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LukeLetellier

Velocity Flickering in Viscous Fluid

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I have a vat of viscous fluid in which nothing should occur. For the first 24 frames it slowly settles, as one would expect. Then on frame ~25 the particle velocities start to flicker like mad: on/off, on/off - like a lightening storm. I have no idea what's causing it to happen. 

https://www.dropbox.com/s/u39mfmboaqqizeg/ViscousFluid.hiplc?dl=0

A more complex version of this file has spheres pushing up from the bottom of the fluid (acting as bubbles). This causes even more erratic flickering, as you can see the video clip linked to below -  but the core problem is present in the above scene file.

https://www.dropbox.com/s/61j4g1fphrhtv6h/ViscousFlicker_01.mp4?dl=0

Any idea why this is happening?

 

Thanks!

Luke

Edited by LukeLetellier

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1. Posted scene doesn't work (missing emitter from alembic and incomplete asset definition WELD). If you expect someone's help try to check scene before you post, to be sure it will work properly on other computers.

 

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I re-downloaded the file, and things are still working fine over here even in a different directory. While the emitter did reference an alembic at one point, the object merge node is locked - so no other files should be needed.

I'm not sure why you're having an incomplete asset issue - as I just used the generic Houdini weld node. Perhaps you're using a different build? I'm on H15 Indie 416.

 

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H 15.0.423.

I see locked ObjectMerge node which reports (1 points, 1 primitives, 1 vertices, 1 packed alembic) with WARNING: Geometry contains degenerate primitives.

Next node Unpack reports (0 points, 0 primitives, 0 vertices)

Such LOCK obviously keeps only path to alembic not the geometry data. Try export your geometry to file, then load it using File node and then use LOCK. Such LOCK will work.

EDIT:

You probably changed original asset WELD to LL_WELD1 and saved it to type library and not to hip file. So instance of your LL_WELD1 (in scene LL_WELD) tries to find it's original definition (LL_WELD1) which is stored to your local type library.

Edited by djiki

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Thank you for your time! I'm learning more each day.

Good catch on the weld. I see now that when a digital asset appears in a node list, it's listed by the Label. But once you place the node in your scene, the node's name becomes the operator name (rather than the label its listed under). When creating assets in the future I'll have to ensure that my Labels & operator names are identical so that I don't repeat this mistake again when sharing files. 

I exported the geometry to file & included it in within the Zip file attached to post to ensure it gets transferred (it's merged into the scene, but not locked).

Out of curiosity, I kept the original locked & unpack node in the scene but detached from the data flow - as I'd like to see if anyone else has issues with it or not. I removed the path to the alembic file just to be sure it was working as I thought it was, and used that locked node (with a blank obj path) to generate the geometry file that's in the zip file. Just seems strange that its working on two different systems over here, but not on yours. So if anyone else can replicate it either way to provide another data point, that'd be swell. 

Thanks again!

ViscousFluid.zip

MiddleClick.jpg

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On 4/18/2016 at 8:43 PM, LukeLetellier said:

I have a vat of viscous fluid in which nothing should occur. For the first 24 frames it slowly settles, as one would expect. Then on frame ~25 the particle velocities start to flicker like mad: on/off, on/off - like a lightening storm. I have no idea what's causing it to happen. 

 

Sadly it's almost certainly due to your GasSurfaceTension node.  I only tried the .zip file above, but with surface tension disabled it's completely stable.  The GasSurfaceTension node adds an explicit force on the fluid and is fairly unstable at high Surface Tension values and low substeps.  The workarounds are generally to use a lower Surface Tension setting (0.1 was still stable in your test file) or use more FLIP Min Substeps if you really need the high Surface Tension.

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Hi, sorry, so how do i get this file to run if i download the zip?

I opened the file in Houdini but I have no idea how to initialize it with the accompanying geo?

 

thanks

Nigel.

 

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11 hours ago, johner said:

Sadly it's almost certainly due to your GasSurfaceTension node.  I only tried the .zip file above, but with surface tension disabled it's completely stable.  The GasSurfaceTension node adds an explicit force on the fluid and is fairly unstable at high Surface Tension values and low substeps.  The workarounds are generally to use a lower Surface Tension setting (0.1 was still stable in your test file) or use more FLIP Min Substeps if you really need the high Surface Tension.

Very good to know about the instability of the Surface tension node. Thank you for your help!

 

Quote

 

Hi, sorry, so how do i get this file to run if i download the zip?

I opened the file in Houdini but I have no idea how to initialize it with the accompanying geo?

Hey Nigel,

Once its unzipped, you should be able to simply double-click on the HIP file to have things working right off the bat. The Geo Setup node is currently activated, and in there I've created by emitter geometry & the geometry for the fluid container. The three nodes to the right (Source_particles, AutoDopNetwork, Fluid_Meshing) are where the fluid sim resides. Turn off visibility for the Geo_setup node, and turn on visibility for the AutoDopNetwork, and you should be good to go.

Edited by LukeLetellier

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