Prescribed velocities boundary

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Dylan van der Schoot
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Prescribed velocities boundary

Post by Dylan van der Schoot » Mon Apr 15, 2019 4:44 am

Hi all,

When I'm applying a steady parabolic flow on the inlet, I see that for some reason in the calculation of this profile not only a velocity in the required direction is present, but there is also a small parabolic velocity profile in the other two directions (It is in the order of 10^-4 of the velocity in the normal direction). Anybody has an idea why this is? For fully developed flow the velocities in the other directions should ofcourse be zero.

Thanks in advance!

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Weiguang Yang
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Re: Prescribed velocities boundary

Post by Weiguang Yang » Mon Apr 15, 2019 1:01 pm

The inlet profile prescribed by bct.dat file should give zero velocity in the non-axial direction. In the domain, probably you won't get 0.0 exactly. 1e-4 doesn't seem too bad. If you want to further reduce it, you can consider extending the pipe. L~10D may not be sufficient.

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Dylan van der Schoot
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Re: Prescribed velocities boundary

Post by Dylan van der Schoot » Tue Apr 16, 2019 12:35 am

Hi,

Thanks for your reply. I've checked the bct.dat file and the prescribed velocities in the non-axial direction are not exactly zero. I've attached the file here: https://we.tl/t-zVyxgqr3Oq
Any idea what causes this?

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Dylan van der Schoot
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Re: Prescribed velocities boundary

Post by Dylan van der Schoot » Tue Apr 16, 2019 1:14 am

I found the problem. For some reason, if I apply inflation layers in my mesh, the mapping of the velocity profile on the inlet boundary introduces non-axial velocity components (approx. 10^3 times smaller than the velocity in the axial direction). When I'm not using inflation layers in my mesh, this non-axial velocities are approx. 0 (in the order of 10^-12 to 10^-20, but still not completely 0). This is for both parabolic and womersley velocity profiles (I didn't check plug). Is this a bug in the creation of the bct.dat file?

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David Parker
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Re: Prescribed velocities boundary

Post by David Parker » Tue Apr 16, 2019 6:30 pm

Hi Dylan,

I think that the velocity profile mapping should be the same wether you are using boundary layers or not.

Please file a bug for this on GitHub (https://github.com/SimVascular/SimVascular/issues) and I'll have a look. Be sure to include any data files (mesh, bct.dat, etc) for both cases.

Thanks,
Dave

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Dylan van der Schoot
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Re: Prescribed velocities boundary

Post by Dylan van der Schoot » Wed Apr 17, 2019 1:44 am

Hi David,

Thanks for your reply, I've filed the bug on the GitHub.

Thanks in advance for the help,

Dylan

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