Showing papers on "Shock (mechanics) published in 1974"

Behavior of the flare-produced coronal MHD wavefront and the occurrence of type II radio bursts

Abstract: The propagation of the weak MHD fast-mode shock emitted into the corona by flares at their explosive phase is computer-simulated. It is shown as the result that the shock wave is refracted towards the low Alfven velocity regions pre-existing in the corona, and the strength of the shock, which is otherwise weak, is drastically enhanced on encountering low- V A regions due to the focussing effect by refraction and also due to the lowered propagation velocity of the shock in such regions. It is expected that electron acceleration takes place in such a drastic strengthening of the shock, leading to the local excitation of plasma waves and eventually to the occurrence of radio bursts at such locations. Such locations of shock strength enhancement, when computed by using HAO realistic models of coronal density and magnetic field of the day of certain type II burst events, actually coincide roughly with the observed positions of type II bursts. Peculiar configurations of type II burst sources as well as their occurrence even beyond the horizon of the responsible flare are explained consistently by the large scale refraction and the local enhancement of the shock due to the global and local distribution of Alfven velocity in the corona. A unified interpretation is given for the occurrence of type II bursts and Moreton's wave phenomena, and also the relation of our MHD fast-mode disturbance with other flare-associated dynamical phenomena is discussed.

Effects of interplanetary shock waves on energetic charged particles

Abstract: Experimental data on the influence of interplanetary perpendicular and oblique shock waves on the ambient energetic protons are presented along with a theoretical analysis of the acceleration of particles in almost perpendicular shock waves. It was found that low-energy protons can be accelerated in perpendicular shock waves by repeated crossings of the shock front up to a maximum energy given by the product of their initial energy times the ratio of the magnetic fields. High-energy protons need to stay at the shock front for longer times than low-energy protons in order to reach the same relative energy gain. In the theoretical study of proton acceleration at almost perpendicular shock waves, it was found that protons reflected at shock waves with the angle between the upstream magnetic field and the shock normal greater than about 80 deg achieve large energy gains at the shock front. The larger this angle, the higher the energy gain. However, the reflection and energization of protons at these shock waves is not 'instantaneous', neither is it a one-step process: it is performed through repeated crossings of the shock front.

Shock‐wave compaction of porous aluminum

Abstract: Experimental data on the shock‐wave compaction of 78% dense porous aluminum are presented and compared with theoretical predictions from a mathematical theory of time‐dependent pore closure for ductile materials with isolated spherical voids. A recently modified form of the theory was used which includes deviatoric stresses and material viscosity. Incorporation of the work‐hardening properties of the solid resolved previous discrepancies between measured hydrostats and predictions assuming elastic‐perfectly plastic deformation of the matrix. Generally good agreement was also observed between experimental quasistatic and shock data, although there was some evidence that the quasistatic data were strain‐history dependent. Finally, a satisfactory check of the theory was obtained by comparing predicted steady‐wave rise times with measured stress‐wave profile data. These results suggest that the current version of the theory is a significant improvement over past models, because it permits a more accurate esti...

Thermal relaxation at interfaces following shock compression

Abstract: Thermal conduction processes at material interfaces representative of those produced by shock compression are studied in order to understand the temperature history at the interface. The transient effects due to small gaps and thin layers are calculated, as well as the modifications due to a melting transition in one of the materials.

Safety hat energy absorbing liner

Abstract: An energy absorbing liner for a safety hat includes a curved shell and a plurality of laterally spaced stiff permanently deformable hollow shock absorbing members having inner and outer ends integrally connected to the shell and substantially perpendicular to it. The liner is of a shape to fit inside a safety hat with the shock absorbing members substantially perpendicular to the overlying wall of the hat.

Temperature deposition caused by shock interactions with material interfaces

Abstract: In shock‐wave compression experiments in which the interface temperature between two different materials is important, it is necessary to take account of more than the usual ideal shock impedance matching conditions. Several examples are discussed by means of hydrodynamic analysis of the interaction of strong shock waves with nonideal interfaces. It is demonstrated that significant residual thermal inhomogeneities exist near the interface which may be of use in understanding and measuring thermal properties of shock‐compressed materials.

