Electromagnetic-Structural Coupling — Lorentz Forces & Magnetostriction

How are electromagnetic forces transferred to a structural model?

The Maxwell stress tensor provides electromagnetic force density at every point. For current-carrying conductors in a magnetic field, Lorentz forces F = J x B are computed from current density and field. These become body loads on the structural model — either one-way (fixed EM forces) or two-way (if structural deformation changes the EM geometry, like a solenoid pulling a plunger).

What is magnetostriction and why does it cause transformer hum?

Magnetostriction is deformation of ferromagnetic material due to changing magnetization — the material expands or contracts as domains align with the applied field. In power transformers, the core is magnetized at 50/60 Hz, causing strain at twice the electrical frequency (100/120 Hz). This vibration creates the characteristic transformer hum. Simulation quantifies the strain magnitude from coupled EM-structural analysis.