• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.813-820
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• 2005

In this study, finite element modeling and structural vibration analyses of a gyrocopter have been conducted considering dynamic hub-loads due to rotating blades. For this research, 3D CATIA models for most mechanical parts are exactly prepared and assembled into the final aircraft configuration. Then the dynamic finite element model including several non-structural parts are constructed based on the exact 3D CAD data. Computational structural dynamics technique based on finite element method is applied using both MSC/NASTRAN and developed in-house code which can largely reduce the pre and postprocessing time of general transient dynamic analyses. Modal based transient and frequency response analyses are used to efficiently investigate vibration characteristics. The results include natural frequency comparison for different fuel and pilot conditions, fundamental natural mode shapes, frequency responses and transient acceleration responses of the present gyrocopter model.

• Structural Engineering and Mechanics
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• 제42권6호
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• pp.815-829
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• 2012

This paper proposes a nonlinear computational modeling approach for the behaviors of structural systems subjected to fire. The proposed modeling approach consists of fire dynamics analysis, nonlinear transient-heat transfer analysis for predicting thermal distributions, and thermomechanical analysis for structural behaviors. For concretes, transient heat formulations are written considering temperature dependent heat conduction and specific heat capacity and included within the thermomechanical analyses. Also, temperature dependent stress-strain behaviors including compression hardening and tension softening effects are implemented within the analyses. The proposed modeling technique for transient heat and thermomechanical analyses is first validated with experimental data of reinforced concrete (RC) beams subjected to high temperatures, and then applied to a bridge model. The bridge model is generated to simulate the fire incident occurred by a gas truck on April 29, 2007 in Oakland California, USA. From the simulation, not only temperature distributions and deformations of the bridge can be found, but critical locations and time frame where collapse occurs can be predicted. The analytical results from the simulation are qualitatively compared with the real incident and show good agreements.

• 전기학회논문지
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• 제58권5호
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• pp.873-878
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• 2009

When the transmission lines are initially energized for power system restoration, the power system suffers the various overvoltages that can be classified as steady-state, transient, and dynamic overvoltages. For the accurate analyses of these overvoltages, many researchers utilize different simulation tools such as Power System Simulator for Engineering(PSS/E). Although PSS/E provides good solutions in steady-state and dynamic overvoltages, it is not suitable for transient overvoltages. Therefore, transient overvoltages are simulated by using Electro-Magnetic Transients Program(EMTP) developed for the analysis of transients in the power system. Recently, EMTP can be also used to simulate dynamic behavior of the system. In order to analyze the transient overvoltages with steady-state and dynamic overvoltages, the authors adopt EMTP as the simulation tool for the analysis of overvoltages. This paper presents the simulation results for the analyses of various overvoltages, and the possibility of EMTP to be used for these types of analyses.

• Journal of Advanced Marine Engineering and Technology
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• 제17권4호
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• pp.87-99
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• 1993

Nowadays, the cartridge valve can be controlled proportionally in remote place by adopting proportional solenoid and it becomes widely used as control component in hydraulic systems. Especially, multi stage proportional valve is attractive because it consumes less input power though its characteristics might slightly be defected. But, the system parameter should be carefully chosen to obtain optimistic characteristics. This study concerning three stage proportional throttle control valve is purposed to examine the influences of paameters to the dynamic characteristics. The typical transient and frequency responses of proportional throttle control valve were inspected through the experiments and compared to those derived from the theoritical analyses. And it was confirmed that the analyses are appropriate. Then the influences of various system parameters to the dynamic characteristics were examined by means of simulations. For the analyses, the basic equations derived from lumped model were linearized and the linearized equations were transformed to the transfer functions between inputs and outputs. Then the transient responses and frequency responses were obtained from transfer functions. 1. It is appropriate to estimate the dynamic characteristics of valve which has relatively sophisticated structure by means of system analyses using linearized equations. 2. Though the valve has two pilot stages, fairly good characteristics can be obtained by carefully choosing system parameters. 3. Main valve very quickly follows the movement of second pilot valve when the parameters of main valve(the oil supply passage and discharge passage fpr second pilot valve) are appropriately chosen.

