Spherical Shock Wave Research Articles

衝撃波の放出によって誘起される管開口端近くにおける非定常流れの可視化

When the shock wave propagating the straight circular tube reaches at the open end, the impulsive wave is generated by the emission of a shock wave from an open end and the unsteady pulse jet is formed near the open end behind the impulsive wave under the specific condition. This paper aims to clear the mechanism of generating the unsteady pulse jet near the open end and the numerical analysis carried out for the emission of propagating the shock wave from an open end of a tube in this study. The flow field is visualized by the computed shadowgraph method using the axisymmetric two-dimensional density distribution contained the axis, which is obtained by the numerical calculation. In this paper, the mechanism of generating the unsteady pulse jet and the characteristics of a pressure distribution in the flow field, the secondary and spherical shock waves behind the impulsive wave are discussed.

813 管内を伝ぱする衝撃波の管開口端からの放射 : パルス波から球面衝撃波への移行

813 管内を伝ぱする衝撃波の管開口端からの放射 : パルス波から球面衝撃波への移行

Modeling shock loading behavior of concrete

Abstract In order to tackle behavior of individual components in concrete cells under shock loading, a multi-part model for concrete is presented, wherein mortar and aggregate are assumed to be in mechanical equilibrium and compressed or released isentropically. Computational simulations of plate shock experiments using the multi-part model for concrete are performed. Computational velocity histories of the free surface of the target are compared with experimental results. Nonlocal response of the multi-part model for concrete to uniform shock loading is presented. The irregular aggregate distribution in actual concrete is replaced by a distribution of single-sized equally separate aggregates and the radius of influence surrounding each aggregate is given. The phenomena accompanied by the passage of a spherical shock wave through the mortar and aggregate are discussed. It is shown that Rayleigh–Taylor instability would cause separation of mortar and aggregate seriously for concrete with porous mortar at low initial density. It is shown that the behavior of the interface between mortar and aggregate under shock loading is captured qualitatively by the multi-part model for a simulated concrete cell. The multi-part model presented in this paper can be expected to numerically simulate shock loading behavior of concrete.

General Attenuation Laws for Spherical Shock Waves in Pure and Dusty Gases

General Attenuation Laws for Spherical Shock Waves in Pure and Dusty Gases

Parametric Study of Weighted Essentially Nonoscillatory Schemes for Computational Aeroacoustics

Based on the dissipation and dispersion relations, two groups of weighted essentially nonoscillatory (WENO) schemes are investigated for computational aeroacoustics. For high-order accuracy, all of the WENO schemes are required to be at least fourth-order accurate. Therefore, with a reasonable number of grid points, they can simulate the low-frequency waves with high-order accuracy. Also, for the higher frequency waves, two parameters in the WENO schemes are introduced to reduce their dissipation and dispersion errors. Both upwind and central schemes are considered and compared for order of accuracy and capability of wave capturing. A sequence of numerical simulations is carried out. These test problems are propagation of a sine-wave packet, propagation of a spherical wave, shock and sine wave interactions, and propagation of acoustic, vorticity, and density pulses in a freestream.

On the eigenvalue problem of imploding shock waves

The motion of an adiabatic converging spherical or cylindrical shock wave in perfect gas can be described by a self-similar solution governed by only one single ordinary differential equation. The solving of this differential equation is a nonlinear eigenvalue problem complicated by the occurrence of a singular point in the phase plane. In this paper a new approximation method of determining the eigenvalue is presented. It is based on a quasi-removal of the singularity by some simple algebraic rearrangements of the differential equation. For various adiabatic coefficients in either cylindrical or spherical geometry this method guarantees eigenvalues which are almost as accurate as the eigenvalues achieved by the most sophisticated series expansion methods so far available.

A Comparative study between two models of propagation of spherical and cylindrical shock waves with varying energy in self-gravitating, magneto-radiative non-uniform atmosphere

Two theoretical models, spherical and cylindrical, of propagation of shockwaves with varying energy in a rotating, magneto-radiative,self-gravitating non-uniform atmosphere have been developed. Subsequently,a comparison between the two models has been drawn with the aid ofvariation of flow variables with distance graphically. Significant is thedifference between two models, when one observes the variations of radialvelocity, pressure, mass, radiation flux, magnetic field and energy withdistance. Also, the respective influences of radiation flux, magneticfield and rotational velocity on the variations of the flow variables havebeen studied.

