Integration of current density in 2D Axi symmetric steady state to obtain current in circular wire

Numerical methods and mathematical models of Elmer
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FFF
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Integration of current density in 2D Axi symmetric steady state to obtain current in circular wire

Post by FFF »

Hello Elmer community,

I want to integrate the current density over a wire's cross section in a steady state 2Daxi simulation.

To do so, I followed the following post:
viewtopic.php?f=3&t=7521&hilit=boundary+integrals
Unfortunately I don’t get results.

In the name output of savescalars, the boundary integral is listed but the magnitude is zero.

I work on windows and use Version: 9.0 (Rev: Release, Compiled: 2021-06-15)

Could anybody be so kind and have a look at my case?
current2Daxis.zip
(185.64 KiB) Downloaded 18 times
current2Daxis.sif
(3.46 KiB) Downloaded 24 times
current2Daxis.msh
(101.47 KiB) Downloaded 21 times
Your help would be much appreciated.

Felix
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Re: Integration of current density in 2D Axi symmetric steady state to obtain current in circular wire

Post by raback »

Hi Felix,

Did you use the last setup as verified by laurent on May 31st in that thread? I see some small differences in the SaveScalars operation.

-Peter
FFF
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Re: Integration of current density in 2D Axi symmetric steady state to obtain current in circular wire

Post by FFF »

Hi Peter,

thank you for your fast reply.

Yes, as far as I see it is pretty equal. Please see my code below:

Code: Select all

Solver 2
  Equation = MgDynPost
  Calculate Magnetic Field Strength = True
  Procedure = "MagnetoDynamics" "MagnetoDynamicsCalcFields"
  Potential Variable = String "Potential"

  Calculate Nodal Fields = False
  Calculate Elemental Fields = True
  Calculate Nodal Forces = True

 Calculate Magnetic Field Strength = True
 Calculate Electric Field = True
 Calculate Current Density = True
  
End


Solver 3
  Exec Solver = After All
  Equation = SaveScalars
  Procedure = "SaveData" "SaveScalars"
  Filename = "data2d.dat"
  Save Component Results = logical true
  File Append = Logical True
     Variable 1 = current density e 
   Operator 1 = boundary int 
    Mask Name 1 = curr
   
End

Boundary Condition 3
  Target Boundaries(1) = 1
  Name = "excitation"
  !save scalars = Logical True
     curr=logical true
End

As you can see I use the command

Code: Select all

Mask Name 1= curr
I also tested it with

Code: Select all

save scalars = Logical True
But in both versions the numerical output is zero.

What is diffrernt from laurent, is that I use

Code: Select all

Body Force 1
  Current Density = 828736! J=1.1 A / (pi* rW^2) -> Radius of Wire -> rW=0.65e-3
   ! curr=logical true
	!Save Scalars = Logical True
End
But when I enable Save Scalars or curr there is no output (dat.names) at all.

Any ideas what went wrong?

Best regards,

Felix
Rich_B
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Joined: 24 Aug 2009, 20:18

Re: Integration of current density in 2D Axi symmetric steady state to obtain current in circular wire

Post by Rich_B »

Would you please post your solver log file? The log file is always helpful.

Thanks, Rich.
FFF
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Re: Integration of current density in 2D Axi symmetric steady state to obtain current in circular wire

Post by FFF »

Hi Rich,

sure!
solver.log
(7.65 KiB) Downloaded 20 times
I am suspicious about the following line:

Code: Select all

CheckKeyword:  Unlisted keyword: [curr] in section: [boundary condition 3]
but when I skip the command of mask name 1 in SaveScalars

and implement the following:

Code: Select all

Boundary Condition 3
  Target Boundaries(1) = 1
  Name = "excitation"
  save scalars = Logical True
   !  curr=logical true
End
The numerical output is still empty.

Can you see something else form solver.log?

