• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.629-634
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• 2000

Dynamic behavior of an automatic dynamic balancer is analyzed by a theoretical approach. Using Lagrange's equation, we derive the non-linear equations of motion for an automatic dynamic balancer equipped in a rotor with the bending flexibility with respect to the rectangular coordinate. Considering the rotor bending flexibility we analyze out-of-plane vibrations as well as in-plane vibrations of the automatic dynamic balaner. The time responses are computed from the non-linear equations by using a time integration method. We also investigate the effect of rotor flexibility on the behavior of the automatic dynamic balancer

• Structural Engineering and Mechanics
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• 제44권3호
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• pp.339-361
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• 2012

Large amplitude free vibration and thermal post-buckling of shear flexible Functionally Graded Material (FGM) beams is studied using finite element formulation based on first order Timoshenko beam theory. Classical boundary conditions are considered. The ends are assumed to be axially immovable. The von-Karman type strain-displacement relations are used to account for geometric non-linearity. For all the boundary conditions considered, hardening type of non-linearity is observed. For large amplitude vibration of FGM beams, a comprehensive study has been carried out with various lengths to height ratios, maximum lateral amplitude to radius of gyration ratios, volume fraction exponents and boundary conditions. It is observed that, for FGM beams, the non-linear frequencies are dependent on the sign of the vibration amplitudes. For thermal post-buckling of FGM beams, the effect of shear flexibility on the structural response is discussed in detail for different volume fraction exponents, length to height ratios and boundary conditions. The effect of shear flexibility is observed to be predominant for clamped beam as compared to simply supported beam.

• Structural Engineering and Mechanics
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• 제54권3호
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• pp.597-605
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• 2015

In this study, linear vibrations of an axially moving beam under non-ideal support conditions have been investigated. The main difference of this study from the other studies; the non-ideal clamped support allow minimal rotations and non-ideal simple support carry moment in minimal orders. Axially moving Euler-Bernoulli beam has simple and clamped support conditions that are discussed as combination of ideal and non-ideal boundary with weighting factor (k). Equations of the motion and boundary conditions have been obtained using Hamilton's Principle. Method of Multiple Scales, a perturbation technique, has been employed for solving the linear equations of motion. Linear equations of motion are solved and effects of different parameters on natural frequencies are investigated.

• 대한토목학회논문집
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• 제29권6A호
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• pp.617-624
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• 2009

이 논문은 선형 변단면 정확탄성곡선형 아치의 자유진동에 관한 연구이다. 정확탄성곡선형 아치의 선형은 Bernoulli-Euler 보 이론을 이용하여 산정하였다. 이러한 선형을 갖는 아치의 자유진동을 지배하는 미분방정식을 유도하고 이를 수치해석하여 무차원 고유진동수를 산출하였다. 수치해석 예에서는 세 종류의 선형 변단면과 두 종류의 지점조건을 채택하였다. 이 연구의 결과를 검증하기 위하여 이 연구와 SAP 2000의 고유진동수를 비교하였다. 수치해석의 결과로 지점조건, 변단면 형상, 세장비 및 단면비가 최저차 4개의 무차원 고유진동수에 미치는 영향을 분석하였다.

• Wind and Structures
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• 제9권1호
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• pp.75-93
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• 2006

This paper presents a quasi-steady model of vibrations of two cylinders in a side-by-side arrangement. The cylinders have flexible support and equal diameters. The model assumes that both cylinders participate in the process of vibration, each of them having two degrees of freedom. The movement of cylinders is described by a set of four non-linear differential equations. These equations are evaluated on the basis of a numerical simulation and experimental data. Moreover many features of cylinder vibrations are found from numerical results and are described in this paper.

