• 한국철도학회:학술대회논문집
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• 한국철도학회 2004년도 춘계학술대회 논문집
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• pp.690-695
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• 2004

In order to develop a high speed train, various conditions have been considered. Fatigue strength assessment by the fluctuation of pressure is an important one. In this study, the fluctuation and frequency of pressure is measured when KHST(Korean High Speed Train) passes through tunnels in the Kyung-Bu high-speed line. And the characteristics of pressure fluctuation is analysed and formulated. The results of analysis are as follows. The train entering speed and fluctuation value are related. The pressure increasing is generated in proportion to train velocity at leading car. When two train is passing through the tunnel, the pressure value is $1.5\~2$ times higher than one train is passing. The damping ratio of pressure fluctuation is about $92\%$. The number of pressure fluctuation in a tunnel is 4 to 6 times. The result in this study would be a good guidance to calculate the fatigue life and the reliability index of body structure.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.2
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• pp.1109-1112
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• 2004

This study reports on the pressure relief design and braided composite of surge arrester. Surge arresters with porcelain housing must not have explosive breakage of the housing to minimize damage to other equipment when subjected to internal high short circuit current. As a solution, this study describes pressure relief design performance of arresters with braided composite module. In general, braided composite has Potential for improved impact and delamination resistance. Manufacturing processes of the braided composite could also be automated and could potentially lead to lower costs. Therefore, in consideration of characteristics of pressure relief for polymer arrester, the fabric pattern of braided composite was decided. And Polymer arrester module was manufactured with braid. The mechanisms of pressure occurrence and relief were investigated basically by analyzing arc energy and the correlation between thermal shock and indoor pressure in pressure relief test.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.118-123
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• 2001

The linear compressor have been widely used for pressure wave generation in the Stirling cryocooler and Stirling type pulse tube cryocooler for tactical purpose. The linear compressor has small and compact structure, and long life due to having non-contact sealing mechanism. and the pressure drop through regenerator was ver important role in the motion of displacer in the expander of the Stirling cryocooler. In this study, the characteristic of the linear compressor and the pressure drop through regenerator in the expander was experimentally investigated. The results show the resonance of the compressor is very important to get maximum performance. and the gas spring force in the compression space of the compressor has effect on the characteristic of reonance. and the results show the pressure drop through regenerator is very small than operating pressure change.

• 대한통합의학회지
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• 제7권1호
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• pp.75-80
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• 2019

Purpose : This study investigated the effect of bamboo stepping exercises on the blood pressure of the elderly. This study was performed for 8 weeks. Methods : The study participants included 25 people aged 65 and over. Of the participants, 16 were in the hypertensive elderly group and 9 were in the normal blood pressure elderly group. The participants stepped on semicircular bamboo for 20 minutes 3 times a week for 8 weeks. The participants' blood pressure was measured 3 times before and after 8 weeks of exercise. The mean values of the 3 before and after measurements were compared and analyzed statistically. Results : The systolic blood pressure of the hypertensive elderly group decreased significantly from $134.6{\pm}21.1mmHg$ to $119.9{\pm}18.1mmHg$ (p<.05). The diastolic blood pressure of the hypertensive elderly group decreased from $70.2{\pm}10.5mmHg$ to $66.1{\pm}9.8mmHg$, but the difference was not significant. The systolic blood pressure of the normal blood pressure elderly group decreased significantly from $127.2{\pm}18.7mmHg$ to $115.5{\pm}19mmHg$ (p<.05). The diastolic blood pressure of the normal blood pressure elderly group decreased from $72.6{\pm}11.3mmHg$ to $68.2{\pm}12mmHg$, but the decrease was not significant. Conclusion : After completing 8 weeks of the bamboo stepping exercises, the elderly participants' systolic blood pressure was effectively reduced. Today, lifestyle modifications, such as daily exercise, are necessary to control the blood pressure of the elderly. We hope that the bamboo stepping exercises, which are easy to perform and are not restricted by place and time, will become part of the elderly health policy.

• 한국정밀공학회지
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• 제31권8호
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• pp.677-682
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• 2014

One of the most important element technologies for achieving high-precision in machine tool spindle systems is preload technology for the bearing of spindle systems. Fixed position preload, constant pressure preload, conversion preload and variable preload methods have been applied for the spindle systems. In this study, a new variable preload method using centrifugal force and rubber pressure is used for reducing installation costs through simplifying its structure. The main objective of the work is the verification of the operability in a preload device using the rubber pressure by the finite element analysis. It is shown that the variable preload device proposed in this study is applicable to high speed machine tool spindles.

