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Particle tracing - particle counting

Posted May 2, 2012, 6:56 a.m. EDT Ray Optics, Results & Visualization Version 5.1 21 Replies

Stefanos Michael
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Hello to everyone,

Im new to COMSOL and currently trying to work with particle tracing for fluid flow.
The model we are working on is part of vascular network and we are using as physics : structural mechanics, laminar flow, darcy flow, and particle tracing for fluid flow. Everything is working up to the point where we can calculate the particles trajectories but we need to be able to calculate how many particles pass though a specific area section. I have tried to use the Total number of particles in selection, Particle density, Particle position from the results in order to accomplish this. Unfortunately when i try this i get the following error:

CANNOT EVALUATE EXPRESSION
failed to evaluate variable -
Geometry -
Domain -

I have tried to toggle " compute particle mass" on from the particle tracing menu but then when i do this and try to calculate the solution i get another error:

Solution cannot be updated. Clear Solution to expunge.
Failed to evaluate expression.
Failed to evaluate variable.
- Variable: mod1.mp
- Geometry: 2
- Boundary: 1
Failed to evaluate expression.
- Expression: mod1.mp


I have checked the example of laminar_mixer_particle and the model but at that particulate example it only calculates trajectories and nothing more.
I've also tried to export the particle coordinates (designated as q) to excel spreadsheet file so i can process them elsewhere but been also unsuccesfull at that.

If someone has a solution please respond
Thank you,

SM
21 Replies Last Post Aug 11, 2016, 2:50 p.m. EDT
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Hello Stefanos Michael

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Robin Kieser
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Posted: 1 decade ago Aug 10, 2012, 5:23 a.m. EDT
"cannot evaluate expression" means that the expression you selected does not fit to the kind of plot ur using ( slice, streamline or whatever). im still searching myself for certain combinations.. its kind of a guessing game
"cannot evaluate expression" means that the expression you selected does not fit to the kind of plot ur using ( slice, streamline or whatever). im still searching myself for certain combinations.. its kind of a guessing game
Ashish Goel
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Posted: 1 decade ago Oct 9, 2012, 10:50 p.m. EDT
Hi.

I am facing the exact same problem as Stefanos. When I try to integrate the number of particles over a selected surface, I get the 'failed to evaluate variable' error. My model file can be found here www.mediafire.com/?q6twua5qiu5pg9t. Any help in this regard would be greatly appreciated.

Thanks
Ashish
Hi. I am facing the exact same problem as Stefanos. When I try to integrate the number of particles over a selected surface, I get the 'failed to evaluate variable' error. My model file can be found here http://www.mediafire.com/?q6twua5qiu5pg9t. Any help in this regard would be greatly appreciated. Thanks Ashish
Magnus Ringh COMSOL Employee

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Posted: 1 decade ago Oct 10, 2012, 3:41 a.m. EDT
Hi,

The variable cpt.Nsel contains the total number of particles in a selection (of domains), so use a Global Evaluation node under Derived Values to evaluate cpt.Nsel for a Particle data set (no integration is needed). If you want the particles in a specific domain instead of the entire geometry, add a Selection subnode to the Particle data set and use it to restrict the partuicle data to the domains selected in the settings for the Selection subnode.

Best regards,
Magnus Ringh, COMSOL
Hi, The variable cpt.Nsel contains the total number of particles in a selection (of domains), so use a Global Evaluation node under Derived Values to evaluate cpt.Nsel for a Particle data set (no integration is needed). If you want the particles in a specific domain instead of the entire geometry, add a Selection subnode to the Particle data set and use it to restrict the partuicle data to the domains selected in the settings for the Selection subnode. Best regards, Magnus Ringh, COMSOL
Marco Miller
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Posted: 1 decade ago Oct 23, 2012, 3:50 p.m. EDT
Yes indeed it is - A guessing game on particle counting
-------------------------------------------------------------------------
www.avl.com/particle-counter - en.wikipedia.org/wiki/Particle_counter - www.comsol.com/video/
Yes indeed it is - A guessing game on particle counting ------------------------------------------------------------------------- https://www.avl.com/particle-counter - http://en.wikipedia.org/wiki/Particle_counter - http://www.comsol.com/video/
Uttam Pal
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Posted: 1 decade ago Feb 7, 2013, 6:25 a.m. EST
Yah we can find the total number of particles using Derived values > Global Evaluation. But if we want to plot how the number of particles sticking on a surface(boundary) are varying along the surface, then how do we do it?

