Hyun-Su Kim

Optimization Techniques for the Inverse Analysis of Service Boundary Conditions in a Porous Catalyst Substrate with Fluid-Structure Interaction Problems

This paper presents a solution to the inverse problem for the service boundary conditions of thermal-flow and structure analysis in a catalyst substrate. The exhaust-gas purification efficiency of a catalyst substrate is influenced by the shape parameter, catalyst ingredients and so on and is estimated by the thermal flow uniformity. The formulations of the inverse problem of obtaining the thermal-flow parameters (inlet temperature, velocity, heat of reaction, convective heat-transfer coefficient) and the direct problem of estimating from a given outlet temperature distribution are described. An experiment was designed and the response-surface optimization technique was used to solve the proposed inverse problem. The temperature distribution of the catalyst substrate was obtained by thermal-flow analysis for the predicted thermal-flow parameters. The thermal stress and durability assessments for the catalyst substrate were performed on the basis of this temperature distribution. The efficiency and accuracy of the inverse approach have been demonstrated through the achievement of good agreement between the thermal-flow response surface model and the results of experimental vehicle tests.

Structural Integrity Assessment of High-Strength Anchor Bolt in Nuclear Power Plant based on Fracture Mechanics Concept

The failure of a bolted joint owing to stress corrosion cracking (SCC) has been considered one of the most important structural integrity issues in a nuclear power plant. In this study, the failure possibility of bolting, which is used to support the steam generator of a pressurized water reactor, owing to SCC and brittle fracture was evaluated in accordance with guidelines proposed by the Electric Power Research Institute, which are called the Reference Flaw Factor method. For this evaluation, first, detailed finite element stress analyses were conducted to obtain the actual nominal stresses of bolting in which either service loads or bolt preloads were considered. Based on these nominal stresses, the structural integrity of bolting was addressed from the viewpoints of SCC and toughness. In addition, the accuracy of the EPRI Reference Flaw Factor for assessing bolting failure was investigated using finite element fracture mechanics analyses.

A DESIGN STUDY OF 100㎓ BAND LOCAL OSCILLATOR SYSTEM BY USING YIG OSCILLATOR

In this paper, we make a design study for a local oscillator system of the 100 ㎓ band cosmic radio receiving system. We use the YIG oscillator with digital driver which is the main oscillator. This oscillator has a good frequency and phase stability at some temperature variation, and the easy computer aided control characteristics. This total system designed to two subsystem, first is the oscillator system include YIG oscillator, tripler, harmonic mixer and triplexer etc., second is the PLL system to supply the precise and stable local oscillator frequency to mixer. The proposed local oscillator system in this paper can be used in a single or multi pixel receiver because this system can be lock the local oscillator frequency automatically using PC.

Structural Optimization for Nonlinear Dynamic Response of Solenoid Actuator

Abstract : This paper proposes a design optimization approach for core of solenoid actuators by combining optimization techniques with the finite element method (FEM). A solenoid is an important element part which hydrau-lically controls a transmission system, etc. The demanded feature of the solenoid is that it performs an electromagnetic force output being constant regardless of the stroke and being proportional to coil current. The plunger compresses a spring with a minimum force of 12 N over an 1.7 mm travel. The orthogonal array, analysis of variance (ANOVA) techniques and response surface optimization, are employed to determine the main effects and their optimal design variables. The methodology is demonstrated as a optimization tool for the core design of a solenoid actuator. Key words : Electromagnetic analysis(전자기 해석), Solenoid actuator(솔레노이드 액추에이터), Dynamic response (동적응답), Polynomial surrogate model( 다항식 대리모델), Structural optimization(구조최적설계) 1. 서 론 1) 차량의 변속기용 솔레노이드 밸브(Solenoid valve)는 유압을 제어하는 유압부와 밸브의 동작을 담당하는 액추에이터(Actuator)로 구성된다. 자동변속시 제어 압력을 생성하는 솔레노이드 밸브는 변속성능과 품질에 밀접한 관계가 있다. 따라서 솔레노이드 액추에이터의 설계는 액추에이터 거동에 대해 정확한 제어 특성과 범위에 대한 예측이 필요하다.솔레노이드 액추에이터는 작은 변위에 대해 직선 운동이 가능하고 구조가 간단하여 신뢰성과 제작의 편리성이 있다. 액추에이터는 플런저(Plunger)의 이

Assessment of Interaction Effect Between Two Aligned Surface Cracks in Elbows Subjected to Internal Pressure

Adjacent multiple cracks can be found in power plant components such as pressure vessel, piping and so forth. If multiple cracks are detected, it can be affected significant effect to structure integrity due to high interaction effect of the multiple cracks. Therefore general fitness-for-service (FFS) codes and standards propose assessment method for the multiple cracks. The Section XI of ASME Code suggests crack coalescence method for multiple cracks. It employs the approach combining neighbored cracks as single crack if the distance between them is close. In some cases, since this combined rule can be considered as a conservative approach, more accurate investigation of the interaction effect between multiple cracks is needed. In this study, the interaction effect between two aligned coplanar circumferential surface cracks in elbows subjected to internal pressure was investigated. Since most previous studies dealt with only plates or straight pipes, the present research was centered on cracked elbow. FE (Finite element) limit analyses were carried out by changing elbow geometries and crack shapes. Also, applicability of the current criterion for the multiple cracks was discussed.Copyright

Environmental Fatigue Evaluation of a Korean Nuclear Power Plant

In accordance with the recommendation of USNRC and the U.S. license renewal experiences, the effects of reactor coolant environment on the fatigue life have to be considered for the continued operation of operating nuclear power plants as well as for the design of new plants. Although various evaluation methodologies have been suggested to date, a wide range of comparison of the existing methodologies has not been performed. The purpose of this paper is to evaluate the environmental effects on the fatigue life of a reactor pressure vessel and ASME Class 1 piping by the various methodologies and to investigate the effects of the pressure and moment stress histories on the environmental fatigue evaluation. The evaluation results show that the environmental fatigue evaluation results based on the design cumulative usage factors for the reactor pressure vessel and ASME Class 1 piping satisfy the requirement of the ASME code except for charging nozzle. However, when using operating cumulative usage factor, the environmental fatigue evaluation result for the charging nozzle satisfies the ASME code allowable. And the effects of the pressure and moment stress histories on the environmental fatigue evaluation are considered to be small when using the modified rate approach.© 2008 ASME

Restrained Bending Effect by the Support Plate on the Steam Generator Tube with Circumferential Cracks

The steam generator in a nuclear power plant is a large heat exchanger that uses heat from a reactor to generate steam to drive the turbine generator. Rupture of a steam generator tube can result in release of fission products to environment outside. Therefore, an accurate integrity assessment of the steam generator tubes with cracks is of great importance for maintaining the safety of a nuclear power plant. The steam generator tubes are supported at regular intervals by support plates and rotations of the tubes are restrained. Although it has been reported that the limit load for a circumferential crack is significantly affected by boundary condition of the tube, existing limit load solutions do not consider the restraining effect of support plate correctly. In addition, there are no limit load solutions for circumferential cracks in U-bend region with the effect of the support plate. This paper provides detailed limit load solutions for circumferential cracks in top of tube sheet and the U-bend regions of the steam generator tube with the actual boundary conditions to simulate the restraining effect of the support plate. Such solutions are developed based on three dimensional finite element analyses. The resulting limit load solutions are given in a polynomial form, and thus can be simply used in practical integrity assessment of the steam generator tubes.