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Showing papers on "Shock wave published in 1992"


Book
01 Jan 1992
TL;DR: In this article, the authors describe shock wave reflection phenomena from a phenomenological point of view and present criteria for their formation and termination, and their governing equations are solved analytically and graphically and compared with experimental results.
Abstract: This text describes shock wave reflection phenomena from a phenomenological point of view Organized in five parts, the book covers an introduction to oblique shock wave reflection and the governing equations of the two- and three-shock theories; shock wave reflection in pseudo-steady flows; and reflection phenomena in steady flows and unsteady flows With regard to pseudo-steady, steady and unsteady flows, the possible types of specific reflections are described, criteria for their formation and termination are presented and their governing equations are solved analytically and graphically and compared with experimental results Modification of the governing equations by accounting for viscous and real gas effects are suggested In addition, unresolved problems are pointed out and ideas for future research are suggested The fifth part of the book constitutes a detailed source list of most of the scientific papers and reports which have been published in the subject area

541 citations


Journal ArticleDOI
TL;DR: In this paper, a self-consistent solution of the time-dependent 1D equations of non-LTE radiation hydrodynamics in solar chromospheric conditions is presented.
Abstract: We present, for the first time, a self-consistent solution of the time-dependent 1D equations of non-LTE radiation hydrodynamics in solar chromospheric conditions. The vertical propagation of sinusoidal acoustic waves with periods of 30, 180, and 300 s is calculated. We find that departures from LTE and ionization recombination determine the temperature profiles of the shocks that develop. In LTE almost all the thermal energy goes into ionization, so the temperature rise is very small. In non-LTE, the finite transition rates delay the ionization to behind the shock front. The compression thus goes into thermal energy at the shock front leading to a high temperature amplitude. Further behind the shock front, the delayed ionization removes energy from the thermal pool, which reduces the temperature, producing a temperature spike. The 180 s waves reproduce the observed temporal changes in the calcium K line profiles quite well. The observed wing brightening pattern, the violet/red peak asymmetry and the observed line center behavior are all well reproduced. The short-period waves and the 5 minute period waves fail especially in reproducing the observed behavior of the wings.

327 citations


Journal ArticleDOI
TL;DR: In this article, the theoretical properties of relativistic, transverse, magnetosonic collisionless shock waves in electron-positron-heavy ion plasmas of relevance to astrophysical sources of synchrotron radiation are investigated.
Abstract: The theoretical properties of relativistic, transverse, magnetosonic collisionless shock waves in electron-positron-heavy ion plasmas of relevance to astrophysical sources of synchrotron radiation are investigated. Both 1D electromagnetic particle-in-cell simulations and quasi-linear theory are used to examine the spatial and kinetic structure of these nonlinear flows. A new process of shock acceleration of nonthermal positrons, in which the gyrating reflected heavy ions dissipate their energy in the form of collectively emitted, left-handed magnetosonic waves which are resonantly absorbed by the positrons immediately behind the ion reflection region, is described. Applications of the results to the termination shocks of pulsar winds and to the termination shocks of jets emanating from the AGN are outlined.

327 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe the overall evolution of wind-blown bubbles in a uniform medium from the initial, freeexpansion stage to the final stage in which the pressure of the ambient medium is significant.
Abstract: The paper describes the overall evolution of wind-blown bubbles in a uniform medium from the initial, free-expansion stage to the final stage in which the pressure of the ambient medium is significant. The concepts of slow and fast winds, which naturally arise from consideration of radiative losses at the free-expansion stage, are introduced. The evolution of bubbles in a plane-parallel disk, where the density decreases steeply along a vertical direction, is considered. The questions of when a bubble can break out of a thin galactic disk and how they evolve after the breakout are discussed. After breakout, bubbles can evolve into jets. Steady, collimated jets can form only over a limited range of wind luminosity and Mach number; astronomical jets are likely to be unsteady and/or hydromagnetic. The results are applied to the neutral stellar wind in the HH 7-11 region, to the north polar spur, and to the galactic winds in starburst galaxies. The evolution of wind-blown bubbles in a power-law density distribution is investigated. Characteristic evolutionary time scales, as well as the equation of motion for both the swept-up gas and the wind shock in each evolutionary stage are obtained.

