Showing papers on "Shock (mechanics) published in 1975"

On the formation of auroral arcs and acceleration of auroral electrons

Abstract: It is suggested that the highly structured auroral arc is caused by a current-driven laminar electrostatic shock oblique to the geomagnetic field. Electrons are accelerated by the potential jump associated with the shock. The shock is assumed to be confined to a plane. Self-consistent solutions to the Poisson-Vlasov systems are calculated for the electrostatic potential. Adiabatic theory is used to calculate the ion number density in terms of the electrostatic potential and its derivatives. The electrons are assumed to be highly magnetized so they can only move parallel to the magnetic field. Solutions are exhibited for two plasma models: (1) streaming electrons and a two-temperature distribution of ions and (2) streaming electrons and ions and thermal electrons and ions. In the latter model, solutions can be obtained for an arbitrary potential jump across the shock. The shock is identified with the linear electrostatic ion cyclotron wave, and stability of these waves is examined to determine conditions for the formation of oblique shocks. Finally, the theory is discussed in the context of the magnetosphere, and possible model shocks are exhibited and discussed in terms of auroral arc formation.

Shock wave oscillation driven by turbulent boundary layer fluctuations

Abstract: Pressure fluctuations due to the interaction of a shock wave with a turbulent boundary layer were investigated. A simple model is proposed in which the shock wave is convected from its mean position by velocity fluctuations in the turbulent boundary layer. Displacement of the shock is assumed limited by a linear restoring mechanism. Predictions of peak root mean square pressure fluctuation and spectral density are in excellent agreement with available experimental data.

Electric energy generation by shock compression of ferroelectric ceramics: Normal−mode response of PZT 95/5

Abstract: Reproducible and predictable electrical pulses with peak powers of a few hundred kilowatts lasting for a few microseconds can be obtained from shock−wave compressed ferroelectrics. In this work, impact−loading techniques are used to investigate the electromechanical response of poled specimens of a ferroelectric ceramic, PZT 95/5, to long−duration shock pulses. The experiments are conducted in the normal mode in which the shock propagation vector is perpendicular to the remanent polarization. Current histories are obtained as a function of load resistance for a fixed shock amplitude of 1.4 GPa, and few additional experiments investigate the stress dependence of the electrical response. A simple, though specific, model is developed that gives good agreement with observed results. The extension of this model to other materials and shock−loading conditions is discussed.

Energization of auroral electrons by electrostatic shock waves

Abstract: Electrostatic shock waves are proposed as a possible mechanism for energizing electrons which are responsible for discrete auroras. It is shown that electrostatic shock solutions can exist in a Ti ≫ Te plasma carrying a field-aligned electron current if the plasma in the high-latitude plasma sheet has an earthward flow component. The model is formulated within the framework of the Vlasov-Poisson equations. The reflection of incident ions upstream, the trapping of electrons downstream, and the magnetic mirror of the earth's field are included in the present model. It is found that under the high-latitude plasma sheet conditions, a field-aligned potential jump of several kilovolts can be produced by the shock. Electrons passing through the shock are accelerated at the expense of the ion kinetic energy.

Structure of the quasi‐perpendicular laminar bow shock

Abstract: It was found that low solar wind parameters M (less than or around 2.5) and beta (much less than 1) and high angles to the local shock normal, theta (greater than or around 65 deg), produced oblique laminar shock profiles as expected from theory, with marginal or vanishing upstream standing whistlers probably damped by acoustic or other plasma wave instabilities. The whistler mode appeared to dominate the electromagnetic spectrum. The laminar shock ramp thickness was several hundred kilometers and equal to (2-4)c/omega-pi. Composition of the shock as an accumulation of near-standing waves and an evidently reproducible varying flux pattern was discernible. Electron thermalization occurred early in, or just before, the magnetic ramp, while proton thermalization appeared to occur later in the ramp. Instantaneous shock velocities derived from the standing whistler wavelength were consistent with average velocities derived from the elapsed time estimates and were as high as 200 km/sec.

