Investigation on the Time-Varying Inductance Gradient of Railgun

The inductance gradient of railgun is one of the key factors in the EM railgun launcher. Generally, people take it as a constant value during simulation, but in fact it is variable in firing. Better understanding of the inductance gradient during launching is helpful to the predicting of the armature transition velocity. To obtain the waveform of the time-varying inductance gradient, the experimental current waveform was analyzed with time-frequency analysis tools. Thus the frequency-time waveform (f-t waveform) of the load current was obtained. The 3-D railgun model was setup in Maxwell 3D modular of Ansoft Corporation. Frequency points of the f-t waveform corresponding with B-dot signals were input to the simulation model to calculate the corresponding inductance gradient and the time-varying inductance gradient was gained. It is indicated that the inductance gradient of the railgun is decreased rapidly before the load current reaches its peak value. The propelling force on the armature is calculated with the inductance gradient waveform and the load current waveform. The armature's mass will show pseudo increase at the rise of current and decrease rapidly when the armature's wings are soft enough.