## Sliding mesh for electrical machines (3D) / mortar

Numerical methods and mathematical models of Elmer
mb5
Posts: 20
Joined: 10 Jun 2017, 18:07
Antispam: Yes

### Sliding mesh for electrical machines (3D) / mortar

Hi,

I`ve got a problem with the sliding/moving mesh for a electrical machine. In my problem I have an outer iron ring with a magnet and air body. For rotation I have a rotating square core with air. All outer boundaries are Vpot=0.
bodies.png (43.78 KiB) Viewed 2548 times
My sif file:

Code: Select all

``````\$ p = 1             ! pole pairs
\$ dangle = 45       ! angle for d-axis in degree
\$ skew_angle = 00   ! skewing angle in degree
\$ skew_length = 100 ! base length for skewing (epM: stack length)

\$ speed = 1000      ! rotational speed in rpm
\$ N_period = 1      ! number of electrical periods
\$ Nsteps = 90       ! number of steps

\$ w_mech = 2.0*pi*speed/60.0
\$ T = 1.0/(speed/60.0*p)*N_period
\$ dt = T / Nsteps

CHECK KEYWORDS Warn
Mesh DB "mesh" "."
Include Path ""
Results Directory "results"
End
!// include "mesh/entities.sif"

Simulation
Max Output Level = 3
Coordinate System = "Cartesian 3D"
Coordinate Scaling = 0.001

Simulation Type = Transient
Timestep Size = \$dt
Timestep Intervals = \$Nsteps+1
Timestepping Method = BDF
BDF order = 2

Steady State Max Iterations = 10
Output Intervals = 100
Use Mesh Names = Logical True

!// !!!!!!!! mesh interpolation tolerances
Interpolation Numeric Epsilon = Real 5.0e-9
End

!!!!!!!!!!!!!!!!!!!!!!!!!!  Materials !!!!!!!!!!!!!!!!!!!!!!!!!!!
Material 1
Name = "Air"
Relative Permeability = 1
End

Material 2
Name = "iron"
Relative Permeability = 1000
End

Material 3
Name = "Ferritband"
Relative Permeability = 1.05
Magnetization 1 = 187196.5283
Magnetization 2 = 0
Magnetization 3 = 0
End

!!!!!!!!!!!!!!!!!!!!!!!!!!  Boundary conditions  !!!!!!!!!!!!!!!!!!!!!!!!!!!

Boundary Condition 1
Target Boundaries(11) = 2 3 4 5 6 7 8 9 10 11 12
Name = "Boundary_Outer"
AV {e} = Real 0
End

!!!!!!!!!!!!!!!!!!!!!!!!!!  Solver parameters !!!!!!!!!!!!!!!!!!!!!!!!!!!

! solver for magnetic vector potential A [Vs/m]
Solver 1
Equation = "MGDynamics"
Procedure = "MagnetoDynamics" "WhitneyAVSolver"
Variable = "AV"

Apply Mortar BCs = Logical True

! Fix Input Current Density = Logical True
Nonlinear System Convergence Tolerance = 1.0e-4
Nonlinear System Max Iterations = 50
Nonlinear System Relaxation Factor = 1
Newton-Raphson Iteration = Logical True

! Linear System Solver = Direct
! Linear System Direct Method = UMFPACK

Linear System Symmetric = Logical True
Linear System Solver = "Iterative"
Linear System Preconditioning = None
Linear System Convergence Tolerance = 1e-8
Linear System Residual Output = 100
Linear System Max Iterations = 5000
Linear System Iterative Method = CG   ! CG CGS BiCGStab l TFQMR GMRES GCR
End

Solver 2
Equation = "MGDynamicsCalc"
Procedure = "MagnetoDynamics" "MagnetoDynamicsCalcFields"
Linear System Symmetric = True
Potential Variable = "AV"
!// Apply Mortar BCs = Logical True

Calculate Magnetic Field Strength = Logical True
Calculate Current Density = Logical True
Calculate nodal forces = logical true
Calculate Magnetic Vector Potential = Logical True

! Linear System Solver = Direct
! Linear System Direct Method = UMFPACK
Linear System Solver = "Iterative"
Linear System Preconditioning = None
Linear System Residual Output = 100
Linear System Max Iterations = 5000
Linear System Iterative Method = CG
Steady State Convergence Tolerance = 1e-6
Linear System Convergence Tolerance = 1.0e-8
End

!save to VTU format for ParaView with faces' IDs
Solver 3
Exec Solver = After Timestep
Procedure = "ResultOutputSolve" "ResultOutputSolver"
Output File Name = "step"

!  Save Nodal Fields = Logical True

Vtu Format = True
Binary Output = True
Single Precision = True
Save Geometry Ids = True
End

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

!!!!!!!!!!!!!!!!!!!!!!!!!!  Bodies are here !!!!!!!!!!!!!!!!!!!!!!!!!!!
Body 1
Name = "yoke"
Equation = 1
Material = 2
End

Body 2
Name = "magnet"
Equation = 1
Material = 3
End

Body 3
Name = "air2"
Equation = 1
Material = 1
End

Body 4
Name = "air1"
Equation = 1
Material = 1
Body Force = 1
End

Body 5
Name = "core"
Equation = 1
Material = 2
Body Force = 1
End
``````
Without defining the slide mesh / mortar the results (flux density) looking correct.
induction.png (70.64 KiB) Viewed 2548 times

