Resistance value for boundary conditions and 4D Video

[Luca Borro]

Hi everyone,
I'm a biomedical engineering student and I'm trying to learn how to use SimVascular for CFD simulation of aortict coarctations.
I understand the general operation of the software and I offer my congratulations to the developers and to community.
However i've got some problems with the definition of boundary conditions.
Reading the software pdf guide I noticed that there is a value of "Resistance" like as you can see in the attached image.
How was this value obtained? where does it come from?
I also followed all the tutorial with the "demo project" files and I've exported everything in paraview. Here i can only see static images but i can not see dynamic (4D) images of the flow like this: https://www.youtube.com/watch?v=fqbjInQJtzU
Why? Where I'm doing wrong?
Thank you for help.
Best Regards
Luca

[Luca Borro]

Someone who can help me?
Thank you

[Weiguang Yang]

The resistance boundary condition models the downstream vasculature (beyond the 3D model) as a resistor. Using a circuit analogy and Ohm's law, the pressure drop across a resistor (downstream vasculature) is equal to flow times resistance (Q*R). If a ground pressure of 0 mmHg is used, at the outlet of the 3D model, the pressure should rise from 0 to 0+Q*R. You can see that the pressure at the 3D outlet is a function of outflow. In the tutorial, it assumes that a target outlet pressure for the cylinder is ~100mmHg. Thus the resistance value is derived from this target pressure and the flow rate.

You can get more details (implementation and application) about resistance boundary conditions in these two papers.
https://www.scorec.rpi.edu/REPORTS/2006-22.pdf
http://biomechanical.asmedigitalcollect ... id=1430878

To view dynamic results or create a video, you need to run an unsteady flow simulation first and then load multiple vtu files with the same prefix into the paraview (file->open->select the vtu files, note that you can load them by one click because the files are collapsed in the window.), display the quantity of interest (say streamline or velocity vector), and click the play button or click file->save animation.

[Luca Borro]

Thank you for your very useful reply.
I'm trying to work on venous cerebral vessels for studying.
I don't know if Simvascular is a good solution for this type of simulation or if it's dedicated only for big vessels like aorta ora pulmonary artery.
Sorry but i'm new with this technology and i've got a bit of questions:
1) How can i obtain a plot of flow (ml/s --> t) at the inlet face? With other software i suppose, software with which i can get quantitative data about 4D Flow in MRI sequence (like, for example, magnitudo of velocity). Can you cite some software that does this?

2) I could be wrong but if i consider only the waveform of flow applied on inlet face this isn't a 4D representation of velocity but only 2D interpolated result between inlet face (with stead.flow file applied) and outlet face (with RCR or orther boundary condition applied). It's correct?

Thank you again
Best Regards
Luca

[Luca Borro]

Hi,
No up for me?
Thank you again
Luca

[Weiguang Yang]

1) How can i obtain a plot of flow (ml/s --> t) at the inlet face? With other software i suppose, software with which i can get quantitative data about 4D Flow in MRI sequence (like, for example, magnitudo of velocity). Can you cite some software that does this?

I know there is a software segment that allows you to process 2D PCMRI data to extract flow waveforms(flow rate vs time). http://medviso.com/segment/
For 4D MRI data, I guess you may work with radiologists to extract velocity and time information from dicom files. I don't know if there is any software available to public. Most are in-house codes, to my limited knowledge,

2) I could be wrong but if i consider only the waveform of flow applied on inlet face this isn't a 4D representation of velocity but only 2D interpolated result between inlet face (with stead.flow file applied) and outlet face (with RCR or orther boundary condition applied). It's correct?

sorry I don't get your second question. Please rephrase it.

[Ryan Pewowaruk]

RE: 4D Flow MRI

Most use an in-house code to convert 4D Flow MRI data to a file that can be read in some other post-processor.

I believe if you are using the GE 4D Flow sequence GE has it's own software for processing.