Distal Pressure in RCR Model

[Alan Wei]

Happy New Year, all,

We have a query regarding the influence of distal pressure (P_d) in the RCR model within SimVascular.

We ran a set of 3D CFDs with a simple case to test the P_d. Our case involves simulating 3D single-phase Newtonian flow within a cylindrical straight, rigid vessel with a constant flow rate at the inlet and the RCR model applied at the outlet.

We conducted three simulations, varying only the P_d in the RCR model.

• In 1st simulation, the default P_d value of 0 was used.

• In 2nd simulation, P_d was set to 20 Pascal.

According to the equation

2024-01-02 21 10 44.png (22.91 KiB) Viewed 694 times

As provided in Vignon-Clementel et al.'s 2010 study in "Computational Methods in Biomechanics and Biomedical Engineering", we anticipated the pressure at the outlet in the 2nd simulation to be 20 Pascal higher than the first.

Surprisingly, it was 40 Pascal higher, as shown in this figure:

2024-01-02 21 19 31.png (82.4 KiB) Viewed 694 times

We then tried the third simulation with P_d set to (-20 Pascal), resulted in an outlet pressure 40 Pascal lower than the first simulation.

This outcome suggests that the outlet pressure is influenced by twice the value of the defined P_d.
Are we possibly misinterpreting the equation from the referenced paper?

Many thanks!
Alan

[Weiguang Yang]

I expect to see a pressure difference of 20 Pa instead of 40 Pa. Can you check if the two rcrt.dat files differ in the last two rows only.
Take the rcrt file used in the Simvascular cylinder demo project as an example.
The original Pd was prescribed as follows,
0.0 0.0
1.0 0.0

To change to Pd=20Pa, set
0.0 200.0
1.0 200.0
Can you confirm that you have the same issue when you run the demo case (steady_rcr) with a non-zero Pd?
Thanks!