Mach Shock Waves Research Articles

Analytical and numerical studies of gas discharge out of gun barrel tube

Abstract This paper investigates the characteristics of the discharge of gases out of gun barrel tube. The paper gives an insight into the physical principles that govern gas discharge through the presentation of analytical and two different numerical approaches. The analytical model is based on the well-known Bravin’s model, whereas the numerical approaches involve single- and two-phase flow numerical simulations conducted by utilities of Computational Fluid Dynamics (CFD). The differences between analytical and numerical results are analysed, from which the numerical approach is found to be capable of capturing the interacting phenomena due to the discharge of hot and high-pressure gases. The visualisation of flow parameters manifests the complex dynamics evoked by flow patterns and the formation of Mach disc and shock waves. It is found that the analytical Bravin’s model underestimates the pressure decay inside the barrel due to gas discharge compared to both the single- and two-phase flow numerical approaches.

Hyperbolicity, Mach Lines, and Super-Shear Mode III Steady-State Fracture in Magneto-Flexoelectric Materials, Part I: Methodology

Abstract This work examines the sub-shear and super-shear steady-state growth of mode III fractures in flexoelectric materials, nonetheless, exhibiting Mach type shock wave patterns that resemble reported lattice dynamics results and three-dimensional calculations and experiments. Our mathematical models provide weak discontinuous solutions of the steady-state dynamic equations. In flexoelectric solids, super-shear rupture is possible with Mach lines appearing at sub-shear as well as super-shear crack rupture velocities. This is contrary to classical singular elastodynamics, where the notions of super-shear growth and hyperbolicity coincide. The results show that the deformation near the crack-tip agrees with studies based on lattice dynamics. In the first part of this work, a novel finite element approach has been developed where the problem is decomposed into two prestressed plates that are interconnected, resulting into the predicted radiation patterns and Mach lines. The polarization field is obtained from the calculated displacement field and is used in turn to calculate the magnetic and the electric fields. The analysis offers an analogy to the co-seismic magnetic fields encountered during mode III dominated earthquake rupture events.

Study on the influence of helicopter rotor flow on projectile motion

In this paper, the muzzle flow field generated during helicopter gun firing is numerically studied. Based on Navier-Stokes equation and Standard k − ε turbulence model, the projectile motion is realized by using overlapping mesh technology. The development of the muzzle flow field formed by complex wave systems such as Mach disk and shock wave under the influence of helicopter rotor flow at different speeds, as well as the force and motion state of the projectile in the flow field are analysed. The results show that the degree of asymmetry of the flow field, the force and offset of the projectile are positively correlated with the rotor flow velocity. The research will help to improve the understanding of the muzzle flow field of helicopter gun and provide a new idea for improving the firing accuracy of helicopter gun..

Hydrodynamic effects of shock interactions on initial flame kernel development of close dual-point laser induced sparks

Flame kernel formations of close dual-point laser induced sparks were investigated experimentally, focusing on the hydrodynamic effects induced by an interaction of shock waves produced by the laser induced sparks. Dual sparks were produced near the center of the combustion chamber by splitting of a ray emitted by a 532 nm Nd:YAG laser. Methane/air mixtures were ignited under a quiescent condition in a constant volume chamber with detailed measurements of the ignition energy and the pressure history. The minimum ignition energy was derived as an ignition energy having an ignitability of 50% using the logistic regression method. The flame kernel initiation process was also observed by Schlieren photography using a high-speed video camera. The offset of laser induced sparks were adjusted by tuning angles of mirrors and lenses. The ignition performance of single- and close dual-point laser breakdown induced sparks was investigated in detail in terms of the minimum ignition energy and the combustion induction time. Time resolved Schlieren photographs indicated that two hump shaped kernels grew rapidly during the initial stage in the vicinity of the plane of symmetry defined by the laser sparks under certain conditions. Their formation was due to the hydrodynamic effects induced by Mach shock waves, which resulted from interactions of the dual shock waves. The minimum ignition energy of the close dual-point laser induced sparks near the lean limit at 1.0 MPa was much lower than that of single-point laser induced sparks, although it was greater than that of the single ones at 0.1 MPa. The combustion induction time, which was defined as the time corresponding to the maximum pressure increase rate, was shortened for close dual-point laser induced sparks, especially for lean mixtures at high pressure. Robust flame kernels were formed by close dual-point laser induced sparks with Mach shock wave formation, and improved ignition performance for lean mixtures at high pressure was observed.