Zones of shock metamorphism at the Charlevoix impact structure, Quebec

Abstract: The distribution of particular shock metamorphic effects has been determined in the central uplift of the Charlevoix impact structure. Planar deformation features in quartz occur as much as 10 km from the central peak (Mont des Eboulements), whereas equivalent shock features in K-feldspar are restricted to within 2 km of the crater center. Weak planar features in K-feldspar are narrow (≤ 1 µm) but can become broad (4 to 8 µm) deformation twins in_more highly shocked samples. Common orientations are (24 (see PDF for formula)), ( (see PDF for formula) 41), and (110) in orthoclase, and (13 (see PDF for formula)) and (110) in microcline, and the relative abundance of specific orientations does not change with shock level. Film perthite lamellae in K-feldspar break down to spindle microperthite within 6 km of the center, either as a result of shock or as a function of original depth of burial. Shock pressures were estimated for Charlevoix samples by equating observed planar feature development with experimental data. For example, type A shocked quartz develops above 7.5 GNm −2 , type B above 10 GNm −2 , type C above 14 GNm −2 , and type D above 16 GNm −2 . Maximum shock levels preserved on the central peak resulted from an estimated 22.5 GNm −2 . Shock level contours at 5-GNm −2 intervals are broadly concentric with Mont des Eboulements. The transient cavity of the Charlevoix impact was reconstructed with a radius of 13.5 ± 2 km and a depth of 9.5 ± 1.5 km (r√2). The distribution of peak shock pressure levels in basement rocks beneath the transient cavity was calculated from theoretical pressure attenuation rates. Using a model for central uplift formation, these rocks were elevated to positions underlying the central uplift. The resulting configuration of shock pressure zones agrees with the surface expression of shock zones mapped from planar features and confirms the validity of current theories of cratering and shock pressure attenuation.

The role of regression and range effects in determination of the power function for electric shock

Abstract: A scale for the apparent intensity of electric shock applied to the forearm was derived from cross-modality matching functions relating noise level, number, and force of handgrip to both line length and shock. For each response mode, the effects of psychophysical regression were estimated from the line judgments and used to make adjustments in the corresponding shock judgments. For shocks ranging from (1.0 to 5.5 mA, combined estimates of subjective magnitude were found to grow as the 2.26 power of the stimulating current.

Approximate spherical blast theory including source mass

Abstract: Equations including source mass are presented for strong spherical blasts in cases where the source mass is not negligible Analytic solutions are obtained for shock speed, position, and overpressure as a function of radius Approximations similar to those used in the Taylor−Sedov approximate theory are employed Shock positions as functions of time are obtained via evaluation of incomplete elliptic integrals Sample calculations are presented for a laser−initiated 1−MJ (debris energy) pellet microexplosion, and compared to Taylor−Sedov approximate theory solutions

Shock magnetization and demagnetization of basalt by transient stress up to 10 kbar

Abstract: The effect of stress waves on the magnetization of basalt was studied. The stress waves were generated by impacting cylindrical basalt samples with aluminium projectiles. The 3 mm thick aluminium plates were accelerated in a non-magnetic compressed air gun accelerator to velocities ranging from 20 to 160 m/s, corresponding to peak stresses in the basalt between 2.5 and 10 kbar. The duration of the stress impulse was about several micro-seconds. For the experiments a basalt with well-known magnetic properties was used (Rauher Kulm, Germany). The magnetizing effect of the stress waves was determined as a function of the number of impacts, the intensity and direction of the applied magnetic field ( < 10 Oe) and the peak stress amplitude. In the used stress range the measured shock remanent magnetization (SRM) tends to a final steady value after 5 or 6 impacts. This value is proportional to the intensity of the applied field and increases with the peak stress applied. The produced SRM can be erased with maximum ac-fields of about 150 to 200 Oe. Any dependance of SRM on the direction of the applied magnetic field could not be recognized within the accuracy limits of the experiments. The demagnetizing effect of stress waves on the highfield (1000 Oe) isothermal remanent magnetization, the low-field (1 Oe) thermoremanent magnetization and the natural remanent magnetization was studied as a function of the number of impacts and the peak stress. A final steady state of magnetization is generally obtained after 4 or 5 impacts. With increasing peak stresses increasingly harder remanent magnetizations can be demagnetized, with stresses of 2.5 kbar corresponding to coercive forces of about 75 Oe, 5.5 kbar to about 125 Oe and 8 kbar to about 175 Oe.

