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Derivative Boundary Condition

Posted Oct 20, 2010, 5:26 p.m. EDT Version 3.5a 6 Replies

Josue Cruz Perez
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Hi

I'm modeling with the PDE Coefficient Form Time-dependent analysis in 1D module two equations with two dependent variables. One of my boundary conditions is a derivative with respect to time (dh/dt|x=1 =constant). Is there anyway I can enter this boundary condition into my model?

Thank you for any help I can get.
6 Replies Last Post Apr 14, 2012, 2:06 p.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Oct 21, 2010, 7:08 a.m. EDT
Hi

by default COMSOL implements several derivatives (spatial and temporal) have you checked the equations view to see if also in raw PDE mode, these are generated by default ? I cannot remember just now which are present) In the 3.5 doc there was a list of all variables for each "application mode", I havent seen it updated in V4 yet

--
Good luck
Ivar
Hi by default COMSOL implements several derivatives (spatial and temporal) have you checked the equations view to see if also in raw PDE mode, these are generated by default ? I cannot remember just now which are present) In the 3.5 doc there was a list of all variables for each "application mode", I havent seen it updated in V4 yet -- Good luck Ivar
Magnus Ringh COMSOL Employee

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Posted: 1 decade ago Oct 21, 2010, 10:28 a.m. EDT
This is a bit tricky but possible.

In version 4, add a Constraint node and specify that R is the constraint R = 0 is

1-ut

ut is COMSOL syntax for du/dt. This constrains du/dt to 1 at the boundary where the Constraint node is active. You also need to make the following modifications in the Settings window for the Constraint node:

- Select "Unidirectional" from the "Constraint type" list because the bidirectional constraint attempts to apply the test function on the time derivative of u, which is not supported.

- Select the "Use weak constraints" check box because pointwise constraints for time derivatives are not supported.

Magnus Ringh, COMSOL
This is a bit tricky but possible. In version 4, add a Constraint node and specify that R is the constraint R = 0 is 1-ut ut is COMSOL syntax for du/dt. This constrains du/dt to 1 at the boundary where the Constraint node is active. You also need to make the following modifications in the Settings window for the Constraint node: - Select "Unidirectional" from the "Constraint type" list because the bidirectional constraint attempts to apply the test function on the time derivative of u, which is not supported. - Select the "Use weak constraints" check box because pointwise constraints for time derivatives are not supported. Magnus Ringh, COMSOL
Josue Cruz Perez
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Posted: 1 decade ago Oct 21, 2010, 2:52 p.m. EDT
Thank you for your time. I will try these solutions. If I can't find anything I will ask again with more details.
Thank you for your time. I will try these solutions. If I can't find anything I will ask again with more details.
Yunxing Song
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Posted: 1 decade ago Apr 5, 2012, 6:25 a.m. EDT

This is a bit tricky but possible.

In version 4, add a Constraint node and specify that R is the constraint R = 0 is

1-ut

ut is COMSOL syntax for du/dt. This constrains du/dt to 1 at the boundary where the Constraint node is active. You also need to make the following modifications in the Settings window for the Constraint node:

- Select "Unidirectional" from the "Constraint type" list because the bidirectional constraint attempts to apply the test function on the time derivative of u, which is not supported.

- Select the "Use weak constraints" check box because pointwise constraints for time derivatives are not supported.

Magnus Ringh, COMSOL

Hi, I use comsol3.5a. I met the same erro during a transient elasto-plastic analysis. In my model, the identity pairs is also used. I selected the weak constraints as you recommended,but it didn't work. Looking forward to your help

[QUOTE] This is a bit tricky but possible. In version 4, add a Constraint node and specify that R is the constraint R = 0 is 1-ut ut is COMSOL syntax for du/dt. This constrains du/dt to 1 at the boundary where the Constraint node is active. You also need to make the following modifications in the Settings window for the Constraint node: - Select "Unidirectional" from the "Constraint type" list because the bidirectional constraint attempts to apply the test function on the time derivative of u, which is not supported. - Select the "Use weak constraints" check box because pointwise constraints for time derivatives are not supported. Magnus Ringh, COMSOL [/QUOTE] Hi, I use comsol3.5a. I met the same erro during a transient elasto-plastic analysis. In my model, the identity pairs is also used. I selected the weak constraints as you recommended,but it didn't work. Looking forward to your help
Lakshmi Selvakumaran
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Posted: 1 decade ago Apr 5, 2012, 8:03 a.m. EDT
Hi, I am trying something similar where I am trying to specify a periodic boundary condition between two boundaries and equate it to the average of the strain over the volume multiplied with the difference in position vector. I tried it in verson 4.2 in stationary mode with a thermal strain but COMSOL is unable to solve it. Could you help?
Hi, I am trying something similar where I am trying to specify a periodic boundary condition between two boundaries and equate it to the average of the strain over the volume multiplied with the difference in position vector. I tried it in verson 4.2 in stationary mode with a thermal strain but COMSOL is unable to solve it. Could you help?
Abdul Halim
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Posted: 1 decade ago Apr 14, 2012, 2:06 p.m. EDT
Hi all,


Now I am trying to model a rotating machinery in AC/DC Module. It is exactly an axial flux permanent magnet synchronous generator.
I`ve finished the geometry and model of the generator. Yes, It`s like a disc, so it will be more efficient than the radial one.

These are the explanation of my model:
- Permanent magnet poles are pleced in the back yoke of rotor.
- Stator, which consist of some winding/coil, are placed between the two rotor. I`m using coreless stator one.
- There is air gap between rotor and stator.

I have adjusted the subdomain physics settings by choosing the material and the H-B equation, but I have no idea, what I have to do next.. So users, please suggest me what I have to adjust next.

- How to adjust the boundary settings?
- What function and equation that I`ve to give for the model.. In what part?
- and how to visualize the outcoming voltage of every phase of the generator??


Thank you
Halim, Zahari
Hi all, Now I am trying to model a rotating machinery in AC/DC Module. It is exactly an axial flux permanent magnet synchronous generator. I`ve finished the geometry and model of the generator. Yes, It`s like a disc, so it will be more efficient than the radial one. These are the explanation of my model: - Permanent magnet poles are pleced in the back yoke of rotor. - Stator, which consist of some winding/coil, are placed between the two rotor. I`m using coreless stator one. - There is air gap between rotor and stator. I have adjusted the subdomain physics settings by choosing the material and the H-B equation, but I have no idea, what I have to do next.. So users, please suggest me what I have to adjust next. - How to adjust the boundary settings? - What function and equation that I`ve to give for the model.. In what part? - and how to visualize the outcoming voltage of every phase of the generator?? Thank you Halim, Zahari

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