• 한국강구조학회 논문집
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• 제24권1호
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• pp.119-128
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• 2012

본 연구에서는 실험적 모드해석 기법을 이용하여 외부환경에 직접 노출되어 있는 실제 철도판형교의 full-scale 동적 테스트가 수행되었다. 충격해머 모드실험에 의해 얻어진 철도판형교의 모드 매개변수를 유한요소해석으로부터 구한 고유진동수와 모드형상과 비교, 분석하였다. 실험적 모드해석에 의해 측정된 실험 데이터와 해석적 진동분석에서 얻어지는 출력만의 데이터를 교량 부재의 기하학적 특성 및 재료적 특성을 다양하게 고려하여 모델보정 테크닉에 적용하였다. 철도판형교의 실험적 모드해석 결과를 검증하기 위한 유한요소모델이 모드인식 기법을 이용하여 보정되었다. 실험 데이터와 유한요소해석 기준모델의 모델보정과정의 결과와 함께 부재특성의 변화를 통하여 이루질 수 있는 손상평가에 대한 기초적 데이터베이스가 제공된다.

• 한국자동차공학회논문집
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• 제18권6호
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• pp.130-137
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• 2010

Due to test facility and specialty, it is physically difficult to conduct the modal tests of large-sized structures such as truck, bus and airplane. So, in case of a large-sized truck, the mode analysis on a full vehicle model comprised of reliable cabin, frame, and deck has been generally performed. However, the reliability of overall vibrational characteristics of the analytic model has not been fairly guaranteed by the testified models of each subsystem owing to the existence of cab suspension and the nonlinear mounting between a chassis frame and a special deck system. In this paper, a method to find out the modal characteristics of a large-sized military truck is presented. New modal test equipment is developed to set the boundary conditions of three military truck variants as close as a free-free condition. And the mode analysis method using coupled structure and dynamic models is established to consider the above-mentioned dynamic non-linearities of the vehicle itself. The usefulness of the suggested method is verified by comparing with the modal test results. Finally, the modal parameters of the final variant are extracted using the proved analytic method.

• Smart Structures and Systems
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• 제16권2호
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• pp.295-328
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• 2015

In recent years the monitoring of structural behavior through acquisition of vibrational data has become common practice. In addition, recent advances in sensor development have made the collection of diverse dynamic information feasible. Other than the commonly collected acceleration information, Global Position System (GPS) receivers and non-contact, optical techniques have also allowed for the synchronous collection of highly accurate displacement data. The fusion of this heterogeneous information is crucial for the successful monitoring and control of structural systems especially when aiming at real-time estimation. This task is not a straightforward one as measurements are inevitably corrupted with some percentage of noise, often leading to imprecise estimation. Quite commonly, the presence of noise in acceleration signals results in drifting estimates of displacement states, as a result of numerical integration. In this study, a new approach based on a time domain identification method, namely the Unscented Kalman Filter (UKF), is proposed for correcting the "drift effect" in displacement or rotation estimates in an online manner, i.e., on the fly as data is attained. The method relies on the introduction of artificial white noise (WN) observations into the filter equations, which is shown to achieve an online correction of the drift issue, thus yielding highly accurate motion data. The proposed approach is demonstrated for two cases; firstly, the illustrative example of a single degree of freedom linear oscillator is examined, where availability of acceleration measurements is exclusively assumed. Secondly, a field inspired implementation is presented for the torsional identification of a tall tower structure, where acceleration measurements are obtained at a high sampling rate and non-collocated GPS displacement measurements are assumed available at a lower sampling rate. A multi-rate Kalman Filter is incorporated into the analysis in order to successfully fuse data sampled at different rates.

