. I already played a bit with the some particle attributes and I got it working that the particles are emitted from a circle and with a little twist in them. But that's it. Would be great if you can tell me if I am on the right way or would be fluids better? What shapes should I use and most important how to shade them right? What parameters do I have to change so everything behaves correctly? I guess I need some fields, but I don't know which kind and how many. A step by step description would be really awesome but I would be thankful for any kind of help! ^^ Thanks in Advance! --Markus
TheNeverman
02-20-2009, 07:13 PM
Did mine with a 2d fluid container... easy-to-make swirl action - though big hit on rendertime. Particles would prolly be more efficient (if speed is a concern).

Aikiman
02-20-2009, 08:51 PM
Fluids are a good idea for this because they create the velocity swirl that is harder to reproduce with particle expressions or a number of different fields. That isnt to say it is not possible to do with those, just a lot harder IMO. AFAIK there are two solutions for this. One is to just use a 3D fluid with a setFluidAttr on density to place a whole lot of density on the bottom plane and to set initial state on it. Then attach a motion field or some sort of field to your helicopter that will blow the density around as it gets close. This means your density and velocity grids need to be dynamic. The other method could be to use particles with a volume shader on it and control the particles with a fluid. This would give you much the same effect as the first method if you lay a grid of particles on the ground and attach the fluid as a field to the particles. Generally the particle conserve has to be close to zero to be effective.

BaiLong
02-22-2009, 04:51 PM

@Neverman: Looks great, but (I've no idea about these things) I don't know if 2D Fluids work for me, because rendertime is a concern and also I want a closeup of the landing and so of the dust, to make it more dramatical. But if you would say 2D or 3D doesn't matter (because I don't want to move the camera that much while the landing, or if only with cuts), then please tell me how to do it. :)

@Aikiman: Both of your Ideas sound good, as far as I understood them but far beyond my understanding of particles and/or fluids. :)
Can you please give me more advises or a tutorial which goes in a comparable direction?

Cheers
--Markus

Aikiman
02-22-2009, 07:39 PM
Yeah I guess at the end of the day it depends on how realistic you want the effect. I was going for more realism than the stylised effect Neverman has used but I think maybe a combination of them both would enhance the effect even more. USing my methods dont give you the nice rolling effect of Nevermans but instead adds a lot of randomness which may be great for secondary detail. If you combine that with the rollling dust it may be what you are looking for. I can explain to you how to do both and if Neverman describes his method then maybe if his is better you can use that instead.

Let me start with just the secondary dust effect using just fluids. (in fact there are a ton of ways to do this but Ill just explain one). If you create a 3D container without an emitter to the size and resolution you need. You can go quite high cause you will be solving just density and velocity. Make sure both these grids are dynamic. Now in the script editor type this in...

setFluidAttr -at "density" -fv 4 -yi 0 fluid1;

This will give you a dust cover of density on the bottom of your fluid. Now set initial state on your fluid otherwise you'll lose it when you rewind. With the fluid selected choose a volume axis field and stick it right amongst the density layer and play. You should see some movement in the density. On the fluid get rid of the bouyency on the density and increase velocity swirl to 15. You can add a little turbulence as well say .1
That should get you going. You can play around with the fields magnitude and max distance settings to control the fluid and even change the field to find one that suits what you need. If you like you can animate the field moving down or parent it to your helicopter. You can also up the simulation rate on the fluid to speed up the sim if you want say 1.5 - 2.0 may be good.

Have a play! Ill explain the rolling effect later, since you may be happy with just this as it is.

BaiLong
02-22-2009, 11:19 PM
It doesn't have to be hyper realistic. A stylised look would be enough.

I still have some problems... it seems that the number of particles in the container increases over playtime. This means at first the volume axis field has an small effect but after about 150 frames I have a completely filled square and nothing happens anymore.
Also I wonder why everything moves upward even if I set the volume axis field to along axis -1. A gravity Field didn't work as well.

Could you tell me as well how to get particles driven by fluids? Because I figured out that rendering fluids with RenderMan isn't as easy as it is with particles. I would have to write some scripts and so as I read in some forums.

