Shock wave

About: Shock wave is a research topic. Over the lifetime, 36184 publications have been published within this topic receiving 635848 citations. The topic is also known as: Shock waves & shockwave.

An integrated wave-effects model for an underwater explosion bubble

Abstract: A model for a moderately deep underwater explosion bubble is developed that integrates the shock wave and oscillation phases of the motion. A hyperacoustic relationship is formulated that relates bubble volume acceleration to far-field pressure profile during the shock-wave phase, thereby providing initial conditions for the subsequent oscillation phase. For the latter, equations for bubble-surface response are derived that include wave effects in both the external liquid and the internal gas. The equations are then specialized to the case of a spherical bubble, and bubble-surface displacement histories are calculated for dilational and translational motion. Agreement between these histories and experimental data is found to be substantially better than that produced by previous models.

The Bakerian Lecture, 1961. Sound Generated Aerodynamically

Abstract: The author’s original theory of sound generated aerodynamically, that is, of sound radiation fields which are by-products of airflows, has been extended and improved by Curie and Ffowcs Williams. It is explained in this lecture fully but simply, and used as a framework for short analyses of our experimental knowledge on pulse-jet noise, hydrodynamic sound generation, aeolian tones, propeller noise, and boundary-layer noise, as well as for a somewhat extensive discussion of the noise of jets, both stationary and in flight. Improved knowledge of space-time correlations in turbulent flow is used to throw new light on the noise radiated by turbulent boundary layers, as well as by jets at the higher Mach numbers. Supersonic bangs and the scattering of both sound and shock waves by turbulence are briefly touched upon. The lecture ends with a discussion of the methods used for the reduction of jet aircraft noise, in the light of our knowledge of its physical basis.

The Chemistry of Explosives

Abstract: Explosive devices may be mechanical, chemical, or atomic. Mechanical explosions occur when a closed system is heated—a violent pressure rupture can occur. However, this doesn’t make a heated can of soup an explosive. An explosive substance is one which reacts chemically to produce heat and gas with rapid expansion of matter. A detonation is a very special type of explosion. It is a rapid chemical reaction, initiated by the heat accompanying a shock compression, which liberates sufficient energy, before any expansion occurs, to sustain the shock wave. A shock wave propagates into the unreacted material at supersonic speed, between 1500 m/s and 9000 m/s.

Fast radiation mediated shocks and supernova shock breakouts

Abstract: We present a simple analytic model for the structure of non-relativistic and relativistic radiation mediated shocks. At shock velocitiessvs/c & 0.1 the shock transition region is far from thermal equilibriu m, since the transition crossing time is too short for the production of a black-body photon density (by Bremsstrahlung emission). In this region, electrons and photons (and posit rons) are in Compton (pair) equilibrium at temper- atures Ts significantly exceeding the far downstream temperature, TsTd � 2("nu¯ 3 c 3 ) 1/4 . Ts & 10 keV is reached at shock velocitiess � 0.2. At higher velocities, �s & 0.6, the plasma is dominated in the transition region by epairs and 60 keV. Ts . 200 keV. We argue that the spectrum emitted during the breaking out of supernova shocks from the stellar envelopes (or the surrounding winds) of Blue Super Giants and Wolf-Rayet stars, which reachs > 0.1 for reasonable stellar parameters, may include a hard component with photon en- ergies reaching tens or even hundreds of keV. Our breakout analysis is restricted to temperatures Ts . 50 keV corresponding to photon energies h� . 150 keV, where pair creation can be neglected. This may account for the X-ray outburst associated with SN2008D, and possibly for other SN-associated outbursts with spectra not extending beyond few 100 keV (e.g. XRF060218/SN2006aj). Subject headings: shock waves — radiation mechanisms: nonthermal — X-rays: bursts — supernovae: general : individual (SN 2008D)

A new model of magnetic storms and aurorae

Abstract: To explain the sudden commencement (SC) of magnetic storms, the reverse sudden commencement (SC*), and pre-SC disturbances, we invoke the following model: The solar eruption produces a shock wave which arrives at the Earth 22-34 hours later. Highvelocity particles having a smaller interaction precede the shock wave and cause the pre-SC bay-like disturbances at high latitudes. The shock wave itself is retarded by the body forces produced by the geomagnetic field, but speeds up as it enters the auroral zones. In pushing out lines of force, it creates the polar SC* events. Charge separation in the shock wave produces the driving force for the SC currents, which flow in the atmosphere (in accordance with Vestine's analysis). The storm decrease is produced by the high-velocity particles following the shock wave (up to nine hours later) which enter because of field perturbations into the normally inaccessible Stormer regions around the dipole. Here they are trapped and will drift, producing the ring current which gives rise to the storm decrease. Particles with a small pitch angle, however, can reach the Earth's atmosphere and contribute to aurora, the airglow, and ionospheric ionization. These particles are replenished by perturbations produced by solar influences having a 27-day recurrence. Many other particles are absorbed or scattered out of the trapping regions so that their number diminishes rapidly in a day or so, as does the magnetic-storm decrease. The model thus attempts to explain for the first time the cause of the SC*, the atmospheric nature of SC, the delay between SC and the main phase, and the formation and decay of the ring current. A by-product is auroral-particle acceleration by a Shockwave. New experimental tests are suggested by the model: (a) Acoustic observations with balloons to look for the shock wave penetrating into the atmosphere in the auroral zones, (b) Observations with rockets or satellites to establish the location of the SC and main-phase currents, (c) Measurements of the nature and energy of the auroral particles.