Global evaluation is giving only time selection as parameter.


Hi,

The variable cpt.Nsel contains the total number of particles in a selection (of domains), so use a Global Evaluation node under Derived Values to evaluate cpt.Nsel for a Particle data set (no integration is needed). If you want the particles in a specific domain instead of the entire geometry, add a Selection subnode to the Particle data set and use it to restrict the partuicle data to the domains selected in the settings for the Selection subnode.

Best regards,
Magnus Ringh, COMSOL


Yah we can find the total number of particles using Derived values > Global Evaluation. But if we want to plot how the number of particles sticking on a surface(boundary) are varying along the surface, then how do we do it? Global evaluation is giving only time selection as parameter. [QUOTE] Hi, The variable cpt.Nsel contains the total number of particles in a selection (of domains), so use a Global Evaluation node under Derived Values to evaluate cpt.Nsel for a Particle data set (no integration is needed). If you want the particles in a specific domain instead of the entire geometry, add a Selection subnode to the Particle data set and use it to restrict the partuicle data to the domains selected in the settings for the Selection subnode. Best regards, Magnus Ringh, COMSOL [/QUOTE]
Nicholas Campbell
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Posted: 1 decade ago Jun 26, 2013, 11:53 a.m. EDT
Has anyone found a good way to quantify the particles passing a boundary?

I am using the mathematical particle tracing module with the Hamiltonian analogy to simulate optical ray tracing. I want to be able to quantify the distribution of rays that reach specific boundaries in 2D and/or a surface in 3D.

Any help would be greatly appreciated. Thanks!

-NC
Has anyone found a good way to quantify the particles passing a boundary? I am using the mathematical particle tracing module with the Hamiltonian analogy to simulate optical ray tracing. I want to be able to quantify the distribution of rays that reach specific boundaries in 2D and/or a surface in 3D. Any help would be greatly appreciated. Thanks! -NC
Jingyuan Yan
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Posted: 10 years ago May 21, 2015, 7:12 p.m. EDT
Hi,

I have the same question. I could not find a way to (automatically) count the particle number passing a boundary, though manually count is OK. But what if when there is a huge bunch of particles...

Thanks in advance for anyone who knows the answer.
Hi, I have the same question. I could not find a way to (automatically) count the particle number passing a boundary, though manually count is OK. But what if when there is a huge bunch of particles... Thanks in advance for anyone who knows the answer.
Farhad Aalizadeh
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Posted: 9 years ago Jun 1, 2015, 12:46 a.m. EDT
Hi,
I have the same question as well!!!
did you find any answer?
would you please help me?

thanks
Hi, I have the same question as well!!! did you find any answer? would you please help me? thanks
Jingyuan Yan
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Posted: 9 years ago Jul 6, 2015, 11:39 a.m. EDT
Hi，

I haven't got a solution yet, but I found this post:

www.comsol.com/community/forums/general/thread/34641/

Probably we should use the LiveLink for Matlab... I am going to study this.

Jingyuan
Hi， I haven't got a solution yet, but I found this post: http://www.comsol.com/community/forums/general/thread/34641/ Probably we should use the LiveLink for Matlab... I am going to study this. Jingyuan
Jingyuan Yan
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Posted: 9 years ago Jul 9, 2015, 10:19 p.m. EDT
I just figured this out. You should refer to Magnus's answer above, really helpful. Pay attention:
1) The subnode should be under the "Derived Values" node
2) Add a "Global Evaluation" subnode instead of "Particle Evaluation" subnode.
I just figured this out. You should refer to Magnus's answer above, really helpful. Pay attention: 1) The subnode should be under the "Derived Values" node 2) Add a "Global Evaluation" subnode instead of "Particle Evaluation" subnode.
Wu Zhang
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Posted: 9 years ago Jul 26, 2015, 6:15 p.m. EDT
Hi, I added the node as you suggested, may I know where to get the solution to the particle number? Thank you!
Hi, I added the node as you suggested, may I know where to get the solution to the particle number? Thank you!
Jingyuan Yan
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Posted: 9 years ago Jul 28, 2015, 12:29 p.m. EDT
Hi,
Under the "Global Evaluation" node, select "particle1" for "Data Set". You need also to add the "fpt.Nsel" under "expression".
Hi, Under the "Global Evaluation" node, select "particle1" for "Data Set". You need also to add the "fpt.Nsel" under "expression".
Wu Zhang
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Posted: 9 years ago Jul 28, 2015, 5:26 p.m. EDT
Thank you! I did the setting but where I can see the results after computing please?
Also, if I want to count the particle number in a specific region or passing through specific cutting surface, may I know how to do the setting? thanks for the time!
Thank you! I did the setting but where I can see the results after computing please? Also, if I want to count the particle number in a specific region or passing through specific cutting surface, may I know how to do the setting? thanks for the time!
Jingyuan Yan
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Posted: 9 years ago Jul 29, 2015, 1:26 p.m. EDT
You can see the no. of particles on the bottom right frame. It will show the result if you click "Evaluate". If you could not see it, try to change the tag of the bottom right frame to "Table 1".

