Numerical Analysis of the Transient Inductance Gradient of Electromagnetic Launcher Using 2-D and 3-D Finite-Element Methods

We present analyses of the transient inductance gradient of an electromagnetic launcher with the sliding contact between rails and armature. When the armature moves along the rails, electrical current concentrates on the contact trailing edge of the armature due to the velocity skin effect, affecting input current spreading into the rail. This effect also induces the temporal variation of inductance gradient. Using the 2-D finite-element method (FEM), the rail inductance gradient without an armature is calculated and compared with the propulsive inductance gradient with a moving armature calculated by 3-D FEM. Using the 3-D simulation, the influence of the step on the height difference between the rail and the transient moving armature is investigated. The result shows that the average of transient inductance gradients during acceleration is 10% larger than Kerrisk's inductance gradient. Also, we found that the axial force on the armature is not significantly affected by the velocity of the armature, while the lateral force on it whose direction is outside the rail increases with the velocity. The circuit simulation using both inductance gradients shows good agreement with the measured current and velocity.