But now I want to move the core and the inner mesh. Therefore I use the mortar boundary:

Code: Select all

``````
\$ p = 1             ! pole pairs
\$ dangle = 45       ! angle for d-axis in degree
\$ skew_angle = 00   ! skewing angle in degree
\$ skew_length = 100 ! base length for skewing (epM: stack length)

\$ speed = 1000      ! rotational speed in rpm
\$ N_period = 1      ! number of electrical periods
\$ Nsteps = 90       ! number of steps

\$ w_mech = 2.0*pi*speed/60.0
\$ T = 1.0/(speed/60.0*p)*N_period
\$ dt = T / Nsteps

CHECK KEYWORDS Warn
Mesh DB "mesh" "."
Include Path ""
Results Directory "results"
End
!// include "mesh/entities.sif"

Simulation
Max Output Level = 3
Coordinate System = "Cartesian 3D"
Coordinate Scaling = 0.001

Simulation Type = Transient
Timestep Size = \$dt
Timestep Intervals = \$Nsteps+1
Timestepping Method = BDF
BDF order = 2

Steady State Max Iterations = 10
Output Intervals = 100
Use Mesh Names = Logical True

!// !!!!!!!! mesh interpolation tolerances
Interpolation Numeric Epsilon = Real 5.0e-9
End

!!!!!!!!!!!!!!!!!!!!!!!!!!  Materials !!!!!!!!!!!!!!!!!!!!!!!!!!!
Material 1
Name = "Air"
Relative Permeability = 1
End

Material 2
Name = "iron"
Relative Permeability = 1000
End

Material 3
Name = "Ferritband"
Relative Permeability = 1.05
Magnetization 1 = 187196.5283
Magnetization 2 = 0
Magnetization 3 = 0
End

!!!!!!!!!!!!!!!!!!!!!!!!!!  Boundary conditions  !!!!!!!!!!!!!!!!!!!!!!!!!!!

Boundary Condition 1
Target Boundaries(11) = 2 3 4 5 6 7 8 9 10 11 12
Name = "Boundary_Outer"
AV {e} = Real 0
End

Boundary Condition 2
Target Boundaries(1) = 1
Name = "slide"
Discontinuous Boundary = Logical True
!// Save Line = True
Mortar BC = 3
!// Discontinuous BC = 3
!// Galerkin Projector = Logical True      ! programm error on step 2
!// Rotational Projector = Logical True    ! too much mesh skew
Sliding Projector = Logical True       ! programm error on step 2
!// Cylindrical Projector = Logical True   ! too much mesh skew
!// Level Projector = Logical True         ! leads to singular matrix
!// Plane Projector = Logical True         ! too much mesh skew
End

!!!!!!!!!!!!!!!!!!!!!!!!!!  Body Forces  !!!!!!!!!!!!!!!!!!!!!!!!!!!

!// rotation of the rotor
Body Force 1
Name = "BodyForce_Rotation"
Mesh Rotate 3 = Variable time, timestep size
Real MATC "180/pi*w_mech*(tx(0)-tx(1))" ! in degrees
End

!!!!!!!!!!!!!!!!!!!!!!!!!!  Solver parameters !!!!!!!!!!!!!!!!!!!!!!!!!!!

!mesh rotation
Solver 1
Exec Solver = Before Timestep
Equation = MeshDeform
Procedure = "RigidMeshMapper" "RigidMeshMapper"
End

! solver for magnetic vector potential A [Vs/m]
Solver 2
Equation = "MGDynamics"
Procedure = "MagnetoDynamics" "WhitneyAVSolver"
Variable = "AV"

Apply Mortar BCs = Logical True

! Fix Input Current Density = Logical True
Nonlinear System Convergence Tolerance = 1.0e-4
Nonlinear System Max Iterations = 50
Nonlinear System Relaxation Factor = 1
Newton-Raphson Iteration = Logical True

Linear System Symmetric = Logical True
Linear System Solver = "Iterative"
Linear System Preconditioning = None
Linear System Convergence Tolerance = 1e-8
Linear System Residual Output = 100
Linear System Max Iterations = 5000
Linear System Iterative Method = CG   ! CG CGS BiCGStab l TFQMR GMRES GCR
End

Solver 3
Equation = "MGDynamicsCalc"
Procedure = "MagnetoDynamics" "MagnetoDynamicsCalcFields"
Linear System Symmetric = True
Potential Variable = "AV"

Calculate Magnetic Field Strength = Logical True
Calculate Current Density = Logical True
Calculate nodal forces = logical true
Calculate Magnetic Vector Potential = Logical True

Linear System Solver = "Iterative"
Linear System Preconditioning = None
Linear System Residual Output = 100
Linear System Max Iterations = 5000
Linear System Iterative Method = CG
Steady State Convergence Tolerance = 1e-6
Linear System Convergence Tolerance = 1.0e-8
End

!save to VTU format for ParaView with faces' IDs
Solver 4
Exec Solver = After Timestep
Procedure = "ResultOutputSolve" "ResultOutputSolver"
Output File Name = "step"

!  Save Nodal Fields = Logical True

Vtu Format = True
Binary Output = True
Single Precision = True
Save Geometry Ids = True
End

!// save scalar variables - torque T [Nm]
Solver 5
Exec Solver = After Timestep
Filename = "scalars.dat"
Procedure = "SaveData" "SaveScalars"
Show Norm Index = 1
End

Equation 1
Name = "ModelDomain"
Active Solvers(5) = 1 2 3 4 5
End

!!!!!!!!!!!!!!!!!!!!!!!!!!  Bodies are here !!!!!!!!!!!!!!!!!!!!!!!!!!!
Body 1
Name = "yoke"
Equation = 1
Material = 2
End

Body 2
Name = "magnet"
Equation = 1
Material = 3
End

Body 3
Name = "air2"
Equation = 1
Material = 1
End

Body 4
Name = "air1"
Equation = 1
Material = 1
Body Force = 1
End

Body 5
Name = "core"
Equation = 1
Material = 2
Body Force = 1
End
``````
But on exute with ElmerSolver I get a segmentation fault.

