I have a ball that moves through an inverted obstacle (it has the shape of the letter 'P'). When the ball moves through the liquid, it doesn't seem to move and push the liquid, but it appears to remove it. As a result, when the liquid comes to rest, the amount of liquid is obviously way less.

Couple frames of the simulation

The balls movement is done using keyframes on its position. The liquid is there from the start of the scene using a Fluid object. So part of my inverted object is filled with liquid. There are no inflows or outflows in the scene.

Is there a setting I have turned the wrong way or is there another reason why this behaviour is happening?

My current settings are

Blender frame rate: 24
FLIP Fluid frame rate: 24
Resolution: 200
Min and max substeps: 1 and 24
Enable Adaptive Time Stepping for Objects: on
Fluid settings: all default
Ball object settings - Export Animated Mesh: on

I have run the simulation with a min substeps amount of 6, but that didn't change anything.

  • 1
    $\begingroup$ Please show your inflow and outflow settings. $\endgroup$ – atomicbezierslinger Mar 1 '20 at 2:07
  • $\begingroup$ Please show your normals for an obstacle. What do you mean inverted? Blender can annotate frames with a frame number with a few clicks. Although the reader might guess the order of your images ... its not really educational to guess. $\endgroup$ – atomicbezierslinger Mar 1 '20 at 2:11
  • $\begingroup$ @atomicbezierslinger, I've improved the image. With inverted I mean the obstacles basically becomes a domain for the fluid. So the obstacle becomes hollow and everything outside becomes solid. Just making sure, did you see I'm using the FLIP Fluid add on for this simulation? $\endgroup$ – Bassie-c Mar 1 '20 at 2:22
  • $\begingroup$ What is the effect you want? Realistic or Special Effect. You may try a much smaller sphere to compare results. You can have a smaller sphere follow a path with the [follow path constraint]. I have used the older fluid sim. I would avoid this unusual idea to have to solid pass through another solid. I think the more typical case is to have a solid pass through fluid. Hopefully others can comment. Please try such a scenario and see if the results are more aligned to your expectation $\endgroup$ – atomicbezierslinger Mar 1 '20 at 4:40
  • 1
    $\begingroup$ @Bassie-c, There is a bug in the current FLIP Fluids addon version (v1.0.7) that can cause regular obstacles not to interact properly with the liquid if there is an inverted obstacle present in the scene. This issue has been recently fixed and we will be releasing a version update (v1.0.8) that includes this fix within the next few days. This version will be available on the Blender Market as well as our GitHub project page. Apologies for this issue and the inconvenience. $\endgroup$ – RLGUY Mar 1 '20 at 10:30

This issue is caused a bug in FLIP Fluids addon versions 1.0.7 or lower that can result in regular obstacles not interacting properly with the liquid if there is an inverted obstacle present in the scene. This issue has been fixed and this fix is included in FLIP Fluids version 1.0.8 or later. This version is available on the Blender Market, in our Free Trial, and on our GitHub project page.


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