I have sims looking good at a lower res (Particle Seperation .1) but I can't find a way to keep them relatively the same when increasing ( .07-.02 )

the Overall motion is staying similar enough but the surface particles are flying around far to quickly and erratically, even with nothing but a gravity force acting on them, iv tried using the ignore mass and what not but not much luck, can any one give me some pointers on keeping this is control while increasing resolution?

-Nick

What kind of simulation are you doing? Just water falling onto a groundplane? Water filling a glass? Water flowing down a riverbed…? Wild character interactions?

“ the surface particles are flying around far to quickly and erratically” That sounds like something else is going on. I haven't had many problems with the new solver in h12… even when changing resolution. Though, a few things to try would be more substeps on the solver, and increasing smoothing. More details of the sim in question would be helpful.

the shot is a dam break with the water spraying/shooting out. Im largely Basing my set up on the waterfall tutorial. I get the main body of water working as i want at low res then when I Crank the resolution it gets messy, It looks like the noise in the velocity is way to strong but even when i bypass all the added velocity to the emitter and what not the surfaces to the water body are just moving way to quickly and wild for water of this scale. If this isn't usually an issue it probably just takes more tweaking on my end, which will be difficult due to simulation time…

Scale can also play a large part in the scenes. If you model everything out right, it helps a lot. So, make sure you are working in real units if at all possible. Try the things i mentioned earlier, you can also try the “Collision Detection”, changing it to move to the particles to the surface instead of using particle collisions. Double check the static geometry to make sure the collision geo looks good, and doesn't have any weird spikes or holes in it too. Oh, also, you could turn off ‘ballistic’ mode for the under resolved particles. Set that to none, and it should smooth particles that would otherwise stop reacting to the flip forces. This is great for making splashier stuff, which may be happening in your case a little too strongly.

Scale and collisioon geo and all that are good, so far it looks like the ballistic thing is doing the trick. thanks alot!

I also have a problem where it seems that when i emit the fluids higher than a certain velocity, the leading parts of the fluid seem to flatten and i get kind of flat leading faces of the sim, this seems to get worse when i upres aswell. im not sure if maybe the particles are collapsing in on themselvs at that high of speed or something, but then why would that get worse with more particle seperation.. kinda thinking out loud here.. any opinions?

Any chance you can post a video of the sim? I've had collapsing fluids, but not so much in h12 now. If you've modified the reseeding parameters, you can get a reduction or increase of volume, defaults work pretty well here (overall actually I find I don't have to modify too many settings). I tend to keep ‘apply particle separation’ off too. I've actually had that give me unexpected results in the past (not sure if this was improved at all in 12, but it hasn't seemed necessary). You might want to play with the particle radius on the flipfluidobject – default is 1.2, you can try increasing that a little bit to see if it helps a little too.

nikmolson
I also have a problem where it seems that when i emit the fluids higher than a certain velocity, the leading parts of the fluid seem to flatten and i get kind of flat leading faces of the sim, this seems to get worse when i upres aswell.

You probably need to increase the Max Cells to Extrapolate setting under Volume Motion | Solver. With low substeps and high resolution volumes, the particles can move outside the bounds of the underlying volume in one timestep and run into zero velocities, hence the flattening. Increasing this value should alleviate the problem.

Thank you both! i used a bit of everything but the Max Cells to extrapolate seemed to do the trick. That put me back on track