• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.4
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• pp.363-372
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• 2016

When a system consisting of rigid and flexible bodies is optimized to improve its dynamic characteristics, its eigenfrequencies are typically maximized. While topology optimization formulations dealing with simultaneous design of a system of rigid and flexible bodies are available, studies on eigenvalue maximization of the system are rare. In particular, no work has solved for the case when the target frequency becomes one of the repeated eigenfrequencies. The problem involving repeated eigenfrequencies is solved in this study, and a topology optimization formulation and sensitivity analysis are presented. Further, several numerical case studies are considered to demonstrate the validity of the proposed formulation.

• Computational Structural Engineering
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• v.9 no.4
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• pp.117-126
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• 1996

Damage detection methods using structural tests can be divided into two methods, i.e., static and dynamic. The static methods which use the stiffness properties of the structure are simpler than the dynamic methods. However, static approaches are very sensitive to the displacement measurement noises and modeling errors. The dynamic methods also have limitations in acquiring the natural frequencies and mode shapes of the high frequencies. In this study, a method for the structural damage assessment using sensitivity matrices is developed, in which the drawbacks of the static and dynamic methods can be compensated. Based on the measurement data for the static displacements and dynamic modal properties, the damage locations and the degree of damage are determined using the presented sensitivity matrix method. The efficiency of the proposed method has been examined through numerical simulation studies on truss type structures.

• Proceeding of KASS Symposium
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• 2006.05a
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• pp.246-255
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• 2006

In these days the floor vibration is beginning to make its appearance of the environmental dispute in apartment building. Standard floor system are suggested for the settlement of this issue by government. The sound of floor impact sound is needed to secure comfortable quality in housing. Also, it is required an accurate analysis and a proper evaluation for floor vibration. Refine model is necessary for the floor system of housing to analyze accurately the floor vibration. But this refine model is not efficient because it is required so much running time for vibration analysis and it is difficult of modeling of standard floor slab. In this paper, new modeling methods of standard floor slab are proposed for the accurate rigidity evaluation. By using the new modeling method, the accurate vibration response can be obtained and can accurately evaluate the rigidity of standard floor system with resilient materials. Therefore the proposed modeling method is of practical use for vibration analysis of floor system of apartment building.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.7
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• pp.585-596
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• 2013

This study introduces a hybrid approach combining numerical results with pre-developed analytical calculations for the sound radiation from the modal vibration of a thick, finite length cylinder with various boundary conditions. Structural vibrations of the cylinder are numerically investigated with the finite element method, and distributions of vibratory displacements on the cylinder surface are idealized as simple mathematical expressions based on the numerical results. Sound radiations from the normal vibration of the cylinder are calculated based on idealized modal displacements using a previously introduced theoretical solution. The results are confirmed with numerical analyses using the boundary element method. Based on these results, it can be concluded that the solutions suggested in this study have good accuracies in calculating the vibro-acoustic properties of a thick, finite cylinder with various boundary conditions. Also, the sound radiation characteristics of many practical components such as brake drums and motor housings are expected to be investigated using the procedure proposed in this study.

• Journal of Convergence for Information Technology
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• v.11 no.9
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• pp.130-137
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• 2021

The characteristics of forced vibration by an external excitation force having a frequency were analyzed according to the amplitude and frequency of the excitation force. To obtain displacement, velocity, and acceleration, numerical analysis was performed to obtain the frequency response, and in particular, each FRF(Frequency Response Function) was analyzed to reveal the location of the system natural frequency and excitation frequency in the frequency domain. In the vibration model caused by external excitation, the natural frequency and distribution of the surrounding excitation mode in displacement, velocity and acceleration FRF. The FRF was also shown in the power spectrum and FRF of real and imaginary parts. The external excitation force was approximated with the excitation force of a sine wave by giving the amplitude and frequency, the mode generated by this excitation force could be distinguished. After numerical analysis by changing the equivalent mass, damping and stiffness, the forced vibration response characteristics by external excitation force were systematically analyzed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.12
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• pp.32-40
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• 2018

In order to avoid excessive vibration, it is required to carry out a vibration analysis of heat-exchanger/nuclear-reactor at the design stage. Information of eigen-frequency in the vibration problem is required to evaluate safety of heat-exchange/nuclear reactor. This paper describes a numerical method, Galerkin's method, to solve the eigenvalue problem occurred in a cantilever beam. The beam is restrained with added mass and spring at the free end or a node point of a mode shape. The numerical results of eigen-frequency were compared with simple analytical and experimental results given by simple approach and simple test, respectively. It is found that Galerkin's method is applicable to estimate the eigen-frequency of the cantilever beam. The frequencies become lower with increasing the added mass and the frequencies increase with the spring force. It is shown the heavy added mass has a role of support on the flexible tube. The eigen-frequency of the first mode, for the system with the added mass mounted at the free end, can be calculated by the approximate analytical method existing with more or less accuracy.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.1
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• pp.39-48
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• 2021

