Investigations on the Influence of Augmented Rail Geometry on Rail Gun Design Parameters using Finite Element Method

The performance of a rail gun depends on the current density distribution over the rail and armature as it determines the force that accelerates the projectile of the rail gun. A finite element method (FEM) coupled with Simplorer was developed to model and study the performance of the rail gun. The rail gun was modeled using an ANSYS eddy current field solver to determine the current density distribution and equivalent rail gun circuit for the given rail gun geometry. The armature velocity was then calculated using Simplorer by coupling the obtained equivalent rail gun circuit and exciting the rails using a capacitor-based pulsed power supply (PPS) system. The FEM coupled with Simplorer method was verified by numerical calculations for the rectangular rails and also with other researchers’ value, and that showed a good agreement between the results. Further, the current density distribution over rails and armature and velocity of the armature was calculated for different rail cross sections such as circular concave, circular convex, rectangular concave, rectangular convex, T-shaped concave, and T-shaped convex with a C-shaped armature. It was observed that the circular convex rail gun with C-shaped armature showed minimum current density distribution and gives a higher value of armature velocity compared with other rail gun structures. Thus, the circular convex armature was found to be suitable for the electromagnetic (EM) rail gun launchingsystem.

Understanding the behaviour of magnetic field distribution of railgun under transient conditions using finite element method

The purpose of modeling the rail gun is to provide a theoretical understanding of how the design parameters of rail gun such as magnetic flux density between the rails, maximum current density over the rail cross section, repulsive force acting on the rail, and inductance gradient of the rail react under different conditions like the boundary conditions and variation in dimensions. Finite element analysis technique is employed to calculate the rail gun design parameters using two-dimensional analysis. The rail gun design parameters mainly depend on rails and armature, geometry and dimensions. This paper investigates how the rail dimensions affect the rail gun design parameters using finite element technique.

This article proposes a method to design a three-stage induction coilgun system using the finite-element method (FEM). The system is designed to launch a 21.5 kg projectile. The method which is used to calculate the mutual inductance and the mutual inductance gradient between the two coils is expressed. Furthermore, the variation of mutual inductance and its gradient with respect to the distance between the two coils is indicated. The system parameters (i.e., coil currents, mutual inductance, mutual inductance gradient, force, velocity, and magnetic field distribution) are calculated and analyzed utilizing ANSYS Maxwell software. To verify the performance of the initial design, its analytical model is developed and validated in MATLAB software. The results of the analytical model are compared with the results obtained from the FEM method, and it is shown that they are well-matched in all waveforms. Besides, the efficiency of the system is improved through optimization by applying a genetic algorithm (GA). In this way, the efficiency of the system is enhanced from 29% to 36.6% and also the muzzle velocity is increased from 128 to 143 m/s. This method can be used to design a large-scale multistage induction coilgun (MSIC) for launching massive projectiles and reach high velocities.

In order to study the spatial-temporal distribution characteristics of electromagnetic rail gun temperature, based on moving grid processing method and mod function method, a 3-D geometric model of electromagnetic rail gun under single launch mode, a 2-D geometric model of electromagnetic rail gun under continuous-fire mode, and the corresponding transient electromagnetic field-temperature field coupling model are established by using the finite element analysis software COMSOL Multiphysics, and the temperature spatial-temporal distribution characteristics in the rail-armature contact area, cross section of rail, and along the rail axis is simulated under single launch and continuous launch. The results show that, under the conditions of single launch and natural cooling, the high temperature area in the rail-armature contact surface is located at the rear of the armature due to the skin effect. The temperature distribution along the axial inner side of rail tends to be higher near the tail and lower near the muzzle, it increases with time, but the peak temperature does not exceed the melting point of copper. Under the continuous launch and natural cooling, after five launches, the peak temperature of the rail increases to 709 °C, which is close to the melting point of copper. Continued launching will cause rapid accumulation of heat in the rail and a rapid increase of peak temperature, resulting in shortened life of the launcher and even launch failure. Therefore, without active cooling measures, the electromagnetic rail gun cannot be used in actual combat. The results of the study are an important guide for the design and thermal management of the cooling system of electromagnetic rail gun.