A Primary-Auxiliary Coupled Neural Network for Three-Dimensional Holographic Particle Field Characterization

Particle field measurement is an important topic in many industrial branches. However, there are always complex imaging scenes in the engineering experiments, resulting in severe imaging artifact, noise, and blur, such as the optical holography. In this article, we propose a primary-auxiliary coupled neural network (PANet) for 3-D holographic particle field characterization, which can obtain a comprehensive particle measurement, including the identification, focus determination, segmentation, and size estimation. PANet is constituted by two subnets that are arranged in a coupled architecture, i.e., a Primary-Net (PNet) and an AuxiliaryNet (ANet). As the main frame, PNet is designed to accomplish the detection of most particles, while ANet aims to detect the tiny particles that PNet cannot identify. We exploit an alternative training method to realize their functional differentiation and complementation. PANet is evaluated on two kinds of holographic particle field data, i.e., high-energy laser shock aluminum target and droplet breakup in high Mach shock wave. By means of semisupervised learning and a specific loss function, the effect of deficient particle labeling can be alleviated. Experimental results demonstrate that PANet can achieve excellent performance in particle field characterization, especially for those with a wide size span and complex image background.

Mechanism of hysteresis in shock wave reflection.

This paper reports on the mechanism of the hysteresis in the transition between regular and Mach shock wave reflections. We disclose that, for a given inflow Mach number, a stable reflection configuration should maintain the minimal dissipation. As the wedge angle varies, the set of the minimal dissipation points forms the valley lines in the dissipation landscape, and these valley lines compose the hysteresis loop. The saddle-nodes, intersections of the ridge line, and the valley lines are actually the transition points. Additionally, the predicted reflection configurations agree well with the experimental and numerical results, validating this theory.

Wavelet Analysis of Produced Pions in 24Mg-Ag/Br Interactions at 4.5 A GeV/c

Angular spectra of the unusual superspiky events produced in 24Mg-Ag/Br interactions at 4.5 A GeV/c are analyzed by the method of continuous wavelet transform in different scale for the ring-like structures which could indicate either the production of Cherenkov gluons or the occurrence of Mach shock waves in excited nuclear matter. The analysis is based on the assumption that the presence of abovementioned effects would be manifested by excess of particles at some characteristic pseudorapidities. The irregularities are revealed in the wavelet pseudorapidity spectra in the scale pseudorapidity region. These irregularities are interpreted as the preferred pseudorapidities of groups of emitted particles.

Optical detection of mach shock wave cones in water using refracto-vibrometry

Recently, a hydrophone array was used to demonstrate Mach shock wave cone formation in water when 1m diameter steel pile rods for civil structures were driven into the ground by massive impact hammers. These shock wavefronts are of concern for marine mammals and fish. In the current project, Mach shockwave cones were directly imaged using refracto-vibrometry. A Polytec PSV-400 laser Doppler vibrometer was directed through a water tank towards a stationary retroreflective surface. The density variations of acoustic wavefronts which pass through the laser cause variations in the optical path length between the laser and retroreflector. This results in a time-varying modulation of the laser signal returning to the vibrometer, enabling optical detection of the acoustic wavefronts. A 35 mm diameter rod (steel or other metal) immersed in a water tank was repeatedly “impacted” by narrow pulses from a 1 MHz ultrasound transducer. The vibrometer sampled numerous scan points to generate videos of the time evolution of a Mach cone wavefronts launched as the compressional and shear waves travel through the rod. The angle of the Mach cone produced is consistent with the speed of waves in the rod.

Моделирование перехода между регулярным и маховским отражением ударных волн с помощью неявной схемы на основе методов LU-SGS и BiCGStab

Моделирование перехода между регулярным и маховским отражением ударных волн с помощью неявной схемы на основе методов LU-SGS и BiCGStab

Boundaries of the ambiguity area upon reflection of compression shock waves

Oblique shock waves can be reflected from hard walls, the axis, or the plane of symmetry, as well as from other counterpropagating shock waves with the formation of regular and Mach shock wave configurations. The specific form of shock wave structures is determined by the parameters of the problem: Mach number and intensity of incident shock waves. On the plane of parameters, there exists an ambiguity area in which laws of conservation admit both the regular and Mach reflection of shock waves. The boundaries of this region have been determined.

