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Creating Drag Force Or Pump Object With Falloff Around The Edges Of FL


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Hey guys,

I am current working on a water explosion effect/large splash, below is a video of where it is currently at:


I pretty happy with the way it is looking at the moment, but as you can see it is hitting the edge of the container. Instead of re-sizing the container what I am wanting to do is kill/reduce the velocities as they get closer to the edge of the container and I want it to fade down over a specific area. I can kill off the velocities in a certain area using a pump object which multiplies the velocities it interacts with by 0 therefore resulting in a velocity of 0. However this happens very abruptly (as soon as it hits the edge of the pump object). So what I'm wondering is, is there any way to add a falloff to a pump object or drag force's effective areas?


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try a sop solver that compares the velocity of the fluid agains a threshold and when its to high multiplies it by 0.5 or something like that.

What you can also do is great a second gravity controlled by a field and set it over the water... lets say that the second gravity starts at 5 meters over the water.

That way the water that rises to far will slow down and fall down faster.

Both of those methods together should bring you closer to the result you want.

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you can do this with different methods, attribute transfer, using point clouds or with a SDF to get the threshold from the borders.

I create a simple scene for you with the first method mentioned. Take a look at it. The method is simply to create a bounding box the same size as your container and scatter points on it. Therafter you can use an attribute tranfer node inside a sopsolver within DOPs to transfer the attributes you want from the bounding box to the fluid particles. Soing so you can tweak the blend amount(in the attr transfer node) and so on to get the smothness you want. Afterwards you need to create an vopsop and multiply the velocity with the color attribute (since I painted the points based on the velocity I wanted them to get)

I hope this helps. The method is a bit slow to compute (with huge amount of particles) since the vel-attribute transfer is on the particle level and not on the voxel level. To change the vel in the voxel-level you would need to play around with fields intead. But this is much easier to get :)

See attatched hipnc-file


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Sure thing mate! If I were you I would definitely create a larger box for that fluid sim of yours since it is kind of wild. If you don't create a larger box the damping velocity method won't work very well. You will see that your particles will almost create a small wave on the smooth blend corner. Where the velocity starts to get damped. Well, good luck!

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Yeah, the more I re-watch the sim the more I think I need to extend it a lot haha, looks like that is going to be a sim for the weekend then. Just been experimenting with your sop solver method in a separate test scene and I have managed to get it working really well for what I was after, so thanks again for that, really helpful!

Edited by Neo222
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