Qingjie Jiao

Measure Variation of Magnetic Field Waveforms Above Rails of a Railgun During Launching Period

To analyze the variation of magnetic field waveforms above rails of the railgun during the launching period, the magnetic fields are measured by loop probes. According to the armatures different moving statements and measurement positions, magnetic waveforms are distinguished with each other. The experiment results show that magnetic field waveforms above the rails change at different positions, and the output voltages of probes become larger with the higher velocities. The truncated waveforms expand the spectrum of signals around the rails. The waveforms at different positions are compared with each other, which can inflect the magnetic field distribution along the rails during the launching period. The results are useful in analyzing the interference of the transient environment for the rail launcher and the electromagnetic interference design of railgun systems.

Plasma Armatures for Railguns

Renewed interest has arisen in plasma armatures as evidenced by two papers presented at the 2008 EML Symposium. It is hoped that the work at the University of Texas described in these papers succeeds. There may, however, be some uncertainties related to the nature of plasma armatures in that work. The thoughts we offer here may help. It is not yet obvious how the 6-km/s velocity limit encountered in the Canberra railgun can be overcome. In the years following this discovery, a considerable number of experiments were conducted on the subject with no clear outcome. One strategy for overcoming the velocity limit may be to vent the bore behind the armature. In order to do this, it is necessary to find out how long the armature must be to be effective. Too long would make the venting process unwieldy. Too short and the armature losses will rise to unacceptable levels. Further, the method we suggest for implementing the venting strategy may be extended to prevent damage to the railgun rails caused by the arcing current transfer from rails to armature. We examine the possibilities and implications involved in implementing these strategies.

Study on mechanical character of armature and rail with non-rectangular cross section in EML

How to raise launching efficiency and prolong working life are the key bottleneck problems in applying the electromagnetic launch (EML) technology to the military and civil use in future. During the launching process, control of rail deformation in a small range is very important for successful launch. Besides the rail support and containment, the shape of rails cross section has significant influence on its deflection under EM force load. Rectangular cross-section rails are most commonly used in railguns. However, some non-rectangular cross-section rails show performance improvement. We investigate some of these. We derive the expression for moment of inertia for several rails with non-rectangular cross section, and compare their resistance to bending with those of rectangular rails. Using Matlab software, we make numerical simulations to study the effect of the rails width, height, the inner radius of rail with curved surfaces, and the angle on the rail deflections. The mechanical behaviors of solid armatures, matching with non-rectangular cross section rails, are also investigated by using finite element analysis software LS-DYNA. The results indicate that non-rectangular rails maybe a good choice for future railgun weapons if adequate machining precision can be obtained.

Study of Properties of the Double-Deck Rail in the Electromagnetic Launching System

Give the fact that the double-deck rail demonstrates excellent performance in preventing rails melting and gouging during EML tests, theory and simulation research was carried out on the lateral vibration of the double-deck rail and contact properties between the armature and the rail in this paper. We deduced the lateral vibration contact equations of the double-deck rail by simplifying electromagnetic rail launcher as Bernoulli-Euler model based on the elastic foundation. A finite element code was used to help us model the launch progress. Influence of the double-deck rail scheme and rail height ratio was also analyzed. Both the characteristics of the contact surface between the rail and the armature and the displacement of the armature were considered. The results show that the double-deck rail can inhibit the propagation of bending waves and efficiently reduce rail gouging, beside, the double-deck rail height ratio has much influence on this effect.

Analysis and Measurement of Transient Currents in Railgun With Loop Probes

Several loops are placed at one side of the rails along a straight line, and the transient current is calculated with the measured magnetic field waveforms and distances between probes and currents for the long-line current models. According to the skin effect and the deformation of rails, distances between currents and probes are hard to get for each shot. If two probes are used together, it is easier to measure the single line current waveform, without measuring the distance between probes and currents beforehand. The current waveforms can be calculated only with the calibrated distance between two probes and field waveforms. For the railguns rail currents, we can use three loop probes. The current waveforms can be easily obtained from the three magnetic field waveforms without knowing the shift positions of the rail currents. The commercial Pearson current monitor model 1423 is used to calibrate and verify the results. The results are compared with each other for the single loop, two loops, and three loops. The results show that, while it is good to measure the transient currents with one or two loops, it is better when three loops are used. The method is especially useful for situations in which the huge Rogowski current probes are hard to use because of limited space.

