Mortar#

The mortar section is used when simulating rotor-stator geometries, in which the rotor mesh is attached to the stator by mortar elements.

subsection mortar
  set enable = true
  subsection mesh
    set type                   = dealii
    set grid type              = subdivided_hyper_rectangle
    set grid arguments         = 1,1,1 : -1,-1,-1 : 1,1,1 : true
    set initial refinement     = 0
  end
  set rotor boundary id   = 4
  set stator boundary id  = 2
  set center of rotation  = 0, 0
  set rotation axis       = 0, 0, 1
  subsection rotor rotation angle
    set Function expression = 0
  end
  subsection rotor angular velocity
    set Function expression = 0
  end
  set penalty factor      = 1.0
  set oversampling factor = 2
  set verbosity           = verbose
end

  • The mesh parameters in the Mesh subsection refer to the stator domain. The mesh subsection herein mentioned contains the parameters of the rotor domain; nonetheless, the input format is the same as in Mesh.

Note

The initial number of cells at the rotor-stator interface has to be the same; the simulation will be aborted if that is not respected. This restriction will be automatically constrained throughout the simulation if the mesh is refined.

  • The rotor boundary id and stator boundary id refer to the boundary index at the rotor-stator interface.

Warning

In dealii meshes the boundary IDs are automatically assigned to the geometries using the deal.II colorization function, and thus the rotor/stator IDs might be duplicated. To circumvent this, the rotor boundary IDs are shifted. The rotor boundary id entry refers to the shifted ID number, assuming that the enumeration starts sequentially from the last entry of the stator boundary IDs.

  • The center of rotation is the reference point for the prescribed rotation at the rotor domain.

  • The rotation axis is the unit vector that defines the rotor axis of rotation.

  • The rotor rotation angle subsection allows the imposition of a constant or time-dependent rotation angle for the rotor.

  • The rotor angular velocity subsection allows the imposition of a constant or time-dependent angular velocity for the rotor.

Warning

The rotor angular velocity expression needs to correspond to the time derivative of the rotor rotation angle.

  • The penalty factor is used for the weak imposition of the mortar coupling at the interface. This parameter is akin to the symmetric interior penalty factor in SIPG (Symmetric Interior penalty Galerkin Method) [1].

  • The oversampling factor is used to increase the number of quadrature points. This feature is used to better approximate the weak imposition of the interface coupling.

  • When enabling verbosity (set verbosity = verbose), the rotor rotation information is printed at every iteration.

Reference#