RLC Boundary Conditions

[Amirtaha Taebi]

Hi SimVascularers,

I am wondering if there is a way to apply RLC BCs to the flow outlets. I see that there are different BC options available including prescribed velocity, resistance, RCR, and coronary. Is there a way that we can define inertance at the outlets?

Thanks,
Amirtaha

[Nathan Wilson]

Hi Amirtaha,

There is no built in RLC boundary conditions, although you could check out the general closed loop BC code to see if you could code up your own circuit models. This would be complicated but may be possible.

Nathan
SimVascular Support Team

[Amirtaha Taebi]

Hi Nathan,

Thanks! Then can you please help me to understand something about the BCs available in SimVascular. First let me explain my problem statement.

I have a geometry that was extracted from CT scans. I have the inlet flow rate and pressure profiles. But I don't have the outlet BCs. However, I have information about the pressure values somewhere in the downstream of my arterial tree. Therefore, there is a domain between my vascular model and those known pressure values. So, I am planning to use a classical (or inverse) L circuit model, estimate the pressure at the outlets of the arterial tree, and use these new pressure values as my CFD outlet BCs. Now, what is the best way to apply these values to the outlets in SimVascular? I see that in the "resistance" BC type, we can define distal pressure. I assume that this is one possibility, i.e. set a 0 resistance and distal pressure equal to the estimated pressure values from my RLC model. Do you have any suggestions? In addition, what about the inlet pressure? Should I take care of it anywhere? Please note that my outlet pressure will have a constant value over time, while the inlet pressure depends on time (something similar to the blood pressure in aorta).

Thanks,
Amirtaha

[Weiguang Yang]

If I understand correctly, you plan to use an RLC model to represent the domain between the CFD model outlets and the point with a known pressure. You need to implement a user-defined lumped parameter model linked to the 3D domain using GenBC in Simvascular. I am not sure if it is better than an RCR model. I suggest you try RCR first. For outlets, you can set the constant distal pressure Pd to the pressure value measured in the downstream and prescribe your inflow waveforms at the inlet. Then use the inlet pressure data to adjust RCR values.

[Amirtaha Taebi]

Dear Weiguang,

Thanks for your reply.

Yes, you got it correctly. I get BCs (e.g. pressure) from a 0-D model that I have previously built. Now, I need to link those BCs to my CFD model using a RLC model. I will also try the built-in RCR of SimVascular. I would appreciate it if you let me know of any documentations that help understand how prepare a GenBC?

For outlets, you can set the constant distal pressure Pd to the pressure value measured in the downstream and prescribe your inflow waveforms at the inlet. Then use the inlet pressure data to adjust RCR values.

Is there any example for this? In this case, RCR values are unknown and we are tuning them this way?

Thanks,
Amirtaha