Showing papers on "Shock wave published in 1970"

Shock‐Wave Studies of PMMA, Fused Silica, and Sapphire

Abstract: The shock‐wave propagation characteristics of polymethyl methacrylate (PMMA), fused silica, and sapphire were measured for both compressive and rarefaction waves using plate‐impact experiments and interferometer instrumentation techniques The peak stress levels in the experiments were 22, 65, and 120 kbar, respectively The high‐resolution measurements of the stress wave profiles showed the PMMA to be a complex material whose wave propagation is influenced by nonlinearity, strain‐rate dependence, and elastic‐plastic effects in which plastic working increases the zero‐pressure volume of the material The fused silica is very well characterized as a nonlinear elastic material having the interesting property of propagating stable rarefaction shock waves The sapphire was nearly linear elastic to 120 kbar The use of these three transparent materials as ``windows'' in laser interferometer instrumented shock‐wave studies of other materials is discussed The effect of the shock‐induced variation of the index o

Vela 4 plasma observations near the Earth’s bow shock

Abstract: Concurrent measurements of electron and proton differential energy spectrums (each spectrum measurement requiring from 0.1 to 0.3 sec) have been obtained near the earth’s bow shock with the Vela 4B electrostatic analyzer. The following results have been derived from an analysis of 26 shock crossings during May and June 1967: (1) The jump in proton temperature is 2 to 4 times greater than the jump in electron temperature. (2) In the magnetosheath the proton temperature is nearly always greater than the electron temperature. (3) Te/Tp, upstream from the shock ranges between 0.6 and 4, and the shock remains well defined over this range. (4) Electron thermalization usually occurs in much less than 3 sec and has been observed to occur in ≈ 0.03 sec. (5) The magnetosheath electron velocity distribution is flat-topped or sometimes somewhat concave in shape within at least a few RE of the shock. (6) Evidence has been found that electrons are thermalized in a thin region upstream from the region in which most of the proton thermalization occurs. The observed increase in Te/Tp resulting from electron preheating may account for destabilization of electrostatic ion waves that may then produce strong ion heating by nonlinear Landau damping. Representative proton and electron velocity distributions from which the above results were derived are presented.

Shock Waves from Line Sources. Numerical Solutions and Experimental Measurements

Abstract: The cylindrical pressure wave resulting from instantaneous energy release along a line in a quiescent atmosphere has been studied by numerical integration of the equations of gas dynamics. Atmospheres obeying both the ideal gas law, and a realistic equation of state for air at high temperatures, were employed. The effects of varying the initial distribution of mass and energy in space were also investigated. The computations were carried well into the weak shock region, and agree well with asymptotic solutions for very strong and very weak shock waves. The effects of deviations from the initial assumptions of the strong shock asymptotic solutions are discussed. An approximate equation for the radial dependence of shock strength, applicable to most of the numerical solutions, is presented. Experimental measurements of shock strengths from detonation of long high explosive charges are shown to be in good agreement with the numerical solutions.

Theory of generation of bow-shock-associated hydromagnetic waves in the upstream interplanetary medium

Abstract: Bow shock associated hydromagnetic waves generation in upstream interplanetary medium, constructing model in terms of ion cyclotron resonance

Aspects of the Structure of Strong Shock Waves

Abstract: The direct simulation Monte Carlo method has been used to study the structure of strong shock waves in a gas of point center of repulsion molecules. The values obtained for the maximum density slope thicknesses agree with the predictions of the Mott‐Smith method. The results for the effect of molecular model on the rate of change of this thickness with shock Mach number are in agreement with the common prediction of the Mott‐Smith and Navier‐Stokes theories. The velocity distribution function within the wave is illustrated by computer display photographs with the molecules represented as dots in the plane of longitudinal and lateral velocity. This also gives qualitative support to the bimodal model. However, it is found that the density profile has a significant degree of asymmetry, contrary to the bimodal prediction. Results are also presented for the profiles of the higher moments of the distribution function.

