The problem happens because smoke collides only with the surface of the
collider and uses incompressible fluid solver. This means that scaling
the collider tries to compress or decompress fluid within the volume of
the collider, which can't be handled by the simulation. Fast rotation
likely also causes transient scaling due to emulation of arcs by chords.
This can be fixed by finding compartments completely isolated by obstacles
from the rest of the domain, and forcing total divergence within each one
to be zero so that equations are solvable. Physical validity is somewhat
dubious, but without this the solver simply breaks down.
From the physics point of view, the effect of the correction should be
similar to opening a hole from every cell to another dimension that lets
an equal amount of air to pass through to balance the change in volume.
Reviewers: miikah, lukastoenne
Reviewed By: lukastoenne
Subscribers: dafassi, scorpion81, #physics
Maniphest Tasks: T43220, T47551
Differential Revision: https://developer.blender.org/D2112
Visual representation of fire was generated before simulation step took place. This caused fire to essentially lag one simulation step behind, even though all emission areas were up to date.
This was caused by a "hack" Daniel Genrich introduced in his moving obstacles commit in r46050. I suppose it was originally added to prevent issues with too fast moving obstacles, but now it ended up limiting maximum velocity of higher resolution simulations.
Here is an comparision of 184 resolution simulation (simulation area limited by adaptive domain):
https://www.miikah.org/blender/smoke_with_pressure_limit_hack.pnghttps://www.miikah.org/blender/smoke_without_pressure_limit_hack.png
I now reverted that hack until a better solution is found. Daniel, can you check this out? Pressure was limited to maximum of dt * dx (= dt / res) which doesn't make sense to limit pressure based on grid resolution. Maybe better to limit with a constant factor instead?
Documentation & Test blend files:
------------------
http://wiki.blender.org/index.php/User:MiikaH/GSoC-2012-Smoke-Simulator-Improvements
Credits:
------------------
Miika Hamalainen (MiikaH): Student / Main programmer
Daniel Genrich (Genscher): Mentor / Programmer of merged patches from Smoke2 branch
Google: For Google Summer of Code 2012
Detail: Smoke solver and Blender side of smoke now share the same cell length.
First reported by the Sintel artists long ago, again reported by MiikaH.
Part of my Smoke Development Project Phase III.
Sponsored by the Blender Development Fund.
http://www.blender.org/blenderorg/blender-foundation/development-fund/
Remarks:
The original code was not designed to support moving obstacles so I had to introduce some velocity constraints into the code to prevent smoke from exploding. If this causes problems with "fire" emulation, please let me know.
* Better (and windows enabled) OpenMP handling (> 2x-5x speed)
* More Volumetric Texture mapping options (heat, etc) <-- Matt if that's not to your liking, just revert that part, it's separate anyway
* Initial velocity taken from particle settings (no more slow starting)
* Option to select compression method (there seem to be a bug in my high compression usage, at least it's been reported to result in exploding smoke - better use low compression for the time being)
It's been tested since a while but as usual please report any (new!) bugs. ;-)
* Totally new try to get cache running
* Didn't try "bake" and such things yet
Hint
* Very verbose yet
* Please do only test new blend files, not old ones!
Please give me feedback on my blog about the old crashers.
* Enable cache for high res + new preview
* Bugfix for smoke banding (in cooperation with N_T)
Hint: Work-in-progress regarding collision objects so can be broken, didn't test
Hint2: jahka enabled a general particle panel but
* bake button doesn't work
* step is not supported for cloth
* several other things there ;)
* cache for low res (deactivating high res for now)
* new way of view3d rendering of smoke (no longer 3 axes) -using 3dtexture now (introduced into gpu/intern)
* introducing LZO and LZMA libs into extern (makefiles missing for now)
* reducing memory usage after simulating for the frame ended (freeing temporary buffers)
* splitting smoke into 2 modifier for the cache-sake (it cannot handle more than 1 cache on the same modifier-index)
* no color on gui anymore
* fixing non-power-of-2 resolutions (hopefully)
* fixing select-deselect of domain drawing bug
* fixing drawobject.c coding style (making Ton happy) ;-)
HINT #1: If scons doesn't work -> cmakefiles are up-to-date, couldn't test scons (but i tried to mantain them, too)
CODERS HINT #1: we really need a way to disable adding all modifiers through "Add Modifiers" dropdown!
WARNING #1: before applying this commit, deactivate your SMOKE DOMAIN in your old files and save them then. You can open them then savely after that.
WARNING #2: File and cache format of smoke can be changed, this is not final!
a) fixing domain boundaries
b) fixing flow gui (no more velocity there - taken from particles)
c) Outflow available (deletes smoke from scene)
d) deactivating other noise options for now
e) base for render/preview settings
f) fixing collisions to be working again
Not working:
a) rendering (since volumterics branch is not merged yet)
b) moving collision objects of any kind
c) saving of collision objects (because that's what I am working on)
d) pointcache
e) A bunch of other things I already know of
So please do not report any bugs on this one yet :-)