In this paper, an analytical model is proposed for assessing the natural frequency of barrettes subjected to vertical loading. The differential equation governing the free vibration of rectangular friction piles embedded in inhomogeneous soil is derived. The governing equation is numerically integrated by Runge-Kutta technique and the eigenvalue of natural frequency is computed by Regula-Falsi method. The numerical solutions for the natural frequency of barrettes compare well with those obtained from finite element analysis. Illustrated examples show that the natural frequencies increase with an increase of the cross-sectional aspect ratio, the friction resistance ratio and the soil stiffness ratio, and decrease with an increase of the friction aspect ratio, the slenderness ratio and the load factor, respectively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.10a
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• pp.208-216
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• 1995

대형선박, 항공기, 초고층 건축물 등은 얇은 박판 형태의 보로 이상화하여 구조 및 진동해석을 수행할 수 있다. 이러한 형태로 이상화한 구조물은 비틀림 강도면에서 매우 취약함을 보이고, 굽힘-비틀림 진동은 단면형상에 따라 연성도가 심화된다. 상하 굽힘 진동은 탄성거동 영역에서 도심과 전단중심이 일치하는 대칭 진동(Symmetric vibration) 현상을 보인다. 그러나, 수평 굽힘 진동은 도심과 전단중심의 차이가 커질수록 즉, 연성도가 높아질수록 비틀림 진동과 복합되어 복잡한 비대칭 진동(Antisymmetric vibration) 현상을 나타낸다. 본 논문에서는 연성효과에 의한 수평 굽힘 진동과 비틀림 진동 현상에 대한 연구를 수행하였고, 진동계산을 위해서 전달행렬법(Transfer Matrix Method)을 사용하였다. 수치계산은 첫번째로, 도심과 전단중심의 차이가 매우 작아 연성도를 무시할 수 있을 정도의 구조물에 대해서 일반적인 수평 굽힘 진동 현상과 비틀림 진동 현상을 연구하였다. 두번째로, 연성도가 매우 심할 경우에 굽힘-비틀림 연성 진동 현상을 Timoshenko 보의 이론과 Vlasov 보의이로네 따라 각각 계산을 수행하였다. 마지막으로, 첫번째와 두번째 구조를 결합한 경우에 대해서 굽힘-비틀림 연성 진동 현상을 연구하였다. 이 경우에 두 구조물의 결합부에서 비틀림 강성과 Warping 강성의 심한 변화로 인한 불연속 경계면이 발생하게 되고 이때의 진동해석을 위해서 보 이론에 기초를 두고 상당히 높은 정확도를 제공하는 Haslum[2] 등과 Pedersen[3]이 제시한 이론을 이용하였다.

• Proceedings of the KSR Conference
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• 2003.10b
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• pp.423-428
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• 2003

본 논문은 열차 곡선부 노선에서 발생하는 진동크기의 예측을 위한 것으로, 곡선부를 주행하는 틸팅차량에 의해 발생하는 진동크기를 수치해석적으로 예측한 결과이다. 곡선부를 주행하는 틸팅차량에 의한 진동의 특징으로, 진동의 방향성분을 들 수 있다. 진동의 방향성분은 직선 구간에서는 수직성분이 월등히 우세하나, 곡선구간에서는 수평성분이 크게 증가한다. 틸팅차량의 경우, 일반열차에 비해 곡선구간에서의 높은 속도로 인해 수평성분이 크게 발생한다. 따라서 틸팅차량의 주행에 의한 인근 지역에서의 진동환경을 파악하기 위해서는 수직성분 뿐 아니라 수평성분의 정확한 파악도 필요하다. 이러한 진동의 방향성분은 근거리 또는 원거리 영역에 따라 달라져, 이의 파악을 위한 연구가 필요하다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.5
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• pp.345-357
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• 2011

Recently, as part of diversifying energy sources and earth environmental issues, technology development of new renewable energy using wave energy is actively promoted and commercialized around Europe and Japan etc. In particular, OWC(Oscillating Water Column) wave power generation system using air flow induced by vertical movement of the water surface by waves in an air-chamber within caisson is known as the most efficient wave energy absorption device and therefore, is one of the wave power generation apparatus the closest to commercialization. This study examines air flow velocity, which operates turbine(Wells turbine) directly in oscillating water column type wave power generation structure from two-and three-dimensional numerical experiments and discusses optimal shape of oscillating water column type wave power generation structure by estimating the maximum flow rate of air according to change in shape. The three-dimensional numerical wave flume was applied in interpretation for this study which is the model for the immiscible two-phase flow based on the Navier-Stokes Equation. From this, it turned out that size of optimal shape appears differently according to the incident wave period and air flow is maximized at the period where minimum reflection ratio occurs.