Showing papers on "Shock (mechanics) published in 1969"

Numerical simulation of flare‐generated disturbances in the solar wind

Abstract: The propagation of flare-generated shock waves through the solar wind is examined using numerical solutions of the time-dependent hydrodynamic equations. These solutions are valid for all shock strengths, including the intermediate values that have been observed in the solar wind, and take into account the variation of the properties of the ambient solar wind. The entire range of time scales for energy deposition in the disturbance, from impulsive (producing ‘blast waves’) to continuous deposition, is considered. For the former class of disturbances the solutions approach a limiting form dependent only on the total energy in the wave. Relationships among the energy, shock strength at 1 AU, and transit time to 1 AU are found in the blast wave limit. For disturbances with energies near 1031 ergs, the wave propagates from the sun to 1 AU in ∼60 hours, and is preceded by an intermediate strength shock at the latter distance. Both the transit time and shock strength are in good agreement with directly observed values.

A point explosion in a cold exponential atmosphere

Abstract: The problem considered is that of a strong shock propagating from a point energy source into a cold atmosphere whose density varies exponentially with altitude. An explicit analytic solution is obtained by taking the flow field as ‘locally radial’ and using an integral method with an energy constraint. A scaling law is given which eliminates the parametric dependence of the solution on the explosion energy, scale height, and atmospheric density at the point of the explosion. The scaling law also transforms the infinity of solutions for various polar angles into two distinct solutions which show that all motions of the ascending portion of the shock may be scaled from the vertically upward behaviour and all motions of the descending portion of the shock may be scaled from the vertically downward behaviour. The limit in the lateral direction of both of the fundamental solutions corresponds to the case of the uniform density atmosphere. The results for the uniform density atmosphere show remarkable agreement with the exact Taylor—Sedov results. Comparison with finite difference calculations of Troutman & Davis for the vertically upward and downward directions shows excellent agreement with respect to the prediction of shock propagation velocity, position, and the flow variables behind the shock. A scaling law for the time, shock velocity, and pressure for different values of the adiabatic exponent γ is proposed which correlates the results of the present analysis for different values of γ over the entire range of shock positions where the analysis applies. The solution shows that, contrary to the result obtained by Kompaneets, there is no theoretical limit as to how far downward a strong shock may propagate. The far field behaviour of the shock wave in the upward and downward directions is found to be of the same form as the self-similar asymptotic solutions obtained by Raizer for a plane shock. It is shown by relaxing the energy constraint in the vertically downward direction that the asymptotic result obtained agrees closely with that obtained by Raizer. The energy constraint, however, is the appropriate one for all but the far field behaviour. The far field limit of the present solution in the upward direction is found to compare favourably with the approximate asymptotic calculations of Hayes for an ascending curved shock. The empirical concept of ‘modified Sachs scaling’ for calculating the overpressure is considered and shown within this model to have a justification in the downward direction but a limited range of applicability in the upward direction.

Comparative Study of Optimization Techniques for Shock and Vibration Isolation

Abstract: : Several optimum and sub-optimum isolators are discussed with respect to three different criteria appropriate to shock and vibration isolation. In attempting to show the limitations of performance of a system optimized according to one criterion when considered from the point of view of another criterion, a number of advantages and disadvantages of the optimum systems are made evident. The results are presented in trade-off diagrams which allow a continuous range of choice in penalizing measures of relative displacement and force or acceleration of the isolated element. (Author)

Plastic film wrapping material

Abstract: TRANSPARENT FILM WRAPPING MATERIAL HAVING HEMISPHERICAL PROTUBERANCES SPACED THEREON IS DESCRIBED HEREIN. EACH OF THE PROTUBERANCES IS PROVIDED WITH A PLURALITY OF FACETS THEREON TO PROVIDE RIDGES THEREBETWEEN THAT WILL DISPERSE A CRUSHING FORCE IN SEVERAL DIFFERENT RESULTANT DIRECTIONS. THUS, THE WRAPPING MATERIAL ABSORBS THE SHOCK AND MAINTAINS THE ITEM WRAPPED THEREIN IN A SAFE CONDITION.

