Showing papers on "Shock wave published in 1980"

Phenomenological model of shock initiation in heterogeneous explosives

Abstract: An ignition and growth concept is used, within the framework of a one‐dimensional Lagrangian hydrodynamic code, to model the shock initiation of heterogeneous solid explosives. The leading shock wave of an initiating pulse is assumed to ignite a small fraction of the explosive at localized heated regions. These ignited regions then grow as material is consumed at their boundaries. The growth rate for a particular material is assumed to have the characteristic pressure dependence of high‐pressure laminar burning experiments. Results of the model calculations are in good quantitative agreement with recent manganin pressure gage and particle velocity gage measurements of the buildup of the initiating shock front to detonation for both sustained and short duration pulses in four solid explosives: PBX−9404, TATB, cast TNT, and PETN. The predicted run distances to detonation as functions of shock pressure at various initial densities and the predicted reaction zone lengths of the fully developed detonation waves also correlate well with experimental data for these four solid explosives.

Interstellar shock waves with magnetic precursors

Abstract: The structure of steady, radiative, one-dimensional shock waves in partially ionized gas with a transverse magnetic field B/sub 0/ is investigated. Under a broad range of conditions applicable to the interstellar medium it is found that such shocks may be preceded by a magnetic precursor which heats and compresses the medium ahead of the front where the neutral gas undergoes a discontinuous change of state; indeed, if B/sub 0/ is sufficiently large, a shock can exist with no discontinuities in hydrodynamical variables. Within this magnetic precursor both ions and electrons stream through the neutral fluid with velocities which may be a significant fraction of the shock speed. The physical processes operative in such shocks are examined, including the effects of charged dust grains in dense molecular clouds. Numerical examples are shown for v/sub s/ = 10 km s/sup -1/ shocks propagating into diffuse H I or H/sub 2/. Shocks with magnetic precursors may have important consequences for the interstellar medium, some of which are briefly considered.

The optical emission from a fast shock wave with application to supernova remnants.

Abstract: We have observed the spectrum of Tycho's supernova remnant and have detected only the H..cap alpha.., H..beta.., and H..gamma.. lines. The H..cap alpha.. line profile can be divided into two components: one with a width consistent with the instrumental resolution and one with a full width at half-maximum (FWHM) of 1800 +- 200 km s/sup -1/. The two components have similar intensities. The observations are interpreted in terms of a shock wave model. The shock wave is presumably encountering neutral atoms that have some probability of giving line emission before being ionized by the post-shock gas. Charge exchange can occur in the post-shock region, giving rise to a broad emission component from a population of fast neutral atoms. The ratio of broad to narrow emission components is a sensitive function of shock velocity because the charge-exchange cross section depends strongly on the proton velocity. For Tycho's remnant, both the ratio of broad to narrow emission and the FWHM of the broad emission can be fitted if the shock velocity is 2300 +- 500 km s/sup -1/. Combined with the proper motion of the filament as found by Kamper and van den Bergh, the distance to Tycho's remnant is about 2.3more » +- 0.5 kpc. The absolute photographic magnitude of Tycho's supernova at maximum is then -18.8 +- 1.3, which is consistent with the absolute magnitudes of extragalactic Type I supernovae at maximum light.The shock model can be applied to some other emission nebulae. We predict that a broad emission component should be present in the H..cap alpha.. line profile of the remnant of SN 1006. If the model applies to the high-velocity emission regions in the Cygnus Loop observed by Kirshner and Taylor, we expect the high-velocity components to have a width approximately equal to half their velocity shift and to be unobservable in forbidden emission lines of heavy elements. The model may also apply to the high-velocity emission region observed by Elliott near eta Carinae.« less

Calibration of foil‐like manganin gauges in planar shock wave experiments

Abstract: Commercial manganin gauges were calibrated in a series of plane shock wave experiments. The calibration curve obtained is linear in the 0–1.5‐GPa range and curves for higher stresses (1.5–18.1 GPa). The linear portion is attributed to the elastic behavior of the gauge. This was confirmed by experiments which included rarefactions from free surfaces. The onset of hysteresis was found to be at 1.5 GPa. The experiments demonstrated that the gauge’s response does not depend on the target material in which the gauge is embedded. Also the thickness of the insulating layer which surrounds the gauge does not have any influence on its relative resistance changes.

