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Hello,

I am attempting to run a simple steady flow test on simple rigid vascular geometry with one inlet and two outlets, using a zero pressure boundary condition at the outlets. As I understand, the zero pressure BC is achieved by using the resistance BC with p_0=0 and R=0. The issue is that running a simulation with this configuration results in non-zero (but relatively small) pressure at both outlets. Is this due to the weakly-prescribed BC, or could there be another issue I am overlooking? Any help would be greatly appreciated. Thanks.

For the resistance BC, we set boundary traction h=T \dot n= (-pI + \mu(\del u + \del U^T) \dot n=-p(R,Q)n=-RQn. My understanding is that the pressure=0 is not exactly satisfied if there is a perturbation in (\delU+\del U^T) even if the traction is 0. It might be more noticeable when the outflow velocity profile is not uniform. You can try to set the number of resistance surfaces to 0. By default, it is a "zero pressure" BC. I am not sure if it helps. Maybe you can give it a try.