Influence of height of confined space on explosion and fire safety

Experiments were carried out in the test section of a wind tunnel to simulate the role of the heights of confined space on formation of shock waves due to a high-speed subsonic flow of air interacting with blockages placed in the flow path. The blockage ratio considered was 0.13 and the medium used was air. A Mach stem shock wave structure was seen to be formed in the flow field downstream of the blockages for small heights of the test section while no shock waves were formed for larger heights of the test section. The turbulent velocities, turbulent intensities and length scales of turbulence were also measured. Test sections of smaller heights were shown to generate higher levels of turbulence in the flow field following the blockages due to the complex shock interactions. As a result, ignition of combustible gas mixtures from an accidental release or leakage in a confined space having small height could form a turbulent flame brush or a detonation. The requirement of larger heights of confined spaces is seen to be desirable from explosion safety point of view.

Mach Reflection of a Shock Wave from the Symmetry Axis of the Supersonic Nonisobaric Jet

The purpose of the study is to determine the conditions of Mach disk (direct shock wave) in a supersonic nonisobaric jet. Brief details on shock waves triple configurations, Mach reflection of a shock wave from a rigid wall and the axis of symmetry are given. Various known semi-empirical model of calculating the Mach disc diameter in a supersonic jet and its removal from the nozzle are discussed. It is shown that the Mach disk in the jet is corresponded by the so-called stationary Mach shock waves triple configuration, in which the intensity of the main shock (Mach disk) is the maximum possible for a given Mach number. The theoretical and calculative-experimental validation of the Mach disk formation model in a supersonic non-isobaric jet is provided. The results of calculation are in satisfactory match with experiment.

Azimuthal structure of charged particle emission in 28Si–Ag/Br interaction at 14.5A GeV and 32S–Ag/Br interaction at 200A GeV

Presence of unusual azimuthal structures in the particle emission data obtained from the 28 Si – Ag / Br interaction at 14.5A GeV and from the 32 S – Ag / Br interaction at 200A GeV, are investigated in the framework of the Cherenkov gluon emission and/or Mach shock wave formation in nuclear/partonic medium. Nuclear photographic emulsion technique is used to collect the experimental data. The experiment is compared with the predictions of two simulations, namely (i) the Relativistic Quantum Molecular Dynamics (RQMD) and (ii) the Ultra-relativistic Quantum Molecular Dynamics (UrQMD). A charge reassignment algorithm is implemented over the outputs of the simulations to mimic the Bose–Einstein correlation (BEC) effect. Our analysis confirms presence of jet-like structures in both experiments beyond statistical noise. Such structures are more pronounced in the 32 S data than in the 28 Si data.

Conical emission: p T and system dependences and the first result with identified particles from STAR

We present the analysis of three-particle correlation with respect to reaction system, transverse momentum (pT) of associated and trigger particles measured by STAR experiment at RHIC. Our preliminary results indicate presence of conical emission of charge particles correlated with high pT trigger particles in central A+A collisions. The measured conical emission angle is independent of pT of associate hadrons, possibly consistent with Mach cone shock wave mechanism. The first result on PID three-particle correlation with identified associated particles is also reported.

Mach cone signal and energy deposition scenarios in linearized hydrodynamics

Particle correlation measurements associated with a hard or semihard trigger in heavy-ion collisions may reflect Mach cone shock waves excited in the bulk medium by partonic energy loss. This is of great interest because, when compared with theory, such measurements can provide information on the transport properties of the medium. Specifically, the formation of Mach cone shock waves is sensitive to the viscosity and speed of sound, as well as the detailed nature of the jet-medium interaction. However, modeling the physics of shock-wave excitation to obtain a meaningful comparison with measured correlations is very challenging, as the correlations arise from an interplay of perturbative as well as nonperturbative phenomena at different momentum scales. In this work we take a step in that direction by presenting a systematic study of the dependence of azimuthal particle correlations on the spatiotemporal structure of energy deposition into the medium. Our results indicate that detailed modeling of the evolution of an initially produced hard parton and the interaction of this evolving state with the medium is crucial, as both the magnitude and the shape of the shock-wave signal show a strong dependence on the assumptions being made.