• 대한전자공학회논문지SD
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• 제38권1호
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• pp.1-12
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• 2001

2차원 소자 시뮬레이터를 이용하는 혼합모드 과도해석을 통해, NMOS 트랜지스터를 ESD 보호용 소자로 사용하는 CMOS 칩에서의 HBM ESD 현상에 대한 과도해석 방법론을 제시하고 HBM 방전 미케니즘에 대해 상세히 분석하였고, 보호용 소자 내에서의 2차항복 현상을 성공적으로 시뮬레이션하여 소자 파괴에 이르는 미케니즘을 설명하였다., 보호용 소자 구조의 변화가 방전 특성에 미치는 영향을 조사하기 위해 DC 해석 결과와 혼합모드 과도해석 결과를 비교 분석하였고, 분석 결과를 근거로 하여 HBM ESD에 보다 견고한 보호용 소자의 구조 설계에 대해 논의하였다.

• 한국전산유체공학회지
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• 제7권2호
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• pp.17-24
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• 2002

The transient flow fields in a direct injection engine was analyzed by using the STAR-CD CFD code doting the intake/compression processes. The analyses were focused on the computation grid generation by using the IC3M code which is a pre-developed and especially well adapted for the analyses of internal combustion engine. The results showed that the used grid generation technique was well suited for the flow analyses on any internal combustion engine.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2001년도 추계 학술대회논문집
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• pp.63-69
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• 2001

The transient flow fields in direct injection engines were analyzed by using the STAR-CD CFD code during the intake/compression processes. The analyses were focused on the computation grid generation by using the IC3M code which is a pre-developed and especially well adapted for the analyses of internal combustion engines. The results showed that the used grid generation technique was well suited for the flow analyses on any internal combustion engines.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.1000-1007
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• 2007

In this study, structural vibration analyses of a smart unmanned aerial vehicle (UAV) have been conducted considering dynamic hub-loads of tilt rotor. Practical computational structural dynamics technique based on the finite element method is applied using MSC/NASTRAN. The present UAV(TR-S5-04) finite element model is constructed as a full three-dimensional configuration with different fuel conditions and tilting angles for helicopter, transient and airplane flight modes. In addition, the 3-dimensional supporting equipment structures of electronic devices are considered for vibration analysis. As the results of this study, transient structural displacements and accelerations are presented in detail. Moreover, vibration characteristics of structural parts and installed equipments are investigated for different fuel conditions and tilting angles.

• 한국항공우주학회지
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• 제32권3호
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• pp.58-65
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• 2004

유한요소법을 이용하여 액체 로켓 엔진 터보 펌프 터빈의 천이 열전달 및 구조 해석이 수행되었다. 해석 모델은 3차원 8절점 등매개변수 솔리드 요소로 구성되었으며, 전체 모델의 1/80만이 해석되었다. 열 스파이크를 포함하는 시동 조건과 정상상태에서의 하중이 고려되었다. 블레이드 면 위의 열전달 계수는 상용 열유동 해석 프로그램인 Fluent를 이용하였다. 개발된 유한 요소 코드를 이용하여 시동 및 정상상태에서 천이 열전달 응답을 구하였다. 또한, 원심력과 열하중이 가해질 때, 최대 응력 및 슈라우드의 변위를 구하였다.

• 대한기계학회논문집A
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• 제33권9호
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• pp.949-956
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• 2009

The C(t)-integral describes amplitude of stress and strain rate field near a tip of stationary crack under transient creep condition. Thus the C(t)-integral is a key parameter for the high-temperature crack assessment. Estimation formulae for C(t)-integral of the cracked component operating under mechanical load alone have been provided for decades. However, high temperature structures usually work under combined mechanical and thermal load. And no investigation has provided quantitative estimates for the C(t)-integral under combined mechanical and thermal load. In this study, 3-dimensional finite element analyses were conducted to calculate the C(t)-integral of elastic-creep material under combined mechanical and thermal load. As a result, redistribution time for the crack under combined mechanical and thermal load is re-defined through FE analyses to quantify the C(t)-integral. Estimates of C(t)-integral using this proposed redistribution time agree well with FE analyses results.