ageing reseeded particles in flip sim

[dayvbrown]

Hi guys,

 

I have a slow moving flip sim (think a fluid expanding on a surface... like blood pooling) and to get a nice stable edge i'm using the reseeding function in the flip solver. I'm having to retime the sim after the fact (yay!) and whilst i've got the correct age attribute running on the main sim i can't get it to work how i'd like with the reseeded particles.

 

So what's happening is they are suddenly being birthed between frames and causing my surface to "pop" on, making it appear that the retime has no subframes to work from. I'm timeblending the flip using id to do the retime itself and that appears to be working well on the main sim points.

 

So the "gas seed markers" dop that appears to be creating the reseeded particles is picking up the relevant attributes from the existing particles surrounding them such as pscale and Cd and, i'm guessing, age (The "copy nearest Surfel" toggle). What I was trying to do was to scale the reseeds over a few frames once they're born so they don't just pop on in the retimed sim.

 

I'm trying to slap together a quick example file to upload but any initial thoughts would be greatly appreciated.

Cheers,

Dave.

 

 

[dayvbrown]

hmm ok so whilst I managed to work around the age problem (after not being able to recreate the issue in a basic scene to upload... sigh) for this shot one of the main things I found to be useful is bypassing the "Gas Intermittent Solve" dop called intermittent_reseed inside the flip solver.

 

This dop appears to restrict the reseeding to only happen on frames, regardless of substeps of the sim itself, so when you're retiming sims after the fact it can give you a "jump" on those frames where particles are reseeded into the surface sdf, particularly at boundaries. This will obviously still happen if you're using a non linear retime and getting down into subframes that don't exist in the sim but it should alleviate the issue somewhat for most cases I think... perhaps.

 

Would be curious to get to grips with controlling the reseeding particles a bit more, having access to them separately.

 

Anyway hopefully that snippet of info might be useful for someone if they stumble on this in the future, if anyone has any "OMG YOU SHOULD NEVER DO THAT" reasons i'd love to hear them! I guess the main one would be it might put the sim in danger of gaining volume too quickly? Hmm not sure.

Cheers,

Dave.

[Skybar]

If it works for you, great! However I would be careful bypassing that Gas Intermittent Solve DOP. It could potentially become a problem. I would read up on what it does and instead change its parameters to fit your needs, rather than disabling it.

[dayvbrown]

Hi Skybar,

 

Yes I most definitely was careful

 

Based on the description\help file\testing essentially what it's doing is restricting the reseeding, or rather the "Gas Seed Markers" dop plugged into it, to only be calculated on frames, it's another one of those fun esoteric microsolvers that could be used in any number of situations.

 

The first thing I tried was to set it to 0.25 frames (with four substeps on the sim) but that didn't seem to do the trick.

 

I think the major issue is likely to be that the fluid will gain in volume too quickly rather than breaking the sim\solver itself. Thankfully in my case the sim remained how I wanted it and also didn't break, which is a bonus, but i'd love to hear of any other issues which are likely to occur without this particular dop in place.

 

Cheers,

Dave.