This study explored the practicality of a two-phase flow model for water droplets in elucidating the blast mitigation mechanism of water droplets. To validate the model, the numerical data were compared with previous experimental results in terms of the evaporation of a single water droplet, and the interaction between the shock/blast waves and water droplets. Results of the validation confirmed good agreement and consistency between both data by combining the existing models for droplet breakup. Next, the blast-mitigation effect of water droplets sprayed around a high explosive was investigated, where the main parameter was the layer radius. A thicker layer further mitigated the blast wave, but there was a limit to the blast-mitigation effect when the layer radius was greater than a critical value. The high-temperature and high-pressure detonation products should interact with the water droplets, which absorb their momentum and energy. The critical layer radius was equivalent to the dispersion distance of the detonation products. To quantitatively understand the blast-mitigation mechanism of water droplets, the transferred energies by drag force, convective heat transfer, radiative heat transfer, and evaporation were computed. A strong correlation between the blast wave strength and the sum of transferred energies by the drag force and convective heat transfer was obtained in the case that the initial diameter of the water droplets was of the order of millimeters.

The collapse of a cavitation bubble is always associated with the radiation of intense shock waves, which are highly relevant in a variety of applications. To radiate a strong shock wave, it is necessary to converge energy at the collapse, and understanding generation processes of multiple shock waves at the collapse is a key issue. In the present study, we investigated the formation of multiple shock waves generated by the collapse of a laser-induced bubble. We used a high-speed imaging system with unprecedented spatiotemporal resolution. We developed a triggering procedure of high precision and reproducibility based on the deflection of a laser beam by the shockwave passage. The high-speed videos clearly show that: (A) a first shockwave is emitted as the micro-jet hits the bottom of the bubble interface, followed by a second shock wave due to the collapse of the remaining toroidal bubble; (B) a sequential collapse of elongated bubbles, where the top part of the bubble collapses slightly before the bottom of the bubble; and (C) the formation of compression shock waves from multiple sites on a toroidal bubble.

<title>Abstract</title>This paper reports the experiments on the shock standoff distance (SSD) around spheres flying at Mach numbers from slightly below 1.0. Spheres of the same diameter but three different densities were launched in a ballistic range by a light-gas gun, and the flow field around each sphere was measured by optical visualization. The purpose of this study is to investigate how projectile deceleration influences the SSD by comparing the results for projectiles of the same shape, size, and Mach number but different densities. The location history of the sphere center is obtained by fitting a formula derived from the equation of motion of a decelerating object, and the history of the instantaneous projectile Mach number is obtained by differentiating this formula.The SSDs of the projectiles with different densities are the same at higher Mach numbers, but different at lower Mach numbers, and the SSD decreases with decreasing projectile density. Seemingly, because projectile deceleration is related to the flow unsteadiness, steady flow cannot be assumed in the present range of Mach number with the different SSDs. At Mach numbers close to one, that of the propagating detached shock wave is higher than that of the flying projectile.

In the present study, the visualization of compressible flow around a particle/particles including wake vortices and drag estimation were conducted through shock-particle interaction experiments. An experimental method that can investigate flow over isolated and clustered particle(s) (with a minimum diameter of 0.3 mm) interacting with a planar shock was established. For flow visualization, the Mach number (M) and Reynolds number (Re) based on the relative velocity between the particle and the quantities behind the planar shock wave were 0.46 ¯ M ¯ 1.24 and 3500 ¯ Re ¯ 9800, respectively. The present measurement system succeeded in visualizing flow structures not only for shock waves, but also wake structures formed behind the particle(s) under subsonic and transonic conditions, and the Mach number effect was provided. The mean drag coefficient was estimated from the time-position data of the particle at 3100 ¯ Re ¯ 9800 and M = 0.46. The estimated drag coefficient was close to that of the value estimated by the drag model and previous experiments. The flowfield around clustered particles was visualized and its breakdown process was observed. The particle cluster dispersed due to aerodynamic interference. Particularly, the particles located on the upper side of the particle cluster moved upward against the gravitational force.

Three-dimensional density measurement of unsteady flow field around a projectile (phi = 8mm) is carried out in the ballistic range at Institute of Fluid Science, Tohoku University. The purpose of this study is to obtain the density distribution including its wake region in non-axisymmetric unsteady flow. The projectile's Mach number in the experiment is 1.35. Simultaneous multi-angle BOS measurement system using twelve digital cameras and pulsed LEDs is installed in the test chamber of the ballistic range. The Color-Grid Background Oriented Schlieren (CGBOS) technique is used in the measurement system to obtain the projection data of density gradient. Algebraic Reconstruction Technique (ART) method and Successive Over Relaxation (SOR) method are used to obtain the density distribution from projection data. To improve the accuracy of 3D reconstruction, we evaluate the view-angle of the measurement system in the present study. The result shows that the bow shock, expansion wave and recirculation zone can be confirmed by the proposed method. However, bow shock in each method are thicker than the schlieren image due to the blur of the CGBOS images. Even then, the 3D shape of density distribution reconstructed by proposed method can be reliable, and the relative error of obtained density between the theoretical value for normal shock relation is about 5% at the bow shock.