• 한국농공학회지
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• 제42권6호
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• pp.122-129
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• 2000

The purpose of this study is to investigate both the fundamental and some higher natural frequencies and mode shapes of compressive members resting on the linear elastic foundation. The model of compressive member is based on the classical Bernoulli-Euler beam theory. The differential equation governing free vibrations of such members subjected to an axial load is derived and solved numerically for calculating the natural frequencies and mode shapes. The Improved Euler method is used to integrate the differential equation and the Determinant Search method combined with the Regula-Falsi method to determine the natural frequencies, respectively. In numerical examples, the hinged-hinged, hinged-clamped, clamped-hinged and clamped-clamped end constraints are considered. The convergence analysis is conducted for determining the available step size in the Improved Euler method. The validation of theories developed herein is also conducted by comparing the numerical results between this study and SAP 90. The non-dimensional frequency parameters are presented as the non-dimensional system parameters: section ratio, modulus parameter and load parameter. Also typical mode shapes are presented.

• Smart Structures and Systems
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• 제20권6호
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• pp.669-682
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• 2017

The normalised version of bispectrum, the so-called bicoherence, has often proved a reliable method of damage detection on engineering applications. Indeed, higher-order spectral analysis (HOSA) has the advantage of being able to detect non-linearity in the structural dynamic response while being insensitive to ambient vibrations. Skewness in the response may be easily spotted and related to damage conditions, as the majority of common faults and cracks shows bilinear effects. The present study tries to extend the application of HOSA to damage localisation, resorting to a neural network based classification algorithm. In order to validate the approach, a non-linear finite element model of a 4-meters-long cantilever beam has been built. This model could be seen as a first generic concept of more complex structural systems, such as aircraft wings, wind turbine blades, etc. The main aim of the study is to train a Neural Network (NN) able to classify different damage locations, when fed with bispectra. These are computed using the dynamic response of the FE nonlinear model to random noise excitation.

• 한국농공학회:학술대회논문집
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• 한국농공학회 1999년도 Proceedings of the 1999 Annual Conference The Korean Society of Agricutural Engineers
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• pp.206-211
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• 1999

The purpose of this study is to investigate the natural frequencies and mode shapes of beam-columns on the non-homogeneous foundaion. The beam model is based on the classical Bernoulli-Euler beam theory. The linear foundation modulus is chosen as the non-homogeneous foundation in this study . The differentidal equation goeverning free vibrations of such beam-columns subjected to axial load is derived and solved numerically for calculting the natural frquencies and mode shapes. In numerical fivekinds of end constraint are considered, and the lowest four natural frquencies and corresponding mode shape are obtained as the non-dimensional forms.

• International Journal of Aeronautical and Space Sciences
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• 제13권2호
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• pp.210-220
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• 2012

The model-free control of aeroelastic vibrations of a non-linear 2-D wing-flap system operating in supersonic flight speed regimes is discussed in this paper. A novel continuous robust controller design yields asymptotically stable vibration suppression in both the pitching and plunging degrees of freedom using the flap deflection as a control input. The controller also ensures that all system states remain bounded at all times during closed-loop operation. A Lyapunov method is used to obtain the global asymptotic stability result. The unsteady aerodynamic load is considered by resourcing to the non-linear Piston Theory Aerodynamics (PTA) modified to account for the effect of the flap deflection. Simulation results demonstrate the performance of the robust control strategy in suppressing dynamic aeroelastic instabilities, such as non-linear flutter and limit cycle oscillations.

• 한국소음진동공학회논문집
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• 제21권1호
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• pp.66-73
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• 2011

This paper deals with free vibrations of the tapered beams with the constant surface area. The surface area of the objective beams are always held constant regardless shape functions of the cross-sectional depth. The shape functions are chosen as the linear and parabolic ones. Ordinary differential equations governing free vibrations of such beams are derived and solved numerically for determining the natural frequencies. In the numerical examples, hinged-hinged, hinged-clamped and clamped-clamped end constraints are considered. As the numerical results, the relationships between non-dimensional frequency parameters and various beam parameters such as section ratio, surface area ratio, end constraint and taper type are reported in tables and figures. Especially, section ratios of the strongest beam are calculated, under which the maximum frequencies are achieved.