Ocean Waves using Flip

[Guest frostbite]

Hi guys,

So I recently dived into flip fluids inside Houdini. Currently I am doing this small personal project to get an understanding around Flip pipeline in Houdini. And I am stuck. So I'd figure I will ask you people.

Anyway, the problem that I seem to have is that I have a flip tank and I am generating a simulation inside with some pump and custom velocity field. I have done the white water sims as well. Everything is working fine except that I want an ocean waves underneath and then this flip simulation on the top. Otherwise the whole scene doesn't look like an ocean which is my agenda here. Check this project by Graham Mathew (

). He has a base layer of ocean which I am pretty sure is a part of flip simulation and on the top of that he is doing this crazy simulation with running motor boats.

Now after digging around and asking the expert Igor on this topic, I have come to known that the best way to do this is to compute the velocity of the ocean surface and scatter points and then use those points as a field force in DOPs. I have tried connecting a field force and sop geo together but it doesn't seem to work.

Any help or any scene files explaining the process on the same would be greatly appreciated. I have attached a flipbook of my scene.

Cheers,

frost

pump_flip.rar

[teratera]

Is that possible that you want quite the opposite, i.e. ocean deformer on top of your FLIP sim? That's what I believe we're seeing in your reference.

If so, here are some tips:

a) After meshing stage isolate fluid top plane by a box bound (much easier to handle and when shading too). You probably seen that elsewhere, just try Delete SOP.

Try blending your ocean deform with your sim by velocity magnitude (vector length) mask.

c) Try PolyStitch to merge with bigger ocean plane. You could also try to flatten areas near the edge in your sim for better merging (VOP SOP).

d) Use different deformers for different detail levels. You can use some noise masking to breakup tiling. You can also use Ocean Deformer on rendertime, for that volume sample in shader.

However if pumping up velocities into the sim is the case, then yes, you can use Field Force DOP (just search forums, there been some examples), or you can use Source Volume DOP taking the velocity volume of the deformer or even using the Pump tool from the shelf.

Edited September 21, 2013 by teratera

[Guest frostbite]

Thanks for your reply. Nope I don't want the opposite. The reason for this is because using flip even for ocean simulation gives correct results when the pump simulation is done on the top of that.

I have been trying to search the threads that explains the process of using field force in such cases but no luck. Any links to the thread that you might know? I would really appreciate it. Thanks!

[teratera]

Here you can check the file, I took a scene from Solitude with a cool setup masking velocity field above surface (not to affect your splashes) and added same setup but using field force, if you're curious.

http://forums.odforc...ous-wave-motion

oceanwaves_to_flip_h125.hipnc

Edited September 21, 2013 by teratera

[Guest frostbite]

Oh man thank you so much for this setup. That solves my problem. I have a couple of doubts though.

So you have a plane geometry which is there as a result of ocean specturum/evaluate nodes and then you are masking that with the actual flip surface? So this means that the size of the waves and the plane is gonna be directly proportional to the size of the waves in the flip tank? If yes then I understood this setup very correctly. I really appreciate your help.

Also I was trying this a different way as well. So what if I compute the velocity of the ocean surface in SOPs using a trail sop and then add scatter points over it and then use those points as a field force in DOPs? Now this is not my idea but I have heard that this setup is pretty fast. Any ideas on that? In the meantime I am trying this setup of yours which solves my purpouse as well. Thanks again!

[teratera]

This is a basic setup that you get when you use Wave Tank shelf tool, you only pump velocities into FLIP explicitly.

Yes you can sample velocities from geometry, but since you'll have to stamp a volume from those points anyway, that doesn't make much sense because Ocean Evaluate already makes this velocity volumes for you. You just use them.

Btw, you won't need to use Trail anyway, there's a Point velocity checkbox which adds v to your preview grid.