New to Houdini here.

I'm melting a cube that is floating in the air as a sphere used as a temperature source passes through it, but when the simulation starts the cube falls down due to gravity. I want it to stay in the air, except for the parts that are melting. So I was thinking I would set gravity's Activate property to 1 if a particle's temperature is higher than 0, and then check if then for those particles clamp the activation to 1 so it stays affected by gravity even if it was to cool down afterwards.

This way I should have a floating cube, and the parts that melt fall as they melt.

Except I have really no idea how to go about the expression. I have looked at some tutorials on expression, but it's still rather unclear to me

Thanks

The gravity force can affect a group so you may want to take that approach. Migrate particles to the gravity group based upon temperature. Sorry I don't have an exact expression or setup for you.

Check out the example files under the help card of the PopObject. There are quite a few examples that show how to manipulate popstreams (stream essentially are groups).

Thanks Enivob, Grouping sounds like a good idea. I'll be going through the example files.

if you send me a scene file i can modify it to make it work..

Hello Patar,

I added the scene, hopefully you can open it.

I tried groups, since streams don't work with flipfluid object, but it didn't workout. I'm not able to figure out where to put the group (after the solver I assume?) nor how to write the expression properly to get the resulting group desired, etc. I tried putting @temperature >0 in the group expression, but it always returns 0 since I presume it only checks for the temperature at the start, not every frame.

Here is my attempt at trying to solve this. I used a PopWrangle to add particles to the group “hot” when the temperature is over 0.38, however, even though the group is created, the Gravity node can not detect that the group exists?

When I specify the hot group manually in the gravity node nothing moves.

Maybe someone at SideFX can look into this. I thought this was supposed to work…?

Hi this is the fix
the first couple of frame the unaffected by gravity is also going downward this is due to cohesion with the affected particles if you dont want this you can use ballistic attribute to ignore it theres a switch1 built in
play with it…
hopes it helps

Best regards
Patar

Thanks for posting that fix. This is a nice example file on the technique.

Thank you Patar, it works nice!