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How to connect electrostatic module to creeping flow

Posted Sep 7, 2017, 2:29 a.m. EDT Low-Frequency Electromagnetics, Computational Fluid Dynamics (CFD), Microfluidics Version 5.2 5 Replies

Enrico Freda
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As you know we have a volume force term in navier stokes equation which is due to electric field or electric potential gradient (ρe*E ,E = −∇ϕ ) I want to introduce this force in volume force but I don't know how to write gradient term, I mean I cannot find the annotation or syntax to introduce gradient to COMSOL.
5 Replies Last Post Sep 17, 2017, 6:54 a.m. EDT
NDN UNIST/Mechanical Engineering
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Posted: 7 years ago Sep 8, 2017, 2:00 p.m. EDT
You can search key "Operator" in Help
To couple the two Study together, following steps maybe applied
For example:
Study 1 solving for Electrostatic
Study 2 solving for Fluid module

Now you wanna couple Study 1 and 2 together, that means, in Fluid module, you need to use some value of Electrical field which are solved by Study 1. So you need to "link" them togethe by:

In Study 1 > Value of variables not solve for : Initial Expression in Method and Zero Solution in Study
In Study 2 > Value of variables not solve for : Solution in Method and Study 1,...... in Study

Good luck !
You can search key "Operator" in Help To couple the two Study together, following steps maybe applied For example: Study 1 solving for Electrostatic Study 2 solving for Fluid module Now you wanna couple Study 1 and 2 together, that means, in Fluid module, you need to use some value of Electrical field which are solved by Study 1. So you need to "link" them togethe by: In Study 1 > Value of variables not solve for : Initial Expression in Method and Zero Solution in Study In Study 2 > Value of variables not solve for : Solution in Method and Study 1,...... in Study Good luck !
Tausif Mulla
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Posted: 7 years ago Sep 8, 2017, 10:39 p.m. EDT
Use Comsol tutorial to model the electrical volume force in the Laminar flow. It can be modeled for creeping flow as well.

"Separation Through Electrocoalescence"

You can get the required file here

''www.comsol.com/model/separation-through-electrocoalescence-8592"
Use Comsol tutorial to model the electrical volume force in the Laminar flow. It can be modeled for creeping flow as well. "Separation Through Electrocoalescence" You can get the required file here ''https://www.comsol.com/model/separation-through-electrocoalescence-8592"
Enrico Freda
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Posted: 7 years ago Sep 15, 2017, 2:02 a.m. EDT

You can search key "Operator" in Help To couple the two Study together, following steps maybe applied For example: Study 1 solving for Electrostatic Study 2 solving for Fluid module

Now you wanna couple Study 1 and 2 together, that means, in Fluid module, you need to use some value of Electrical field which are solved by Study 1. So you need to "link" them togethe by:

In Study 1 > Value of variables not solve for : Initial Expression in Method and Zero Solution in Study In Study 2 > Value of variables not solve for : Solution in Method and Study 1,...... in Study

Good luck !

Thanks for your quick response and excuse me for my late reply, I was busy taking run from my model and It took a couple of days to solve. Your answer to my question helped me a lot, I really appreciate it. I have another question, maybe you could help me on, I want to get result from part of my whole domain. Consider a rectangular channel that I want to get the result( e.g velocity field near the wall), How could I do that? (I mean extracting a near-wall velocity field from the whole-domain velocity field)

>You can search key "Operator" in Help >To couple the two Study together, following steps maybe applied >For example: >Study 1 solving for Electrostatic >Study 2 solving for Fluid module > >Now you wanna couple Study 1 and 2 together, that means, in Fluid module, you need to use some value of Electrical field which are solved by Study 1. So you need to "link" them togethe by: > >In Study 1 > Value of variables not solve for : Initial Expression in Method and Zero Solution in Study >In Study 2 > Value of variables not solve for : Solution in Method and Study 1,...... in Study > >Good luck ! Thanks for your quick response and excuse me for my late reply, I was busy taking run from my model and It took a couple of days to solve. Your answer to my question helped me a lot, I really appreciate it. I have another question, maybe you could help me on, I want to get result from part of my whole domain. Consider a rectangular channel that I want to get the result( e.g velocity field near the wall), How could I do that? (I mean extracting a near-wall velocity field from the whole-domain velocity field)
Enrico Freda
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Posted: 7 years ago Sep 15, 2017, 2:11 a.m. EDT

Use Comsol tutorial to model the electrical volume force in the Laminar flow. It can be modeled for creeping flow as well.

