• 한국전산구조공학회논문집
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• 제17권4호
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• pp.351-363
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• 2004

비보존력을 받는 보-부재의 질량행렬, 탄성강도행릴, circulatory비보존력의 방향변화로 인한 load correction강도행력, 그리고 Winkler 및 Pasternak지반강도행렬을 고려한 운동방정식을 유도하고 divergence 및 flutter에 의한 안정성 해석을 수행한다. 또한 내적 및 외적 감쇠계수를 운동방정식에 포함시킴으로써 감쇠효과를 고려하고, 2차 고유치문제의 해법(quadratic eigen problem solution)을 적용하여 flutter에 미치는 영향을 조사한 후, Beck's column, Leipholz's column 및 Hauger's column에 대하여 비보존력의 방향파라미터 ${\alpha}$에 대한 임계하중의 영향, 내적 및 외적 감쇠계수 및 Winkler 및 Pasternak지반에 의한 임계하중의 영향을 각각 조사한다.

• Composites Research
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• 제15권3호
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• pp.52-61
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• 2002

압전재가 부착된 원통형 패널의 공력열탄성학적인 해석을 수행하기 위하여, 다분야 층별 이론에 기초하여 기하학적 비선형 유한 요소를 개발하였다. Han Krumhaar의 초음속 피스톤 이론을 적용하여 압전재가 부착된 원통형 패널에 대하여 열하중과 열변형에 따른 초음속 플러터 해석을 수행하였다. 플러터 임계동압을 증가시키고, 압전재 층의 열탄성학적 변형을 줄이는 가능성에 대하여 압전 작동기를 사용하여 검토하였다. 이 논문의 해석 결과들은 압전 작동기가 플러터 모드의 병합을 늦추고, 열하중을 상쇄하여 임계 동압을 효과적으로 증가시킬 수 있음을 보였다.

• 한국군사과학기술학회지
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• 제9권4호
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• pp.104-113
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• 2006

To identify aeroelastic characteristics of wings with double-folding mechanism, aeroelastic analyses are performed. There are four wing models which consist of one linear model and three nonlinear models. The nonlinear models have one or two freeplay nonlinearties. The describing function method is used to approximately examine nonlinear effects. The aeroelastic module in MSC/NASTRAN is used to study the aeroelastic characteristics of the considered wing models. The effects of the folding mechanism and amplitude ratio are examined. As the amplitude ratio increases, the flutter speeds approach to those of the wing model with only one nonlinearity. The numerical results show that the flutter speeds of the wings with double-folding mechanism can be lower or higher than those of the wing model with only one folding mechanism depending upon the direction of the second folding mechanism.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 춘계학술대회 논문집
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• pp.339-344
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• 2011

In the past much effort has been made to utilize advanced computational fluid dynamic (CFD) programs for aeroelastic simulations and analysis. However, it is limited in the field of unsteady aeroelasticity due to enormous size of computer memory and unreasonably long CPU time. Recently, AAEMS(Aerodynamics is Aeroelasticity minus Structure) was developed for linear time-invariant, coupled fluid-structure systems. In this paper, to demonstrate further the efficiency and accuracy of the new model reduction method, we successfully examine AGARD 445.6 wing modeled by FLUENT CFD, FSIPRO3D and NASTRAN FEM(Finite Element Method) programs. Using the ROM(Reduced Order Modeling) one can predict flutter boundary as a function of the dynamic pressure.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.677-683
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• 2002

The analytical and experimental studies on aerodynamic flutter instability of rotating disks in information storage devices are investigated. The theoretical analysis uses a fluid-structure model where the aerodynamic force on the rotating disk is represented in terms of lift and damping forces. Based on the analytical approach, it is shown that the backward natural frequency of the disk is equal to that of the case without aerodynamic effect at the flutter onset speed. In post-flutter regions, the natural frequencies are larger than those in vacuum conditions without aerodynamic effect. The analytical predictions on the natural frequencies of rotating disks with/without aerodynamic effect are experimentally verified using a vacuum chamber and ASMO optical disks.

• 한국소음진동공학회논문집
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• 제12권11호
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• pp.864-872
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• 2002

In this study, the effect of planform curvature on the stability of coupled flow/structure vibration is examined in transonic and supersonic flow regions. The aeroelastic analysis for the frequency and time domain is performed to obtain the flutter solution. The doublet lattice method(DLM) in subsonic flow is used to calculate unsteady aerodynamics in the frequency domain. For all speed range, the time domain nonlinear unsteady transonic small disturbance code has been incorporated into the coupled-time integration aeroelastic analysis (CTIA). Two curved wings with experimental data have been considered in this paper MSC/NASTRAN is used for natural free vibration analyses of wing models. Predicted flutter dynamic pressures and frequencies are compared with experimental data in subsonic and transonic flow regions.

