• Journal of Energy Engineering
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• v.7 no.2
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• pp.202-208
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• 1998

As in the other industrial processes, a nuclear power plant involves a steam relieving process through which condensable steam is discharged and condensed in a subcooled pool. An analysis of steam discharge transients was carried out using the method of characteristics to determine the flow characteristics and dynamic loads of piping that are used for structural design of the piping and its supports. The analysis included not only the steam flow rate but also the flow rates of the air and water which originally exist in the pipe. The analytical model was developed for a uniform pipe with friction through which the flow was discharged into a suppression pool. Including the combinations of system elements such as reservoir, valve and branching pipe lines. The piping flow characteristics and dynamic loads were calculated by varying system pressure, pipe length, and submergence depth. It was found that the dynamic load, water clearing time and water clearing velocity at the water/air interface were dependent not only on the system pressure and temperature but also on the pipe length and submergence depth.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2006.03a
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• pp.195-203
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• 2006

The crossing construction under railroad have two methods which are cut and cover and trenchless method. first, cut and cover method is an extremely limited method concerning non-running time. Whereas, trenchless method is free from restriction such as train speed and running time, and has the strong points of safe and rapid construction. Front Jacking method, one of the trenchless methods, is frequently applied recently due to its stability during construction and vantage of assuring schedule reliability. The procedure is that after minimizing interlocking friction with structure and earth pressure due to jacking the small steel tube, pulling the precast box manufactured at the field in the ground using PC strand and hydraulic Jack. This method is able to be applied regardless of section size and length of box and condition of ground. And that is also pro-environmental. This paper presents the case of Daejeon E. W. perforate Road Project applied with the Front Jacking method.

• Journal of Korean Society of Transportation
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• v.31 no.4
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• pp.58-66
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• 2013

Due to the characteristics of urban freeways such as heavy traffic and high speed, work zone on urban freeways causes the increase of not only the likelihood of crash occurrence but also traffic congestion caused by lane drop, lane change, acceleration/deceleration, and etc. This paper aims to determine the proper length of transition area that satisfies two criteria, mobility and safety, to make the operation of work zone more efficient. For the analysis, three different scenarios were developed by the number of lanes and the proper length of transition area were determined by changing the length from 100m to 500m in 100m increments. The results showed that the proper length of transition area for 3- and 4-lane freeways is 300m, whereas the proper length of 2-lane freeways is 200m. The results indicated that the different length of transition area based on the number of lanes is more desirable and efficient.

• Journal of the Korea Convergence Society
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• v.8 no.5
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• pp.179-184
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• 2017

The cage of a tapered roller bearing keeps the gap between the rollers, which prevents friction, wear and suppresses heating. The material of the cage is changing from metal to plastic for lightening the weight. If the cage is severely deformed due to resonance, the roller may not be able to roll and even get off the cage. In this paper, the dynamic characteristics of the cage is analyzed according to the cage material. Under the assumption that a train runs at the highest speed, frequency harmonics of that speed is calculated, and the comparative analysis is carried out in order to select the optimum thickness of the cage, which is easy to change among the cage design variables for avoiding the resonance.

• Proceedings of the KSR Conference
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• 2005.05a
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• pp.646-654
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• 2005

The crossing construction under railroad have two methods which are cut and cover and trenchless method. First, cut and cover method is an extremely limited method concerning non-running time. Whereas, trenchless method is free from restriction such as train speed and running time, and has the strong points of safe and rapid construction. Front Jacking method, one of the trenchless methods, is frequently applied recently due to its stability during construction and vantage of assuring schedule reliability. The procedure is that after minimizing interlocking friction with structure and earth pressure due to jacking the small steel tube, pulling the precast box manufactured at the field in the ground using PC strand and hydraulic Jack. This method is able to be applied regardless of section size and length of box and condition of soil. And that is also pro-environmental. This paper presents the case of Daejeon E. W. perforate Road Project applied with the Front Jacking method.

• Explosives and Blasting
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• v.23 no.1
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• pp.9-17
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• 2005

This study is to clarify the comparative relationship and mechanical anisotropy of granite distributed in the Nam-weon on the subject of weathered rock mass sea water surroundings. Artificial weathering test is defined as a test, which controls the weathering rate and agents by controlling the weathering rate and agents by artificial environmental of salt water. Increased weathering degree is large indicated by weathering salt water, such as apparent specific gravity, absorption, porosity, uniaxial compression strength, P-wave velocity, slake durability, shore hardness, indirect tensile strength(brazilian test) and cohesion were measured. As the Weathering salt water proceeds, cracks develope increasingly. A number the cracks affect the rock deformation. Therefore, stress-strain curve of weathered salt water rock in one confined state are quite differ from weathered fresh water rock those. A reason of their deformation type is the formation of micro-cracks and potential porosity caused by artificial weathering test.