• Journal of Advanced Marine Engineering and Technology
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• 제27권1호
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• pp.57-64
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• 2003

The characteristics of fuel spray have an important effect on engine performance such as power, specific fuel consumption and emission because fuel spray controls the mixing and combustion process in an engine. Therefore, if the characteristics of fuel spray can be measured, they can be effectively used for improving engine performance. The major factors controlling fuel spray are injection pressure, ambient pressure and engine speed. In this study, the experiment is performed in a high temperature and high pressure chamber. In experiments, spray tip penetration, spray angle and spray tip velocity are measured at various injection pressure (10 and 14 MPa), ambient pressure(3,4 and 5 MPa), fuel pump speed(500, 700 and 900 rpm). Experimental results are useful for deriving an experimental spray equation and design an optimal engine. The results showed that injection pressure, ambient pressure and fuel pump speed are important factors influencing on the characteristics of spray. 1) Injection pressure influences on the characteristics of spray. That is, as injection pressure is increased, spray angle is decreased but spray penetration and spray tip velocity is increased. 2) Spray angle and spray penetration are increased as fuel pump speed is increased.

• 한국자동차공학회논문집
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• 제7권8호
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• pp.150-159
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• 1999

Exhaust system is composed of several parts. Among, them , design of muffler system strongly influences on engine efficiency and noise reduction. So , through comprehension of flow characteristics inside muffler is necessary . In this study , three-dimensional steady and unsteady compressible flow analysis was performed to understand the flow characteristics, pressure loss and amplitude variation of pulsating pressure. The computational grid generation was carried out using commercial preprocessor ICEM CFD/CAE. And the three-dimensional fluid motion inside the muffler was analyzed by STAR-CD, the computational fluid dynamics code. RNG k-$\varepsilon$ tubulence model was applied to consider the complexity of the geometry and fluid motion. The steady and unsteady flow field inside muffler such as velocity distribution, pulsating pressure and pressure loss was examined. In case of unsteady state analysis, velocity of inlet region was converted from measured pulsating pressure. Experimental measurement of pressure and temperature was carried out to provide the boundary and initial condition for computational study under three engine operating conditions. As a result of this study, we could identify the flow characteristics inside the muffler and obtain the pressure loss, amplitude variation of pulsating exhaust gas.

• 대한기계학회논문집B
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• 제22권5호
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• pp.618-626
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• 1998

This paper describes a series of fundamental studies on reflection and emission of weak pressure waves from an open end of a pipe. Acoustical theories which have been employed in the plane pressure waves inside a pipe are applied to the present study. The objective of the present study is to investigate the reflection or emission coefficient of pressure wave at an open end of a pipe, the length of open end correction, and the directivity characteristics of the pressure waves emitted from the pipe. The results show that the reflection coefficient of pressure wave at an open end and the length of open end correction decrease for the wave length of pressure wave to increase. It is also found that the reflection coefficient for a baffle plate at the exit of pipe is larger than that for no baffle plate.

• 대한기계학회논문집A
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• 제29권7호
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• pp.947-954
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• 2005

The purpose of this study is to develop failure pressure evaluation models, which are applicable to straight pipes and elbows containing an internally wall thinning defect induced by flow-accelerated-corrosion (FAC). In this study, thus, three dimensional finite element (FE) analyses are performed to investigate the dependences of failure pressure of internally wall thinned pipe on the defect shape, the pipe geometry, and the defect location and bend radius of elbow. Also, the existing failure pressure assessment models for externally wall thinned pipes are examined. Based on these, the new models for assessing failure pressure of piping components with an internally wall thinning defect are proposed. Comparison of failure pressure, predicted by proposed models, with FE analysis result shows good agreement regardless of pipe type, defect shape, and defect location and bend radius.

• 대한가정학회지
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• 제47권8호
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• pp.119-130
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• 2009

The purpose of this study was to investigate the interaction and effects of shame and parent-child communication on children and early adolescents' peer pressure. The subjects of this study were 359 children and early adolescents from 5th grade in elementary school to 2nd grade in middle school (187 boys, and 172 girls) in Daejeon city. The results of this research indicated that gender and age played a significant role on the effects of shame and parent-child communication on peer pressure. Open communication with mothers showed a positive relationship with boys' peer pressure, whereas open communication with father showed a negative relationship with boys' peer pressure. The interaction effects of shame and open-communication with fathers and mothers worked differently on peer pressure across gender and age. Interaction effects of shame and open communication with fathers and mothers were significant for boys, but not for girls. Interaction effect of shame and open communication with mothers was significant for children and adolescents.