• 한국전산구조공학회논문집
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• 제17권3호
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• pp.271-278
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• 2004

본 논문에서는 토목 구조물에 대한 바람의 영향을 알아보기 위하여 수치 기법으로 해석하였다. 지간이 긴 현수교는 바람에 의한 공력탄성학적 분안정성에 놓일 수 있으므로, 설계 시 공기력은 주요한 고려사항이며 공탄성 안정성은 반드시 확인되어야 한다. 풍속이 임계 플러터 속도를 넘어서면, 교량 구조물은 바람과 상호작용에 의한 플러터 현상으로 인해 붕괴된다. 교량 단면의 공탄성 해석을 위해 전산유체역학과 전산구조해석을 이용하였으며, Navier-Stokes방정식을 사용하여 공기력을 구하였다. 본 연구에서는 구조 강성에 따른 교량 구조물의 임계 플러터 속도가 연구된다. 교량 단면의 임계 플러터 속도는 구조강성의 변화에 민감함을 확인할 수 있었다.

• Steel and Composite Structures
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• 제52권5호
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• pp.515-524
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• 2024

The principal goal of the present study is to examine the aeroelastic analysis of cylindrical laminated shells with curvilinear fibers. To attain this objective, the equations of motion are firstly extracted according to the first-order shear deformation theory (FSDT). The linear piston theory is then implemented to estimate aerodynamic loads for various airflow angles over the cylindrical shell area, providing the aeroelastic equations. The well-known isogeometric analysis based on the NURBS basis functions is subsequently developed to discretize the aeroelastic equations of the considered problem. Finally, by writing the resultant equations in the standard form of an eigenvalue problem, the panel flutter analysis of a cylindrical variable stiffness composite laminated (VSCL) shell will be carried out. The comparison and validation of achieved results with the results of references mentioned in the literature are made to demonstrate the accurateness of the present formulation. Also, the influence of various parameters, including the airflow angle, fiber path orientation, radius of curvature, and converting symmetric lay-up to unsymmetrical lay-up on the flutter threshold is studied.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.1648-1653
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• 2003

The paper studies effect of quasi-periodic or airplane flutter phenomenon on television broadcasting signal. Airplane flutter is a very important problem. It causes the receiving antenna to receive both direct signal by the Tx (Transmitter antenna) and reflected signal scattered by the airplane with phase delay. The sum of two signals results in fading, sometime collapse and distortion of picture on TV screen. We performed measurement and modeling this phenomenon on TV signal when the airplane flew across and range Tx and Rx (Receiver antenna). The frequency 60.75MHz (Aural frequency of CH3) is used under tests. A single scatter multipath model is introduced. It is used to duplicate some of the measured data and show the dependence of power variation on the airplane fluttering. The fluctuation of the airplane flutter phenomenon was calculated to be around 2-4dB. The Yaki antenna is used for improving airplane flutter problem because it can make high gain and high directivity.

• Steel and Composite Structures
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• 제39권5호
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• pp.615-630
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• 2021

The main purpose of the present work was to study the dynamic instability of a three-layered, thick composite sandwich beam with the functionally graded (FG) flexible core subjected to an axial compressive follower force. Flutter instability of a sandwich cantilever beam was analyzed using the high-order theory of sandwich beams, for the first time. The governing equations in general for sandwich beams with an FG core were extracted and could be used for all types of sandwich beams with any types of face sheets and cores. A polynomial function is considered for the vertical distribution of the displacement field in the core layer along the thickness, based on the results of the first Frosting's higher order model. The governing partial differential equations and the equations of boundary conditions of the dynamic system are derived using Hamilton's principle. By applying the boundary conditions and numerical solution methods of squares quadrature, the beam flutter phenomenon is studied. In addition, the effects of different geometrical and material parameters on the flutter threshold were investigated. The results showed that the responses of the dynamic instability of the system were influenced by the follower force, the coefficients of FGs and the geometrical parameters like the core thickness. Comparison of the present results with the published results in the literature for the special case confirmed the accuracy of the proposed theory. The results showed that the follower force of the flutter phenomenon threshold for long beams tends to the corresponding results in the Timoshenko beam.