• Bulletin of the Korean Chemical Society
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• 제35권3호
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• pp.875-880
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• 2014

Adsorption of 4,4'-bis(mercaptomethyl)biphenyl (44BMBP) on silver nanoparticles has been investigated by surface-enhanced Raman scattering (SERS) spectroscopy. In addition, the Raman spectra of 44BMBP in solid state and in basic condition have been obtained for comparative study to elicit the characteristics of adsorption. The observed Raman and SERS spectra were analyzed comparing with the normal modes and vibrational frequencies from density functional theory (DFT) calculations performed for the feasible structures of 44BMBP molecule. On the basis of excellent agreement between the calculated and the experimental results, the molecule is found to have both the cis- and trans-forms for the mercaptomethyl groups in the solid state as well as in the basic condition. In contrast, the molecule is found to be chemisorbed on the silver surface by forming two Ag-S linkages only in the cis-form but not in the trans-form due to the steric interruption, which indicates the parallel orientation of molecules on the surface. Particularly, the spectral features in the SERS spectra such as the absence of the C-H stretching band and enhancement for the out-of-plane skeletal modes are confirmatory for the parallel geometry through ${\pi}$ interaction between the phenyl rings and the metal surface, based on the electromagnetic surface selection rule.

• 한국지반환경공학회 논문집
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• 제10권2호
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• pp.45-50
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• 2009

지반이 연약하거나 지하수 유동에 따른 응력의 변화로 인하여 부등침하가 발생하면 구조물이 경사지거나 변형되어 균열이 발생하게 된다. 부등침하로 인하여 구조물의 기초부분이 변형되면, 지반의 지지력을 보강하는 방법으로 현재 까지 국내에서 주로 그라우팅공법을 사용하였다. 그러나 이 공법은 보강효과가 장기간동안 지속되지 못하며, 원하는 강도를 발휘하기 위해서는 오랜 시간이 필요한 단점이 있다. 급속팽창재료(GPCON) 주입공법은 기계적 물성 및 내구성이 우수하며 시공이 간편한 장점을 지니고 있으며 고결시간도 매우 빨라 하부지반에 물질을 분사하여 흙입자 사이의 지반 간극을 채움과 동시에 팽창 고결하여 지지력과 전단력을 증가시킬 수 있는 공법이다. 본 연구에서는 고밀도 급속 팽창 지피콘을 이용하여 반복 하중에 의한 변형특성과 진동 저감효과를 분석하고 철도 및 지하철에서 기초침하 복원성을 평가하였다.

• Steel and Composite Structures
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• 제35권1호
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• pp.111-127
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• 2020

The goal of this study is to fill this apparent gap in the area about investigating the effect of porosity distributions on vibrational behavior of FG sectorial plates resting on a two-parameter elastic foundation. The response of the elastic medium is formulated by the Winkler/Pasternak model. The internal pores and graphene platelets (GPLs) are distributed in the matrix either uniformly or non-uniformly according to three different patterns. The model is proposed with material parameters varying in the thickness of plate to achieve graded distributions in both porosity and nanofillers. The elastic modulus of the nanocomposite is obtained by using Halpin-Tsai micromechanics model. The annular sector plate is assumed to be simply supported in the radial edges while any arbitrary boundary conditions are applied to the other two circular edges including simply supported, clamped and free. The 2-D differential quadrature method as an efficient and accurate numerical approach is used to discretize the governing equations and to implement the boundary conditions. The convergence of the method is demonstrated and to validate the results, comparisons are made between the present results and those reported by well-known references for special cases treated before, have confirmed accuracy and efficiency of the present approach. It is observed that the maximum vibration frequency obtained in the case of symmetric porosity and GPL distribution, while the minimum vibration frequency is obtained using uniform porosity distribution. Results show that for better understanding of mechanical behavior of nanocomposite plates, it is crucial to consider porosities inside the material structure.