Have fun with the Academy Awards, from Germany. ;)

--Markus

Aikiman
02-23-2009, 12:37 AM
Increase the magnitude of your field to say 200 and see if that blasts your density to pieces, if so then work backwards until you find the correct mag. Also the reason why your container is filling up is that there is no dissipation on your density and that your container has boundaries on it so your density cant escape. Either add some dissipation or create a hole in your boundary, I would go with dissipation. Lastly like I mentioned, your density is moving up because it has bouyency, get rid of that.

Particles > Fluids.

Create a nurbs plane smaller than your fluid and add a surface emitter emit 10,000 particles for 5 seconds with no speed so they stay where they emit. Connect particles with fluid via the Dynaimcs Relationship editor. Now set initial state on particles and rewind. Reduce emission back to zero or a very low number, its up to you. Now set particle conserve value to zero also. That should do it.

Another option instead of volume axis field is to use the Motion field under the fluids menu. You need to create a nurbs sphere, select it and the fluid then go and make a motion field. From there I animated the nurbs sphere down through the fluid and through the particles to get some nice movement.

BaiLong
02-23-2009, 03:43 AM
Now I can blast the fluids, but I can't get them to work properly.

I understand why they say Fluids are much harder to control, because when you do it like me you get more like an angry but confused blob instead of something acting like influenced by forces. ;)

I set boundarys from all to none except of Y in every combination,
Density and Velocity to Dynamic Grid
Buoyancy first to 0 now also negative values
velocity swirl = 15 to 0
turbulence strength = 1 and 0
the rest is all the default settings.

Volume axis field magnitude from 5 to 1000 in some steps.

Did I forget something you said?

This time it reacts like there is a whirlpool, or a boil but after 500 frames the container starts running empty.

Can you just post a file where I can compare the values? To save you some times and nerves. ;)

I start thinking that fluids isn't the right choice for my skills... :)

How would you shade the particles to look like a sandy dustcloud and not like smoke, spheres or dots?

Aikiman
02-23-2009, 05:46 AM
You kinda have bitten off more than you can chew, I should've made it a lot more simpler and stylistic like Nevermans example. Anyway...

Most likely your values are way too high..

I set boundarys from all to none except of Y in every combination,
I would leave them set to their default

Buoyancy first to 0 now also negative values
Leave at zero for now

velocity swirl = 15 to 0
Leave at 15

turbulence strength = 1 and 0
Make it 0.1

Volume axis field magnitude from 5 to 1000 in some steps.
Should work at 50 with max distance on

Turn on velocity draw to see your velocity vectors in yellow, they shouldnt be so big, just nice and small like my picture.

This is using multi-point particles so you can render them with motion blur if you like. I dont think introducing you to the cloudy shader is a good idea for now.

TheNeverman
02-23-2009, 02:29 PM
The pacing in my scene was fast enough I was able to cut several corners with the dust swirl - so you'll have to do some more testing on your side to see if this will work, but basically I just used a quick-and-dirty 2d fluid positioned near the ground with heavy gravity, a bit of viscosity - and an emitter attached to the bottom of the UFO so it would emit once the UFO was near the ground (and fluid container).

As Aikiman pointed out - definetly on the side of stylization than realism, but might get yah pointed in the right direction - (needs work on the shading side)

Here's a file you can play around with (http://www.freewebtown.com/n8skow/CGTalk/dustSwirl.mb.zip)

This work is also 3 years old (when I was just starting out with Maya Fluids), Aikiman's skills are definetly ahead of my own
=o)

Think I'm gonna have to play around with his method myself...

BaiLong
02-26-2009, 01:26 PM
Thank you both!

Now I have something to work with in a satisfying look.

Thanks a lot, you really helped me!

BillyTheKid123
03-02-2009, 06:33 PM
I've used the fluid particle interaction method before and it works great, the question I have is for rendertime do u need to cache the fluids, particles, or both?

copain
08-03-2009, 06:46 PM
Hey Markus, did you get it working for you?

-Nathan and Jeremy thanks guys just what I am looking for, will try this out.

thx steve

BaiLong
08-04-2009, 01:27 PM
Hey Steve,

yes I did. But because of my CPU power and the lack of time I just used particles emitting from a NURBS circle. It is by far not as cool and correct as the solutions by Aikiman and TheNeverman, but it was easy and straightforward.

Cheers
--Markus

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