• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2524-2529
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• 2008

The thermal system like a combustion chamber is believed to experience a significant instability problem with vibration in case that the thermal energy or the acoustic energy are transformed into a different form through a relevant path. This study deals with a numerically- predicted, Thermoacoustic instability in a Rijke tube by using a non-linear model for a heat source. The heating part where the energy transformation occurs actively is modeled after simulating two-dimensional cylinder case with constant surface temperature, and a nonlinear model that accounts for the transfer function of magnitude- and phase-characteristics is properly implemented so as to be dependent on the pulsation strength in the tube. The heat source model is observed to result in equivalent Thermoacoustic instabilities in the Rijke tube except low flow-rate cases in which the natural convection is dominant.

• 대한조선학회논문집
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• 제45권2호
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• pp.186-191
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• 2008

A lot of equipments installed in ships must be isolated for relaxing the shock, vibration and noise using the elastic mounts. Most of the elastic mounts are made of the rubber, however it is not easy to design the effective rubber mount. Because, in general, the rubber has a non-linear constitutive characteristics especially for a large deformation. So, there are many difficulties to estimate the accurate structural response of rubber which is the basis of the shape design of the mounts. In this study, the detailed non-linear viscoelastic large deformation finite element analysis method was dealt with. And to verify validity of the present analysis scheme, the results were compared with experiments.

• Steel and Composite Structures
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• 제19권3호
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• pp.635-659
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• 2015

In this study, natural frequency analysis of a large deflected cantilever laminated composite beam fixed at both ends, which forms the case of a pre-stressed curved beam, is investigated. The laminated beam is considered to have symmetric and asymmetric lay-ups and the effective flexural modulus of the beam is used in the analysis. In order to obtain the pre-stressed composite curved beam case, an external vertical concentrated load is applied at the free end of a cantilever laminated composite beam and then the loading point of the deflected beam is fixed. The non-linear deflection curve of the flexible beam undergoing large deflection is obtained by the Reversion Method. The curved laminated composite beam is modeled by using the Finite Element Method with a straight-beam element approach. The effects of orientation angle and vertical load on the natural frequency parameter for the first four modes are examined and the results obtained are given in graphics. It has been found that the effect of the load parameter, which forms the curved laminated beam, on the natural frequency parameter, almost disappears after a certain value of the load parameter. This certain value differs for each laminated curved beam and each vibration mode.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2012년도 춘계학술대회 논문집
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• pp.420-424
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• 2012

A 2-axis gimbal system is one of main disturbance sources affecting on image jitter response of a satellite. The gimbal system can be rotated on its azimuth and elevation axes, resulting in variation of its moment of inertia and structural modes, so that generates non-linear vibration characteristics. In order to estimate the jitter response, it is an indispensable process to characterize micro-vibration disturbance of the 2-axis gimbal system. In the present research, the vibration characteristics of the 2-axis gimbal system was investigated with respect to the types of stepping motors. The micro-vibration tests were performed for 2-phase and 5-phase stepping motors. The test results show that the disturbance can be reduced with vibration attenuation ratio of 60% by replacing the 2-phase stepping motor with the 5-phase one.

• Steel and Composite Structures
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• 제26권4호
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• pp.453-461
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• 2018

In this paper, nonlinear vibrations of the unsymmetrical laminated composite beam (LCB) on a nonlinear elastic foundation are studied. The governing equation of the problem is derived by using Galerkin method. Two different end conditions are considered: the simple-simple and the clamped-clamped one. The Hamiltonian Approach (HA) method is adopted and applied for solving of the equation of motion. The advantage of the suggested method is that it does not need any linearization of the problem and the obtained approximate solution has a high accuracy. The method is used for frequency calculation. The frequency of the nonlinear system is compared with the frequency of the linear system. The influence of the parameters of the foundation nonlinearity on the frequency of vibration is considered. The differential equation of vibration is solved also numerically. The analytical and numerical results are compared and is concluded that the difference is negligible. In the paper the new method for error estimation of the analytical solution in comparison to the exact one is developed. The method is based on comparison of the calculation energy and the exact energy of the system. For certain numerical data the accuracy of the approximate frequency of vibration is determined by applying of the suggested method of error estimation. Finally, it has been indicated that the proposed Hamiltonian Approach gives enough accurate result.

