Frame Jump on continue simulation

Discussion
1

I’ve run into an issue and was curious if anyone else had the same problem or a solution for it.

I have a large burning ground plane emitting smoke… all in the Temperature channels.

If I stop the simulation and then hit continue later on … i get a slight jump in the simulation frames… so the playback looks like a frame has been missed. ( making it useless)

I don’t have velocity channel enabled … so i assumed that may be the issue… in that it doesn’t have the velocity data in memory to continue smoothly. - but wasn’t sure…
Anyone else ran into this problem?

Problem number 2… When i dramatically slow down a simulation using the timescale… the simulation becomes quite soft and looses the finer details before the slow down…
Anyone have nay thoughts on how to avoid that?

many thanks.

2

are you using and sub grid noise in the render settings? This is independent of the container time scale. I have only seen that issue when using SG Noise.

3

As to Q2 I do not think all the settings are actually in synch with the time scale settings… but I will leave it to Jascha to comment

5

If you stop the simulation as opposed to aborting it, the entire simulation state gets stored to the last_sim_state.bcf file regardless of the cache setting. This then allows continuing the simulation properly. The abort option is there because storing the full sim state takes some time, which can be annoying when you don’t need it.

With extreme time scale settings, the effect of some simulation operations can become weaker than the smoothing side-effect they may have. This depends on the specific configuration, though and cannot be generalized. I would recommend reducing the simulation to as few active operations and channels as possible to observe their effects under extreme time scale settings.

6

Having not heard back from Raoul I can only restate that the times I have seen this have been when I have used render time sub pixel noise that is animated and I have stop and then continued a render… Perhaps this could also have an effect on turbulence in the container settings ?

7

Hi and thanks for the thoughts Paul and Jascha… Apologies for my tardy reply…

So firstly. Running on Mac OS. T4D 1447. Cinema r19.

So for problem 1.
Im actually rendering in Octane. so no Sub pixel render time stuff. I can see the frame jumps even in straight hardware render / editor view.

Also im not aborting the sim… All I ever do is hit stop. never abort. So i’m assuming that isn’t the problem. it feels a bit like it picks back up the sim (when i hit continue) a frame later?

As to problem 2… The blurriness to the sim happens in most scenarios. i don’t have to change the time scale that dramatically… lts something like from 200% down to 50%, this will happen. You end up with very different characteristics. usually very smooth and all the fine/medium detail disappears.

Hard for me to know if its specific to my version/settings/hardware… or would be the same on all other computers.

anyway… any help you can give would be great.

8

Do you have a example scene with the issues we can test…if so does the issue #1 happen anywhere or on a specific frame ? v 1450 is the latest stable for MAC can you upgrade ?