Discussion Forum

Hello everyone,

I am modeling pulsatile flow in cerebral arteries using COMSOL and have defined a piecewise inlet velocity function based on three polynomial segments. These segments are defined as follows: InletVelocity1(t) for 0≤t≤0.115:

-8.579e+08t^8 + 4.059e+08t^7 - 7.817e+07t^6 + 7.994e+06t^5 - 4.835e+05t^4 + 1.782e+04t^3 - 321.6t^2 + 3.215t + 0.1423

InletVelocity2(t) for 0.115<t≤0.315:

-4.32e+06t^8 + 7.94e+06t^7 - 6.298e+06t^6 + 2.82e+06t^5 - 7.809e+05t^4 + 1.37e+05t^3 - 1.484e+04t^2 + 901.9t - 22.87

InletVelocity3(t) for 0.315<t≤0.890:

-5.123t^4 + 14.15t^3 - 14.21t^2 + 5.865t - 0.5696

I have combined these functions into a piecewise function named CombinedInletVelocity(t) using the following logic:

if(t <= 0.115, InletVelocity1(t), if(t <= 0.315, InletVelocity2(t), InletVelocity3(t)))

However, I keep encountering a singularity error with the message: “The maximum number of Newtonian iterations may be reached.” I have tried numerous suggestions found online, such as refining the mesh, adjusting solver settings, changing tolerances, and modifying the time stepping, but none have resolved the issue.

I have also uploaded the geometry for reference. I used spf laminar flow, with constant pressure at outlet and no slip BC for the wall. Any guidance on resolving this error would be greatly appreciated. Could the problem be related to the defined inlet velocity functions, or is it likely due to some other aspect of the model setup?

Thank you for your help!