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post processing: project 2D data onto 1D axis

Posted 1 nov. 2018, 17:45 UTC−4 Chemical Reaction Engineering, Bioengineering, Results & Visualization Version 5.3a 5 Replies

Emily
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Hi, I was trying to compute the profile of molecule concentration (which is the result of certain stationary or time-dependent study) by projecting the 2D data onto a 1D axis. Like showing in the attached graph, molecules can only diffuse in the blue region and I want to look at it concentration profile in the horizontal direction (x-direction) by averaging its concentration in the vertical direction at every x location. I understand this can be done by exporting all of the data and using MATLAB to do the averaging part. But the exported data files are huge for the real geometry I am looking at. I wonder if this can be done within COMSOL? Thank you!

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5 Replies Last Post 9 nov. 2018, 11:07 UTC−5
Niklas Rom COMSOL Employee

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Posted: 7 years ago 2 nov. 2018, 04:26 UTC−4
Updated: 7 years ago 2 nov. 2018, 04:30 UTC−4

Hi Emily, in COMSOL Multiphysics, use the Linear Projection, or General Projection couplings.

Read up on this is the documentation (Press F1 in COMSOL to bring the doc up). Then go to the section COMSOL Multiphysics Reference Manual > Global and Local Definitions > Component Couplings and Coupling Operators.

Attached is an example:

http://cds.comsol.com/mg/25bdc08cc48522.zip Estimated size: 4.8 MB This link expires November 9, 2018. Please make sure to download before that date.

Included files: * ProjectionCouplingExample.mph * ProjectionCouplingExampleV43a.pptx

Kind regards

Niklas Rom, COMSOL

Hi Emily, in COMSOL Multiphysics, use the Linear Projection, or General Projection couplings. Read up on this is the documentation (Press F1 in COMSOL to bring the doc up). Then go to the section COMSOL Multiphysics Reference Manual > Global and Local Definitions > Component Couplings and Coupling Operators. Attached is an example: [http://cds.comsol.com/mg/25bdc08cc48522.zip](http://cds.comsol.com/mg/25bdc08cc48522.zip) Estimated size: 4.8 MB This link expires November 9, 2018. Please make sure to download before that date. Included files: * ProjectionCouplingExample.mph * ProjectionCouplingExampleV43a.pptx Kind regards Niklas Rom, COMSOL
Emily
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Posted: 7 years ago 8 nov. 2018, 16:14 UTC−5
Updated: 7 years ago 8 nov. 2018, 16:55 UTC−5

Hi Niklas, Thank you very much for your reply. I tried the General Projection on a simple rectangular domain but still have trouble getting the correct solution. The model file is attached and the model problem is described as follows.

Molecules undergo diffusion (with rate D2) and degradation (with rate kdl) in a rectangle, where the concentration of the molecule on the left boundary is fixed at c_max. When I solve the system using Time Dependent study, it works fine. But the stationary study gives oscillatory negative values, which I don't quite understand. I wonder if you have any idea what is wrong here? Thank you very much.

Best, Emily

Hi Niklas, Thank you very much for your reply. I tried the General Projection on a simple rectangular domain but still have trouble getting the correct solution. The model file is attached and the model problem is described as follows. Molecules undergo diffusion (with rate D2) and degradation (with rate kdl) in a rectangle, where the concentration of the molecule on the left boundary is fixed at c_max. When I solve the system using Time Dependent study, it works fine. But the stationary study gives oscillatory negative values, which I don't quite understand. I wonder if you have any idea what is wrong here? Thank you very much. Best, Emily

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Lasse Murtomäki
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Posted: 7 years ago 9 nov. 2018, 02:54 UTC−5

Hi

Steady-state has a closed form solution

c/c_max = cosh[lambda·L(z-1)]/cosh[lambda·L]

where z = x/L, lambda² = kdl/D2 and L = the length of the domain (50 m).

As you see, the problem is in 1-D, really. I also was pondering the dimensions of the simulation domain (50 m) but then realised that your diffusion coefficient was 0.1 m²/s, making lambda·L ≈ 1.58. Did you think of making the problem dimensionless?

I also got an oscillatory steady-state :)

Hi Steady-state has a closed form solution c/c_max = cosh[lambda·L(z-1)]/cosh[lambda·L] where z = x/L, lambda² = kdl/D2 and L = the length of the domain (50 m). As you see, the problem is in 1-D, really. I also was pondering the dimensions of the simulation domain (50 m) but then realised that your diffusion coefficient was 0.1 m²/s, making lambda·L ≈ 1.58. Did you think of making the problem dimensionless? I also got an oscillatory steady-state :)
Lasse Murtomäki
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Posted: 7 years ago 9 nov. 2018, 07:03 UTC−5

Aargh!

The reaction term must be of course -kdl*c. The it works fine

Aargh! The reaction term must be of course -kdl*c. The it works fine
Emily
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Posted: 7 years ago 9 nov. 2018, 11:07 UTC−5

Thank you Lasse! Yes, the reaction term should be -kdl*c. That's a stupid mistake.

Thank you Lasse! Yes, the reaction term should be -kdl*c. That's a stupid mistake.

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