Closed-loop circulation model

[menon-karthik]

Currently we can only model open-loop models, i.e. models that terminate with prescribed distal boundary conditions (like a distal pressure). I am adding the following:

• A heart/pulmonary circulation block that will connect outlet BCs back to the inlet of the model in a closed-loop fashion. Ref [1] for details.
• Blocks to model coronary and RCR BCs that do not have a prescribed distal pressure, and can be connected either to the heart/pulmonary circulation on the distal side (closed-loop) or to a prescribed pressure block (open-loop).
• Other functions to incorporate these blocks, perform usual book-keeping, etc.
• There is no simple analytical test case for this. So I will add a test case to compare this with existing solvers used in previous papers [2]-[3].

Any suggestions on better/different tests?

Refs:
[1] Sankaran, S. et al. (2012).Patient-specific multiscale modeling of blood flow for coronary artery bypass graft surgery. Annals of Biomedical Engineering, 40(10), 2228–2242.
[2] Tran, J. S., et al. (2017). Automated tuning for parameter identification and uncertainty quantification in multi-scale coronary simulations. Computers and Fluids, 142, 128–138.
[3] Tran, J. S., et al. (2019). Uncertainty quantification of simulated biomechanical stimuli in coronary artery bypass grafts. Computer Methods in Applied Mechanics and Engineering, 345, 402–428.

[menon-karthik]

Updates:

1. I have finished implementing the model in ref. [1] above.
2. The new blocks are closed-loop RCR outlets, closed-loop coronary outlets, and the heart/pulmonary circulation model.
3. Added two git test cases for closed-loop models: (i) a single vessel with RCR outlet connected on either side to the closed-loop heart model; (ii) a system with 4 parallel vessels, two with RCR outlets, one with left coronary outlet, and one with right coronary outlet, all connected on either side to the heart model. The test cases compare results with solvers used in refs. [2]-[3] mentioned above.
4. The heart model requires specific initial conditions, which have also been added. The steady state initial condition does not work for the heart model.

[mrp089]

Now merged into https://github.com/StanfordCBCL/svZeroDSolver

[mrp089]

Reopening as @menon-karthik is also implementing a Python version of the boundary condition in this repository