Cavitation phenomena in extracorporeal microexplosion lithotripsy

An experimental investigation was made of cavitation phenomena induced by underwater shock wave focusing applied to the extracorporeal microexplosion lithotripsy (microexplosion ESWL). Firstly an underwater microexplosion generated by detonation of a 10 mg silver azide pellet was studied and secondly underwater shock focusing and its induced cavitation phenomena were investgated. Underwater shock wave was focused by using a semi-ellipsoidal reflector in which a shock wave generated at the first focal point of the reflector was reflected and focused at the second focal point. It is found that an explosion product gas bubble did not produce any distinct rebound shocks. Meantime cavitation appeared after shock focusing at the second focal point where expansion waves originated at the exit of the reflector were simultaneously collected. A shock/bubble interaction is found to contribute not only to urinary tract stone disintegration but also tissue damage. The cavitation effect associated with the microexplosion ESWL was weaker in comparison with a spark discharge ESWL. The microexplosion ESWL is an effective method which can minimize the number of shock exposures hence decreasing tissue damage by conducting precise positioning of urinary tract stones.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Gas combination for shock wave enhancement

It was recently demonstrated that shock wave enhancement could be achieved when a shock propagates in a constant cross-section duct through pairs of air–helium layers having a continually decreasing width (Igra and Igra in Shock Waves 16(3):199–207). A parametric study was conducted aimed at finding a two-layered, light–heavy gas arrangement that yields maximal shock enhancement; the heavy and the light gases used were air and helium, respectively. Effects associated with changes in following parameters were investigated: the number of alternating heavy/light gas layers, the applied reduction ratio between successive layers thickness, and the initial shock wave Mach number.      

On shock wave propagation in a branched channel with particles

The problem of wave propagation in a dust–air mixture inside a branched channel has not been studied widely in literature, even though this topic has many important applications especially in process safety (dust explosions). In this paper, a shock wave interaction with a cloud of solid particles, and the further behaviour of both gas and particulate phases were studied using numerical techniques. The geometry mimicked a real channel where bends or branches are common. Two numerical approaches were used: Eulerian–Eulerian and Eulerian–Lagrangian. Using Eulerian-Lagrangian simulation, it was possible to include the effects of particle–particle and particle–wall collisions in a realistic and direct manner. Results are mainly shown as snap-shots of particle positions during the simulations and statistics for the particle displacement. The results show that collisions significantly influence the process of particle cloud formation. PACS47.40.Nm, 02.60.Cb, 47.55.kf     

Oblique shock wave with sweep

An attached planar, oblique shock with sweep is investigated for the inviscid flow of a perfect gas. The ratio of specific heats, freestream Mach number, and wedge angle in the plane of the freestream velocity are prescribed, with the sweep angle as a free parameter. Explicit relations are provided for jump and detachment conditions. A number of trends, some non-intuitive, are discussed, e.g., the downstream Mach number may increase with sweep.     

Modelling a shock wave source for seismic well survey

The shock wave seismic source has specific advantages for reservoir survey, particularly in the technique of vertical seismic profiling. This paper is concerned with the modelling of the characteristics of a shock wave device under conditions typical of its use as a surface seismic source. Such modelling necessitates numerical solution of the time-dependent conservation equations for axi-symmetric geometry under conditions where the fluid in the surface borehole may be air or water. A version of the piecewise parabolic method has been used to take account of the two-phase behaviour based on the formal properties of the well-known Tait equation of state for water. Results are presented which enable predictions to be made for use in the field of the pressure and velocity signatures of the shock wave source in terms of axial and radial profiles. Such information is significant in the assessment of the degrees of compressional- and shear-wave energies delivered by the source in vertical seismic profiling surveys of reservoirs. Received 6 November 1997 / Accepted 3 March 1998     

Color schlieren methods in shock wave research

Schlieren methods are widely known and well established to visualize refractive index variations in transparent media. The use of color allows one to obtain more data and previously inaccessible information from a picture taken with this technique. In general, a hue can be related to a certain strength or a certain direction of a refractive index gradient. While the first case essentially corresponds to the usual black- and-white system the latter correlation cannot be made adequately evident without the use of color. Two color schlieren techniques are presented here, which reach or even exceed the quality and sensitivity range of conventional black- and-white methods. Using a powerful short duration light source these methods are applied to visualize transient flow phenomena in a shock tube.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1990.     

