• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.84-91
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• 2003

Flow-Induced Vibration of steam generator tubes may result in fretting wear damage at the tube-to-support locations. KSNP(Korean Standard Nuclear Power plant) steam generators experienced fretting wear in the upper part of U-bend above the central cavity region of steam generators. This region has conditions susceptible to the flow-induced vibration, such as high flow velocity, high void fraction, and longer unsupported span. To improve its performance, APR1400 steam generator is designed with additional supports in this region to reduce unsupported span and to reduce peak velocity in the central cavity region. In this paper, we examined its performance improvement using ATHOS code. The thermal-hydraulic condition in the region of secondary side of APR1400 steam generator is obtained using the ATHOS3 code. The effective mass for modal analysis is calculated using the void fraction, enthalpy, and operating pressure information from ATHOS3 code result. With the effective mass distribution along the tube, natural frequency and mode shape is obtained using ANSYS code. Finally, stability ratios and real mean squared displacements for selected tubes of the APR1400 steam generator are computed. From these results, the current design of the APR1400 steam generator are examined.

• Journal of Advanced Marine Engineering and Technology
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• 제25권4호
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• pp.817-824
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• 2001

In the present study, flow characteristics of turbulent oscillatory flows in the exit region connected to the square-sectional $180^{\circ}$curved duct was investigated experimentally. The experimental study for air flows was conducted to measure velocity profiles, shear stress distributions by using the Laser Doppler Velocimetry(L.D.V) system with the data acquisition and processing system of Rotating Machinery Resolver(R.M.R) and PHASE software. The results obtained from the experimentation were summarized as follows : The critical Reynolds number for a change from transitional oscillatory flow to turbulent oscillatory flow was about 75,000 in the 90 region of dimensionless axial position (x/Dh) which was considered as a fully developed flow region. In the turbulent oscillatory flow, velocity profiles of the inflow period in the entrance region were gradually developed, but those of the outflow period were not changed nearly. Shear stress distributions of turbulent oscillatory flow was gradually increased as the flow proceeds to downstream.

• 대한기계학회논문집B
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• 제32권3호
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• pp.173-180
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• 2008

Diurnal variation of the flow over a forest canopy on a mountain slope is simulated numerically. In the daytime, the earth surface is heated by the solar radiation and the flow goes up the mountain due to the buoyancy force, and during the night, the air is drained downward along the slope owing to the cooling of the surface by radiation. In this flow process the forest canopy that consists of leaf region and the trunk region plays a dominant role as a momentum sink to the flow, thus the modeling of the leaf area region and trunk region is critical to the successful flow simulation. In the present study, a field measurement in an experimental forest in the State of Oregon in the United States is numerically analyzed. The resistance to the flow in the leaf region is directly related to the leaf area density (LAD), and the trunk is modeled as a cylinder.

• Educational Technology International
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• 제21권1호
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• pp.31-67
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• 2020

The purpose of this study was to propose an education cooperation model for Human Resources Development (HRD) in Asia-Pacific region in response to environmental changes in business and industry. In order to carry out the model, this study reviewed the key features of human resources in the APEC which is a symbolic regional integration entity in Asia-Pacific region, shaped critical issues related with HRD in this region and then analyzed the trends of education cooperation projects conducted by the APEC in terms of topics, implementation methods and proposing economies of the projects. In result, this study proposed a triangular education cooperation model for HRD consisting of three elements: Voluntary Partnership, Information on Needs and Support for Cooperation. These interconnected and interdependent elements were designed to encourage actors to participate in education cooperative activities with their own willingness, produce and manage research-based information required for sustainable cooperation and support communication and connectivity among actors for effective activities. Also, this study expected that this model would make a commitment to narrowing educational divides, enhancing global-standard skills development, facilitating public and private partnership and organizing the foundation of future education for cultivating creative talents in the era of innovation for APEC members.

