Hello!

im new to Houdini and im stumbling upon a few basics here from time to time.
Which brings me to my topic “TIME”. (smooth transition i know :wink: )

I have a Flip simulation with a basic Lava simulation.
I added a heat object into the sim. So far so good, everything works fine.
BUT when i change the FPS from 24 to 50 via global animation options, the heat object will simply quit to affect my simulation.
Any suggestions?!

Cheers

Lukas

Don't change the FPS, change the TimeScale of the simulation located on the FLIP solver node.

If you double your FPS you will double the number of frames you have to simulate and finally render.

Thanks for your reply Enivob.
The thing is that my production framerate is 50 fps.
So i have to double the number of the frames.

Has anyone experience with higher framerates inside simulation in Houdini?

Cheers

Lukas

Well if you are messing with the FPS and want everything to stay the same you need to avoid using anything referencing frames, like $F, $SF, @Frame etc and you need to use @T, @ST for referencing time instead. That way your expressions will stay the same no matter what the FPS is.
I'd start by looking and converting all these over before you adjust your FPS. but other than that I think Houdini should be pretty robust when changing FPS… not that i have tried!!!

Thanks for your reply. I didn't use any of those expressions.
I only used shelf tools to build up this setup.
if you take a look at my scene file, u can see that the heat object is affecting my particles.
if you then change the FPS via global animation options, the heat object stops affecting the particles. Even if you just increase it from 24 to 25 FPS.

What works is to change the framerate from 24 to 48 and then bisect the Timescale inside the FLIP solver, which is by default set to 1.
But when I change the FPS to 50 and set the Timescale to 0,48 it stops working.

I do not understand this.

Thank you

Thanks for your reply. I didn't use any of those expressions.
I only used shelf tools to build up this setup.
if you take a look at my scene file, u can see that the heat object is affecting my particles.
if you then change the FPS via global animation options, the heat object stops affecting the particles. Even if you just increase it from 24 to 25 FPS.

What works is to change the framerate from 24 to 48 and then bisect the Timescale inside the FLIP solver, which is by default set to 1.
But when I change the FPS to 50 and set the Timescale to 0,48 it stops working.

I do not understand this.

Thank you

Ok, looks like there is a bug in the heatingvolume1 node. If you allow editing, go into the popvop1 and look at the mulconst1 node, it is hard coded to multiply the timeInc by 24… change it to 50 and it works when you are at 50fps.

By the way DONT change the Timescale when you change the FPS. time scale is based on seconds, not frames, so you dont need to update this. If you look onyour AutoDop at the Time Step you will notice it update correctly when you change the FPS

Thanks Jordan,

That did the trick! Super awesome.
I owe you one!

Cheers Lukas

Ok, so I was wrong, it not a bug, its actually that the Increase Range should only be set to a value from 0-1. Setting it to 3 broke the maths (as it uses a power function that needs a 0-1 to be correct). Doing what I said above will give you very different results.

What you want to change is your Output Range to add more temperature, so set that to 0-3 and put the Increase Rate back to something more useful, like 0.9

The real bug is that the top level parameter is supposed to be clamped 0..1. So when it is set to 10, it is in undefined behaviour land. 1 means “instantly heat to target temperature” and will work whether you have 24 or 50 fps.

The hard-coded 24 is just to convert from seconds to artist-friendly ranges. It intentionally is NOT FPS because we don't want the simulation changing when FPS changes.