Passage of a Bubble-Detonation Wave into a Liquid

The passage of a detonation wave from a chemically active bubble media into a chemically inert medium (liquid) is studied experimentally. The structure of the transmitted wave and the wave reflected from the butt-end of a shock tube (post-detonation waves) is investigated, and the pressures of these waves for different liquids are measured. The evolution of the post-detonation waves is traced, their velocities are measured, and the attenuation constants of these waves are determined. The energy-dissipation mechanisms for post-detonation waves in liquids are analyzed qualitatively.     

INTERFACIAL INTERACTIONS AND SECONDARY FLOWS IN STRATIFIED TWO-PHASE FLOW

In this paper are analysed the interactions between a surface wave field and the kinematic structures above and below the waves, in gas-liquid stratified flow in a rectangular cross sectional channel. The analysis is based on experimental data both on the local structure of the flows and on the deformation of the gas-liquid surface. The basic phenomena that have been observed are: on the one hand, the waves that propagates over the liquid surface can exhibit a crosswise distribution of amplitude; on the other hand, secondary flows can be generated both in the gas and in the liquid. A theoretical attempt is developed to explain the distribution to wave amplitude: in fact, the waves propagate over a non uniform liquid current. On the one hand, the wave field interact with the liquid current to generate secondary flows below the waves. On the other hand, the wave amplitude distribution interacts with the gas flow; the wave distribution can be considered as a non uniform interfacial roughness which generates Prandtl second type secondary flows above the waves. These physical mechanisms which are based on the analysis of experimental results are also validated with numerical simulations.     

PS/PMMA共混物中超声波传播特性研究

利用自行设计的装置,采用改变入射角的方法将超声波纵波和横波导入不相容的聚苯乙烯/聚甲基丙烯酸甲酯(PS/PMMA)共混物体系中。研究了两种波的声速和声衰减随共混体系共混比变化的情况,并结合扫描电子显微镜(SEM)检测得到的相畴尺寸进行了分析。结果表明:共混物中的相畴尺寸与其散射衰减之间存在对应关系;由于横波波长更为接近共混体系中的相畴尺寸,横波的散射衰减明显大于纵波。     

Interactions of Impact Shock Waves in a Thin-Walled Explosive Container. I. Impact by a Flat-Ended Projectile

Interaction of impact shock waves that could detonate an explosive (Composition B) confined in a thin-walled container impacted by a cylindrical projectile is numerically studied, based on the Forest Fire explosive reaction rate model. After the impact, rarefaction waves from projectile periphery and front cover–explosive interface catch up the forward-moving shock fronts in the explosive as well as in the projectile. At a high impact velocity, the transmitted shock front induces detonation at the front cover–explosive interface. At an intermediate velocity, the rate of energy release from the shock-compressed volume in the explosive is such that the associated effects prevail over the effects caused by rarefaction waves, leading to detonation after the shock wave travels a certain distance in the explosive. There is a range of minimum impact velocities at which the effect of rarefaction waves prevails over the energy release; hence, the detonation is excited not behind the shock-wave front moving over the explosive but only after shock-wave reflection from the high-impedance back plate. It is suggested that, in interpreting the detonation behavior of an explosive confined by a high-impedance container, one should take into account the effects of shock-wave interaction with container walls.     

Transformation of shock waves at the interface of bubble media

The transition of shock waves from a bubble medium into a liquid or into another bubble medium with different properties is considered experimentally. Data on the structure, velocity, and pressure in the shock wave incident onto the interface, transmitted wave, and reflected wave are obtained. Experimental results are compared with numerical data. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 97–104, March–April, 2006.     

Seismic, Hydroacoustic, and Acoustic Action of Underwater Explosions

Results of a fullscale study of hydroacoustic, seismic, and acoustic effects of an underwater explosion of charges of a chemical high explosive are described. The study had a comprehensive character and included video filming of surface phenomena at the explosion epicenter, registration of hydroacoustic waves in water, seismic waves on the ground, and acoustic waves in air at distances of 0.08–30 km from the explosion epicenter. Parameters of these waves and the character of their decay with distance were obtained, and the wave spectra were analyzed. It is shown that the main specific feature of the wave shapes of hydroacoustic, seismic, and acoustic signals is caused by oscillations of the cavity filled by detonation products, which can be used to identify underwater explosions.     

