I was getting really slow simulations that were using practically no cpu power and I only had the domain set to a resolution of 100. 200 would take an hour plus for a simple sim. Long story short, I have blender set to 15 fps by default. This causes the sims to take extra steps I'm assuming because my renders come out different when set to 60 fps.
I didn't see this in any documenting.
Anyway I just tested this with the blender scene and it went from 8 minute render to 3 minutes but the results are different. Just figured I should post this because it would save a lot of noobs time if they have a scene set to a different frame rate by default.
Hi, changes in accuracy of the simulation can affect the result. Factors that change the accuracy are frame-rate/substeps and domain resolution.
This is due to the nature of how physics calculations are computed and is something to keep in mind when working with this simulator and also other physics simulation systems in general. Simulation physics are computed sequentially where the next simulation step relies on data of the previous simulation step. Small changes in accuracy can produce a different result that increasingly affects the future computed steps as the simulation continues to run. More information on this can be found in this topic: Scene Troubleshooting > Fluid behaviour changes when increasing resolution.
As for performance, smaller simulations may not be able to take advantage of the entire processing power of the CPU. It can also be possible that running too many threads can result in extra overhead that increases simulation baking time compared to running a lower number of threads. For more information on how the simulator uses the CPU, see this topic: FAQ > My CPU is running under 100% usage while simulating. Is this normal?
And for tips on optimizing the simulation for performance, see this topic: Scene Troubleshooting > Simulation baking is taking too long to compute!
Hope this info helps!
I might have added too much info to the post. My main reasoning for posting was so you maybe want to document fps in the faq or how to videos. It's something people can easily overlook and wonder why their sims aren't functioning right or taking too long. I was getting wacky results and was scratching my head wondering why.
Thanks for the suggestion! I can see that it can be difficult to locate this information in the documentation and that some information is missing.
I have updated the documentation to make this info easier to find and have added some extra related topics on settings that can cause other side effects. I'll link in the topics here so others can find the related topics:
- Added scene troubleshooting topic: Fluid behaviour changes when changing Frame Rate, Speed, or Substeps
- Added Domain > Simulation > Resolution Side Effects topic to simulation settings documentation
- Added Domain > Simulation > Frame Rate and Time Settings Side Effects topic to simulation settings documentation
- Added Domain > Advanced > Substep Side Effects topic to advanced settings documentation
- Added Domain > Whitewater > Side effects that affect whitewater emission topic where increases in simulation substeps can result in less whitewater being generated
- Added Domain > World > Viscosity > Side effects that affect viscosity topic where increase in simulation accuracy can result in more viscosity experience
- Added Domain > World > Sheeting Effects > Side effects that affect sheeting topic where an increase in simulation substeps can result in a higher sheeting strength experienced
- Added Domain > World > Boundary Friction > Side effects that affect friction topic where an increase in simulation substeps can result in a higher friction experienced
- Added note to Domain > World > Surface Tension settings documentation where changes in surface tension can result in a change in required substeps which in turn can affect simulation results
