Can someone please explain these settings?

[beenyweenies]

I've gone through the manual and done quite a bit of testing, and these items are still unclear to me:

- Grid Unit Scale - Assuming my scene is built to scale, when I create a simulator from scratch, is there any reason I should not just set Unit Scale to 1, with Cell Size being the primary control for sim resolution?

- Simulate Air Effects - Does this ONLY impact the sim if Splash/Mist is enabled? Since it's in the main Liquid section, I'm not sure if it's impacting standard liquids as well.

- Surface Tension - the manual suggests this is crucial to sense of scale for liquid sims, but provides no practical example. Is there a formula that can be leveraged? For example, if my scene is built to real world scale, cm units, table-top sized simulations, how do I set this for realistic water?


Thanks in advance, LOVING PhoenixFD so far!

[georgi.zhekov]

Hey,

For the Grid Unit Scale - you can stick to 1 and if you need to adjust the scale of your simulation you can do that from the "Scene scale" in the Dynamics tab. Mind that the Grid Resolution (how many cells there are in your simulator) and the Scene scale are different things. The first one will control resolution while the second one will affect the behavior of the sim.

- Simulate Air Effects - yes this will affect only the splash/mist particles.

- Surface Tension - for water you can stick to the default value and you should be good.

[beenyweenies]

Thanks for the help! With regard to surface tension, the default value is 0. Would that value be increased for larger scale sims? When does it come into play?

[flipbook]

Come into play for small scale sims and things like paint splats etc

[georgi.zhekov]

If you are doing water - 0 will be good in large scales as well. If you go for something like paint, you can increase the value. It all depends on the look you are after.

If you are using the nightlies (if you don't have access send a mail to support@chaosgroup.com) we have made some improvements to the way the surface tension works.

Strength - Controls the force produced by the curvature of the liquid surface. This affects the elasticity of the liquid surface, which allows the liquid to retain its typically spherical shape. When an external force overwhelms the surface tension strength, the liquid will burst or spread to form droplets or tendrils depending on the Droplet Breakup parameter. As a result, lower values will cause the liquid to form droplets or tendrils easier; higher values will prevent the liquid from breaking apart.

Droplet Breakup - Balances between the liquid forming tendrils or droplets. When set to a value of 0, the liquid forms long tendrils. When set to a value of 1, the liquid breaks up into separate droplets.

Droplet Radius - Controls the radius of the droplets formed by the Droplet Breakup parameter.

[beenyweenies]

These improvements sound promising, I've contacted support for access.

I would like to go back to Grid Unit Scale if possible. The preset Tap Water sets both the Unit Scale and Cell Size according to the size of the emitter. If I double the size of the emitting object, the Unit Scale halves and the Cell Size doubles. Why is it handled this way, rather than leaving Unit Scale at 1 and only adjusting Cell Size as we've discussed here?

I'm just trying to understand why I might ever adjust Units Scale when the scene scale has not changed.

[georgi.zhekov]

The tap water and the rest of the presets are made this way so no matter what size your object is 10 cm or 1000 cm you should get pretty much the same result. Not everyone is building their scenes to the right scale and we wanted to have consistent results for most of the users.

[beenyweenies]

Thanks a lot for all the help!