人工地震采油技术机理研究与分析

人工地震采油技术是利用一定的设备在油层附近产生频率很低的机械波,通过声波的特性在油层发生一系列的波动效应,达到多口井增产增注的一种物理采油方法。它是一种适应低渗透、高含水中后期油田开发的比较理想的物理法采油技术。作者对其作用机理进行了理论分析、归纳和总结,为该技术的进一步深入研究做铺垫。     

Die anodische oxydation des p-Methoxystyrols an der ring-scheibenelektrode in abhängigkeit von der pyridin-konzentration

The chemical reactions following the anodic formation of PMOS monocations in the presence of varying concentrations of pyridine were investigated using the ring-disc electrode. In the absence of pyridine a cathodic proton-wave was observed at the ring. This wave decreased to the same extent as the more cathodic pyridinium wave increased with increasing pyridine content. On further raising the pyridine concentration of the solvent the pyridinium wave at the ring began to disappear. At this point the first anodic PMOS wave at the disc started rising. This means that the reaction between pyridine and the protons formed by monocation decomposition is faster than the reaction between pyridine and radical cations. On further increasing the pyridine content the proton formation becomes slower than the pyridine complexation. 3,4-dimethoxypropenylbenzene behaved similarly and pyridine could be replaced by quinilone. The non-dependence of the height of the waves on rate of rotation showed that all reactions are very fast. The observation that a pyridine content which was less than equimolar sufficed to cause the proton wave to disappear may be shown to be due to the geometry of the ring-disc electrode and follows from an elementary relation for this arrangement.     

THE EFFECT OF VARIOUS PARAMETERS ON THERMOACOUSTIC CONVECTION

Thermoacoustic convection, that is, convection generated in a compressible fluid due to rapid heating of one of the enclosing walls, was studied numerically. Acoustic waves were found to be generated by sinusoidal heating of the wall as well as by a step function. In a finite layer of fluid the pressure wave is reflected back and forth until dissipated by viscosity. The fluctuating velocity generated by the pressure wave greatly enhances the rate of heat transfer over that for pure transient conduction. The same qualitative behavior but widely varying quantitative behavior was computed for different conditions. The simple theory of adiabatic waves, which neglects the diffusion of momentum and energy, accurately predicts the inter-relationship between the various dependent variables but neither the strength of the wave nor the rate of decay. Hence, these two approaches are complementary.     

JHB-1C传爆药高应变率力学行为的实验方法

利用实验测试和数值模拟相结合的手段,对传统SHPB实验方法进行了改进,研究了JHB-1C传爆药高应变率力学行为.采用半导体应变片测试技术记录低阻抗材料微弱的透射信号.通过相对校验技术消除半导体应变片的温度效应.为实现常应变率加载,对几种试样的尺寸进行了数值模拟.结果表明,试样直径为8 mm,厚度为2 mm时更适合于火炸...     

Effects of air voids on ultrasonic wave propagation in early age cement pastes

The objective of this paper is to investigate effects of air voids on ultrasonic wave propagation in fresh cement pastes, and relate ultrasonic wave parameters to cement setting times. First, Biot's theory was used to analyze wave propagation in poroelastic media containing air bubbles. Then, in the experimental study, both the compressional (P) and shear (S) waves were monitored in cement pastes with different water/cement ratios (w/c = 0.4 and 0.5) and various air void content (0.1%–5.3% by cement paste volume). Experimental results indicated that existence of air bubbles in cement paste significantly decreases the P wave velocity, but has little effect on the shear wave propagation. Further analysis shows that the shear wave velocity corresponding to the Vicat initial setting times is a relatively constant value for the investigated air content range. This study shows the potential of using shear waves to monitor setting and hardening process of cement.     

