Unwanted movement of still standing tank and render artifacts with all objects that aren't 90 degrees straight

[TripleDots]

Issue 1

There is often a lot of unwanted movement. I noticed this first with higher viscosity (20) as with a lower one, while it happens, is not much of an issue.

Issue 2
With rendering all objects that do not look like a tube you get these rendering artifacts. (which is probably caused by the same bug as #1)

Both are repeatable in every scene I made and it happens on both CPU and GPU.
I also tested it on 0.1.1b and 0.1.2b (still same results) but the full renders in the video are 0.1.2b.

Video:
https://gfycat.com/ReadyDirtyFoxterrier

[rlguy]

Hey TripleDots thanks for reporting these and for including a helpful video!

Issue 1

This is caused by how the simulator 'solves' the fluid equations. The simulator isn't able to calculate an exact solution to the fluid physics equations, it can only make a very good guess. The movement is caused by numerical differences between the 'solved' approximation and a theoretical exact solution. This is more noticeable in slower moving simulations, such as those with visosity.

The solver may be able to compute a better solution if you allow it take more calculation substeps. This can be done by increasing the 'Min Time Steps' value in the FLIP Fluid Advanced panel, but this will take more time to compute and may not improve the solution by a beneficial amount.

Issue 2

I have opened an improvement issue to fix this (issue #158). The issue also contains some workarounds.