General attenuation laws for spherical shock waves in pure and dusty gases

General attenuation laws for spherical shock waves in pure and dusty gases

Interaction of shock waves with cavitation bubble: Application of Ho:YAG pulse laser irradiation for cerebral thrombolysis

This paper reports on the application of underwater shock waves and vapor cavities for cerebral thrombolysis. The energy source was a Q-switched Ho:YAG laser (Nippon Infrared Industries Co., Ltd.) with 91 and 140 mJ/pulse energy measured at the end of a 0.60-mm-diam glass optical fiber, pulse duration of 200 ns, and wavelength of 2100 nm. The whole sequences of the shock-wave propagation and growth of the cavitation bubbles from the end of the optical fiber were visualized by high-speed photography using an Imacon 468 camera (Hadland Photonics Ltd.). The shock-wave generation was associated with the laser breakdown in the water. The laser interaction produced a microplasma and heated the liquid in front of the fiber. The plasma drove spherical shock wave in water, followed by the formation of a high-temperature vapor cavity. Collapse of the cavity produced a secondary spherical shock wave in water. Successive generation and collapse of the bubbles were visualized. Pressure histories were measured by PVDF needle hydrophones. The underwater shock waves and the vapor cavities were successfully applied for disruption of artificial thrombosis. The result clearly shows potential extension of this method to precise medical treatment for revascularization in neurosurgery.

Structure, phase composition, and properties of an Al-Hf alloy subjected to isentropic spherical shock waves

The dimensions of characteristic zones of transformations related to the high-strain-rate deformation of the alloy in the solid state and its melting in stress waves, as well as partial evaporation of the shocked melt during unloading into the central cavity that is formed behind the front of a spherically divergent shock wave have been determined. The chosen regime of the explosive loading of the sphere led to melting at the isentrope and at the adiabat in shock waves in various zones along the radius, and to the subsequent formation of two zones with cast structures differing in the grain size, degree of supersaturation of the α-solid solution, and the size and shape of the precipitated aluminide particles. In the zone that underwent melting and high-rate solidification, metastable aluminides Al 3 Hf were revealed inside the adiabatic shear bands. The main features of the evolution of the structures of the matrix and the aluminides in the field of the solid-state transformation were revealed. As a result of high-rate loading and subsequent unloading, the brittle phase was shown to undergo fragmentation and fracture, while the aluminum matrix acquires the structure of a hot-worked material.

Scattered waves generated by shock wave and vortex ring interaction

Scattered waves generated by interaction of a vortex ring and a shock wave are studied experimentally and theoretically. Acoustic pressure is detected by microphones. A polar diagram of the acoustic pressure (with respect to time) constructed from the detected signals shows the waves clearly and the angular distribution of the acoustic pressure is captured visually. Mechanism of noise generation is also investigated. Theoretical formulation for sound scattering by vortex field is applied to describe shock–vortex interaction. Forms of the waves generated by the interaction are calculated by using the velocity field of a typical incident spherical shock wave and compared with the experimental data. Sound scattering by the density inhomogeneity inside a vortex core is also estimated. Some characteristic features of the scattered waves are described.

Study of weak underwater shock waves generated by Ho:YAG pulse laser beam

For medical application of underwater shock waves as a less-invasive approach, a reliable micro shock wave source is required. The present paper reports progress in production of underwater micro shock waves by direct irradiation of pulse laser beam. Energy source was a Q-switched Ho:YAG laser (Nippon Infrared Industries Co. Ltd.) with 91 mJ/pulse energy measured at the end of a 0.60-mm diameter glass optical fiber, pulse duration of 200 ns, and wavelength of 2.1 μm. The laser beam was focused and transmitted through the optical fiber. The generation and propagation of underwater shock waves from the roughened end of the fiber were quantitatively visualized by double-exposure holographic interferometry. Sequential flow visualization revealed that plasma generated by the laser beam drove spherical shock waves. The diameter of plasma region increased, then reduced and detached from the fiber end. Heat-induced flow in front of the fiber vanished after 100 ms. Peak overpressures were measured at various stand-off distances. The weak shock waves produced by this method have potential to be applied for precise medical procedures such as revascularization in neurosurgery.

