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Exploding vellum grains

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Hi guys,

I'm currently trying to setup a test of vellum grains with loose sand and clumps falling from 1m down on a pighead-collider (grain size of around 0.001).  I did lots of tests already but can't manage to get a stable result where the clumps (more or less) keep together on impact. They stick together mid air, but as soon as they hit, explode and spread in numerous pieces. Scene and sim is according to realworld scale.

 

Settings I use are all default but:

 

Common-Tab:

Substeps 12

Constr. Iterations 2000 (That high since I was told it needs to be roughly the amount of grains you want to pile up, and having grains around 0.001 in size makes pretty huge stacks.)

Static Friction 0.75

Dyn. Friction 0.15

 

Advanced Tab:

Repulsion: 1500

Attraction weight 1 (weighted/multiplied with a point attribute (0 to 1 values) that defines loose sand and clumps based on a noise pattern.)

Attraction 100

 

It would be very cool if someone help me figure out why this is not working. Any hint or even a example-scene is much appreciated. Thanks in advance for your time!  

 

Edited by Scratch

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Hi Philipp ;)

Can you post your test scene?

Edit: Maybe try lowering the repulsion and attraction values as these can cause some high velocity values.

Edited by LucaScheller

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Hey Luca ;)

Thanks for your hints! Can't post the Hip-File unfortunaety since it's project based, and wasn't able to recreate it at home yet. But I got a somehow stable result now by lowering the constraint iterations to 1000, and lowering attraction to around 25. Repulsion is also critical as it seems and the default value of 10000 looks to be too high for some cases. Those settings will cause the clumps to break up on impact, but on second thought, when you drop wet sand from 1m onto a collider in the real world, it will inevitable break up on impact so it should be ok for now.

 

Edited by Scratch
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do you try to use a custom constraint with Vop and color for the clumps?

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Hey Matteo,

Atm, I only use the

attractionweight

point-attribute that is driven by a noise to control clumping with the built in attraction settings of the vellum solver (advanced tab).

 

Constraint-whise, I only have a

 vellum configure grains

in my network.

 

Edited by Scratch

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For constraint you can use an attribute cop between the vellum grain sop and constraint sop and setting inside one color with turbolance or voronio and export (bind) the constraint attribute. Then you can load it in the vellum constraint sop.

If I remember well you can find one example files inside the folder "help" in Houdini director on your system (e.g. in Windows under the program files->sidefx->etc...etc....).

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@matEvil: Thanks man! I will have a look at this!

@tamagochy: Also thanks to you! I tried that but it unfortunately leads to a lot of volume loss. But reducing it further from my initial settings did help a bit :)

I have a version now that I'm quite ok with, but I will continue testing on the side. Thanks to all of you!

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