Hello,

I have been working on a project the requires modeling blood flow in the carotid artery.

What I have is a very basic elastic tube model.

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.
• Carreau blood Viscosity 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 (almost as if it is exploding) 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.

As far as i have learnt from researching different papers and forums, is that FSI simulations that involve relatively thin boundaries with low modulus of elasticity tend to be very unstable. What I would like to know is that what is the nature of these instabilities (are they related to the model set up or are they numerical instabilities) and how can I overcome this issue ?

Your answers are much appreciated and any supporting resources are highly encouraged.