Hey,

I've got a question about the FLIP solver, especially with a high resolution. When I decrease the particle separation to a certain level the collisions stop working properly. But thats not the only problem. The bigger one is that the fluid itself starts to behave strange. For example the FLIP fluid just starts to fly away in the air slowly. I tried to increase substeps, adjustet the collision separation but nothing helps here. So even with high res sims everything fits in the memory but the solver starts to produce stupid results.

Is there a way to make sure it works properly, maby some special settings?

Thanks!

The first thing that comes to mind is scale. What scale are you trying to simulate? Can you post the problem HIP file?

Its about 40 meter. I merged a flip mesh with an ocean surface. But its strange, because it works when I delete the old dop network and create a complete new one. Its a lot of work because I introduceda lot of nodes and expressions….Otherwise there is no way to get it run properly again. Maby a bug.

Well, there is always something wrong with this file. Not enough I have to rebuild the netword, now only the particles on the left side of the boat interact properly with the geometry

I'll just post the scene file, maby you see whats wrong there

In the geometry folder “Boat” you just have to replace the file with something else and it'll run through the network. A longish cube for example.

Some colliders require a higher resolution to construct the correct collision volume than the base sim.

On the Flip Object DOP, you need to enable the “Collision Separation” parameter and set it to a proper resolution to construct the FLIP collider correctly.

To see the FLIP collider, on the FLIP Object DOP enable the Collision option on to see the collider that the FLIP solver is actually using.

Note that you may have to temporarily turn off the display of the Collider geometry in DOPs and turn off display other objects in the viewport to see the FLIP collider.

Note that if the Collision geometry is outside of the FLIP tank, it won't be constructed in the FLIP object and you won't see it. You may have to play forward to see the FLIP collider as it enters the FLIP container.

Hey, thanks for your replie but I already played around with the collision separation. That doesn't seem to help here. When I'm not convinced with the result and try to resimulate the whole flip thing suddenly the uv transfer doesn't work. Its a really strange situation here, always something new. It works again when I rebuild it..

I have had that happen as well. Rebuild a scene and the problem is no longer there.

Problem is that I have to rebuild it again and again when I want an iteration. Its annoying. I add a viewport capture so you can see whats happpening there. The flip solver makes absolutely no sence.

I would say it is related to the fact that the ship is instantly in collision with the fluid. Try animating the ship into the FLIP area, from outside the FLIP area,then set the whole thing in motion.

There may be some information here as well.
https://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=37761&highlight= [sidefx.com]

I wonder about two things

- almost all problems of this kind I've ever encountered come down to unsuitable geometry being used for the collision object. FLIP absolutely hates complex geometry with thin elements and especially any holes. Holes will cause explosions… anywhere in the mesh, no matter how minor.
The simplest way to avoid those issues is to skip using your main model as a collider altogether, and rebuild a very simple collision proxy to use in its place. The chunkier the better, and make absolutely certain it's a fully enclosed mesh, no holes, no lamina faces, etc, etc.

- the other possibility is that you might simply be trying to make the ship move too fast. From your video clip, I presume it's supposed to be some form of large battleship/frigate, and that the scene is scaled accordingly.
It moves its entire length in 5 seconds… which for, say, a 150m-long frigate, would mean it's traveling 30m/s - that's up there with high performance offshore powerboat racing (/the legal speed limit on UK motorways), and well, them powerboats tend to kick up some spray! :-)
I realise the speed may just be for aesthetic appeal, but FLIP fluids really don't care about creative license - they freak out if you try to break the laws of physics too much.

Hey,

I came up with that solution too. Insteat of using the geometry I switched to volume based collision detection and blew ithe volume up a little bit.
I can make some iterations now without having to rebuild the whole thing.

But strange that Houdini was willing to work properly at first but stopped its support for further iterations.

Now it looks something like this:

If you furthermore have some good tips for good looking foam, I'll take them!