Showing papers on "Projectile published in 2007"

Unified force law for granular impact cratering

Abstract: Experiments on the low-speed impact of solid objects into granular media have been used both to mimic geophysical events1,2,3,4,5 and to probe the unusual nature of the granular state of matter6,7,8,9,10. Observations have been interpreted in terms of conflicting stopping forces: product of powers of projectile depth and speed6; linear in speed7; constant, proportional to the initial impact speed8; and proportional to depth9,10. This is reminiscent of high-speed ballistics impact in the nineteenth and twentieth centuries, when a plethora of empirical rules were proposed11,12. To make progress, we developed a means to measure projectile dynamics with 100 nm and 20 μs precision. For a 1-inch-diameter steel sphere dropped from a wide range of heights into non-cohesive glass beads, we reproduce previous observations6,7,8,9,10 either as reasonable approximations or as limiting behaviours. Furthermore, we demonstrate that the interaction between the projectile and the medium can be decomposed into the sum of velocity-dependent inertial drag plus depth-dependent friction. Thus, we achieve a unified description of low-speed impact phenomena and show that the complex response of granular materials to impact, although fundamentally different from that of liquids and solids, can be simply understood.

An analytic solution of projectile motion with the quadratic resistance law using the homotopy analysis method

Abstract: We consider the problem of two-dimensional projectile motion in which the resistance acting on an object moving in air is proportional to the square of the velocity of the object (quadratic resistance law). It is well known that the quadratic resistance law is valid in the range of the Reynolds number: 1 × 103 ~ 2 × 105 (for instance, a sphere) for practical situations, such as throwing a ball. It has been considered that the equations of motion of this case are unsolvable for a general projectile angle, although some solutions have been obtained for a small projectile angle using perturbation techniques. To obtain a general analytic solution, we apply Liao's homotopy analysis method to this problem. The homotopy analysis method, which is different from a perturbation technique, can be applied to a problem which does not include small parameters. We apply the homotopy analysis method for not only governing differential equations, but also an algebraic equation of a velocity vector to extend the radius of convergence. Ultimately, we obtain the analytic solution to this problem and investigate the validation of the solution.

Role of Electronic Excitations in Ion Collisions with Carbon Nanostructures

Abstract: By combining ab initio time-dependent density functional calculations for electrons with molecular dynamics simulations for ions in real time, we investigate the microscopic mechanism of collisions between energetic protons and graphitic carbon nanostructures. We identify not only the amount of energy lost by the projectile, but also the electronic and ionic degrees of freedom of the target that accommodate this energy as a function of the impact parameter and projectile energy. Our results establish validity limits for the Born-Oppenheimer approximation and the threshold energy for defect formation in carbon nanostructures.

Impact of a projectile on a granular medium described by a collision model.

Abstract: We propose a model for the propagation of energy due to the impact of a granular projectile on a dense granular medium. Energy is transferred from grain to grain during binary collision events. The transport of energy may then be viewed as a random walk with a split of energy during successive collisions. There is a qualitative and quantitative agreement between this simple description and experimental results.

Shape of impact craters in granular media.

Abstract: We present the results of experiments studying the shape of craters formed by the normal impact of a solid spherical projectile into a deep noncohesive granular bed at low energies. The resultant impact crater surfaces are accurately digitized using laser profilometry, allowing for the detailed investigation of the crater shape. We find that these impact craters are very nearly hyperbolic in profile. Crater radii and depths are dependent on impact energy, as well as the projectile density and size. The precise crater shape is a function of the crater aspect ratio. While the dimensions of the crater are highly dependent on the impact energy, we show that the energy required to excavate the crater is only a tiny fraction (0.1%-0.5%) of the kinetic energy of the projectile.

