As electromagnetic launcher (EML) is an apparatus that uses the electromagnetic (EMAG) force to propel an armature along a rail. An applied electric current, coupled with the resulting magnetic field, creates an EMAG force capable of accelerating an armature to velocities up to several thousand meters per second. The high sliding velocity, coupled with the electric current density, creates extreme thermal conditions at the interface between the rail and the armature that can cause melting at the interface. This project considers a lab-scale EML which is pre-loaded to establish the initial contact between arils and armature. This contact area influences the flow of the electric current and, therefore, it affects the thermal conditions significantly. This work presents a finite-element analysis (FEA) of the aforementioned physical phenomena of the lab-scale EML. This work is aimed at improving the understanding of the armature-to-rail performance and the useful life of an EML by developing a computer simulation which can be used as a design tool to acquire conditiodecoup for the best performance. A two-dimensional structural FEA is used to determine the structural deformation, the contact area, the contact pressure, the von Mises stress, and the material properties of the structural compliance. The vibration characteristics of the lab-scale EML armature are studied using Modal analysis. A three-dimensional electromagnetic FEA is performed to determine the EMAG force. Frictional and Joule heating are determined from a two-dimensional thermal FEA. The commercial finite-element package, ANSYS, is used in the simulation.

In electromagnetic launcher (EML) systems, the behavior of the materials and forces at the armature-rail interface involves fluid mechanics, electromagnetics, thermal effects, contact mechanics and deformation mechanics. These factors must interact successfully in order for a launch to be successful. A lubricant film either deposited on the rails prior to launch or injected from the armature during launch has been suggested as a means of improving the electrical conductivity of the rail-armature interface and of avoiding the occurrence of arcing. The fluid pressure generated by such film, together with the magnetic force, the contact force and the uneven temperature field in the armature, deforms the armature and changes the interface gap shape. An analytical model to study the interfacial behavior under these influences is necessary in order to predict the performance of a potential EML design and to provide optimization information. Studies of this interfacial behavior have been done by a number of researchers. However, many critical factors were not included, such as surface roughness, cavitation, injection, magnetic lateral force, interface deformation and thermal effects. The three models presented in this study investigate the influence of those factors on the EML interface problem. The magneto-hydrodynamic (MHD) model establishes a description of the lubrication process under electromagnetic stress but neglects interface deformation. The magneto-elastohydrodynamic (MEHD) model extends the MHD model by considering the lateral magnetic force, interface contact force and elastic deformation. Finally, the magneto-elastothermohydrodynamic (METHD) model adds the thermal effects to the deformation analysis. A coupled analysis of the interface behavior with the METHD model is developed and the history of a typical launch is studied. Detailed injection, lubrication and launch processes are revealed and the performance is predicted. A failed launch is simulated and the cause of failure is identified to be debris left on the rails. Several operation and design parameters, such as rail surface profile, electric current pattern, reservoir load, lubrication length, pocket size and geometry, injection conduit diameter, are analyzed and a recommended injection design procedure is developed. A scaling study is performed by doubling the dimensions to predict the scaling effects. In the end, the base case configuration and scaled configuration are optimized using the technique developed in this study.

This thesis derives working expressions from electromagnetic physical laws to gain a deeper understanding of the nature of railguns. The expressions are refined for ease of use and then compared to electromagnetic simulators that solve complex equations that arise from different rail geometry. Further simplifications lead to an expression for the final velocity of the projectile and showcase the importance of the system resistance to projectile flux gain ratio. A Simulink simulation then incorporates the resulting non-linear differential equations and approximates the projectile velocity over time based on physical dimensions and material properties. Some equations derived can be found in literature regarding the subject but often lack explanation. This work is intended to provide a thorough derivation of all the relative constituent relations between the critical characteristics of the gun such as the strength of the forces acting on the rail and projectile, rail current, and initial velocity of the projectile. This makes it easier to identify what influences acceleration of the projectile, how much bracing each rail needs, how much initial velocity to give the projectile, etc. Design options discussed besides the standard design include the augmented rail system, a magnetic shell design, and a “wrap around” design. The tradeoffs encountered in each design are discussed in length. Due to the lack of a sufficient power source during testing the projectile was unable to travel down the length of the rails due to metal binding, insufficient pulse duration, and too much circuit resistance. It was found that using copper tungsten for the rails ensures that the rails can withstand the arcing inflicted by the kilo-Ampere current along the rails very well compared to other materials. Also, the copper in the tungsten alloy ensures high conductivity while the tungsten provides structural integrity to the rails during arcing between them and the projectile. Frequency response of conductive projectiles is characterized and improvements such as laminated projectiles are suggested as solutions to mitigate eddy currents induced in the projectile and improve performance.