Menu

Discussion Forum

New Discussion
查找

Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

Integration of a value over cross-section

Posted 2011年12月5日 GMT-5 10:54 Fluid & Heat, Computational Fluid Dynamics (CFD), Chemical Reaction Engineering, Parameters, Variables, & Functions Version 4.2a, Version 4.4 6 Replies

Fabien
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hello everyone,

I have a model of molecular diffusion in a cylinder (axisymmetric geometry), and after solving (stationary solver) I get the concentration field c(r,z).

I would like to get rid of the r dependency and have access to the average concentration per cross-section

c_average(z)=2*pi*int(r*c(r,z),0,R)/(pi*R^2)

where R is the radius of the cylinder.

I managed to get the value for any fixed value of z using Results > Derived Value > Line integration, but I would like to define this variable for any value of z to be able to plot c_average(z) vs z.

Is there a way to do this?

Thanks a lot for your help!

Fabien


6 Replies Last Post 2014年5月14日 GMT-4 17:51
Fabien
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 2011年12月6日 GMT-5 12:01

Actually after some efforts I found the solution using linear projection:

2*linproj1(r*c)/R^2

Regards

Fabien
Actually after some efforts I found the solution using linear projection: 2*linproj1(r*c)/R^2 Regards Fabien
ArseneNoume
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 2012年1月10日 GMT-5 05:07
i would like to do the same operation, on a 2D system to evaluate the cross sectional temperature average all along the x direction.
Can you tell me in detail how did you solve it?

Thankyou
i would like to do the same operation, on a 2D system to evaluate the cross sectional temperature average all along the x direction. Can you tell me in detail how did you solve it? Thankyou
Fabien
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 2012年1月10日 GMT-5 08:24

Hello Arsene,

I describe here my understanding of the linear projection which is in my sense not very well documented and quite obscure.

To do this you have to add an linear model coupling: right click on 'definitions' under your 'model' node and add a 'model coupling: linear projector' (by default linproj1).

Then you can select the domains where this projector applies and using the vertices you can define the source (define the plane Oxy by adding the corresponding points) and destination (line Oy) dimensions.

The linear projection gives the integral of the value so you have to divide by the length of the line on which the value was integrated to get the average (refered as 'length' in the formula below).

I think you have to relaunch the computation after adding the model coupling to be able to use it.

To plot the average temperature you have to add the boudaries along Oy of the domains you are interested in, then use as y-axis data expression:

linproj1(T) / length

where h is the length of cross-section, and y as x-data expression.

I hope this helps!

All the best,

Fabien
Hello Arsene, I describe here my understanding of the linear projection which is in my sense not very well documented and quite obscure. To do this you have to add an linear model coupling: right click on 'definitions' under your 'model' node and add a 'model coupling: linear projector' (by default linproj1). Then you can select the domains where this projector applies and using the vertices you can define the source (define the plane Oxy by adding the corresponding points) and destination (line Oy) dimensions. The linear projection gives the integral of the value so you have to divide by the length of the line on which the value was integrated to get the average (refered as 'length' in the formula below). I think you have to relaunch the computation after adding the model coupling to be able to use it. To plot the average temperature you have to add the boudaries along Oy of the domains you are interested in, then use as y-axis data expression: linproj1(T) / length where h is the length of cross-section, and y as x-data expression. I hope this helps! All the best, Fabien
ArseneNoume
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 2012年1月10日 GMT-5 10:28
Thankyou Fabien, for this detailed explanations!
It seems to be clear, I'll try and hope it'll work!

Kind regards
Thankyou Fabien, for this detailed explanations! It seems to be clear, I'll try and hope it'll work! Kind regards
Jorge Concepcion
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 2013年8月29日 GMT-4 17:01
Hi:

And what If I want the the same, but I have to integrate in a 3d domain i.e. the average over every cross section x,y and plot this average with respect to z.

Thanks
Hi: And what If I want the the same, but I have to integrate in a 3d domain i.e. the average over every cross section x,y and plot this average with respect to z. Thanks
Panagiotis Giotakos
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 2014年5月14日 GMT-4 17:51
Hi to everyone,

I would be grateful if someone could help me out with this noob problem.
I have little experience with COMSOL and I've never used any model couplings before. I need to find out how to use "Definition - Model Couplings - Linear or general projection", or another way, to calculate and plot the average velocity in y*z cross-section over the length of a rectangular pipe, (spanning across the x direction).
I've searched the forum and the documentation and I haven't manage much :-(

Thank you in advance

Panagiotis
Hi to everyone, I would be grateful if someone could help me out with this noob problem. I have little experience with COMSOL and I've never used any model couplings before. I need to find out how to use "Definition - Model Couplings - Linear or general projection", or another way, to calculate and plot the average velocity in y*z cross-section over the length of a rectangular pipe, (spanning across the x direction). I've searched the forum and the documentation and I haven't manage much :-( Thank you in advance Panagiotis

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content