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Ansys Learning Forum › Forums › Discuss Simulation › Fluids › Fluent intrinsic FSI, negative cell volumes in the solid body › Reply To: Fluent intrinsic FSI, negative cell volumes in the solid body

May 9, 2024 at 10:31 pm
Marcin Nowak
Subscriber

I tried:
define → models → structure → controls → enhanced-strain? ->yes
define/models/structure/controls/numerical-damping-factor? -> I set value of 0.5
define → models → structure → controls → unsteady-damping-rayleigh? ->yes
These options, have no effect on the mesh motion. However “enhanced strain” option gave slightly higher deformations (diameter was higher by 2.4%). 

The timestep size does not have impact on the results or the mesh motion – I checked two smaller time step sizes.


I was able to mitigate somehow a problem, by setting a mesh bias factor – having less dense solid mesh at the fluid-solid interface region, at the beginning of the computation. But this does not solve my problem completely as I was not able to perform full transient calculations (but I was able to get further in time). 

Also I dont want to use “bias factor” as the results are quite highly dependent on this (I checked it). By the way, I was performing a mesh sensitivity analysis for the solid body mesh, by using different number of mesh layers (from 2 to 8) and the solution in the Intrinsic FSI Fluent solver, is very different for these meshes (stabilizes at 6 layers). Whereas for the Mechanical-only (applying constant pressure inside a pipe) with multiple substeps, the solution was not dependent on the number of mesh layers.

To sum up, I would like to find an option in Fluent, which will let me to regulate the solid body mesh motion, to have more uniform mesh motion in the solid body domain (now the nodes moves primarily in the layers that are closer to the fluid). Please let me know whether there are such options.

 

I have also another idea. Check the real-scale deformation field below, for the Mechanical-only simulation. It can be observed, that there are present negative cell volumes, however this does not affect the solution process, also I dont receive any error or warning. I think that in the FEM calculations the cell volumes do not matter. So maybe there is an option to turn-off the calculation abortion in Fluent, when the negative cell volume in the solid mesh is present?

 

 

Regards