The impingement of underexpanded, axisymmetric jets on perpendicular and inclined flat plates

Abstract: This paper reports on an extensive experimental study of the flows due to under-expanded axisymmetric jets impinging on flat plates. The range of plate locations extends to a point where the jet is just subsonic but the main emphasis is on the behaviour in the first shock cell. Plate inclinations from 90° to 30° were investigated by means of comprehensive surface pressure measurements and shadowgraph pictures. Wherever possible, the main features of the results have been reconstructed using inviscid analyses of the wave interactions.The flows are shown to be extremely complex due to the local structure of the free jet and, particularly, due to interactions between shock waves in the free jet and those created by the plate. In the near field, these interactions tend to be the controlling factors but at larger distances from the nozzle, mixing effects become increasingly important.The maximum pressure on the plate when it is inclined can be very much larger than when the plate is perpendicular, owing to the possibility of high pressure recoveries through multiple shock systems. Correlations are presented for some of the main features on perpendicular plates and it is shown that the integrated pressure loads for both normal and inclined plates can be predicted well by a simple momentum balance.

Shock acceleration of energetic particles in corotating interaction regions in the solar wind

Abstract: A simple shock model for the acceleration of energetic particles in corotating interaction regions (CIRs) in the solar wind is presented. Particles are accelerated at the forward and reverse shocks which bound the CIR by being compressed between the shock fronts and magnetic irregularities upstream from the shocks, or by being compressed between upstream irregularities and those downstream from the shocks. Particles also suffer adiabatic deceleration in the expanding solar wind, an effect not included in previous shock models for acceleration in CIRs. The model is able to account for the observed exponential spectra at earth, the observed behavior of the spectra with radial distance, the observed radial gradients in the intensity, and the observed differences in the intensity and spectra at the forward and reverse shocks.

Shock-wave structure via nonequilibrium molecular dynamics and Navier-Stokes continuum mechanics

Abstract: A strong steady dense-fluid shock wave is simulated with 4800-atom nonequilibrium molecular dynamics. The resulting density, stress, energy, and temperature profiles are compared with corresponding macroscopic profiles we derive from Navier-Stokes continuum mechanics. The differences found are relatively small.

Plasma waves associated with energetic particles streaming into the solar wind from the earth's bow shock. Progress report for period ending jul 80

Abstract: In the upstream solar wind, three dominant types of plasma waves are observed associated with energetic particle streams coming from the earth's bow shock: ion-acoustic waves, electron plasma oscillations, and whistler-mode waves. The ion-acoustic waves occur simultaneously with either ion beams or a dispersed ion population in the energy range from approximately 0.5 to greater than 45 keV. These short-wavelength electrostatic waves are very impulsive and the peak amplitudes increase with increasing ion flux and at spatial gradients in the energetic ion densities. The electon plasma oscillations are long-wavelength nearly monochromatic electrostatic wave which are closely correlated with the flux of low energy electrons, especially in the 0.2 - 1.5 keV range. In the presence of only enhanced electron fluxes, the average amplitudes of the electron plasma oscillations approach the peak amplitudes. (Author)

Energization of solar wind ions by reflection from the Earth's bow shock

Abstract: The existence of ion beams with energies a few times the solar wind energy and streaming outward from the earth's bow shock has been known for some time. To explain the observed ion energies, a simple reflection model has been proposed in which the particles gain energy by displacement parallel to the interplanetary electric field. In this model the energy gained in the reflection can be described as a function of the angles between the interplanetary magnetic field, the solar wind velocity, and the local shock normal. Ion beams under widely varying conditions have been observed in ISEE 1 and 2. For 18 cases, with beam energies ranging from approximately 1.4 to 30 times the solar wind energy, a comparison between the observed and the predicted beam energies has been made.

