• Journal of the Korean Society for Railway
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• v.16 no.6
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• pp.454-459
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• 2013

Pressure waves are generated and propagate in a tunnel when train enters tunnel high speed. A compression wave due to the entry of train head propagates along the tunnel and is reflected at tunnel exit as an expansion wave. An expansion wave due to the entry of the train tail propagates along the tunnel and is reflected at tunnel exit as a compression wave. These pressure waves are repeatedly propagated and reflected at the tunnel entrance and exit. Severe pressure changes causes ear-discomfort for passengers in the cabin and micro pressure waves around the tunnel exit. It is necessary to analyze the transient pressure phenomena in tunnels qualitatively and quantitatively, because pressure change rate is considered as one of the major design parameters for optimal tunnel cross sectional area and repeated fatigue force on car body. In this study, we developed a characteristics method based on a fixed mesh system and boundary conditions for crossing trains and analyzed this system using an X-t diagram. The results of the simulation show that offsetting of pressure waves occurs for special entry conditions of a crossing train.

• Transactions on Electrical and Electronic Materials
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• v.9 no.5
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• pp.213-219
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• 2008

Pulse waves continuously change with respect to the characteristics and status of the cardiovascular system and in relation to the blood pressure (BP) and the pulse wave velocity (PWV). Monitoring the vascular condition by analyzing the variations in pulse waveforms has been used to diagnose vascular disorders and in drug treatment of arteriosclerosis and peripheral circulatory obstruction. In this paper, we investigated the vascular characteristic index with regard to the BP and classified by pulse wave signals. The pressure pulse wave and photoplethysmography (PPG) were measured simultaneously while subjects exercised, producing changes in the BP, to analyze the variation in the vascular characteristic index. We investigated the correlation between the BP and vascular characteristic index with regard to the classification methods of the pulse wave. The reflection index (RI) and vascular stiffness index were correlated with the diastolic BP, but no correlation was found between these parameters and the systolic BP. These results suggest the possibility of estimating BP through simple measurements of pulse waves.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.792-797
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• 2003

A helical vane is applied to reduce the magnitude of the impulse wave discharged from the exit of a duct. A shock tube with an open end is used to investigate the effect of the helical vanes on the impulse wave magnitude. Four different types of helical vanes are installed into the low-pressure tube of shock tube. The magnitude of the incident shock wave is varied below 1.25, and the magnitude of impulse wave is measured using a pressure transducer mounted on a wedge probe. Instant images of the impulse wave are obtained by means of the Schlieren optical method. The present experimental results show that the helical vane considerably reduces the magnitude of the impulse wave and the vane effects are more remarkable for stronger incident shock wave.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.4
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• pp.439-445
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• 2017

Plunging breaker slamming pressures on vertical or sloping sea dikes are one of the most severe and dangerous loads that sea dike structures can suffer. Many studies have investigated the impact forces caused by breaking waves for maritime structures including sea dikes and most predictions of the breaker forces are based on empirical or semi-empirical formulae calibrated from laboratory experiments. However, the wave breaking mechanism is complex and more research efforts are still needed to improve the accuracy in predicting breaker forces. This study proposes a semi-empirical formula, which is based on impulse-momentum relation, to calculate the slamming pressure due to plunging wave breaking on a sloping sea dike. Compared with some measured slamming pressure data in two literature, the calculation results by the new formula show reasonable agreements. Also, by analysing probability distribution function of wave heights, the proposed formula can be converted into a probabilistic expression form for convenience only.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.81-86
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• 2001

Interfacial pressure jump terms based on the physics of phasic interface and bubble dynamics are introduced into the momentum equations of the two-fluid model for bubbly flow. The pressure discontinuity across the phasic interface due to the surface tension force is expressed as the function of fluid bulk moduli and bubble radius. The consequence is that we obtain from the system of equations the real eigenvalues representing the void-fraction propagation speed and the pressure wave speed in terms of the bubble diameter. Inversely, we obtain an analytic closure relation for the radius of bubbles in the bubbly flow by using the kinematic wave speed given empirically in the literature. It is remarkable to see that the present mechanistic model using this practical bubble radius can indeed represent both the mathematical well-posedness and the physical wave speeds in the bubbly flow.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.335-340
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• 2001

There are many tunnels located apart short distance from each other in mountainous country like Korea. Serial tunnels are connected by snow shelter in many cases. This study presents some countermeasures against micro-pressure wave at the tunnel exit using snow shelter. Through 1/60 scale model laboratory test, we find that snow shelter with 3.6m slit and slit cover show the effect of reducing the micro pressure wave to about 50.6%.

