Lorentz Coupling
The Lorentz Coupling () is a multiphysics coupling feature between the Magnetic Fields interface and the Solid Mechanics interface. It passes the Lorentz force F = J × B from the Magnetic Fields interface to the Solid Mechanics interface and, passes the induced electric field E = v × B from the Solid Mechanics interface to the Magnetic Fields interface. 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 Lorentz force and induced electric field can also be added separately from the interfaces, for instance, by using the Body Load feature from the Solid Mechanics interface and the Velocity (Lorentz term) feature (in 2D and 2D axisymmetric) from the Magnetic Fields interface. Once the Lorentz Coupling feature is applied, those interface features with the same purpose should not be used to avoid double counting. When modeling electroacoustic transducers, like loudspeakers, the coupling is typically added in the voice coil domain.
The Lorentz Coupling feature is available in 2D, 2D axisymmetric, and 3D geometries and is allowed for both time-dependent and frequency-domain studies (including frequency domain perturbation and eigenfrequency studies). The coupling feature handles frames as well as the correct formulation for transient and frequency domain problems. For time-dependent studies, it only accounts for the Lorentz force contribution when the Include geometric nonlinearity check box (in Study settings) is selected. When the displacement of the vibrating or moving part of the model cannot be neglected (when topology changes are important), the Moving Mesh feature (added from the Definitions) is usually used together with the Lorentz Coupling feature.
When the Lorentz Coupling feature is applied to a domain with magnetic materials such as a magnetizable armature, the Lorentz force is no longer the only force contribution. In this case, the force contribution from the magnetic polarization might need to be considered. This can be done by adding a Force Calculation feature from the Magnetic Fields interface and adding a Body Load feature from the Solid Mechanics interface. Note that the Force Calculation feature includes the force contribution not only from magnetic polarization but also from the Lorentz force, that is, the total electromagnetic force. Therefore, when the coupling between the Magnetic Fields interface and Solid Mechanics interface is implemented with the Force Calculation feature and Body Load feature, the Lorentz Coupling feature should not be used at the same domain.
The Magnetomechanics multiphysics interface () can be used for modeling deformation of magnetically actuated structures, which includes interaction of magnetic fields with magnetic materials and current carrying elements such as coils and wires.
Settings
The Label is the multiphysics coupling feature name. The default Label (for the first multiphysics coupling feature in the model) is Lorentz Coupling 1.
The Name 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 Name field. The first character must be a letter.
The default Name (for the first multiphysics coupling feature in the model) is ltzc1.
Coupled Interfaces
This section defines the physics involved in the multiphysics coupling. The Magnetic fields and Solid mechanics lists include all applicable physics interfaces.
When the Lorentz Coupling node is added from the Physics ribbon (Windows users), Physics 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.
You can also select None from either list to uncouple the Lorentz Coupling node from a physics interface. If the physics interface is removed from the Model Builder, for example Solid Mechanics is deleted, then the list defaults to None as there is nothing to couple to.
There are several library examples that demonstrate its usage:
Loudspeaker Driver — Frequency-Domain Analysis: Application Library path Acoustics_Module/Electroacoustic_Transducers/loudspeaker_driver
Loudspeaker Driver — Transient Analysis: Application Library path Acoustics_Module/Electroacoustic_Transducers/loudspeaker_driver_transient
Magnetic Damping of Vibrating Conducting Solids: Application Library path ACDC_Module/Motors_and_Actuators/magnetic_damping
Magnetomechanical Forces
In models where the Lorentz Coupling is not applicable, for example, for magnetizable armatures in transducers, the Magnetomechanical Forces multiphysics coupling should be used. For details see the Magnetomechanical Forces and the The Magnetomechanics Interface documentation of the Structural Mechanics User’s Guide.