Influence of Reflected Shock and Boundary‐Layer Interaction on Shock‐Tube Flows

Abstract: During the last decade the study of the interaction between normal shocks and boundary layers in the shock tube has been carried out by many research workers. This interest has been fostered by the requirement to understand the effects that this phenomenon may have on the flow properties in the region between the reflected shock and the end of the tube. This so‐called reflected shock region is important in chemical kinetics studies and as a reservoir of gas for hypersonic shock tunnels. In this paper a review is given of the various analyses of the problem together with the results of experimental studies. Reflected and transmitted shock bifurcation, the rate of growth of the bifurcated foot, and the effects of transition to turbulence are discussed. The influence of bifurcation on the flow in the shock tube is assessed, especially as a mechanism for transporting cold driver gas to the end plate, causing early cooling of the gas on the reflected shock region.

Radio controlled animal training device

Abstract: For use in training an animal with equipment including a transmitter and a receiver attached to a collar or harness on the animal, the improvement which incorporates a receiver circuit communicated with a suitable amplifier for transmitted signals and a suitable voltage which provides a slight shock to the animal as an aid in training, the voltage being adjustable to reduce or increase the amount of shock applied to the animal.

Deformation of experimentally shocked biotite

Abstract: Shock experiments (10-40 kb) on lepidomelane show that kinking occurs at pressures as low as 9 kb; the intensity is related to peak pressure and shock pulse duration (0.7-0.3µ sec.), and is produced by shocks propagated along [hk0] and not along [001]. The shock-induced kinks have a wider range of their angle of external rotation (19-121°) than their static counterparts (40-60°). The ratio of the kink angles, e and δ, scatters widely, indicating shock induced kinking is highly asymmetrical. A marked decrease of 2V from 24 to 7° with increasing pressure is observed. Laue transmission patterns show that permanent angular rotations as great as 4.4° are induced by shock pressures of 37.5 kb. In individual samples the increase in permanent angular rotations and decrease in 2V can be closely correlated.

Determination of Release Adiabats and Recentered Hugoniot Curves by Shock Reverberation Techniques

Abstract: Release adiabats and Hugoniot curves centered at shock states can be readily determined by impacting a projectile disk onto a stationary reverberation disk made of a linear elastic material of known shock properties. The reverberation disk may have a free back surface or may be backed by a buffer disk made of the specimen or some other material. The reverberation disk is very thin compared to the thicknesses of the other disks so that many wave reverberations occur in it during the experiment. Depending on the impedance of the reverberation disk relative to the other disks, each reverberation successively unloads, or loads, the projectile disk, thus establishing points on a release adiabat or on recentered Hugoniot curves of the specimen material. The technique is particularly valuable for measurements on compressible nonlinear materials, and it generates a large amount of information in a single experiment. Experiments have been performed with X‐cut quartz, Lucalox, and 60° orientation sapphire reverbera...

Molecular Velocity Distribution Function Measurements in a Normal Shock Wave

Abstract: Molecular velocity distribution functions have been measured throughout a normal, M = 1.59 helium shock wave that was formed in a low‐density wind tunnel. The measurements were obtained by using the electron beam fluorescence technique. Throughout the shock transition, distributions of random velocities were observed from directions both parallel and perpendicular to the flow. Also, direct measurements were made of the density and the flow velocity. The shock wave satisfied the continuity, momentum, and energy equations within the accuracy of the measurements. Parallel and perpendicular temperatures compare favorably to predictions derived from the Navier‐Stokes equations. In the upstream portion of the shock the distributions of parallel peculiar molecular velocities predicted according to the Chapman‐Enskog first iterate differ significantly from the experimental results, although as mentioned the second moments or temperatures agree with the Navier‐Stokes values.

Effects of solar flare duration on a double shock pair at 1 au.

