Force field repel

[nquire]

Hi,

I find much success with forum. I search, but could not find topic similar so I post for ideas. I am trying to work on proof of concept force field that repels volumes, ie fire mainly. The fire will need to almost interact with force field but go around it in a manner that is dispersed. Any idea how to achieve? A work partner just use static sphere with flames hitting it, but does not give interesting look. I appreciate any assit. Thank you.

N

[outtacontex]

For sake of simplicity, you could just try using a metaball/magnet force around the geometry used for your force field. A positive value on the magnet force pulls the volume in towards it and a negative value repels. It would be cool, like in your first reference image, to be able to dictate where exactly you want the most repulsion to occur at. Custom VOPs force anyone? I'll give it a go.

[JuriBryan]

here is a two minute set up showing the principal that I would use to make such a shot work.

I am using an animated sphere with a noise pattern to break up the collision geo for the fire in Dops.

I feed it into dops not as an RBD (way to slow with animated geo) but as a collision volume (very fast, at least here).

This also allows me to easily define some curl noise velocity on the volume to break the motion up even further (you can also "paint/direct" the vel in what ever direction you want since you are using sops)

Thats what I would be using for the simulation, its fast and gives a lot of control. for extra little tweaks I would go with magnet forces... and not with the vop force they seam to be very slow.

Also a lot of the effects that you posted here ( everyone besides the fire shot) don't look like full sims to me, but rather like shaders (Spheres with displacement maps and so on).

Hope that helps you a bit,

Cheers,

Juri

FireForceField.hipnc

[nquire]

Thanks for replies,

outtacontex,

I try your method and it seems very simple using metaball magnet force. Breaks up organically, but my case user want full control over direction of repulsed flames and where they stop at. So far I have piped in custom vel from sops to dops and use a vop force to apply impulse vel/repulse force. I just need figure out a way to kind o stick and deform volume around surface of force field.....like creep sop functionality.

JuriBryan,

Thank you. I will look at scene shortly. I had a polygon sphere with mountain sop attached and offset by $T to give fluid like movement to force field. I turn off diffuse, minimal refl and high refraction for the force field it self with other minor tweak. The shading looks good. I did not think to try actual fluids for it, simple, clean but dirty if necessary to get job done fast. I do not like to over complicated things, only when necessary. You make good points about collsion volume. Check back with you soon.

Thank you again.

[nquire]

JuriByran,

I download your scene. I like it. Very simple and fast approach. Gives me good idea to try. I will randomize temperature values on surface of collision geo as well. This should give interesting feel too. Any way you know to deform flame around shape of geo?

[JuriBryan]

yeah, randomizing heat and temperature fields will help you as well!

Try some vorticles in the end:)

Here is a quick example showing one of many many methods to create custom velocity fields on the collision geo.

You could also bring it in as a nother source volume or feed such a volume into micro solvers, but this is the fast way:)

Hope you see the advantage:)

Cheers,

Juri

PS:on the dop that brings in the collision geo is a velocity slide... change that for more extreme/less effects

FireForceField.hipnc

[nquire]

JuriBryan,

Just want to update you. I just turn in proof of concept to client and they like it, say it feels good. I ended up just using two magnet forces, one scale down inside sphere (forcefield) and one scale up outside sphere. Outer one has negative value, inner one has positive value and I ramp both scales in chops with noise. I did not have much time to test what I wanted to do.

Now, I have to expose force field only in area where the flames collide. Is there a way to use the volume collision data and group that area and delete non select. I've done this on regular geo, but no for volumes.

[JuriBryan]

I would use an attribute transfer to get a bit more of an organic look to it.

Here are two ways, the first using the collision volumes (problem it is always represented when it is inside of the container so it is expanding when your container expands and not when your flames hit it.

The second version is using advected particles to colour the force field geo.

Cheers,

Juri

FireForceField.hipnc

[mawi]

Havent tried it but you might get a cool result from using the new "gas stick on collision DOP".

Default it creates a tangent and a normal force based on collision and collisionvel. If you set a high Normal stickyness and 0 tangent the flames should "lick" around your object almost like a flip solve...

It can also take a maskfield for the effect...

Edit...

A fast file...

And you need Houdini 12.5.425 or later...

stickOnColl.hip

Edited June 18, 2013 by mawi

[nquire]

Thank you Juri and mawi,

I will check both later today. But serious can not thank you enough. gas stick on collision DOP sounds exact like what I was going to attempt in gas field vop, but that node slow down entire scene by itself! I have more time for rnd now, so will build asset.