Small Scale Flip Sims are Unstable

[HappehLemons]

Looking for some help on this one, also been getting conflicting information.

I hear from a lot of people to scale up small scales sims and adjust the settings to "fake" them being small because Houdini doesn't handle small scale sims well.

I've also been told that later versions of Houdini DO handle them well, and you should always work in the proper scale.

Well I'm trying very hard to work within the proper scale, but it seems I always run into issues. Truthfully, I should be going even smaller then this, but I can't even get this scale to work (Shown below)

My example is crude, but in practice the scale should be relevant to pouring chocolate on a strawberry. I want to do this in scale if possible, but it seems like not only is the sim very very slow, but it becomes very unstable. Here's my example:

Scene File:

Small Scale Flip.hipnc

Settings:

Particle Separation: 0.001

Substeps: 10

Can someone point me into the right direction of not only speeding the sim up, but getting it to work more accurately at very small scales?

 

 

Edited September 22, 2018 by HappehLemons

[Atom]

One of the most important concepts when working with FLIP is the bounding box area. That is what particle separation is dividing. You'll want to keep that as close to your collision space as possible.

flip_sphere_drip.mp4

You can activate the RED BOX handles by selecting the FLIP Solver, then move your mouse into ther 3D viewport and press the ENTER key. Press SPACE-G to frame the large box in the viewport. Make sure your fluid emitter exists within the red box.

 

Then your fluid sim will run much better and at a higher quality using less memory.

ap_Small Scale Flip.hipnc

Edited September 22, 2018 by Atom

[HappehLemons]

2 hours ago, Atom said:

One of the most important concepts when working with FLIP is the bounding box area. That is what particle separation is dividing. You'll want to keep that as close to your collision space as possible.

flip_sphere_drip.mp4

You can activate the RED BOX handles by selecting the FLIP Solver, then move your mouse into ther 3D viewport and press the ENTER key. Press SPACE-G to frame the large box in the viewport. Make sure your fluid emitter exists within the red box.

 

Then your fluid sim will run much better and at a higher quality using less memory.

 

ap_Small Scale Flip.hipnc

 

So, this is very helpful, but still leaves me with some questions. Scaling down the bounding box sped up by sim by 2x. A huge improvement. 

 

However, the bugs still persist with meshing instability (Although the particles stopped escaping when bringing down the grid scale), I matched your setting, (but kept the viscosity high). See here below.

Also I noticed you changed a few settings. Could you explain why? What is the logic behind changing the Grid Scale to 1, and enabling the Closed Boundaries option. I also see something called "Voxel Estimate" why is that now an option in your scene, it's not something I see at all in my scene. Also you adjusted the Reseeding settings. I understand that'll get you a better looking mesh at a much lower cost, but what's the idea behind the Particles Per Voxel vs the Surface Oversampling. How do you determine the balance between the two? 

From what I've gathered, Grid Scale and Particle Radius Scale (You didn't touch this one though) are just multipliers for Particle Separation and should be generally left alone. Is that not correct?  

 

Thank you, sorry for all the questions. Really trying to get this down.

 

 

Edited September 22, 2018 by HappehLemons

[Atom]

Try unchecking Limit Bandwidth on the fluidcompress node. That should help remove those long horizontal bars.

I created the Voxel Estimate value as a way to know what the current particle separation vs box area size will produce in voxel count. If you left click on the label "Voxel Estimate" you can see the expression.

Edited September 22, 2018 by Atom

[HappehLemons]

55 minutes ago, Atom said:

Try unchecking Limit Bandwidth on the fluidcompress node. That should help remove those long horizontal bars.

I created the Voxel Estimate value as a way to know what the current particle separation vs box area size will produce in voxel count. If you left click on the label "Voxel Estimate" you can see the expression.

heyyy now that fixed it! You're truly an expert. Thanks for the help, it means a lot.