• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.409-410
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• 2013

최근 연비 개선 문제에서 전 세계적으로 화두가 되고 있는 ISG라 함은 IDLE STOP & GO의 약자로 공회전시 낭비되는 연료를 저감하고 배출가스를 최소화 하는 친 환경 저연비 시스템이다. 차량의 성능 향상 및 안락함과 안전도의 개선을 위하여 차량에 사용되는 전기 시스템은 점차 증가하고 있으며, 전기시스템의 증가에 따라 차량에 작용하는 전기 부하량은 매년 늘어나고 있다. 이와 같은 ISG 구동을 위해서는 대전력 응용에 적합한 컨버터 연구가 활발히 진행되고 있다. 본 논문에서는 10kW급 고전압 직류 변환장치(High voltage DC-DC Converter ; HDC)와 1.5kW급 저전압 직류 변환장치(Low voltage DC -DC Converter : LDC) 설계하여 검증하였다.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.116-120
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• 2001

In swash plate type axial piston hydraulic pump and motor, the piston shoe is periodically pressurized with square function shape by supply pressure load as rotation of cylinder barrel. Therefore the recess pressure on bottom part of piston shoe is suddenly increase through orifice in the piston shoe. In this study, we simulated that the frequency response of the recess pressure against with change of supply pressure with analysis tool. Also, we evaluate the dynamic response characteristics of overbalanced hydrostatic bearing with change of the orifice diameter.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.961-966
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• 2004

The cylinder without seal has a piston with air bearing which is partly cylindrical and conical shape. The description of system geometry is deviation by the flow rate equation. Then pressure distribution and bearing force equations are derived. Several non-dimensional parameters are suggested. The relationship among bearing force, leakage flow and geometry of the bearing is investigated by simulation. And determination method for optimal design of sealless cylinder is given. A prototype of sealless cylinder which had rod bearing with four pockets, five pockets, and six pockets was built respectively. As a result of leakage flow test, it is evaluation to air bearing in sealless cylinder.

• Journal of Chest Surgery
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• v.30 no.2
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• pp.119-124
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• 1997

Using isolated rat heart preparations, we observed the protective effe ts of verapamil cardioplegia on ischemic myocardial injury. Isolated rat hearts were subjected to global ischemia at $25^{\circ}C$ Twenty four isolated Sprague Dawley rat hearts underwent 30 minutes of the retrograde nonworking perfusion with Krebs-Henseleit buffer solution followed by $25^{\circ}C$ cardioplegic solution (St. Thomas'Hospital Cardioplegic Solution) for 60 minutes. Before ischemic arrest, rat hearts were treated with cold cardioplegic solution in control group (n=12) and cold cardioplegic solution with verapamil (1 mg/L) in experimental group (n=12). After 60 minutes of ischemia, hemodynamic and biochemical parameters such as heart rate, left ventricular pressure (LVP), + dp/dt max, coronary flow and creatine phosphokinase (CPK) were measured before giving cardioplegia and 30 minutes after reperfusion. Verapamil group exhibited greater recovery of heart rate, LVP, +dpldt max, coronary flow and CPK than control group (p < 0.05).

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.1
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• pp.83-92
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• 2007

There are many numerical methods to solve large-scale fluid-structure interaction(FSI) problems. However, these methods require very fine mesh to achieve the reasonable numerical accuracy and stability due to the concentrated and volatile hydrodynamic pressure caused by the liquid sloshing. Consequently, the numerical analysis targeting for the long-period time response with the desired numerical accuracy Is very highly time-consuming. The aim of this paper is to suggest a new method to analyze the hydroelastic behavior of the LNGC containment by using the global-local numerical approach. The reliability of the presented method is firstly examined, and then its efficiency is demonstrated by presenting that the long-period local responses of the LNGC containment are obtained with relatively short CPU time.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.4
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• pp.171-187
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• 1991

In the present study, an analytical solution method is proposed for the seismic design of cantilever sheet pile walls and anchored sheet pile walls used in harbor construction. Seepage pressures, together with a change in magnitudes of effective horizontal soil pressures, are included in the proposed solution method. Also, the Mononobe-Okabe analysis as well as the Westergaard and Matsuo-Ohara theory of hydrodynamic pressures is used in the proposed method. Further, the choice of values for safety factors is examined for the seismic design of anchored sheet pile walls, and the effects of various parameters(dredge line slope, differential in water levels, anchor position, and wall friction angle) on embedment depth, anchor force, and maximum bending moment are analyzed for anchored walls in dense sand deposits. In addition. the tables that could be used for preliminary seismic design of anchored walls in dense sands are presented. The proposed method deals with the sheet pile walls with free earth support.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.1
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• pp.111-117
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• 2010

A three-dimensional numerical model is employed to investigate wave deformation due to a submerged structure. The three-dimensional numerical model solves the spatially averaged Navier-Stokes equations for two-phase flows. The LES(large-eddy-simulation) approach is adopted to model the turbulence effect by using the Smagorinsky SGS(sub-grid scale) closure model. The two-step projection method is employed in the numerical solutions, aided by the Bi-CGSTAB technique to solve the pressure Poisson equation for the filtered pressure field. The second-order accurate VOF(volume-of-fluid) method is used to track the distorted and broken free surface. A simple linear wave is generated on a constant depth and compared with analytical solutions. The model is then applied to study wave deformation due to a submerged structure and the predicted results are compared with available laboratory measurements.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.59-59
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• 2011

