Slowing down sim while keeping original characteristics?

[dgould]

So I've got my simulation looking exactly as I want at Time Scale = 1.0. I'd now like to slow the whole sim down to 25% for a smooth slomo explosion.

I tried to two different approaches:

a) When I set Time Scale = 0.25 and run the sim again it looks completely different from the Time Scale = 1.0 version.
b) I left Time Scale = 1.0 and changed the Input | Play Speed to 0.25. I tried both Blend Methods but both times got smoke rather than the fireball. It also caused Maya to slow up significantly.

Any suggestions on slowing down a sim while keeping its original characteristics?

Thanks.

[Ivaylo Katev]

i suppose the first method failed because the SPF is reaching some of the limits, upper or lower. be sure that the SPF remains unlimited, or force it to value that is changed with the timescale. for example if you run simulation with ficed SPF=3, to slow it down four times (scale 0.25) you have to force the SPF value to 3*0.25=0.75

[dgould]

How do you set a fixed SPF?

I currently have:

Time Scale = 1.0
Maximal Step = 6.0
SPF Upper Limit = 0.25
SPF Lower Limit = 0.1

For example if I want the sim to run at half speed I tried the following scenarios:

a) Time Scale = 0.5. The simulation comes out much more puffy/smoother. Much of the fine detail is lost and the characteristics are quite different.
b)

Time Scale = 0.5 (halved)
Maximal Step = 6.0 (original)
SPF Upper Limit = 0.125 = 0.25 * 0.5 (halved)
SPF Lower Limit = 0.05 = 0.1 * 0.5 (halved)

The result is very similar to scenario A. The sim is much less detailed and "puffy"

c)

Time Scale = 1.0 (original)
Maximal Step = 3.0 = 6.0 *0.5 (halved)
SPF Upper Limit = 0.125 = 0.25 * 0.5 (halved)
SPF Lower Limit = 0.05 = 0.1 * 0.5 (halved)

This produces a more pleasing result though the sim doesn't full expand as it does in the original version. It expands then stops just burning in place rather than continuing to expand.

d) Leaving the original sim settings I also tried using the Input | Play Speed set to 0.5. The intraframe interpolation doesn't produce a very good result. In fact it either repeats a given frame twice or interpolates between two frames but the result is a lot lighter than the surround frames. When you render out a sequence and play it back the results are two identical frames, an interpolated but lighter frame, another two identical frames, and so on.

Any further suggestions would be greatly appreciated.

Thanks.

[Ivaylo Katev]

the fixed SPF mode is when the lower and upper SPF are equal.
well, obviously the SPF and advection adjustment is the most complicated part in phoenix. we have to rework this, but for now just keep the lower and upper limits equal and set the maximal step=100.
if you have problems with the stability , just decrease the vorticity.