247 citations


Journal ArticleDOI
TL;DR: In this article, a two-temperature radiation hydrodynamics code was used to model the UV burst from SN 1987A using a two temperature radiation hydrogrographic code.
Abstract: Detailed models for the UV burst from SN 1987A are calculated using a two-temperature radiation hydrodynamics code The sequence of events which occur during shock breakout is described, including the formation of a radiative precursor, the disappearance of the shock, and the growth of a thin, dense shell above the photosphere which gives rise to a new viscous, isothermal shock Continuum spectra are calculated under the assumption that the emergent radiation is a dilute blackbody with a color temperature equal to the radiation temperature at the thermalization depth This color temperature is 2-3 times higher than the effective temperature Light-travel-time corrections have been included in the light curves and the spectra Quantities most relevant to accurate modeling of the fluorescing ring around SN 1987A are highlighted

238 citations


Journal ArticleDOI
TL;DR: In this paper, a detailed analysis of short large-amplitude magnetic structures (SLAMS) observed at an encounter of the quasi-parallel blow shock by the AMPTE UKS and IRM satellites is presented.
Abstract: Results of a detailed analysis of short large-amplitude magnetic structures (SLAMS) observed at an encounter of the quasi-parallel blow shock by the AMPTE UKS and IRM satellites are presented. Isolated SLAMS, surrounded by solar wind conditions, and embedded SLAMS, which lie within or form the boundary with regions of significant heating and deceleration, are identified. The duration, polarization, and other characteristics of SLAMS are all consistent with their growth directly out of the ULF wave field, including the common occurrence of an attached whistler as found in ULF shocklets. The plasma rest frame propagation speeds and two-spacecraft time delays for all cases show that the SLAMS attempt to propagate upstream against the oncoming flow, but are convected back downstream. The speeds and delays vary systematically with SLAMS amplitude in the way anticipated from nonlinear wave theory, as do their polarization features. Inter-SLAMS regions and boundary regions with solar wind contain hot deflected ions of lesser density than within the SLAMS.

214 citations


Journal ArticleDOI
TL;DR: Observations suggest that the shedding of an imploding shock mediates between the bubble collapse and light emission.
Abstract: Light scattering is used to measure the dynamics of the repetitive collapse of a sonoluminescing bubble of gas trapped in water. It is found that the surface of the bubble is collapsing with a supersonic velocity at about the time of light emision which in turn precedes the minimum bubble radius by about 0.03% of the period of the acoustic drive. These observations suggest that the shedding of an imploding shock mediates between the bubble collapse and light emission

190 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the dependence of the development of the K-H instability on magnetosheath velocity shear layers, and showed that the velocity boundary layer is formed by the instability inside of the magnetopause, and it becomes wider for a smaller magnetoheath sonic Mach number.
Abstract: It has recently been demonstrated, by means of a two-dimensional MHD simulation, that a finite thick velocity shear layer with super-Alfvrnic velocity jump at the magnetospheric boundary is unstable to the Kelvin-Helmholtz (K-H) instability no matter how large the magnetosheath sonic Mach number (Ms)' a result suggesting that the tail flank boundary of the magnetosphere is unstable to the K-H instability. In order to investigate this consequence further, the dependence of the development of the K-H instability on Ms is studied in detail. For all magnetosheath sonic Mach numbers a velocity boundary layer is formed by the instability inside of the magnetopause, and it becomes wider for a smaller magnetosheath sonic Mach number. A flow vortex is excited at the inner edge of the velocity boundary layer for all sonic Mach numbers, and the magnetopause boundary is more highly nonlinearly corrugated by the instability for a smaller sonic Mach number. The net energy and momentum flux densities into the magnetosphere are calculated just prior to the saturation stage' for 1.0 < M s < 3.0 the energy flux density into the magnetosphere is approximated by O.054MsPoCs3/2 = O.045VoPo (where P0 is the unperturbed magnetosheath plasma density, P0 is the unperturbed magnetosheath pressure, V0 is the unperturbed magnetosheath flow velocity, and Cs is the magnetosheath sound speed), and the momentum flux density into the magnetosphere or the tangential (shearing) stress at the boundary is approximated by 0.083p0. The anomalous viscosity by the instability decreases in the absolute magnitude with increasing Ms' this result suggests that the dayside (except the subsolar region) and the dawn-dusk magnetopauses, where the magnetosheath flow remains subsonic, are the most viscous parts of the boundary, although the tail flanks are also found to be viscous enough for the viscous interaction. The structure of the weak shock in the magnetosheath developed from the K-H instability and the asymptotic eigenmode structure of the instability are elucidated. The relevance of the simulation results to the viscous interaction and a ULF wave generation is finally discussed.