An Analytic Expression of Inductance Gradient for Rail-Type Electromagnetic Launcher

The rail-type electromagnetic launcher (EML) has good development and applied prospects for military and civilian dual purpose. The inductance gradient is an important parameter to design the EML structure and evaluate the system performance. Based on the Biot-Savart law and current skin-effect behavior, we derive an analytic formula to predict the EML inductance gradient, which expands Battehs formula by introducing rail thickness w and skin depth δ. Our expression is more accurate because the geometrical parameters of both rails and armature are considered in this paper. We investigate the inductance gradient change as a function of the ratio of bore width to height s/ha, rail thickness w, and two-rail interval s. Finally, our results at different scales are compared with those of other formulas of the inductance gradient. This paper could be used directly to design and optimize the rail-type EML.

Simulation Study on Mechanical Response of Cambered Surface Armature and Rail Under Electromagnetic and Thermal Loads

In this paper, an indirect decoupling method is established to simulate the physical process of an electromagnetic launch considering electromagnetic force, thermo-softening of metallic material, and melting interface layer effects. The dynamic responses of cambered surface rail and armature under electromagnetic and thermal loads are analyzed and a simulation method is provided for the engineering applications of electromagnetic launch technology.

Measure variation of magnetic field waveforms above the rails of rail-gun during the launching period

The rail-gun has two rails with an armature sliding along the rails, and the armature is accelerated by the transient current. In order to analysis variation of magnetic field waveforms above rails of the rail-gun during the launching period for EMI designs, the magnetic fields are measured by loop probes, and current waveforms are measured by calibrated probes. The magnetic fields waveform besides static rails has the same raise time and width time as the main current. According to the armature movement states and measurement positions, magnetic waveforms are distinguished with each other. The experiment results show that magnetic field waveforms above the rails change for the different positions. There are narrower raise time and last time with higher velocities. The truncated waveforms introduce new spectrum signals around the rails. The waveforms at different positions are compared with each other, which can inflect the magnetic field distribution along the rails during the armature is launching. The results are useful to analysis the interference of the transient environment for the rail launcher and it is also useful for the EMI design of rail-gun systems.

Analysis and measure the transient currents of rail-gun with loop probes

Loop probes are used to measure the magnetic field nearby the rails of the rail-gun, and the total current can be measured by these loops too. Several loops are placed at one side of the rails along a straight line, and the transient current can be calculated with the measured magnetic field waveforms and distances between probes and currents for the long line current models. According to the error of fixing probes, and the position shift of the current for skin and adjacent effects and electromagnetic forces, distances between currents and probes are hard to get for each shot. If two probes are used together, it is easier to measure the single line current waveform. It is needless to get the distance between probes and currents beforehand. The current waveforms can be calculated only with the calibrated distance between two probes and field waveforms. For the rail-guns rail currents, which have the same amplitudes but reverse directions, we can use three loop probes. The current waveforms can be easily got from the three magnetic field waveforms without knowing the shift positions of the rail currents. The commercial PEARSON current monitor model 1423 is used to calibrate and verify the results. The results are compared with each other for the single loop, two loops and three loops. The results show that it is proper to measure the transient currents with one loop or two loops, while it would be better when the three loops are used. The method is useful especially for the situations that the huge ROGOWSKI current probes are hard to fix with limited volume space.

Influences of shields to the inductance with transient currents

Frequency of currents, material properties and physical shapes can influence the inductance. Especially for the transient current and linear medium, the current density may vary greatly to change the inductance. Based on the analysis of inductance calculation, a transformer model is introduced to illustrate the contributions of parameters to inductances. Numerical experiments are given to verify the results using software ANSOFT Maxwell SV. The results show that influences of the shields to the inductance with certain transient currents can be neglected.