Dynamic Response of Cantilevered Rail Guns Attributed to Projectile/Gun Interaction—Theory

Abstract: An analytic approach is proposed to investigate the dynamic behavior of laboratory rail guns resulting from launching a projectile. The rail gun is modeled as a beam of finite length sitting on an elastic foundation with cantilevered support at the breech end of rails. The structural response of the rail is governed by a transient fourth-order differential equation with an extra term of elastic support (containment and insulator) subjected to a transient forcing function (a moving magnetic pressure). The complete solution of the governing equation is derived and illustrated in details. The displacement solution can be further derived to obtain strain and stress profile as well as dynamic response of the rail gun. This paper mainly reports the theoretic solution which provides a step forward to predict the dynamic behavior of rail guns

Dynamic Response and Armature Critical Velocity Studies in an Electromagnetic Railgun

Abstract: A model is developed to investigate the dynamic response of an electromagnetic railgun structure, induced by a moving magnetic pressure during launch of projectiles. When railgun armature velocity achieves critical velocity, resonance in railgun can occur and cause high amplitude stress and strain in armatures passage and causes life decreasing and damaging in rails. Critical velocity can be considered as one of the railgun dynamic design parameters. In this study, governing equations for rails under dynamic loading conditions has been investigated. Armature critical velocity according to design parameters has also been studied. The results show that dynamic response of the EM barrel becomes critical for increased projectile velocity and lightweight barrel designs. Also, the results of numerical simulation of the bore deformation are presented in this paper under applied loads. The algorithm is used to study the dynamics of tensile stresses near the electrode surface. Accordingly, the model that accounts for projectile velocity and gun construction can be used to guide and improve barrel design

On the Design of Coilguns for Super-Velocity Launchers

Abstract: This paper deals with the design of a super-velocity launcher with muzzle velocity up to 8 km/s. It addresses the design specifications of the linear induction section of the launcher having a 4-km/s breech velocity, and utilizing a projectile weighing 1 kg. The overall launcher is a hybrid design, using a gas gun to obtain the initial 4-km/s speed at the input to the coil launcher. The design sequence starts with the maximum temperature allowed by the sleeve material; continues by selecting the required number of sections in the barrel; the dimensions of the drive coils are determined; and our existing computer code is used to optimize the transition between the gas gun and the first section of the coil gun, and between successive sections of the barrel. The code utilizes our latest design scheme; that is, the drive coils are connected in parallel; one flywheel generator per pole is used; and all of the generators in a given section are shaft-coupled, so that they all rotate at the same speed. The design specifications are presented in this paper together with simulation results for the phase voltages, the currents, and the acceleration forces

Numerical computations of dynamic derivatives of a finned projectile using a time- accurate cfd method

Abstract: This paper describes a computational study undertaken to compute the dynamic derivatives of a finned projectile using an advanced unstructured time-accurate NavierStokes computational technique. The numerical procedure uses an advanced coupled computational fluid dynamics (CFD)/rigid body dynamics (RBD) technique that provides for a grid motion capability to fly a projectile on the supercomputers. As a special case, this procedure can be run very easily in an uncoupled mode to model motions such as the pitching and the rolling of a projectile and compute the dynamic derivatives from these unsteady simulations. Time-accurate numerical computations have been performed for a finned body at different Mach numbers across the speed regime from subsonic to supersonic conditions using unstructured grids and the dynamic derivatives have been extracted from the uncoupled time-accurate CFD/RBD computations. Computed dynamic derivatives have been compared with actual data measured from free flight tests and experiments and are found to be generally in good agreement.

keV fullerene interaction with hydrocarbon targets: Projectile penetration, damage creation and removal

