Optimization of a Convex Rail Design for Electromagnetic Launchers

A rail geometry with a convex cross section instead of a rectangular one provides a higher contact area, uniform current density, and less transition on the contact surface, and it increases the performance in electromagnetic launchers. In addition, the design of convex rails should be considered together with armature structure, the distance between rails, rail length, and parasitic masses that all have an influence on the overall efficiency and armature/rail transition. A novel complete rail and launch package optimization method is presented in this article. In the first part of this article, the optimum convex rail cross sections for five different separation values are found to obtain uniform current density distribution on rail cross section. For this part, a transient finite element (FE) model in 2-D is developed to calculate the current density distribution and combined with a real-coded genetic algorithm (GA). Then, the armature and sabot petal masses are calculated for each optimized rail geometry and each separation values. In the second part, the efficiency of each optimum design with different separation values is evaluated by a transient 3-D FE model with transient solver taking the calculated armature and sabot petal masses into account. Finally, the length of the rails of the final design is investigated for the transition phenomena. It is observed that 48-mm rail separation with 12.9- and 21-mm elliptical cross-sectional parameters has the highest exit velocity (2355 m/s) for 400-g projectile with uniform current density at inner rail surfaces.