Shock compression of liquid argon, nitrogen, and oxygen to 90 GPa (900 kbar)

Abstract: Dynamic equation‐of‐state data for liquid Ar, N2, and O2 were measured in the shock pressure range 21–91 GPa (210–910 kbar) by means of a two‐stage light‐gas gun. The liquids were shocked from initial states near their saturation curves at 0.1 MPa (1 bar) and 80 K. The cryogenic target system is described. The initial liquid densities were obtained by measuring the temperature and pressure of the specimens and calculating the densities from published equations of state. Shock velocities were measured to 0.5–1.1% accuracy with an electronic detection system with subnanosecond time resolution. Impactor velocities in the range 4–7 km/s were measured to 0.1% accuracy with a flash radiographic technique. Mass velocities were obtained by the method of shock impedance matching. The data are discussed in terms of the statistical–mechanical theories of Ross and Ree.

Repulsive forces of simple molecules and mixtures at high density and temperature

Abstract: Shock wave data for liquid Ar, Xe, N2, O2, CO2, CH4, and CO have been used to test the possibility that the repulsive pair potential of these fluids scale in accordance with the ’’Law of Corresponding States.’’ This is found to be approximately valid to a compression of about 2.5 times liquid density. The law has been applied to compressed mixtures of N2 and O2 and a theoretical prediction of the detonation velocity and pressure of liquid NO is found to be in excellent agreement with experiment.

Supernova shock acceleration of cosmic rays in the Galaxy.

Abstract: The regeneration of galactic cosmic rays by first-order Fermi acceleration due to supernova shock waves traversing interstellar space is investigated. It is shown that if most of the volume of the interstellar medium comprises a low density ''coronal'' phase and supernova blast waves can propagate for more than 100 pc, then reacceleration of existing cosmic rays is important. Model Green's functions describing this redistribution in energy are calculated, and their properties are contrasted with stochastic and source function acceleration schemes. Shcok wave acceleration is incorporated in a model containing simple treatments of escape, ionization, radiation, and spallation loss. The injection of low energy particles treated in an ad hoc fashion. It is shown that it is possible to reproduce the observed cosmic ray spectra for protons, electrons, light, medium and heavy nucleons up to energies < or approx. =1000 GeV per nucleon with an effective galactic supernova rate that can be as low as 8 kpc/sup -2/ Myr/sup -1/. The relative importance of direct acceleration of suprathermal particles produced in a shock front and reacceleration of existing cosmic rays may be best gauged by observing the energy dependence of the abundance ratio of light to medium nucleons and the lowmore » energy proton and electron spectra. Observational tests for the importance of this acceleration mechanism are proposed.« less

Deceleration of the solar wind upstream from the earth's bow shock and the origin of diffuse upstream ions

Abstract: Observations with the Los Alamos Scientific Laboratory/Max-Planck-Institut crossed-fan solar wind ion experiment on ISEE I reveal that the solar wind is decelerated and deflected away from the direction of the earth's bow shock as it enters that portion of the upstream region populated by diffuse bow shock ions and long-period (10-60 s) waves. Typically, the average directed velocity vector changes by 7-10 km/s as it enters the wave region. At times, average speed changes as large as 25-40 km/s are observed. Superposed upon these changes in average flow speed are large amplitude (+ or - 15) fluctuations in flow speed associated with the waves themselves. The observations suggest that the solar wind deceleration is the result of momentum transfer from reflected bow shock ions to the wind via the long-period waves as the reflected ion beams go unstable. The broad angular distributions of the diffuse ions thus appear to be produced as a consequence of the disruption of reflected ion beams.

Singly‐ionized helium in the driver gas of an interplanetary shock wave

Abstract: The interplanetary shock wave observed on Jan. 29, 1977 by the HELIOS-1 plasma instruments shows an unusual feature: in the cold tenuous piston plasma following this shock, there appears a third peak in the energy per charge (E/q) spectra, in addition to the normal proton and alpha-particle peaks. The peak is located at E/q ? 4 and persists for about 14 hours, with slowly varying intensities. Independent simultaneous measurement of these particles' charge yields a value of approximately 1. These ions are thought to be He-4(+) ions travelling with the same speed as protons and alpha particles. The occurrence of He-4(+) indicates the possibility that during eruptive prominences or other solar transients, 'cold' chromospheric plasma might escape from the sun without undergoing the normal coronal heating process.

