COMSOL 6.4 - AC/DC Module

The new multiphysics coupling connects a boundary feature in the Magnetic Fields interface or the Magnetic Fields, No Currents interface (such as the , the , or the boundary condition) to the mechanical Shell or Membrane interfaces. For each of the four physics combinations, a predefined multiphysics interface is available (as listed below). In addition to this, manually constructed combinations of the multiphysics coupling and the four physics interfaces are supported.

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The multiphysics interface couples a boundary feature in the Magnetic Fields interface (such as the , the , or the boundary condition) to a mechanical Shell interface, using the multiphysics coupling.

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The multiphysics interface couples a boundary feature in the Magnetic Fields interface (such as the , the , or the boundary condition) to a mechanical Membrane interface, using the multiphysics coupling.

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The multiphysics interface couples a boundary feature in the Magnetic Fields, No Currents interface (such as the boundary condition) to a mechanical Shell interface, using the multiphysics coupling.

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The multiphysics interface couples a boundary feature in the Magnetic Fields, No Currents interface (such as the boundary condition) to a mechanical Membrane interface, using the multiphysics coupling.

These multiphysics interfaces require the Structural Mechanics Module, together with the AC/DC Module.

The and the in the Magnetic Fields interface now support the study type. The supports , , and , where “thick” or “thin” refers to the thickness of the layer with respect to the skin depth δ at the typical operating frequency — note that the is a “very thick layer” by definition. For the very thick layer, the boundary conditions use auxiliary degrees of freedom to provide an approximation of the surface admittance. This approximation is optimized before solving using a partial fraction fitting approach. For thin and very thin layers, a precomputed approximation of sufficient order is used, which does not require fitting.

As a result of this addition, thin, highly conductive plates, layers, and coatings can now be modeled in the time domain using the , without having to resolve the skin effect in the material using a boundary layer mesh. This feature can also be used for bulk materials with such a small skin depth that the electromagnetic field hardly penetrates at all, meaning that the interior of the material (typically a metal) does not need to be included in the model: The modeling domain is simply truncated at the material boundary, and the is used to model the skin effect in the material.

The domain feature in the Magnetic Fields, No Currents interface now supports different methods for force calculation (with being the new default). The setting uses the , combined with boundary layer mesh suggestions. This method makes it possible to compute the clamping forces on a magnet when it is attached to an identical magnet, for example — a use case where the old method would return zero, since it does not take into account the fact that air would fill the gap when the two magnets are pulled apart. The new method typically enables a more accurate local field evaluation, improving most force computations. Note that the approach used in earlier versions is still available.

Furthermore, a new feature is available in the Magnetic Fields, No Currents interface. It provides functionality that is similar to the regular feature but is more suitable for thin structures.

For the feature in the Rotating Machinery, Magnetic interface (in 2D), the winding layout configuration has been improved to find the “most practical” layout for virtually all slot-pole combinations with dual-layered slots. Note that you can still modify the layout after it has been generated.

Furthermore, a new feature, , has been added to model exterior boundaries that should not allow for an outflow of induced currents (this is typically used for modeling symmetry). The solver defaults have been updated as well to improve both solving speed and robustness. The new solver defaults differentiate between 2D and 3D models.

A new boundary feature has been added to the Magnetic Field Formulation interface. The feature applies periodic conditions to the Magnetic Field (the degree of freedom). Support for twisted periodicity and sector periodicity is included. This addition greatly simplifies the modeling of periodic structures and sector models such as twisted superconducting cables or toroidal helical coils.

The in the Magnetic Fields interface, the Magnetic and Electric Fields interface, and the Magnetic Field Formulation interface now uses as the default elementwise mapping. Since these three physics interfaces use curl elements to discretize the degree of freedom, it is important to have matching meshes on the source and destination boundaries of the periodic condition.

The setting performs an analysis of the source and destination mesh and checks that the mesh nodes match within a certain tolerance. Without it, interpolation errors may occur, reducing both performance and accuracy. The new default setting only applies to new models. Existing models will continue to function as before.

In the section of the feature (which is activated through the option in the dialog), there is now support for a . This multiplication factor can be used to model the effects of symmetry. When a symmetry condition has been used such that the surface area of the terminal feature selection represents half of the surface area of the full device, use a multiplication factor of two. A connected load or circuit will then perceive the full device even though the model includes only part of it (higher values can be used for sector symmetry, for instance).

The feature in the Electric Currents interface has been deprecated and replaced with a feature and a feature, with being the new default feature. The chosen reference frame — Lagrangian or Eulerian — affects how Maxwell’s equations should be interpreted (in particular, this applies to material properties and induced electric fields). The two new features provide a more user-friendly implementation that helps to ensure that the appropriate reference frames are used for liquids, gases, and vacuum on one hand, and solid objects on the other.

The Electric Currents in Shells interface now supports both the multiphysics coupling, as well as the multiphysics coupling (before, it only supported the layered shell version). This allows for easier modeling of nonlayered shells in the context of Joule heating.

The dependent sources in the Electrical Circuits interface — the , the , the , and the — have been extended to support multiple current or voltage dependencies. This increases the feature’s flexibility and improves compatibility with the SPICE import format. In particular, support has been added for the SPICE “poly” statement in which the current or voltage depends on a polynomial which is based on several currents or voltages elsewhere in the circuit.

For all physics interfaces in the AC/DC Module, the feature context menu and the toolbar (or ribbon) have been completely renewed. Features have been organized by type and popularity. Common features like the feature or the feature are exposed and at the top of the menu, while more exotic features like the are at the bottom (and typically hidden in a subcategory).

Features from different physics interfaces with similar properties are organized similarly, and some features are renamed to reduce ambiguity and to better reflect what they do. This allows for a quicker workflow for both simple and advanced models.

The AC/DC material library has been updated with new magnetic materials from Bomatec®. The materials include NdFeB grades (regular sintered, corrosion stable, corrosion and temperature stable, hot pressed, bonded compressed, injection molded, and extruded), Ferrite (dry pressed, wet pressed, and injection molded), SmCo and SmFeN (injection molded), SmCo5 and Sm2Co17 (sintered), and AlNiCo (cast and sintered).

In addition to this, the entire branch in the material library has been reprocessed using the updated B-H Curve Checker app to remove nonmonotonic behavior of the differential permeability around the zero point, and to provide better extrapolation into the fully saturated region.

When performing a measurement on a soft magnetic material (extracting a B-H curve) it is not uncommon for the curve to start at a moderate slope around the zero point, before proceeding to a steep slope and then reaching saturation. This initial slope typically does not contribute to the numerical analysis since: 1) completely unsaturated regions contribute little to the overall reluctance of a magnetic circuit such as a laminated core, and 2) most electrical machines are designed to operate reasonably close to saturation (since not doing so would imply having an excess of material, increasing cost). At the same time, the moderate initial slope can have a severe impact on nonlinear (and transient) solver performance. Overall, the newly processed curves give better solver performance while having a negligible impact on the solution.

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The feature now issues a warning when its selection overlaps with a material having “nonfree space”-like material properties. This reduces the risk of ignoring material properties due to assuming vacuum conditions.