Amplification of a magnetic field in systems with a finite electric conductivity

In this study we investigated the kinematics of electromagnetic fields with various configurations of the magnetic and electric fields in systems with spherical and cylindrical symmetry using the exact solutions to the diffusion equation for the electromagnetic field in systems with moving boundaries. In the class of self-similar solutions we determined analytically conditions for the amplification of the electromagnetic field as functions of material velocity and electric conductivity. We investigated also the effects of the amplification of an electromagnetic field during propagation of a spherical shock wave in a dielectric material whereby the shock wave causes transformation of a material into a conductor.

Study of the plume generated by Nd:YAG laser ablation of a hydroxyapatite target

The plume generated by Nd:YAG laser ablation of a hydroxyapatite target has been investigated in vacuum and at 0.1 and 0.2 mbar of water vapor. The investigation has been carried out by means of fast intensified CCD imaging with the aid of bandpass interferential filters that allow the following single species to be isolated: neutral calcium, calcium oxide radicals and neutral oxygen. Results obtained in vacuum reveal that expansion takes place at a constant velocity of about 2×104 m/s for the atomic species and about 3×103 m/s for the molecular ones and that emission is completely dominated by emissive neutral calcium. When ablation is carried out in a water atmosphere, the background gas confines the species in the leading edge of the plume, which results in the formation of a planar shock wave at 0.1 mbar and a spherical shock wave at 0.2 mbar. Comparison of the images with those obtained at 0.1 mbar of Ne has revealed the existence of chemical reactions between the plume and the water atmosphere, leading to the formation of calcium oxide radicals. In that case, plume emission is dominated by these molecular species.

Passing through resonance of spherical waves

In the trans-resonant frequency band a balance between the nonlinear, spatial, dissipative and dispersive effects varies together with the excited frequency. Therefore nonlinear resonant waves may be excited in spherical resonators which it is difficult to classify as well known soliton- or conoidal- or shock- or breather-type waves. It follows from the presented theory that spatial and dissipative effects are very important for spherical waves. These effects can prevent the formation of diverging and converging spherical discontinuous shock waves. Oscillating localized waves focusing at the origin are responsible for the sonoluminescence at the exact resonance.

Evidence of chemical reactions in the hydroxyapatite laser ablation plume with a water atmosphere

The expansion dynamics of the ablation plume generated by KrF laser irradiation of hydroxyapatite targets in a 0.1 mbar water atmosphere has been studied by fast intensified charge coupled device imaging with the aid of optical bandpass filters. The aim of the filters is to isolate the emission of a single species, which allows separate analysis of its expansion. Images obtained without a filter revealed two emissive components in the plume, which expand at different velocities for delay times of up to 1.1 μs. The dynamics of the first component is similar to that of a spherical shock wave, whereas the second component, smaller than the first, expands at constant velocity. Images obtained through a 520 nm filter show that the luminous intensity distribution and evolution of emissive atomic calcium is almost identical to those of the first component of the total emission and that there is no contribution from this species to the emission from the second component of the plume. The analysis through a 780 nm filter reveals that atomic oxygen partially diffuses into the water atmosphere and that there is a contribution from this species to the emission from the second component. The last species studied here, calcium oxide, was analyzed by means of a 600 nm filter. The images revealed an intensity pattern more complex than those from the atomic species. Calcium oxide also contributes to the emission from the second component. Finally, all the experiments were repeated in a Ne atmosphere. Comparison of the images revealed chemical reactions between the first component of the plume and the water atmosphere.

Shock wave-inertial microbubble interaction: methodology, physical characterization, and bioeffect study.

