Analyzing Influence of Barrel Shell on Launching Performance of Electromagnetic Rail Launcher
Zhai Xiaofei1, Zou Kun1,2, Li Peifei1, Peng Zhiran1, LiuHua1
1. National Key Laboratory of Science and Technology on Vessel Integrated Power System Naval University of Engineering Wuhan 430033 China; 2. School of Electrical Engineering Southeast University Nanjing 210096 China
Abstract：As part of the electromagnetic launcher (EML), the barrel shell mainly provides preloading force for the rails to constrain the expansion and deformation of the EML, and at the same time provides support stiffness for the rail to ensure the straightness of the EML. During the launch process of the armature, the instantaneous change of rail current will induce a huge eddy current on the metal barrel shell of the EML, and the eddy current magnetic field of the shell has a certain weakening effect on the magnetic field inside the device, and will also affect the current distribution of the rails, thereby affecting the electrical features and mechanical properties of the EML, affecting the launching performance such as the exit speed of the armature. Since the shell structure and material will affect the shell eddy current, it is necessary to analyze the influence of the shell material and structure on the electromagnetic parameters of the EML and the force of the armature and rails, so as to obtain the influence law of the shell on the launching performance. Firstly, the magnetic field control equation considering the eddy current of the shell is established, and the finite element model (FEM) of three shell structures is established: the integral structure shell, the upper-lower separated structure shell and the laminated structure shell. After the speed frequency is introduced, the frequency changed current excitation is used to simulate the velocity skin effect caused by the launching of the armature in the bore, so as to obtain the inductance gradient and shell loss with frequency change curve, as well as the electric density distribution of the rails and the eddy current distribution cloud in the shell. Secondly, the simulation of electromagnetic-structural is carried out, and the stress distribution of each component of the EML is obtained. The system electrical simulation is established, and the launching simulation results of the three shell structures are compared. The results of the electromagnetic-structural simulation and system launching simulation show that the laminated structure shell has the smallest eddy current, the largest inductance gradient, the largest stress of the device components, and the highest armature exit speed, while the integral structure shell has the largest eddy current, the largest shell loss, the smallest inductance gradient, the smallest stress of the device components, and the lowest armature exit speed. Finally, the simulation and test results of the laminated structure shell EML are compared, and the error of both the armature exit speed and the current peak is less than 1%. Under the condition of satisfying the support strength of the EML, the selection of materials with high permeability and low conductivity and the design of the shell structure that suppresses eddy currents are conducive to improving the exit speed and system efficiency of the EML. In addition, reducing the eddy current of the shell is conducive to increasing the electromagnetic thrust of the armature, but it will also increase the external expansion force of the rails, which requires increasing the structural strength of the shell to provide higher preloading force, therefore, the structural design and material selection of the shell should take into account both electromagnetic properties and mechanical properties to obtain excellent launching performance.
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