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교량-차량 동적상호작용을 고려한 시간가변적 시스템 특성 분석
이재훈,이영재,김은주,Lee, Jaehun,Lee, Young Jae,Kim, Robin Eunju 한국전산구조공학회 2022 전산구조공학 Vol.35 No.1
Natural frequency variations in a vehicle-bridge interaction system is examined. The interaction system is designed for a simple beam subject to a moving vehicle. The equation of motion for the system is derived under the quarter-car condition, and numerical simulation is performed. Frequency amplification ratio (FAR) is defined as a ratio between the initial and the varying natural frequency of the system; a discontinuity in the FAR implies a resonance condition. Analysis is mainly focused on patterns, frequency variation characteristics, and discontinuity points of the FAR under the vehicle mass and tire stiffness variations. The result reveals that the interactions between the system affects the natural frequency of both the vehicle and the bridge in similar frequency regions that can be visually identified at the middle of the span using the FAR.
보간법 기반의 파라메트릭 차수축소모델을 이용한 구조최적설계
이재훈(Jaehun Lee),조맹효(Maenghyo Cho) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
In this study, design optimizations for structural parameters have been conducted by using the interpolation-based parametric reduced order model (IBPROM). In particular, the substructuring scheme was selectively employed for a certain type of design parameters to enhance the efficiency of the optimization. For the design optimization of size parameters, the parameters are affinely decomposed from the system matrices. Therefore, it is easy to reduce the full order model by using various reduction techniques, i.e., proper orthogonal decomposition. On the other hand, the shape parameters cannot be exactly decomposed due to the non-affine characteristics. In this case, we need to apply the congruence transformation in order to interpolate the each reduction mode in Euclidean space. Various design optimization examples are studied to demonstrate the efficiency and accuracy of the proposed IBPROM.
오일러 방정식과 자유 후류법을 이용한 헬리콥터 로터의 비정상 공력 해석 연구
이재훈(Jaehun Lee),위성용(Seongyong Wie),권장혁(JangHyuk Kwon),이덕주(Duckjoo Lee),김대희(Dahee Kim) 한국전산유체공학회 2007 한국전산유체공학회 학술대회논문집 Vol.2007 No.-
In this study the unsteady aerodynamic analysis of a hovering helicopter rotor is performed For the accurate flow field analysis Euler equations and the free wake method are coupled The Euler equations are solved to find the pressure distribution around the rotor, and free wake method is used to give the boundary condition for the solution of Euler equations. Also, vortex strength and wake motion after the rotor are simulated by the free wake method The accuracy of the present method is compared with the source sink model. The present method is applied to the hovering Caradonna-Tung rotor and compared with experimental results.
이재훈(Jaehun Lee),김수환(Suwhan Kim),안중기(Joongki Ahn),권장혁(Jang Hyuk Kwon) 한국전산유체공학회 2004 한국전산유체공학회 학술대회논문집 Vol.2004 No.-
In gradient based optimization methods, the finite differencing which uses small perturbations in the design variables has been used to calculate the sensitivity. Recently, the automatic differentiation has been widely studied to calculate the function value and the sensitivities simultaneously. In this paper, the applicability of the automatic differentiation in the aerodynamic design optimization is studied, ADIFOR and TAPENADE are used to generate the codes which give the function value and the sensitivities for 2D compressible inviscid flows.
이재훈(JaeHun Lee),박순영(Soon-Young Park),정원일(Warnill Chung),배해영(Hae-Young Bae) 한국정보과학회 2003 한국정보과학회 학술발표논문집 Vol.30 No.1A
분산된 공간 데이터를 효과적으로 저장, 관리하고 공유하기 위하여 분산 공간 데이터베이스 시스템의 필요성이 대두되었다. 분산 공간 데이터베이스 시스템은 많은 변화가 있는 환경이기 때문에 최적화된 질의 플랜을 작성하기가 어렵고 또한 고비용의 공간 연산 비용을 고려해야 하는 문제를 가지고 있다. 본 논문은 질의 실행 시간에 변화된 분산 데이터베이스 환경을 고려하여 질의를 수행하여 공간 조인을 병렬적으로 수행하는 동적 콜렉터를 제안한다. 동적 콜렉터는 분산 데이터베이스 환경의 변화에 적응할 수 있으며 분산 공간 조인을 효율적으로 처리할 수 있다.
PARSEC 함수를 이용한 에어포일의 공력 형상 설계 연구
이재훈(Jaehun Lee),정경진(Kyungjin Jung),권장혁(JangHyuk Kwon),안중기(Joongki Ahn) 한국전산유체공학회 2007 한국전산유체공학회 학술대회논문집 Vol.2007 No.-
In the shape design optimization of an airfoil, the shape function has been used to find the optimal airfoil shape for given conditions. The parameters determining the airfoil shape are used in the shape design optimization as design variables. However, they usually don’t have physical meaning. The PARSEC(Parametric Shapes) function is a recently proposed shape function and its parameters have the physical meaning. In this study the usefulness of the PARSEC is tested for the RAE2822 airfoil in the transonic flow region to reduce the shock strength and the result is compared with Hicks-Henne function. The optimized airfoils reduce the shock strength and they show similar result.