Abstract: Numerical solutions of the time-dependent equations of motion for spherically symmetric flow are obtained to study the propagation and modification of the forward-reverse shock pair in the region between the sun and 1 AU. For cases where the duration of the disturbance is long compared to T, the shock transit time to 1 AU, a double shock pair that resembles those predicted by similarity theory occurs at 1 AU. In cases where the duration of the solar disturbance is less than about 0.45T, the shock pair structure is appreciably altered by a rarefaction, initiated at the end of the solar disturbance, which has caught up with the shock pair. In cases where the duration is less than about 0.1T, the rarefaction completely destroys the reverse shock, leaving a single shock. This analysis indicates that a forward-reverse shock pair will not be observed at 1 AU unless the time duration of the solar disturbance is greater than about 5 hours. Since solar flares that last this long are quite rare, it is concluded that observation of a flare-associated forward-reverse shock pair at 1 AU is unlikely.

Laboratory experiments related to the solar wind and the magnetosphere.

Abstract: The increasing number of laboratory experiments related to the solar wind and the magnetosphere calls for a critical review of the conditions under which a laboratory experiment can provide information about space phenomena. Naturally, the starting point is a discussion of the problem of physical similarity. For a unified presentation of the several sets of scaling laws that have been used, it is convenient to use the similarity laws of the Vlasov theory as a reference system. Clearly, the biggest obstacle for a strict reproduction of the solar-wind-magnetosphere interaction in the laboratory is collisional interaction. In the solar wind at the earth's orbit, strict simulation is possible only for phenomena with a dimension of the order of a few hundred kilometers or smaller, such as the bow shock structure. A discussion of the existing terrella experiments shows that most of them obtain similarity by scaling the interplanetary field and the geomagnetic field differently. This determines the processes for which quantitative agreement can be expected, e.g., the shape of the frontal part of the cavity boundary and the approximate shape and position of the bow shock. Strict similarity can be achieved in simulating the structure of the bow shock wave. The over-all ranges of the shock parameters of seven collision-free shock experiments discussed cover substantial parts of the bow shock parameter ranges. A comparative discussion of the magnetic-field profiles of the estimated shock width and of the appearance of oscillatory structures shows strong resemblances between space and laboratory observations. Several other experiments related to the solar wind and the magnetosphere are also listed.

Radio evidence of directive shock-wave propagation in the solar corona.

Abstract: Radioheliograph observations at 80 MHz are reported of a flare-associated event in which two type II bursts occur in four different sources. The projected centres of the sources lie along an arc subtending an angle of about 150° at the optical flare centre. If the arc represents the projection on the Sun's disk of a shock front passing through the 80 MHz plasma level, the source configuration suggests that the shock wave has originated from the optical flare region and propagated into the corona within a limited cone. On the opposite side of the flare centre, outside the shock cone, there was a stable bipolar source. Strong magnetic fields in this source may have acted as a ‘magnetic wall’ to the shock wave and inhibited its propagation in this direction.

Shock‐Wave Strengthening of Copper and Nickel

Abstract: Final yield strengths of metals plastically deformed in one‐dimensional strain by shock compression are calculated from the theory of shock propagation and work hardening. An energy analysis of the shock‐relief cycle employs a Mie‐Gruneisen‐type equation of state and appropriate Hugoniot compressibility curve to determine the thermodynamic states of the material and the plastic work done. The residual elastic strain energy stored in the metal was estimated assuming that a portion of the plastic work remains in the form of lattice defects. Results for copper and nickel are found to be in reasonable agreement with experimental data.

The shock and vibration bulletin

Abstract: : Contents: Electrical generation of motion in elastomers; Controlled deceleration specimen protection systems for electrodynamic vibration systems; Control techniques for simultaneous three-degree-of-freedom hydraulic vibration system; Initial report on equivalent damage measurement by utilizing S/N fatigue gages; Hologram interferometry as a practical vibration measurement technique; Response of an elastic structure involving cross correlations between two randomly varying excitation forces; Automatic normalization of structural mode shapes; Resonant beam high 'G' vibration testing; The use of liquid squeeze- films to support vibrating loads; Point-to-point correlation of sound pressures in reverberation chambers; Environmental laboratory missile failure rate test with aerodynamic function simulation; Apollo CSM dynamic test program; Modal survey results from the Mariner Mars 1969 spacecraft; Uprated Saturn I full scale dynamic test correlation; An approach for duplicating spacecraft flight- induced body forces in a laboratory; Flexure guides for vibration testing; A compression-fastened general-purpose vibration and shock fixture; Vibration equivalence, fact or fiction; Providing realistic vibration test environments to tactical guided missiles; The reduction of the vibration level of a circular shaft moving transversely through water at the critical Reynolds number; Analysis and design of resonant fixtures to amplify vibrator output.