Formation of solar-type stars in spherical symmetry. I - The key role of the accretion shock

Abstract: Time-dependent hydrodynamical calculations of the self-gravitational collapse of a homogeneous Jeans unstable 1 M/sub sun/ protostellar cloud are examined to determine the extent to which the physical results reported in the literature depend on the particular numerical methods employed. It is found that the use of large artificial viscosity in the numerical treatment of shock fronts over-estimates the heating of the gas, underestimating the rate of production of radiation. Damping of core oscillations by increasing the inertial mass in contraction phases artificially slows the contraction, therefore overestimating the core radius. Large discretization errors lead to difficulties with numerical energy conservation, resulting in overlarge values for radius and total luminosity. A calculation employing a numerical method seeking to avoid these difficulties is presented. When numerical uncertainties are taken into account, the most likely physical solution produces a radius for the final core of about 2 R/sub sun/ and a total luminosity of order 1 L/sub sun/ when all the mass is assembled in the core. The maximum luminosity during the accretion phase is approximately 30 L/sub sun/. In the shock front surrounding the stellar core almost all the kinetic energy gained from the gravitational acceleration is directly transformed into outgoing radiation more » and is not deposited in the internal energy of the gas, in good agreement with the assumptions of the early work of Larson. The structure of the second shock front during the main accretion phase is examined in detail, and the evolution in the Hertzsprung-Russell diagram is discussed. « less

Forward diffraction of Stokes waves by a thin wedge

Abstract: The diffraction of a steady Stokes wave train by a thin wedge with vertical walls is studied when the incident wave is directed along the wedge axis (grazing incidence). Parabolic approximation applied recently by Mei & Tuck (1980) to linear diffraction is extended to this nonlinear case. Significant effects of nonlinearity are found numerically, in particular the sharp forward bending of wave crests near the wedge. The computed features are found to corroborate the existing experiments only qualitatively; the controlling factors in the latter being not completely understood. An analytical model of stationary shock is proposed to approximate the numerical results of Mach stems.

Melting of iron under core conditions

Abstract: Melting in iron has been detected in shock wave experiments. Release wave velocities are determined using the overtaking rarefaction technique. Upon melting the shear modulus becomes zero leading to a decrease in the acoustic wave velocity behind the shock front. Two velocity discontinuities have been detected: (1) 200 ± 2 GPa at a calculated temperature of about 4000K and (2) 250 ± 10 GPa at a calculated temperature of about 5500-6000K. The evidence indicates that the e-γ transition occurs at 200 GPa and that γ iron melts near 250 GPa along the iron Hugoniot.

Conditions for acceleration of energetic ions ≳30 keV associated with the Earth's bow shock

Abstract: A statistical analysis of particles (greater than 30 keV/charge) upstream of the earth's bow shock is conducted and shows that the rate of occurrence of upstream particle events is relative to the angle between the magnetic field and the shock normal at the shock intersection point as well as relative to the angle between the magnetic field and the radial direction (i.e., the sun-earth line). In addition, the occurrence rate of upstream particle events relative to the bow shock connection time of a field line convected with the solar wind is presented for a model bow shock. A linear dependence of the diffusion coefficient on energy per charge is apparent with the value of the mean free path of a 30-keV proton found to be about 4 earth radii, and the free escape boundary to be at about 30 earth radii in front of the bow shock.