Diaphragm opening process in shock tubes

Abstract: An experimental study of the diaphragm opening process for various types of diaphragms and shock tube configurations is presented. A qualitative description of the opening process is given. A normalized curve is presented which permits prediction of the functional dependence of the diaphragm opening aperture with time for different experimental conditions.

Unitary tie-down panel apparatus

Abstract: The tie-down panel apparatus comprises one or more unitary, preferably extruded panel elements each having a structurally uniting tie-down channel integral to and running lengthwise of the panel element and having side sections parallel with the tie-down channel and mateable with other panel elements to provide a vertical self-aligning mechanical interlock. Two or more extruded panel elements can be bonded together at their mating end sections with a structural epoxy adhesive or angle members, thus permitting the user to fabricate any width of panel. Since the panel elements are of a single structure, they can be cut to any desired length, to augment the design flexibility of the panel elements for specific applications. The top surface of each tie-down panel element is covered with a skid and mar resistant, resilient material which has a limited amount of shock and vibration cushioning value. This material is bonded to the top surface of each panel element. Equipment, containers for goods, machinery, etc., are secured to the tie-down apparatus with adjustable straps.

Vehicle body construction

Abstract: A unitized body construction incorporating longitudinal and lateral reinforcing members providing also yieldable shock absorbing members.

A theoretical analysis of the shock compression experiments of the liquid hydrogen isotopes and a prediction of their metallic transition

Abstract: Shock compression experiments in which the liquid hydrogen isotopes were compressed as much as sevenfold in density to pressures of the order of 900 kbar are analyzed to obtain an effective intermolecular potential. Because temperatures as high as 7000°K are generated during the shock process, this potential is most accurate in the highly repulsive, small separation region, and is thereby well suited to calculate the properties of dense molecular hydrogen in the region of the metallic transition. By equating the Gibbs free energies of the metal and molecular phases, we calculate the pressure and density of the metallic transition. Unfortunately, the large experimental error and the sensitivity of the transition to the free energy allows us only to estimate a lower bound of 2 to 3 Mbar for the transition pressures.

Frangible shock absorbing bumper

Abstract: A frangible shock absorbing and non-rebounding bumper that comprises positioning a metal honeycomb material between a forward impact bumper and a back plate, all being in the same plane. The cells in the honeycomb material extend throughout the thickness of the honeycomb material and in a direction normal to the plane, whereby major impacts against the forward impact bumper sandwiches the honeycomb material between the impact bumper and the back plate compressing and deforming the honeycomb material therebetween, and with the honeycomb material being selectively replaceable.

Shapes of strong shock fronts in an inhomogeneous solar wind

Abstract: The shapes expected for solar-flare-produced strong shock fronts in the solar wind have been calculated, large-scale variations in the ambient medium being taken into account. It has been shown that for reasonable ambient solar wind conditions the mean and the standard deviation of the east-west shock normal angle are in agreement with experimental observations including shocks of all strengths. The results further suggest that near a high-speed stream it is difficult to distinguish between corotating shocks and flare-associated shocks on the basis of the shock normal alone. Although the calculated shapes are outside the range of validity of the linear approximation, these results indicate that the variations in the ambient solar wind may account for large deviations of shock normals from the radial direction.

The Interaction of a Reflected Shock Wave with the Boundary Layer in a Shock Tube

Abstract: The region behind the reflected shock in a shock tube is used as a reservoir of gas for a hypersonic tunnel and in chemical kinetics studies. In order to clarify the gas properties in this region, the interaction phenomenon of the reflected shock with the boundary layer must be made clear. Although many studies have been carried out about this interaction, they are not comprehensive. In this paper, this interaction was observed optically by schlieren method, and the growth rate of the bifurcation and the velocity of the reflected shock were clarified. Furhter, based on the present and previous experimental data, and modifying the previous flow models, a new flow model was presented on the interaction of the reflected shock with the boundary layer. The growth rate of the bifurcation and the velocity of the reflected shock calculated by this model are in fair by good agreement with experimental results.