• Tunnel and Underground Space
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• v.22 no.5
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• pp.354-364
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• 2012

In order to evaluate the physical properties of rock which might serve as a database for both mining and civil works, a lot of laboratory tests for Jecheon limestones were conducted to find unit weight, absorption ratio, porosity, elastic wave velocity, uniaxial compressive strength, Young's modulus, poisson's ratio, tensile strength, shore hardness, friction angle and cohesion. On investigation of the mechanical properties of both the gray limestone and the clayey limestone distributed in the studied region, the clayey limestone turned out to have more weak mechanical properties which might come from low unit weight, high absorption ratio and high porosity of rocks. The failure criteria of Jecheon limestones were discussed by means of both Mohr-Coulomb criterion and Hoek-Brown criterion. Regression analyses of the physical properties obtained from a lot of laboratory tests were also conducted by means of both linear and multiple regression analyses.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.95-95
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• 2010

자동차 산업에서 차체를 성형하는 프레스 금형 산업은 꾸준히 증가하고 있는 자동차 생산대수와 함께 성장해가고 있으며, 자동차 산업의 국제 경쟁이 심해지고 소비자들의 요구가 다양해짐에 따라 신제품 개발주기에 발맞추어 금형의 제작에도 단납기 및 비용절감을 위한 노력과 제품의 품질 향상을 위해 신기술, 신공법이 적용되고 있다. 한편 자동차 차체를 제작하는 프레스 금형가공은 박판소재를 원하는 형상으로 제작하는 공정으로써, 프레스의 상 하 운동을 이용하여 강판을 성형한다. 이러한 금형의 형태는 곧 자동차 차체 제품의 형태를 완성하므로 제품을 성형하는 도중에 금형과 소재의 마찰에 의해 금형의 마모나 마멸이 발생하여 제품의 품질을 저하시킬 우려가 있다. 따라서 금형의 내마모성 및 수명을 향상시키기 위한 방안들 중 표면경화처리가 행해지고 있으며, 그중 공정 속도가 빠르고 국부적인 열처리가 가능한 레이저 표면처리 방법이 많은 관심을 받고 있다. 본 연구에서는 이러한 금형의 성질을 향상시키기 위해 고출력 다이오드 레이저를 이용하여 프레스 금형공정 중 드로잉(drawing) 공정에의 적용을 위한 표면경화처리를 실시하였다. 최대출력 4.0kW의 다이오드 레이저를 사용하였으며, 6축 외팔보 로봇에 열처리용 광학계를 장착하여 열처리를 실시하였다. 또한 광학계 부근에는 적외선 온도센서가 부착되어있어 열처리시 시험편의 표면온도를 실시간으로 측정할 수 있도록 구성되어져있다. 시험편은 금형재료용 구상흑연 주철인 FCD550 소재를 사용하였으며, 공정변수에 따른 열처리 특성을 파악하고, 그 경화특성을 평가하였다. 실험 결과, FCD550 소재의 표면 열처리시 레이저 출력 3.5kW, 빔 이송속도 3mm/sec에서 최적의 열처리 특성을 나타내었으며, 이때의 최고 경도는 930Hv을 나타내며 모재에 비해 경도가 3배 정도 상승하는 우수한 경화특성을 보였다.

• Journal of the Korean Geotechnical Society
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• v.30 no.9
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• pp.5-17
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• 2014

A series of model tests were conducted in order to observe the failure surface generated around a diaphragm wall embedded in ground with high groundwater table. Images of the soil deformation around the model wall were captured during the test. The configuration of the failure surface in soil around the model wall could be obtained from analyzing the image of the soil deformation. Based on the configuration of the failure surface observed in the model test, an analytical approach was proposed to predict the uplift capacity of a diaphragm wall installed in ground. The analytical approach considers not only the wall properties such as length, thickness and surface roughness of diaphragm walls but also the soil strength properties such as the internal friction angle and the cohesion of soil. The predicted uplift capacity of a diaphragm wall shows a good agreement with the experimental one measured in the model test.

• Water for future
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• v.27 no.2
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• pp.111-120
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• 1994

In this experimental research, the maximum scour depth at pier was studied. The model of the pier of San Gye bridge in the Bocheong stream was set for experimental pier scour studies. Several model verification processes were conducted through the roughness comparisons between model and prototype, pursuring scour depth variations with time depending upon channel bed variation, the comparison of the ratio between falling velocities and shear velocities in the model and prototype, and the comparison of pier scour between experimental data and field measuring data. The experiments were conducted in the free flow conditions and pressure flow conditions. The maximum scour depth at piers in the pressure flow conditions is twice as much as compared to the free flow conditions. Also, the maximum scour depth variations are indicated in the figures based on the Froude numbers, opening ratios, water depths and approaching angles in the free surface flow conditions.