Airgap Remeshing Workflow

The general workflow for applying airgap remeshing requires that you divide the input geometry parts into four groups, and then manually create the contacts between the relevant parts in each group. After creating the mesh and necessary motions, you choose the Airgap Remeshing model from the physics continuum associated with the airgap regions.

For a practical example with detailed steps, refer to the tutorial Airgap Remeshing: Electronic Speedometer.
  1. Create the required geometry parts, which can be divided into four groups:
    • fixed parts that are meshed only once
    • moving parts that are meshed only once
    • fixed airgap part
    • moving airgap part
  2. Create in-place contacts between contacting part surfaces, in the usual manner (either automatically when creating the parts or manually).
    The only contact between fixed and moving parts is between the airgap parts.
When modeling only a sector of the full geometry, you also require periodic contacts:
  1. Create periodic contacts between the side surfaces of the sector geometry.
  2. Sector geometries also require a repeating interface between the sliding parts, to allow for snap-back of the moving part (see Repeating Interface Topology). To create this interface, you require a periodic contact between the moving and the fixed airgap part surfaces:
    1. Before you create the required periodic contact, delete any existing in-place contact between the moving and the fixed airgap parts.
    2. Create a periodic contact between the contacting airgap part surfaces.
Create the relevant regions. For the airgap, you require two regions—a moving region and a stationary region:
  1. Assign all parts to regions. The required regions depend on the components and physics that you are modeling. In general, you require at least four regions:
    • one region for the fIxed parts
    • one region for the moving parts
    • two regions for the airgap (a moving region and a stationary region)
Define an appropriate motion for the moving regions:
  1. Under the Tools > Motions node, create the required motion. In general, for rotor-stator electric machines, you define a rotation motion for the rotor.
  2. Assign the motion to each moving region, including the moving airgap region.
    Later, you also set up a motion-driven transform for the moving airgap part.
  3. Create interfaces between the different regions, in the usual manner. Specifically:
    1. Create the required in-place interfaces, including internal interfaces between parts of the same region, and contact interfaces between different regions in contact.
    2. When modeling only a sector of the full geometry, create periodic interfaces between the side surfaces of the domain.
In addition, airgap remeshing requires the sliding interface to be a repeating interface (see Repeating Interface Topology):
  1. Create an interface between the airgap fixed region and the airgap moving region. Set the interface Topology to Repeating.
To define the meshing pipeline:
  1. Expand the Geometry > Operations node.
  2. For geometry parts other than the airgap parts, define mesh operations in the usual manner, as required by your analysis.
For the airgap parts, define the following mesh operations, in order:
  1. Define a motion-driven transform operation for the moving airgap part. At each time-step, this operation aligns the airgap part with the other moving parts before remeshing:
    1. Right-click the Geometry > Operations node and select New > Surface Preparation > Transform.
    2. In the Create Transform Operation dialog, select the moving airgap part and click OK.
    3. Right-click the Operations > Transform > Transforms node and select New > Motion.
    4. Select the Transforms > Motion node and select the motion that you assigned to the moving airgap part.
  2. Define an imprint operation between the moving airgap and the fixed airgap parts:
    1. Right-click the Geometry > Operations node and select New > Boolean > Imprint.
    2. In the Create Imprint Operation dialog:
      1. Select both the moving and fixed airgap parts.
      2. Activate Perform CAD Imprint.
      3. Click OK.
    3. Select the Operations > Imprint > Controls > Resulting Part Surfaces node and set Put Results In to New Part Surfaces.
  3. Define a mesh operation for the airgap parts. Typically, you create a tetrahedral mesh, which can be optionally extruded.
Make sure that the airgap meshes are conformal with the meshes of the contacting non-airgap parts. When using the tetrahedral mesher, you can specify the contacts that must be conformal:
  1. Edit the Operations > [Airgap Tetrahedral Mesh Operation] > Conformal Contacts node and select the contacts between the airgap parts and their contacting non-airgap parts.
The imprint operation between the airgap parts results in new part surfaces. Before you can generate the mesh for the airgap, these new surfaces must be assigned to region boundaries:
  1. Right-click the Geometry > Operations > Imprint node and select Execute.
    Simcenter STAR-CCM+ adds new part surfaces named Imprint for both the moving and fixed airgap parts.
  2. Under the Geometry > Parts node, expand the airgap part nodes. For both parts, assign the Surfaces > Imprint surface to a boundary in the respective airgap region.
The regions layout and meshing pipeline are now complete. To generate the mesh and complete the simulation set up:
  1. Click (Generate Volume Mesh).
    For airgap remeshing, running the meshers in parallel is recommended to speed up the simulation.
  2. Define physics continua for the electromagnetic analysis and assign them to the relevant regions. The air regions require their own separate continuum.
    For guidelines and instructions, see Modeling Magnetic Fields.
  3. In the physics continuum associated with the airgap regions, add the Airgap Remeshing model.
    With this model, Simcenter STAR-CCM+ remeshes the airgap regions, whereas the rest of the mesh remains fixed. The entire mesh remains conformal throughout the operation.
The Airgap Remeshing model requires you to specify the mesh operation that is executed at every time-step. When the meshing pipeline for the airgap includes multiple dependent operations, you only specify the last operation that is executed. At every time-step, Simcenter STAR-CCM+ automatically finds all dependencies and execute the required operations in order:
  1. Select the Continua > [airgap physics continuum] > Models > Airgap Remeshing node and set Mesh Operations to the last mesh operation for the airgap parts. If the mesh is not extruded, the last operation is typically the automated mesh operation that generates the tetrahedral mesh.
    The simulation is fully set up for airgap remeshing.
  2. Initialize the interfaces and check that they are conformal.
  3. Complete the simulation set up following the guidelines in Modeling Magnetic Fields.