• 한국안전학회지
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• 제28권5호
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• pp.21-26
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• 2013

Delamination of cover concrete due to re-bar corrosion is a critical damage reducing structural safety of reinforced concrete structures. Therefore, it should be detected and evaluated to provide appropriate maintenance to recover structural integrity. Impact-echo method, which utilizes thickness vibration characteristics of delaminated concrete section, is effective for detection and evaluation of small areal size delamination. However, it may not be applicable for large areal size delamination in which flexural vibration modes are dominated. In this study, applicability of vibration mode shapes of delaminated concrete section is investigated for visualization of delamination region in concrete structures. Numerical and experimental modal tests are performed to estimate mode shapes of delaminated concrete section and linear absolute summation technique is proposed for effective visualization of delamination region based on estimated mode shapes.

• 한국자동차공학회논문집
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• 제16권4호
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• pp.29-37
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• 2008

Vehicle stability is a very important subject in vehicle design and control, because vehicle safety is closely dependent upon its dynamic stability. For the vehicle stability analysis, the nonlinear vehicle model of a mid-size car with three DOF - longitudinal, lateral and yaw - is employed. A rigorous method is used to determine the vehicle stability region in plane motion. An algorithm is used to materialize a topology theorem, which enables to find the exact stability region. A stability criterion for the critical cornering is proposed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 D
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• pp.1337-1339
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• 1998

The trench termination scheme is introduced for high voltage devices. The curvature of the depletion region at field limiting ring is critical factor to determine the breakdown voltage. The smooth curvature of the depletion junction alleviate the electric field crowding effect around this region. In the trench field limiting ring, the radius of the depletion region is smaller than conventional field limiting ring, but the distance between every trench is spaced small enough to punchthrough before initiation of local breakdown. The trench field limiting ring on silicon can ne formed by RIE followed by oxidation on side wall surface of the trench, and polysilicon filling. The combined termination of this trench floating field ring and field plate have been designed and analyzed. The breakdown simulation by 2-dimensional TCAD shows that the cylindrical junction breakdown voltage for substrate doping might be 99 percent of the ideal breakdwon voltage for substrate doping concentration of $3\times10^{14}cm^{-3}$ with about $100{\mu}m$ of lateral termination width.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.521-524
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• 2002

In the present study, kinetic energy of laminar steady flow in the exit region connected to the square-sectional $180^{\circ}$curved duct was investigated experimentally. The experimental study for air flows was conducted to measure kinetic energy distributions by using the Particle Image Velocimetry(PIV) system with the data acquisition and processing system of Cactus 2000 software. The results obtained from experimental studies are summarized as follows : (1) The critical Reynolds number for a change from laminar steady flow to transitional steadt flow was about 1910, in the 50 region of dimensionless axial position (x/Dh) whirh was considered as a fully developed flow region. (2) Maximum kinetic energy of laminar steady flow was gradually increased as the Reynolds number increased.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1995년도 추계학술발표회논문집(1)
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• pp.315-320
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• 1995

The CHF phenomenon has been investigated for water flow under forced and natural circulation modes with vertical round tubes at low pressure and low flow condition. Experiments have been performed by using three different test sections for mass fluxes below 400 kg/㎡s under near atmospheric pressure. The experimental data for forced and natural circulation are compared with each other. To predict the flow rate at the two-phase region our test condition has been analyzed by RELAP5/MOD3 because the local two-phase condition inside the stainless steel tube cannot be directly measured. To predict the CHF with accuracy we have to consider the parameters at the single-phase region as well as the flow behavior at the two-phase region.

• 수산해양기술연구
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• 제17권1호
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• pp.35-40
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• 1981

회전축계의 모델로서 구동원과 상호작용을 고려한 2개원판이 부착된 비대칭축계의 안정성을 연명하기 위해 안정오을 유도하고 수치계기을 행하여 제일, 이공진검성의 불안정구간을 구하였다. 비대칭축계의 위험속도 초과시의 불안정은 축의 비대칭도에 의한 불안정과 Torque 특성에 발생하는 불안정의 2종류로 분류된다. 편심의 위상용이 불안정에 미치는 영향은 매우크며, 이는 후자에 의한 불안정에 기인한다. 감양는 전자에 의해 생기는 불안정을 감소 시키나, 후자에 의한 불안정은 오히려 증가시켜서 자려진동을 유발하므로 주의를 요한다.