## Magnetodynamics Solver, wrong magnetic field strength?

Numerical methods and mathematical models of Elmer
Bavragor
Posts: 32
Joined: 07 Nov 2013, 14:10
Antispam: Yes

### Magnetodynamics Solver, wrong magnetic field strength?

Hi community,

I have a problem with an electromagnetic model. The model describes a single wire surrounded by air and and an iron cylinder (picture). The solution of the magnetic field strength is lower at increasing distance to the wire than it should be (f.e. r=50mm -> H=1450A/m instead of 2500A/m or r=100mm -> H=200A/m instead of 1250A/m).

Anyone an idea what i have done wrong?

SIF-file:

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_fine.sif
Post File = sw_fine.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 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 3"
Equation = 2
Material = 3
End

Solver 2
Equation = MgDyn
Variable = AV
Fix Input Current Density = True
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 3
Equation = MgDynPost
Calculate Magnetic Field Strength = True
Potential Variable = AV
Procedure = "MagnetoDynamics" "MagnetoDynamicsCalcFields"
Calculate Electric Field = 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
End

Solver 1
Equation = Static Current Conduction
Calculate Volume Current = True
Variable = Potential
Procedure = "StatCurrentSolve" "StatCurrentSolver"
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 = sw_fine
Exec Solver = After Timestep
End

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

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

Material 1
Name = "Copper"
Electric Conductivity = 59.59e6
Porosity Model = Always saturated
Density = 8960.0
Relative Permeability = 1
End

Material 2
Name = "Steel"
Electric Conductivity = 1.449e6
Porosity Model = Always saturated
Density = 7850.0
Relative Permeability = 1000
End

Material 3
Name = "Air"
Electric Conductivity = 0
Porosity Model = Always saturated
Density = 1.205
Relative Permeability = 1
End

Body Force 1
Name = "BodyForce 1"
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(1) = 8
Name = "Ground"
Potential = 0
End

Boundary Condition 2
Target Boundaries(1) = 2
Name = "Current"
Current Density = 1e7
End

Boundary Condition 3
Target Boundaries(3) = 1 7 10
Name = "Border"
AV {e} = 0
End
``````
Attachments model.png (131.1 KiB) Viewed 1940 times
Last edited by Bavragor on 26 Apr 2016, 11:25, edited 1 time in total.
Bavragor
Posts: 32
Joined: 07 Nov 2013, 14:10
Antispam: Yes

### Re: Magnetodynamics Solver, wrong magnetic field strength?

wire:
r=5mm
l=100mm

core:
r=10mm
R=100mm
l=100mm

boundary:
r=120mm
l=120mm

The assigned boundary is only the lateral area of the outer cylinder.
If someone want the project files, I will upload them.
kataja
Posts: 74
Joined: 09 May 2014, 16:06
Antispam: Yes

### Re: Magnetodynamics Solver, wrong magnetic field strength?

Hi

I think you might be missing a keyword "electric current density" on the wire ends (BCs 1 and 2) that is used to tell the AV solver what should be the current at the boundary. If its not given, the Helmholtz projected input current might look unexpected (see around pp. 86 in the Elmer Models Manual).

-Juhani