• International Journal of Aeronautical and Space Sciences
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• 제13권2호
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• pp.199-209
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• 2012

An advanced aeroelastic formulation for flutter analyses is presented in this paper. Refined 1D structural models were coupled with the doublet lattice method, and the g-method was used for flutter analyses. Structural models were developed in the framework of the Carrera Unified Formulation (CUF). Higher-order 1D structural models were obtained by using Taylor-like expansions of the cross-section displacement field of the structure. The order (N) of the expansion was considered as a free parameter since it can be arbitrarily chosen as an input of the analysis. Convergence studies on the order of the structural model can be straightforwardly conducted in order to establish the proper 1D structural model for a given problem. Flutter analyses were conducted on several wing configurations and the results were compared to those from literature. Results show the enhanced capabilities of CUF 1D in dealing with the flutter analysis of typical wing structures with high accuracy and low computational costs.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.344-347
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• 2007

In this paper, the stability of a cracked cantilever beam subjected to follower force is presented. In addition, an analysis of the flutter instability(flutter critical follower force) of a cracked cantilever beam subjected to a follower compressive load is presented. Based on the Timoshenko beam theory. The vibration analysis on such cracked beam is conducted to identify the critical follower force for flutter instability based on the variation of the first two resonant frequencies of the beam. Besides, the effect of the crack's intensity and location on the flutter follower force is studied. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations. Generally, the critical follower force for flutter is proportional to the crack depth.

• 한국군사과학기술학회지
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• 제10권4호
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• pp.73-80
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• 2007

Modern aircraft are required to carry various external stores mounted at different locations on the wing. Sometimes the attachment of stores to an aircraft wing leads to flutter speed reduction, which is a very severe aeroelastic problem. In order to suppress structural vibration and expand the flutter boundary of the aircraft with stores, it is necessary to investigate the main problems and characteristics of them. In addition, active vibration control may be required because passive vibration isolators show limited capabilities for the various wing/store configuration. In this paper, therefore, the flutter stability to the various wing/store configurations was investigated and active vibration control of wing/store model was performed using a piezoelectric actuator.

• 소음진동
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• 제5권4호
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• pp.525-536
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• 1995

In this study, an ROC(Reduced Order Controller) is designed to increase the flutter velocity of an aircraft wing, and the effect of ROC on the flight performance is also analyzed. The aircraft wing used in the paper is modelled as a 3 DOF two-dimensional rigid body. In the disign of controller, LQG and BACR(Balanced Augmented Controller Reduction) strategy is used as control algorithm and controller reduction method respectively. Simulation has been conducted to evaluate the effectiveness of ROC on the active flutter control, compared to FOC(Full Order Controller). It has been found that ROC using BACR is much effective than FOC in the sense of computation effort, without sacrificing the active flutter control performance.

• International Journal of Aeronautical and Space Sciences
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• 제7권2호
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• pp.121-127
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• 2006

An analysis procedure for the combined problem of control algorithm and aeroelastic system which is based on the computational fluid dynamics(CFD) technique has been developed. The aerodynamic forces in the transonic region are calculated from the transonic small disturbance(TSD) theory. An linear quadratic regulator(LQR) controller is designed to suppress the transonic flutter. The optimal control gain is estimated by solving the discrete-time Riccati equation. The system identification technique rebuilds the CFD-based aeroelstic system in order to form an adequate system matrix which involved in the discrete-time Riccati equation. Finally the controller, that is constructed on the basis of system identification technique, is used to suppress the flutter phenomenon of the airfoil with attached store. This approach, that is, the CFD-based aeroservoelasticity design, can be utilized for the development of effective flutter controller design in the transonic region.

• Wind and Structures
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• 제8권1호
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• pp.1-12
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• 2005

A simplified analysis able to point out the most relevant geometrical and aerodynamic parameters that can influence the flutter of long span modern bridges is the aim of the paper. With this goal, by using a continuous model of the suspension bridge and by a quasi stationary approach, a simple formula of the combined vertical/torsional flutter wind speed is given. A good agreement is obtained comparing the predictions from the proposed formula with the flutter speeds of three modern suspension or cable stayed bridges: the Great Belt East Bridge, the Akashi and Normandie bridges. The paper ends with some comments and comparisons with the well known Selberg formula.

• Wind and Structures
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• 제14권2호
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• pp.153-165
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• 2011

The alternative solution for flutter and buffeting stability of a long suspension bridge will be a passive control using flaps. This method not only enables a lightweight economic stiffening girder without an additional stiffness for aerodynamic stability but also avoid the problems from the malfunctions of control systems and energy supply system of an active control by winglets and flaps. A mechanically control using flaps for increasing flutter speed and decreasing buffeting response of a suspension bridge is experimentally studied through a two dimensional bridge deck model. The result shows that the flutter speed is increased and the buffeting response is decreased through the mechanical drive of the flaps.

• Structural Engineering and Mechanics
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• 제64권6권
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• pp.723-730
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• 2017

This paper studies on dynamic and stability behavior of a clamped-elastically restrained nanobeam under the action of a nonconservative force with an emphasis on the influence of surface properties on divergence and flutter instability. Using the Euler-Bernoulli beam theory incorporating surface effects, a governing equation for a clamped-elastically restrained nanobeam is derived according to Hamilton's principle. The characteristic equation is obtained explicitly and the force-frequency interaction curves are displayed to show the influence of the surface effects, spring stiffness of the elastic restraint end on critical loads including divergence and flutter loads. Divergence and flutter instability transition is analyzed. Euler buckling and stability of Beck's column are some special cases of the present at macroscale.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계 학술대회논문집(수송기계편)
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• pp.49-52
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• 2005

Flutter analysis procedure can be divided into two steps such as the computation of generalized mass, stiffness, and unsteady aerodynamic matrices and the calculation of major vibration modes frequency and damping values at each flight speed by solving the complex eigenvalue problem. In aircraft flutter analyses, most of the time is spent in the process of computing the unsteady aerodynamic matrices at each Mach-reduced frequency pairs defined. In this study, the method has been presented for computation and extraction of unsteady aerodynamic matrix portions dependent only on aerodynamic model using DMAP ALTER in MSC/NASTRAN SOL 145. In addition, efficient flutter analysis method has been suggested by computing and utilizing the unsteady generalized aerodynamic matrices for each analysis condition using the unsteady aerodynamic matrix portions extracted above.

• Journal of Mechanical Science and Technology
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• 제18권12호
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• pp.2148-2157
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• 2004

The paper deals with the vibration and dynamic stability of cantilevered pipes conveying fluid on elastic foundations. The relationship between the eigenvalue branches and corresponding unstable modes associated with the flutter of the pipe is thoroughly investigated. Governing equations of motion are derived from the extended Hamilton's principle, and a numerical scheme using finite element methods is applied to obtain the discretized equations. The critical flow velocity and stability maps of the pipe are obtained for various elastic foundation parameters, mass ratios of the pipe, and structural damping coefficients. Especially critical mass ratios, at which the transference of the eigenvalue branches related to flutter takes place, are precisely determined. Finally, the flutter configuration of the pipe at the critical flow velocities is drawn graphically at every twelfth period to define the order of the quasi-mode of flutter configuration.