With the increasing miniaturization of electronic devices and systems, the dimension of solder joints and pitches has been continuously scaling down, while the current density carried by solder joints increasing significantly, consequently a critical issue, electromigration (EM), has become a key reliability concern. The EM behavior in the solder joint is mainly dependent on the magnitude and distribution of the current density, and may be influenced by the temperature distribution induced by Joule heating effects in the solder. In this study, three-dimensional thermo-electrical finite element analysis is employed to characterize the current density and temperature distributions, current crowding effects as well as thermal gradients in micro-scale Sn3.5Ag solder joints with different sizes and geometries. Results show that, both the maximum and average current densities in the solder increase dramatically by power functions with the scaling down of the solder size. Accordingly, as the solder size is reduced, the serious Joule heating effect takes place and both temperatures and thermal gradients of solder joints increase significantly. Moreover, with increasing standoff height, the maximum current density increases, while the average current density decreases, which results in the increase of the crowdedness of current density defined by the ratio of the maximum current density to average current density (i.e., the crowding ratio). In addition, the thermal gradient in the solder decreases with increasing standoff height. However, compared with the increase of standoff height, the increase of contact angle has quite opposite effect on the maximum and average current densities, crowding ratios as well as thermal gradients in solder joints, respectively. Further, both the standoff height and contact angle have very limited influence on the temperature of solder joints.

Induction coilgun works on the principle of electromagnetic induction between an array of coils, which are wound on a long insulating barrel of appropriate length, and an electrically conducting projectile placed inside the barrel. Previously charged high voltage capacitor banks are sequentially discharged into the coils through high voltage solid-state switches leading to the generation and flow of high magnitude impulse currents through the coils. Time-varying magnetic flux thus produced by the pulsed currents through the coils interact with the projectile inside and induce a resultant current on it. The electromagnetic force exerted on the projectile is a product of the excitation current through the coil (i <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> ), induced current on the projectile (i <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> ), and the mutual inductance gradient (dM <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cp</inf> /dx, i.e., the change in mutual inductance between the coil and the projectile as the projectile travels through the coil). The induced current on the projectile depends on the level of magnetic coupling between the coil and the projectile, which is governed by their geometric property, viz., diameter, number of winding layers in the coils, and number of winding turns per layer of the coils; diameter, length, shape, and material of the projectile as well as the projectile’s position w.r.t. the coils as it moves along the barrel. In this paper, the following parameters, viz., number of winding layers of the coil, number of winding turns per layer of the coil, and the projectile length are varied, keeping the pulsed power source (PPS) parameters as well as the projectile’s outer diameter and mass fixed. The analysis is performed using a commercially available Finite Element Method (FEM)-based software, Ansoft Maxwell. Results obtained from the analysis are used to design and develop a two-stage induction coilgun in the author’s laboratory.

Nowadays lunching masses to faraway distances is an important issue. One of important electromagnetic launcher for this purpose is duble-projectil railgun because it can launch synchronously two separated projectiles. It has been obtained before that two-turn railgun have better inductance gradient and performance than simple railgun. Also, self-inductance gradient and mutual-inductance gradient in two-turn railgun depend on the initial position of armatures. In this paper, we want to calculate the inductance gradient of a new structure that we named it plus railgun. The plus railgun has one barrel between two-pair rails by two separated armatures and two pairs of rails are powered by one pulse power at the same time. A 3-D finite-element method is applied to the transient analysis of the magnetic field, current distribution, and the inductance gradient of railguns. Finally, we will compare the parameters of two-turn and plus railguns.

