Why the flip ocean wave so crazy?

[saotome_rui]

hi guys.

i a new user for houdini flip.

when i simulated a fluid about a boat in the river. the water wave is so crazy like the picture i uploaded.

And the boat animation was imported from 3dsmax by use FBX. it is a small boat and not very fast. the result looks like a surfboat in crazy ocean.

i always use naiad to simulate fluid. when i tried houdini flip. it's pretty fast.

the boat simulation is 500frames. simulation time just 1.5 hour. and the disk cache is about 78G.

i think it's a great tool.

so it will be great if anybody could give me a help.

[wateryfield]

Increase the smooth

Or add a drag force may help.

[JuriBryan]

also when the boat is already in the "water" when the sim starts the points inside of it will not know what to do so they kinda freak out.

just use a sopsolver and a group by geo and then a delete followed by a switch that only activates the deleting process on the first frame.

That way the sim has no points inside the collision geo and it should no longer freak out.

Also check the scale of everything. one unit==1 meter... lay down a box and scale it to the length of your boat and see if it is the length it should be... if not change it:)

[old school]

There are a few things you can do to tweak the water's reaction to your boat.

The first is to reduce the Velocity Scale on the Flip Solver's Volume Motion/Collisions tab. It defaults to 1 and min is 1 on the slider but you can set this to say 0.8 to 0.5 and the amount of wake after the boat and the amount of splashing will be reduced.

Another thing you can try is the Spatial Scale parameter as that scales a whole bunch of various internal parameters on the Flip Solver including the velocity scale. It works fairly well but in my quick internal test the Velocity Scale had a better effect of diminishing the amount of splashing.

Yet another thing you can try is the Transparency feature on the FLIP solver introduced in H12.5. The Transparency parameter also in the Collision tab a few down from the Velocity Scale is meant for objects skimming or slightly submerged in the fluid plowing along. Think of a submarine just skimming along with sheeting water over it. Transparency allows some of the velocity and particles to actually pass through the object thereby reducing the displacement and the energy. So yes with higher values of Transparency you will have some fluid leaking in to your collision object. You can remove these particles post sim quite easily.

In effect Transparency makes the FLIP sim a bit or a lot transparent to collision geometry.

The effect of Transparency is very effective in reducing the amount of energy moved in to the surrounding FLIP fluid. In my quick test of a boat skimming on the surface even a value of 0.1 for Transparency and leaving Velocity Scale and Spatial Scale at 1 worked very well at reducing the amount of wake after the boat.

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After my quick tests, I'd try a wee bit of Transparency first to reduce the splashes.

Btw to get bigger splashes, reverse what I said above about Velocity Scale and Spatial Scale.

[Hudson]

About what Juri meant here is an example file I did for another topic :http://forums.odforc...ssue-with-sink/

I had not seen this post before so wasn't sure if using a switch was the best method. But maybe it is.

Edited September 15, 2013 by Hudson