Impulsive Pressure Wave Research Articles

1119 開口部付き緩衝工から放射される微気圧波に関する模型実験と解析(OS11-4 流体関連振動・騒音,OS11 流体関連振動・騒音)

An impulsive pressure wave emitted from a tunnel portal, called a micro-pressure wave, is one of the important wayside environmental problems in high-speed railways. A tunnel hood with openings on its side wall installed at the portal of the train entrance side is the principal countermeasure for reducing the micro-pressure wave. However, the micro-pressure wave tends to have large peak value around openings of the hood when the micro-pressure wave is emitted from the tunnel exit portal with the hood. In this study, we carried out the model experiment focused on the effects of the tunnel hood with openings installed at the portal of the train exit side. In addition, we developed a simple theoretical model simulated the micro-pressure wave around openings of the hood.

Dynamic responses of a solid wall in contact with a bubbly liquid excited by thermal shock loading

Several MW-class spallation neutron sources are being developed in the world. Specifically, intensive and high energy protons are injected into heavy liquid metals (mercury, lead or lead–bismuth eutectic) to induce the spallation reaction that produces neutrons. At the moment when the proton beams are injected, thermal shock occurs in the liquid metal, causing pressure waves to propagate in the liquid metal, collide against the container and damage it. It is proposed that microbubbles are injected into the liquid metal to mitigate the impulsive pressure waves by means of absorption and attenuation effects. These effects are dependent on the relationship between bubble size and the rate of pressure increase. In the present experiment, a very rapid rise in pressure in the order of MPa/μs, equivalent to the rise in pressure due to proton beam injection, was simulated by the electric discharge method in a water loop test to investigate the impulsive pressure mitigation effect of injected microbubbles. The solid wall response was measured using an accelerometer, and the dynamic responses of microbubbles were observed using an ultra-high-speed camera filming at 5 × 10 5 frame/s. The sound velocity in bubbly water was estimated using a differential image technique. It was confirmed from the experimental results that microbubbles are effective in reducing impulsive pressure waves and to suppressing the impact vibration of the solid wall in contact with the liquid.

Optimization of Train Nose Shape for Reducing Micro-Pressure Wave Radiated from Tunnel Exit

When a compression wave generated by a high-speed train entering a tunnel propagates through the tunnel and arrives at the tunnel exit, an impulsive pressure wave (micro-pressure wave) is radiated from the tunnel exit. Improving the train nose shape is one of the techniques for suppressing the micro-pressure wave. Furthermore, tunnel entrance hoods are required for long concrete slab tunnels in order to suppress the micro-pressure wave. The effect of the tunnel entrance hood on the compression wave generated by the train can be evaluated by means of a rapid computational scheme devised and validated experimentally by Howe et al. In this study, the optimal longitudinal distribution of the cross-sectional area of the train nose shape was determined by using the rapid computational scheme and a genetic algorithm. The effect of the nose shape optimization was confirmed through experiments using scale models.

Development of Solid-Gas-Liquid Coupling System by using CADMAS-SURF/3D

It is important to develop the Solid-Gas-Liquid coupling system for analyzing the mechanism of failure of structures on land by Tsunami. At first, the numeric wave tank, whose name is CADMAS-SURF/3D, is improved to correspond to two phase incompressible fluid. This two phase flow tank is applied to the impulsive wave pressure problem. As a result, it is confirmed that a numeric noise, which is called Spike Noise, is removed and the accuracy of the result is good agreement with the single phase model. Next step, the coupling system with DEM method is developed. The wall destruction test by fluid is conducted. The appearance of the wall destruction adjusted the large-scale experiment, and the validity of three phase coupling system is confirmed qualitatively.

Influence of Covering State of Wave-Dissipating Blocks and Waves Randomness on Probability Distribution of Wave Pressure acting on a Breakwater

Reliability design of maritime structures based on the deformation level will be one of the most important future design tools. However, it has not been fully applied to actual design since it is very difficult to take the various design condition into account. The present paper points out on the basis of the experimental results in random wave field, the influences of the state of wave-dissipating blocks on the wave pressures at several cross sections of a breakwater, and the stochastic characteristics of obtained data was examined. The random wave experiment data and the regular wave data correspond well when the impulsive wave pressure is not generated, however when the impulsive wave pressure is generated, the wave pressure on still water level of both experiments are greatly different.

Effects of Deformation of Wave-Dissipating Works on Wave Forces Acting on Caisson Breakwaters

The evaluation of wave forces acting on caisson breakwaters with deformed wave-dissipating works is important from the view point of caisson sliding. Wave pressures and wave forces acting on caisson breakwaters were measured to investigate the effect of the deformation of the wave-dissipating works on wave pressures and wave forces. Several cross sections of wave-dissipating works defined based on the previous study. When the crown of wave-dissipating work settles near the still water level, the impulsive wave pressure occurs and leads to increase in wave force. This wave force increases with progress of wave-dissipating works deformation indicated with a settlement of crown and decrease in the width of wave-dissipating works.