Superconducting augmentation consists of a superconducting coil operating in the persistent mode closely coupled magnetically with a normally conducting rail gun. A theoretical investigation of the effect of this system on a rail gun has shown that two benefits occur. Projectile velocities and launch efficiencies increase significantly depending on the magnetic coupling between the rail and augmentation circuits. The previous work [1] evaluated an idealized system by neglecting energy dissipation effects. In this paper, we extend the analysis to include the neglected terms and show improved actual launch efficiencies for the SARG configuration. To evaluate this concept, a one meter, 0.95 cm square bore rail gun powered by a 5 KV, 1440 µf capacitor discharging into a pulse shaping inductance of about 5µh was constructed. This system will accelerate a 4 g armature type projectile to the 0.8 km/sec range. Superconducting augmentation will be accomplished using a 4 Tesla dipole magnet recently acquired from DOE's Lawrence Berkeley Laboratory. This magnet system, originally designed as an ESCAR bending magnet, has been modified to a warm bore configuration operating in either the persistent or constant current mode powered by 1600 amp DC supplies. These modifications will allow the above rail gun to be inserted and tested in the SARG configuration. Several factors, including magnetic quench protection, reproducibility of results, relatively low magnetic coupling coefficients, minimazation of rail wear, etc., indicated that this experimental evaluation be conducted with an armature device. An advanced armature design is incorporated in our projectiles. In this paper, we will discuss these details in more depth and present preliminary results of rail gun performance.

Convex shaping process simulation during counter-rotating electrochemical machining by using the finite element method

Numerical investigation and entropy generation for flow boiling evaporation in U-bend tube heat exchanger with elliptical and circular cross-sections

Effect of active cooling on the thermal effect of electromagnetic rail under single launch mode

This study quantifies the correlations between crack evolution and electrical performance degradation of the Al metallization in insulated gate bipolar transistor (IGBT) modules. The resistance of the Al metallization under different power cycling times was measured by the four-point probe method. The cracks that occur in the Al metallization were investigated by measuring crack geometric parameters, e.g., shape, geometric size and density. Simplified analytical models containing different crack geometric parameters were established by the finite element method (FEM). The influences of crack evolution on the resistance and current density of the Al metallization were quantitatively analyzed. The results indicate that the crack depth has the largest effect on the Al metallization resistance compared with the crack length and width. At the later stage of power cycling, increasing the crack depth plays a critical role in metallization resistance degradation. In addition, cracks affect the current flow direction and the maximum current density in the Al metallization. With increasing crack depth and length, the maximum current density in the crack vicinity increases continuously. However, increasing the crack width reduces the maximum current density.

Aim. To assess the dependence of electrodontometry indicators on the configuration of the root canal and to determine the value of the resultant action of the current at which patients have a response to electrodontometry.Materials and methods. The research consisted in the creation of computer models of teeth and their analysis by the finite element method in the COMSOL Multiphysics program. The removed tooth 2.2 was chosen as a prototype for 3D computer models. The tooth was dissected into fragments 2 millimeters thick, from which the geometric parameters of hard tissues and the position of the root canal were removed. Based on these data, a 3D model of the tooth was built. Based on the 2.2 tooth model, 5 models of the same tooth were constructed, simulating the stages of its root formation.Results. In all models, with an increase in the channel width in the apex area from 0.3 mm to 2.55 mm, the current density in this area decreased from 26.92 A/m2 to 0.63 A/m2. The maximum current density in the models was recorded in the narrowest part of the root canal and ranged from 26.01 A/m2 to 26.75 A/m2.Conclusions. The strength of the diagnostic current that causes a response in patients during electrodontometry depends on the configuration of the root canal, namely, on the cross–sectional area in the narrowest part of the root canal, where the maximum current density is recorded. The current density at which patients have a response to electrodontometry is 26-27 A/m2.

The electromagnetic gun is a new type of weapon equipment powered by electric energy. Compared with the traditional artillery, the electromagnetic gun has the obvious advantages of high and controllable initial velocity, no explosive in the bore, and high safety. It is a new concept weapon that will be developed in the future. At present, there are many researches on the launching mechanism of electromagnetic gun, but the related research on the matching ammunition supply system is not yet mature. Therefore, in this paper, aiming at the characteristics of electromagnetic gun without propellant, through the comparison and selection of various ammunition supply system schemes, the ammunition supply scheme of horizontal magazine was determined, and the structural design and strength check were carried out to complete the model of each component and the overall assembly of ammunition supply system. After that, the finite element method was used to check the strength of the sprocket, and the dynamic simulation analysis of the ammunition supply system was carried out, so as to complete the design work of the whole ammunition supply system. This paper provides a certain reference for the development of electromagnetic gun feeding system.