Measurement of Light scattered from Density Fluctuations within a Collisionless Shock

Abstract: WE have previously described a collisionless shock with low Alfven Mach number (MA), which propagates perpendicular to a magnetic field1–3. The shock is produced by the radial compression of an initial hydrogen plasma within a linear z-pinch. The initial plasma is 85 per cent ionized with electron density = 6.4 × 1020 m−3, and temperatures = = 1.2 eV, and is in an axial magnetic field = 0.12 Wb m−2. The shock propagates radially inwards through the initial plasma with a steady velocity Vs = 240 km s−1 (MA = 2.5), and with a steady structure of width Ls = 1.4 mm and compression ratio F = 2.5. The measured electron temperature behind the shock, = 44 eV, implies a resistivity within the shock about two orders of magnitude greater than the classical collisional value4. This demonstrates the collisionless nature of the shock. The effective mean resistivity (η), obtained from the power balance equation corresponds to a colision frequency The currently accepted theories of such shocks3,5,6 invoke ion wave turbulence7 to explain the structure and collisionless heating.

Analytical Study of Hugoniot in Unidirectional Fiber Reinforced Composites

Abstract: : A theory based on flow across a selected control volume is developed to predict the Hugoniot of a shock moving along the longitudinal direction of a unidirectional fiber reinforced composite. From this theory the Hugoniot of a composite may be calculated from the equations of state of its constituents. The shear force along the matrix-fiber interface can also be computed. A sample calculation using polyethylene as matrix and beryllium as fiber has been made. The calculated shock Hugoniot is not far from linear. (Author)

Automatically adjustable shock absorbers

Abstract: A FLUID PRESSURE SHOCK ABSORBER OF THE TYPE HAVING A CYLINDER WITH A PISTON SLIDABLY MOUNTED THEREIN SEPARATING THE CYLINDER INTO VARIABLE VOLUME CHAMBERS, THE PISTON MOVEMENT DECREASING THE SIZE OF ONE OF THE CHAMBERS IN RESPONSE TO THE SHOCK LOAD EXERTED THEREON CREATING A PRESURE IN SUCH CHAMBER WHICH IS FUNCTION OF THE SHOCK LOAD. A PLURALITY OF SPACED APART PORTS IN THE CYLINDER CONNECT THE CHAMBERS THROUGH WHICH FLUID IS FORCED FROM ONE CHAMBER TO THE OTHER WHEREIN THE RATE OF SAID FLUID FLOW CONTROLS DECELERATION OF THE PISTON AS A SHOCK LOAD IS DISSIPATED, AND INCLUDING MEANS FOR AUTOMATICALLY VARYING THE RATE OF FLUID FLOW THROUGH THE PORTS AS A FUNCTION OF A PRESSURE FORCE IN SAID ONE CHAMBER.

Investigations of the Aerodynamic Characteristics of the Shock Tubes : (Part 1, The Effects of Tube Diameter on the Tube Performance)

Abstract: The effects of tube diameter on the propagation behavior of a shock front were investigated by using two shock tubes with different sizes and by comparing with the other data. The process of the formation of a shock front when the diaphragm was ruptured was observed by schlieren method. From this experiment, it was found that the observed shock Mach numbers were larger than the values obtained by the simple theory. Such result depends on the opening time of the diaphragm and the diameter of the tube. Therefore, the various factors influencing the opening time of the diaphragm and the shock formation distance were discussed and the functional relations between these factors were clarified using the dimensional analysis. The expression for the shock formation distance derived by the dimensional analysis was in satisfactory agreement with the experimental results.

