• Journal of Advanced Marine Engineering and Technology
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• 제39권10호
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• pp.1011-1016
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• 2015

Gas piping systems in power plants and factories are always influenced by the mechanical vibrations of rotational machines such as pumps, blowers, and compressors. Unusual vibrations in a gas piping system influence possible leakages of liquids or gases, which can lead to large explosive accidents. Real-time measurements of unusual vibrations in piping systems in situ prohibit them from being possible leakages owing to the repeated fatigue of vibrations. In this paper, a non-contact 3-dimensional measurement system that can detect the vibrations of a solid body and monitor its vibrational modes is introduced. To detect the displacements of a body, a stereoscopic camera system is used, through which the major vibration types of solid bodies (such as X-axis-major, Y-axis-major, and Z-axis-major vibrations) can be monitored. In order to judge the vibration types, an artificial neural network is used. The measurement system consists of a host computer, stereoscopic camera system (two-camera system, high-speed high-resolution camera), and a measurement target. Through practical application on a flat plate, the measured data from the non-contact measurement system showed good agreement with those from the original vibration mode produced by an accelerator.

• 한국농공학회논문집
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• 제57권6호
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• pp.117-123
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• 2015

An experimental study of model truss-type vertical gate consisting of a truss and a plate was presented in this paper to examine the structural dynamics of the gates. A 1:61 scale model was constructed for the 95 m prototype gate using an acrylic truss and an acrylonitrile butadiene styrene plate. The scaled model was tested in a 1.6 m wide concrete flume for two orientations to determine the effects of gate orientation on structural vibrations. Natural frequencies of the model gate was measured and calibrated with FEM predictions. Vertical vibrations were measured under various operational conditions, including a range of bottom opening heights and different upstream and downstream water levels. The gate model with reverse direction was preferred due to its low overall vibrational response and flow level combinations. The test results also provide a basic dataset for development of operations guidelines that minimize flow-induced vibrations of the gates.

• Steel and Composite Structures
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• 제24권6호
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• pp.711-726
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• 2017

In the present work, by considering the agglomeration effect of single-walled carbon nanotubes, free vibration characteristics of functionally graded (FG) nanocomposite sandwich plates resting on Pasternak foundation are presented. The volume fractions of randomly oriented agglomerated single-walled carbon nanotubes (SWCNTs) are assumed to be graded in the thickness direction. To determine the effect of CNT agglomeration on the elastic properties of CNT-reinforced composites, a two-parameter micromechanical model of agglomeration is employed. In this research work, an equivalent continuum model based on the Eshelby-Mori-Tanaka approach is employed to estimate the effective constitutive law of the elastic isotropic medium (matrix) with oriented straight CNTs. The 2-D generalized differential quadrature method (GDQM) as an efficient and accurate numerical tool is used to discretize the equations of motion and to implement the various boundary conditions. The proposed rectangular plates have two opposite edges simply supported, while all possible combinations of free, simply supported and clamped boundary conditions are applied to the other two edges. The benefit of using the considered power-law distribution is to illustrate and present useful results arising from symmetric and asymmetric profiles. The effects of two-parameter elastic foundation modulus, geometrical and material parameters together with the boundary conditions on the frequency parameters of the laminated FG nanocomposite plates are investigated. It is shown that the natural frequencies of structure are seriously affected by the influence of CNTs agglomeration. This study serves as a benchmark for assessing the validity of numerical methods or two-dimensional theories used to analysis of laminated plates.

• 자연과학논문집
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• 제1권
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• pp.1-6
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• 1987

공진기 안에 Ge 에탈론을 넣은 TEA $CO_2$ 레이저에서 다중 전이선이 발진할 때 발진전이선 사이에서 시간 지연이 생겼다. 이때 생긴 지연효과를 좀 더 정확히 보기 위해 에탈론 대신 한 쪽은 40 % 반사율을 가지고 또 다른 한 쪽은 투과되도록 코팅된 ZnSe반반사 거울을 넣었다. 이때 출력거울의 각도를 조금씩 틀어줌에 따라 두 전이선이 발진할 때 발진시간을 조절할 수 있었고 출력의 세기도 조절할 수 있었다. 이 결과는 높은 최대출력과 짧은 레이저 출력시간을 얻기 위해서 다중전이선을 발진시킬 때에는 출력전이선들끼리의 이득경쟁효과가 비슷하여 서로 비슷한 세기의 출력을 가져야만 된다는 것을 보여준다.

