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### Calculate magnetic torque

Posted: 05 Sep 2016, 16:46
Hi everyone!
I have some Problem with the calculation of magnetic torque. I found 2 possibilities in Elmer:

1. as a component:

Code: Select all

``````Component 1
Name = string "metal"
Master Bodies(1) = integer 4
Torque Origin(3) = Real 100 0 -100
Torque Axis(3) = Real 0 0 100
Calculate Magnetic Force = Logical True
Calculate Magnetic Torque = Logical True
End
``````
2. as a group

Code: Select all

``````...
Body 4
Target Bodies(1) = 4
Name = "Body 4"
Equation = 1
Material = 1
Body Force = 2
Torque Groups(1) = integer 1
End
...
Solver 3
Equation = MgDynPost
Potential Variable = AV
Calculate Current Density = True
Procedure = "MagnetoDynamics" "MagnetoDynamicsCalcFields"
Calculate Electric Field = True
Calculate Magnetic Field Strength = True
Exec Solver = Always
Stabilize = True
Bubbles = False
Lumped Mass Matrix = False
Optimize Bandwidth = True
Steady State Convergence Tolerance = 1.0e-5
Nonlinear System Convergence Tolerance = 1.0e-7
Nonlinear System Max Iterations = 20
Nonlinear System Newton After Iterations = 3
Nonlinear System Newton After Tolerance = 1.0e-3
Nonlinear System Relaxation Factor = 1
Linear System Solver = Iterative
Linear System Iterative Method = CG
Linear System Max Iterations = 5000
Linear System Convergence Tolerance = 1.0e-10
BiCGstabl polynomial degree = 2
Linear System Preconditioning = Diagonal
Linear System ILUT Tolerance = 1.0e-3
Linear System Abort Not Converged = False
Linear System Residual Output = 1
Linear System Precondition Recompute = 1

Torque Group Origins(1,3) = Real 100 0 0
Torque Group Axes(1, 3) = Real 0 0 1
Calculate Electric Field = True
Calculate Magnetic Field Strength = True
Calculate Nodal Forces = Logical True
End``````
My problems are so far:

1. When i use coordinate scaling=1e-3 a point at 100mm in x-direction is still Torque Group Origins(1,3) = Real 100 0 0?

2. Whats the right way when i want a torque axis from f.e. A=(10 20 -30) to b=(10 20 30):

Code: Select all

``````Torque Origin(3) = Real 10 20 -30
Torque Axis(3) = Real 0 0 30``````
or

Code: Select all

``````Torque Origin(3) = Real 10 20 -30
Torque Axis(3) = Real 10 20 30``````
?

### Re: Calculate magnetic torque

Posted: 06 Sep 2016, 09:41
Hi

1) Scaling is applied to the mesh when reading it in so Elmer loses all information of the original coordinates. Therefore use the scaled coordinates always.

2) The 1st alternative.

-Peter

### Re: Calculate magnetic torque

Posted: 06 Sep 2016, 10:14
Thank you ### Re: Calculate magnetic torque

Posted: 14 Sep 2016, 14:36
I have another question: in Which way does the torque calculation work? I had some problems with my model (squared core with an airgap, within the airgap a single wire):

I've got the problem that the magnetic torque isn't zero when the axis is through the middle of the wire:

4: component 1: res: magnetic force 1= 3.734628378772E+000
5: component 1: res: magnetic force 2 = -1.101039591209E-003
6: component 1: res: magnetic force 3 = 6.378247999766E-004
7: component 1: res: magnetic torque = -3.516128841510E+003

When I use an axis parallel to the wire in an distance of 10mm i get the following result:

4: component 1: res: magnetic force 1= 3.734628378772E+000
5: component 1: res: magnetic force 2 = -1.101039591209E-003
6: component 1: res: magnetic force 3 = 6.378247999766E-004
7: component 1: res: magnetic torque = -1.197103472730E+006

Another unexpected effect is that the length of the axis influences the magnitude of the torque. For example when the axis is the length of the wire ( Torque Origin(3) = Real 100 0 -10; Torque Axis(3) = Real 0 0 20) the torque is -4.379584261120E+002.

What I'm doing wrong? The force seems to be ok (direction and magnitude). Is there some problem with the coordinates?

The SIF:

Code: Select all

