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Hello -

We are having issues getting a periodic solution. When we tried the simulation with our own code, the solution reached a periodic waveform within 3 cycles. However, SimVasc appears to need up to 7 or 8 cycles (the attached image shows the first 4 cycles of increasing pressure).

This seems like an initial condition issue, but I'm surprised that our own code didn't have the same problem.

Thank You,

Vitaly

Is this pressure an outlet pressure with an RCR boundary condition? If so, it is likely that the gradual increase in pressure is caused by a relatively large RC constant. If I remember correctly, the RCR analytical solution includes a term for initial conditions, which decays as exp(-t/(C*Rd)). If C*Rd is small, the influence of initial values disappears quickly and the solution reaches a stable periodic state in a couple of cycles. You can verify how many cycles it takes to become stable for given RCR values by plugging periodic flow to an RCR circuit model.

Thank You for your response. This pressure is the inlet pressure (we are applying flow as the inlet BC), but we are using an RCR outflow boundary condition. If I plug our flow directly into an RCR circuit (with the same RCR values), we see convergence in 2 cycles.

This is a good point though. It never occurred to me to think about the outflow BC. I kept focusing on the initial values within the domain. Although, if it is the BCs, I am not sure what can be done about that.

I really appreciate any suggestions!

Best,

Vitaly