Showing papers on "Rarefaction published in 1975"

Hugoniot sound velocities and phase transformations in two silicates

Abstract: Rarefaction wave velocities have been used to estimate sound velocities on the Hugoniot for a quartz rock and for a perthitic feldspar. The Hugoniot states and rarefaction wave velocities were determined with multiple manganin stress gages placed between successive slabs of the sample material. Hugoniot stress states were produced by impact from explosively driven flyer plates. The sound velocity was determined from the transit time across gage planes of the initial characteristic of the rarefaction wave originating at the flyer plate free surface. Sound velocities (referred to Eulerian coordinates) measured in quartzite were 7.6, 8.1, and 10.5 mm/μS at Hugoniot stresses of 220, 250, and 355 kbar, respectively. Sound velocities measured in feldspar were 7.4, 8.7, and 9.2 mm/μs at Hugoniot stresses of 255, 345, and 460 kbar, respectively. These velocities are close to estimated bulk velocities and imply an almost complete loss of material strength behind the shock front. On the basis of our measured sound velocities and earlier observations by others we suggest that the Hugoniot yielding phenomenon is an adiabatic shear process resulting in partial melting behind the shock front. We further suggest that inhomogeneity in the adiabatic shear process may account for many details of the nonequilibrium mixed phase Hugoniot observed in silicates.

Alfvén wave refraction in high‐speed solar wind streams

Abstract: We use a simple physical theory to calculate the variation of Alfven wave amplitudes and the wave refraction in a schematic model for a high-speed solar wind stream. The results are as follows. (1) The wave amplitudes 〈δB²〉1/2 are larger in the compression region of the stream than in the rarefaction region. (2) The relative amplitudes 〈δB²〉1/2/B0 are larger in the rarefaction region than in the compression region, this result indicating that nonlinear effects may be more important in the rarefaction region. (3) The azimuthal velocity gradient in the stream leads to the result that k is no longer nearly radial at 1 AU, in contrast to predictions based on a spherically symmetric solar wind structure. In the rarefaction region, k turns into the direction of B0, whereas in the compression region, k turns away from the direction of B0. This predicted result in the rarefaction region agrees with direct in situ observations at 1 AU. (4) Waves that start near the sun with different k all tend to be refracted into the same direction by the time that they reach 0.5 AU. This result indicates that plane wave analyses will be appropriate beyond 0.5 AU.

A new technique for the study of test time and rarefaction wave effects in hypersonic shock tubes

Abstract: A knowledge of test time in shock tubes is important. Calculated values are unreliable because of the large role played by non-ideal effects such as turbulent flow through the opening diaphragm and by boundary layer phenomena. Moreover, in the case of combustion-driven and arc-driven shock tubes the driver gas state is usually only poorly known. For these reasons the test time must be evaluated experimentally. The author has developed a technique which employs a smear camera to measure the test time. The technique also provides a method for determining that regime of shock tube operation where the rarefaction wave reflected from the driver section plays a dominant role.

Mach waves and reflected rarefactions in aluminum

Abstract: A rarefaction wave in aluminum shocked to 27.7 GPa (277 kbar) is examined with radiographic techniques, and the bulk sound speed is determined. A Mach reflection in aluminum is also examined radiographically and the results are compared with the simple three‐shock theory of Mach waves. Then a modified three‐shock model is developed which is consistent with the experimental results. The modified model leaves some quantities undetermined but closely bounded.

Measurement of Thermal Conductivity in a Laser-Heated Plasma

Abstract: The plasma thermal conductivity has been measured in a CO$sub 2$-laser- heated Z pinch at a number density of 8times10$sup 16$ cm$sup -3$. Ruby-laser scattering was used to monitor the heating and rarefaction. Comparison with a numerical simulation indicates that the thermal conductivity is about a factor of 2 below that predicted by classical theory.

The problem of spurious oscillations in the numerical solution of the equations of gas dynamics

Abstract: One of the purposes of the present study was to show how the analysis of the equivalent system corresponding to the general class of schemes, ℒ β ∝ is useful for determining the relative merits of these schemes ; hence, it is possible to find a scheme well-suited to a specific problem. The schemea ℒIV is the best among all ℒ β ∝ for representing compression or shock waves even if it may give oscillations when the dispersion is too large. A similar conclusion (α # 2) was obtained in [8] from numerical experiments with ℒ 1 2/∝ . On the other hand, this advantage becomes a disadvantage in a rarefaction wave ; but the oscillations are damped with time because the gradients tend to decrease in such a wave (compare fig. 2 and fig. 3). Moreover, since the couple \(( \propto = 1 + \tfrac{{\sqrt 5 }}{2},\beta = \tfrac{1}{2})\) minimizes the \(\mathop {Max}\limits_{\eta \in [ - 1,1]}\) E2. with the constraint E2⩾O , the scheme ℒIV is, among the ℒ β ∝ which are dissipative in compression and shock waves, also the best one to represent rarefaction waves.

Shock wave in a gas-liquid medium

Abstract: The propagation of weak shock waves and the conditions for their existence in a gas-liquid medium are studied in [1]. The article [2] is devoted to an examination of powerful shock waves in liquids containing gas bubbles. The possibility of the existence in such a medium of a shock wave having an oscillatory pressure profile at the front is demonstrated in [3] based on the general results of nonlinear wave dynamics. It is shown in [4, 5] that a shock wave in a gas-liquid mixture actually has a profile having an oscillating pressure. The drawback of [3–5] is the necessity of postulating the existence of the shock waves. This is connected with the absence of a direct calculation of the dissipative effects in the fundamental equations. The present article is devoted to the theoretical and experimental study of the structure of a shock wave in a gas-liquid medium. It is shown, within the framework of a homogeneous biphasic model, that the structure of the shock wave can be studied on the basis of the Burgers-Korteweg-de Vries equation. The results of piezoelectric measurements of the pressure profile along the shock wave front agree qualitatively with the theoretical representations of the structure of the shock wave.

Analysis of the 31 Oct. 1972 Interplanetary Shock Wave and Associated Unusual Phenomena

Abstract: We analyze in detail the disturbed time period Oct 31-Nov 1, 1972 using magnetic field, plasma, and energetic particle data as well as magnetic field data In particular, we discuss an interplanetary forward shock wave accompanied by a traditional shock-spike event in the energetic particles, a large tangential discontinuity correlated with a geomagnetic storm main phase, and a reverse interplanetary shock This forward and reverse shock pair was caused by a 2N solar flare which occurred some 47 hours earlier We also discuss an unusual rarefaction in the solar wind following (and probably related to) the shock pair, wherein the Alfven Mach number abruptly decreased from about 45 to about 15, allowing the earth's bow shock to move outward at least 20 earth radii beyond its nominal position

Laboratory simulation of the solar wind-moon interaction

Abstract: The plasma parameters in this experiment are chosen on the basis of the principle of restricted simulation. The plasma stream contains a frozen-in magnetic field and a glass sphere is used as the lunella. It is shown that on the night side a conical cavity is formed with enhanced magnetic-field strength. The flow of plasma into the cavity takes place at the ion-sound velocity and is accompanied by the formation of a rarefaction wave with wave front lying on the surface of the Mach cone. An increase in the field in front of the rarefaction wave is observed only for a conducting lunella.