Prediction of Electromagnetic Fields Generated by Rail Guns.

Rail guns generate electromagnetic signatures that contain frequencies extending from quasi-DC to tens of kHz. The characterization of these fields for electromagnetic compatibility concerns remain, however, largely unexplored. Accordingly, this paper includes a discussion of the theoretical models used to predict the inductance gradient, the transient behavior of the currents produced in the rail gun structure, the dynamical generation of the external fields, and a comparison of the theoretical model with experimental data. The predicted rail inductance gradient of L'/sub R/=0.52 /spl mu/H/m compares very well with the measured value of 0.522 /spl mu/H/m. The existence of an inductance gradient efficiency factor, E/sub o/, is demonstrated, with a derived value of 0.75. This produces an effective inductance gradient of L'=E/sub o/L'/sub R/=0.39 /spl mu/H/m which leads to a predicted muzzle velocity of 525 m/s that is within 5% of the measured value. Predicted magnetic field waveshapes are in good agreement with observations close to the bore center. For radial distances greater than a foot, measured peak fields exceed predictions by a factor of two to three. This issue is being investigated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electromagnetic launching system is composed of the Electromagnetic Railgun (EMRG) and the large-scale Pulse Power System (PPS). According to the different test requirements of PPS and EMRG, the special master-slave distributed data acquisition software for electromagnetic launching system is designed by using LabVIEW graphic language. The test host and the sub-machines are multi-channel transient data acquisition systems based on PXI bus. The host PXI is used to measure the comprehensive parameters of the EMRG in multi-physical field. All sub-PXIs are used to diagnose the discharge current signals of each Pulse Forming Unit (PFU). The database management software uses C# programming language to design a friendly human-computer interaction interface, and uses SQL Server software to establish and manage the database, which realizes the comprehensive management of experimental data, tasks and resources involved in the EMRG experiments. The experimental information and experimental data are classified and filed, and the experimental data can be queried, and the experimental results can be analyzed and compared. The data acquisition and experimental database management software has perfect functions, friendly user interface, convenient operation, good versatility, and can also be used in other experimental occasions.

As the most efficient and compact sources in pulsed power supply for electromagnetic launchers, the air-core pulsed alternator can supply a current as high as 1 MA with a voltage reached several kilovolts. The machine performs various functions, such as kinetic energy storage, electromechanical energy conversion, and power conditioning, making the electromagnetic launch system compact and lightweight. But due to the short history of the machine and the absence of fabrication experience in China, the air-core pulsed alternator is still in an exploratory stage, and there are lots of key technologies and problems needed to be researched deeply. Taking technical risks and manufacturing costs into consideration, a seven-phase air-core pulsed alternator has been proposed and the machine is under development. In this paper, operation principles of the electromagnetic launch system are presented in detail. The mathematical models of the seven-phase alternator and the rail gun are introduced. Based on the mathematical models, a simulation model about the electromagnetic launchers is built, and it is useful to help us figure out the operation characteristic when the self-excitation machine drives the electromagnetic rail gun with a 200-g projectile. As a result, it is convincing by simulation to prove the drive current can be as high as 1 MA and the projectile is with a velocity of 2 km/s at the exit. Simultaneously, violent transient situations will be illustrated in this text, such as the electromagnetic torque and the rotor speed. Meanwhile, simulation results can verify the analytical method and present the current and voltage straightforwardly. They also have great significance on choosing the proper high power switching devices.

A general dynamic system model of an augmented electromagnetic launch (EML) system was developed. This model was used to characterize the augmentation effect on EML system performance by a direct comparison to a nonaugmented or simple railgun system. The results of these calculations indicate that increasing rail augmentation increases both Joule heating losses and total EML system inductance. These losses and the larger system inductance were shown to decrease system efficiency despite the lower peak rail current required to induce the same Lorentz force on the projectile in the simple EML system. The Joule heating loss was shown to be reduced by decreasing the initial augmentor rail temperature or by increasing the augmentor rail area. This paper discusses the augmented EML system model and reports the results of the parametric calculations.

