Pressures are additive over multiple cycles error

[Joanne Sarsam]

Hello,

I am running a rigid wall simulation, prescribing pulsatile flow to the input (aorta model). I am running the simulation through SV GUI, using svPre as the solver. For some reason, in every simulation, i get a result that shows additive pressures over the course of multiple cardiac cycles, instead of the pressures stabilizing as they should. Could someone guide me as to why this may be happening? I run the simulation for 500 time steps with a step size of 0.0043 secs, to simulate 5 cardiac cycles for a cycle of length 0.43 secs. When I convert my result files after the completion of the simulation, I convert from steps 0 to steps 500. Is the conversion of all 500 timesteps causing the additive nature of my results?

For reference, here are plots of the pressures at different outlets in the model. These numbers were derived from the all_pressures.txt file.

Screenshot (16).png (97 KiB) Viewed 546 times

Thanks!
Joanne

[David Parker]

Hi Joanne,

What do you mean by in every simulation, i get a result that shows additive pressures ?

Cheers,
Dave

[Martin Pfaller]

You probably have RCR boundary conditions. Since they include a capacitor, it can take several cardiac cycles to be "charged." This means that when you initialize your simulation from zero velocity and pressure, you will see the pressure building up over several cardiac cycles as you did. The time constant R_d * C [s] will give you a metric for how many cardiac cycles it will take to reach a periodic state. Have a look at this paper for more explanations and a method of how to use fewer cardiac cycles: https://link.springer.com/article/10.10 ... 21-02796-x