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[fares abbara]

For better understanding of my model, here is a summarized problem statement.

Model Specifications are as follows:

 

• Linear elastic tube with young’s modulus 0.108 MPa and 0.49 Poisson ratio.
• Tube thickness 1mm and inner diameter 8.5mm.
• Non-Newtonian fluid model.
• Outlet boundary condition: 1300 Pa.
• Inlet boundary condition: time dependent sinusoidal velocity (amplitude 0.1 m/s, frequency 2Hz).

The model runs without errors with time step of 0.01s. Model becomes highly unstable with unreasonable deformations in the tube when the simulation runs at 0.001s time step size. (other time steps lower than 0.01 also cause failure).

 

I have tried to:

• Check the contact between the solid and fluid domain for any gaps that could be causing instability.
• Experiment with constant and time dependent linear inlet velocity profile.
• Running the simulation in steps (run fluent first and then export data as initial conditions for coupled analysis).
• Experimented with numerical stabilization controls in the structural domain.