• Smart Structures and Systems
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• 제22권2호
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• pp.133-137
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• 2018

Increasing interest in prognostics and health management has heightened the need for wireless sensor networks (WSN) with efficient power sources. Piezoelectric energy harvesters using Pb(Zr,Ti)O3 (PZT) are one of the candidate power sources for WSNs as they efficiently convert mechanical vibration energy into electrical energy. These types of devices are resonated at a specific frequency, which has a significant impact on the amount of energy harvested, by external vibration. Hence, precise prediction of mechanical deformation including modal analysis of piezoelectric devices is crucial for estimating the energy generated under specific conditions. In this study, an experimental vibrational system capable of controlling a wide range of frequencies and accelerations was designed to generate mechanical vibration for piezoelectric energy harvesters. In conjunction with MATLAB, the system automatically finds the resonance frequency of harvesters. A small accelerometer and non-contact laser displacement sensor are employed to investigate the mechanical deformation of harvesters. Mechanical deformation under various frequencies and accelerations were investigated and analyzed based on data from two types of sensors. The results verify that the proposed system can be employed to carry out vibration experiments for piezoelectric harvesters and measurement of their mechanical deformation.

• 한국산학기술학회논문지
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• 제14권9호
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• pp.4136-4141
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• 2013

전자기 진동 가진기를 적용한 전기 집진기의 효과적인 탈진 여부를 판단할 수 있는 기준은 집진기내 집진판들의 진동 가속도이다. 이러한 진동 가속도는 외부로부터의 가진 주파수와 시스템의 고유주파수의 일치로 인하여 공진이 일어날 때 간헐적으로 최대치를 보이며 효율적인 탈진성능을 기대할 수 있다. 본 연구에서는 한대의 전자기 진동 가진기를 이용하는 단일 객체를 대상으로 한 관점에서 더 나아가, 실제 현장에서 복수의 전기집진탈진기가 설치됨을 고려하여 진동 탈진기의 설치방식에 따라 시스템을 모델링 하였다. 이러한 직렬 및 병렬회로로 연결된 가진기를 적용한 시스템을 대상으로 진동 가속도 계측 실험을 수행하여 직렬 및 병렬식 연결에 따른 진동 가속도의 차이를 비교함으로써 가진기의 배열 방식과 그에 따른 기대 탈진 성능 및 소비전력의 유효성을 검증하였다. 최종적으로 직렬 배열형 모듈이 증가할수록 선형적으로 필요전류량이 증가할 것으로 예상하였으나 급격한 감소나 (6.9% ~ 37.6%) 증가를 (5% ~ 45%) 보여주었다. 단독의 가진기가 사용된 병렬 배열보다, 2대의 가진기가 사용되고 그 전기회로의 연결이 병렬일 때 동일한 전류가 인가되었음에도 약 11.64% 의 가속도 감소 현상을 보였다. 2대의 가진기를 사용하고 입력전류의 값을 소비 전력의 관점에서 동일하게 보정하였을 경우 약 16.80 % 의 가속도 증가 현상을 확인하였다.

• Nuclear Engineering and Technology
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• 제42권1호
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• pp.97-108
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• 2010

Fluid-elastic instability and turbulence-induced vibration of steam generator U-tubes of a nuclear power plant are studied numerically to investigate the effect of design changes of support structures in the upper region of the tubes. Two steam generator models, Model A and Model B, are considered in this study. The main design features of both models are identical except for the conditions of vertical and horizontal support bars. The location and number of vertical and horizontal support bars at the middle of the U-bend region in Model A differs from that of Model B. The stability ratio and the amplitude of turbulence-induced vibration are calculated by a computer program based on the ASME code. The mode shape with a large modal displacement at the upper region of the U-tube is the key parameter related to the fretting wear between the tube and its support structures, such as vertical, horizontal, and diagonal support bars. Therefore, the location and the number of vertical and horizontal support bars have a great influence on the fretting wear mechanism. The variation in the stability ratios for each vibrational mode is compared with respect to Model A and Model B. Even though both models satisfy the design criteria, Model A shows substantial improvements over Model B, particularly in terms of having greater amplitude margins in the turbulence-excited vibration (especially at the inner region of the tube bundle) and better stability ratios for the fluid-elastic instability.