Compared with steam catapult system, electromagnetic launcher (EML) system is highly integrated, and it has high and well matching performance. It will be widely used aircraft carriers ejection, rocket launchers etc in future. Double-side tabular permanent magnet linear synchronous motor (PMLSM) for electromagnetic launcher can meet the requirements of big thrust and high efficiency etc. It can accelerate the launcher at the expected speed in short time. The thrust characteristic of the launcher is essential to the whole electromagnetic launcher system. Large thrust and small thrust ripple are both expected. This paper studies thrust characteristic of different pole arc coefficients, compares the series and parallel magnetic circuit structures, and analyses the method of staggering a certain distance between poles on both sides. In order to achieve the goal of large thrust, the Launcher is often designed with high current density. As a result, it is of great loss and has quick temperature rise. This paper establishes numerical model of the two-dimensional (2D) primary transient temperature field. The temperature field of the short-term system is analyzed. The calculated and experimental results of the electromagnetic launchers can provide a basis for optimum design.

A large-scale railgun is being considered by the U.S. navy as a future long range (>200 nm) naval weapon system. The notional concept includes a 15 kg projectile with a 2.5 km/sec muzzle velocity. The choice of bore and rail geometry for such a weapon can influence key aspects of the total system design. This study explored a range of bore and rail geometries and looked at their effects on key railgun system parameters such as parasitic mass, inductance gradient, linear current density, required pulse forming network (PFN) size, and barrel mass. Preliminary solid modeling and structural analysis of the integrated launch package was performed in order to quantify parasitic mass. Inductance gradient calculations were based on a current density distribution analysis. A PFN/Launcher numerical simulation model was then used to determine linear current density and PFN size. Finally, barrel mass was estimated by structural analysis based on calculated rail repulsive forces. Trends and sensitivities of the different parameters to changes in the bore and rail geometries are presented and conclusions are given.

Current probe is a detection method commonly used in electromagnetic compatibility. With the development of power electronics technology, the power level of power conversion devices is constantly increasing, and the power current of the electric energy conversion device in the electromagnetic launch system can reach 10kA. Current probe conventionally used in EMC (electromagnetic compatibility) detection cannot meet the test requirements on high current system due to the magnetic saturation problem. The conventional high current sensor is also not suitable for the RF (Radio Frequency) interference current measurement in high current power device due to the high noise level in the output of active amplifier. In this paper, a passive flexible current probe based on Rogowski coil and matching resistance is proposed that can withstand high current and has low noise level, to solve the measurement problems of interference current in high current power converter. And both differential mode and common mode current detection can be easily carried out with the proposed probe because of the probe’s flexible structure.

In order to study the factors affecting the launch efficiency of the distributed-energy-store (DES) railgun, a numerical calculation model of the DES railgun is established in this article. Taking the six-stage equidistant DES railgun with 4-MJ initial energy storage as an example, the simulation results show that the launch efficiency of DES railgun is 21.14%, and the resistance loss and the residual magnetic energy of rail account for a small proportion of 6.47% and 3.77%, respectively. The resistance loss of power supply and other energy losses (the losses caused by the equivalent resistance produced by the armature and its related physical effects) accounted for the highest proportions, respectively, 23.91% and 37.52%. Therefore, these two parts of losses should be reduced to further improve the system launch efficiency. The influence of system parameters on launch efficiency was analyzed, and the parameters include capacitance, charging voltage, inductance, equivalent internal resistance, rail length, interval of current feed point, armature mass, inductance gradient, and rail height. Among them, inductance gradient has the most significant impression on launch efficiency, followed by equivalent internal resistance, rail length, and interval of current feed point. The conclusions can guide the selection of the feeding mode of the electromagnetic launch system and provide reference to the further optimization of the DES railgun launch system.

A simplified rail gun model is established and three dimensional finite element method of electromagnetic (EM) field is used to analyze the model parameters. The parameters include: inductance gradient, resistance gradient, magnetic induction intensity, magnetic force etc. The simulation result indicates that the load of rail gun may be equivalent to the nonlinear resistance, inductance and back electromotive force.

