The Magnetic Field Formulation (mfh) interface (
), found under the
AC/DC branch (
) when adding a physics interface, is used to compute magnetic fields and induced current distributions. It is especially suitable for time-domain magnetic modeling of materials with a strongly nonlinear E-J characteristic such as superconductors. Stationary, frequency-domain, small-signal analysis and time-domain modeling are supported in 2D and 3D. Note that the formulation requires a nonzero conductivity everywhere.
The main node is Faraday’s Law, which adds the equation for the magnetic field and provides an interface for defining the constitutive relations and its associated properties such as the relative permeability.
When this physics interface is added, these default nodes are also added to the Model Builder —
Magnetic Field Formulation,
Faraday’s Law,
Magnetic Insulation (the default boundary condition),
Initial Values, and
Magnetic Gauss’ Law. Then, from the
Physics toolbar, add other nodes that implement, for example, boundary conditions and external currents. You can also right-click
Magnetic Field Formulation to select physics features from the context menu.
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
mfh.
Select Components —
Out-of-plane magnetic field,
In-plane magnetic field (the default), or
Three-component magnetic field for the magnetic field. This choice affect also the directions in which the electric current is allowed to flow: the magnetic field and electric currents are orthogonal.
When In-plane magnetic field or
Three-component magnetic field is selected, the
Magnetic Gauss’ Law node becomes available, and is added as default.
The dependent variable is the Magnetic field H. You can change both its field name and the individual component variable names. If the new field name coincides with the name of another magnetic vector potential field in the model, the interfaces share degrees of freedom and component names. The new field name must not coincide with the name of a field of another type or with a component name belonging to some other field. Component names must be unique within a model, except for fields of the same type sharing a common field name.
The Activate divergence constraint check box is selected by default, which enables the default
Magnetic Gauss’ Law node. Click to clear the check box to disable the Magnetic Gauss’s Law node and remove it from the physics interface.
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.
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