One-dimensional shock turbulence in a compressible fluid

Abstract: The interactions of weak nonlinear disturbances in a compressible fluid including shocks, expansion waves and contact surfaces are investigated by making use of the reductive perturbation method. It is found that the nonlinear waves belonging to different families of characteristics behave almost independently of each other, while those belonging to the same family are governed by either the Burgers equation or the equation of heat conduction. Thus the statistical properties of one-dimensional shock turbulence in a compressible fluid are reduced to those of the solutions of the Burgers equation. In particular, the law of energy decay of shock turbulence is shown to be identical to that of Burgers turbulence.

Impact fracture of compact bone in a shock tube

Abstract: A shock tube technique was utilized to assess the impact fracture of bovine femur compact bone, in the form of cylindrical tube specimens. The effect of wall thickness on the fracture pressure was established and an unique hoop stress (= 18.0 MN m−2) for fracture obtained. In addition, the effect of crack length and radius of curvature of the crack tip on the fracture hoop stress was established, together with a determination of Young's modulus at the shock loading rate. The possible correlations of these results with fracture mechanics concepts are discussed.

Adhesive surface dart and shock absorbing target

Abstract: A target game is provided composed of a missile and a target, each containing respective portions thereof shaped with filamentary hook-like formations. The target is so constructed that a portion thereof is yieldable, permitting the missile to strike same and the hook-like formations thereof to engage and hold those hook-like formations of the target without disengagement due to bounce.

A hypersonic interpretation of the development of the spark channel in gases

Abstract: A new mechanism for the development of the spark channel in gases is proposed, in which it is assumed that the shock wave, known to exist after the channel is complete (Freeman and Craggs 1969), actually develops while the channel is still in formation. The paraboloidal shock is thought to derive its power from the transfer of energy only from the electrons pre-heated in front of the developing channel by field concentration to the neutrals and ions behind it (detonation wave mechanism). Neutral gas in front of the channel is considered to be cold. Analytical expressions for the velocity and position of the detonation wave are derived, and experiments by the authors and by previous workers tend to confirm the mechanism for certain low-density gases. The `radiation overshoot' characteristic of shock transmission through some gases has been observed, suggesting that a shock indeed exists prior to completion of the spark channel.

Shock absorber for a vehicle

Abstract: In a shock absorber assembly for a vehicle, a closed flexible hollow body mounted on a rigid support member, such as a part of the vehicle understructure, and a highly compressible fluid medium, for instance air, is filled into the hollow body. Another rigid support member of closed hollow construction is mounted against the opposite side of the hollow body from the support member on the vehicle understructure. The hollow support member can be lined interiorly with a closed bladder-like member and connected by a throttling member to the hollow body to act as an equalizing member when the hollow body is compressed by shock forces. As an alternative, two similar shock absorber assemblies can be spaced apart on a vehicle with each including one of the closed flexible hollow bodies and with the throttling member connected between the hollow bodies in the separate shock absorber assemblies.

