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quinton

Best practices and tips for fluid and ice in glass

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Hi guys,

I'm started on a H16 sim where I have a cup of ice and fluid and another piece of ice that will dive in and float back up (animated).  

I've almost always dealt with larger water sims and don't have much Houdini experience with small scale sims  

I figured some people here have experience with such simulations and would like to ask if there are any best practices and tips here? I have some questions myself  

1. How important is it to try to simulate and keep everything to scale for rbd and flip sims of this sort?

I have found in my initial bullet tests that just trying to fill the glass with ice at scale tends to give me exploding rbd sims. In this case, I had the ice cubes and glass modeled in maya. When I brought it into Houdini I scaled it down by 100x to match the meter scale in Houdini. I tried adjusting the collision padding to stabilize the sim but to no avail. I had no issues when I worked at 100x scale. I'm curious if anyone else has experienced this?

However, not working to scale meant that my flip sims feel larger in scale, like a swimming pool and not a cup. Increasing gravity 3x has helped the sim look more to scale. But that seems very arbitrary to me. I'm more inclined to work at a bigger scale as adjusting to smaller scales have given me all kinds of problems from unstable rbd sims to leaking water particles and decreasing water levels.

2. Is flip the the recommended approach for these fluid sims? I've seen sph being recommended. But honestly, I don't even know where the sph tools are 'hidden' these days in Houdini. And I know these days SideFX recommends flip for everything.

3. What is the best way to get some of the ice to interact with the water sim? Via density and flip solver feedback or the bouyancy force dop node?

4. Any tips on dealing with collisions and keeping things water tight in a thin lip glass that still needs water to splash out of the glass? When testing, I often found that it was very easy to leak fluid from the container even though my flip collision guide shows that there isn't any holes in glass collision.

5. Any tips in meshing the fluid with regards to lighting and rendering? I've seen it recommended that the water geometry be slightly larger then the glass. How are folks doing that with flip sims? 

I'll try posting an example file whenever I get to a good point. I really would like to benefit from the experience of folks who have done this sort of sim.

Thanks in advance. 

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