Showing papers on "Rarefaction published in 1987"

Rarefaction waves in liquid and gas-liquid media

Abstract: The thermodynamics of a substance in the critical state has been exten­ sively studied, and a strong dependence of the thermodynamic parameters on the temperature and pressure near the critical point has been revealed. However, processes such as heat exchange and finite-amplitude waves (shock waves) have not been as thoroughly investigated in the region of the critical point. In fact, the question of the dynamics of finite-amplitude perturbations of pressure, density, and temperature in the critical region has not been considered at all. One should mention just one study devoted to shock waves near the critical point, namely that by Zel'dovich (1946), who analyzed the entropy condition for shock-wave stability and theo­ retically the possible existence of rarefaction shock waves. The effect of the sign of (iJ2p/iJV2)s on the structure of compression and rarefaction waves was discussed by Thompson & Lambrakis (1973).

Asymptotics toward rarefaction wave of solutions of the Broadwell model of a discrete velocity gas

Abstract: This paper studies the asymptotic behavior toward rarefaction wave for solutions of the initial value problem to the one-dimensional Broadwell model of the Boltzmann equation. When the Riemann problem for the Euler equation, derived from the Chapman-Enskog expansion, admits the solution of weak rarefaction wave, we also call the corresponding local Maxwellian of the original Broadwell model “rarefaction wave”. Then if the initial data are suitably close to the rarefaction wave at the initial time, the solution is proven to tend toward the rarefaction wave as time goes to infinity. The proof is given by an elementaryL2 energy method.

High Knudsen Number Molecular Rarefaction Effects in Gas-Lubricated Slider Bearings for Computer Flying Heads

Abstract: Effets de rarefaction moleculaire avec nombre de Knudsen eleve dans une glissiere a gaz (tete oscillante d'ordinateur)

Chapter viii – sound

Abstract: Publisher Summary This chapter discusses sound waves. A body oscillating in a fluid causes a periodic compression and rarefaction of the fluid near it, thereby producing sound waves. The energy carried away by these waves is supplied from the kinetic energy of the body. Monochromatic waves are important as any wave can be represented as a sum of superposed monochromatic plane waves with various wave vectors and frequencies. This decomposition of a wave into monochromatic waves is simply an expansion as a Fourier series or integral. The terms of this expansion are called the Fourier components of the wave. The energy flux density in a plane sound wave equals the energy density multiplied by the velocity of sound. The propagation of a sound-wave packet is accompanied by the transfer of fluid and is a second-order effect. Turbulent velocity fluctuations also are a cause of sound excitation in the surrounding fluid. If there is something in the path of propagation of a sound wave, then the sound is scattered. Beside the incident wave, there appear other scattered waves, which are propagated in all directions from the scattering body. The existence of viscosity and thermal conductivity results in the dissipation of energy in sound waves, and the sound is consequently absorbed, that is, its intensity progressively diminishes.

Rarefaction shock in the near wake

Abstract: Laboratory experiments and fluid theory find a stationary rarefaction shock in the near wake of an electrically grounded obstacle placed in a steady state, supersonic plasma flow The shock is only found when two electron temperatures, differing by at least an order of magnitude, are present These shocks are analogous to rarefaction shocks in plasma free expansions

Energy and momentum transport by sputtered and reflected streams in a glow discharge

Abstract: Extending established concepts from the field of atomic collisions in solids we evaluate, for planar geometry, the spatial profile of the energy deposited in the gas phase by the streams of particles emitted at the cathode. Both sputtered and reflected energetic streams are considered. It is estimated, also, the pressure profile due to the transport of momentum both by the emitted streams, and by the elastic collision cascades generated by them. The analysis of the transport of momentum and matter is useful for a quantitative understanding of the dynamic rarefaction which is measurable in the vicinity of the cathode in a glow discharge.

Rarefaction velocities in shocked lead

Abstract: By use of the optical analyzer technique, the bulk sound velocity in shocked lead has been measured at nine points along its Hugoniot in the pressure range 54.5 to 380 GPa. The lowest-pressure points exhibit no sign of solid behavior. The bulk sound velocity is essentially linear with respect to density, and the Gruneisen parameter, ..gamma.., fails to follow a constant p..gamma.. model. Results are consistent with zero-pressure values.

Vented safety vessel with acoustic trap for rarefaction waves

Abstract: An acoustical wave trap is combined with the rupture disc or relief valve used in vessels for storing potentially explosive materials. The acoustical wave trap operates to substantially reduce the magnitude of the rarefaction wave produced within the vessel when the rupture disc or relief valve opens, and thereby simplifies the pressure relief requirements.

Subjective Rarefaction in Illusory Figures: The Inadequacy of Apparent Lightness as an Explanation

Abstract: Apparent rarefaction in subjective figures seems to violate the principle of size scaling. It has been claimed that this anomaly is due to a difference in illusory lightness which counteracts the expected effect of illusory depth. Qualitative evidence is presented that neither illusory lightness nor illusory depth have a relevant part in the phenomenon. An alternative account, in which contrast and size are shown to play major roles, is presented and discussed.