Oblique shock wave with sweep II

This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Reflection of a ring shock wave from a rigid wall

A new type of an implosion has been observed experimentally and simulated in a numerical calculation: the formation of a quasi-spherical converging shock wave after the reflection of a ring shock wave from a solid wall. The conversion of the ring shock wave into the quasi-spherical converging shock wave intensifies the local implosion properties.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Experimental and numerical studies of underwater shock wave attenuation

The attenuation of an underwater shock wave by a thin porous layer is studied both experimentally and numerically. The shock waves are generated by exploding 10 mg silver azide pellets and the pressures at different distances from the explosion center are measured. Measurements are also carried out with a gauze layer placed between the explosion source and the pressure gauge. The results with and without the gauze layer are compared evaluating the shock wave attenuation. Numerical simulations of the phenomenon are also carried out for a simple wave attenuation model. The results are compared with the experimental data. Despite the simple mathematical model of wave attenuation, the agreement between the experimental and numerical results is reasonable.Received: 22 October 2002, Accepted: 17 June 2003, Published online: 5 August 2003PACS: 47.11.+j, 47.40.Nm, 47.55.Mh     

The formation of a secondary shock wave behind a shock wave diffracting at a convex corner

This paper deals with the formation of a secondary shock wave behind the shock wave diffracting at a two-dimensional convex corner for incident shock Mach numbers ranging from 1.03 to 1.74 in air. Experiments were carried out using a 60 mm 150 mm shock tube equipped with holographic interferometry. The threshold incident shock wave Mach number () at which a secondary shock wave appeared was found to be = 1.32 at an 81° corner and = 1.33 at a 120° corner. These secondary shock waves are formed due to the existence of a locally supersonic flow behind the diffracting shock wave. Behind the diffracting shock wave, the subsonic flow is accelerated and eventually becomes locally supersonic. A simple unsteady flow analysis revealed that for gases with specific heats ratio the threshold shock wave Mach number was = 1.346. When the value of is less than this, the vortex is formed at the corner without any discontinuous waves accompanying above the slip line. The viscosity was found to be less effective on the threshold of the secondary shock wave, although it attenuated the pressure jump at the secondary shock wave. This is well understood by the consideration of the effect of the wall friction in one-dimensional duct flows. In order to interpret the experimental results a numerical simulation using a shock adaptive unstructured grid Eulerian solver was also carried out. Received 1 May 1996 / Accepted 12 September 1996     

Some aspects of streamwise vortex behavior during oblique shock wave/vortex interaction

An experimental study of the flowfield generated by the interaction of a streamwise vortex having a strong wake-type axial Mach number profile and a two-dimensional oblique shock wave was conducted in a Mach 2.49 flow. The experiments were aimed at investigating the dynamics of supersonic vortex distortion and to study downstream behavior of a streamwise vortex during a strong shock wave/vortex encounter. The experiments involved positioning an oblique shock generator in the form of a two-dimensional wedge downstream of a semi-span, vortex generator wing section so that the wing-tip vortex interacted with the otherwise planar oblique shock wave. Planar laser sheet visualizations of the flowfield indicated an expansion of the vortex core in crossing a spherically blunt-nose shock front. The maximum vortex core diameter occurred at a distance of 12.7 mm downstream of the wedge leading edge where the vortex had a core diameter of more than double its undisturbed value. At distances further downstream the vortex core diameter remained nearly constant, while it appeared to become more diffused at distances far from the wedge leading edge. Measurements of vortex trajectory revealed that the vortex convected in the freestream direction immediately downstream of the bulged-forward shock structure, while it traveled parallel to the wedge surface at distances further downstream. The turbulent distorted vortex structure which formed as a result of the interaction, was found to be sensitive to downstream disturbances in a manner consistent with incompressible vortex breakdown. Physical arguments are presented to relate behavior of streamwise vortices during oblique and normal shock wave interactions. Received 7 September 1996 / Accepted 10 February 1998     

A holographic interferometric study of shock wave focusing in a circular reflector

A holographic interferometric study was made of the focusing of reflected shock waves from a circular reflector. A diaphragmless shock tube was used for incident shock Mach numbers ranging from 1.03 to 1.74. Hence, the process of reflected shock wave focusing was quantitatively observed. It is found that a converging shock wave along the curved wall undergoes an unsteady evolution of mach reflection and its focusing is, therefore, subject to the evolution of the process of shock wave reflections. The collision of triple points terminates the focusing process at the geometrical focus. In order to interprete quantitatively these interferograms, a numerical simulation using an Eulerian solver combined with adaptive unstructured grids was carried out. It is found numerically that the highest density appears immediately after the triple point collision. This implies that the final stage of focusing is mainly determined by the interaction between shock waves and vortices. The interaction of finite strength shock waves, hence, prevents a curved shock wave from creating the infinite increase of density or pressure at a focal point which is otherwise predicted by the linear acoustic theory.     

Reconsideration of pseudo-steady shock wave reflections and the transition criteria between them

The shock wave reflection phenomenon in pseudosteady flows was reconsidered by replacing the Law-Glass assumption by models accounting for the interaction of the shock wave reflection and the shock induced flow deflection processes. As a result, the analytical predictions of the location of the kink of a transitional-Mach reflection and the second triple point of a double-Mach reflection improved tremendously. It has also been proven that based on gas dynamic considerations a triple-Mach reflection wave configuration is physically impossible. In addition, the transition lines between the various reflection configurations were also found to better agree with the experimental results when they were calculated using the proposed models.     