186 citations


Book
01 Dec 1992
TL;DR: In this paper, the effect of high dynamic pressure on the acceleration and deformation of the velocity of a single wave in a single-dimensional model of a solid body is investigated.
Abstract: MECHANICS OF CONTINUOUS MEDIA Stresses and Strains in a Solid Body Equations of One-Dimensional Motion of Compressible Media, Shock Waves Interpretation of Detection Data on Compression and Rarefaction Waves EXPERIMENTAL TECHNIQUES OF THE PHYSICS OF HIGH DYNAMIC PRESSURE Explosive Generation of Dynamic Pressure Ballistic Experiments with a Shock Wave Promising Sources of High Dynamic Pressure Discrete Measurement of Wave and Mass Velocities Pressure Profiles Recorded with Manganin Sensors Measurement of the Velocity of Matter ELASTOPLASTIC PROPERTIES OF SHOCK-LOADED SOLIDS Basic Relationships and Models Moduli of Elasticity and the Velocity of Sound in Shock Compressed Metals Dynamic Yield Point Structure of Plastic Compression Waves Compression and Rarefaction Waves in Shock-Compressed Metals Compaction of Porous Media in Shock Waves Catastrophic Thermoplastic Shear under Dynamic Deformation. Impact Compression of Brittle Materials Methods of Studying High Dynamic Deformations Microscopic Models of Strain Dynamics EVOLUTION OF LOAD PULSES IN MEDIA WITH POLYMORPHIC PHASE TRANSITIONS The Structure of Compression and Release Waves in Iron The Graphite to Diamond Transition under Shock Compression Properties of the Phase Transition Induced by Shock FRACTURE UNDER PULSED LOADING. SPALLING STRENGTH Dynamics of Wave Interactions During Spalling Spalling Strength of Metals Work of Spalling Fracture Determination if Tensile Stress Behind the Spall Plane Resistance of Polymers, Brittle Materials, and Liquids to Spalling Fracture Mechanism and Kinetics of Dynamic Fracture of Metals SHOCK AND DETONATION WAVES IN SOLID EXPLOSIVES Basic Concepts and Models Kinetics of Dissociation of Explosives Deduced from Analyses of Evolution of Shock Waves Semiempirical Macrokinetic Equations of Solid Explosives MODEL EQUATIONS OF STATE FOR A WIDE RANGE OF PRESSURE AND TEMPERATURE General Analysis of Phase Diagram Quasi-Harmonic Model of a Solid Equation of State for Condensed Phase at High Temperatures Evaporation Effects and Generalized Equations of State Tabulated and Approximate Equations of States GENERALIZED EQUATIONS OF STATE FOR METALS Cold Compression Curve Electron Component Thermal Excitation of the Crystal Lattice Liquid Phase Procedure for Constructing Semiempirical Equations of State for Metals THERMODYNAMIC PROPERTIES OF METALS Aluminum Copper Lead Lithium FURTHER BRIEF NOTES ON CONTINUUM MECHANICS Equation of Motion Shock Waves Characteristic Form of Gas-Dynamic Equations. Simple Waves The Structure of a Shock Wave Decay of a Random Discontinuity in Hydrodynamics Equation of Motion for Porous Condensed Media DYNAMICS OF CONDENSED MEDIA WITH ALLOWANCE FOR THEIR STRENGTH Equations of Motion. Divergence Form Characteristics Form on Equations of Motion Simple Waves Shock Waves in a Hyperelastic Medium Decay of an Arbitrary Discontinuity Equations of Motion for a Hyperelastic Medium in an Arbitrary Curvilinear Set of Coordinates Equations of Motion of a Maxwell Viscoelastic Medium Nonlinear Waves in a Viscoelastic Medium BRIEF REVIEW OF COMPUTATIONAL TECHNIQUES FOR THE DYNAMICS OF CONDENSED MEDIA Method of Particles in Cells Method of Large Particles Godunov's Method Lagrangian Methods NUMERICAL MODELING OF CONDENSED MEDIA UNDER INTENSIVE PULSED LOADING Tabulated Form of the Equation of State High-Speed Collisions Irregular Collisions of Strong Shock Waves in Metals Numerical Modeling of the Effect of Relativistic High-Current and High-Energy Ion Beams on Metal Targets Effect of an Explosion on an Iron Plate Impactor Penetration of an Obstacle of Finite Thickness Impact of a Micrometerorite on a Spacecraft Shield References Index