A method of generating in situ shock wave-inertial microbubble interaction by a modified electrohydraulic shock wave lithotripter is proposed and tested in vitro. An annular brass ellipsoidal reflector (thickness = 28 mm) that can be mounted on the aperture rim of a Dornier XL-1 lithotripter was designed and fabricated. This ring reflector shares the same foci with the XL-1 reflector, but is 15 mm short in major axis. Thus, a small portion of the spherical shock wave, generated by a spark discharge at the first focus (F1) of the reflector, is reflected and diffracted by the ring reflector, producing a weak shock wave approximately 8.5 microseconds in front of the lithotripter pulse. Based on the configuration of the ring reflector (different combinations of six identical segments), the peak negative pressure of the preceding weak shock wave at the second focus (F2) can be adjusted from -0.96 to -1.91 MPa, at an output voltage of 25 kV. The preceding shock wave induces inertial microbubbles, most of which expand to a maximum size of 100-200 microns, with a few expanding up to 400 microns before being collapsed in situ by the ensuing lithotripter pulse. Physical characterizations utilizing polyvinylidene difluoride (PVDF) membrane hydrophone, high-speed shadowgraph imaging, and passive cavitation detection have shown strong secondary shock wave emission immediately following the propagating lithotripter shock front, and microjet formation along the wave propagation direction. Using the modified reflector, injury to mouse lymphoid cells is significantly increased at high exposure (up to 50% with shock number > 100). With optimal pulse combination, the maximum efficiency of shock wave-induced membrane permeabilization can be enhanced substantially (up to 91%), achieved at a low exposure of 50 shocks. These results suggest that shock wave-inertial microbubble interaction may be used selectively to either enhance the efficiency of shock wave-mediated macromolecule delivery at low exposure or tissue destruction at high exposure.

Shock wave–inertial microbubble interaction

To produce in situ shock wave–inertial microbubble interaction, an annular ellipsoidal reflector, confocal but 15 mm shorter in major axis than the ellipsoidal reflector of a XL-1 lithotripter, was fabricated and combined with the XL-1 reflector. With this modification, a small portion of the spark-generated spherical shock wave is reflected and diffracted by the annular reflector, producing a weak shock wave approximately 8.5 μs in front of the lithotripter pulse. This preceding shock wave (−0.96<P<−1.91 MPa at 25 kV) induces inertial microbubbles, which expand to a maximum size of 100 to 200 μm before being collapsed in situ by the ensuing lithotripter pulse. High-speed shadowgraph imaging and passive cavitation detection have revealed strong secondary shock wave emission immediately following the propagating lithotripter shock front and microjet formation along the wave propagation direction, features that are absent from the standard lithotripter pulses. With optimal pulse combination, membrane permeabilization of mouse lymphoid cells produced by the modified shock waves is substantially enhanced (up to 91%) at low dosage (<50 shocks), and cell injury is significantly increased (up to 50%) at high dosage (>100 shocks), compared to standard lithotripter pulses. [Work supported by NIH R21 HL60327.]

Shock waves from cavitation bubbles

Cavitation bubbles are produced in water by focused laser light with pulse durations in the 100-fs and 10-ns range. Special attention is paid to the shock waves during breakdown and first collapse of the bubble or bubbles generated. The special focusing properties of femtosecond pulses lead to cylindrical shock waves from elongated breakdown channels and to more complicated shock wave patterns in the pre-breakdown region. Bubble collapse leads to spherical outgoing shock waves in the case of spherical shrinking of the bubble and to a sequence of distinct shock waves in the case of aspherical shrinking. The shock waves are made visible with shadowgraph techniques, including femtosecond pulses for illumination, and are measured with a fiberoptic hydrophone. [Work supported by the Deutsche Forschungsgemeinschaft.]

SHOCK WAVE PROPAGATION IN GASES UNDER SUBATMOSPHERIC PRESSURE

In the present paper the results of the experiments on the shock wave dynamics under subatmospheric pressure in neutral gases are presented. The characteristics of spherical and plane configuration shock wave excitation and propagation are studied in the pressure region 1 torr<p<760 torr. It is shown that whenp=3 torr it is still possible to fix successfully the shock wave appearance and propagation in various neutral gases. The pressure dependence of the shock wave propagation velocity and amplitude is determined experimentally. It is shown that when the pressure decreases the shock wave amplitude decreases and an increase of the Mach number takes place. In the case of plane shock wave the Mach number reaches the valueM=5.2 under the pressurep=3 torr.