The Rotating Machinery, Magnetic Interface
The Rotating Machinery, Magnetic (rmm) interface (), found under the AC/DC>Electromagnetics and Mechanics branch when adding a physics interface, is used for design and analysis of electric motors and generators. Stationary and time-domain modeling is supported in 2D and 3D.
The physics interface solves Maxwell's equations formulated using a combination of magnetic vector potential and magnetic scalar potential as the dependent variables. For a theoretical discussion, see The A Formulation, The Vm Formulation, and The A–Vm Formulation.
When this physics interface is added, these default nodes are also added to the Model Builder — Electric Field Transformation, Ampère’s Law, Mixed Formulation Boundary, Magnetic Insulation (the default boundary condition), and Initial Values. Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions and point conditions. You can also right-click Rotating Machinery, Magnetic to select physics features from the context menu.
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The physics interface only works correctly if the geometry is created as an assembly pair from individual composite objects for the rotor and stator parts. An Identity Boundary Pair feature must also be defined for the rotor-stator physics interface boundaries under the Model>Definitions node in the Model Builder. This is usually done by choosing Form Assembly in the finalization node of the geometry sequence.
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It is important to avoid having scalar potential regions that surround vector potential regions in which nonclosed currents can flow. For a detailed analysis, see this blog post https://www.comsol.com/blogs/how-to-model-rotating-machinery-in-3d/
Physics-Controlled Mesh
The physics-controlled mesh is controlled from the Mesh node’s Settings window (if the Sequence type is Physics-controlled mesh). There, in the table in the Physics-Controlled Mesh section, find the physics interface in the Contributor column and select or clear the check box in the Use column on the same table row for enabling (the default) or disabling contributions from the physics interface to the physics-controlled mesh.
Information from the physics, such as the presence of an infinite elements domain or periodic condition, will be used to automatically set up an appropriate meshing sequence.
In the COMSOL Multiphysics Reference Manual see the Physics-Controlled Mesh section for more information about how to define the physics-controlled mesh.
Only nodes unique to the Rotating Machinery, Magnetic interface are described in this section. Most nodes are described for The Magnetic Fields Interface or The Magnetic Fields, Currents Only Interface.
Settings
The Label is the default physics interface name.
The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.
The default Name (for the first physics interface in the model) is rmm.
Background Field
Select an option from the Solve for list — Full field (the default) or Reduced field. For Reduced field specify a Background magnetic vector potential Ab (SI unit: Wb/m). The entered expressions must be differentiable.
Notice that expressions including coupling operators are not differentiable and cannot be used as background fields.
The total field used in the physics and equations are given by the sum of the reduced and background fields.
Components
For 2D components, select the Components — Out-of-plane vector potential (the default), In-plane vector potential, or Three-component vector potential.
Thickness
For 2D components, enter a value or expression for the global Out-of-plane thickness d (SI unit: m). The default value of 1 m is typically not representative for a thin domain. Instead it describes a unit thickness that makes the 2D equation identical to the equation used for 3D components.
Port Sweep Settings
Select the Activate port sweep check box and enter a Sweep parameter name in the field. The default is PortName.
The lumped parameters computed can be subject to a Touchstone file export. To activate this functionality, enter a file path or click Browse to navigate to a file. Select a Parameter format (value pairs) for the Touchstone export — Magnitude and angle (MA) (the default), Magnitude in dB and angle (DB), or Real and imaginary parts (RI). Select the desired operation to perform from the If file exists list — Overwrite (the default) or Create new. The latter is useful when the model is solved multiple times with different settings. Enter a Reference impedance, Touchstone file export Zref (SI unit: Ω). The default is 50 Ω.
Error Check
To display this section, click the Show More Options button () and select Advanced Physics Options.
When the Check applicability of features in study check box is selected, any features that are incompatible with the study will generate an error message when trying to solve or show the default solver. No solver will be generated. Deselect it and you will be able to run the model, possibly with runtime errors instead. It is available to allow the advanced user to tweak any feature and use it outside of its intended study scope.
Dependent Variables
The dependent variables (field variables) are the magnetic vector potential A and the magnetic scalar potential Vm. The name can be changed but the names of fields and dependent variables must be unique within a model.
Discretization
Select the shape order for the Magnetic vector potential and the Magnetic scalar potential dependent variables — Linear, Quadratic (the default), or Cubic. For more information about the Discretization section, see Settings for the Discretization Sections in the COMSOL Multiphysics Reference Manual.
Domain, Boundary, Edge, Point, and Pair Nodes for the Rotating Machinery, Magnetic Interface
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Generator in 2D: Application Library path ACDC_Module/Devices,_Motors_and_Generators/generator_2d
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Rotating Machinery 3D Tutorial: Application Library path ACDC_Module/Devices,_Motors_and_Generators/rotating_machinery_3d_tutorial