파랑의 전파와 변형에 대한 연구에는 수심방향으로 적분한 2차원방정식인 완경사방정식과 Boussinesq 방정식을 기반으로 한 수치모형을 이용한 연구가 최근까지 가장 활발하게 진행되어 오고 있다. 그러나 실제 구조물의 설계에는 2차원 수치모형에서 고려할 수 없는 수심방향 유속에 기인한 정확도의 문제로 인해 구조물의 형상과 재원을 설계하기 위한 정교한 수치모형실험이 어려워 주로 수리모형실험에 의존해 왔다. 수리모형실험은 실제 현상을 가장 잘 재현해낼 수 있어 신뢰성이 매우 높지만 다양한 실험을 수행하기가 어렵고 많은 시간과 비용이 소요되는 단점이 있다. 이에 따라 최근 수심방향으로 완전한 운동방정식인 Navier-Stokes 방정식을 푸는 3차원 수치모형에 대한 연구가 활발히 진행되고 있다. 이론적으로 매우 우수한 모형이긴 하나 정확도 높은 결과를 얻기 위해서는 매우 조밀한 격자를 필요로 하기 때문에 아직까지 막대한 계산시간이 필요하다는 단점이 있으나 컴퓨터 기술이 급격한 속도로 발전하고 있어 Navier-Stokes 방정식 모형의 적용 가능성은 계속 높아지고 있다. 파랑변형을 다루는 수치모형실험을 수행할 때 외부조파를 사용할 경우 구조물이나 지형에 의해 반사되어 나온 파랑이 조파지점에 도달할 때 실험영역으로 재 반사되는 문제가 발생한다. 이를 해결하기 위해 내부조파기법의 개발에 대한 연구가 필수적이었으며, 자유수면변위를 변수로 사용하는 모형의 경우 그 연구가 매우 활발하게 진행되어 왔다. 한편, Navier-Stokes 방정식 모형의 경우 자유수면변위를 변수로 사용하는 2차원 모형에 비해 상대적으로 연구가 미흡하였다. 본 연구에서는 기존의 연직 2차원 Navier-Stokes 방정식 모형에 사용된 연속방정식에 질량 원천항을 추가하는 내부조파기법을 도입하여 3차원 수치모형에서 고립파를 내부조파하고, 급경사에서의 고립파의 처오름 및 처내림 현상을 수리모형 실험결과와 비교 및 분석하였다. 수치모형은 Navier-Stokes 방정식을 엇갈림 격자체계에서 계산하는 동수압 모형으로서, Two-step projection 기법을 사용하는 유한차분모형을 사용하였다. 본 수치모형은 난류의 해석을 위해서 상대적으로 큰 에디(eddy)만을 고려하는 SANS(spatially averaged Navier-Stokes) 방정식을 계산하는 LES(large-eddy-simulation) 기반의 수치모형으로, 난류 모델링을 위해 Smagorinsky LES 모형을 사용한다. 또한, 압력장의 계산을 위해 Bi-CGSTAB 기법을 이용하여 Poisson 방정식의 해를 구하였으며, 자유수면 추적을 위하여 2차 정확도의 VOF(volume-of-fluid) 기법을 사용하였다. 수치모형실험이 전체적으로 수리모형실험에서 관측한 파랑의 처오름 및 처내림 현상을 잘 재현하고 있는 것으로 나타났으며, 정량적인 비교를 통해 수치모형의 성능을 검증하였다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.1
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• pp.18-24
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• 2010

In this study, a tsunami fragility methodology was determined for a probabilistic safety assessment(PSA) induced tsunami event in Nuclear Power Plant(NPP) site. For this purpose, a fragility evaluation method was presented using previous external PSA method. Failure mode and failure criteria about major safety related equipments and structures were determined. Finally, a tsunami fragility assessment was performed for offsite transformer in NPP site. For the fragility evaluation, structural failure like overturning and sliding and functional failure induced by inundation. Through this study, it can be concluded that a functional failure according to inundation height was governed total probability of failure of offsite transformer in NPP.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.1
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• pp.95-104
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• 2003

This paper deals with the analytic and FEM analyses of sloshing frequency response of incompressible, invicid and irrotational flow in two dimensional rectangular tank. We use Laplace equation based on potential theory as governing equation. For small amplitude sloshing motion, the linearized free surface condition was applied and the analytic solution as obtained by the separation of variables. To simulate the effect of the energy dissipation due to viscous damping, artificial viscous coefficient is introduced and the divergence of response at resonance frequencies may be avoided by this coefficient. This problem was solved by FEM using 9-node elements in order to predict the maximum amplitude of sloshing response. Numerical results of free surface height, fluid pressure and fluid force show good agreement with those by analytic solution. After verifying the test FEM program, we analyze the frequency response characteristics of sloshing to the fluid height.