183 citations


Journal ArticleDOI
TL;DR: In this article, one-dimensional particle-in-cell plasma simulations are used to examine the mechanical structure and thermalization properties of collisionless relativistic shock waves in electron-positron plasmas.
Abstract: One-dimensional particle-in-cell plasma simulations are used to examine the mechanical structure and thermalization properties of collisionless relativistic shock waves in electron-positron plasmas. Shocks propagating perpendicularly to the magnetic field direction are considered. It is shown that these shock waves exist, and that they are completely parameterized by the ratio of the upstream Poynting flux to the upstream kinetic energy flux. The way in which the Rankine-Hugoniot shock jump conditions are modified by the presence of wave fluctuations is shown, and they are used to provide a macroscopic description of these collisionless shock flows. The results of a 2D simulation that demonstrates the generality of these results beyond the assumption of the 1D case are discussed. It is suggested that the thermalization mechanism is the formation of a synchrotron maser by the coherently reflected particles in the shock front. Because the downstream medium is thermalized, it is argued that perpendicular shocks in pure electron-positron plasmas are not candidates as nonthermal particle accelerators.

181 citations


Journal ArticleDOI
TL;DR: In this article, the authors considered the gas flow, stellar wind collision, and generation of X-ray emission in massive binary systems and obtained the distributions of the hot gas temperature and density in the shock layers.
Abstract: The gas flow, stellar wind collision, and generation of X-ray emission in massive binaries are considered. X-ray emission of such binaries is caused by gas heating to temperatures of 10 7 -10 8 K behind the front of shock waves which are formed due to the collision of the stellar wind flowing out from the components of binary system either with the surface of the other component or with the stellar wind flowing out from the other component. The distributions of the hot gas temperature and density in the shock layers are obtained

Journal ArticleDOI
TL;DR: In this paper, the effects of increasing impact shock levels on the spectral characteristics of impact shock and impact shock wave attenuation in the body during treadmill running were investigated, and it was found that the greatest attenuation of the shock transmitted to the head occurred in the 15-50 Hz range.
Abstract: The purpose of this study was to determine the effects of increasing impact shock levels on the spectral characteristics of impact shock and impact shock wave attenuation in the body during treadmill running. Twelve male subjects ran at 2.0, 3.0, 4.0, and 5.0 m s−1 on a treadmill. Axial accelerations of the shank and head were measured using low-mass accelerometers. The typical shank acceleration power spectrum contained two major components which corresponded to the active (5–8 Hz) and impact (12–20 Hz) phases of the time-domain ground reaction force. Both the amplitude and frequency of leg shock transients increased with increasing running speed. Greatest attenuation of the shock transmitted to the head occurred in the 15–50 Hz range. Attenuation increased with increasing running speed. Thus transmission of the impact shock wave to the head was limited, despite large increases in impact shock at the lower extremity.

