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Changing Scale Time value changes simulation result -why?


art3mis

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Hi

Have a simple FLIP sim with a torus falling into a FLIP tank. I want to create my sim in 'slow motion' so have only reduced the Scale Time from 1.0 to 0.25.

But this ALSO changes the look of the splash. ie reduces the amount of splashed particles.

Why is this happening and how can I maintain the look of my fluid sim when slowing it down? Is there a better way of creating 'slow motion' fluid sims?

 

Scale Time 0.25

ScaleTime 1.0

 

Edited by eco_bach
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op here. Am replying with what I think is the correct answer so others may benefit. 

Scale Time IS NOT the same as Timescale. The latter is found on the actual flipsolver inside the DOP network while the former is on the DOP itself. Not sure if there are other things I should change.

 

 

Also Jeff Wagner briefly discusses alternatives in the webinar here

https://www.sidefx.com/tutorials/houdini-illume-webinar-flip-fluids/  starting at 2:08:30 though he just refers to the Time step or parameter.

And Atom (thanks Atom!) has a mini tutorial on creating Bullet time in a FLIP

 

Edited by eco_bach
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I have a short video on how to do a Bullet Time FLIP tank. One thing I noticed back in H14 was that not all the time scale parameters inside the FLIP HDA were actually linked to the channel one level up. This means if you try to animate the time scale things might not work as expected. This may have been fixed if a SideFX dev happened to watch my video, but I have not actually checked to see if it is fixed.

FLIP is not something you can play around with at a low resolution and then simply crank up some parameters and expect an exact replica of the low resolution version at hi-res. In my experience I have always had to choose a particle separation and time scale, at the start, as my target values and work from there.

Which is why FLIP work is the slowest possible effect for a beginner to start with.

 

 

Edited by Atom
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"Which is why FLIP work is the slowest possible effect for a beginner to start with."

 

Unfortunately I am just finding this out:(

Sometimes I feel I am playing whack a mole. I change one FLIP parameter, and another part of my sim doesn't work! Spent the entire weekend playing with initial velocity, feedback, buoyancy and timescale for a VERY simple FLIP sim, rendering out low res flipbbooks(over 100?) after changing just one parameter at a time. At least I learned to keep my particle separation consistent!

That's definitely a great tip, settling on particle separation and time scale at the beginning of any FLIP sim!

I have to figure out how to use slices for making quick FLIP fluid previews!

At least I am learning, or so I like to tell myself :)

Edited by eco_bach
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