Changing Simulation Speed/Frame Rate

Hi - is there a way to change the speed of a simulation without changing its overall evolution and appearance?

When changing the Timestep in the Simulation-Time Control settings, often the simulation itself changes drastically. For example, the volcano preset (009-Volcano.ember) doesn’t create a massive explosion cloud when the Timestep is changed from 60 to 960.

The appearance I am after is something more like filming the simulation at a higher frame so that it can be slowed down in post production.

I’m guessing changing the Timestep doesn’t work as it impacts all the evolutions that happen per second so I’m hoping its possible at the Render or Camera stage but I can’t see anything related to time in those nodes.

Or is Timestep the only way to do this meaning that other parameters will then need to also be scaled accordingly?

No way to do this yet. We have plans for retiming in our big update early next year. I’d not recommend using timescale as it breaks everything you had. If you want a faster sim, do it in post. If you want a slower sim, use optical flow in post.

Thanks for your reply, that’s good to know - I’ll look into the post methods for now.

Do you think it would be possible (with enough knowledge how the physics of EmberGen simulations work) to build a super slow sim from the ground up? That is - start with a much larger timestep and scale all the variables based on that from the outset?

Does that require expert level physics knowledge or is it just not possible because of how the underlying equations work?

Just an update to this question. I tried the optical flow methods and for complex simulations like fire, the estimation algorithm doesn’t work nearly as well as adjusting the timestep which really does produce the look of high frame rate photography.

In some sims, it’s possible to tweak the settings to re-create something like its original appearance so it seems technically possible but once the timestep goes paste 240, they generally break.

Are there any further resources to study to help get a sense of how to build simulations from the ground up?

The documentation is great but it I’m wondering whether its essential to study the underlying physics in order to produce new custom simulations from scratch.

So the problem with adjusting timestep is that it introduces significant issues with the simulation and you often will not get much detail at all.

As for resources for building simulations from scratch, you can either watch some of the live streams on our youtube channel where I do things live, or just mess with the settings in the simulation node.

Want the smoke/fire to raise faster? Use buoyancy. Need heavy smoke? Increase the smoke weight. Want fuel to burn faster? Increase oxygen amount, maybe reduce smoke production, and increase fuel consumption.

Honestly, best learning resource besides our live streams is just playing with parameters. The great thing about EmberGen is that it instantly responds to inputs.

Thanks for your reply Nick. I’ve been going through the live streams and they’ve been very helpful

One suggestion though - the live streams seem to cover alot of different tutorial info but in no particular order and without a way to know what content is in what stream. I’m currently having to keep a separate document with timestamps grouped into content areas.

It would be great if the streamed tutorials could focus on single topics for longer in a such a way that they really that cover specific content area in depth in a single video. For example - a video that just looks at how to get the best results for a certain kind of simulation (e.g. fire explosions). Watching the streams, it always feels like there is a huge chunk of information left out as it’s always a quick summary of a particular preset or technique.

Perhaps a walk through of building some of the more complicated presets from the ground up would help us understand what we need to in order get better at building our own custom sims.

Just a suggestion.

Thanks again.

I have plans for a serious tutorial series vs having people rely on live streams like they do now. Live streams are typically for going over new features and how to use them. We haven’t done a serious string of tutorials due to us knowing the UI was going to change drastically throughout the beta. After January, you’ll see our in-depth series of tutorials start to come out.