Journal ArticleDOI
TL;DR: In this article, a two-dimensional method was used to observe the interactions of plane shock waves with single cavities, which allowed study of processes occurring within the cavity during collapse.
Abstract: A two-dimensional method was used to observe the interactions of plane shock waves with single cavities. This allowed study of processes occurring within the cavity during collapse. Results were obtained from high-speed framing photography. A variety of collapse shock pressures were launched into thin liquid sheets either by firing a rectangular projectile or by using an explosive plane-wave generator. The range of these shock pressures was from 0.3 to 3.5 GPa. Cavities were found to collapse asymmetrically to produce a high-speed liquid jet which was of approximately constant velocity at low shock pressures. At high pressures, the jet was found to accelerate and crossed the cavity faster than the collapse-shock traversed the same distance in the liquid. In the final moments of collapse, high temperatures were concentrated in two lobes of trapped gas and light emission was observed from these regions. Other cavity shapes were studied and in the case of cavities with flat rear walls, multiple jets were observed to form during the collapse.

Journal ArticleDOI
TL;DR: In this article, two-dimensional electromagnetic particle simulations evidence a self-reformation of the shock front for a collisionless supercritical magnetosonic shock propagating at angle θ 0 around 90°.
Abstract: Two‐dimensional electromagnetic particle simulations evidence a self‐reformation of the shock front for a collisionless supercritical magnetosonic shock propagating at angle θ0 around 90°, where θ0 is the angle between the normal to the shock front and the upstream magnetostatic field. This self‐reformation is due to reflected ions which accumulate in front of the shock and is observed (i) in both electric and magnetic components, (ii) for both resistive and nonresistive two‐dimensional shocks, and (iii) over a cyclic time period equal to the mean ion gyroperiod measured downstream in the overshoot; resistive effects may be self‐consistently included or excluded for θ0≂90° according to a judicious choice of the upstream magnetostatic field orientation. The self‐reformation leads to a nonstationary behavior of the shock; however, present results show evidence that the shock becomes stationary for θ less than a critical value θr, below which the self‐reformation disappears. Present results are compared to p...

Journal ArticleDOI
TL;DR: In this article, the structure of fin-induced, swept shock/boundary-layer interactions was investigated using planar laser scattering (PLS) imaging technique and six detailed flowfield maps which take advantage of the inherent quasiconical behavior of the class of interactions considered.
Abstract: New data are presented on the structure of fin-induced, swept shock/boundary-layer interactions. These data are obtained using a nonintrusive planar laser scattering (PLS) imaging technique. A range of interaction strengths, from barely separated to very strongly separated, is covered for freestream Mach numbers of 3 and 4. These new data, when combined with previous results on the flowfield and interaction "footprint," are sufficient to allow the construction of a physical model for the swept interaction flowfield structure and behavior. This physical model is presented and discussed in terms of six detailed flowfield maps which take advantage of the inherent quasiconical behavior of the class of interactions considered.

Journal ArticleDOI
TL;DR: Analytical simplifications are described which make feasible the numerical calculation of the second-order news function, which gives partial information about the angular distribution of gravitational radiation emitted in the axisymmetric collision of two black holes at the speed of light.
Abstract: This paper describes analytical simplifications which make feasible the numerical calculation of the second-order news function, which gives partial information about the angular distribution of gravitational radiation emitted in the axisymmetric collision of two black holes at the speed of light. In the preceding paper, paper I, the curved radiative region of the space-time, produced after the collision of the two incoming plane-fronted shock waves, was treated using perturbation theory by making a large Lorentz boost to a frame in which a weak shock of energy λ scatters offa strong shock of energy v>>λ

Journal ArticleDOI
TL;DR: In this paper, it is shown that a new type of instability of a light field in a dissipative medium (spatiotemporal instability) can be observed by controlling the spatial scale and the topology of the transverse interactions of light fields in a medium with cubic nonlinearity.
Abstract: It is shown that a new type of instability of a light field in a dissipative medium (spatiotemporal instability, which causes the generation of new types of nonlinear light wave) can be observed by controlling the spatial scale and the topology of the transverse interactions of light fields in a medium with cubic nonlinearity. The excitation conditions for optical reverberators, rotating helical waves, and various dissipative structures are experimentally determined. Transformations and interactions of the structures lead to optical turbulence in both space and time. Physical interpretation of these phenomena is based on the parabolic equation for the nonlinear phase shift. It is found that this theoretical model allows one not only to obtain the excitation conditions but to investigate thoroughly such phenomena as hysteresis and nonlinear interactions of structures.