Shock wave propagation in a branched duct

The propagation of a planar shock wave in a 90° branched duct is studied experimentally and numerically. It is shown that the interaction of the transmitted shock wave with the branching segment results in a complex, two-dimensional unsteady flow. Multiple shock wave reflections from the duct's walls cause weakening of transmitted waves and, at late times, an approach to an equilibrium, one-dimensional flow. While at most places along the branched duct walls calculated pressures are lower than that existing behind the original incident shock wave, at the branching segment's right corner, where a head on-collision between the transmitted wave and the corner is experienced, pressures that are significantly higher than those existing behind the original incident shock wave are encountered. The numerically evaluated pressures can be accepted with confidence, due to the very good agreement found between experimental and numerical results with respect to the geometry of the complex wave pattern observed inside the branched duct. Received 15 July 1996 / Accepted 20 February 1997     

On the relation between particle velocity and shock wave speed for thermoelastic materials

Results of shock-wave experiments in solids often suggest a nearly-linear relation between the particle velocity behind the shock and the shock wave speed. The present note reconsiders the question of whether thermoelastic material models may be consistent with such observations. Emphasis is placed on the role played by the response of the material in severe compression, as distinguished from its response for small or moderate deformations. The details are illustrated for materials of Mie-Grüneisen type. Received 21 December 2001 / Accepted 22 April 2002 Published online 8 July 2002     

Numerical simulations of shock wave propagation in condensed multiphase materials

We propose to find out numerical solutions of a travelling shock wave in condensed mixtures by using a direct numerical simulation. Condensed multiphase materials under shock wave conditions are mechanically characterized by a unique pressure and a unique velocity. In this study, the mixture is considered as a collection of grains separated by interface between each material: this problem of interfaces is solved by a diffuse interface method. The results will be compared to existing one-dimensional numerical models, analytical solutions and also experimental data. The volume fraction (or the phase temperature) is not measured in experiments and it is then important to verify the behaviour of a phase quantity through various methods. A non-monotonous evolution of the volume fraction is obtained with analytical solution as well as numerical simulation.      

Numerical study of rate-dependent strength behavior under ramp and shock wave loading

The main objective of the current study was to gain a detailed understanding on the rate-dependent strength behavior under ramp and shock wave loading. A forward, numerical-simulation-based cause and effect analysis was used to address the research objective. The apparent strength associated with shock and ramp wave loadings with different risetimes and shapes was investigated. It was shown that intrinsic material strength could vary with pressure, temperature, and deformation history, but the apparent strength, which was larger than the intrinsic strength, was a result of the interaction between the rate sensitivity of the strength and the rate of the external loading. The degree of interaction led to different levels of mechanical and thermal dissipations and their partition, which was manifested by different temperature, stress, and deformation histories.     

Nano-particle sizing by laser-induced-incandescence (LII) in a shock wave reactor

Abstract. Laser-Induced Incandescence (LII) is a relatively new optical diagnostic for particle sizing which is currently used in combustion science. Its advantage against light extinction and light scattering methods is the possibility of getting size information with high time and space resolution even for nano-particles. LII is mostly applied to particle formation or particle removal in reactive stationary flows, but it can also be used in shock-induced reactive flows. This is demonstrated in three examples: soot particle formation during high temperature pyrolysis of benzene, iron particle formation from iron pentacarbonyl, and formation of carbon-coated iron particles. From the principles of LII, it is not possible to obtain a complete particle growth curve from one individual shock tube experiment. Therefore, the kinetics of particle growth evolution must be determined from several “identical” shock tube experiments with a delayed triggering of the heat-up laser. The principles of LII, the in-situ measurement of particle size, and the comparison to beam-collected particles, which were visualized by a high resolution transmission electron microscope (HRTEM), are demonstrated. It was found that the energy accommodation coefficient during the particle cooling is for a soot surface but is significantly lower e.g. for an iron surface. Received 30 April 2002 / Accepted 9 December 2002 Published online 4 February 2003 Correspondence to: R. Starke (e-mail: starke@ivg.uni-duisburg.de)     

Numerical simulation of the reflection of a planar shock wave over a double wedge

A numerical code based on the upwind TVD scheme for simulating the various reflection processes of a planar shock wave over a concave or convex double wedge has been developed. The numerical results were compared with actual experiments and excellent agreement was obtained. The excellent agreement serves also as a validation of the shock-capturing performance of the numerical scheme.     

Air shock wave interaction with an obstacle covered by porous material

The interaction between an air shock wave and a rigid wall covered by a porous screen is investigated numerically and experimentally. A mathematical two velocity with two stress tensors model is used for studying the wave processes in saturated porous media. The process of reflection of a step-type wave from a rigid wall covered with a porous layer is considered, the effect of the porous medium and wave parameters on the reflection is analyzed, and the numerical results are compared with the experimental data.Received: 30 July 2002, Accepted: 24 December 2002, Published online: 27 May 2003