New Features like Viscosity Diffusion and different Viscosities, Active Bodies

[themaxxer]

Hi there

I downloaded the newest Nightly and have some Questions about a few new Features. What exactly is Viscosity Diffusion? How can i add different Viscosities in one Phoenix Grid? I saw a Video about this. How does the Active Body work? Are there any Tutorials or can you describe hot these Features work?
Thanks in Advance.

Kind Regards David

[flipbook]

Viscosity diffusion the same as RGB diffusion in effect. The different viscosity values will mix together basically. Just set different viscosity values per emitter in the source helpers, as simple as that. Active bodyyou set in the phoenix object properties.. have a play. It's a bit unstable at the moment though.

[Guest]

Hi,

Emitters now have a Viscosity parameter. If you want different viscosities set different values for the different emitters. From Output rollout enable Viscosity Grid channel and Viscosity Particle system. Then in the Grid Texture select the Viscosity Channel. For Viscosity=1.0 you'll get white color and for 0.0 black color (for all other values would be shades of grey). If the Viscosity Diffusion is enabled then diffusion between different viscosities will occur. There's a Viscosity Preview so, you can watch how different viscosities blend (or not). Also, there's a parameter called Default Viscosity in Dynamics rollout. This works for Initial Fill up option or Initial Liquid Fill object property for example and will not override the emmiter's viscosity.

Active body feature is not so stable yet but you can do some tests. Create an object -->right click on it --> Phoenix FD object properties --> Check Active Body option. Set object mass and friction with the fluid. Note that the liquid has a density similar to the water ~ 1000 kg/m3 so, knowing the volume of the geometry will help for setting its mass.

We're developing these features now and in the near future we'll make some helpful materials for them too.

Cheers!

[ben_hamburg]

Uh...active bodies sound like something very exciting to finally find its way to phoenix...I did not even notice this when upgrading to the newest nightly...But either I am doing something wrong or you still need a while til this is production ready...
I am getting lots of weird flipovers and jiggling. I first thought it might bebecause of some mesh inconsistency, but it also seems to happen with a normal box.

But if this is NOT just work in progress on your side, here are a couple of things I am wondering, which you maybe can answer quicker than I can figure them out myself....

1. Do I just need to increase SPF for this?
2. Is scene scale affectin the active body feature somehow? In my test scene I have set a scene scale of 0.3 adn I am not sure if I have to adjust the mass accordingly for example...
3. How is mass supposed to work? Lets say i have a kajak that is roughly modeled in real world scale and I know how it weighs 80kg in real life...do I just put in 80kg in its active body mass box?
4. How is the center of mass calculated? Its not simply the pivot, right? So if I noticed you can override the center of mass, but putting the object to 0,0,0 coordinates I?d then have to put a helper where I think the center of mass should be and write down the coordinates of that helper, so I can put that in the override coordinates and then put the object back to its original place....seems a bit too complicated...
6. Will it be possible in the future to also use the active body feature on animated objects? Because I think one of the most frequent uses for this feature would be to use it to animate a boat/ship moving through the water, so it would be great if you could just animate a general direction and speed and let phoenix do the rest...but thats probably not possible...
7. Wohoo! Active bodies!

[nikola.bozhinov]

Hi,

The Active Bodies are all work in progress at the moment and they are far from being production ready. Yet from our tests it seems they can be quite usable for some simple animations with a little bit of parameter tweaking.

On your specific questions:

1. Yes in general you need more SPF when using Active Bodies to achieve stable simulation, than you would need on the same scene without them.
2. Yes, the scene scale affects the calculated size of the Active Bodies, as well as the general dynamic of the fluid. So you need to set the scene scale to a value, such that the simulator and the objects in it would have realistic dimensions. You can check the physical dimensions of the simulator in the grid rollout.
3. Yes, the mass is set in kilograms and you should set it according to the real world dimensions of your object. If you modify the scene scale you should take care modify the mass accordingly. Please have in mind that the volume (and the mass respectively) scales at a power of 3, so if you multiply the scene scale by 2, you will have to multiply the mass by 8.
4. The center of mass is calculated automatically during the voxelization. You can also offset it manually its coordinates are it he body's local space. Having visual aid for setting the center of mass is close to the top of our to-do list.

When setting the mass and especially the center of mass, you should bear in mind that most real life boats are not solid on the inside. On the contrary they are hollow and most of their weight is concentrated towards the bottom. However if those cavities are not explicitly modeled in the object you use for Active Body, the simulator will assume it is filled on the inside and has constant density across its volume and this often results in having the auto-calculated center of mass higher than the real one. This makes the boat more unstable. If the center of mass is offset from its real position too much, the simulation tends to explode really quickly.

6. Yes, it is possible to use animated objects for the Active Bodies right now. The movement of the original body will be used as a guidance for the clone created by the simulation and the fluid will push it too. However the movement is taken in relation to the simulation grid, so you can not set the boat to always move forward. You can set it to move along the x-axis for example and even if it gets rotated by the flow it will try to move sideways and continue along the x-axis. Having better control of that is in the to-do list as well.

Please understand that this feature is still under development and there are currently a lot of problems with it and can't tell you when they will be fixed. As any other feature under development, this can get worse before it gets up to quality.

If you manage to do anything exciting with the Active Bodies, please share it.

Have a nice time simulating!