THE EFFECT OF VARIOUS PARAMETERS ON THERMOACOUSTIC CONVECTION

Thermoacoustic convection, that is, convection generated in a compressible fluid due to rapid heating of one of the enclosing walls, was studied numerically. Acoustic waves were found to be generated by sinusoidal heating of the wall as well as by a step function. In a finite layer of fluid the pressure wave is reflected back and forth until dissipated by viscosity. The fluctuating velocity generated by the pressure wave greatly enhances the rate of heat transfer over that for pure transient conduction. The same qualitative behavior but widely varying quantitative behavior was computed for different conditions. The simple theory of adiabatic waves, which neglects the diffusion of momentum and energy, accurately predicts the inter-relationship between the various dependent variables but neither the strength of the wave nor the rate of decay. Hence, these two approaches are complementary.     

Experimental Investigation and Numerical Simulation of an Expanding Multifront Detonation Wave

Results of experimental investigations of an expanding multifront detonation wave are presented. Two stages of spontaneous formation of new disturbances and transverse waves on the expanding detonationwave front are observed. The main mechanisms of reinitiation of detonation waves are discussed. Twodimensional numerical simulation of the dynamics of a multifront detonation wave in a linearly expanding channel is performed. The effect of spontaneous formation of new disturbances and new transverse waves is confirmed by computations, and the main mechanism of multiplication of transverse waves is the instability of detonationwavefront elements at the stage they cease to be in the overdriven state and are attenuated during expansion.     

应用二维黏性CE/SE方法模拟挡波墙对爆炸流场的影响

应用高精度的二维黏性CE/SE方法模拟爆点周围有挡波墙的爆炸流场,分析了挡波墙与冲击波相互作用的规律,得到了能够反映波系结构变化的压力等值线图.数值计算结果显示了冲击波遇挡波墙发生反射、绕流等现象;通过与无挡波墙时的爆炸流场对比,分析了挡波墙的削波作用;同时考察了挡波墙的高度、厚度对远场压力的影响.数值计算结果对于爆炸流场的防护具有理论指导意义.     

Numerical simulation on wave behaviour and flow dynamics of laminar‐wavy falling films: Effect of surface tension and viscosity

Numerical simulation has been made on wave behaviour and flow dynamics of falling films of aqueous lithium bromide solution along a vertical wall in the present study. Volume of fluid model is used to track the free surfaces and continuum surface force model is used for dynamic boundary conditions considering the effect of surface tension. A small amplitude forcing perturbation is introduced at the inlet of the flow boundary. Effect of surface tension and viscosity on wave behaviour and flow dynamics has been investigated. The simulation results indicate that wave peak height decreases with increasing surface tension and the number of capillary waves in front of a large wave increases. With the decrease of viscosity wave shape changes from the sinusoidal shape to the solitary one. Furthermore, the flow dynamics underneath the typical waves are analysed, especially the pattern of backflow. © 2011 Canadian Society for Chemical Engineering     

Measurement of alkali-silica reaction progression by ultrasonic waves attenuation

Development of non-destructive methods, developed specifically for assessing the damage induced by alkali-silica reaction (ASR) in concrete structures, is needed in order to carry out a systematic evaluation of the concrete condition. The aim of this study is to monitor the evolution of the ASR-damage in laboratory with concrete samples with ultrasonic pulse velocity and attenuation of ultrasonic waves methods. For this study, results of both methods were compared with expansion and mass variation.One reactive concrete mixture was made with reactive aggregate, and one other mixture, incorporating non-reactive aggregate, was made as a control. Specimens were kept at 38 °C in a 1 mol l^− 1 NaOH solution to accelerate the reaction. Attenuation of transmitted ultrasonic waves appeared to be more appropriate for the evaluation of ASR-damage compared with pulse velocity. The attenuation of accelerated reactive concrete cylinders increased by 90% after 1 year while it increased by 40% for the non-reactive concrete used as a control. Major part of the attenuation increase in the non-reactive concrete is due to liquid absorption.This work suggests that in-situ non-destructive techniques based on ultrasonic wave attenuation, like ultrasonic attenuation tomography, should be developed in order to evaluate the development of ASR in concrete structures. Petrographic examination confirmed that damage to concrete is associated with ASR.     