Experimental Study on Damage to Wave Splash Barrier for a Coastal Road

National Route E is a coastal road where overtopping waves cause frequent traffic disturbances. High waves resulting from a storm surge damaged the wave splash barrier for length of 78m out of 400m in October 2006. Impulsive wave pressure, acted on sections that were rendered incomplete due to scattering of wave-dissipating blocks as a result of the high waves and abnormal tide level, caused the damage of the wave splash barrier. The results of experiments revealed that the ratio of the critical wave force to the wave force acting on the barrier ranged from 2.6 to 3.0 in the damaged section, while the corresponding value in the undamaged section was 1.7 to 2.2

High Waves Disaster Mechanism of Fishing Ports in Sado Island on Februay, 2008

Several fishing ports in Sado Island, especially on its east part, were damaged extensively by high waves on February, 2008. This study investigates high waves disaster damage of fishing ports in Sado from conditions of the weather and numerical simulation by energy balance equation . As a results, it became clear that high and long period waves attacked from NNE with little sheltered area of capes, and impulsive wave pressure acted under the influence of submarine topography around damaged fishing ports. Moreover, it was suggested that cautions are required for a future high waves from NNE on some fishing ports designed by waves from N.

Pressure Waves Generated When a Train Passes a Nearby Structure

When a high-speed train enters or leaves a tunnel, impulsive pressure waves are radiated from the entrance/exit portal toward the outside of the tunnel. The waves are called a “micro-pressure wave, ” a “tunnel entry wave” and a “tunnel exit wave.” A similar phenomenon occurs when a train passes a short structure in axial length in an open section (such as an over-bridge). We call it a “structure-passing wave.” The length of the structure along the railway is several times or less the diameter of the structure cross-section. Although the structure-passing wave is weak at present, it could cause an environmental noise problem of a low-frequency (which has become public concern) as the train speed increases. This paper describes the characteristics of the structure-passing wave based on the results of model experiments and acoustic analyses. The results obtained from the acoustic analyses were in good agreement with the result of the experiment except for the very short length structures. This implies that the structure-passing wave can be modeled on a superposition of the pressure waves radiating from both sides of the structure.

Field Measurement of Wayside Low-Frequency Noise Emitted from Tunnel Portals and Trains of High-Speed Railway

In order to determine the actual circumstances of wayside low-frequency noise and infrasound generated by high-speed trains (Shinkansen), field measurements were performed at two sites, one near a tunnel portal and the other in a fully open section. The measurements were based upon the manual issued by the Ministry of the Environment of Japan in October 2000 and conducted to obtain G-weighted SPL, 1/3-octave band spectra, velocity dependence and distance attenuation of SPL. The measured results show that major components of the low-frequency noise from the tunnel portal are impulsive micro-pressure waves and continuous pressure waves, while those in the open section are near-field hydrodynamic pressure variations and far-field acoustic pressure waves.

113 列車が沿線近傍構造物を通過する際に発生する圧力波((1)低周波・超低周波音の最新技術,騒音・振動改善技術)

When a high-speed train enters or leaves a tunnel, impulsive pressure waves are radiated from the entrance/exit portal toward the outside of the tunnel. A similar phenomenon occurs when a train passes a short structure (such as an over-bridge) in an open section. We call it a "structure-passing wave." Although the structure-passing wave is weak at present, it could cause an environmental problem as the train speed increases. In addition, people have become more and more interested in low-frequency noise. This paper describes the characteristics of the structure-passing wave based on the results of model experiments and acoustic analyses.

列車が沿線近傍構造物を通過する際に発生する圧力波の模型実験(環境,省エネ,リサイクル,LCA,OS6 環境,省エネ,リサイクル,LCA)

When a high-speed train enters or leaves a tunnel, impulsive pressure waves are radiated directly from the entrance/exit portal toward the outside of the tunnel. A similar phenomenon occurs when a train passes a short structure (such as an over-bridge) in an open section. We call it a "structure-passing wave." Although the structure-passing wave is usually weak, it could cause an environmental problem as the train speed increases. In addition, people are taking interest increasingly in low-frequency noise. This paper describes the characteristics of the structure-passing wave based on the results of model experiment.

マウンド上に設置されたフレア型護岸の水理特性に関する実験と数値解析

Flaring Shaped Seawall (FSS) can drastically reduce a crest height and wave overtopping volume in comparison with a conventional upright one, and a top area of the FSS can be used effectively. In this study, hydraulic experiments and numerical simulations for the FSS on the mound have been carried out using a twodimensional flume model. As a result, the wave overtopping rate and flow velocity by the numerical simulations are in agreement with those by the experiments. Good agreement between numerical results and experimental ones is found in not impulsive wave pressure. However, it is necessary to investigate an impulsive wave pressure furthermore.

