[Soc-2017-dev] Weekly Report #11 - Mantaflow Particles and Fluid Guiding

[Sebastián Barschkis]

Hello everyone,

my progress report for week 11 is now online:

https://wiki.blender.org/index.php/User:Sebbas/GSoC_2017/Reports/Week_11

= Week 11 =

This week I worked on some of the bugs and on fluid guiding.

=== What's been done ===

* I looked a bit further into the (still unresolved) velocity bug. As Nils
pointed out last week, setting velocities in inflow regions explicitly
seems to matter. I found this made sense and so I made a test to prove this
point: First I added an inflow velocity setup to the Mantaflow script that
reproduces the bug. Then I compared the outcome with the old setup that did
not use inflow velocities.

* My first impression from the previews is that manually setting inflow
velocities definitely improves stability. Setups with open domains now look
much alike to setups with closed domains (as it should be). I tested a
range of inflow velocities and at no time did I encounter scenes where
velocities exploded / "behaved unphysically" (as it happens when there are
no inflow velocities set explicitly).

* So there is a chance that this resolves the issue. For the final verdict
though, I'd like to know why setting velocities matters. Right now, I think
velocity extrapolation plays a role here too: If no velocities get set in
inflow regions, the extrapolation builds up velocities in that region at
every step, up to a point where the simulation becomes unstable.

* There was a problem with thin obstacles. In the levelset generating
function thin obstacle meshes and planes were not considered. You'd always
have to make obstacles sufficiently thick with respect to domain size to
get an obstacle effect. I created a new setup which fixes this by searching
for the nearest points on the mesh surface in addition to finding distances
to the mesh surface via raycasts.

* For fluid guiding I have nothing new or tangible to show yet. I think I
have landed a good setup though. More on that next week.

=== Next up ===

* Continue with last weeks goals (especially particle refactoring and
cleanup).

* No matter what the cost, fluid guiding needs to be finished by next week.
(Not trying to sound overly dramatic here. It's just that the week
thereafter it's already time to write the documentation).

=== Questions ===

* No

Best wishes,
Sebastián
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