Mechanism of the Shock Wave Generation and Energy Efficiency by Underwater Discharge
Osamu HigaRyo MatsubaraKatsuya HigaYoshitaka MiyafujiTakashi GushiYukimasa OmineK. NahaKen ShimojimaHiroshi FukuokaHironori MaeharaShigeru TanakaTakumi MatsuiShigeru Itoh
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We are developing the rice powder manufacturing system using an underwater shock wave. The purpose of this study is to research a mechanism of the shock wave generation and energy efficiency by underwater discharge in order to increase energy of the underwater shock wave. We observed the shock wave generation using the visualization device with a high speed camera, and measured voltage current characteristics at the same time. As a result, it was clarified that countless underwater shock waves were generated at the time of water plasma expansion by discharge. But, the shock wave was not confirmed at the time of after a second peak of the damping oscillation. It was clarified that one part of charging energy was used to generation of the shock wave. Therefore, it was clarified that to release energy by the critical oscillation is desirable for efficient generation of the shock wave.Keywords:
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The structures and the behaviors of shock waves propagating through a gas and solid particle mixture are studied by shock-tube experiments and by two methods of wave analysis. The shock waves concerned are incident on the mixture dispersed uniformly in downstream part of the driven section. Pressures and shock velocities are measured under the condition that the particle loading ratio and the shock Mach number are both less than two. The final equilibrium pressures behind the waves and the velocities of the fully decayed shock fronts agree well respectively with the results of the usual shock theory on the mixture and those of the model analysis on a perfect "effective" gas. The analysis by the method of characteristics is satisfactorily applied to give a good explanation of the observed process whereby a shock wave decays to a weak wave with continuous wave form. And, the authors point out some problems relating to the relaxation process and some inconsistencies of the "effective" gas theory when analyzing the unsteady wave motions.
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Perfect gas
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In this paper, the pseudo-shock wave produced in the process of the interaction of the reflected shock wave with the contact surface in a shock tube were investigated numerically in order to crarify the mechanism of its production. The computations were carried out by solving the two dimensional and compressible Navier-Stokes equations by means of TVD method. The calculations were performed for the various strengths of the shock waves, and the flow fields were expressed by means of the contour lines of the presure and the density, velocity vectors, pressure distributions and the distance-time diagrams of the shock waves. The numerical results showed clearly the process of the production and the development of the pseudo-shock wave, and the effects of the strength of the reflected shock wave and Reynolds number of the flow were clarified.
Compressible flow
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It is a well known but puzzling result that zones within star formation regions sometimes show molecular hydrogen emission at very high (∼100 km s−1) velocities. These kinds of observations are somewhat difficult to explain because non-magnetized, J-type shock waves of velocities above ∼20 km s−1 mostly dissociate the molecules present in the preshock medium, and therefore produce almost no H2 emission. We quantify this result by presenting models of steady shock waves moving into a molecular environment, which show that the H2 molecules are indeed dissociated in the immediate postshock region for higher shock velocities. We argue that the total destruction of molecules by high-velocity shocks is a direct result of the assumption of an instantaneous ‘turning on’ of the flow that is generally done in computing shock models. We present models in which a shock wave gradually accelerates over a period of ∼1000 yr as would be expected, for example, from the ‘turning on’ of an outflow from a young star. We find that such shock waves are indeed able to accelerate significant masses of molecular material to velocities of ∼100 km s−1, and are a plausible explanation for widely observed high-velocity H2 emission.
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Hydrogen molecule
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Underwater explosion
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It is important to investigate a pressure profile when a diffracted shock wave interacts with a reflector from a safety point of view. Because the diffracted shock waves are often generated by the explosions of combustible gases to cause serious damages against human race and surrounding buildings. The maximum pressure behind reflected shock wave is one of the most important parameter and this report is concerned with the evaluation of maximum pressure, which might be a function of Mach number of the shock wave, distance from a source of the shock wave, initial pressure of the gas, and initial diameter of the shock wave, etc. In this study, a detonation-driven shock tube of 14 m long and 50 mm diameter is used to generate a strong shock wave of propagating Mach number MS=3.0∼5.2. The shock wave is diffracted from an open end of the shock tube of 25 mm diameter and reflected from a cylindrical reflector of 50 mm diameter. These phenomena are observed using color-schlieren optical techniques and the pressure histories at the stagnation point of the reflector are simultaneously measured. As a result, (i) The behaviors of the diffracted shock wave and complicate flow-fields behind reflected shock wave are observed. (ii) An empirical equation to calculate the maximum pressure behind reflected shock wave is estimated by the results of experimental and numerical simulation.
Shock diamond
Reflector (photography)
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Shock wave simulations have been carried out to 800 planes for BCC iron using a Morse potential. Analysis showed that the Hugoniot conservation relations are obeyed even for non-constant shock profiles if appropriate averages over the complete shock region are used. Various definitions of temperature for the shocked region were examined. The anomalies reported by Tsai and MacDonald (1973) were not observed.
Constant (computer programming)
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The aim of this letter is to present an original experimental technique to study weak shock wave in a minitube. Thus, we designed an apparatus that can be connected to any classical shock tube in order to characterize high speed flows induced by the shock wave transmission in minitubes. We proposed appropriated measurements based on high speed strioscopy coupled with pressure sensors. Two minitube diameters are considered: 1.020±0.010 and 0.480±0.010 mm. We realized preliminary experimental and numerical campaigns with an incident shock wave Mach number at 1.12±0.01. The generation of a microshock wave was observable in the two minitubes. For the smallest minitube, we found an attenuation of the strength of the shock wave with a decrease of 1.8% of the Mach number.
Mach reflection
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We have observed the structure and velocity of laser-driven shock waves in aluminum foils. We have measured shock velocities as high as 13 km/s and shock luminosity rise-times less than 50 ps, and we have inferred pressures of 200 GPa and shock-front thicknesses 0.7 \ensuremath{\mu}m. These results suggest that such techniques may be used for measuring equation-of-state parameters and studying the detailed structure of shock fronts.
Shock front
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Nitrogen or hydrogen gas is set to spurt from a small circular hole located at the endplate of shock tube at about 0∼9 ms before the shock wave arrives and reflects there. Interacting with the jet the reflected shock wave changes its shape from a plane shock wave to a curved one. We observed the phenomenon by the use of a schlieren system, time counters and pressure gauges. The results of the observation are as follows : (1) It is confirmed that an unstable, curved, reflected shock wave turns back to a stable plane shock wave within 0.1 ms. (2) The pressure and the temperature values behind the reflected shock wave derived from its distance-time relation show a certain amount of jump, which indicates the amount of the interaction between the spurting gas and the shock wave. (3) It is seen that hydrogen jet starts to burn at about 500∼600μ s after the shock reflection is taken place.
Shock diamond
Reflection
Mach reflection
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