"Separation Through Electrocoalescence"

You can get the required file here

''https://www.comsol.com/model/separation-through-electrocoalescence-8592"

Dear Tausif Mulla Your answer was fantastic, I really appreciate it! You don't know how your answer eased my simulation, the model you shared in the answer was fantastic and in great relation with my model. Excuse me for my late reply as I was busy running my model and solving its error a couple of days. I have another issue in order to validate my model with papers available I should extract velocity field contour absolutely adjacent to the wall. I’ve extracted the whole domain velocity field but I don’t know how I can extract this velocity field just near to the wall. Yours sincerely Enrico

>Use Comsol tutorial to model the electrical volume force in the Laminar flow. It can be modeled for creeping flow as well. > >"Separation Through Electrocoalescence" > >You can get the required file here > >''https://www.comsol.com/model/separation-through-electrocoalescence-8592" Dear Tausif Mulla Your answer was fantastic, I really appreciate it! You don't know how your answer eased my simulation, the model you shared in the answer was fantastic and in great relation with my model. Excuse me for my late reply as I was busy running my model and solving its error a couple of days. I have another issue in order to validate my model with papers available I should extract velocity field contour absolutely adjacent to the wall. I’ve extracted the whole domain velocity field but I don’t know how I can extract this velocity field just near to the wall. Yours sincerely Enrico
NDN UNIST/Mechanical Engineering
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Posted: 7 years ago Sep 17, 2017, 6:54 a.m. EDT

You can search key "Operator" in Help To couple the two Study together, following steps maybe applied For example: Study 1 solving for Electrostatic Study 2 solving for Fluid module

Now you wanna couple Study 1 and 2 together, that means, in Fluid module, you need to use some value of Electrical field which are solved by Study 1. So you need to "link" them togethe by:

In Study 1 > Value of variables not solve for : Initial Expression in Method and Zero Solution in Study In Study 2 > Value of variables not solve for : Solution in Method and Study 1,...... in Study

Good luck !

Thanks for your quick response and excuse me for my late reply, I was busy taking run from my model and It took a couple of days to solve. Your answer to my question helped me a lot, I really appreciate it. I have another question, maybe you could help me on, I want to get result from part of my whole domain. Consider a rectangular channel that I want to get the result( e.g velocity field near the wall), How could I do that? (I mean extracting a near-wall velocity field from the whole-domain velocity field)

Theorically, all of your solved datas were stored in "Data Sets" of Result section. In your case, you wanna derive the value of velocity near the wall. Hence, the first thing you have to specify the position of point you wanna get this value. To do that, using Cut Point 2D in Dataset section. Note that in Data set, it stored many of Solution you have already solved, therefore the impotant thing must select the proper solution the in the Data set sub-section of Cut Point 2D. Finally, you can use Plot command in the Cut point 2D, or use 1D Graph Group > Point Graph BG Nhan ND

>>You can search key "Operator" in Help >>To couple the two Study together, following steps maybe applied >>For example: >>Study 1 solving for Electrostatic >>Study 2 solving for Fluid module >> >>Now you wanna couple Study 1 and 2 together, that means, in Fluid module, you need to use some value of Electrical field which are solved by Study 1. So you need to "link" them togethe by: >> >>In Study 1 > Value of variables not solve for : Initial Expression in Method and Zero Solution in Study >>In Study 2 > Value of variables not solve for : Solution in Method and Study 1,...... in Study >> >>Good luck ! > >Thanks for your quick response and excuse me for my late reply, I was busy taking run from my model and It took a couple of days to solve. >Your answer to my question helped me a lot, I really appreciate it. I have another question, maybe you could help me on, I want to get result from part of my whole domain. Consider a rectangular channel that I want to get the result( e.g velocity field near the wall), How could I do that? (I mean extracting a near-wall velocity field from the whole-domain velocity field) Theorically, all of your solved datas were stored in "Data Sets" of Result section. In your case, you wanna derive the value of velocity near the wall. Hence, the first thing you have to specify the position of point you wanna get this value. To do that, using Cut Point 2D in Dataset section. Note that in Data set, it stored many of Solution you have already solved, therefore the impotant thing must select the proper solution the in the Data set sub-section of Cut Point 2D. Finally, you can use Plot command in the Cut point 2D, or use 1D Graph Group > Point Graph BG Nhan ND

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