An experimental investigation was conducted to compare the blast mitigation performances of water layers, whose mass ratios to an explosive were mW/mE=12.2,44.5,and107.2, with water droplets surrounding the explosive. The blast waveforms were measured using pressure transducers, and the motion of the water layer was recorded using a high-speed camera. When m /m was equivalent between the water layer and water droplets, the water layer exhibited less mitigation of the peak overpressure and positive impulse than the water droplets. The results demonstrated high efficiency of the water droplets in blast mitigation and the existence of an optimal apparent density of the water barrier. The velocities of the water layers determined using high-speed photography agreed with the prediction model of the barrier material accelerated by explosion. It suggested that the primary cause of the blast overpressure mitigation by the water layer was the allocation of the explosion energy into the kinetic energy of the water. W E

In this study, free-flight tests of a sphere for Reynolds numbers between 3.9 × 103 and 3.8 × 105 and free-flight Mach numbers between 0.9 and 1.6 were conducted using a ballistic range, and compressible low-Reynolds-number flows over an isolated sphere were investigated with the schlieren technique. The flow visualization was carried out under low-pressure conditions with a small sphere (minimum diameter of 1.5 mm) to produce compressible low-Reynolds-number flow. Also, time-averaged images of the flow near the sphere were obtained and compared to previous numerical results for Reynolds numbers between 50 and 1000. The experimental results clarified the structure of shock waves, recirculation region, and wake structures at the Reynolds number of 103–105 under transonic and supersonic flows. As a result, the following characteristics were clarified: (1) the amplitude of the wake oscillation was attenuated as the free-flight Mach number increased; (2) use of singular value decomposition permitted extraction of the mode of the wake structure even when schlieren images were unclear due to severe condition, and different modes in the wake structure were identified; (3) the Reynolds number had little effect on the separation point, but the length of the recirculation region increased as the Reynolds number decreased; and (4) the wake diameter at the end of the recirculation region decreased as the Mach number increased.

爆風損傷は爆発に伴い発生する爆風に暴露され生じる．一般の臨床医が経験する外傷機転に加えて，穿通物による機序，衝撃波を伴う圧損傷による機序が複合的に生体に影響を及ぼし，損傷が発生する．外傷初期診療ガイドラインに沿った対応を行うとともに，損傷時の状況の把握を含めて衝撃波を伴う圧損傷のリスク階層化と病態を考慮した治療を行う．通常の外傷とは異なる点があり，外科的あるいは脳血管内治療に際しては特徴を理解しておく必要がある． 2020年東京オリンピック，パラリンピックを迎えるにあたり，わが国においても救急に携わる医療従事者，関係者も病態と診断・治療に関する一定の知識を持っていることが望ましい．本稿では，爆風損傷の機序，病態生理も含めた特徴，爆風による傷病者への初期対応を含めた診断，治療について概説する．衝撃波工学の見地から衝撃波，爆風の生体に及ぼす作用，爆風による外傷性脳損傷の発生機序，現在の爆風による外傷性脳損傷研究の問題点についても概説する．

The objective of this study is to investigate thermochemical processes in the shock layer by shock-tube experiments. In this study, the temporal profile of radiation intensity is observed by time-resolved emission spectroscopy. The measured radiation profiles are compared with the calculated radiation profiles to validate the chemical reaction processes considered in the calculation. The measured radiation profiles are different from the calculated ones, especially in the region ahead of the shock front. The measured radiation intensities for N2, N2 +, and N start to increase ahead of the shock front. On the other hand, the calculated radiation intensities start to increase at the shock front. This difference could be caused by precursor phenomena which are not considered in the present calculation. The details of precursor phenomena has not been clarified. However, the present study has indicated some of the interesting results. From the radiation profiles observed in the region ahead of shock front, electronic excitation of N2, photoionization and photodissociation of N2 are found to occur. It is also found that the radiation profiles between experiment and calculation differ in the shock layer, showing that precursor phenomena have a great influence on thermochemical processes in the shock layer. In future, thermochemical processes should be modeled by incorporating precursor phenomena.

Traumatic injury caused by explosive or blast events is traditionally divided into four mechanisms: primary, secondary, tertiary, and quaternary blast injury. The mechanisms of blast-induced traumatic brain injury (bTBI) are biomechanically distinct and can be modeled in both in vivo and in vitro systems. The primary bTBI injury mechanism is associated with the response of brain tissue to the initial blast wave. Among the four mechanisms of bTBI, there is a remarkable lack of information regarding the mechanism of primary bTBI. On the other hand, 30 years of research on the medical application of shock waves (SWs) has given us insight into the mechanisms of tissue and cellular damage in bTBI, including both air-mediated and underwater SW sources. From a basic physics perspective, the typical blast wave consists of a lead SW followed by shock-accelerated flow. The resultant tissue injury includes several features observed in primary bTBI, such as hemorrhage, edema, pseudo-aneurysm formation, vasoconstriction, and induction of apoptosis. These are well-described pathological findings within the SW literature. Acoustic impedance mismatch, penetration of tissue by shock/bubble interaction, geometry of the skull, shear stress, tensile stress, and subsequent cavitation formation are all important factors in determining the extent of SW-induced tissue and cellular injury. In addition, neuropsychiatric aspects of blast events need to be taken into account, as evidenced by reports of comorbidity and of some similar symptoms between physical injury resulting in bTBI and the psychiatric sequelae of post-traumatic stress. Research into blast injury biophysics is important to elucidate specific pathophysiologic mechanisms of blast injury, which enable accurate differential diagnosis, as well as development of effective treatments. Herein we describe the requirements for an adequate experimental setup when investigating blast-induced tissue and cellular injury; review SW physics, research, and the importance of engineering validation (visualization/pressure measurement/numerical simulation); and, based upon our findings of SW-induced injury, discuss the potential underlying mechanisms of primary bTBI.