• Advances in concrete construction
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• 제14권3호
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• pp.169-183
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• 2022

In this article, vibrational behavior and wave propagation characteristics in (FG) functionally graded plates resting on Kerr foundation with three parameters is studied using a 2D dimensional (HSDT) higher shear deformation theory. The new 2D higher shear deformation theory has only four variables in field's displacement, which means has few numbers of unknowns compared with others theories. The shape function used in this theory satisfies the nullity conditions of the shear stresses on the two surfaces of the FG plate without using shear correction factors. The FG plates are considered to rest on the Kerr layer, which is interconnected with a Pasternak-Kerr shear layer. The FG plate is materially inhomogeneous. The material properties are supposed to vary smoothly according to the thickness of the plate by a Voigt's power mixing law of the volume fraction. The equations of motion due to the dynamics of the plate resting on a three-parameter foundation are derived using the principle of minimization of energies; which are then solved analytically by the Navier technique to find the vibratory characteristics of a simply supported plate, and the wave propagation results are derived by using the dispersion relations. Perceivable numerical results are fulfilled to evaluate the vibratory and the wave propagation characteristics in functionally graded plates and some parameters such wave number, thickness ratio, power index and foundation parameters are discussed in detail.

• 마이크로전자및패키징학회지
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• 제13권3호
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• pp.9-12
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• 2006

전기도금 방법으로 유리기판 위에 제작한 코일과 영구자석을 이용하여 초소형발전기를 제작하였다. 여러 크기의 코일 구조를 설계한 마스크를 제작하고, 이를 이용하여 MEMS 코일을 제작하였다. 그 중 두께가 $7{\mu}m$ 선폭이 $20{\mu}m$ 길이가 1.6 m인 코일을 선택하여 실험하였다. 광학현미경과 SEM을 사용하여 제작된 코일의 구조를 분석하였다. 또한 모터의 회전운동을 진동운동과 유사한 선형운동으로 변환하는 진동발생시스템을 제작하였고, 자석과 코일을 진동발생장치에 설치하고 진동을 발생시키면 교류 전압이 발생한다. 0.5Hz에서 8Hz까지 진동주파수를 변화시켜 특성을 측정하였다. 발생된 전압은 3Hz에서 106mV가 발생하였고, 6Hz에서 198mV가 발생하였다. 본 연구의 목적은 쓸모없이 버려지는 진동에너지를 유용한 전기에너지로 변환하는 초소형발전기 소자를 제작하는 것이다.

• Structural Engineering and Mechanics
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• 제63권6호
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• pp.735-742
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• 2017

Steel cables as the most important components are widely used in the certain types of structures such as cable-supported bridges, but the long-span structures may result in an increase in fatigue under high stress and corrosion of steel cables. The traditional steel cable is becoming a more evident hindrance. Fiber Reinforced Polymer (FRP) cables with lightweight, high-strength are widely used in civil engineering, but there is little research in vibrational characteristics of FRP cables, especially on the damping characteristic. This article studied the two methods to evaluate dynamical damping characteristic of basalt FRP(BFRP) and glass FRP(GFRP) cables. First, the vibration tests of the B/G FRP cables with different diameter and different cable force were executed. Second, the cables forces were calculated using dynamic strain, static strain and dynamic acceleration respectively, which were further compared with the measured force. Third, experimental modal damping of each cables was calculated by the half power point method, and was compared with the calculation by Rayleigh damping theory and energy dissipation damping theory. The results indicate that (1) The experimental damping of FRP cables decreases with the increase of cable force, and the trend of experimental damping changes is roughly similar with the theoretical damping. (2) The distribution of modal damping calculated by Rayleigh damping theory is closer to the experimental results, and the damping performance of GFRP cables is better than BFRP cables.