swirling particles

[tony]

Hi.

I was just wondering if anyone could point me in the direction of a good method to get particles to swirl. I want them to swirl up from the ground into a kind of funnel shape. Its for some smoke i am making and I want to get some nice swirling movement into it as it looks bit static at the moment. I'm using the thick smoke fx tool as my starting point and changing its pops network to get the shape i want from it.

So far i've tried:

- An orbit force - This just seems to make them go into a circle and I can't seem to get them to funnel because they stick to strongly to the circle.

- An attractor force with a rotating sphere and passing the particles through it - Doesn't seem to get enough swirling movement into them.

- Applying a particle SOP after the POP network and then using a force SOP and metaball combination using its vortex force. This seems to kind of work, but makes the renders take ages and makes all of the metaballs, that the thick smoke tool copies onto the particles, really small (obviously the metaball size is not a major problem as I can just make them bigger, but then i lose the part where the metaballs grow in size as they get older which was working quite nicely for my probject).

- Putting the particles into dops and using the vortex force - I kind of adapted the example in the help, but couldn't really get this to work properly.

I am wondering about the avenue of advecting by volumes but haven't had the chance to pursue that yet. I have also looked at the 3d buzz tornado tutorial, but that seems to be using the particle SOP and not a POP network so i think that this is kind of like the solution in the third bullet point and would run into the same problems.

I would really appreciate any help on the situation.

Thanks

Tony

[brianburke]

Hi tony. One way to get particles to swirl in a non-orbit-pop way is to use a VOP POP. You can subtract the positions of each particle by a point to get a vector that points from the particles to the center point. Then you can use the transform matrix to rotate this vector by 90 degrees or so to have them point in a circular way, you can the normalize these vectors and set them to velocity, or add them to the existing velocity (with some drag probably).

Hopefully this makes sense, I'll post a .hip file when I have Houdini in front of me later today.

[brianburke]

Here's a .hip of swirling particles along the ground.

You could add vertical velocity to the spiraling area to build a funnel in the air.

Hopefully this helps at all.

brn_swirl.hip