An experimental demonstration was carried out in a ballistic range at high Mach numbers with the low specific heat ratio gas hydrofluorocarbon HFC-134a to observe the unstable bow-shock wave generated in front of supersonic blunt objects. The shadowgraph images obtained from the experiments showed instability characteristics, in which the disturbances grow and flow downstream and the wake flow appears wavy because of the shock oscillation. Moreover, the influence of the body shape and specific heat ratio on the instability was investigated for various experimental conditions. Furthermore, the observed features, such as wave structure and disturbance amplitude, were captured by numerical simulations, and it was demonstrated that computational fluid dynamics could effectively simulate the physical instability. In addition, it was deduced that the shock instability is induced by sound emissions from the edge of the object. This inference supports the dependence of the instability on the specific heat ratio and Mach number because the shock stand-off distance is affected by these parameters and limits the sound wave propagation.

This paper reports a preliminarily experimental result of high-speed shadowgraph optical visualization of underwater expansion wave focusing by using a simple two-dimensional wedge model for understanding of shock wave interaction phenomena in simulated biomedical materials. Underwater shock wave generated by detonating a micro-explosive (10 mg silver azide pellet) in a small chamber. The generated underwater shock wave was interacted with a wedge shaped interface between water and air divided by a thin film, and an expansion wave was generated by reflection at the interface. The process of underwater expansion wave generation and focusing phenomena was visualized by shadowgraph method and recorded by ultra-high-speed framing camera. Underwater shock wave was reflected as an expansion wave from the interface between water and air at the both side and focused and then cavitation bubble was created by pressure decreasing at the expansion wave focusing area. The pressure histories were measured simultaneously with highspeed optical visualization by a needle type pressure sensor. At the focusing area, the pressure was decreased rapidly, the negative peak pressure was the lowest.

The high-speed liquid (water) jet has distinctive characteristics in surgical applications, such as tissue dissection without thermal damage and small blood vessel preservation, that make it advantageous over more conventional instruments. The continuous pressurized jet has been used since the first medical application of water jets to liver surgery in the 1980s, but exhibited drawbacks partly related to the excess water supply required and unsuitability for application to microsurgical instruments intended for deep, narrow lesions (endoscopic instrumentation and catheters) due to limitations in miniaturization of the device. To solve these issues, we initiated work on the pulsed micro-liquid jet. The idea of the pulsed micro-liquid jet originated from the observation of tissue damage by shock/bubble interactions during extracorporeal shock wave lithotripsy and evolved into experimental application for recanalization of cerebral embolisms in the 1990s. The original method of generating the liquid jet was based on air bubble formation and microexplosives as the shock wave source, and as such could not be applied clinically. The air bubble was replaced by a holmium:yttrium-aluminum-garnet (Ho:YAG) laser-induced bubble. Finally, the system was simplified and the liquid jet was generated via irradiation from the Ho:YAG laser within a liquid-filled tubular structure. A series of investigations revealed that this pulsed laser-induced liquid jet (LILJ) system has equivalent dissection and blood vessel preservation characteristics, but the amount of liquid usage has been reduced to less than 2 l per shot and can easily be incorporated into microsurgical, endoscopic, and catheter devices. As a first step in human clinical studies, we have applied the LILJ system for the treatment of skull base tumors through the transsphenoidal approach in 9 patients (7 pituitary adenomas and 2 chordomas), supratentorial glioma (all high grade glioma) in 8 patients, including one with fine perforating vessel involvement, and cerebrovascular disease (1 arteriovenous malformation and 2 intracerebral hemorrhages) in 3 patients. Precise dissection and mass reduction of the tumor were obtained in all tumor cases except for one chordoma with significant fibrosis. Small arteries down to 100 were preserved, allowing subsequent microsurgical devascularization. Veins were also preserved occasionally. The arachnoid membrane and the tumor capsule were resistant to the LILJ except for one case with prolonged exposure. No complications related to use of the LILJ system were observed. No disturbance of the surgical field by splashing, aerosol, or dissemination of pathological tissue occurred with placement of the optimal suction system. The Ho:YAG LILJ system enhances the advantages of commercialized pressure-driven continuous liquid jet instrumentation in terms of small vessel preservation and accessibility in confined spaces for minimally invasive neurosurgery, and solves some of the drawbacks involved with excessive liquid use and size.