What I am doing wrong with the sliding mesh?

Best regards
Martin
Attachments
mesh.zip

raback
Posts: 3705
Joined: 22 Aug 2009, 11:57
Antispam: Yes
Location: Espoo, Finland
Contact:

### Re: Sliding mesh for electrical machines (3D) / mortar

Hi

Didn't try your case. However, the choices for mortar projector cannnot work. You could try to use these at the air gap:

Code: Select all

``````  Rotational Projector = Logical True  ! map rotating interface to plane
Galerkin Projector = Logical True     ! at the plane perform optimal weak projector
Projector Skip Nodes = Logical True  ! if interface is nonconducting you can skip the nodes
``````
-Peter

mb5
Posts: 20
Joined: 10 Jun 2017, 18:07
Antispam: Yes

### Re: Sliding mesh for electrical machines (3D) / mortar

I`ve tried these projectors. With direct solver (UMFPACK) I always get a segmentation fault. With iterative solver (CG) I have to reduce the Linear System Convergence Tolerance (1e-6) to get the calculation convergent. If I don't use the boundary in the airgap (no rotation) the iterations are about 10 times faster.
So I think I have a general problem with the mortar boundary.

Is there anything I could try?

Regards
Martin
Attachments
data.zip

raback
Posts: 3705
Joined: 22 Aug 2009, 11:57
Antispam: Yes
Location: Espoo, Finland
Contact:

### Re: Sliding mesh for electrical machines (3D) / mortar

Hi

The linear system becomes much harder to solve with the continuity constraints over the rotating interface added.

