Showing papers on "Shock (mechanics) published in 1970"

Numerical solution of the hypersonic viscous shock-layer equations

Abstract: Viscous shock layer equations of laminar hypersonic flow past blunt body at moderate to high Reynolds numbers

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.

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.

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

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.

Hugoniot Equation of State and the Effect of Shock Stress Amplitude and Duration on the Hardness of Hadfield Steel

Abstract: The effect of shock stress amplitude and duration on the hardness and microstructure of Hadfield steel has been investigated over the pressure range of 5–480 kbar. Electron microscopy techniques were used to examine the microstructure and measure the dislocation density of shock loaded specimens. Stacking fault and twin fault probabilities were estimated from x‐ray diffeaction experiments. For a given peak shock stress the time duration of the stress pulse greatly affected the hardness and microstructure of the shocked material. The Hugoniot equation of state of Hadfield steel is reported for shock stresses of 5–500 kbar.

Periodic Permanent Roll Waves

Abstract: Two theories for periodic permanent roll waves are presented which are based on the shallow-water wave equations for the gradually varied portion of the wave profile, and the shock conditions for the rapidly varied portion. In the first theory the channel slope, S 0 , is assumed to be sufficiently small that the weight of the shock can be neglected in the shock condition. Comparison of results from this theory for small S 0 with experimental results reveals good agreement for S 0 = 0.019, but rather large discrepancies for S 0 = 0.050, 0.084, and 0.12. In the second theory the shock weight is included in the shock condition. Using the measured shock profiles to evaluate the weight of the shock yields theoretical predictions which are in substantial agreement with the experimental results.

The solar wind interaction with the geomagnetic field

Abstract: Solar wind-geomagnetic field interactions, considering day and night hemispheres, satellite observations, shock and magnetopause motion, shock structure, etc

On the structure of shock waves in liquid-bubble mixtures

Abstract: The structure of shock waves in liquids containing gas bubbles is investigated theoretically. The mechanisms taken into account are the steepening of compression waves in the mixture by convection and the effects due to the motion of the bubbles with respect to the surrounding fluid. This relative motion, radial and translational, gives rise to dissipation and to dispersion caused by the inertia of the radial flow associated with an expanding or compressed bubble. For not too thick shocks the dissipation by radial motion around the bubbles dominates over the dissipation by relative translational motion, in mixtures with low gas content. The overall thickness of the shock appears to be determined by the dispersion effect. Dissipation, however, is necessary to permit a steady shock wave. It is shown that, analogous to undular bores, a stationary wave train may exist behind the shock wave.

Prediction of electron density in the boundary layer on entry vehicles with ablation

Abstract: Computer code for numerical solution of laminar boundary layer and thin shock layer equations predicting electron density around reentry vehicle

Shock isolation mounts for fragile devices

Abstract: Shock isolation mounts for miniature microphones, sound reproducers, and other fragile devices, in which the device is suspended between thin film support members mounted on a rigid frame in a configuration such that shock stresses of substantial magnitude occurring in either direction along a given path are absorbed almost entirely by tensional stress of one or more of the film support members. Vibration isolation is also provided, separately from the shock isolation, by means of one or more vibration absorption elements, formed of rubber or other material of high resilience and high compliance in compression, interposed between the fragile device and support members or between the support members and the frame or between the frame and an external support structure. The support members are usually made of plastic, such as a polyester film, and may be pre-formed to fit the external configuration of the transducer or other device or may be flat strips with no pre-forming required.

Adhesively releasable and reusable shock load absorbing system

Abstract: A shock-absorbing strap system including a tensile load-bearing basic strap which has a looped portion secured by an adhesive connection designed to fail in above-load conditions to absorb the initial shock before transferring the load to the basic strap.

Dual satellite observations of earth's bow shock. I - The thick pulsation shock

Abstract: Dual satellite magnetic field and plasma measurements of earth bow thick pulsation shock by Vela 3A and Explorer 33

Energy absorbing shock isolation stabilizing arrangement

Abstract: An energy absorbing shock isolation stabilizing arrangement for providing shock and vibration isolation of an object within a supporting enclosure. The arrangement provided is passive and has energy absorption means for absorbing energy during relative motion of the object within the enclosure from a base position to displaced positions at a comparatively high energy absorption rate that preferably is constant and substantially independent of the magnitude of the relative velovity. Restoring means comprising return means also are included for returning the object from the displaced position to the base position and a comparatively low level of energy is absorbed during this return. Such shock isolation can be provided for each degree of freedom of the object within the enclosure.

