Viscous Flip Travelling on Geometry

[csp]

http://www.artofthetitle.com/title/the-girl-with-the-dragon-tattoo/

at 0:20 you can see for few seconds the liquid flowing on the surface, any ideas how to approach this kind of effect?

What comes in my mind is that probably it will need to scatter points on the surface and direct their velocity to specific direction (for -x to x) and adding some noise to that. But how can I still keep the natural flowing motion of that kind of liquid?

[Skybar]

Have you tried just pouring it? Combined with the carvings on the colliding geo it will probably take you quite far already.

[csp]

will the actual shot that I am working on is a bit more complex from that reference. I am afraid that can't cheat it.

the first test with method I described above, transferring velocity from the surface to the particles seems to work, but it needs more work. If anyone has any tips please do not hesitate.

Edited August 7, 2013 by cparliaros

[Hudson]

I would definitelly go for transfering vel from a surface to the attributes method. You could do that with VDB as well. See the attached hip-file I created for doing it with the volume from atrr and the VDB-method in this topic as an introduction:

http://forums.odforc...ibute-for-flip/

Once you have set it up you could also apply a density to your field by colouring it in SOPS or chnage the vel. So I would go for that method.

If the case is that your geometry is too complex so it would take time for you to create a surface on it I would go for this method to create the surface and vel:

1.Paint(example red) the faces oin your geometry you would like your fluid to have as a path. delete the non-painted faces

2.The tricky part is to make the vel- follow the surfaces into a direction. You could do that calculating the cross product of the point normals and a direction where you want your fluid to head to. In my example(Attached) it is towards the y-axis in other words towards the sky. In this part you could create a point cloud for diferent directions you would like your fluid to head and create a vector from the origin of the fluid and where it shoud head depending on the point clouds. This is if you don't want all of your fluid to go towards one direction

3. extrude those faces and transfer vel attribute so it matches the ones in the step 2)

4. in to DoPs as a vel field

5. to control the fluid even further, normalize the vel in step 2) (as in my example) and multiply it by a painted color on the surface of your geometry

I really hope this will help you out!

PS* I don't have houdini 12.5 at home so I can't really test my scene using VDB. Altough you have the velocity on the geometries in this one. And when I did it at work it worked by transfering the vel-attr using a VDB solution instead of volume from attribute.

Good luck

VDB_for_fluid_follow_path.hipnc

[csp]

Thanks for the reply Hudson, tomorrow at work I will try to implement your ideas and the hip files. The vdb sounds very intersting - I am using it already for collisions.

[Hudson]

Alright! Feel free to post quick questions tomorrow during the day. I am doing some simulations with a lot of different iterations at work so I might have some time over to take a look at it. But I think you got the main concept and I tried to explain the difficult parts in the hip as well

[csp]

Good morning, I will come back with questions later today. Iterations... you mean on meshing? I did that yesterday

[Hudson]

I hope it went well.

I meant different iterations of one simulation to meet up with the art-director's request. It is a destruction sim as well so quite tricky

[csp]

vdb works quite well but is not that interesting, I would like the leading particles more "exotic" motion as on the reference of the film. I am working on that...

[Hudson]

You could use the vel from vdb as a base simulation and add more detail and controll to the fluid(or less control) with different methods. Create a velocity field using vdb or volumes will create a quite uniform motion on the fluid. Altough I think it is a good start and easy to change afterwards.

Btw, between 0:20 and 0:26 seconds in the clip you have shared has five different shots and I would not do all of them in the same way. If you are just loking to do one of those point it out. If you want to do all of those with one simulation or tool it might take some time to set it up.

You will require a bit of imagination as well. Like combining vel-fields, using the shape of your geometry to affect the particles.

An example could be to add a different velocity to the leading particles. That could be easily done if your geometry has a quite uniform shape. You could compare the distance between all particles and the goal of the fluid and affect the leading ones. You could do that in a SOP-solver using a vopsop and point clouds. You could probably do that using fields as well but I am not sure how to

Your imagination and time will set the limits on what you could do