Journal ArticleDOI
TL;DR: In this paper, the analysis of wind bubbles and superbubbles was extended to the case of power-law energy injection, where the wind velocity was assumed to be constant and the energy injection rate was proportional to the mass injection rate.
Abstract: The analysis of wind bubbles and superbubbles in Paper I is extended to the case of power-law energy injection [L in (t)∞t ηin−1 ] in a medium with a power-law density distribution [ρ a (r)∞r −kρ ]. As before, the wind velocity is assumed to be constant, so that the energy injection rate is proportional to the mass injection rate, L in (t)∞M˙ in (t). The shock in the ambient medium is assumed not to accelerate which requires k ρ ≤3−η in . The evolution is followed from the free-expansion stage, in which the mass of the wind dominates the sweptup mass, through the self-similar stage, to the stage in which the bubble is confined by the pressure of the ambient medium

Journal ArticleDOI
TL;DR: In this paper, the authors describe the hydrodynamic interaction between supernova nebulae and a pulsar while the pulsar is in a constant power output phase if the surrounding density profile is a power law in radius.
Abstract: Pulsars are expected to be born inside Type II supernovae, and the nebulae generated by their spin-down power thus initially interact with the expanding supernova gas. The hydrodynamic interaction can be described analytically while the pulsar is in a constant power output phase if the surrounding density profile is a power law in radius. The power generated by the shock front driven into the supernova gas is about 1.5% of the pulsar power, and, for typical parameters, the shock wave remains in a radiative phase for at least hundreds of years

Journal ArticleDOI
TL;DR: In this article, the authors investigated eight molecular species in the hot dense clump IC 443G, believed to be impacted by the shock wave from the SNR IC 443, and found that fractional abundances fit ND shock models if L is about 6.6 x 10 exp 15 cm.
Abstract: Eight molecular species, in the hot dense clump IC 443G, believed to be impacted by the shock wave from the SNR IC 443, are investigated. The clump consists of two distinct regions, one relatively cool, and one hotter and denser. Region 1 contains CO, HCO(+), HCN, and CN, whose abundances may be explained either by ion-molecule chemistry, or by a D shock of 60-90 km/s, passing through a clump of about 100,000/cu cm. Region 2 gives rise to SiO, CS, SO, and H2CO, and requires an ND shock of 5-15 km/s passing through a region of about 1,000,000/cu cm. Observed fractional abundances fit ND shock models if L is about 6.6 x 10 exp 15 cm. In general, observed line widths vary inversely with derived excitation density, while centroid velocities of all species are essentially identical.

Journal ArticleDOI
TL;DR: In this paper, a planar laser-induced fluorescence (PLIF) was used to visualize the mixing induced by the interaction of a weak shock wave with a cylindrical volume of a gas (helium) that is lighter than its surroundings (air).
Abstract: Experiments have been carried out to quantify the mixing induced by the interaction of a weak shock wave with a cylindrical volume of a gas (helium) that is lighter than its surroundings (air). In these experiments a round laminar jet was used to produce the light-gas cylinder, and planar laser-induced fluorescence (PLIF), utilizing a fluorescent tracer (biacetyl) mixed with the helium, was used to visualize the flow. These techniques provide a higher quality of flow visualization than that obtained in previous investigations. In addition, the PLIF technique could be used for the measurement of species concentration. The distortion of the helium cylinder produced by the passing shock wave was found to be similar to that displayed by images from previous experimental and computational investigations. The downstream displacement of several points on the boundary of the light-gas cylinder are measured and agree reasonably well with the results of earlier experimental and theoretical studies as well. Because the mixing process causes the helium originally contained within the cylinder to be dispersed into the surrounding air, the PLIF image area inside the contour at one half the maximum concentration of the fluorescent tracer decreases as the two gases mixed. The change in this area is used as a measure of the mixing rate, and it is found that the time rate of change of this area divided by the area of the initial jet is approximately - 0.7 X 10^3 S^(-1).

