Rocket launch Jitter(?)

[anthonyh]

Hi,
I`ve finally gotten around to playing with Phoenix again and I`m working on a rocket launch for a job, just a short shot not the whole thing.
I simmed a lowish detail temperature/smoke and then ran a resimulation on it. When rendered it seems to jump/jitter a bit like the sim has changed as if it sinks back/collapses in certain areas and continues. It`s not a single incorrect frame because the sim continues on smoothly from that point until it does it again. It happens quite strong early on and then more smaller jumps later on. Is there anything obvious I might have missed ?
Before sending to backburner I point the input channel to the resim files and turn off the resim tick boxes because i`m using a seperate file to render it out as a matte.
I`m guessing I`ll have to rerun the sim at some point but I`d like to know what I`m doing wrong before I do because of the time it takes to calculate.
I`m using one of the latest nightlies 28902. I can see there are later ones which maybe I`ll try and I also need to maybe try rendering locally as well although in case it`s that but that wouldn`t be feasible for the final render.
thanks
anthonyh

[georgi.zhekov]

Can you show us how it looks and show us your settings?

[Svetlin.Nikolov]

Hey,

Most importantly when doing resims - are you using more than 1 step per frame? This is the most common reason for large differences between sim and resim.

If this does not help, something else you could try after this would be switching from PCG to Direct Symmetric for both the sim and resim.

Not completely sure that these might be the solutions - if it's not under NDA, could you attach a short video of how the issue looks in motion?

Cheers!

[anthonyh]

Thanks for the reply. I`ve not attached a video before but I`ll give it a go. No real NDA but generally not for public viewing but so far I`ve only rendered the phoenix bit anyway so it`s fine.
Had to zip it. You should be able to see where it it `Jinks` occasionally. I thought maybe I should just up the grid and run the sim straight rather than resim. I`ll photoshop settings although they should be pretty much the large smoke preset and the fast smoke/fire volumetric preset.
I`m using the default 1 step per frame as per Large Smoke Preset and left Resim at defaults too.
Photoshopping the settings makes me wonder if I can just save my settings from pheonix and upload them. I can certainly strip out the geometry and send the scene, it`s just a large smoke sim.
Movie.zip

[anthonyh]

Settings attached

[Svetlin.Nikolov]

Hmm, indeed, this seems like an issue I've seen with PCG, very high discharge and a lot of obstacles in the simulation. Definitely try switching to Direct Symmetric.

Cheers!

[anthonyh]

I`ll give Direct a go later, thanks for the suggestion. I needed a lot of velocity to make it go faster. There aren`t actually that many objects in the way during the simulation. I simulate with the ground and rocket trench but then unhide the other objects to render a matte pass later. Didn`t seem any need to complicate it too much during simulation, still works about the same.
I`ll let you know how it goes. I need a faster machine !
thanks
anthonyh