Shock-wave structure and intermolecular collision laws

Abstract: The nonlinear Boltzmann equation has been solved for shock waves in a Max-wellian gas for eight upstream Mach numbers M1 ranging from 1·1 to 10. The numerical solutions were obtained by using Nordsieck's method, which was revised for use with the differential cross-section corresponding to an intermolecular force potential following an inverse fifth-power law. The accuracy of the calculations of microscopic and macroscopic properties for this collision law is comparable with that for elastic spheres published earlier (Hicks, Yen & Reilly 1972).We have made comparisons of the detailed characteristics of the internal shock structure in a Maxwellian gas with those in a gas of elastic spheres. The purpose of this comparative study is to find the shock properties that are sensitive as well as those which are insensitive to the change in collision law and to find effective ways to study them.The variation of thermodynamic and transport properties of interest with respect to density and to each other was found to depend only weakly on the change in collision law. The principal effect on the macroscopic shock structure due to the change in intermolecular potential is in the spatial variation of the macroscopic properties. The spatial variation of macroscopic properties may be determined accurately from the corresponding moments of the collision integral, especially in the upstream and downstream wings of the shock wave. The results for the velocity distribution function exhibit the microscopic shock characteristics influenced by a difference in intermolecular collisions, in particular the departure from equilibrium in the upstream wing of the shock and the relaxation towards equilibrium in the downstream wing. The departure of several characteristics of weak shock waves from those of the Chapman-Enskog linearized theory and the Navier-Stokes shock is also insensitive to the change in collision law. The deviation of the half-width of the function ∫fdvyduz from the Chapman-Enskog first iterate at M1 = 1·59 is in agreement with an experiment (Muntz & Harnett 1969).

Structure of the terrestrial bow shock

Abstract: Preliminary results of a bow shock study which isolates various parameters are reported. The main findings are successful isolation of shock structures by parameter set, and correlated diagnostic behavior. Conventional shock structural nomenclature is first modified to suit the results of spacecraft observations and to provide the terminology needed in the remainder of the paper. Several examples of shock morphology for a wide range of plasma states are then displayed, as seen with various diagnostics. The bow shock is described as a system in the solar wind. Advantages of the bow shock as an object of shock investigation are pointed out, and a few aims of future study are outlined.

Strong Planar Shock Waves Generated by Explosively-Driven Spherical Implosions

Abstract: Implosions were used to raise the pressure and temperature of a driver gas to extreme values. Strong planar shock waves were thereby generated. A theoretical and experimental study was conducted on the performance of a 2.54-cm-diam shock tube driven by a 20-cm-diam hemispherical implosion driver. The analytical performance of the shock tube was predicted by numerically solving the set of governing nonlinear partial differential equations including appropriate loss mechanisms in the different regimes of the flow. The actual performance of the shock tube was determined experimentally by monitoring the shock velocity, flow uniformity, and test time for different driver conditions. These included stoichiometric hydrogen-oxygen mixtures with and without a PETN explosive liner. Planar shock waves were produced up to 11 km/sec without PETN and up to 19 km/sec with the addition of only 113 g of PETN explosive. Uniform test times of about 2-1 / sec were available at a distance of 33 m from the diaphragm (where the shock velocities were now 9 and 14 km/sec).

Analysis of Gas-Solid Particle Flows in Shock Tubes

Abstract: Theme T use of shock tubes for experimental investigations of high-speed suspension flows has motivated the development of a corresponding numerical calculation procedure. The Particle-In-Cell (PIC) method has been adapted to handle suspension flows by treating each phase as a set of discrete "mass points." As in the single-phase PIC calculation the flowfield is divided into small regions fixed in space (cells), but in the modified procedure phase interactions are incorporated into the equations for the changes in the properties of the materials occupying the cells. Details of the calculation are given in Ref. 2. The purpose of this study was to investigate the dependence of the calculated results on the assumed phase interaction (drag and heat transfer). The behavior of suspension flows in shock tubes also was investigated for the limiting case of problem times that are large compared with the characteristic velocity and thermal equilibration times. In this case, there exists a zone behind the shock within which the phases are in velocity and thermal equilibrium. These equilibrium properties, as well as the equilibrium shock speed, can be calculated by applying the shock tube equations to an "equivalent gas" defined in terms of the properties of the suspension, thereby providing a check on the calculated flow properties.

Shock compression of two-component paraffin-tungsten mixtures

Abstract: Up to pressures of 2 mbar, curves have been recorded experimentally for the shock compression of paraffin and for two paraffin-tungsten mixtures, containing 66.2 and 84.0 wt.% tungsten. It is shown that over the whole range of pressures investigated experimentally, the mixture shock adiabatic curves satisfy the principle of additivity. Attention is called to the great potential of the method of weighting additives for the investigation of light media at high shock pressures. The criteria for the applicability of the principle of additivity have been analyzed.