Advice for making paint flow down a wall

[ubernaut21]

Hi fellow Houdini masters.

I'm still quite new to doing fluid sims in Houdini.
I am trying to create an effect of paint-like fluid flowing down a wall, colliding with a bottle and then continue flowing off the edge. I've set up a simple set up with shelf tools and controlling the emitter velocity with simple VEX.

So the desired effect is to have the fluid flowing down the entire wall smoothly with a curvy edge, collide and fills up around the bottle, and then continue flowing off the edge and down. The surface has to remain thin, smooth and complete with no holes, similar to pouring paint down a wall.

However, here are the problems i faced with my simulation. I've attached the flipbooks below too.
1) The fluid is too thick. I tried scaling the scene from small (<1m) to big (around 2m) and it still looks the same. The fluid gets really really thick when it reaches the bottom. I was thinking that increasing the scene scale would make the liquid thinner but seems like that doesnt do the trick.
2) After the fluid collides with the bottle, I can't seem to force the fluid to go around the bottle and fill back up. I've tried using a pop attractor but the results look unnatural.
3) For some reason, even though my wall volume collider guides look smooth, the fluid doesnt flow down the wall smoothly and seems to bounce off the surface.
4) Even stranger, when the fluid reaches halfway down, they start to float above the collider surface. This is very apparent in the side view flipbook. I thought it was some collision volume offset, but it was set to 0. And in other areas, the fluid was nicely touching the surface. Totally got me confused here!

I've attached the hip file (with stickynotes annotations) and flipbooks of where I'm stuck at. Would be so grateful if I can get some tips of how I could achieve this effect. In my mind, I thought it was a relatively simple set up where I can just make a collider and emit viscous fluid down and let it simulate and flow down without changing so many settings. But damn its difficult.. =(

 

Thanks!

Wall Flow V01.zip

cascadeFall_side.mp4

cascadeFall_front.mp4

[zjie]

Same I need help with this as well, somehow the liquid is just too thick and I couldn't control it no matter what attribute I adjust.

[kleer001]

From what I understand you want the fluid to reconnect into a coherent stream after colliding with the bottle. This is actually counter to the behavior of the viscosity. Viscosity is basically the fluid trying to move the same as its neighbor. The higher the viscosity the less each point in the sim wants to spread out. And you want some spread. And unless you put in some additional forces to make it flow around the bottle it's never going to happen. Also it looks like your collision object of the wall and floor could use some additional definition. Try upping the divisions to 120 or so until the blue collision preview geo matches more closely to your poly geo.

Here are some things to help make it look like you want: (mix and match at will)

1) Put the bottle in a little divot, in a little downward bump for the fluid to fill up as it goes around. A little smooth cup under the bottle with a wide downward slope. Maybe an extra radius around on each side and as deep as twice to four times your particle separation.

2) Put the whole shelf on a downward angle going down to the back where the wall is. Just one degree or less. Make sure you have enough definition in your collision object.

3) Make an advection field around your bottle. This is probably one of the trickier solutions and might look odd and require a bit of fussyness. It's more of an advanced trick.

4) Radically reduce your viscosity. You can thicken up the fluid later when you're surfacing or turn down gravity if it's flowing too fast.