On the Use of Composite Charges to Determine Insensitive Explosive Material Properties at the Laboratory Scale

Laboratory-scale air-blast experiments an gram-range composite explosive charges are presented. The composite charges consist of a spherical booster charge surrounded by a concentric, spherical “candidate material” shell charge. By way of composite charge explosive characterization, the candidate explosive material is able to be characterized through the “removal” of the known booster effects. Using peak shock wave pressures, a method is developed to remove the booster effects from the composite charge’s signature to yield the sole effects of the candidate explosive material, permitting its characterization. Air-blast explosive tests are conducted using digital high-speed shadowgraph visualization to measure the resulting shock wave radial position as a function of time. Booster and composite charge data are converted to Mach number versus shock wave radius profiles and subsequently to peak shock wave pressure versus shock wave radius profiles for characterization of the shell material. Explosives tested include: PETN, RDX, HMX, and Alliant Bullseye® SP.

Equation of state dependence of Mach cone-like structures in Au+Au collisions

In jet quenching, a hard QCD parton, before fragmenting into a jet of hadrons, deposits a fraction of its energy in the medium. As the parton moves nearly with the speed of light, much greater than the speed of sound of the medium, jet quenching can generate Mach shock waves. We have examined the possibility of Mach shock wave formation due to jet quenching. Assuming that the deposited energy quickly thermalizes, we simulate the hydrodynamic evolution of the QGP fluid with a quenching jet and subsequent particle production. Angular distribution of pions, averaged over all the jet trajectories, resembles ‘conical flow’ due to Mach shock wave formation. However, the speed of sound dependence of the simulated Mach angles is at variance with that due to shock wave formation in a static medium or in a medium with finite velocity.

Transition scattering in stochastically inhomogeneous media

When a physical object ("a source") without its own eigenfrequency moves through an acoustically homogeneous medium, the only possible form of acoustic radiation is the emission of Mach shock waves, which appear when the source velocity surpasses sonic speed. In nonhomogeneous media, in nonstationary media, or in the neighborhood of such media, the source motion is accompanied by the so-called "transition" radiation (diffraction or scattering), which has place even when the source moves with subsonic velocity. Key features pertaining to the formation of the acoustical transition scattering in media with fluctuating acoustical parameters are established. To analytically study the effect, the Green's function method formulated in terms of functional derivatives is used. The relationship between the wave number and frequency, k=k(omega), for acoustic waves is found. The results serve to determine the phasing conditions necessary for opening the transition scattering and Cherenkov radiation channel and to establish the physical explanation for the phenomenon-scattering (transformation) on inhomogeneities of the accompanied source field; i.e., formation of radiation appears when the attached field readjusts back to the equilibrium state after being deformed while passing through the fluctuations of the medium.

HYDRODYNAMICAL SIMULATIONS OF MACH CONE

In jet quenching, a hard QCD parton, before fragmenting into a jet of hadrons, deposits a fraction of its energy in the medium, leading to suppressed production of high-pT hadrons. The process can generate shock waves. We study the distortion of Mach shock waves due to jet quenching in central Au + Au collisions and its effect on particle production.

Electron Injection at High Mach Number Quasi‐perpendicular Shocks: Surfing and Drift Acceleration

Electron injection process at high Mach number collisionless quasi-perpendicular shock waves is investigated by means of one-dimensional electromagnetic particle-in-cell simulations. We find that energetic electrons are generated through the following two steps: (1) electrons are accelerated nearly perpendicular to the local magnetic field by shock surfing acceleration at the leading edge of the shock transition region. (2) the preaccelerated electrons are further accelerated by shock drift acceleration. As a result, energetic electrons are preferentially reflected back to the upstream. Shock surfing acceleration provides sufficient energy required for the reflection. Therefore, it is important not only for the energization process by itself, but also for triggering the secondary acceleration process. We also present a theoretical model of the two-step acceleration mechanism based on the simulation results, which can predict the injection efficiency for subsequent diffusive shock acceleration process. We show that the injection efficiency obtained by the present model agrees well with the value obtained by Chandra X-ray observations of SN 1006. At typical supernova remnant shocks, energetic electrons injected by the present mechanism can self-generate upstream Alfven waves, which scatter the energetic electrons themselves.