Longitudinal waves in a perpendicular collisionless plasma shock: I. Cold ions

Abstract: This paper considers electrostatic waves in a Vlasov plasma of unmagnetized ions and magnetized, Maxwellian electrons. The linear dispersion relation is derived for waves in a perpendicular shock such that the most important sources of instability are the E × B and ∇B electron drifts. For the case of cold ions, propagation perpendicular to the applied magnetic field, and the E × B drift alone, a numerical analysis of frequency vs. wave-number is presented. The effects of the ∇B drift are also considered, and it is shown that the maximum growth rate can be larger than the maximum growth rate for the zero magnetic field ion acoustic instabifity under comparable conditions.

Hydrodynamic Behavior of Solid Deuterium under Laser Heating

Abstract: A theoretical interpretation is suggested in order to explain the inward propagation of luminous fronts when a powerful laser beam is focused on solid deuterium ice. This model is based on the propagation of a shock wave followed by a laser flux driven deflagration. Calculations have been made and compared with experimental results.

OGO 5 observations of electrostatic turbulence in bow shock magnetic structures

Abstract: Electrostatic turbulence in bow shock magnetic structures observed by OGO 5, explaining turbulence as ion acoustic or Buneman mode due to two stream instability

Self-Similar Strong Shocks with Radiation in a Decreasing Exponential Atmosphere

Abstract: The self‐similar one‐dimensional flow behind a plane shock propagating upward into an exponentially decreasing atmosphere is considered. The flow is taken to be isothermal in view of the large radiation mean free paths associated with high altitudes and the intense radiation heat transfer accompanying the high temperatures characteristic of an accelerating shock wave. The equations of motion are formulated in Lagrangian coordinates and are integrated exactly for all values of the shock density ratio. Solutions are presented for the cases where the boundary conditions at the shock correspond to a Hugoniot shock and to a Chapman‐Jouguet shock. A significant result of the analysis is that in both of these cases the shock propagates much faster than for the case of adiabatic flow.

Dissipation discontinuities in hydromagnetic shock waves

Abstract: Within the hydromagnetic approximation, the effects of resistive, viscous, and thermal conduction dissipation on the structure of shock waves is studied. A Perturbation analysis about the upstream and downstream stationary points is developed, which, when coupled with the shock evolutionary conditions, determines the conditions for the formation of discontinuities in the shock structure. The Viscous subshock for fast shock waves and the hydromagnetic analogue of the gas dynamic isothermal discontinuity for fast and slow shocks are analyzed. Very oblique fast shocks require both resistive and viscous dissipation for a steady shock structure. Strong slow shocks propagationg nearly along the magnetic field fail to steepen if only resistive dissipation is included. The rotational discontinuity does not possess a stable shock structure for any of the dissipation processes considered.

Shock-Wave Radiation from a Supersonic Ducted Rotor

Abstract: Over the subsonic speed range, the pressure field attached to a ducted rotor decays rapidly with distance away from the rotor. This exponential decay, coupled with the low radiation efficiency of a subsonically rotating pressure pattern, is generally sufficient to bring the radiated sound power well below that produced by interaction of the rotor with disturbances in the flow. This is particularly true for multibladed rotors as used in aircraft-engine fans and compressors, and accounts for the importance of rotor-stator interaction as a source of noise at subsonic tip speeds.

Aerodynamic Separation Effect on Gas and Isotope Mixtures Induced by Invasion of the Free Jet Shock Wave Structure

Abstract: The shock wave system of the underexpanded free jet, in a region where the pressure is in the range of 10−2 up to 1 torr, is partly invaded by background molecules, these latter being pumped and carried by the supersonic flow. When a gas mixture is introduced into the nozzle chamber and outside the shock barrel, this aspiration acts very selectively on the light molecules, and a mixture enriched in lighter species is attainable by skimming the free jet. This new aerodynamic separation effect, which is applicable to isotopic mixtures, is very strong in comparison to the efficiency of an elementary gaseous diffusion membrane.

