## 7.3. Modeling Magnetic Contact

You can use surface-to-surface contact elements or the node-to-surface contact element to model magnetic flux across two contacted bodies. The following situations are possible.

• Non-perfect contact to account for the effects of a small air gap between mating components. This typically occurs at the interface between adjoining bodies. In this situation, there is a gap permeance effect where an MMF drop occurs. You can model this effect by inputting the gap permeance real constant, MCC. This option works best if the magnetic flux is normal to the gap interface.

• Perfect contact across dissimilar meshes. This is typically used to model the air gap in a machine, for example, where the rotor and stator meshes meet.

For both types of magnetic contact, you must set KEYOPT(1) = 7 to select the degree-of-freedom option. For the 2-D case, the magnetic potential degree of fredom, AZ, is active. For the 3-D case, only the scalar potential degree of freedom, MAG, is active, and scalar potential formulations (reduced (RSP), difference (DSP), or general (GSP)) are available (see MAGOPT).

 Note: 3-D magnetic contact is not supported for the MVP formulation (AX, AY, AZ), and the edge-based formulation (AZ).

 Note: Non-perfect magnetic contact is only available for the 3–D contact elements, CONTA173 and CONTA174.

For more information on which element types should be used for a particular analysis, see the element discussions in the appropriate chapter of the Low-Frequency Electromagnetic Analysis Guide. For information on the use of the AZ degree of freedom, see Specifying Element Types and Options. For more information on the use of the MAG DOF, see Build the Model.

For details on how to set up a contact analysis, see Steps in a Contact Analysis.

For an example input listing showing a 2-D static magnetic contact analysis, see Doing an Example 2-D Static Magnetic Contact Analysis (Command Method).

### 7.3.1. Using MCC

The magnetic flux across the contacting interface is defined by:

MFLUX = MCC x (Mt - Mc)

where:

 MFLUX = magnetic flux density Mt , Mc = magnetic potential at the contact points on the target and contact surfaces MCC = contact permeance coefficient (Henries/meters2 in MKS units)

The MCC value is input through a real constant, which can be a function of temperature [(Tt + Tc)/2], pressure, and time, by using the %TABLE% option. MCC values can be approximated as μ/t, where μ is the gap permeability and t is the gap width.

If the "no-separation contact" or "bonded contact" option is set (KEYOPT(12) = 4 or 5), contact interaction can occur between two surfaces separated by a narrow gap.

### 7.3.2. Modeling Perfect Magnetic Contact

Perfect magnetic contact supports dissimilar meshes on both sides of the contacting interface (MCC = infinity). You must use the internal MPC approach by setting KEYOPT(2) = 2. You must also set KEYOPT(4) = 1 or 2 for contact nodal detection, and KEYOPT(12) = 5, 6 for bonded contact.