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Dynamic meshing cell stretch

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Old   April 7, 2022, 04:23
Arrow Dynamic meshing cell stretch
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I simulate an object oscillating in water (multiphase flow, VOF). My mesh needs to be dynamic to follow the motion and therefore I am using triangular cells (refined locally down to 0.1m size) and a remeshing method with rigid body motion.

I defined a sphere encapsulating my object and I move this sphere using a UDF CG MOTION following a sinus curve up to 1.95m/s with a period of 10s, to oscillate at the water interface. The BC are defined as all walls, and the water is still (no waves).

The problem I get is that the cells at the edge of my sphere are stretching too much and cause a negative cell volume error, even when I decrease the timestep down to 0.01s. And I can't reduce it more for computation time reasons.

I recently tried the implicit update option, but it failed as well a couple of seconds later than the simulation without the option.

As the remeshing method concerns the whole domain, these stretched cells are too big compared to the surrounding ones, but still smaller than the ones far from the object: so Fluent doesn't get that it should remesh it. I tried constraining the cell, face skewness and using every other option available in the remeshing method but without success.

Does anyone have an idea on how to solve this, please?

Thanks a lot in advance for your help !

Attachment 89210
hull in water.PNG
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dynamic mesh, negative cell volume, remeshing

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