Hugoniot and release‐adiabat measurements for selected geologic materials

Abstract: Release-adiabat curves have been determined for playa alluvium, tonalite, and novaculite shocked to stresses between 1 and 50 kb by plane impact from a light-gas gun. Particle-velocity/time profiles through the shock compression and the following release were measured at interfaces within the rock target and at the free surface using the principle of a moving conductor in a magnetic field. Steep release-adiabat curves in the stress-volume plane and high rarefaction velocities have been determined for alluvium and tonalite, indicating irreversible compaction. For alluvium, the initial rarefaction velocities are twice the shock velocities, which would cause rapid attenuation of the shock wave propagated in a field experiment. For novaculite, shocked below the Hugoniot elastic limit, the release-adiabat curve lies very close to the Hugoniot. The techniques should be applicable at higher stresses to study such problems as the kinetics of shock-induced phase changes.

Shock Wave from a Four-Meter Spark

Abstract: The shock wave emitted by a 4‐m spark of energy 2×104 J has been measured at distances from spark midgap of between 0.34 and 16.5 m. Close to the spark, a single dominant shock wave is observed; farther from the spark, a number of significant shock waves (generally 3 or 4) are observed. For distances less than 2 m, both the shock overpressure and the duration of the overpressure are between a factor of 1.5 to 5 less than predicted by cylindrical shock‐wave theory. The discrepancies between the experimental data and cylindrical shock‐wave theory are partially explained by consideration of the spark channel tortuosity.

Fluid amplified liquid spring shocks and/or shock absorbers

Abstract: A shock absorber which uses fluid amplification to provide programmed fluid flow and highly efficient shock curves without the necessity of expensive and inefficient metering holes, metering pins, and/or pressure responsive valves is provided by the interaction of: (1) a fluid passage clearance between a shock piston head or vane and the chamber, which houses and is swept by the head or vane, (2) an indentation formed around the periphery of the head or vane, and (3) a plurality of openings between the head or vane and the indentation formed around the periphery of the head or vane.

Shock Propagation in a Composite Material

Abstract: A procedure for calculating the pressure, densities, internal energies and particle velocities behind a plane shock in an infinite composite consisting of alternate layers of two materials or of parallel fibers imbedded in a matrix is presented. The direction of shock propagation is assumed to be parallel to the layers or fibers. Cal culated values of the shock parameters are given for a hypothetical aluminum polymethylmethacrylate composite. Shock speeds in the composite which are lower than the sonic velocity of one of the constituents are found to be possible.

Shock Tube Study of the Decomposition Kinetics of SO2F2

Abstract: Recent thermal decomposition studies of SF6 have led to interest in its principal oxidation product, sulfuryl difluoride. In the present study the thermal stability of SO2F2 at high temperatures has been investigated. Highly dilute SO2F2–Ar mixtures (∼ 0.1%) were shock heated in a conventional 1.5″ stainless‐steel shock tube. The SO2F2 concentration was monitored as a function of time behind the incident shock wave by its infrared emission at 11.7 μ utilizing a liquid helium cooled Cu:Ge detector. The initial pressure in the shock tube was varied from 30 to 600 torr and the temperature range covered was 1900–2300°K. The monitored radiation was shown to be transparent over the range of densities employed. Effective first‐order rate constants were evaluated from the logarithmic initial slopes of the radiation decay curves. For the 30‐torr data, a unimolecular rate constant fit to the data is keff = 2.1 × 1011exp(− 39 200 / T) sec−1. The data are analyzed in the light of several modern unimolecular rate theo...

Supersonic air inlet control system

Abstract: A fluid flow stabilizing and terminal or normal shock wave stability control system, utilizing fluidic vortex throttling valves can be integrated with the intake of a jet propulsion power plant, to attenuate gust disturbances and the intake''s terminal or normal shock wave movement, thereby preventing unstart or undesirable terminal shock wave expulsion from the intake during transonic or supersonic mode. Further, the vortex valve terminal shock stability system can be used for preventing unchoking of the intake during a noise abatement mode of operation, wherein the shock wave is positioned within the intake forward of the engine section to prevent the engine compressor noise from passing out through the cowl entrance. The vortex valve shock stability system can also stabilize buzz for mixed, internal, or external compression intakes.

Engine usage indicator

Abstract: Intervals between overhaul are determined by continuously measuring power turbine temperature and shaft speed and by converting the collected data into numbers of pulses proportional to creep, low cycle fatigue, and temperature shock fatigue. The number of pulses is then summed in digital counters. The total number of pulses due to creep, low cycle fatigue, and temperature shock fatigue are used as a measure of the exhausted life of the engine.

Vibration isolation mount and shock absorber

Abstract: An elastomer vibration or sound attenuating material isolates two elastic-plastic spring shock absorbers. Expected operational sound or vibrational loads are essentially absorbed by the elastomer and for these loads the device acts as a low-frequency isolation mount. For mechanical shock forces beyond limits of sound or vibration the elastic-plastic springs responsively deform thereby absorbing and attenuating the shock force transmitted through it.