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artcross
04-30-2010, 07:57 PM
Hello, I'm trying to create a wind tunnel effect that turns into a vortex. Basically i have to illustrate how an object sucks up air on top of it. I used the wind tunnel 3d example that comes with Maya and enables collisions on the object. That part works great. However, if I try to add a vortex field to simulate the object sucking up the smoke tracers, the simulation goes crazy. I know fluids can be unpredictable and admittedly I don't have much experience working with them, so I'm hoping someone can either suggest a solution, or an alternative. thanks! (I tried using particles, but can't get them to flow around the object like fluids do. I also tried having fluids drive particles, but again, when I add the vortex, the simulation becomes unpredictable).

Duncan
04-30-2010, 08:49 PM
The fluid attempts to solve for an incompressible air flow, so it can only move in certain ways( like real air ). The vortex field is a spinning simulation like a tornado. Perhaps you want more of a mushroom shaped vortex, in which case you could try using a volume axis field with a torus shape(use aroundAxis and make awayFromAxis zero). One needs to be careful when using fields with fluids as they tend to inject energy into the simulation (one could potentially combine a field with a matching bounded drag field to avoid buildup of energy). The field will try to push the fluid in a certain direction, but if that push does not satisfy the incompressibility of the flow the fluid will fight it.

At the risk of making a bad pun... you need to go with the flow.
Duncan

artcross
04-30-2010, 09:47 PM
many thanks Duncan, I tried doing just that, but I still can't get it to "swirl". it's almost as if the fluid is just avoiding the field rather than being affected by it (the tracer hits the volume axis field, then almost begins to move around the axis, but seems to break free of the force at the other end and continues in a straight line). I've played with the attenuation, even added the drag field like you suggested to sort of control the "conserve" of the fluid, but to no avail. I may just need a better grasp of fluids before I can make this work. The end effect i'm trying to go for is something like a whirlpool.

Duncan
04-30-2010, 09:53 PM
The tracers will tend to diffuse and break up as they go around a vortex. The high detail solve method combined with higher resolution simulations and some viscosity will help to hold tracer lines together.

You should enable display of the velocity arrows to see what your field is doing to the simulation.

Duncan

artcross
04-30-2010, 10:41 PM
thanks again Duncan! this may work after all...just need to spend a few hours tweaking settings and i think i might have something usable. Your advice is very much appreciate. Quick question, with the wind tunnel example, is there an easy way to manipulate the tracer emitters?

Duncan
04-30-2010, 10:44 PM
The tracers are just added by an expression. Under extra attributes you can set the number but you can't move them without editing the expression.

In Maya2011 one can construct a wind tunnel without an expression because the inflow - outflow can now be set with two emitters that emit speed using the replace method( instead of setAttr in the expression ). (one can't use fields because they continually add velocity rather than setting to a fixed value)

The tracers are just emission points and you can create your own by just simply adding emitters( to match the windTunnel tracers one can use the replace method for density, although for the tracers the add method is also usable ).

Duncan

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