Velocity and pressure units

[Gianmarco Di Vina]

Hello everyone,
I have just finished running a simulation of an aorta and have some doubts about the units in post processing: i should have been consistent with CGS system, ie:
- Model in cm
- Flow rate in cm^3/s
- Rp and Rd in g/(cm^4*s)
When i convert results and select 'Sim units cm', are the velocity values calculated in cm/s?
The doubt comes because i think i have set the parameters correctly but when studying in Paraview, i get rather low values.
Finally, still using the same units, what would be the units of the calculated pressure?

Best regards,
Gianmarco.

[David Parker]

Hi Gianmarco,

The svSolver does not assume any units. The units of your mesh, boundary condition data and physical constants just need to be consistent.

The Sim units cm option is used to write flow data to a text file, it does not affect the simulation results stored in VTK files.

Pressure would be in dyne/cm^2 for CGS units.

Does the simulation converge to a steady state ?

Cheers,
Dave

[Gianmarco Di Vina]

Hi Dave,

I thank you for the help you gave me last time, but at the moment a new problem has arisen.

I tried to run a new simulation with new parameters and when I go to analyze the results, it is as if the fluid is not flowing in the aorta for all the time instants. I have tried to evaluate all the possible errors but I cannot find the solution.

The parameters were provided to me by PIVLAB analysis and are expressed in SI.
I would be very grateful if you could help me.

Best regards,
Gianmarco.

https://drive.google.com/drive/u/0/fold ... y6Jo-5Qo5i

[David Parker]

Hi Gianmarco,

I ran a simulation with your data but did not understand what you meant by fluid is not flowing in the aorta for all the time instants.

Note that your inflow data is zero after 0.377 sec.

You might want to use parabolic rather than plug flow and maybe first perform a simulation without a boundary layer, just to simplify things a bit.

Cheers,
Dave

[Gianmarco Di Vina]

Hi David,
Thanks for your quick reply!
By fluid does not flow in the aorta for all instants of time I mean that at each instant when I analyse the velocity over the various required sections, the velocity is approximately zero, regardless of the phase of the cardiac cycle.
I have studied about thirty instants and the result is very similar to the screenshot below. Could there be a problem with the RCR parameters provided experimentally? They seem rather small values to me.

Thanks again for your help.
Best regards, Gianmarco.

[David Parker]

Hi Gianmarco,

If the results are not what you expect then it is usually a good idea to simplify the simulation (i.e. BCs) so you can better understand the results.

Cheers,
Dave

P.S. I'll not be answering Forum questions the next 2-3 weeks.