• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.332-335
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• 2011

바람에 의해 발생하는 장대교량의 진동현상은 버펫팅과 와류진동 그리고 플러터 등으로 구분할 수 있으며, 특히 설계풍속에 해당하는 강풍에 안전한 교량을 설계하는 것이 주된 관심사항이다. 이러한 장대교량의 공기역학적인 안정성 검토에 사용되는 플러터 계수를 풍동실험을 통하여 산정하였다. 본 논문에서는 일반적인 플레이트 거더교의 강풍에 대한 안정성을 검토하기 위하여 풍동실험을 수행하였으며, 자유진동 기법과 강제진동 기법을 사용하여 추출한 플러터 계수를 비교하였다. 자유진동 기법은 교량단면에 초기변위를 주어 상하 및 회전 진동을 하는 교량단면의 변위를 측정한 후 system identification 기법으로 플러터 계수를 구하게 된다. 그리고 강제진동 기법은 상하방향의 강제진동과 회전방향의 강제진동 실험을 독립적으로 수행하여 교량단면에 작용하는 풍하중과 단면의 진동을 분석함으로써 플러터 계수를 추정하게 된다. 그리고 플러터 계수의 비교를 통하여 강제진동 기법과 자유진동 기법의 장단점을 분석하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.2
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• pp.99-105
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• 2017

Wind tunnel test which is one of the method to predict the aeroelastic characteristics has difficulties to make scale-down structural model and achieve a specified free stream velocity. It is very costly and complicated to consider similarity relationships between real structure and scale-down structural model. "Dry Wind-Tunnel(DWT)" was proposed to overcome these difficulties. This is made up of Ground Vibration Test hardware and software to compute the aerodynamic forces. In the present study, program for computing the real-time unsteady aerodynamic forces which is an important part of DWT system was developed by Matlab Simulink and dSPACE. In addition, using this program and software which is a part of the test structure, a real-time flutter analysis was conducted and the results are verified by ZAERO.

• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.4
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• pp.486-492
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• 2013

The pivoting composite wing is developed for the kit to be mounted on the external stores. The wing has a pivoting structure for the installation to an aircraft and high aspect ratio to increase lift drag ratio. The wing needs to be light and have sufficient strength and stiffness to satisfy structural design requirements. The wing is designed with carbon fiber composite and the structural parts are integrated to reduce cost to manufacture. In order to verify the structural performances, the design load analysis and flight load survey, the static analysis and test, the ground vibration test and flutter analysis are performed. It is shown that the wing has sufficient structural strength and stiffness to satisfy the structural design requirements.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.865-868
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• 2006

In this paper, a dynamic behavior(natural frequency) of a cracked simply supported pipe conveying fluid is presented. In addition, an analysis of the flutter and buckling instability of a cracked pipe conveying fluid due to the coupled mode (modes combined) is presented. Based on the Euler-Bernouli beam theory, the equation of motion can be constructed by using the Lagrange's equation. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments. The stiffness of the spring depends on the crack severity and the geometry of the cracked section. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations. This study will contribute to the safety test and stability estimation of structures of a cracked pipe conveying fluid.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.458-464
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• 2011

A new method identifies coupled fluid-structure system with a reduced set of state variables is presented. Assuming that the structural model is known a priori either from an analysis or a test and using linear transformations between structural and aeroelastic states, it is possible to deduce aerodynamic information from sampled time histories of the aeroelastic system. More specifically given a finite set of structural modes the method extracts generalized aerodynamic force matrix corresponding to these mode shapes. Once the aerodynamic forces are known, an aeroelastic reduced-order model can be constructed in discrete-time, state-space format by coupling the structural model and the aerodynamic system. The resulting reduced-order model is suitable for constant Mach, varying density analysis.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.1 s.118
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• pp.10-16
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• 2007

