Armature Shape Optimization of an Electromagnetic Launcher Including Contact Resistance

Barrel and pulsed power supply modules are two crucial parts of an electromagnetic launcher (EML), in terms of overall efficiency. One of the most important features of the barrel side is the armature geometry. In this paper, the shape of the armature of an EML with 10-MJ current pulse generator, 1000-kA peak current, and 4.5-ms excitation time is optimized by using independent variables to define the exact geometry of the armature. The main goal is to maximize the muzzle kinetic energy of the projectile with 300-g mass including pressure and contact current constraints. Finite-element method (FEM) is used to calculate the muzzle kinetic energy of the EML for different armature geometries. Genetic algorithm is used as the optimization method. Since the contact resistance between the armature and the rail affects the distribution of contact current density, contact resistance is also modeled in FEM. It is observed that armature shape optimization study increases the muzzle kinetic energy to 596 kJ and the muzzle velocity to 1993 m/s.

I. Introduction

Electromagnetic launcher (EML), also called railgun, is a new generation accelerator that uses electrical energy to accelerate its projectile. In order to create maximum kinetic energy using the same amount of electrical energy, a number of parameters both in the barrel side and the pulse power supply should be carefully considered. In particular, the armature shape plays a key role in achieving a high efficiency. In the literature, few different armature designs exist, such as brush, plasma, and C-shaped armatures. In [1], thermodynamic and electrical properties of plasma armature are investigated, while Wild et al. [2] show the differences between C-shaped and brush armature types. Detailed analysis of the performance of brush armature, from the standpoint of contact transition and brush deformation is available in [3]. In addition, for the C-shaped solid armatures, geometric parameters become significant. These parameters influence the electromagnetic force on the armature and contact pressure distribution on the surface between the rails and armature. In [4], the effect of only curve shape of trailing arms of armature on the efficiency of EML is observed. Huang et al. [5] perform finite-element (FE) analysis on the mechanical deformation of the C-shaped armature under the enormous electromagnetic forces. Moreover, armature shape also has an effect on the preload pressure distribution on the contact surface, which is created during the loading process of armature between the rails before the firing. In [6], the main topic focused on is to find the proper armature flange shape, so that a more desirable, spread-out contact pressure distribution is achieved. In addition to its importance in armature preloading process, armature shape is also essential for the current rise time interval of the launching process. In [7], the influence of rail and armature parameters on armature current distribution and the maximum current density is investigated. In addition to the armature design studies, there exist a number of optimization studies with different objective functions and independent variables about EMLs in the literature [8]–[13]. Although different optimization methods are implemented for the circuit model of whole EML system including both pulse power supply and barrel, this paper proposes a new specific optimization approach for the armature design.