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Shear stress on streamlines/pathlines

Posted Feb 1, 2010, 11:32 a.m. EST 6 Replies

J
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Hello guys,

does anyone know how to export into Matlab the values of shear stress found on a streamline or pathline?
Like, I plot my pathline but I'm able just to export the velocity and not other variables.

Hope someone can help me,
Cheers

J
6 Replies Last Post Feb 17, 2010, 6:51 p.m. EST
Tim Maguire
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Posted: 2 decades ago Feb 8, 2010, 9:42 p.m. EST
Did you get an answer? I would like to know the same thing.

Also, is there a way to control the length of the streamlines?
Did you get an answer? I would like to know the same thing. Also, is there a way to control the length of the streamlines?
J
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Posted: 2 decades ago Feb 9, 2010, 12:22 p.m. EST
Hey!

Yes, this is the answer I got. Just be careful that they did a mistake in the formula you have to write (of course is the spatial gradient when you are considering the shear stress).

---------------------------
Regarding streamlines and shear stress: I am not sure if I understand your
question. If you like to extract the shear stress from a streamline, use
Cross-section plot parameters->Line extrusion and plot

shear stress = eta_chns*du/dt

at this line.

Boundary integration: This feature can only be used on boundaries. If you
want to integrate over a certain line in a subdomain, you need to draw this
line at that location.
---------------------------

Regarding the length...there should be, I think I saw it...I'll check!
Hey! Yes, this is the answer I got. Just be careful that they did a mistake in the formula you have to write (of course is the spatial gradient when you are considering the shear stress). --------------------------- Regarding streamlines and shear stress: I am not sure if I understand your question. If you like to extract the shear stress from a streamline, use Cross-section plot parameters->Line extrusion and plot shear stress = eta_chns*du/dt at this line. Boundary integration: This feature can only be used on boundaries. If you want to integrate over a certain line in a subdomain, you need to draw this line at that location. --------------------------- Regarding the length...there should be, I think I saw it...I'll check!
Tim Maguire
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Posted: 2 decades ago Feb 9, 2010, 2:12 p.m. EST
OK:

So you calculated shear stress as eta_chns*du/dy , or eta_chns*dv/dx?


Where does this calculation get entered into.

Thank you so much for the help!
OK: So you calculated shear stress as eta_chns*du/dy , or eta_chns*dv/dx? Where does this calculation get entered into. Thank you so much for the help!
J
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Posted: 2 decades ago Feb 10, 2010, 7:50 a.m. EST
You welcome! I perfectly know how painful is trying to use a complete unknown software!

So, regarding our talk:

Multiphysics --> Cross-Section Plot Parameters --> Line/Extrusion --> y-axis data --> and here you write the expression you need.
Of course if you want the magnitude of the shear stress, just calculate the different components and do the modulus.

Tell me if you have any question...of course I don't know if I'll be able to answer :)
You welcome! I perfectly know how painful is trying to use a complete unknown software! So, regarding our talk: Multiphysics --> Cross-Section Plot Parameters --> Line/Extrusion --> y-axis data --> and here you write the expression you need. Of course if you want the magnitude of the shear stress, just calculate the different components and do the modulus. Tell me if you have any question...of course I don't know if I'll be able to answer :)
J
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Posted: 2 decades ago Feb 10, 2010, 9:30 a.m. EST
I just found that COMSOL is not exporting the data on the specified streamline, but on a line defined by points. I'll tell you something as soon as the support will reply to me.

J
I just found that COMSOL is not exporting the data on the specified streamline, but on a line defined by points. I'll tell you something as soon as the support will reply to me. J
J
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Posted: 2 decades ago Feb 17, 2010, 6:51 p.m. EST
I think I solved the problem in the following way.
I went on plot parameters and used Particle Tracing Plot, that in this case is the same as Streamline since I'm in a steady case. Then inside Line Color I selected, for example, ux (du/dx). Then I exported the Current Plot.
It's an horrible way to export the data, but it works. But really...sucks!
I think I solved the problem in the following way. I went on plot parameters and used Particle Tracing Plot, that in this case is the same as Streamline since I'm in a steady case. Then inside Line Color I selected, for example, ux (du/dx). Then I exported the Current Plot. It's an horrible way to export the data, but it works. But really...sucks!

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