Field Measurement of Pressure Waves Observed When a Train Passes an Over-Bridge

It is well known that when a compression wave generated by a high-speed train entering a tunnel propagates through the tunnel and arrives at the far exit, a “micro-pressure wave” is radiated from the exit portal toward the surrounding area. In addition, the entering/leaving train generates impulsive pressure waves outside the tunnel, which are radiated directly from the entrance/exit portal toward the neighboring area. We call the former a “tunnel entry wave, ” and the latter a “tunnel exit wave.” A similar phenomenon also occurs when the train passes an over-bridge in an open section. Here, we call this an “over-bridge passing wave.” Although, the over-bridge passing wave is usually weaker than the micro-pressure wave, it could cause an environmental problem with increases in the train speed. This paper reports the results of field measurement performed at a Shinkansen over-bridge on a canal to investigate the fundamental characteristics of the over-bridge passing wave.

B113 列車のトンネル突入により発生する非定常流の可視化

The impulsive pressure wave radiated from a tunnel exit (micro-pressure wave) is one of the most important environmental problems of high-speed railways. For solving the problems of micro-pressure waves, the unsteady flow induced by a train entering a tunnel needs to be clarified because the micro-pressure wave is radiated at the arrival of the compression wave generated by the train entry. In this study, we conduct a 1/127 scale model experiment and investigate the unsteady flow induced by the train entering the tunnel by applying the flow visualization technique to use oil mist and a high-speed camera. The results reveal that a jet flow is emitted from the entrance and a vortex ring is generated and collapses thereafter. Furthermore, a jet flow from a window at the tunnel side wall is also observed.

BEHAVIOR OF RC SLAB SUBJECTED TO UP LIFT IMPULSIVE WAVE FORCE

To consider impulsive wave force in design is important for a marine structure. However a impulsive phenomenon is complicated to observe according to various kinds of conditions and to act in very short time. This research aimed at obtaining the fundamental data of reinforced concrete slab by the impulsive wave force through the large-scale waterway test. Strains of the reinforced concrete slab and distribution of impulsive wave pressure are measured to know the phenomenon. An effect of impulsive component is small for strains in RC slabs.

Distortion of Compression Wave Propagating through Slab Track Tunnel with Side Branches

When a high-speed train enters a tunnel, a compression wave is generated and propagates to the tunnel exit. At this moment, an impulsive pressure wave (micro-pressure wave) is emitted out of the exit. If its magnitude is large, it poses environmental problems. The magnitude of the micro-pressure wave is closely related to the pressure gradient of the compression wave arriving at the tunnel exit. Hence, to estimate the magnitude of the micro-pressure wave, it is required to investigate distortion of the compression wave propagating through tunnels. In this study, we investigate the distortion of the compression wave propagating through a slab track tunnel with short side branches by field measurement, numerical analysis and model experiment.

Pressure Waves Radiated Directly from Tunnel Portals at Train Entry or Exit

It is well known that when a compression wave generated by a high-speed train entering a tunnel propagates through the tunnel and arrives at the far exit, a "micro-pressure wave" is radiated from the exit portal toward the surrounding area. In addition, the entering train generates impulsive pressure waves outside the tunnel, which are radiated directly from the entrance toward the neighboring area. A similar phenomenon also occurs when the train leaves the tunnel. We call the former a "tunnel entry wave", and the latter a "tunnel exit wave". Although the tunnel entry/exit wave is usually weaker than the micro-pressure wave, they could cause an environmental problem with increases in the train speed. In this paper, fundamental characteristics of the tunnel entry/exit wave are described based on the results of field measurement, model experiments and simple acoustic analysis.

High strain rate forming using an underwater shock wave focusing technique

This paper proposes an effective method for controlling the morphology of impulsive pressure waves in hydro-spark forming, making use of the technique of underwater shock wave focusing. Free forming experiments using ellipsoidal reflectors with two kinds of minor-to-major axis ratios b / a =0.6 and 0.8 are performed under several blank-setting conditions. The height of the formed product depends solely on the impulse of the shock wave, regardless of its focusing behavior, while the shape of the product is controlled by distribution of the applied pressure wave. It is demonstrated that the reflector having b / a =0.8 yields a wide range of pressure distribution, which can be estimated from the shock wave front distribution calculated considering the effect of non-linear reflection.

Applications of the causality condition to acoustic scattering

The causality condition states that the response of a passive system cannot precede the cause. Under certain conditions, the causality condition leads to a Hilbert transform relation between the magnitude and phase of the complex Fourier transform of a system’s response. This relation has profound implications for those attempting to design passive structures whose desired scattering characteristics are expressed in the frequency domain. Unless the causality condition is satisfied in the frequency domain, the structure is not physically realizable. In this presentation, some novel applications of this relation are developed for a one-dimensional fluid-loaded structure which scatters incident sound in the backward and forward directions. In each application the reflection and transmission coefficients, which are the complex Fourier transforms of the reflected and transmitted pressures due to an impulsive incident pressure wave, are subject to the causality condition. The Weiner–Lee transform, which is derived from the Hilbert transform but is more easily implemented numerically, is used to find complex reflection and transmission coefficients given only their frequency-dependent magnitudes. By using this informa- tion and structural reciprocity, one can find an impedance matrix of a structure which scatters sound in a specified way.