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Research on Momentum Transfer in Simple Railgun



In this paper, the momentum conservation equation in the longitudinal direction for simple railgun was deduced. In this model, a space V with variable volume is taken as the research object. The electromagnetic surface force on the outer surface of V is equal to the sum of the mechanical momentum received by the guide rail and armature in space V and the momentum of the electromagnetic field in V. Then, a three-dimensional model was established and the finite element method was utilized to simulate the problem. Based on the simulation, some results such as the surface force on the electromagnetic field, the electromagnetic force on the conductor in the longitudinal direction were obtained. Compared with the external surface force FSx = 2938.6N and the electromagnetic force Fmx = 2938.7N on the conductor, the electromagnetic force of the electromagnetic field Fex = 6.37e-16N can be ignored. So the volume force Fmx could be characterized by the surface force FSx. Furthermore, results showed that of the six surfaces of V only the longitudinal section surface force FSx(S0) and FSx(Sx) contribute to FSx. It reviewed that the momentum of the railgun system was conserved when the surface force of the electromagnetic field was contained. Then, the surface force density on different longitudinal section of railgun was analyzed and discussed in details. It is showed that the surface force density gradually concentrated from the outside air to the area between the rails. In addition, the surface force disappeared instantly after passing the armature. It reviewed that large amount of longitudinal force was transmitted to the breech by the electromagnetic field in the form of surface force. And the specific position and distribution of recoil were related to the current input device in breech.


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