Journal ArticleDOI
TL;DR: In this paper, the Petschek mechanism, generalized by Priest and Forbes (1986), was studied using a 2D incompressible MHD simulation, and the width and the length of the current sheet for different parameters obtained in the simulations were found to be consistent with theoretical values.
Abstract: The Petschek (1964) mechanism, generalized by Priest and Forbes (1986), was studied using a 2D incompressible MHD simulation. Various regimes predicted by Priest and Forbes are obtained for different boundary conditions on the outflow boundary. They include a weak fast-mode expansion, slow-mode compression, slow-mode expansion, and a hybrid regime of fast-mode and slow-mode expansion. The width and the length of the current sheet for different parameters obtained in the simulations were found to be consistent with theoretical values.

Journal ArticleDOI
TL;DR: In this article, a time asymptotic method was used to obtain 3D steady-state solutions for the MHD flow past an obstacle and the results indicated the formation of a depletion layer near the obstacle due to the increase of the magnetic field.
Abstract: As a step to the study of the large-scale flow in the magnetosheath, the MHD flow past an obstacle is investigated. A time asymptotic method is used to obtain 3D steady-state solutions. The results indicate the formation of a depletion layer near the obstacle due to the increase of the magnetic field. Along the earth-sun line the plasma density increases first and then decreases from the post bow shock to the magnetopause. The local density maximum in front of the magnetopause may correspond to what was recently observed. When the interplanetary magnetic field direction is tilted from the solar wind flow, the IMF influences the shape of the bow shock as well as the location of the stagnation point at the magnetopause in a way consistent with observation. In addition, the results show the existence of a magnetosheath current in the post parallel-shock region.

Journal ArticleDOI
01 Dec 1992
TL;DR: In this article, it was shown that the phase transformation is localized along three types of transformation lamellae (narrow, s-shaped, and wide) which contain fractured and/or high-pressure phases.
Abstract: Shock experiments on quartz single crystals with initial temperatures −170 to +1000°C showed that ambient temperature does not affect the type of defects formed but can lower the pressure of complete amorphization. The amount of glass recovered increases with both pressure and temperature, and the shock-induced phase transformation of quartz is temperature-activated with an apparent activation energy of <60 kJ/ mol. The phase transformation is localized along three types of transformation lamellae (narrow, s-shaped, and wide) which contain fractured and/or high-pressure phases. Transformation lamellae are inferred to form by motion of linear collapse zones propagating near the shock front. Equilibrium phases, such as stishovite, were not recovered and are probably not formed at high shock pressures: the dominant transformation mechanism is inferred to be solid-state collapse to a dense, disordered phase. Melting occurs separately by friction along microfaults, but no high-pressure crystal phases are quenched in these zones. Shock of quartz thus produces two types of disordered material, quenched melt (along microfaults) and diaplectic glass (in transformation lamellae); the quenched melt expands during P-T release, leaving it with a density lower than quartz, while recovered diaplectic glass has a density closer to that of quartz. At low pressures (< 15 GPa), quartz transforms mostly by shear melting, while at higher pressures it converts mostly along transformation lamellae. We find that shock paleopiezometers using microstructures are nominally temperature-invariant, so that features observed at impact craters and the K/T boundary require in excess of 10 GPa to form, regardless of the target temperature. Shock comminution will be much more extensive for impacts on cold surfaces due to lack of cementation of fragments by melt glass; shock on hot surfaces could produce much more glass than estimated from room-temperature experiments. Because of the shock-impedance mismatch between quartz specimen and steel capsule, the incident shock wave reverberates up to a final pressure. The dynamic compression process is quasi-isentropic with high strain rates. Preheating and precooling achieves final shock pressures and temperatures representative of single-shock states of room temperature quartz and of quartz on known planetary surfaces. Stress histories were calculated by detailed 1- and 2-dimensional computer simulations. The stress history throughout the sample is relatively uniform, with minor variations during unloading. Significant differences between impact pressures calculated by the shock-impedance-match method and specimen pressures calculated by computer simulations indicate the importance of modeling shock recovery experiments computationally.