A sonic boom signature with a long rise time has the ability to reduce the sonic boom, but it does not necessarily minimize the sonic boom at the ground level because of the real atmospheric turbulence. In this study, an effect of the turbulence on a long rise-time pressure signature was experimentally investigated in a ballistic range facility. To compare the effects of the turbulence on the long and short rise-time pressure signatures, a cone-cylinder projectile that simultaneously produces these pressure signatures was designed. The pressure waves interacted with a turbulent field generated by a circular nozzle. The turbulence effects were evaluated using flow diagnostic techniques: high-speed schlieren photography, a point-diffraction interferometer, and a pressure measurement. In spite of the fact that the long and short rise-time pressure signatures simultaneously travel through the turbulent field, the turbulence effects do not give the same contribution to these overpressures. Regarding the long rise-time pressure signature, the overpressure fluctuation due to the turbulence interaction is almost uniform, and a standard deviation 1.5 times greater than that of the no-turbulence case is observed. By contrast, a short rise-time pressure signature which passed through the same turbulent field is strongly affected by the turbulence. A standard deviation increases by a factor of 14 because of the turbulence interaction. Additionally, there is a non-correlation between the overpressure fluctuations of the long and short rise-time pressure signatures. These results deduce that the length of the rise time is important to the turbulence effects such as the shock focusing/diffracting. (C) 2016 Elsevier Ltd. All rights reserved.

This paper reports a result of experiments for the determination of reliable shock Hugoniot curves of liquids, in particular, at relatively low pressure region, which are needed to perform precise numerical simulations of shock wave/tissue interaction prior to the development of shock wave related therapeutic devices. Underwater shock waves were generated by explosions of laser ignited 10 mg silver azide pellets, which were temporally and spatially well controlled. Measuring temporal variation of shock velocities and over-pressures in caster oil, aqueous solutions of sodium chloride, sucrose and gelatin with various concentrations, we succeeded to determine shock Hugoniot curves of these liquids and hence parameters describing Tait type equations of state.

This paper reports consideration of the transmission laser energy estimating method for an efficient underwater processing with support form a CO2 laser-induced bubble column. To calculate the transmission laser energy through the laser induced bubble column in water, the experiment of pulsed CO2 laser-induced bubble column formation visualization and laser energy measurement though the CO2 laser-induced bubble column in water was performed. The process of the CO2 laser-induced bubble generation was observed by high-speed video camera. Pulsed 50W CO2 laser beam of 10.6 μm in wavelength was irradiated onto the water surface, and then bubble is generated near the water surface. With further transmission of laser beams through the growing the bubble, local vaporization was continued and the bubble length was elongated. The transmitted energy though the bubble column was estimated by time rate of bubble growth time and was corrected for absorption loss and reflectance loss, and compared with the measured transmitted energy by power meter.

Purpose Primary blast-induced traumatic brain injury (bTBI) is the least understood of the four phases of blast injury. Distant injury induced by the blast wave, on the opposite side from the wave entry, is not well understood. This study investigated the mechanism of distant injury in bTBI. Materials and Methods Eight 8-week-old male Sprague-Dawley rats were divided into two groups: group 1 served as the control group and did not receive any shock wave (SW) exposure; group 2 was exposed to SWs (12.5 +/- 2.5 MPa). Propagation of SWs within a brain phantom was evaluated by visualization, pressure measurement, and numerical simulation. Results Intracerebral hemorrhage near the ignition site and elongation of the distant nucleus were observed, despite no apparent damage between the two locations in the animal experiment. Visualization, pressure measurement, and numerical simulation indicated the presence of complex wave dynamics accompanying a sudden increase in pressure, followed by negative pressure in the phantom experiment. Conclusion A local increase in pressure above the threshold caused by interference of reflection and rarefaction waves in the vicinity of the brain-skull surface may cause distant injury in bTBI.

Bow-shock instability has been experimentally observed in a low-gamma flow. To clarify its mechanism, a parametric study was conducted with three-dimensional numerical simulations for specific heat ratio gamma and Mach number M. A critical boundary of the instability was found in the gamma-M parametric space. The bow shock tends to be unstable with low gamma and high M, and the experimental demonstration was designed based on this result. The experiments were conducted with the ballistic range of the single-stage powder gun mode using HFC-134a of gamma = 1.12 at Mach 9.6. Because the deformation of the shock front was observed in a shadowgraph image, the numerical prediction was validated to some extent. The theoretical estimation of vortex formation in a curved shock wave indicates that the generated vorticity is proportional to the density ratio across the shock front and that the critical density ratio can be predicted as similar to 10. A strong slipstream from the surface edge generates noticeable acoustic waves because it can be deviated by the upstream flow. The acoustic waves emitted by synchronizing the vortex formation can propagate upstream and may trigger bow-shock instability. This effect should be emphasized in terms of unstable shock formation around an edged flat body. (C) 2015 AIP Publishing LLC.

In this study, experiments were conducted to evaluate the accuracy of the pressure measurement system in a ballistic range at Tohoku University. An effect on the near-field pressure waveform by shock wave interaction with a pressure measurement plate instrumented with pressure transducers was investigated. The pressure waveform changed depending on the measurement positions on the plate. It is important to place pressure measurement positions away from the front and rear edges of the plate. In addition, pressure measurement accuracy was validated by comparison of the pressure waveforms between present and previous results. The pressure was measured at a position away from the edges of the plate. The present data corresponds well with existing experimental data. The results show that the pressure measurement system in the ballistic range at Tohoku University has the ability to accurately measure the near-field pressure waveform. (C) 2015 Elsevier Ltd. All rights reserved.