Electromagnetic shock absorber

Abstract: The present invention discloses an electromagnetic shock absorber which may be employed to prevent the bottoming of springs in autos during shock conditions, or to replace, in its entirety, a shock absorber. The present shock absorber includes two electro-magnets, the first having a fixed north-to-south field and the second having a field whose polarity is reversible dependant upon the direction of the shock which is to be absorbed or dampened. Where the undesirable shock involves a movement of the car axle toward the auto frame, the polarity of the magnet having a reversible field causes a repulsion between the two electro-magnets. Where the undesirable motion of the car axle is away from the auto frame, the field of the reversible magnet creates an attraction between the two electro-magnets. Hence, any undesirable motion of the auto axle relative to the auto frame is counteracted by virtue of the present system.

On the possibility of complete condensation shock waves in retrograde fluids

Abstract: Shock discontinuities for which the upstream state is vapour and the downstream state is liquid are considered. The possibility of such shock waves is associated with a large number of molecular degrees of freedom: it is necessary that the ideal-gas specific heat cv [ges ] 24R at the critical temperature, a condition which is met by several common fluids. Shock properties are found from a corresponding-states thermodynamic model and from several calculations based on data for particular fluids. Condensation shock waves satisfy the usual stability conditions and should be found in laboratory experiments.

Acceleration controlled fluidic shock absorber

Abstract: The invention provides a shock absorber for wheeled and track type vehicles in which the conventional compression valve is replaced by an acceleration controlled vortex throttle. A beam deflection amplifier introduces fluid radially, tangentially or at an intermediate position into a vortex chamber under control of an accelerometer. The vortex throttle is controlled such that in the presence of acceleration of a wheel relative to the ground shock motion is lightly resisted while long term movement of the wheel toward the vehicle is strongly resisted so that the wheel more closely follows the terrain contour with reduced energy delivered by the wheel to the vehicle body.

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.

Seismically induced modification of lunar surface features

Abstract: The formation of large impact craters and basins produced not only large volumes of ejecta but also catastrophic seismic waves. Theoretical models, extrapolation of terrestrial explosion data, and extrapolation of lunar impact data suggest surface displacements of 1-10 m at four crater radii from a Copernicus-size impact (4 x 10 to the 30th power ergs). Independent estimates of impact-generated stresses indicate that regions within 4 crater radii of an impact will receive shock waves with pressures exceeding 1 kbar. Greater areas also may receive shock effects as elastic waves following deep ray paths transform into shock waves near the surface. Additional seismic energy will be generated by impacts from secondary ejecta. The resulting large and long-lasting surface movement may contribute to the subdued appearance of the continuous ejecta blanket and secondary craters around large impact craters and to the degradation of small craters outside these zones.

Extensible vehicle bumper

Abstract: A bumper for motor vehicles which is operated by hydraulic slave cylinders connected to the master brake cylinder to extend the bumper upon the application of a predetermined amount of force to the brake to provide the bumper with a greater shock absorbing length of travel under collision conditions while permitting the retraction of the bumper to facilitate in-town maneuvering and parking under normal driving conditions.

Experiments and Analyses on Shock Waves Propagating through a Gas-Particle Mixture

Abstract: The structures and the behaviors of shock waves propagating through a gas and solid particle mixture are studied by shock-tube experiments and by two methods of wave analysis. The shock waves concerned are incident on the mixture dispersed uniformly in downstream part of the driven section. Pressures and shock velocities are measured under the condition that the particle loading ratio and the shock Mach number are both less than two. The final equilibrium pressures behind the waves and the velocities of the fully decayed shock fronts agree well respectively with the results of the usual shock theory on the mixture and those of the model analysis on a perfect "effective" gas. The analysis by the method of characteristics is satisfactorily applied to give a good explanation of the observed process whereby a shock wave decays to a weak wave with continuous wave form. And, the authors point out some problems relating to the relaxation process and some inconsistencies of the "effective" gas theory when analyzing the unsteady wave motions.