Computer simulation studies on free surface reflection of underwater shock waves

Abstract: A computer simulation was used to study the irregular surface rarefaction phenomena produced by an underwater shock wave generated from a strong point explosion. We simulated the explosions with energies near 10/sup 15/ joules at three depths (3 m, 21 m, and 66.5 m) and computed the shock propagation until the peak pressure decayed to less than 0.1 GPa (1 Kbar). The simulations permitted the determination of the onset point of irregular rarefaction on the surface, and of the envelope separating the irregular and regular-rarefaction regions. The theoretical predictions of the onset points are consistent with the code results for all three cases. However, the predicted region boundaries, which are calculated from the arrival of the first rarefaction signal, are in agreement with the simulation results only in the weak shock case (DOB = 66.5 m). For the strong and intermediate shock cases (DOB = 3 m and 21 m, respectively), agreement was not obtained. The implication of the discrepancy in these cases is discussed. 9 refs., 8 figs.

Hugoniot and wave-profile measurements on shock-loaded stainless steel (21Cr-6Ni-9Mn)

Abstract: A series of planar impact experiments has probed the shock response of 21Cr-6Ni-9Mn stainless steel targets loaded to peak stresses of 10 to 20 GPa. The impactor configuration produces a dwell time in the target (nominal thickness = 4 mm) of approx.1 s at the peak stress, followed by unloading to lower stresses through a rarefaction originating at the impactor rear surface. For each experiment, the target plate is backed by a transparent window, and a velocity interferometer monitors the motion of the target/window interface. Resultant velocity histories exhibit a distinct two-wave (elastic-plastic) loading structure from which the Hugoniot Elastic Limit (HEL), Hugoniot, shock strain rate, and shock viscosity for this alloy are determined.

Nonlinear Dynamics of Instabilities in Line-Driven Stellar Winds

Abstract: We have been developing a numerical radiation- hydrodynamics program in order to study the nonlinear evolution of instabilities in line-driven winds from luminous, early- type stars. The present, preliminary version of this program assumes a l-D, spherically symmetric, isothermal stellar wind that is driven radially outward through absorption of a point source of continuum radiation by a fixed ensemble of isolated, pure-absorption lines. Initial tests of the code indicate that the velocity structure of nonlinear pulses in such a wind may be quite different than assumed in previous analyses. For example, the numerically computed structures show much steeper rarefaction and much more gradual compression than the sawtooth periodic shock structures previously assumed by Lucy. If these preliminary results are confirmed by further computations and analysis, they would have important implications for interpreting radio, ultraviolet, and x-ray observations that are thought to be associated with instabilities in hot star winds.

Rarefaction waves in free charges

Abstract: It was established experimentally that the form and velocity of a rarefaction wave in free charges depends on the particle size. Three regimes of wave propagation were observed — wave, with superposed filtration, and filtration through a stationary charge.

Propagating in a heterogeneous system

Abstract: To obtain a general pattern of wave motion along the tube, longtime oscilloscope displays =i0 msec were used. Results of pressure measurements in various sections of the tube A, B, C were used to construct wave diagrams in the plane x (mixture column height)-t (time) (the construction method is explained in [3]). At the beginning and end of each series of shock loadings, calibration experiments were performed with water. A typical test is shown in Fig. i. The intensity of the incident wave Pl = Pe = 2.4 MPa, the initial mixture pressure P0 = 0.i MPa. The wave diagram in the coordinates x, t clarifies the process of passage of the compression (solid curve) and rarefaction (dashed curve) waves. Analysis of the test experiments revealed that the results were in agreement with the acoustical approximation of shock wave theory. 2. Waves in the Kaolinite Suspension

Modeling gas dynamic particle interaction in rarefied gas flows

Abstract: In the case of slow, so-called creeping viscous flow a considerable amount of information on the interaction between individual particles or groups of particles has been obtained theoretically by means of the Stokes equations [1]. Regimes in which it is necessary to take inertia, compressibility and the rarefaction of the medium into account (see, for example, [2]) have received much less attention, especially from the experimental standpoint. As a rule, previous experiments have involved freely falling particles in a viscous fluid, but the experimental possibilities of determining the forces and moments exerted on a particle by a liquid or gas at small Reynolds numbers can be considerably expanded by investigating subsonic, flows of rarefied gas obtained with the aid of porous media. The results of such studies of the flow past a spherical particle and its interaction with another particle are presented in this paper.

Aspects of self-similar diffraction gas flows and their numerical simulation

Abstract: A large number of papers has been devoted to the investigation of the interaction of a plane shock wave with bodies of various geometric shapes, and they have been generalized and classified for a stationary body in [1, 2]. Separate results of experimental and theoretical investigations of the interaction of a shock wave with a wedge, cone, sphere, and cylinder moving with supersonic velocities are contained in [3–9]. Analysis of the available results shows that the features of the unsteady gas flows formed in this case largely depend on the nature of the boundary-value problem that arises for the system of differential gas dynamic equations. The question of the wave structure of the unsteady gas flow and the accuracy of the obtained solution is central to the numerical investigation of the present class of problems. The most characteristic types of unsteady self-similar gas flows that arise on the interaction of a plane shock wave with bodies of a wedge or convex corner type are calculated on the basis of an explicit numerical continuous calculation method of the second order of accuracy. The accuracy of the numerical solutions is discussed on the basis of a comparison with the experimental data. The case of the interaction of a shock wave with the rarefaction wave that arises in a supersonic flow past a convex corner is considered.