mud and water simulation

[luis.alcala86]

Hello my super smart people, I had a small dilemma that I was presented at work. I currently have a fully modeled shoe that is meant to be used at the beach or a hike. My designer would love to see the shoe with some mud and then have an animation where water comes out of a hose, or offscreen, and starts to wash the mud off. Anyone have any suggestions or ideas on how this can be achieved? Been trying to find something out in the internets that would point me in the right direction but Im running into a wall. ANYTHING helps at this point and I am open to any ideas. Would really love to use Maya 2019 + Vray Next and Phoenix FD since thats what I have on hand.

[georgi.zhekov]

Hey,

Sounds like you will need variable viscosity. Here is a little test we made sometime ago - https://www.youtube.com/watch?v=oQBothHKOSM

So you will need two sources - one for the mud with high viscosity and one for the water with zero viscosity. Make sure to turn on the Viscosity checkbox for the grid and the particles in the Output rollout.
As the mud is sticky by nature - turn on the Wetting in the Liquid rollout and add some Sticky liquid.

The shading part is a bit tricky as you will need two shaders for a single liquid and you need the mud to be one color and the water part to be another. So you can use the RGB channel in your sources and then use a Phoenix Grid texture that reads this channel and uses it as a mask for a Blend material.
You can take a look how this works in this tutorial here - https://docs.chaosgroup.com/display/...+and+Chocolate

Hope this helps!

Cheers!

[luis.alcala86]

Georgi,

Ma man. This is exactly what I was looking for. Is there, maybe, a sample scene with this setup that can be shared so I can use it as a guide for my scene?

[georgi.zhekov]

Here you go

[luis.alcala86]

Thanks a bunch man. Going to open this up as soon as I get home and take a look at it. You guys are awesome.

[luis.alcala86]

Finally got some time to look at this and everything else. Going to start the process on using this scene and the tutorial to start working on mine. Hopefully I can continue to get some assistance to help in this matter. Do you think it would be possible to have your assistance with this setup if I provided you with the asset I am looking to accomplish this look for?

[Svetlin.Nikolov]

Hey,

Generally it would be great to help direct you with the right settings and reference scenes, so you can get up to speed yourself

[luis.alcala86]

cool. I understand. So another question for you. How can I limit the liquid to come out of just a face on the emitter I am using? I am trying to disect the scene that Georgi sent out and he has the liquid only coming out of the bottom face of the cylinder. I tried using discharge modifiers on this scene im working on but cant get it to work.

[luis.alcala86]

NVMD, got that part down. Going to keep working on this. Thanks fellas

[Svetlin.Nikolov]

Yup, either discharge modifiers using the geometry nitmals, or the Polygon ID option of the source, or you can mask the discharge with vertex color

[luis.alcala86]

Well I think I'm getting this down but I am having an issue. I managed to get the mud to stick to the shoe and the water emitter to sim the liquid like I want it. When simulating the mud and the water interaction I can see how the water pushes the mud around. The problem is that when I hit render I can see the shoe and mud but the water is not visible.

While looking at the simulation and rendering I can see that the water sim disappears while rendering but comes back after the render is finished. Any ideas on this? I might have setup the vrayblend mat the wrong way.

[georgi.zhekov]

Can you try and switch the places of the mud and the water materials in the Blend material? Probably you got them the other way around.

[luis.alcala86]

Hello Georgi,

I will give that a try man. On my way to the office. I'll post an update after i do some testing.

[luis.alcala86]

Welp this is where I am so far. I managed to get the water and stand-in mud shader to show up with Georgi's help. I did not swap the materials in the VrayBlend, instead I ticked the invert box inside of the Phoenix FD Texture under effects and the liquids started mixing like the help file that you guys sent out. My next questions would be:

1. How can I make the mud on the shoe not look like its sliding/ evaporating before the water comes into contact with it? Before the water comes into frame it looks as if the "mud" is moving, as if it was reacting to a noise or something.

2. The viscocity of the liquid looks a little weird. What would be a recommended value for mud and water? I am assuming I just cant use the viscosity slider in the Grid since that would affect both liquids. As the mud sits on the surface I want to feel thick and heavy but as the water comes in contact with it, it should start loosening up and mixing with the water, right?


Mud_Water_Mix.zip

Any other suggestions and I am all up for them. Thank you all again for the assistance on this. Everyone has been really helpful and I enjoy the knowledge.

[georgi.zhekov]

Hey,

For the sliding of the mud - you will need to make the mud sticky from the Liquid rollout. Play around with the sticky liquid option to find out the right one for you.
The other things that are important are the grid resolution and the steps per frame. From the video it looks like your grid resolution is a bit low so you can try and increase it, though this will make the effect of the viscosity weaker.
You can counter that by increase the scene scale or adding more steps per frame - where increasing the scene scale will change the behavior of the liquid while adding more steps will increase the simulation time so it's a good idea to balance these out.

For the weird viscosity - you can specify the viscosity for the mud and the water in the Liquid sources separately. Take a look at the example scene I have sent you - the mud source has more viscosity while the water one has its viscosity set to 0.
In order to blend the viscosities when they get in contact with each other you can introduce some Viscosity Diffusion (you can find it in the Liquid rollout of the simulator) - a low value will preserve the distinct viscosities, while a high value will allow them to mix together and produce a fluid with a uniform thickness.