``````Header
CHECK KEYWORDS Warn
Mesh DB "." "."
Include Path ""
Results Directory ""
End

Simulation
Max Output Level = 10
Coordinate System = Cartesian
Coordinate Mapping(3) = 1 2 3
Steady State Max Iterations = 1
Output Intervals = 1
Timestepping Method = BDF
BDF Order = 1
Solver Input File = sw.sif
Post File = sw.ep
Coordinate Scaling = 1e-3
End

Constants
Gravity(4) = 0 -1 0 9.82
Stefan Boltzmann = 5.67e-08
Permittivity of Vacuum = 8.8542e-12
Boltzmann Constant = 1.3807e-23
Unit Charge = 1.602e-19
End

Body 1
Target Bodies(1) = 1
Name = "Body Property 1"
Equation = 1
Material = 1
Body Force = 1
End

Body 2
Target Bodies(1) = 2
Name = "Body 2"
Equation = 2
Material = 2
End

Body 3
Target Bodies(1) = 3
Name = "Body Property 3"
Equation = 2
Material = 3
End

Body 4
Target Bodies(1) = 4
Name = "Body 4"
Equation = 1
Material = 1
Body Force = 2
! Torque Groups(1) = integer 1
End

Body 5
Target Bodies(1) = 5
Name = "Body 5"
Equation = 2
Material = 3
End

Solver 3
Equation = MgDynPost
Potential Variable = AV
Calculate Current Density = True
Procedure = "MagnetoDynamics" "MagnetoDynamicsCalcFields"
Calculate Electric Field = True
Calculate Magnetic Field Strength = True
Exec Solver = Always
Stabilize = True
Bubbles = False
Lumped Mass Matrix = False
Optimize Bandwidth = True
Steady State Convergence Tolerance = 1.0e-5
Nonlinear System Convergence Tolerance = 1.0e-7
Nonlinear System Max Iterations = 20
Nonlinear System Newton After Iterations = 3
Nonlinear System Newton After Tolerance = 1.0e-3
Nonlinear System Relaxation Factor = 1
Linear System Solver = Iterative
Linear System Iterative Method = CG
Linear System Max Iterations = 5000
Linear System Convergence Tolerance = 1.0e-10
BiCGstabl polynomial degree = 2
Linear System Preconditioning = Diagonal
Linear System ILUT Tolerance = 1.0e-3
Linear System Abort Not Converged = False
Linear System Residual Output = 1
Linear System Precondition Recompute = 1

!Torque Group Origins(1,3) = Real 100 0 -10
!Torque Group Axes(1, 3) = Real 0 0 20
Calculate Electric Field = True
Calculate Magnetic Field Strength = True
Calculate Nodal Forces = Logical True
End

Solver 1
Equation = Static Current Conduction
Calculate Volume Current = True
Procedure = "StatCurrentSolve" "StatCurrentSolver"
Variable = Potential
Exec Solver = Before Simulation
Stabilize = True
Bubbles = False
Lumped Mass Matrix = False
Optimize Bandwidth = True
Steady State Convergence Tolerance = 1.0e-5
Nonlinear System Convergence Tolerance = 1.0e-7
Nonlinear System Max Iterations = 20
Nonlinear System Newton After Iterations = 3
Nonlinear System Newton After Tolerance = 1.0e-3
Nonlinear System Relaxation Factor = 1
Linear System Solver = Iterative
Linear System Iterative Method = CG
Linear System Max Iterations = 5000
Linear System Convergence Tolerance = 1.0e-10
BiCGstabl polynomial degree = 2
Linear System Preconditioning = Diagonal
Linear System ILUT Tolerance = 1.0e-3
Linear System Abort Not Converged = False
Linear System Residual Output = 1
Linear System Precondition Recompute = 1
End

Solver 4
Equation = Result Output
Procedure = "ResultOutputSolve" "ResultOutputSolver"
Output Format = Vtu
Output File Name = loop
Exec Solver = After Timestep
End