In this study, we tried to conduct time-resolved PSP imaging of sonic-boom phenomena using a high-speed video camera. For this purpose, we visualized sonic-boom passing through a test plate mounted on the inside of the ballistic range by using ultrafast-response PSP and shadowgraph method simultaneously. By combining PSP technique and shadowgraph method, we successfully estimated pitch and yaw angle of free-flight projectile simultaneously. In addition, time-resolved PSP imaging of near-field sonic-boom phenomena using a high-speed video camera was also conducted and flow field was clearly visualized. These visualization results were well agreement compared with pressure profile which was measured by unsteady pressure sensors qualitatively. This means that the qualitative observation of near-field sonic-boom by using PSP technique is available in ballistic experiments.

This paper reports the results of experiments on underwater shock wave propagation and reflection at the interface of certain materials conducted to improve the understanding of shock wave interaction with the interface of materials with different acoustic impedance. An underwater shock wave was generated by detonating a micro-explosive (AgN3) near the interface of materials with different acoustic impedance (water and acrylic/aluminum/stainless steel/air). The process of shock wave propagation was visualized by the shadowgraph method and recorded by an ultra-high-speed camera The pressure history near the interface was measured simultaneously by a needle hydrophone with high spatiotemporal resolution. Time-resolved shadowgraph images show that a compression wave was reflected from a thin interface plate, and an expansion wave, which propagated downward, was then generated in water by reflection from the air. In addition, a cavitation bubble was created behind the expansion wave. The simultaneously measured pressure history also shows that an expansion wave propagated behind the compression wave.

The aim of this study was to clarify the initiation process and the propagation mechanism of positive underwater streamers under the application of pulsed voltage with a duration of 10 mu s, focusing on two different theories of electrical discharges in liquids: the bubble theory and the direct ionization theory. The initiation process, which is the time lag from the beginning of voltage application to streamer inception, was found to be related to the bubble theory. In this process, Joule heating resulted in the formation of a bubble cluster at the tip of a needle electrode. Streamer inception was observed from the tip of a protrusion on the surface of this bubble cluster, which acted as a virtual sharp electrode to enhance the local electric field to a level greater than 10 MV/cm. Streak imaging of secondary streamer propagation showed that luminescence preceded gas channel generation, suggesting a mechanism of direct ionization in water. Streak imaging of primary streamer propagation revealed intermittent propagation, synchronized with repetitive pulsed currents. Shadowgraph imaging of streamers synchronized with the light emission signal indicated the possibility of direct ionization in water for primary streamer propagation as well as for secondary streamer propagation. (C) 2014 AIP Publishing LLC.

A series of images of a generation process of an underwater secondary streamer from a developed primary streamer was visualized by an ultrahigh-speed camera with a microscope lens. The secondary streamer with a filamentary structure propagated with an average velocity of 30 km/s from one of the channel tips of the semispherical primary streamer with an average propagation velocity of 1.8 km/s. The synchronized current waveform showed that pulsed currents of about 100 mA were changed into a continuous current of about 300 mA when the secondary streamer started to propagate. This experiment was carried out by the application of a single-shot pulsed positive voltage to a needle-to-wire electrode system with a gap length of 6 mm.

An underwater secondary streamer for a single-shot pulsed positive voltage was found to propagate with an average velocity of 18 km/s during the appearance of a continuous component on the discharge current waveform. The continuous component was the first discharge current with a direct-current-like component detected after a displacement current. However, the propagation velocity decreased to less than 2 km/s during the appearance of pulsed currents, which followed the continuous component. These results were analyzed by highly spatiotemporal visualization synchronized with the discharge current. Copyright (C) EPLA, 2014

This paper reports establishment of the simultaneous measurement of the flight attitude and flow field visualization for the near-field pressure measurement experiments in a ballistic range. To measure the flight attitude and flow field visualization for a spherical projectile, the simultaneous visualization method, which is combination of the shadowgraph method and the direct photography, was utilized. It is possible to visualize both the flow field around the projectile and the projectile surface. The angles of pitch, roll and yaw can be calculated from the displacement of line markings on the projectile surface. The image of the projectile by the direct photography is distorted because of the aberration of the optical arrangement, the camera lens and the non-uniform thickness of acrylic windows. Image distortion was calibrated by taking images on actual set-up, so that the accuracy of the angles was improved. In addition, the diffuse reflection light from the projectile surface was confirmed not to influence the flow field visualization. This method is useful for the near-field pressure measurement experiments in a ballistic range. The flight attitude affects the near-field pressure value strongly. Since the near-field pressure with a detailed flight attitude is obtained, its influences can be evaluated using the method which has ability of the flight attitude measurement. In addition, a shock interaction around a projectile can be captured.

