Date

2018

Author

Ceylan, Doğa

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Electromagnetic launcher (EML) is an electromagnetic accelerator which uses electrical pulse power instead of conventional gunpowder. A large amount of electric current in the pulse waveform flows in the rails and armature. This current creates large magnetic field between rails. As a result of Lorentz force, armature and projectile accelerate. In this study, finite element (FE) model of an EML which includes both pulsed power supply (PPS) circuits with 2~MJ total electrical energy and barrel with 3~m length is developed. In the barrel side of the model, armature movement is simulated with stationary mesh elements using external variable resistances and inductances depending on the armature velocity, position, frequency of the excitation current and inductance gradient. In addition to the current density and magnetic field distribution in the barrel, alternating current (AC), contact, velocity skin effect and back electromotive force (EMF) resistances are investigated for the described switching scenario of the PPS creating pulsed shaped excitation current with 1~MA peak. Muzzle velocity of projectile and armature with 0.125~kg total mass is found to be 2040~m/s. Total muzzle kinetic energy and system efficiency are calculated as 260~kJ and 13%, respectively. Outputs of the electromagnetic simulations of the designed EML are verified with experimental results. Moreover, the effect of lamination thickness of the containment which supports the rails mechanically is observed. Although using containment in the barrel side is a requirement in order not to lose the contact between the rails and armature, it decreases the efficiency of the launcher because of the eddy currents in the conducting containment. It is concluded that using laminations thicker than 10~mm in the containment is not reliable from the electromagnetic point of view. Finally, armature shape optimization study is presented in the last chapter. The objective function of the optimization study is the muzzle kinetic energy of the projectile. Genetic algorithm (GA) is used as the optimization method. Maximum contact current density and electromagnetic deflection pressure on the armature are chosen as constraints. Since the contact resistance affects the distribution of the contact current density, it is also modeled as thin layers between the rails and armature with variable resistivities depending on the contact pressure values acting on each thin layer.

Subject Keywords

Electromagnetic devices., Finite element method., Electromagnetism., Genetic algorithm.

URI

http://etd.lib.metu.edu.tr/upload/12622547/index.pdf
https://hdl.handle.net/11511/27519

Collections

Graduate School of Natural and Applied Sciences, Thesis