Resim decrease smoke density and temperature

[LarsSonparsson]

I'm creating some explosion tests just to learn things.

I have a 60-300 million voxel adaptive sim that looks good. All channels needed for resim exported. Resim with default settings runs fine. I changed the amp.resolution to 0.5 which doubles the voxel count.

Example frame 37
New shape looks good, but smoke density is cut to half and temperature decreased from 1500 to 1100.

User or calculation error?

Using the latest version for Max 2019

[Svetlin.Nikolov]

Hey,

There are known differences when you are using more than 1 step per frame, or not using Multi-Pass conservation - does any of these two match?

Cheers!

[LarsSonparsson]

I'm using Multi-Pass and spf 3.

So can I do resim with only spf 1 or does it have to be the same as in original sim?

[Svetlin.Nikolov]

Ah, this is most likely the cause of the problem.

You need to simulate the original sim with SPF 1 as well. In case any settings differ between sim and resim, especially the ones under Dynamics, resimulation will be very different.

With many steps per frame the intermediate substeps are not written to the cache files, so the resimulation cannot use their velocity field and the result will be inaccurate.