• Tribology and Lubricants
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• 제17권1호
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• pp.64-71
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• 2001

This paper presents dynamic responses of disk flutter and bump in HDD slider. The slider is modeled for three degree-of-freedom systems, which are capable of lifting, pitching, and rolling motions. In numerical analysis, loads from air pressure, preload and static moments from the slider, and stiffness and damping coefficients of the suspension are considered for investigating the dynamic characteristics analysis. The numerical results are presented as functions of typical parameters such as a disk velocity, stiffness and damping coefficients of the suspension, and skew angle.

• Wind and Structures
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• 제2권2호
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• pp.119-125
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• 1999

The ZG Bridge(preliminary design), with unfavorable aerodynamic stability characteristics, is a truss-stiffened suspension bridge, its critical wind speed of flutter instability is much lower than that of code requirement, In the present paper, based on both aerostatic and aeroelastic section model wind tunnel test, not only effects of some aerodynamic means on aerodynamic stability of its main girder are investigated, but also such effective aerodynamic means of it as flap and plate-like center stabilizer are concluded.

• 대한조선학회지
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• 제10권1호
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• pp.27-32
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• 1973

This paper shows the method for obtaining the body flutter velocity and frequency for flight body which consists of low aspect ratio wing and body combination by assuming slender body of cylinderical shell structure. The stiffness matrix of the cylinderical shell is represented from Donnel eq. by the finite difference method, and also unsteady aerodynamic influence matrix is represented by the Doublet Lattice Method of Albano & Rodden. The flutter matrix can be obtained from those matrices.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2011년도 정기 학술대회
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• pp.228-230
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• 2011

2자유도 풍동실험으로부터 플러터계수를 추출하기 위해서 MITD, MULS와 같은 다양한 기법들이 활용되고 있다. 이러한 기법들은 부분측정(partial measurement)을 기반으로 한 state-space model을 이용하고 있다. 여기서는 완전측정(full measurement)를 기반으로 한 동방정식상의 최소화 기법인 EEE 방법을 제시한다. EEE 기법을 B/D=20의 구형 단면에 적용하고 MITD를 이용한 결과와 비교하여 제안한 방법의 타당성과 실교량에서 적용 가능성을 검증하고자 한다.

• Coupled systems mechanics
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• 제1권3호
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• pp.219-234
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• 2012

Tuned vibration control in aeroelasticity of slender wood bridges is treated in present paper. The approach suggested takes into account multiple functions in aeroelastic analysis and flutter of slender wood bridges subjected to laminar and turbulent wind flow. Tuned vibration control approach is presented with application on actual bridge. Some results obtained are discussed.

• Wind and Structures
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• 제12권5호
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• pp.413-424
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• 2009

A series of wind tunnel free-decay sectional model dynamic tests were conducted to examine the effects of torsional-to-vertical natural frequency ratio of 2DOF bridge dynamic systems on the aerodynamic and dynamic properties of bridge decks. The natural frequency ratios tested were around 2.2:1 and 1.2:1 respectively, with the fundamental vertical natural frequency of the system held constant for all the tests. Three 2.9 m long twin-deck bridge sectional models, with a zero, 16% (intermediate gap) and 35% (large gap) gap-to-width ratio, respectively, were tested to determine whether the effects of frequency ratio are dependent on bridge deck cross-section shapes. The results of wind tunnel tests suggest that for the model with a zero gap-width, a model to approximate a thin flat plate, the flutter derivatives, and consequently the aerodynamic forces, are relatively independent of the torsional-to-vertical frequency ratio for a relatively large range of reduced wind velocities, while for the models with an intermediate gap-width (around 16%) and a large gap-width (around 35%), some of the flutter derivatives, and therefore the aerodynamic forces, are evidently dependent on the frequency ratio for most of the tested reduced velocities. A comparison of the modal damping ratios also suggests that the torsional damping ratio is much more sensitive to the frequency ratio, especially for the two models with nonzero gap (16% and 35% gap-width). The test results clearly show that the effects of the frequency ratio on the flutter derivatives and the aerodynamic forces were dependent on the aerodynamic cross-section shape of the bridge deck.