Currently, further clarification of pre-breakdown phenomena in water such as propagation mechanisms of primary and secondary streamers are needed because applications of aqueous plasma to environmental and medical treatments are increasing. In this study, a series of primary streamer propagations in ultrapure water was visualized at 100-Mega frames per second (100 Mfps) in the range of 400 mu m square using an ultra high-speed camera with a microscope lens when a single-shot pulsed positive voltage was applied to a needle electrode placed in a quartz cell. Every observation was synchronized with the waveforms of the applied voltage and the discharge current. The primary streamer, having many filamentary channels, started to propagate semi-spherically with a velocity of about 2 km/s when the pulsed currents occurred. Although most filamentary channels disappeared 400 ns after the beginning of the primary streamer, a few of them continued propagating with almost the same velocity (about 2 km/s) as long as the repetitive pulsed currents flowed. Shock waves were iteratively generated and streamer channels were formed while the repetitive pulsed currents were flowing. Thus, we concluded that the positive primary streamer in water propagates progressively with each repetitive pulsed current. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4795765]

This paper reports the summary of experiments performed to successive generate small-scale underwater shock waves by means of shock-induced collapse of microbubbles confined in a narrow gap. The project is motivated to develop a method for efficient inactivation of marine bacteria contained in ship ballast water by high impulsive pressure loading. The shock wave-air bubbles interaction was visualized by shadowgraph; the images were recorded by ImaCon200, and simultaneous pressure measurements were performed by using an optical fiber pressure transducer with higher temporal resolution. Attaching small air bubbles on a single nylon fiber and placing it in a confined space, we demonstrated sequential generation of impulsive high pressures at the successive collapses of small bubbles at incident and reflected shock loadings. The values of the very short impulsive pressures that occurred repeatedly for a relatively long term are found high enough to inactivate marine bacteria.

At the event of the atomic bomb dropped in Hiroshima, Danbara district which is located behind Mount Hiji approximately 2.3 km distant from the center of explosion, suffered less damages than surrounding districts. This phenomenon is expressed by the word called as "shade of Mount Hiji" in Hiroshima. In this research, a basic experiment to verify the topographic effects of Mount Hiji on the shock wave of the atomic bomb was carried out. In this basic experiment, by using the shadowgraph method, behaviors of the shock wave passing a topographical model of isosceles triangle and Mount Hiji model. Pressure measurement behind the model was also conducted in the experiment. As a result of the experiment, basic information on the phenomenon in which the shock wave was shielded by Mount Hiji and did not reach much to Danbara district was obtained.

Traumatic brain injury caused by explosive or blast events is traditionally divided into four phases: primary, secondary, tertiary, and quaternary blast injury. These phases of blast-induced traumatic brain injury (bTBI) are biomechanically distinct and can be modeled in both in vivo and in vitro systems. The primary bTBI injury phase represents the response of brain tissue to the initial blast wave. Among the four phases of bTBI, there is a remarkable paucity of information about the cause of primary bTBI. On the other hand, 30 years of research on the medical application of shockwaves (SW) has given us insight into the mechanisms of tissue and cellular damage in bTBI, including both air-mediated and underwater SW sources. From a basic physics perspective, the typical blast wave consists of a lead SW followed by supersonic flow. The resultant tissue injury includes several features observed in bTBI, such as hemorrhage, edema, pseudoaneurysm formation, vasoconstriction, and induction of apoptosis. These are well-described pathological findings within the SW literature. Acoustic impedance mismatch, penetration of tissue by shock/bubble interaction, geometry of the skull, shear stress, tensile stress, and subsequent cavitation formation, are all important factors in determining the extent of SW-induced tissue and cellular injury. Herein we describe the requirements for the adequate experimental set-up when investigating blast-induced tissue and cellular injury; review SW physics, research, and the importance of engineering validation (visualization/pressure measurement/numerical simulation); and, based upon our findings of SW-induced injury, discuss the potential underlying mechanisms of primary bTBI.

This paper reports the result of a primary experimental and analytical study used to explore a reliable technology that is potentially applicable to the inactivation of micro-creatures contained in ship ballast water. A shock wave generated by the micro-explosion of a 10mg silver azide pellet in a 10mm wide parallel test section was used to interact with a bubble cloud consisting of bubbles with average diameter 10µm produced by a swirling flow type micro-bubble generator. Observations were carried out with a high-speed camera, IMACON200, and the corresponding rebound pressures of the collapsing bubbles were measured with a fiber optic probe pressure transducer that provides high spatial and temporal resolutions. We found that micro-bubbles collapse in several hundred nanoseconds after the shock exposure and the resulting peak pressure pulses that repeatedly occurred exceeded well over 200MPa measured at the 20mm distance from the explosion center. These continued for well over 20µs. The experimental pressure responses were explained by solving the one-dimensional bubble Rayleigh-Plesset equation. Such high peak pressures could be used effectively for the inactivation of micro-creatures contained in ship ballast water.

This paper is primarily an assessment of laser-induced water jets for boring rock surfaces. It also reports the result of preliminary experiments of pulsed Ho:YAG laser-induced jets applied to drill a submerged rock specimen. The irradiation of pulsed Ho:YAG laser beams at 3 Hz inside a thin metal tube produces intermittent water vapor bubbles which result in liquid jet discharge from the exit of the metal tube. The laser-induced water jets are visualized by shadowgraphs and images are recorded by a high-speed digital video camera. High stagnation pressures were eventually generated by the jet impingements. Simultaneously shock waves of about 22.7 MPa were generated at bubble collapse, which effectively cracked the surface of the rock specimens. Repeated exposures of these laser-induced jets against submerged rock specimens have a potential to practically bore holes on rock surfaces.