In this paper, the dynamic stability of a cracked simply supported pipe conveying fluid is investigated. In addition, an analysis of the flutter and buckling instability of a cracked pipe conveying fluid due to the coupled mode(modes combined) is presented. Based on the Euler-Bernouli beam theory, the equation of motion can be constructed by using the Galerkin method. The crack section is represented by a local flexibility matrix connecting two undamaged pipe segments. The stiffness of the spring depends on the crack severity and the geometry of the cracked section. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations. This results of study will contribute to the safety test and a stability estimation of the structures of a cracked pipe conveying fluid.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.30A no.3
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• pp.52-60
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• 1993

Fluttering ghost which is the most severs picture impairment in mobile TV reception under multipath fading environments can be detected by measuring the dynamic variation of the synchronizing pulse timing. And also, the occurrence-stucture of fluttering ghost are directly correlated with the multipath parameters. This paper describes the quantitative evaluating method of the mobile TV pictures impaired by multipath parameters by means of the spectral analysis of synchronizing timing fluctuation. The ghost-flutter curve derived from the spatial amplitue spectrum of synchronizing pulse timing fluctuation express well the spatial variation characteristic, and it has been found to be the quantitative evaluating measure of picture impairment in mobile reception. A correspondence between the ghost-flutter curve (and/or index) and picture quality opinion test results is established.

• Wind and Structures
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• v.32 no.3
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• pp.179-191
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• 2021

A series of wind tunnel tests, including 1:50 sectional model tests, 1:50 free-standing bridge tower tests and 1:70 full-bridge aeroelastic model tests were carried out to systematically investigate the aerodynamic performance of the Hong Kong-Zhuhai-Macao Bridge (HZMB). The test result indicates that there are three wind-resistant safety issues the HZMB encounters, including unacceptable low flutter critical wind speed, vertical vortex-induced vibration (VIV) of the main girder and galloping of the bridge tower in across-wind direction. Wind-induced vibration of HZMB can be effectively suppressed by the application of aerodynamic and mechanical measures. Acceptable flutter critical wind speed is achieved by optimizing the main girder form (before: large cantilever steel box girder, after: streamlined steel box girder) and cable type (before: central cable, after: double cable); The installations of wind fairing, guide plates and increasing structural damping are proved to be useful in suppressing the VIV of the HZMB; The galloping can be effectively suppressed by optimizing the interior angle on the windward side of the bridge tower. The present works provide scientific basis and guidance for wind resistance design of the HZMB.

• Journal of Korean Society of Steel Construction
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• v.9 no.2 s.31
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• pp.259-267
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• 1997

Wind tunnel test results and their interpretations focused on the behavior of girder, which were performed to study the aerodynamic stability of a self-anchored suspension bridge with lateral sag of main cable, are presented in this paper The shape of the girder which has the best aerodynamic stability was selected based on the section model test under uniform and turbulent flow conditions. Good performance of the selected section was confirmed in the full bridge model test. Measured flutter derivatives are presented for further study. Buffeting response was investigated to check the fatigue problem and serviceability of the bridge but it was found to be acceptable from the engineering point of view. Even though the drag coefficient of the girder had high value, the amplitude of the lateral vibration was found to be very low. This may be due to the restraint provided by the lateral sag of the cables.

• Advances in aircraft and spacecraft science
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• v.4 no.2
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• pp.169-184
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• 2017

The optimum design of structures with frequency constraints is of great importance in the aeronautical industry. In order to avoid severe vibration, it is necessary to shift the fundamental frequency of the structure away from the frequency range of the dynamic loading. This paper develops a novel topology optimisation method for optimising the fundamental frequencies of structures. The finite element dynamic eigenvalue problem is solved to derive the sensitivity function used for the optimisation criteria. An alternative material interpolation scheme is developed and applied to the optimisation problem. A novel level-set criteria and updating routine for the weighting factors is presented to determine the optimal topology. The optimisation algorithm is applied to a simple two-dimensional plane stress plate to verify the method. Optimisation for maximising a chosen frequency and maximising the gap between two frequencies are presented. This has the application of stiffness maximisation and flutter suppression. The results of the optimisation algorithm are compared with the state of the art in frequency topology optimisation. Test cases have shown that the algorithm produces similar topologies to the state of the art, verifying that the novel technique is suitable for frequency optimisation.