Abstract: The physics of energetic fullerene projectile penetration, damage creation and sputtering in organic solids is investigated via molecular dynamics simulations. Two models are used, the first one based on a full atomistic description of the target and the second one, using a coarse-grain prescription that was recently developed and tested for a benzene molecular crystal [E. Smiley, Z. Postawa, I.A. Wojciechowski, N. Winograd, B. J. Garrison, Appl. Surf. Sci. 252 (2006) 6436]. The results explore the mechanism of energy transfer from the C-60 projectile to the organic target atoms/molecules through the comparison with significantly different projectiles (Argon) and samples (Ag crystal). The effects of the projectile energy on the penetration and fast energy transfer processes (200 fs) are also delineated. The second part of the results investigates the 'long term' consequences (20-50 ps) of fullerene impacts in hydrocarbon sample surfaces. In an icosane (C20H42) solid, a 5 keV C-60 projectile induces a crater of similar to 10 nm diameter surrounded by a similar to 4 rim wide rim and ejects similar to 70 intact molecules. More than 75% of the fragments generated by the fullerene in the surface are also sputtered away by the end of the event. The perspective considers the capabilities of fullerene projectiles for depth profile analysis of molecular samples by particle-induced desorption mass spectrometry. (c) 2006 Elsevier B.V. All rights reserved.

Dynamic shear rupture of steel plates

Abstract: Metallic sandwich panels with prismatic cores offer the potential for superior blast resistance relative to monolithic plates of equivalent areal density. However, under sufficiently high impulse, severe plastic strains can occur at the junctions of the face sheets and the core members shortly after arrival of the pressure wave but prior to significant deformation elsewhere. The potential consequence is localized shear rupture with minimal plastic dissipation. To characterize this failure mode, a combined experimentalnumerical protocol has been used to ascertain the plastic strain for dynamic shear rupture of ductile metals. The experimental component involves firing cylindrical projectiles through plates of the targeted materials and monitoring changes in projectile velocity during penetration. With appropriate combinations of plate thickness and projectile velocity, penetration occurs through propagation of an annular shear crack. In parallel, a numerical model of dynamic deformation and rupture has been employed to infer the critical strain through comparisons with projectile velocity change measurements. Experiments and analyses have been performed on both 304 stainless steel and superaustenitic AL6XN. Effects of mesh size on the resolution of the predicted strain distribution and the plastic dissipation associated with penetration are addressed.

Firearm target assemblies, target systems, and methods for manufacturing firearm targets

Abstract: Firearm target assemblies and associated systems and methods are disclosed herein. In one embodiment, target assemblies are configured for accurately predicting projectile impact points for determining shooting accuracy and consistency. In another embodiment, a target system includes a target assembly having a substrate and a print layer. The substrate may have a low shearing response such that a projectile having a first major cross-sectional dimension transverse to a projectile path forms a hole in the substrate at an impact point in the projectile path. The hole may have an aperture with a second major cross-sectional dimension transverse to the projectile path, wherein the second dimension is approximately the same as the first dimension. The print layer may be at a first side of the substrate and may at least partially define a target image.

Flare-bang projectile

Abstract: A flare-bang projectile is comprised of a weighty ballast in the front leading edge, a flash-bang charge, a transfer charge and a flare charge that is lit by a starter composition located at the rear of the flare charge. When the flare charge is ignited such that it burns during the flight of the projectile, an the projectile path is indicated to thereby provide warning signaling.

Modular polymeric projectile absorbing armor

Abstract: A building block for constructing a projectile absorbing armor. The building block has at least one interlocking male connector and at least one female connector. The interlocking male connector and said female connector are sized for interlocking engagement. The invention is also generally directed to a structure having projectile absorbing armor having at least two building blocks in interlocking engagement. The building blocks are constructed from projectile resistant material and may have various features to prevent the passage of a projectile through the block.

Light projectile scattering off the Color Glass Condensate

Abstract: We systematically compute the Gaussian average of Wilson lines inherent in the Color Glass Condensate, which provides useful formulae for evaluation of the scattering amplitude in the collision of a light projectile and a heavy target.