Transition between stratified and non-stratified horizontal oil-water flows. Part I: Stability analysis

The characteristics of waves at the interface of oil-water stratified flow and at the onset of entrainment, where drops of one phase appear into the other, were studied. Theoretically a model was developed based on Kelvin-Helmholtz instability to predict the critical wave amplitude at which the waves become unstable for a specific wavelength. According to the model, waves become unstable in stratified flow when at a particular wavelength they exceed a critical amplitude, which decreases with increasing wavelength until it acquires an almost constant value. The model predictions showed that for low-viscosity oils the maximum critical amplitude appears at slip velocity close to zero, while for high-viscosity oils, the maximum amplitude appears for water velocity higher than that of the oil. Also the required entrainment wavelength over the pipe diameter, calculated using literature experimental onset conditions, was found to decrease as the viscosity of the oil increased. Experimentally, wave characteristics before and at the onset of entrainment were investigated by measuring the instantaneous fluctuations of the interface between oil (5.5 mPa s, ) and water in a 0.038 m ID stainless steel horizontal pipe using a conductivity probe. The formation of drops and the onset of entrainment were identified using a high-speed video camera. At the onset of entrainment, wave characteristics were above the stability lines predicted by the model. Using a semi-empirical characteristic amplitude and wavelength in the model, it was possible to predict the onset of entrainment and transition from stratified to other mixed flow patterns reported in a number of studies.     

Determination of volumetric water content of concrete using ground-penetrating radar

A large number of reinforced or prestressed concrete pathologies require the presence of water to develop. In this context, the quantification of water content is an important phase for the diagnosis of concrete. The propagation of electromagnetic waves is controlled by its electromagnetic properties, mainly influenced by the presence of water in the case of concrete. We propose to use the direct transmitter-receiver radar wave to determine the moisture of the cover concrete. The Wide Angle Reflection Refraction (WARR) measurement technique is used to obtain the speed of the direct wave. A method is used to extract the group and the phase velocity of this wave. We show that the speed is not dependent to the frequency between 300 MHz and 1.2 GHz in these testing conditions. By using two different concretes partially saturated, we show that there is a linear relation, independent of the concrete, between the volume water content and the propagation velocity of the direct wave on the one hand and its attenuation on the other hand.     

Shock-induced conductivity waves in a conductor placed in an external magnetic field

Electromagnetic processes in a shock-compressed conductor placed in an external magnetic field are analyzed. The motion of the shock wave results in the appearance of two countercurrents that flow ahead of the shock front in the uncompressed-material region and near the back boundary of the conductor, respectively. The observed electromagnetic pattern is due to current diffusion and convective transfer in the conductor. When the shock wave arrives at the conductor, the absolute value of the currents grows tending (in the case of a considerable sample thickness) to a constant determined by the condition of magnetic-field trapping by the material. In this case, the electromagnetic pattern is characterized by two space-separated current waves: a stationary steady wave moving along the uncompressed material with phase velocity and a nonstationary diffusion wave which originates at the back boundary of the conductor. Voltage recordings at one of the sample surfaces can be used to determine the material parameters in a compressed state.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 6, pp. 116–122, November–December, 1996.     

TNT — Equivalent

For engineering purposes, the effects of blast waves on various target structures can be estimated quite easily with the aid of TNT-equivalence. On the one hand, many experimental data are available on the blast damage done to structures, and on the other hand, the energy content of any source can be expressed in terms of an equivalent mass of TNT. The parameters involved in the propagation of a blast wave and in its interaction with target structures are discussed at some length in order to point out the inherent inaccuracies as well as the limits of applicability of the TNT-equivalence method.