The pattern of shock wave reflection over a wedge is, in general, either a regular reflection or a Mach reflection, depending on wedge angles, shock wave Mach numbers, and specific heat ratios of gases. However, regular and Mach reflections can coexist, in particular, over a three-dimensional wedge surface, whose inclination angles locally vary normal to the direction of shock propagation. This paper reports a result of diffuse double exposure holographic interferometric observations of shock wave reflections over a skewed wedge surface placed in a 100 x 180 mm shock tube. The wedge consists of a straight generating line whose local inclination angle varies continuously from 30A degrees to 60A degrees. Painting its surface with fluorescent spray paint and irradiating its surface with a collimated object beam at a time interval of a few microseconds, we succeeded in visualizing three-dimensional shock reflection over the skewed wedge surface. Experiments were performed at shock Mach numbers, 1.55, 2.02, and 2.53 in air. From reconstructed holographic images, we estimated critical transition angles at these shock wave Mach numbers and found that these were very close to those over straight wedges. This is attributable to the flow three-dimensionality.

To explore a reliable technology possibly applicable to the inactivation of micro-creatures in ship ballast water, this paper reports a result of a primary experimental and analytical study. We obtained 10 μm bubbles in averaged diameter by using a swirling flow type micro-bubble generator. We exposed a shock wave generated by a micro-explosion of a 10 mg silver azide pellet to the water containing micro-bubbles filled in a 10 mm wide parallel test section. Observations were carried out with a high-speed camera, and the corresponding rebound pressures of bubbles were measured with a fiber optic probe pressure transducer. We confirmed micro-bubble motion with higher temporal resolution and found that micro-bubble collapse arose in several hundred nano-seconds after the shock loading. The peak pressure generated by bubble collapse was over 200 MPa at the distance of 20 mm from the explosion center. These experimental results were consistent with those analyzed on the basis of the measured pressure data. The presence of such high impulsive pressures upon bubble collapse clearly indicated that the rebound pressure would be effectively applicable to the inactivation of microcreatures in ship ballast water.

This paper reports all experimental result of laser-induced shock waves and bubble generation in muddy water. 5 kW pulsed CO2 laser beams of 10.6 mu m in wavelength diffusively were irradiated repeatedly at 10 Hz onto a biotitegranite surface which was placed at 50 mm deep from clay particle laden water surface. This water mixture was called muddy water of equivalent density of 1.02 g/cc. Repeated exposure of CO2 laser beams firstly induced a cavitation column in muddy water. The laser energy was transmitted in the cavitation column and by its deposited on the biotitegranite surface, the surface was eventually molten producing spherical glass beads. Repeating this procedure, we found that the laser beam irradiation call excavate the submerged rock surface.

The paper reports a result of low temperature hypervelocity impact (HVI) tests of aluminum sphere against a 16-ply quasi-isotropic Carbon Fiber Reinforced Plastic (CFRP) laminate plate at speed ranging from 1.4 to 5.4 km/s in air at 10 Pa. The result was compared with room temperature impacts. At low speed impact on CFRP plates, fracture patterns of specimens varied depending on their temperatures, whereas at high-speed impact, any significant differences in the fracture patterns around penetration holes and independent of the temperatures. (C) 2008 Elsevier Ltd. All rights reserved.

This paper reports the results of hypervelocity impact (HVI) experiments on cryogenic aluminum alloys at 122 K. Target plates were impinged by room temperature aluminum spheres at speeds ranging from 1 to 3.7 km/s in air at 10 Pa. The results were compared with HVI results at room temperature. We visualized the HVI processes by shadowgraph and recorded them with a digital high-speed video camera. We showed temperature effects of target plate physical properties on the formation of debris clouds and impact craters and hence the shielding efficiency of aluminum alloys at low temperature.

This paper is the part 2 of our previous thin film heat transfer measurements. In the first report we measured time variations of heat flux over a cylinder placed in a shock tube flow and compared experimental results with CFD results, Saito et al. (Shock Waves 14:327-333, 2004). We report a result of heat transfer measurements over an 86 degrees apex angle cone surface impinged by a Ms = 2.38 shock wave in air with distributed thin film transfer gauges along cone surface and its comparison with results of numerical simulations. We performed double exposure holographic interferometric observation, and also from the heat transfer measurement and numerical simulation, confirmed the presence of delayed transition from regular to Mach reflection over the cone. The numerical estimation of delayed transition distance from the apex agreed very well with experimental one.

Paper reports a result of experiments of spherical shock waves generated by explosions of micro-explosives weighing from I to 10 mg ignited by the irradiation of Q-switched laser beam and direct initiation to a spherical detonation wave in stoichiometric oxygen/hydrogen mixtures at 10-200 kPa. We visualized the interaction of debris particles ejected micro-explosives' surface with shock waves by using double exposure holographic interferometry and high-speed video recording. Upon explosion, minute inert debris launched supersonically from micro-charge surface precursory to shock waves initiated spherical detonation waves. To examine this effect we attached 0.5-2.0 mu m diameter SiO2 particles densely on micro-explosive surfaces and observed that the supersonic particles, significantly promoted the direct initiation of spherical detonation waves. The domain and boundary of detonation wave initiations were experimentally obtained at various initial pressures and the amount of micro-charges. (c) 2006 Published by Elsevier Inc. on behalf of The Combustion Institute.

