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.

Microscale Laser Shock Peening of Thin Films, Part 1: Experiment, Modeling and Simulation

Abstract: Microscale Laser Shock Peening (LSP), also known as Laser Shock Processing, is a technique that can be potentially applied to manipulate residual stress distributions in metal film structures and thus improve the fatigue performances of micro-devices made of such films. In this study, microscale LSP of copper films on single crystal silicon substrate is investigated. Before and after-process curvature measurement verifies that sizable compressive residual stress can be induced in copper thin films using microscale LSP. Improved modeling work of shock pressure is summarized and the computed shock pressure is used as loading in 3D stress/strain analysis of the layered film structure. Simulation shows that the stress/strain distribution in the metal film is close to equi-biaxial and is coupled into the silicon substrate.

Formation, structure, and stability of MHD intermediate shocks

Abstract: It was recently shown by Wu (1987) that intermediate shocks are admissible and can be formed through nonlinear wave steepening from continuous waves. In this paper, the formation, structure, and stability of intermediate shocks in dissipative MHD are considered in detail. The differences between the conventional theory and the present one are pointed out and clarified. It is shown that all four types of intermediate shocks can be formed from smooth waves. It is also shown that there are free parameters in the structure of the intermediate shocks, and that these parameters are related to the shock stability. In addition, the paper shows that a rotational discontinuity can not exist with finite width, indicates how this is related to the existence of time-dependent intermediate shocks, and shows why the conventional theory is not a good approximation to dissipative MHD solutions whenever there is rotation in magnetic field.

Time-resolved measurements of picosecond optical breakdown

Abstract: Picosecond optical breakdown was investigated in order to assess its potential for performing highly localized incisions for laser surgery. Measurements of breakdown were performed using single 40-ps Nd: YAG laser pulses in distilled water. Novel optical pump-probe techniques were developed to characterize the transient spatial and temporal dynamics of the plasma, shock wave, and cavitation phenomena which are associated with the breakdown. The maximum cavity radius and the shock wave zone are shown to scale as the cube root of the pump pulse energy over almost three orders of magnitude. For pulse energies close to the threshold energy of 8 μJ, the shock range was ∼100–200 μm and the cavity radius was 140 μm. Complementary experiments were performed with 10-ns pulse durations. Since picosecond pulses have high peak intensities with low pulse energies, a significant enhancement in localizability may be achieved. The implications for ophthalmic microsurgery are discussed.

Solar wind electron temperature depressions following some interplanetary shock waves: Evidence for magnetic merging?

Abstract: An investigation of periods of anomalously low solar wind electron temperatures using 14 months of Vela 5, Vela 6, and Imp 6 measurements has shown a very strong tendency for unusually low temperatures to follow interplanetary shock waves by 10–20 hours. Of 12 low-temperature regions observed, 10 occurred in direct association with a well-defined shock-associated ssc. A detailed investigation of these events has shown that (1) the periods persist for 10 to >40 hours; (2) a distinct depression in proton temperature occurs simultaneously; (3) the electron heat flux tends to be significantly reduced, but the velocity distributions are less Maxwellian; (4) for one event the He/H concentration is found to rise significantly at about the time of the initial decrease in temperature; for most of the events the data are not continuous enough to check this association; and (5) about half of the observed shocks were followed by temperature depressions. The existence of regions with abnormally low electron temperatures is consistent with the formation of closed or nearly closed magnetic field configurations that more or less thermally isolate the electrons from the relatively hot corona. The electron component of the plasma within these regions thus cools in relation to plasma electrons embedded in open field regions as the closed or constricted regions expand away from the sun.

Non-equilibrium flow of an ideal dissociating gas

Abstract: The theory of an ‘ideal dissociating’ gas developed by Lighthill (1957) for conditions of thermodynamic equilibrium is extended to non-equilibrium conditions by postulating a simple rate equation for the dissociation process (including the effects of recombination). This equation contains the ‘equilibrium’ parameter of the Lighthill theory plus a further ‘non-equilibrium’ parameter which determines the time scale of the dissociation phenomena.The behaviour of this gas is investigated in flow through a strong normal shock wave and past a bluff body. The assumption is made that the gas receives complete excitation of its rotational and vibrational degrees of freedom in an infinitesimally thin region according to the familiar Rankine-Hugoniot shock wave relations before dissociation begins. The variation of the relevant thermodynamic variables downstream of this region is then computed in a few particular cases. The method used in the latter case is an extension of the ‘Newtonian’ theory of hypersonic inviscid flow. In particular, the case of a sphere is treated in some detail. The variation of the shock shape and the ‘stand-off’ distance with the coefficient Λ, which is the ratio of the sphere diameter to the length scale of the dissociation process, is exhibited for conditions extending from completely undissociated flow to dissociated flow in thermal equilibrium. Results would indicate that significant and observable changes from the undissociated values occur, although values for the non-equilibrium parameter are not, at present, available.