• 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.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1045-1050
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• 2007

Equations of motion of rotating cantilever curved beams are derived based on a dynamic modeling method developed in this paper. The Kane's method is employed to derive the equations of motion. Different from the classical linear modeling method which employs two cylindrical deformation variables, the present modeling method employs a non-cylindrical variable along with a cylindrical variable to describe the elastic deformation. The derived equations (governing the stretching and the bending motions) are coupled but linear. So they can be directly used for the vibration analysis. The coupling effect between the stretching and the bending motions which could not be considered in the conventional modeling method is considered in this modeling method. The natural frequencies of the rotating curved beams versus the rotating speed are calculated for various radii of curvature and hub radius ratios.

• 한국소음진동공학회논문집
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• 제14권12호
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• pp.1314-1321
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• 2004

The non-linear responses of a slender rectangular cantilever beam subjected to lateral harmonic base-excitation are investigated by the 2-channel FFT analyzer. Both linear and nonlinear behaviors of the cantilever beam are compared with each other. Bending mode, torsional mode, and transverse mode are coupled in such a way that the energy transfer between them are observed. Especially, superharmonic, subharmonic, and chaotic motions which result from the unstable inertia terms in the transverse mode are analyzed by the FFT analyzer The aim is to give the explanations of the route to chaos, i.e., harmonic motion \longrightarrow superharmonic motion \longrightarrow subharmonic motion \longrightarrow chaos.

• 한국소음진동공학회논문집
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• 제16권3호
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• pp.263-269
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• 2006

The objective of the present work is to develop a time-domain numerical method of broadband noise in a cascade of airfoils. This paper focuses on dipolar broadband noise sources, resulting from the interaction of turbulent inflows with the flat-plate airfoil cascade. The turbulence response of a two-dimensional cascade is studied by solving both of the linearised and the full nonlinear Euler equations employing accurate higher order spatial differencing, time stepping techniques and non-reflecting inflow/outflow boundary condition. The time-domain result using the linearised Euler equations shows good agreement with the analytical solution using the modified LINSUB code. Through the comparison of the nonlinear time-domain result using the full nonlinear Euler equations with the linear, it is found that the acoustic mode amplitude of the nonlinear response is less than that of the linear response due to the energy cascade from low frequency components to the high frequency ones. Considering the merits of the time-domain methods over the typical time-linearised frequency-domain analysis, the current method is expected to be promising tools for analyzing the effects of the airfoil shapes, non-uniform background flow, linear-nonliear regimes on the broadband noise due to turbulence-cascade interaction.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.812-817
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• 2005

The objective of the present work is to develop a time-domain numerical method of broadband noise in a cascade of airfoils. This paper focuses on dipole broadband noise sources, resulting from the interaction of turbulent inflows with the flat-plate airfoil cascade. The turbulence response of a two-dimensional cascade is studied by solving both of the linearised and full nonlinear Euler equations employing accurate higher order spatial differencing, time stepping techniques and non-reflecting inflow/outflow boundary condition. The time-domain result using the linearised Euler equations shows good agreement with the analytical solution using the modified LINSUB code. Through the comparison of the nonlinear time-domain result using the full nonlinear Euler equations with the linear, it is found that the acoustic mode amplitude of the nonlinear response is less than that of the linear response due to the energy cascade from low frequency components to the high frequency ones. Considering the merits of the time-domain methods over the typical time-linearised frequency-domain analysis, the current method is expected to be promising tools for analyzing the effects of the airfoil shapes, non-uniform background flow, linear-nonliear regimes on the broadband noise due to gust-cascade interaction.