You can try
1) Other linear iterative solvers: GCR, Bicgstabl, Idrs,...
2) The direct solver could work with the tree gauge, maybe you run out of memory?
3) You could add something to the diagonal of the mortar constraints (Solver i::Mortar Diag = Real)
4) You could add a multiplier to the mass matrix to gauge it (Solver i::Mass Regularize Epsilon = Real)
...

etc. Some of these require fresh version. This is a complex problem.

-Peter

mb5
Posts: 20
Joined: 10 Jun 2017, 18:07
Antispam: Yes

### Re: Sliding mesh for electrical machines (3D) / mortar

Thank you very much. I`ve tested different iterative solvers. Now I use the same as the test case "RotatingBCMagnetoDynamics2". With that it works! But with additional mortar boundaries (not a full 360° model) Its very hard to get the convergent solution. For the moment I use the full model.

I've got another question regarding torque calculation. I try to calculate it as "component". But all values for torque and force are zero in the output scalar.dat. In principle the nodel forces are calculated as I see in ParaView.

Code: Select all

``````
\$ p = 1             ! pole pairs
\$ dangle = 45       ! angle for d-axis in degree
\$ skew_angle = 00   ! skewing angle in degree
\$ skew_length = 100 ! base length for skewing (epM: stack length)

\$ speed = 1000      ! rotational speed in rpm
\$ N_period = 1      ! number of electrical periods
\$ Nsteps = 45       ! number of steps

\$ w_mech = 2.0*pi*speed/60.0
\$ T = 1.0/(speed/60.0*p)*N_period
\$ dt = T / Nsteps

CHECK KEYWORDS Warn
Mesh DB "mesh" "."
Include Path ""
Results Directory "results"
End
!// include "mesh/entities.sif"

Simulation
Max Output Level = 3
Coordinate System = "Cartesian 3D"
Coordinate Scaling = 0.001

Simulation Type = Transient
Timestep Size = \$dt
Timestep Intervals = \$Nsteps+1
Timestepping Method = BDF
BDF order = 2

Steady State Max Iterations = 1
Output Intervals = 100
Use Mesh Names = Logical True
End

!!!!!!!!!!!!!!!!!!!!!!!!!!  Materials !!!!!!!!!!!!!!!!!!!!!!!!!!!
Material 1
Name = "Air"
Relative Permeability = 1
End

Material 2
Name = "iron"
Relative Permeability = 1000
End

Material 3
Name = "Ferritband"
Relative Permeability = 1.05
Magnetization 1 = 187196.5283
Magnetization 2 = 0
Magnetization 3 = 0
End

!!!!!!!!!!!!!!!!!!!!!!!!!!  Boundary conditions  !!!!!!!!!!!!!!!!!!!!!!!!!!!
Boundary Condition 1
Target Boundaries(11) = 1 3 4 5 6 7 8 9 10 11 12
Name = "Boundary_Outer"
AV {e} = Real 0
End

Boundary Condition 2
Target Boundaries(1) = 2
Name = "airgap"
Discontinuous Boundary = Logical True
Mortar BC = 3

Galerkin Projector = Logical True      ! programm error on step 2
Rotational Projector = Logical True    ! too much mesh skew
!// Projector Skip Nodes = Logical True
End

!!!!!!!!!!!!!!!!!!!!!!!!!!  Body Forces  !!!!!!!!!!!!!!!!!!!!!!!!!!!
Body Force 1
Name = "BodyForce_Rotation"
Mesh Rotate 3 = Variable time, timestep size
Real MATC "180/pi*w_mech*(tx(0)-tx(1))" ! in degrees
End

!!!!!!!!!!!!!!!!!!!!!!!!!!  Solver parameters !!!!!!!!!!!!!!!!!!!!!!!!!!!

!mesh rotation
Solver 1
Exec Solver = Before Timestep
Equation = MeshDeform
Procedure = "RigidMeshMapper" "RigidMeshMapper"
End

Solver 2
Equation = "MGDynamics"
Variable = "AV"
Procedure = "MagnetoDynamics" "WhitneyAVSolver"

! Fix Input Current Density = Logical True

Nonlinear System Convergence Tolerance = 1.0e-4   !// 1.0e-8
Nonlinear System Max Iterations = 1  !// 50
Nonlinear System Relaxation Factor = 1
Newton-Raphson Iteration = Logical True
Linear System Solver = "Iterative"
Linear System Preconditioning = ILU1