This is basically how to calculate the no. of particles in a chosen boundary. If you want to know the no. of particles in a specific boundary, just choose it. There is also a "time selection" in your "Global evaluation" settings. This indicate the total no. of particles passing your selected boundary from the beginning to your selected time.
You can see the no. of particles on the bottom right frame. It will show the result if you click "Evaluate". If you could not see it, try to change the tag of the bottom right frame to "Table 1". This is basically how to calculate the no. of particles in a chosen boundary. If you want to know the no. of particles in a specific boundary, just choose it. There is also a "time selection" in your "Global evaluation" settings. This indicate the total no. of particles passing your selected boundary from the beginning to your selected time.
Wu Zhang
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Posted: 9 years ago Jul 31, 2015, 11:32 a.m. EDT
hi, thank you so much for kind reply. I can get the total particle number in the area now. But it seems I can not select any boundaries. I tried to go to "outlet" node, in which window it allows me to select boundaries. then go back to "global evaluation", and select one boundary, but the evaluation still gives me the total number (attached Figure). May I know how to solve it please? so appreciate your help!
hi, thank you so much for kind reply. I can get the total particle number in the area now. But it seems I can not select any boundaries. I tried to go to "outlet" node, in which window it allows me to select boundaries. then go back to "global evaluation", and select one boundary, but the evaluation still gives me the total number (attached Figure). May I know how to solve it please? so appreciate your help!

Attachments:

Jingyuan Yan
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Posted: 9 years ago Aug 1, 2015, 2:10 p.m. EDT
Hi,

Please make sure to have this "selection" node under "particles", and choose the boundary you want (see attached file). I believe that is the reason why you only have the total no. of particles.
Hi, Please make sure to have this "selection" node under "particles", and choose the boundary you want (see attached file). I believe that is the reason why you only have the total no. of particles.

Attachments:

Wu Zhang
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Posted: 9 years ago Aug 1, 2015, 5:12 p.m. EDT
Hi, Jingyuan, thank you so much for the instruction, I finally get the results! Have a nice weekend!
Hi, Jingyuan, thank you so much for the instruction, I finally get the results! Have a nice weekend!
Ahmed Dalvi
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Posted: 9 years ago Aug 12, 2015, 10:06 a.m. EDT
Hi,
I'm doing something similar only for a ray trace simulation. How do I count the number of rays in a particular wall?
Hi, I'm doing something similar only for a ray trace simulation. How do I count the number of rays in a particular wall?
Daniel Smith COMSOL Employee

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Posted: 9 years ago Nov 19, 2015, 11:02 a.m. EST
A blog post on counting particles is now available:
www.comsol.com/blogs/different-ways-to-count-particles-in-comsol-multiphysics/
A blog post on counting particles is now available: http://www.comsol.com/blogs/different-ways-to-count-particles-in-comsol-multiphysics/
Jeevan Maddala
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Posted: 8 years ago Aug 11, 2016, 2:47 p.m. EDT
How do you count it manually? from particle trajectories ?
How do you count it manually? from particle trajectories ?
Jingyuan Yan
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Posted: 8 years ago Aug 11, 2016, 2:50 p.m. EDT
You don't need to count manually. The software can automatically count the number. Just follow the options written in the post above.
You don't need to count manually. The software can automatically count the number. Just follow the options written in the post above.

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