Numerical Modeling of Linear and Rotary Motion in Linear Induction Launchers

Electromagnetic launching can be achieved using different systems, which can be divided into two main categories depending on how the armature is accelerated: rail launchers and induction launchers. Among them, the simplest are the rail launchers, which are characterized by a relatively high armature speed during launch, feeding the armature with sliding contacts between the rail and the armature. However, the presence of sliding contacts results in short lifetimes of the launcher due to rail consumption [1]. A viable alternative can be represented by Linear Induction Launchers (LILs), since they accelerate the armature by inducing a current in it, avoiding electrical and mechanical contact between the armature and the stator coil [2]. The main drawbacks related to their use are the relatively low launch speed that can be achieved [3], and the armature post launch stability. A possible solution to mitigate this disadvantage is to add concentrated windings along the axis of the LIL, able to produce a rotating magnetic field inside the launcher [4]. In this way, the armature is twisted during the launch, stabilizing it [5]. Although this configuration can effectively increase the launch overall performance, it requires complex simulation tools able to consider 3D geometries with multiple Degrees of Freedom (DoF), leading to long computation times and convergence problems if Finite Element-based tools are used. In this framework, this contribution proposes the use of the research code “EN4EM” for the performance analysis of a LIL supplemented with coils for armature spinning motion. Such a code is based on the integral formulation of the magnetic diffusion equations, reducing the electromagnetic field calculation to the solution of an equivalent network [6]. Using this approach, the behavior of the system can be determined by meshing only its active parts (e.g., conductors, permanent magnets), exploiting a coarse discretization, and consequently decreasing the computational time required to analyze the system behavior compared to conventional FEM-based software. Determining the 3D distributions of the electromagnetic field components, the torques and forces acting on the armature can be evaluated, allowing the description of the linear and rotary spinning motion of the armature.