The rail inductance gradient is an important parameter of the electromagnetic launcher. The calculation of its value is important for the design of the launcher structure and for predicting the motion behavior of the armature. The current research on the inductance gradient analysis method of the electromagnetic rail launcher mostly does not take into account the effects of launcher size and current diffusion. This method cannot describe its dynamic characteristics, and it results in a large error compared with the actual launch. Therefore, the paper first establishes an electromagnetic rail launcher armature motion model to obtain the rail velocity skin depth under a U-shaped armature. Second, an analytical method for calculating the inductance gradient based on the dynamic skin depth of the rail is obtained, which takes into account the launcher size and velocity skin effect. Finally, the experimental results verify the correctness and accuracy of the method to achieve an accurate prediction of armature speed.

For the electromagnetic launch system, how to realize the wide pulse, fast rise, and small fluctuation of pulse forming network output current is a core problem. A trigger time sequence control method based on fuzzy theory for the pulse forming network is proposed in this paper. First, circuit models of pulse forming unit, pulse forming network, and electromagnetic rail launcher is established. Second, a fuzzy trigger time sequence controller model for pulse forming network is designed by using Simulink. Third, fixed time sequence discharge tests consisting of 20 pulsed forming units on the linear simulation load are carried out to verify the accuracy of the simulation model. Finally, discharge tests on the linear simulation load and launch tests on the electromagnetic railgun are carried out to verify the precision of the fuzzy controller output respectively. The results show that the designed fuzzy trigger time sequence controller can obtain the ideal trigger time sequence, which demonstrates the pragmatic and reliability of fuzzy control algorithm.

In order to not only reduce thrust fluctuations but also improve transient state performance of primary winding segmented PMLSM(PWS-PMLSM) applied in electromagnetic launch system, this thesis proposes the inter-stator current synchronous tracking and predictive control (ISCSTPC) algorithm based on two inverters alternating supply method for multi-stators PMLSM. The study adopts the finite element model (FEM) to calculate variation rules of electromagnetism parameters when shuttle moves among stators. For this, the accurate PWS-PMLSM mathematical model and control system models are established according to the above mentioned rules, respectively. Through the calculation and simulation on inter-stator thrust ripple and on transient response ability, the experimental result illustrates that the current control algorithms achieve the most satisfied effect for EML.

This paper investigates how the shape and dimensions of projectile affect the inductance gradient and current distribution. Inductance gradient plays an important role in the performance of an electromagnetic launcher and it determines the force that accelerate projectile. Many types of projectiles geometry have various shapes such as block shape and C-shape cube with different dimensions. In this paper, these geometries are considered with FEM and analytic methods. In all simulations, the dimensions of the rails and applied current are constant. Analytic solution can be used to consider the effect of projectile geometry on the inductance gradient. In analytic method used the Lorentz force equation to compute the force that accelerate projectile and inductance gradient. The results of this paper show the effect of projectile geometry on the current density distribution and the inductance gradient that are shown in some figures and tables.

A coil-unit barrel for a helical coil electromagnetic launcher is described. It provides better features of high structural strength and flexible adjustability. It is convenient to replace the damaged coil units and easy to adjust the number of turns in the stator coils due to the modular design. In our experiments, the highest velocity measured for a 4.5-kg projectile is 47.3 m/s and the mechanical reinforcement of the launcher could bear 35 kA peak current. The relationship between the energy conversion efficiency and the inductance gradient of the launcher is also studied. In the region of low inductance gradient, the efficiency is positively correlated with the inductance gradient. However, in the region of high inductance gradient, the inter-turn arc erosion becomes a major problem of limiting the efficiency and velocity of the launcher. This modular barrel allows further studies in the inter-turn arc and the variable inductance gradient helical coil launcher.

For the evaluation of electromagnetic railgun efficiency is very important in the study of electromagnetic railgun link. This article describes the electromagnetic rail gun system efficiency and emission efficiency calculations and experimental testing methods. Through the simulation software for electromagnetic rail gun related efficiency assessment parameters were simulated, efficiency of the railgun is obtained by theoretical calculation. Combining with the test launch of a electromagnetic rail gun, described in detail in the testing process, the use of different sensors and instruments, respectively, to obtain breech voltage, rail current, and muzzle velocity orbit test data and other related test methods and procedures, and after analysis calculated to get the related data of evaluating the efficiency of the rail gun. Using the obtained data on the efficiency of electromagnetic railgun carried out the necessary calculations, gaining the measured system efficiency and emission efficiency test of the electromagnetic rail gun, and the results have been compared with numerical simulation.