Linear System Residual Output = 20
Linear System Max Iterations = 3000
Linear System Iterative Method = BiCGStab2
BicGStabL Polynomial Degree = 4
Linear System GCR Restart = 600
Linear System Convergence Tolerance = 1e-8    ! 1e-10
Linear System Abort Not Converged = False

Steady State Convergence Tolerance = 1e-09

Edge Basis = Logical True
Apply Mortar BCs = Logical True
Optimize Bandwidth = False
End

Solver 3
Equation = "MGDynamicsCalc"
Procedure = "MagnetoDynamics" "MagnetoDynamicsCalcFields"
Linear System Symmetric = True
Potential Variable = "AV"

Calculate Magnetic Field Strength = Logical True
Calculate Current Density = Logical True
Calculate nodal forces = logical true
Calculate Magnetic Vector Potential = Logical True
!// Calculate Electric Field = True
!// Calculate Maxwell Stress = Logical True

Linear System Solver = "Iterative"
Linear System Preconditioning = ILU1
Linear System Residual Output = 20
Linear System Max Iterations = 3000
Linear System Iterative Method = BiCGStab2
BicGStabL Polynomial Degree = 4
Linear System GCR Restart = 600
Linear System Convergence Tolerance = 1e-8    ! 1e-10
Linear System Abort Not Converged = False

Steady State Convergence Tolerance = 1e-6
Linear System Convergence Tolerance = 1.0e-8
Discontinuous Bodies = True
Apply Mortar BCs = True
End

!save to VTU format for ParaView with faces' IDs
Solver 4
Exec Solver = After Timestep
Procedure = "ResultOutputSolve" "ResultOutputSolver"
Output File Name = "step"

!  Save Nodal Fields = Logical True

Vtu Format = True
Binary Output = True
Single Precision = True
Save Geometry Ids = True
End

!// save scalar variables - torque T [Nm]
Solver 5
Exec Solver = After Timestep
Filename = "scalars.dat"
Procedure = "SaveData" "SaveScalars"
Show Norm Index = 1
save component results = logical True
End

Component 1
Name = string "rotor"
Master Bodies(2) = integer 13 19

Torque Origin(3) = Real 0 0 0
Torque Axis(3) = Real 0 0 -0.05
Calculate Magnetic Force = Logical True
Calculate Magnetic Torque = Logical True
End

Equation 1
Name = "ModelDomain"
Active Solvers(5) = 1 2 3 4 5
End

!!!!!!!!!!!!!!!!!!!!!!!!!!  Bodies are here !!!!!!!!!!!!!!!!!!!!!!!!!!!
Body 1
Name = "yoke"
Equation = 1
Material = 2
End

Body 2
Name = "magnet"
Equation = 1
Material = 3
End

Body 3
Name = "air2"
Equation = 1
Material = 1
End

Body 4
Name = "air1"
Equation = 1
Material = 1
Body Force = 1
End

Body 5
Name = "core"
Equation = 1
Material = 2
Body Force = 1
End
``````
In the output I get warning regarding torque calculation. Elmer doesn't know the keyword "torque origin". But it is described in the ElmerModelsManual. I use the newest Elmer version from ppa.
MAIN: -------------------------------------
Model Input: Unlisted keyword: [torque origin] in section: [component 1]
Model Input: Unlisted keyword: [torque axis] in section: [component 1]
Has anybody an idea?

Best regards
Martin

mb5
Posts: 20
Joined: 10 Jun 2017, 18:07
Antispam: Yes

### Re: Sliding mesh for electrical machines (3D) / mortar

I got it. My mistake was, that I defined the physical Body indices from the mesh file for torque calculation. To get the correct torque one have to define the Body indices from the "Body" section from the *.sif file.

Code: Select all

``````Component 1
Name = string "rotor"
Master Bodies(3) = integer 1 2 !  << Define the "Body xy" IDs from the following "Body" sections
Calculate Magnetic Force = Logical True
Calculate Magnetic Torque = Logical True
End

Body 1
Name = "yoke"
Equation = 1
Material = 2
End

Body 2
Name = "magnet"
Equation = 1
Material = 3
End
``````