I would highly appreciate if you could have a look.
Rich_B
Posts: 52
Joined: 24 Aug 2009, 20:18

Re: Integration of current density in 2D Axi symmetric steady state to obtain current in circular wire

Post by Rich_B »

This post viewtopic.php?f=9&t=4114 shows how you found a way to integrate the current density over a surface using Paraview. Nicely done!

It seems that SaveScalars and SaveLine aren't suited to provide results over a surface in 2D? One could select a boundary, such as the circle outlining the conductor, which in your case sums to zero since no current crosses the circle. In this 2D case, selecting the body (the conductor) would provide a surface to integrate over, but when you tried to add 'save scalars' to the body, it didn't work. Maybe someone who knows more about the inner workings of SaveScalars and SaveLine could shed some light on this topic?

Rich.
FFF
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Re: Integration of current density in 2D Axi symmetric steady state to obtain current in circular wire

Post by FFF »

Hi all,

Yes in Paraview i get plausible results:)

I did some further tests with the integration of the B-field of the enclosing air.

Please see
IntegrateB-Field2Daxi.png
(290.96 KiB) Not downloaded yet
I get some values of the B-Field integration where the Flux = 9.0E-008
(see fluxdata2d.dat.names and fluxdata2d.dat of
2DaxiFlux.zip
(223.98 KiB) Downloaded 16 times
)

I believe the must be multiplied by 2*pi

Hence the result is around 5.6e-07

The energy of the 2Daxi simulation is around 3.6E-009*2*pi=2.2619e-08 J

The integration of the current density is still zero. I included the solver.log with a Max Output Level = 32

1. I have no clue why this is the case for the integration of current density. Does anybody know?

I did an equal integration of the B-field with the 3D case.
Please see corresponding sif in
3dFlux.zip
(24.67 KiB) Downloaded 17 times
The mesh is too big to upload it here. Hence, I provide the .hdf of Salome. You can compute the mesh there and export it to .unv

Then use the command:

Code: Select all

elmergrid 8 2 Mesh_1.unv
in the Command Prompt of Windows

If you want to compare the Boundary Numbers of the mesh with the sif use the command

Code: Select all

elmergrid 8 4 Mesh_1.unv
in the Command Prompt of Windows and observe it in gmsh.

In 3D case, the simulated flux is 4.22E-008 Wb

I had the chance to simulate this also in comsol and get an equal result of 4.23E-8 Wb

2. Why do I have the deviation in the 2D case?

The energy in the 3D case is similar to the 2Daxi case of elmer with around 2.3E-008 J

In 3D I also get an eddy current power of around 1.02E-003

3. Shouldn’t the eddy current power be zero for a stationary simulation?

I highly appreciate if somebody could have a look at my simulations and/or provide an answer to my 3 questions above.

Felix
FFF
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Re: Integration of current density in 2D Axi symmetric steady state to obtain current in circular wire

Post by FFF »

Hi everybody,

I found the answer to my Question 2 of my previous post.

The problem was the mesh resolution of the edge. See the picture of my changes.
AnswerQuestion2.png
(237.6 KiB) Not downloaded yet
Now I get a coinciding flux of 4.44E-008 Wb

Here you have the updated simulation file with the integration of the Bfield only.
Circular2Daxi_FluxIntegration.zip
(158.35 KiB) Downloaded 5 times
The eddy current power (Question 3) changed back to 0.
Does anybody has further information how eddy current power did appear in the first place?

How to conduct the integration of the current density in the 2Daxi case (Question 1 from previous post) remains still a mystery to me.

I appreciate any hints!

Best regards!

Felix
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Re: Integration of current density in 2D Axi symmetric steady state to obtain current in circular wire

Post by raback »

Hi Felix,

There is nothing to worry about the code not finding "curr". It was just a temporal tag that we know to look for because we given the same in "mask name 1". This way we can refer to the boundaries where we want to operate in.

If you follow my example, the possible problems are:

1) Too old version of code
2) You try to integrate over wrong or non-existing boundary
3) The variable you're interested in does not exist.

You could also try with variable "current density" (without the "e").

The coordinate system should be accounted for in the integration.

-Peter
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