Source dynamics of the Dasht-e Bayāz earthquake of August 31, 1968

Abstract: Radiation patterns of the P -wave first motion and S -wave polarization angle of the Dasht-e Bayāz earthquake of August 31, 1968, as well as its principal aftershock which occurred about 20 hours after the main shock are studied. The main shock data are consistent with the observed left-lateral strike-slip fault which accompanied it. The radiation pattern of the aftershock differs somewhat from that of the main shock and agrees with the directions of the secondary faulting in the area. Several lines of evidence pointing to a multiple source for the main shock are presented. They include complexity of the body phases, low value of the rupture speed as studied from the analysis of the surface wave spectra, reported long duration of shaking and complicated pattern of striations produced by faulting. Energy, moment and stress drop associated with the main shock are estimated. The resulting mean value of stress drop over the faulted surface has a range of 40-100 bars. Based on the age of some well-built structures in the area, it is proposed that no earthquake as severe as the recent one has occurred near the location of the August 31, 1968 earthquake during the last 800 years.

Multiple joint tandem suspension

Abstract: A tandem vehicle suspension having a compensator member pivotally supported on a transverse trunnion depending from a vehicle chassis, independent forwardly and rearwardly extending torque beams pivotally connected to the compensator at one end and to the forward and rearward axles, respectively, at their other ends. Shock absorbing members between the compensator and the torque beams and additional shock absorbing means between the two torque beams. The torque beams are connected to the compensator by resilient bushings and to the axles by resilient trunnions or bushings with the result of automatic tracking by the wheels mounted on the axles. The resilient bushings connecting the torque beams to the compensator are on opposite sides of and below the transverse trunnion so that reacting moments and forces on stopping and starting the truck tend to drive the compensator downwardly, thereby reducing bouncing. IN ONE EMBODIMENT, THE SHOCK ABSORBING MEANS BETWEEN THE TWO TORQUE BEAMS IS A UNITARY ELASTOMER SPRING WITH MOVEMENT OF ONE BEAM TRANSMITTED THROUGH THE SPRING TO THE OTHER BEAM. In another embodiment, the spring is secured at its center plate to the compensator to prevent any such transmission through the spring. In other embodiments these compressible members are air springs.

Principles and techniques of shock data analysis

Abstract: : The book is intended for those concerned with analyses of mechanical shock data. The central intent is to extract information useful for considering system response to the measured transient acting as an excitation. Although the book is not aimed at telling the reader what data analysis approach should be applied in specific instances, it does provide helpful information in this regard. Presented are mathematical bases for the commonly employed Fourier and shock spectrum methods, as well as current techniques for their implementation by analog and digital means. A discussion of analysis errors is also included. Other approaches presented briefly are statistical averaging over an ensemble of events arising from a random transient process, decomposition of a transient in terms of orthogonal polynomials or exponentials, and certain extensions of the fundamental shock spectrum concept. The material presented can be found scattered throughout the literature; however, its collection and organization within this book should prove to be most helpful to novices and practioners alike.

Relative band strengths for the AlO blue-green system

Abstract: Synthetic band profiles are constructed and compared with the experimental spectra of shock heated AlO to estimate the importance of self-absorption on the emission of the blue-green system. The variation of the electronic transition moment is determined and relative band strengths are calculated. The dependence of the results on the potential model chosen for the Franck-Condon factors is investigated and discussed.

Shock deformation of Inconel 600 alloy - Effect of fine coherent precipitates on explosive-shock hardening

Abstract: Sheet samples of pure nickel and Inconel 600 alloy (76% Ni, 16% Cr, 7% Fe) containing a fine precipitate were simultaneously shock loaded in sandwich assemblies at pressures of 50, 100, 150, 200, and 370 kbar by a planar pulse of roughly 2‐μsec duration explosively initiated by a flying plate. The residual microhardness of the nickel was observed to saturate above 300 kbar while that for Inconel continued to increase steadily. Examination of the nickel substructures by transmission electron microscopy revealed a steadily decreasing cell size with increasing shock pressure; with almost no evidence of deformation twins at 370 kbar. The Inconel substructure was characterized by planar dislocation arrays which included an increasing concentration of dipoles and elongated loops to 200 kbar; while at 370 kbar deformation twins having an average thickness of 150 A and occupying 19% of the volume were observed. The coherent precipitates in the Inconel matrix were observed to become incoherent at pressures above 50 kbar, with the concomitant production of dislocation tangles and loops at the particle‐matrix interface. The precipitates were observed to enhance shock hardening by acting as sources for dislocation dipoles and elongated loops.