Shock temperature measurements in Mg2SiO4 and SiO2 at high pressures

Abstract: Temperatures in the high pressure shock state have been determined by measurement of optical radiation from pure samples of forsterite (Mg2SiO4), α—quartz, and fused silica Shock waves of known amplitude were produced by tantalum flyer impact using a two-stage light gas gun Shock pressures in the ranges 150-175 GPa and 70-115 GPa for Mg2SiO4 and SiO2 respectively were achieved, and temperatures in the range 4500-6800 K were measured The observed temperatures in Mg2SiO4 are consistent with the occurrence of a shock-induced phase transition with a transition energy of ∼ 15 MJ/kg Measured Hugoniot temperatures versus pressure in both fused and crystalline SiO2 shocked to the stishovite regime suggest the occurrence of a previously unknown transition, beginning at pressures of approximately 107 GPa and 70 GPa for α—quartz and fused quartz, respectively The energies and temperatures appear to be consistent with the onset of melting of stishovite under shock loading

Observations of large fluxes of He/+/ in the solar wind following an interplanetary shock

Abstract: Los Alamos Scientific Laboratory instrumentation on Imp 7 has detected large fluxes of He(+) within that volume of solar wind plasma believed to be the solar ejecta driving the interplanetary shock wave disturbance of July 29, 1977. The very high He(+)/He(++) abundance ratio of 0.3 measured during this event suggests that this was solar prominence material only partially ionized by its passage through the corona.

Flow past a massive object and the gravitational drag

Abstract: The gravitational interaction between a massive object and ambient gas is considered. We give a description of subsonic and supersonic flows past a massive, mass ejecting object in nonviscous gas, including an estimate of the maximum density enhancements near the shock-front. The drag and the associated gas heating rates are calculated and compared with results for motion through collisionless gas.

Electric gun: a versatile tool for high‐pressure shock‐wave research

Abstract: We have developed a versatile tool for generating planar shock waves. This system, which we call the electric gun, is capable of projecting thin flyer plates with velocities in the range 1–20 km/s. It is presently being used in high‐explosives‐initiation experiments and is being developed for equation‐of‐state measurements in the 1–5 TPa range. We describe the electric gun facilities that are operational at Lawerence Livermore Laboratory and discuss applications of electric gun technology to problems of interest to shock‐wave researchers.

Interplanetary particles and fields, November 22 to December 6, 1977: Helios, Voyager, and Imp observations between 0.6 and 1.6 AU

Abstract: The principal interplanetary events observed are described and analyzed. Three flow systems were observed: (1) a corotating stream and a stream interface associated with a coronal hole; (2) a shock wave and an energetic particle event associated with a 2-B flare; and (3) an isolated shock wave of uncertain origin. Data from 28 experiments and 6 spacecraft provide measurements of solar wind plasma, magnetic fields, plasma waves, radio waves, energetic electrons, and low energy protons.

A macroscopic profile of the typical quasi-perpendicular bow shock - Isee 1 and 2

Abstract: A macroscopic examination of field and particle properties of the bow shock recorded on November 5, 1977, identified earlier as stable features by comparison of Isee 1 and 2 data, is presented. Attention is given to the extent to which the shock was in a typical state, and multidiagnostic observations are combined to define the shock profile. It is found that the shock profile offered several unanticipated structural features, which include a variable directional profile of the reflected proton group passing through the front, an electrostatic boundary effect associated with the reflected protons upstream, and an oscillatory buildup of proton thermalization behind the overshoot portion of the shock signature.

The repulsive forces in dense argon

Abstract: Shock wave compression curves for liquid argon were computed using a number of recently proposed pair potentials. The results are compared to experiment and used to evaluate the accuracy of the repulsive potential. Recent molecular beam results are found to be in excellent agreement with the shock data.

Deceleration of the solar wind in the Earth foreshock region: ISEE 2 and IMP 8 observations

Abstract: The deceleration of the solar wind, in the region of the interplanetary space filled by ions backstreaming from the earth's bow shock and associated waves, is studied using a two-spacecraft technique. This deceleration, which is correlated with the ‘diffuse’ but not with the ‘reflected’ ion population, depends on the solar wind bulk velocity: at low velocities (below 300 km/s) the velocity decrease is ∼5 km/s, while at higher velocities (above 400 km/s) the decrease may be as large as 30 km/s. Along with this deceleration the solar wind undergoes a deflection by ∼1° away from the direction of the earth's bow shock. The energy balance shows that the kinetic energy loss far exceeds the thermal energy which is possibly gained by the solar wind; therefore at least part of this energy must go into waves and/or into the backstreaming ions.