COMSOL 6.4 - Magnetomechanics, Boundary

) coupling to model interaction between magnetic fields and deformable shells and membranes. It can be used to model cases with or without induction currents, depending on which magnetic field physics interface is used. Thus or interfaces can be used and coupled with either structural or interfaces. The coupling can also handle large structural deformations which can significantly affect the magnetic field distribution

The following study types are supported:

The interaction is related to the action of the magnetics Maxwell stress which is a quantity that is quadratic in terms of magnetics fields. Therefore, to perform either eigenfrequency of frequency domain analysis, the presence of a stationary bias magnetic field will be needed. Thus, only Frequency-Domain Perturbation study type is supported for frequency domain computations. You can use one of the following predefined studies which will include a stationary step to compute the bias state:

	The presence of this multiphysics node in the model will enforce the Include geometric nonlinearity option on all applicable study nodes.

The is the multiphysics coupling feature name. The default (for the first multiphysics coupling feature in the model) is Magnetomechanics, Boundary 1.

The is used primarily as a scope prefix for variables defined by the coupling node. Refer to such variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different coupling nodes or physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the field. The first character must be a letter.

The default (for the first multiphysics coupling feature in the model) is mmfb1.

This section defines the physics interfaces involved in this multiphysics coupling. The and lists include all applicable physics interfaces.

The default values depend on how the coupling node is created.

•

If it is added from the ribbon (Windows users), contextual toolbar (macOS and Linux users), or context menu (all users), then the first physics interface of each type in the component is selected as the default.

•

If it is added automatically when the physics interface is chosen in the or window, then the two participating physics interfaces are selected.

You can also select from either list to uncouple the coupling from a physics interface. If the physics interface is removed from the , for example is deleted, then the list defaults to as there is nothing to couple to.

	If a physics interface is deleted and then added to the model again, then in order to reestablish the coupling, you need to choose the physics interface again from the lists. This is applicable to all multiphysics coupling nodes that would normally default to the once present physics interface. See Multiphysics Modeling Workflow in the COMSOL Multiphysics Reference Manual.

All applicable boundaries are selected automatically. Such domains represent an intersection of the applicable boundaries for the physics interfaces selected in the coupling feature.

In the interface, the following boundary material features are applicable:

In both the and interfaces, the following internal boundary conditions can be used for modeling thin layers:

•

. This boundary condition supports both linear and nonlinear (BH curve) magnetization models within the layer. Use this option for modeling of thin layers of ferromagnetic materials such as iron or steel. Note however that this boundary condition is only applicable for stationary study.

•

. Use this option for modeling, for example, flexible thin layers of nonmagnetic material (such as plastic) separating domains of magnetic medium.

In addition, the interface provides on internal boundaries a that supports all study types. Use this option for modeling thin layers of conductive material such as metals. The material can be also ferromagnetic. Note however that this boundary condition only supports linear magnetization model within the layer.

	See The Magnetic Fields Interface and The Magnetic Fields, No Currents Interface in the AC/DC Module User’s Guide.

This section is available only if one of the coupled interfaces is .

Select the checkbox in order to model the interaction by only applying the Lorentz surface force f = Js × B as the load on the structure. This option is useful when modeling thin layers of electrically conductive but nonmagnetic material such as aluminum or copper. The Lorentz force effect on a moving structure is similar to that of the Rayleigh alpha-damping, where the damping coefficient is proportional to the background magnetic field and the material electric conductivity.

The interaction will be limited to the boundaries, where the coupled interface defines surface current Js. The following features are included: