PHX object scale and simulation time/accuracy

[noxxsan]

https://youtu.be/wJVV_xZfIKY?list=PL...KfMvSRrQ&t=171

The video author increased the keyboard to size 4mts, he says using real life scale can skyrocket simulation times if you want a certain amount of accuracy

Is that true? Should i always scale up all the models in my scenes for better phoenixfd efficiency?

[Svetlin.Nikolov]

Hey,

Using real life scale is the way to go if you want to get realistic results.

Simulation times are affected mostly by the grid resolution. The more voxels you have, the slower the simulation, even if the grid dimensions are the same. The more Steps Per Frame you have, the slower the simulation. And for fire/smoke sims - the more Conservation Quality, the slower the simulation, but the more realistic.

If you increase the Scene Scale option of Phoenix in order to cheat the world scale of the sim, this will mostly affect the gravity - everything will start moving more slowly - liquids will drop more slowly, fire and smoke will rise more slowly. When the fluid moves through the grid more slowly, you don't need as many steps per frame as for a faster fluid, so you can speed up sim times, but this will be a completely different simulation nonetheless. Here I've summarized the basics of Phoenix fluid sims and there are more details about Steps per Frame, advection and conservation: https://docs.chaosgroup.com/pages/vi...imulationwork? The later parts of this section are outdated, but the "How Does Phoenix's fluid simulation work?" section described what happens in Phoenix sims currently.

Hope this helps!

[noxxsan]

Yes, thank you for the clarification.