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Mael_P

[SOLVED] Determining a volumes max velocity

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Posted (edited)

Hello !

 

In order to setup my different Disturbances and Turbulences inside of a smoke simulation, I'd like to know what range of velocity I'm dealing with. How would you guys do that ?
If you have the proper method to do that just ignore what's under.


The sim is already cached (density, vel, rest, rest2).

What I'm doing for now :
When looking at the node info there is vel.x, vel.y and vel.z. I don't understand why but I've read that these are scalar values and has to do with how Houdini works so why not. I don't know how to inspect this volume further than that since it's a volume the Geometry Spreadsheet doesn't display anything.

And when I apply a VolumeSlice I get 10 different vel attributes per point. vel[4] matches vel[7], vel[5] matches vel[8] and vel[6] matches vel[9]. But not the rest of the values. This is very confusing to me.

image.thumb.png.ab1501299a468b9ead3e0c434aa581d7.png

Edited by Mael_P

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On the dop i/o, there is a compute min/max option. That will show you the max and min vel for each float of the vector.  I tried to figure out how to get the length of the velocity from that, and I didn't have much success BUT I did think of a potential work around. Since you can get the length of the velocity measured from points, you can use the volume to advect points, and ramp down how much vel is received on the popadvectbyvolume. As long as the points move with the smoke sim, you should be able to use those to get a max length of your velocity.

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- convert your velocity volume to VDB

- make sure it's a single vect3 VDB primitive (VDB Vector Merge SOP)

- convert to speed float VDB (VDB Analysis SOP: Length)

- compute Minimum or Maximum or other and store in Prim attrib or Detail or ... (Volume Reduce SOP)

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