Learning Forum

[Hayden Perrin]

Hello, I am continually getting an error while trying to perform an FSI of a rubber tube with a constriction within the tube and water flow at mass flow rate = .0125*sin(6.28t) +.0635. This is a fluctuating flow of (1GPM). I keep getting an error in my transient CFX saying highly distorted element, and the simulation fails at .6 seconds. When increasing the youngs modulus, or using other materials such as steel, the program works fine. But the moment i bring these values back to 1.5MPa for the rubber I am using I get this error. I can see it seems to be a large jump in the deformation for transient structural at .6 seconds, when using a .1second time step, while the rubber elastic modulus is increased to 2MPa that allowa the simulation to run fully. I have tried to decrease my time step down to .01 but still am getting the same errors. Do I need to reduce this time step even more, or better adjust my mesh in CFX? Any help would be appreciated, thanks.

[Rahul]

Hello 
Before solving FSI coupling, ensure that your coupling participants (CFX and mechanical) are working well alone with representative loads.

Make sure that CFX mesh is of good quality. It it failing due to negative volumes in CFX consider changing mesh deformation settings or reducing the time step. Also, check if the resonable displacement/ Thermal loads received from MAPDL?

If a run fails in the first few time steps, re-run for a limited number of time steps and/or with a limited number of Coupling Iterations so that you can generate results files and examine the results

Please refer CFX user guide to know more about mesh deformation and FSI best practices: 5.1.1. Mesh Folding: Negative Sector and Element Volumes (ansys.com)

System Coupling can automatically stabilize the data transfer using iQN stabilization Improving Coupled Analysis Stability (ansys.com)

For hyperelastic materials try transferring force-density [N/m^2] instead of force [N].

Hope this helps!