This paper reports a result of hypervelocity impact experiments on cryogenically cooled aluminum alloys and a composite material. Experiments are carried out on a target palate at 122 K. Aluminum spheres at 1.95 km/s in 50 kPa air were impinged against the target plate at cryogenic temperature and the result was compared with room temperature target plates. Hypervelocity impact (HVI) processes were visualized with shadowgraph arrangement and recorded with highspeed video camera and to ensure the temperature dependence we compared HVI tests with metal target plates with AUTODYN 2D and SPH numerical simulations. We found that cryogenic impacts created slight differences of impact damage from room temperature ones, i.e., the shape and averaged diameters of HVI crater holes were less at cryogenic impacts. (C) 2006 Elsevier Ltd. All rights reserved.

Paper reports a result of hypervelocity impact experiments on cryogenically cooled aluminum alloys. Experiments are carried out on a target palate at 122 K. Aluminum spheres at 1.95 km/s in 50 kPa air were impinged against the target plate at cryogenic temperature and the result was compared with room temperature target plates. HVI processes were visualized with shadowgraph arrangement and recorded with high-speed video camera and to ensure the temperature dependence we compared HVI tests with metal target plates with AUTODYN 2D and SPH numerical simulations. We fond that cryogenic impacts created slight differences of impact damage from room temperature ones, that is, the shape and averaged diameters of HVI crater holes were less at cryogenic impacts.

The paper reports results of shock tube experiments of the attenuation of shock waves propagating over arrayed baffle plates, which is motivated to simulate shock wave attenuation created accidentally at the acoustic delay line in synchrotron radiation factory upon the rupture of a metal membrane separating the acceleration ring at high vacuum and atmospheric test chambers. Experiments were carried out, by using double exposure holographic interferometry with double path arrangement, in a 100 mm x 180 mm shock tube equipped with a test section of 180 mm x 1100 mm view field. Two baffle plate arrangements were tested: Oblique and staggered baffle plates; and vertical symmetric ones. Pressures were measured along the shock tube sidewall at individual compartments for shock Mach numbers ranging from 1.2 to 3.0 in air. The results were compared with a numerical simulation. The rate of shock attenuation over these baffle plates was compared for vertical and oblique baffle plates. Shock wave attenuation is more pronounced in the oblique baffle plate arrangements than in the vertical ones.

Results of the benchmark test are presented of comparing numerical schemes solving shock wave of M-s = 2.38 in nitrogen and argon interacting with a 43 degrees semi-apex angle cone and corresponding experiments. The benchmark test was announced in Shock Waves Vol. 12, No. 4, in which we tried to clarify the effects of viscosity and heat conductivity on shock reflection in conical flows. This paper summarizes results of ten numerical and two experimental applications. State of the art in studies regarding the shock/cone interaction is clarified.

Applications of shock wave research conducted in Tohoku University are briefly described. Its is emphasized that underwater shock wave research and its connection to bubble dynamics are one of the most important physical backgrounds to interpret tissue damages occurring during shock wave therapy. In addiction to ESWL, revascularization of cerebral thrombosis by using a laser induced liquid jet and its application to the water jet dissection method are presented. Lastly the development of a laser ablation induced drug delivery system is briefly described. In these applications implicitly and explicitly shock waves and their interaction with the bubble always play an important role.

This paper reports the results of experimental results of shock wave/ bubble interaction in a highly viscous liquid. In the medical applications of the shock waves, it is necessary to consider the viscous effect of water. The magma fragmentation is considered to be one of the major mechanisms of the explosive-type volcano eruptions. The dynamic motion of magma should be experimentally investigated from the view point of shock wave dynamics. Silver azide pellet was exploded in silicone oil and starch syrup with various viscosity was visualized by shadowgraph using high speed video camera.

Check valves for checking reverse water flows in drainage systems sometimes make large impacts through their sudden closure caused by accidental cutoff of drain pumps. In order to characterize such phenomena and to find design criteria for impactless check valves, we observed the motion of a check valve and measured its impact acceleration and pressures in the drainage pipe, using a subscale drainage system. Two peaks of impact acceleration were observed The first one seemed due to collision of the check valve and the valve seat, whereas the second one did due to water column separation and recombination caused by the low pressure during the closure state of the valve. The former can be reduced by adding mass to the check valve and by setting an appropriate valve-seat angle. The latter possibly can be reduced by relaxing the low pressure during the closure. Subsequently, the check valve opened through the water-column recombination impacts and sometimes showed opening-closing oscillation.

Shock wave propagation and collapse of gas bubbles caused by a shock in a water containing gas bubbles are of large interest in relation to characteristics of water hammer, blowdown of high pressure liquids in pipes, damping of dynamic influence of shock waves on obstacles, etc. The large-amplitude shock wave propagations in the bubbly liquid are investigated using a two-phase shock tube. Effects of incident shock wave strength and initial void fraction on shock wave pressure characteristics are clarified for incident shock wave strength ranging from 0.06 MPa to 0.25 MPa. Behavior of the bubbles collapsing behind large-amplitude shock waves is also clarified by pressure history measurements and high speed photography.