An analytical solution for blast waves

Abstract: An approximate analytical method that is valid for the very low shock Mach number regime of a blast wave is described in the present paper. The method is based on the assumption of a power-law density profile behind the blast wave. The exponent of the power-law density profile is determined for each local shock Mach number from the mass integral. Solution of the differential equations of continuity and momentum then yield the particle velocity and the pressure distributions. The dependence of the shock decay coefficient on the shock velocity is determined from the energy integral. Comparison with the exact numerical solution of Goldstine and von Neumann and other existing analytical solutions indicates that the present solution is surprisingly accurate for the very low shock strength regime as compared to existing analytical solutions. HE theory of point blast waves is a very fundamental one in gasdynamics and has been applied to a variety of problems in hypersonic aerodynamics/'2 astrophysics,3-4 and hypervelocity impact.5'6 The validity of the classical selfsimilar solution of von Neumann,7 Taylor,8 and Sedov9 is confined to the early time regime when the shock wave is very strong (i.e., 1/MS2 —>• 0). For intermediate times when the shock strength is finite, small departures from the classical self-similar solution due to counterpressu re effects is accounted for in the perturbation solution of Sakurai10 and the "quasi-similar" solution of Oshima. 11 For the asymptotic motion at late times when l/Ms2 -*-1, solutions have been obtained by Whitham 12 and Sedov.9 Apart from exact numerical solutions,13 there appears to be a lack of an accurate analytical solution that provides an adequate description of the blast motion for the entire regime. In the present paper we describe an approximate analytical method that gave a surprisingly accurate solution for the entire propagation regime of a blast wave. The present method is due to Rae 6 who laid down most of the essential steps of the analyses but did not carry out the work to completion. Following Rae, the analysis was further developed by Lee. 14 The essence of the method is to assume a power-law density profile behind the blast wave, the exponent of which is determined from the mass integral. This then enables the particle velocity profile to be obtained from the differential equation of mass conservation. With the form for the density and particle velocity profiles known, the momentum equation can be integrated directly to determine the pressure profile. Substituting these profiles into the energy integral then yields a first-order differential equation for the dependence of the decay coefficient on the shock Mach number. The integration of this equation with the given boundary conditions then completes the solution of the problem. It should be noted that the assumption of a powerlaw density profile was first proposed by Porzel, 15 and it was Rae6 who pointed out the use of the energy integral for the solution of the problem. At the completion of the present work, it was found that a similar attempt has been made by Sakurai 16 to obtain an analytical solution valid for the entire propagation regime of the blast wave. In Sakurai's work, a linear velocity profile

Propagation of steady shock waves in polymethyl methacrylate

Abstract: The particle-velocity histories associated with the compression waves produced by the planar impact of polymethyl methacrylate plates were observed by means of laser interferometry The impact velocity and the thickness of material through which the wave passed were varied from 006 to 064 mm μsec and from 6 to 37 mm respectively Over this range of impact velocities, the observations disclosed a shock followed by a smooth transition to the maximum particle-velocity; the speed and magnitude of the shock varied non-linearly with the impact stress For impact velocities below 03 mm μsec , the wave was steady A steady-wave analysis based on finite linear viscoelasticity theory has been shown to be in good agreement with the experimental observations

Shock-wave ignition of liquid fuel drops

Abstract: Combustion processes and ignition criteria in shock wave ignition of liquid fuel drop in oxidizing atmosphere

