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finding a specified flow rate in a '3D cut plane'

Posted 15 mag 2012, 18:08 GMT-4 Fluid & Heat, Microfluidics, Results & Visualization Version 4.2a 8 Replies

Pooyan Tirandazi
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Hello,

I'm trying to do some postprocessing in a 3D fluid channel flow over a fractured hole.
The channel is filled with water and is laminar.
Here's what I'm trying to do:

1. cut the surface at an arbitrary channel location (i used the 'cut plane')
2. within that surface, I would like to start from one edge and integrate the velocity profile in a prescribed area.
eg) if the surface slice is a 2mmx2mm rectangle, i want to make another rectangle that is 1mmx1mm within that original 'cut plane' and measure the surface integrated velocity value (flow rate).

I was able to cut the surface where I wanted it, but I cannot find a way to resolve what I said in 2.

Any ideas?

Thanks!

TJ
8 Replies Last Post 10 dic 2015, 15:50 GMT-5
Mranal Jain
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Posted: 1 decade ago 16 mag 2012, 02:00 GMT-4
Did you try --derived values--integration--surface--with your new cut plane (the 2nd cut plane).

I should give you the integrated velocity value, also based on what i get from your post, only 2nd cut plane should suffice. You may not need to create the first cut plane if you want to integrate over the 2nd cut plane surface.

Good luck.
Did you try --derived values--integration--surface--with your new cut plane (the 2nd cut plane). I should give you the integrated velocity value, also based on what i get from your post, only 2nd cut plane should suffice. You may not need to create the first cut plane if you want to integrate over the 2nd cut plane surface. Good luck.
Pooyan Tirandazi
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Posted: 1 decade ago 16 mag 2012, 10:34 GMT-4
Hello Mranal,

Thank you for the tip.

I do know the integral function, but I could not separately cut out the 2nd slice.
Even when I performed the 3-points 'cut plane', the slice seemed to cut through the entire geometry passing those three points.

Is there a way to directly specify a small patch with an arbitrary surface area anywhere within the domain?
As you said, I could then just find the flow rate using the integral function in that surface.

Best,
Tae Jin Kim
Hello Mranal, Thank you for the tip. I do know the integral function, but I could not separately cut out the 2nd slice. Even when I performed the 3-points 'cut plane', the slice seemed to cut through the entire geometry passing those three points. Is there a way to directly specify a small patch with an arbitrary surface area anywhere within the domain? As you said, I could then just find the flow rate using the integral function in that surface. Best, Tae Jin Kim
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 16 mag 2012, 10:48 GMT-4
Hi

the cut plane cuts out the full model, if you want to limit the area, you need to multiply your integrand by two bolean operations such as (1<x)*(-1<y)*integrand*(x<2)*(y<3)

but be careful with the average() operator as it considers the full area and not the limited one

--
Good luck
Ivar
Hi the cut plane cuts out the full model, if you want to limit the area, you need to multiply your integrand by two bolean operations such as (1
Mranal Jain
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Posted: 1 decade ago 16 mag 2012, 14:48 GMT-4
As Ivar suggested, the best way is to use logical expressions.

Other option is using parametric surfaces; for instance if you want to cut a circular planar surface; we can use the following:

data sets >> parameterized surface>> s1 varying 0-2*pi>>s2 varying 0-R

expression x = x1 or any value where yz circular plane is located

y = s2*cos(s1)
z = s2*sin(s1)

that should give you a circular surface (of radius R in yz plane at x = x1) in your geometry which you could use for integration or any other operation. But we need to parameterized the surface which would be difficult for irregular shaped surfaces.

Good luck.
As Ivar suggested, the best way is to use logical expressions. Other option is using parametric surfaces; for instance if you want to cut a circular planar surface; we can use the following: data sets >> parameterized surface>> s1 varying 0-2*pi>>s2 varying 0-R expression x = x1 or any value where yz circular plane is located y = s2*cos(s1) z = s2*sin(s1) that should give you a circular surface (of radius R in yz plane at x = x1) in your geometry which you could use for integration or any other operation. But we need to parameterized the surface which would be difficult for irregular shaped surfaces. Good luck.
Mranal Jain
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Posted: 1 decade ago 16 mag 2012, 16:51 GMT-4
I forgot to add in last post; as you have asked for a rectangular yz plane; just vary s1 from y1 to y2 and s2 from z1 to z2

expressions > x = x1; y = s1; z = s2 ... that you give you a small rectangular cut plane.

Good luck.
I forgot to add in last post; as you have asked for a rectangular yz plane; just vary s1 from y1 to y2 and s2 from z1 to z2 expressions > x = x1; y = s1; z = s2 ... that you give you a small rectangular cut plane. Good luck.
Pooyan Tirandazi
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Posted: 1 decade ago 16 mag 2012, 17:42 GMT-4
Hello Mranal and Ivar,

I was curious what the parameterized surface stood for but now I know; it's exactly what I needed.
Thank you so much for the help!

Best,
TJ
Hello Mranal and Ivar, I was curious what the parameterized surface stood for but now I know; it's exactly what I needed. Thank you so much for the help! Best, TJ
Hamid Moezzi
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Posted: 1 decade ago 15 apr 2014, 09:27 GMT-4
hi

i have a similar problem.
i want to find the average velocity(or flow rate) in a section in the middle of my 3D channel but i do not know how!!! i tried to find the velocity using cut plane, cut line 3D and so on, but non of them was useful. would you mind please help me with my problem.
thank you so much
hamid
hi i have a similar problem. i want to find the average velocity(or flow rate) in a section in the middle of my 3D channel but i do not know how!!! i tried to find the velocity using cut plane, cut line 3D and so on, but non of them was useful. would you mind please help me with my problem. thank you so much hamid
Alexey Trukhin
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Posted: 9 years ago 10 dic 2015, 15:50 GMT-5

I forgot to add in last post; as you have asked for a rectangular yz plane; just vary s1 from y1 to y2 and s2 from z1 to z2

expressions > x = x1; y = s1; z = s2 ... that you give you a small rectangular cut plane.

Good luck.

Dear Mranal,
I tried plotting Parameterized Surface as you suggested, but I have got a error (see the attachment). Could you please point out a mistake?
[QUOTE] I forgot to add in last post; as you have asked for a rectangular yz plane; just vary s1 from y1 to y2 and s2 from z1 to z2 expressions > x = x1; y = s1; z = s2 ... that you give you a small rectangular cut plane. Good luck. [/QUOTE] Dear Mranal, I tried plotting Parameterized Surface as you suggested, but I have got a error (see the attachment). Could you please point out a mistake?

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