• Wind and Structures
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• 제29권6호
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• pp.457-469
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• 2019

In this paper, a numerical solution is presented for supersonic flutter analysis of cantilever non-symmetric functionally graded (FG) sandwich plates. The plate is considered to be composed of two different functionally graded face sheets and an isotropic homogeneous core made of ceramic. Based on the first order shear deformation theory (FSDT) and linear piston theory, the set of governing equations and boundary conditions are derived. Dimensionless form of the governing equations and boundary conditions are derived and solved numerically using generalized differential quadrature method (GDQM) and critical velocity and flutter frequencies are calculated. For various values of the yaw angle, effect of different parameters like aspect ratio, thickness of the plate, power law indices and thickness of the core on the flutter boundaries are investigated. Numerical examples show that wings and tail fins with larger length and shorter width are more stable in supersonic flights. It is concluded for FG sandwich plates made of Al-Al₂O₃ that increase in volume fraction of ceramic (Al₂O₃) increases aeroelastic stability of the plate. Presented study confirms that improvement of aeroelastic behavior and weight of wings and tail fins of aircrafts are not consistent items. It is shown that value of the critical yaw angle depends on aspect ratio of the plate and other parameters including thickness and variation of properties have no considerable effect on it. Results of this paper can be used in design and analysis of wing and tail fin of supersonic airplanes.

• 한국항공우주학회지
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• 제34권9호
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• pp.45-52
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• 2006

압전재료를 사용한 복합재료 패널의 플러터 억제 방법으로서 비선형 모델을 기반으로 하는 비선형 제어기법 중의 하나인 궤환 선형화에 의한 제어방법을 소개하였다. 기존의 패널 플러터 제어기에 대한 대부분의 연구들은 선형모델을 기반으로 설계된 선형2차제어기(LQR: Linear Quadratic Regulator)였음에 비해, 본 연구에서 제안한 비선형제어기는 시스템이 갖고 있는 비선형 특성들을 모두 고려해서 설계하였다. 압전 작동기로서는 PZT를 사용하였다. 가상변위의 원리와 4절점 사각형 요소를 사용하여 이산화된 비선형 운동방정식을 유도하였으며 제어기 설계를 위해 모달 변환을 통해 상태공간에서의 비선형 연계-모달 방정식으로 변환하였다. 본 논문에서 제안한 비선형 제어기에 의한 제어 결과와 선형모델을 기반으로 한 LQR 제어결과를 Newmark 수치적분법을 통해 시간영역에서 비교하였다.

• Wind and Structures
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• 제9권1호
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• pp.1-22
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• 2006

The response characteristics and suppression of flow-induced vibrations of rectangular prisms with various width-to-depth ratios were experimentally investigated. The prisms were rigid and elastically mounted at both ends to enable constrained torsional vibrations only. The present study focused on torsional vibrations, one of the three types of flow-induced vibrations generated in a rectangular prism. First, the response characteristics of torsional vibrations generated in rectangular prisms were investigated by free-vibration tests. It was found that the response characteristics of torsional vibrations generated in rectangular prisms could be classified into six patterns depending on the width-to-depth ratio. Next, the response characteristics of torsional vibrations observed in the free-vibration tests were reproduced by forced-vibration tests, and the mechanisms by which the three types of flow-induced vibrations, low-speed torsional flutter, vortex excitation and high-speed torsional flutter, are generated in the rectangular prisms were elucidated on the basis of characteristics of fluid forces and visualized flow patterns. Experiments were also carried out to establish an effective method for suppressing flow-induced vibrations generated in the rectangular prisms, and it was found that low-speed torsional flutter and high-speed torsional flutter could be suppressed by placing a small normal plate upstream of the prism, which results in suppression of the alternating rolling-up of the shear layers separating from the leading edges of the prism. It was also found that vortex excitation could be suppressed by placing a splitter plate downstream of the prism, which results in suppression of the generation of wake vortices.

• 대한토목학회논문집
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• 제30권3A호
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• pp.241-256
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• 2010

본 연구에서는 변장비 70에 가까운 도전적인 현수교 단면을 개발하는데 목적을 두고 있다. 이를 위하여 먼저 강박스 현수교의 제원을 수집 분석하였다. 그 결과를 보면 강박스 현수교에서 경간장과 형상변수(교폭, 형고, 변장비, 고폭비)는 상관관계가 낮았고 고유진동수와 형상변수의 상관관계도 낮은 것으로 나타났으며, 상관관계가 높은 경간장과 고유진동수 관계는 신뢰구간별 추정식을 제시하였다. 그리고 교폭, 진동수비, 질량, 질량관성모멘트, 수직 및 비틈 고유진동수 변화에 따른 플러터 풍속의 민감도 분석을 실시하였는데, 타 변수보다 비틈 고유진동수가 플러터 풍속에 미치는 영향이 가장 큰 것으로 나타났다. 주경간장 1111 m인 현수교의 내풍 단면을 개발하기 위하여 최소 단면폭과 형고를 제약조건으로 하여 총 30개의 단면에 대한 풍동실험을 실시하고, 이로부터 한계풍속 기준을 충분히 만족하는 단면을 찾았다. 그리고 다중모드 플러터 해석으로 개발한 단면의 내풍안정성을 검증하였다. 본 연구에서 제시한 세장 단면은 향후 장대 현수교 설계시 활용할 수 있을 것으로 판단된다.