• Journal of Ocean Engineering and Technology
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• v.9 no.2
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• pp.149-155
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• 1995

This study is to investigate the dynamic pressure caused by breaking waves on a recurved offshore structure. A physical modelling was performed in a two-dimensional wave flume. The measuments from the physical modelling were compared with several known equations. The shock and secondary pressures were found to be dependent on water depth, breaking wave height and the size of the air pocket. The maximum pressure was recorded near the still water level and the secondary pressures near the recurved the recurved structure were found to be less than those experienced in a vertical offshore structure.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.11
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• pp.3075-3083
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• 1994

The applications of the electrical transmission line theory to the pressure propagation characteristics in the volume loaded fluid transmission line with step and impulse input wave is demonstrated in this paper. The method is based on the premise that the time response is the inverse Fourier transform of frequency spectrum of the wave which spectrum is a product of frequency spectrum of input pressure wave and system transfer function. The frequency response and transient response of step and impulse input wave in the volume loaded fluid transmission line is analysed by the Laplace transform and inverse Laplace transform with FFT numerical algorithm. The numerical solution of the distributed friction model is compared with the average friction model and the infinite product model. And the result is showed that FFT method may have major advantages for the simulation of fluid circuitary.

• Journal of the Korean Society of Visualization
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• v.9 no.1
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• pp.55-60
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• 2011

Pulsed supersonic liquid jets injected into an ambient air are empirically studied by using a high pressure ballistic range system. Ballistic range systems which are configured with high-pressure tube, pump tube, launch tube and liquid storage nozzle. Experimental studies are conducted to use with various impact nozzle geometry. Supersonic liquid jets are generated by an impact of high speed of the projectile. High speed liquid jets are injected with M = 3.2 which pressure is 1.19 GPa. Multiple jets which accompany with shock wave and pressure wave in front of the jet were observed. The shock-wave affects significantly atomization process for each spray droplets. As decreasing orifice diameter, the averaged SMD of spray jets had the decreasing tendency.

• Ocean and Polar Research
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• v.30 no.4
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• pp.453-466
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• 2008

In order to examine the generation mechanism of long ocean waves along the west coast of Korea and to understand the amplification process of the long ocean waves, sea level, atmospheric pressure and wind data observed every minute from 2007 March 29 to 2007 April 1 were analyzed and onedimensional numerical ocean model experiments were performed. An atmospheric pressure jump propagated southeastward from Backryungdo to Yeonggwang along the west coast of Korea with speed of $13{\sim}27\;m/s$ between 2007 March 30 23:00 and 2007 April 1 1:30. Average magnitude of pressure jump was 4.2 hPa. As a moving atmospheric jump propagated from north to south along the coast, long ocean waves were generated and the sea level abnormally rose or fell at Anheung, Kunsan, Wido and Yeonggwang. Average amplitude of sea level rise (or fall) was about 113.6 cm. In a one-dimensional numerical ocean model, nonlinear shallow water equations were numerically integrated and a moving atmospheric pressure jump with traveling speed of 24 m/s was used as an external force. While the atmospheric pressure jump travels over 60 m depth ocean, a long ocean wave is generated. Because the propagation speed of the atmospheric jump is almost equal to that of the long ocean wave, Proudman resonance occurs and the long ocean wave amplifies. As the atmospheric pressure jump moves into the coastal area shallower than 60 m, the speed of the long ocean wave decreases and Proudman resonance effect decreases. However, the amplitude of the long ocean wave increases and wave length becomes shorter because of shoaling effect. When the long ocean wave hits the land boundary, amplitude of the long ocean wave drastically amplifies due to reflection. Data analysis and numerical experiments suggest that the southeastward propagation of an atmospheric pressure jump over the shallow ocean, which is a necessary condition for Proudaman resonance, generated the long ocean waves along the west coast of Korea on 2007 March 31 and the ocean waves amplified due to shoaling effect in the coastal area and reflection at the shore.