Implicit approximate-factorization schemes for the low-frequency transonic equation

Abstract: Two- and three-level implicit finite-difference algorithms for the low-frequency transonic small disturbance-equation are constructed using approximate factorization techniques. The schemes are unconditionally stable for the model linear problem. For nonlinear mixed flows, the schemes maintain stability by the use of conservatively switched difference operators for which stability is maintained only if shock propagation is restricted to be less than one spatial grid point per time step. The shock-capturing properties of the schemes were studied for various shock motions that might be encountered in problems of engineering interest. Computed results for a model airfoil problem that produces a flow field similar to that about a helicopter rotor in forward flight show the development of a shock wave and its subsequent propagation upstream off the front of the airfoil.

Collisionless shock waves in space: A very high β structure

Abstract: Measurements from six OGO-5 particle and field experiments are used to examine the structure of the earth's bow shock during a period of extremely high beta (the ratio of plasma thermal to magnetic energy density), as determined from simultaneous measurements of the upstream plasma on board the HEOS satellite. Even though the interplanetary field is nearly perpendicular to the shock normal, the shock is extremely turbulent. Large field increases are observed up to a factor of 20 above the upstream values. Ahead of these large enhancements, smaller magnetic effects accompanied by electrostatic noise, electron heating, and ion deflection are observed for several minutes. These observations suggest that a steady-state shock may not be able to form at very high beta. Further, they show that while the magnetic energy density may be relatively unimportant in the upstream flow, it can become very significant within the shock structure, and hence the magnetic field should not be ignored in theoretical treatments of very high beta shocks.

Nonlinear oblique interaction of interplanetary tangential discontinuities with magnetogasdynamic shocks

Abstract: The nonlinear oblique interaction between a plane tangential discontinuity (TD) and a plane fast magnetogasdynamic shock is treated generally and then applied to the interplanetary TD-bow shock interaction. A number of similarity relations are found for the general problem. For the frequent directional TD's the interaction is strongest if the directional change is 90° and one of the magnetic field vectors is parallel to the shock. Bow shock motions of up to several tens of kilometers per second are induced by these TD's. Tangential discontinuities with density jumps held responsible for geomagnetic sudden impulses lead to a much stronger interaction with the bow shock with nonnegligible strength of the newly generated wave. The oblique interaction requires weaker TD's to produce observed bow shock velocities. It is also shown that complex nonlinear wave patterns very often develop, which have not been predicted in the past in this context.

Shock absorber drive unit

Abstract: A shock absorber drive unit for motor vehicles which translates the vertical reciprocating motion of the under carriage of a motor vehicle to one-way rotary motion through a rack and drive gears connected through one-way clutches to a gear train. Alternators driven by belts from the gear train provide sufficient drag to produce a shock absorbing action for the unit while simultaneously producing electricity for charging batteries or other uses.

Interplanetary shock pair disturbances: Comparison of theory with space probe data

Abstract: Three sets of data for shock pair disturbances, which are assumed to have been formed from stream-stream interactions, are modeled by using two time-dependent numerical codes. One code solves the fluid dynamic equations, and the other solves the magnetohydrodynamic equations. The observed disturbances are simulated by superimposing an initial interaction (a pulse in the dependent variables) onto the ambient solar wind and then following the time evolution of the resulting disturbance with the numerical codes. The magnitude of the initial interaction is such that the calculated solar wind agrees with the solar wind observed by the space probe both prior to the arrival of the forward shock at the space probe location and following passage of the reverse shock. The location of the initial interaction is iteratively chosen so that the simulated time interval between the forward and reverse shocks at the space probe location agrees with the measured value. The large-scale structure in the disturbance is reproduced if (1) the magnetic field and azimuthal velocity are included (that is, if the code which solves the magnetohydrodynamic equations is used), (2) the time dependence of the initial interaction is appropriately selected, and (3) the observed nonradial shock normals are accounted for in the modeling procedure. The relative importance of each of the above requirements varies for each set of data. The first and third requirements played the dominant roles in one data set, while for the other two data sets the second requirement was probably the most important. Hence it is recommended that all three requirements be met in attempting to simulate data for shock pair disturbances.

A Study of the Shock Spectrum of a Two-Degree-of-Freedom Nonlinear Vibratory System.