Journal ArticleDOI
TL;DR: In this paper, a source of upstream turbulence is introduced, which produces an enhanced high energy tail in the upstream particle distribution extending to over a hundred times the plasma flow energy, and a prominent shoulder downstream.
Abstract: We present initial results from one-dimensional hybrid simulations which directly address the problems of using such methods to simulate the acceleration of ions to high energy by parallel shocks. As particles are accelerated from the thermal population, they are repeatedly “split,” thereby ensuring statistically valid energy spectra covering a wide dynamic range. In order to model the complex foreshock, as expected if the simulation domain were large enough, and as seen in observations, we introduce a source of upstream turbulence. This turbulence produces an enhanced high energy tail in the upstream particle distribution extending to over a hundred times the plasma flow energy, and a prominent shoulder downstream.

Journal ArticleDOI
TL;DR: In this paper, the effect of photolysis-shock tube (FP- or LP-ST) technique on the thermodynamic state of the hot gas in the reflected regime is discussed.

Journal ArticleDOI
TL;DR: It is shown that it is possible to obtain precise measurements of the time delay between the separate peaks within the signal burst detected following the secondary shock and this may, as predicted, provide a method of determining the size of bubbles remaining after the primary shock.
Abstract: The acoustic emission from cavitation in the field of an extracorporeal shock wave lithotripter has been studied using a lead zirconate titanate piezoceramic (PC4) hydrophone in the form of a 100-mm diameter focused bowl of 120-mm focal length. With this hydrophone directed at the beam focus of an electrohydraulic lithotripter radiating into water, it is possible to identify signals well above the noise level, at the 1-MHz resonance of the hydrophone, which originate at the beam focus. Light emission, attributed to sonoluminescence, is also shown to originate at the focal region of the lithotripter, and the signal obtained from a fast photomultiplier tube directed at the focus has similarities in structure and timing to the detected acoustic signals. The multiple shock emission resulting from a single discharge of an electrohydraulic source is shown to result in two separate bursts of cavitational activity separated by a period of 3–4 ms. The signal burst corresponding to the primary shock has a duration of about 600 μs with little noticeable structure. The signal burst associated with the secondary shock has a reproducible structure with two distinct peaks separated by about 200 μs depending on the shock amplitude. The timing and structure of each burst is shown to be in reasonable agreement with the theoretical predictions made by Church (1989) based on the Gilmore model of bubble dynamics. In particular, it is shown that it is possible to obtain precise measurements of the time delay between the separate peaks within the signal burst detected following the secondary shock and this may, as predicted, provide a method of determining the size of bubbles remaining after the primary shock.

Journal ArticleDOI
TL;DR: Evidence is provided that the Burnett corrections to the heat flux significantly improve the agreement with the computed values over the Navier-Stokes predictions in the shock-front region.
Abstract: Atomistic simulations of a strong shock wave in a hard-sphere gas are analyzed in terms of thermodynamic forces and fluxes. Evidence is provided that the Burnett corrections to the heat flux significantly improve the agreement with the computed values over the Navier-Stokes predictions in the shock-front region.


Book ChapterDOI
01 Jan 1992
TL;DR: In this article, the formation and propagation of failure waves in shock compressed materials was observed in a series of plane shock wave experiments with glass and fused quartz, and the failure wave nucleates at the surface of the compressed sample and then propagates into the sample with a decreasing subsonic velocity.
Abstract: The formation and propagation of failure waves in shock compressed materials was observed in a series of plane shock wave experiments with glass and fused quartz. Results of stress, free surface velocity wave profile measurements, and computer simulations show that the failure wave nucleates at the surface of the compressed sample and then propagates into the sample with a decreasing subsonic velocity. The dynamic tensile strength is significantly higher than those of ceramics and minerals.