Large‐scale characteristics of flare‐associated solar wind disturbances

Abstract: The large-scale properties of 19 flare-associated solar wind disturbances observed by Vela 3 and Vela 4 satellites between August 1965 and June 1967 have been examined. It is generally found that the solar wind flow speed rises above the value measured immediately after the shock at the leading edge of such disturbances and remains elevated for at least 1 day. The mass and energy fluxes may either rise or fall after the discontinuous change at the shock. Integration of the excess of these fluxes above the preshock or ambient level gives the total mass and energy in the interplanetary disturbance. The average mass is found to be 3×1016 g; the average energy (at 1 AU) is 5×1031 ergs. Both the mass and energy are smaller for disturbances in which the energy flux falls after the shock than for disturbances in which it rises. Both quantities are larger for disturbances observed in early 1967 than for those observed in late 1965, thus suggesting that the mass and energy deposited in the solar wind by individual flares increased with the rise in solar activity during the period under discussion. The energy released by the flare (obtained by correcting for the solar gravitational potential at 1 solar radius) is found to be proportional to the mass released, despite variation of more than an order of magnitude in both quantities.

Initial deceleration of solar wind positive ions in the Earth's bow shock

Abstract: High time resolution (Δt = 0.288 to 9.5 seconds) plasma measurements have been made on the upstream edge of the earth's bow shock by the combination of a Faraday cup with modulation grid and a curved-plate analyzer on the satellite OGO 5. These observations show that the solar wind positive ions often undergo a substantial deceleration just upstream of the shock's steep gradient of magnetic-field strength. This deceleration, which is not necessarily accompanied by a temperature increase, may be caused by a charge-separation electric field on the upstream side of the bow shock.

Effective Drag Coefficient for Gas-Particle Flow in Shock Tubes

Abstract: : Effective drag coefficients for flows of suspensions of spherical glass particles in air were derived from simultaneous measurements of pressure and particle concentration in the flow behind weak shock waves. Average particle diameters were 29 and 62 micrometers. The instantaneous concentration was determined by light scattering, and the results agree well with earlier shock-tube data based on streak records. They exhibit several unexpected features: the correlation between drag coefficient and Reynolds number is much steeper than the generally used 'standard' curve but approaches it at Reynolds numbers of several hundred; the correlation is independent of the particle concentration over the range of experiments, that is, for particle-to-gas flow rate ratios between 0.05 and 0.36; if the Reynolds number immediately behind the shock front is changed by varying the shock strength, the points move along the correlation, but if it is changed by changing the particle size, the entire correlation is shifted although to a smaller extent than would correspond to the direct effect of particle diameter on the Reynolds number. To account for the observations, a flow model is developed which allows for microscopic longitudinal and lateral perturbations of the particle motion that are the result of various causes, such as particle interactions with wakes of other particles, lateral forces caused by particle rotation, or electrostatic forces. (Author)

X-Ray Diffraction During Shock-Wave Compression

Abstract: X-ray diffraction has been observed for the first time from material under shock compression. This was accomplished by directing a single pulse of x rays at LiF which was under compression from a shock wave, and observing the (200) diffraction line from the shock-compressed state. The experimental window for observing the effect was \ensuremath{\sim}20 nsec; the pressure behind the shock front was \ensuremath{\sim}130 kbar.

Proton fluxes at 300 kev associated with propagating interplanetary shock waves

Abstract: Proton fluxes at 300 keV associated with propagating interplanetary shock waves, noting alpha particle enhancement

On frequency and strength of shock waves in the solar atmosphere

Abstract: Comparison of computed radiative energy losses of several new empirical chromospheric models with heating by shock wave dissipation gives information on the frequency and strength of shock waves in the solar chromosphere A mechanical flux of around 25 × 106 erg/cm2 sec is found for the base of the chromosphere The shocks are weak and the wave period is around 10 sec

Droplet Agglomeration Induced by Weak Shock Waves

Abstract: It has been proposed that cloud droplet growth may be induced by weak shock waves. This possibility is presently under experimental investigation, and preliminary results are reported here which support the proposed growth mechanism.

A Study of Drop Breakup Behind Strong Shocks with Applications to Flight

Abstract: : An experimental program has been carried out to determine the modes of raindrop breakup in air after passage of a strong shock wave. Relevant dimensionless parameters have been determined, and the experimental data have been correlated in terms of these parameters. The resulting correlations have been used to determine raindrop breakup in the shock layer of a reentering vehicle passing through a rainstorm.