Phenomenological Electromagnetic Modeling of Laminated-Containment Launchers

Electromagnetic launchers typically feature a containment structure around the rails that is fabricated using high-strength stainless steel laminations. Eddy currents induced in these laminations reduce the propulsive force in the launcher, leading to a reduction in incremental inductance-a fundamental railgun design parameter. Thus, designers need a method to simulate the effect of the laminated containment structure on this parameter. Using finite-element (FE) analysis to model individual laminations is likely to be counterproductive; an impossibly large number of elements would be required to model the laminations, and the insulating layers between them, for the entire railgun. Instead of modeling the physical structure of the laminated containment, it is more productive to model the effect it has on magnetic fields around the armature. The basic idea is to replace the laminated containment material with anisotropic material with different properties in the longitudinal and transverse directions. Both electrical conductivity and magnetic permeability of the containment structure will affect the magnetic field around the armature, and both these properties can be represented by an anisotropic model for the bulk. The phenomenological model discussed in this paper is designed to find the magnetic fields and currents at the sliding armature, so that L´ can be calculated using readily available commercial FE codes