Solver 2
Equation = MgDyn
Fix Input Current Density = True
Variable = AV
Procedure = "MagnetoDynamics" "WhitneyAVSolver"
Exec Solver = Always
Stabilize = True
Bubbles = False
Lumped Mass Matrix = False
Optimize Bandwidth = True
Steady State Convergence Tolerance = 1.0e-5
Nonlinear System Convergence Tolerance = 1.0e-7
Nonlinear System Max Iterations = 20
Nonlinear System Newton After Iterations = 3
Nonlinear System Newton After Tolerance = 1.0e-3
Nonlinear System Relaxation Factor = 1
Linear System Solver = Iterative
Linear System Iterative Method = CG
Linear System Max Iterations = 5000
Linear System Convergence Tolerance = 1.0e-10
BiCGstabl polynomial degree = 2
Linear System Preconditioning = Diagonal
Linear System ILUT Tolerance = 1.0e-3
Linear System Abort Not Converged = False
Linear System Residual Output = 1
Linear System Precondition Recompute = 1
End

Solver 5
Equation = "Savedata"
Procedure = "SaveData" "SaveScalars"
filename = "withouttorque.dat"
save component results = logical true
End

Equation 1
Name = "Wire+SW"
Active Solvers(4) = 3 1 4 2
End

Equation 2
Name = "Air+Core"
Active Solvers(3) = 3 4 2
End

Material 1
Name = "Copper"
Electric Conductivity = 59.59e6
Relative Permeability = 1
Density = 8960
End

Material 2
Name = "Steel"
Electric Conductivity = 1.449e6
Relative Permeability = 1000
Density = 7850
End

Material 3
Name = "Air"
Electric Conductivity = 0
Relative Permeability = 1
Density = 1.205
End

Body Force 1
Name = "Volume Current"
Current Density 1 = Equals  Volume Current 1
Current Density 3 = Equals  Volume Current 3
Current Density 2 = Equals  Volume Current 2
End

Body Force 2
Name = "SW"
Current Density 1 = Equals Volume Current 1
Current Density 3 = Equals Volume Current 3
Current Density 2 = Equals Volume Current 2
End

Boundary Condition 1
Target Boundaries(2) = 4 26
Name = "Ground"
Potential = 0
End

Boundary Condition 2
Target Boundaries(2) = 13 27
Name = "Current Density"
Current Density = 141471061
End

Boundary Condition 3
Target Boundaries(1) = 20
Name = "Border"
AV {e} = Real 0
End

Component 1
Name = string "metal"
Master Bodies(1) = integer 4
Torque Origin(3) = Real 100 0 -20 ! Real 100 10 -20 with torque
Torque Axis(3) = Real 0 0 40
Calculate Magnetic Force = Logical True
Calculate Magnetic Torque = Logical True
End``````

### Re: Calculate magnetic torque

Posted: 20 Sep 2016, 12:35
Nobody any hints?

The project files:

https://www.dropbox.com/s/jitnit6arx2v5 ... m.zip?dl=0

### Re: Calculate magnetic torque

Posted: 20 Sep 2016, 17:59
Hi, I checked the Axis and it seems that it was normalized to unity length. Thus the code relied on the length of the direction being one. I now will add the normalization. -Peter

### Re: Calculate magnetic torque

Posted: 22 Sep 2016, 11:31
To be sure i understand it properly: the problem was, that the coordinate scaling doesn't work for the magnetic torque axis? And the the length of the vector should be 1?
After you add the normalization this

Code: Select all

``````Component 1
Name = string "metal"
Master Bodies(1) = integer 4
Torque Origin(3) = Real 100 0 -20 ! Real 100 10 -20 with torque
Torque Axis(3) = Real 0 0 40
Calculate Magnetic Force = Logical True
Calculate Magnetic Torque = Logical True
End``````
will calculate the torque properly?

### Re: Calculate magnetic torque

Posted: 22 Sep 2016, 18:36
Hi, If you scale the coordinates then also the origin should be scaled. It is not automatically scaled. -Peter

### Re: Calculate magnetic torque

Posted: 04 Oct 2016, 10:30
Thx! The torque is calculated in Nm?

### Re: Calculate magnetic torque

Posted: 04 Oct 2016, 17:26
Another question: is it possible that the axis/compas are arranged in a new order compared to the model or something like that?
When I use an axis parallel to the wire with a distance of 0.1m i get a torque of 7.466260917725E-003Nm. The force is 3.734628378772E+000. (expected a torque of ~3.73E-001Nm)
What's the problem?