### Periodic BC instead of mortar for sliding mesh

Posted:

**03 Jan 2018, 16:16**Hi all,

I'm simulating an electrical machine. The results are good but the convergence is very bad with mortar for the sliding mesh ( see viewtopic.php?f=3&t=4652&sid=b5bd00e8ee ... f4528b99d8). Often I couldn't get the solver converging.

My question: Is it possible to replace the mortar BC for the sliding airgap mesh with periodic boundaries? I have a structured mesh. In every timestep the nodes from moving part matching the nodes of the fixed part. In which way I have to modify the boundary condition?

Best regard

Martin

I'm simulating an electrical machine. The results are good but the convergence is very bad with mortar for the sliding mesh ( see viewtopic.php?f=3&t=4652&sid=b5bd00e8ee ... f4528b99d8). Often I couldn't get the solver converging.

My question: Is it possible to replace the mortar BC for the sliding airgap mesh with periodic boundaries? I have a structured mesh. In every timestep the nodes from moving part matching the nodes of the fixed part. In which way I have to modify the boundary condition?

Best regard

Martin

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
$ Rs = 1.0 ! resistance coil side
$ Nc = 100 ! number of turns per coil
$ Acs = 20*40*1e-6 ! surface of the coil sides
$ curr = 0.0 !20
Header
CHECK KEYWORDS Warn
Mesh DB "mesh" "."
Include Path ""
Results Directory "results"
End
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(15) = 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Name = "Boundary_Outer"
AV {e} = Real 0
End
Boundary Condition 2
Target Boundaries(1) = 1
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
Body Force 2
Name = "BodyForce_Rotation"
Mesh Rotate 3 = Variable time, timestep size
Real MATC "180/pi*w_mech*(tx(0)-tx(1))" ! in degrees
Current Density 1 = Real 0
Current Density 2 = Real 0
Current Density 3 = Real MATC "curr/Acs*Nc"
End
Body Force 3
Name = "BodyForce_Rotation"
Mesh Rotate 3 = Variable time, timestep size
Real MATC "180/pi*w_mech*(tx(0)-tx(1))" ! in degrees
Current Density 1 = Real 0
Current Density 2 = Real 0
Current Density 3 = Real MATC "-curr/Acs*Nc"
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
!// Export Lagrange Multiplier = 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
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
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"
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 "inner"
Master Bodies(3) = integer 5 6 7
!// Calculate Magnetic Force = Logical True
Calculate Magnetic Torque = Logical True
End
Component 2
Name = string "outer"
Master Bodies(2) = integer 1 2
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
Body 6
Name = "c1"
Equation = 1
Material = 1
Body Force = 2
End
Body 7
Name = "c2"
Equation = 1
Material = 1
Body Force = 3
End
```