CFD Prediction of M910 Projectile Aerodynamics: Unsteady Wake Effect on Magnus Moment

Abstract: The aerodynamic coefficients of the 25-mm M910 training projectile were characterized using computational fluid dynamic computations. The results were validated with archival experimental data that were re-processed with modern data reduction software, providing a more exact representation of the aerodynamic coefficients. The present study was an extension of previous work and re-affirmed that the prediction of the M910 Magnus moment in the subsonic and transonic regimes was improved using time-accurate, hybrid RANS/LES computations, while other aerodynamic coefficients were adequately predicted via conventional steady-state RANS computations. Force and moment distributions showed that the effects on Magnus were confined to the rear end of the projectile. These effects include both angle of attack nonlinearity and differences between the steady-state RANS and unsteady RANS/LES predictions.

Electronic stopping in insulators: a simple model

Abstract: A simple model is presented to explore, review and illustrate basic concepts related to the electronic stopping power in large electronic band gap insulators. A projectile shooting through the solid is described by a local potential V (r−vt). The flat band limit is assumed for both valence and conduction bands. The energy-transfer rate is calculated by solving the time-dependent quantum mechanics for the timescale of electron excitation near the trajectory, taking the timescale for electronic energy out-diffusion to be much larger. The threshold effect in the low projectile velocity limit is characterized.

Peripherality of breakup reactions

Abstract: The sensitivity of elastic breakup to the interior of the projectile wave function is analyzed. Breakup calculations of loosely bound nuclei (B8 and Be11) are performed with two different descriptions of the projectile. The descriptions differ strongly in the interior of the wave function, but exhibit identical asymptotic properties, namely the same asymptotic normalisation coefficient, and phase shifts. Breakup calculations are performed at intermediate energies (40-70 MeV/nucleon) on lead and carbon targets as well as at low energy (26 MeV) on a nickel target. No dependence on the projectile description is observed. This result confirms that breakup reactions are peripheral in the sense that they probe only the external part of the wave function. These measurements are thus not directly sensitive to the total normalization of the wave function, i.e., spectroscopic factor. © 2007 The American Physical Society.

Ablation modeling of electro-magnetically launched projectile for access to space

Abstract: It has been proposed to study and identify the technical issues involved in the launch to space of micro-satellite payloads using an electromagnetic launcher (EML). A CFD code was developed to help characterize the aero-thermal issues involved with the flight of the projectile as it exits the Earth’s atmosphere. Initial conceptual geometries were chosen to evaluate the feasibility of launching to orbit from an aircraft. Due to expected high heating fluxes, carbon-carbon was selected for the heat shield. Results of the initial selected geometries are presented and used to evaluate the practicality of a passive thermal protection system.

Frangible non-lethal projectile

Abstract: A non-lethal impact projectile having a nose composed of a frangible, rigid, polymer foam material such that the nose crushes upon impact with a target to disperse energy, thereby reducing the kinetic energy transferred to the target. Most preferably, the munition or projectile is provided with a cavity to retain a payload, such as marker agents, lacrimators, irritants, inflammatory agents, odorants or inert powders, such that the payload is laterally dispersed upon impact to further dissipate energy transferred to the target.

Laser Based Projectile Speed Measurement System

Abstract: The design and construction of a system to accurately determine the speed of a projectile (bullet) by measuring the time of flight between two parallel laser screens is described. Each screen is formed by a laser source and a set of prisms. At the detection end of each of the screens, a collector lens focuses the incident laser light beam onto a photodetector. The collector lens and detector are kept in a recess so that no stray or ambient light falls on the photodetector. Whenever a projectile crosses either of the screens, the corresponding photodetector senses the event, due to partial or full obscuration of the incident energy. An electronic circuit is used to accurately record the time when the projectile crosses each screen, and the time interval gives the time of flight. The distance between the screens being known, the velocity is displayed on a computer screen. Because a single collimated beam of light generates the entire optical curtain, the reduction in incident energy at the photodetector plane is independent of the entry point of the projectile into the screen. Due to the baffling of the photodetector from ambient light, the optical screens can be used at indoor or outdoor ranges equally effectively.