Abstract: : The shock spectrum due to the motion of the foundation or isolator mass of a two-degree-of-freedom vibratory system is studied. The system had a cubic hardening elastic nonlinearity in the foundation or isolator restoring force. The system was impulsively shocked, and analytical, experimental, and numerical methods were used to determine the resulting shock spectrum.... Degrees of freedom, Equations of motion, Nonlinear equations, Numerical methods and procedures, Perturbations, Shock spectra.

Behavior of burst diaphragms in shock tubes

Abstract: Analytical and experimental studies have been carried out on the behavior of strong shock tube diaphragms. These diaphragms exhibit large moments of resistance to opening due to stresses at the hinge line of the diaphragm petal. High speed shadowgraph photographs of the detailed opening process have been obtained and have been shown to compare well with the analytical model derived for flowfield‐diaphragm interaction. A nondimensional resistance parameter is shown to control the behavior of the thick diaphragm and the detailed flow process which controls the opening is identified.

Shock absorbing method and apparatus

Abstract: The damping coefficient and spring constant of shock absorbing struts for commercial jet aircraft landing gears are selected to allow optimum absorption of forces on the landing gears at touchdown for an aircraft that has been descending at the maximum permissible "sinkrate" (descent rate immediately prior to touchdown). When so selected, the shock absorbing struts are unable to effectively dampen vertical oscillations of the aircraft body ensuing from a downward plunging of the weight of the aircraft due to the deployment of lift spoilers immediately after touchdown. To rapidly attenuate these post-touchdown vertical oscillations (for more efficient braking and ground handling), while still affording the proper spring constant and damping coefficient necessary for absorbing touchdown impact forces at maximum "sinkrate", the damping of each shock strut is substantially increased after the first cycle of strut compression and re-extension by automatically sensing the occurrence of touchdown, and after a predetermined time delay therefrom, actuating a damping control within each shock strut, to change the damping coefficient to an increased level.

Measurement of the development and evolution of shock waves in a laser-induced gas breakdown plasma

Abstract: Space‐ and time‐resolved interferometric measurements of electron density in CO2‐laser produced plasmas in helium or hydrogen are made near the laser focal spot. Immediately after breakdown, a rapidly growing region of approximately uniform plasma density appears at the focal spot. After a few tens of nanoseconds, shock waves are formed, propagating both transverse and parallel to the incident laser beam direction. Behind the transverse propagating shock is an on‐axis density minimum, which results in laser‐beam self‐trapping. The shock wave propagating toward the focusing lens effectively shields the interior plasma from the incident beam because the lower plasma temperature and higher plasma density in the shock allow strong absorption of the incident beam energy. By arranging the laser radiation‐plasma interaction to begin at a plasma‐vacuum interface at the exit of a free‐expansion jet, this backward propagating shock wave is eliminated, thus permitting efficient energy deposition in the plasma interior.

Multidirectional shock absorbing device

Abstract: A housing with a mandrel therein is adapted to be connected in a rotary drill string. The housing and mandrel are constructed and arranged to support the work load of the rotary drill string as well as dissipate both longitudinal and radial impact or shock loads that the drill string may encounter. The construction also includes means whereby radial impacts applied to the drilling assembly are connected or translated into longitudinal components of force so that various combinations of longitudinal and/or radial impact or shock loading of the drill string may be dissipated in a manner to inhibit damage to the drill string and its components.

Shock shapes on blunt bodies in hypersonic-hypervelocity helium, air, and CO2 flows, and calibration results in Langley 6-inch expansion tube

Abstract: Shock shape results for flat-faced cylinders, spheres, and spherically blunted cones in various test gases, along with preliminary results from a calibration study performed in the Langley 6-inch expansion tube are presented. Free-stream velocities from 5 to 7 km/sec are generated at hypersonic conditions with helium, air, and CO2, resulting in normal shock density ratios from 4 to 19. Ideal-gas shock shape predictions, in which an effective ratio of specific heats is used as input, are compared with the measured results. The effect of model diameter is examined to provide insight to the thermochemical state of the flow in the shock layer. The regime for which equilibrium exists in the shock layer for the present air and CO2 test conditions is defined. Test core flow quality, test repeatability, and comparison of measured and predicted expansion-tube flow quantities are discussed.