• Journal of Ocean Engineering and Technology
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• v.7 no.2
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• pp.141-149
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• 1993

삼 자유도를 가진 부유물체의 동적 응답을 이론적으로 연구하였다. 평면내 방향 운동모우드에 대한 지배방정식을 선형화한 후, 그들의 조화해를 평명밖 방향 운동모우드의 방정식과 연성시켰다. 그렇게 해서 주어지는 방정식은 시간에 따라 변화하는 계수를 가진 형태로서, 평면밖 방향의 운동만을 보일 것으로 예측되는 부유물체가 평면밖 방향의 운동을 보일 수도 있음을 밝혔다. 동역학적 불안정성과 그 결과로 나타나는 평면밖 방향의 대진폭 운동을 보이고 있다. 본 결과는 주기적으로 동요하는 부유물체가 서로 연성된 운동을 하는 현상으로도 해석할 수 있다.

• Journal of Mechanical Science and Technology
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• v.19 no.9
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• pp.1711-1719
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• 2005

In an electro statically actuated nanoelectromechanical system (NEMS) resonator, it is shown that both the resonance frequency and the resonance quality (Q) factor can be manipulated. How much the frequency and quality factor can be tuned by excitation voltage and resistance on a doubly-clamped beam resonator is addressed. A mathematical model for investigating the tuning effects is presented. All results are shown based on the feasible dimension of the nanoresonator and appropriate external driving voltage, yielding up to 20 MHz resonance frequency. Such parameter tuning could prove to be a very convenient scheme to actively control the response of NEMS for a variety of applications.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.785-790
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• 2008

Vibration of a non-linear system under random parametric excitations was evaluated by probablistic methods. The non-linear characteristic terms of a system were quasi-linearized and excitation terms were remained as they were given. An analytical method where the square mean of error was minimized was ysed. An alternative method was an energy method where the damping energy and rstoring energy of the linearized system were equalized to those of the original non-linear system. The numerical results were compared with those obtained by Monte Carlo simulation. The comparison showed the results obtained by Monte Carlo simulation located between those by the analytical method and those by the energy method.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.892-895
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• 2002

In this study, to grasp the effect of vibration intensity fur the laminated composite plate, the two-dimension plate was shaken by a harmonic point excitation with the natural frequency using the finite element method. As the result, it shows that the vibration intensity according to the change of angle-ply is various and it flows to the direction of length rather than width in the plate. Also this paper represents those results to the vector flow.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.879-882
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• 2002

To control the vibration and sound of structure, it is important to analyze the dynamic action of structure. And through those analysis, the vibration source and the flow path is understood. To grasp that, when the two-dimension plate structure is shaken by a harmonic point excitation with the natural frequency using the finite element method, this paper presents the relation between vibration power flow and mode shape. As those results present to vector flow, the vibration power flow is visualized.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.9 s.102
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• pp.1053-1059
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• 2005

Dynamic stability of an axially accelerating beam structure is investigated in this paper. The equations of motion of a fixed-free beam are derived using the hybrid deformation variable method and the assumed mode method. Unstable regions due to periodical acceleration are obtained by using the Floquet's theory. Stability diagrams are presented to illustrate the influence of the dimensionless acceleration, amplitude, and frequency. Also, buckling occurs when the acceleration exceeds a certain value. It is found that relatively large unstable regions exist around the first bending natural frequency, twice the first bending natural frequency, and twice the second bending natural frequency. The validity of the stability diagram is confirmed by direct numerical integration of the equations of motion.

• Structural Engineering and Mechanics
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• v.38 no.6
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• pp.753-765
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• 2011

The radial vibration behaviors of a circular cylindrical composite piezoelectric transducer (CPT) are investigated. The CPT is composed of a piezoelectric ring polarized in the radial direction and an elastic ring graded in power-law variation form along the radial direction. The governing equations for plane stress state problem under the harmonic excitation are derived and the exact solutions for both piezoelectric and functionally graded elastic rings are obtained. The characteristic equations for resonant and anti-resonant frequencies are established. The presented methodology is fit to carry out the parametric investigation for composite piezoelectric transducers (CPTs) with arbitrary thickness in radial direction. With the aid of numerical analysis, the relationship between the radial vibration behaviors of the cylindrical CPT and the material inhomogeneity index of the functionally graded elastic ring as well as the geometric parameters of the CPTs are illustrated and some important features are reported.

• Structural Engineering and Mechanics
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• v.54 no.3
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• pp.475-489
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• 2015

This study presents the validation of a numerical model developed for dynamic analysis of buildings with roller seismic isolation bearings. Experimental methods allowed validation of the motion equations of a physical model of a building with and without roller bearings under base excitation. The results are presented in terms of modal parameters, frequency response functions (FRFs) and acceleration response. The agreement between numerical and experimental results proves the accuracy of the developed numerical model. Finally, the performance of the constructed seismic protection system is assessed through a parametric study.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1997.04a
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• pp.192-199
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• 1997

The purpose of this paper is to get a powerful tool for response analysis of a spherical dome subjected to dynamic excitation based on mathematically analytical method, i. e., the Galerkin procedure in modal analysis, with sufficient accuracy and practicality. At first, this paper provides an approximate solution of eigen modes, which has sufficient accuracy and praticallity for response analysis in symmetric and antisymmetric state. In the second stage of this paper, response analysis of a dome subjected to horizontal earthquakes is executed as the application of these approximate modes. Many important response characteristics may manifest themselves through parametric survey of material and geometric properties.

• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2716-2727
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• 2021

The core shroud is one of the most important internal components of the reactor vessel internals because it meets the neutron fluence directly emitted by the nuclear fuel. In particular, dynamic effects for an earthquake should be evaluated with respect to the neutron irradiation flux. As a prerequisite to this study, simplified and detailed finite element models are developed for the core shroud using the ANSYS Design Parametric Language. Using the El Centro earthquake, seismic analyses are performed for the simplified and detailed core shroud models. Modal characteristics are obtained and their results are used for a time history analysis. Response spectrum analyses are also performed to access the degree of seismic excitation. The results of these analyses are compared to investigate the response characteristics between the simplified and detailed core shroud models from the time history and response spectrum analyses.