• Journal of Biosystems Engineering
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• 제12권4호
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• pp.9-15
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• 1987

The vibrational characteristics of a radial-ply (155SR13 4PR) and a biased-ply tire (6.15-134PR) were investigated for examining the effects of tires with different structure on the ride characteristics of the vehicle. The natural frequencies at the tread band, mode shapes, and damping factors of two tires at the state of plane vibration were determined experimentally. The test work was performed at four levels of the inflation pressure, ranging from 171.7 kPa to 245.2 kPa, and three levels of the vertical load, deviating by 10% from the standard load designated by the Department of Transportation of the United States of America. The following results were drawn by the analysis of the test results: 1. The first-order natural frequencies of the radial-ply and the biased-ply tires at the tread band were 112 Hz and 159 Hz, respectively, at the state o f the free vibration when the inflation pressure of 196.2 kPa was applied. It was known that the biased-ply tire has higher resonant frequency than the radial-ply tire and the natural frequencies of the both tires move to the high frequency range as t he inflation pressure is increased. 2. The vibration modes of both tires were quite different. No big difference in mode shapes was examined as the inflation pressure was increased. But the natural frequencies of two tires were changed. For the radial-ply tire, no difference in mode shape was found whether the vertical load was applied or not. But a significant difference in mode shape was examined for the biased-ply tire. 3. Any difference was not found in damping factor as the different inflation pressures were applied. 4. When no vertical load was applied, damping factors of the radial-ply and biased-ply tire at the state of the natural vibration ranged from 2.6 to 5.9%, and from 4.1 to 7.8%, respectively. It was estimated that the radial-ply tire would have better cushioning than the biased-ply tire since the vertical spring rate of the radial-ply tire was much less than that of the biased-ply tire, even though the damping effect of the radial-ply tire was smaller than that of the biased-ply tire.

• 한국재난정보학회 논문집
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• 제13권2호
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• pp.249-257
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• 2017

최근 당진-평택시에 위치한 서해대교에서 낙뢰로 인한 케이블 단선사고가 발생하였다. 이것은 자연발생 사고로 결론이 났지만 케이블교량의 단선으로 인하여 안전문제를 재검토하는 과정이 매우 중요한 일임을 상기하게 된 사건이다. 즉, 케이블 교량에서 케이블의 역할은 구조물의 안전에 지대한 영향을 미치며 이로 인해 전체구조체계에 대한 영향을 파악할 필요가 대두 되었다. 케이블 교량은 주 탑을 세우고 바닥판을 케이블로 지지하는 경제적 교량으로 케이블의 영향은 주 부재로써 전 교량시스템의 안전에 영향이 큰 부재이다. 사장교에서 케이블은 케이블의 장력이 변할 때 발생하는 사하중으로 인한 처짐의 변화 때문에 비선형 성을 가진다. 동적해석은 변형 된 사하중 접선강도행렬을 사용하여 되며 새로운 개념은 전체 교량에 대한 케이블 진동 (면내 및 스윙 모두)의 효과를 연구하기 위해 케이블을 여러 요소로 분할하였다. 이 연구의 결과는 전반적인 교량 역학에 케이블 진동의 중요성을 보여준다.

• Smart Structures and Systems
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• 제6권3호
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• pp.183-196
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• 2010

Monitoring and economical design of alternative energy generators such as wind turbines is becoming increasingly critical; however acquisition of the dynamic output data can be a time-consuming and costly process. In recent years, low-cost wireless sensors have emerged as an enabling technology for structural monitoring applications. In this study, wireless sensor networks are installed in three operational turbines in order to demonstrate their efficacy in this unique operational environment. The objectives of the first installation are to verify that vibrational (acceleration) data can be collected and transmitted within a turbine tower and that it is comparable to data collected using a traditional tethered system. In the second instrumentation, the wireless network includes strain gauges at the base of the structure. Also, data is collected regarding the performance of the wireless communication channels within the tower. In both turbines, collected wireless sensor data is used for off-line, output-only modal analysis of the ambiently (wind) excited turbine towers. The final installation is on a turbine with embedded braking capabilities within the nacelle to generate an "impulse-like" load at the top of the tower. This ability to apply such a load improves the modal analysis results obtained in cases where ambient excitation fails to be sufficiently broad-band or white. The improved loading allows for computation of true mode shapes, a necessary precursor to many conditional monitoring techniques.

• 한국자기학회지
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• 제16권1호
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• pp.92-97
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• 2006

C 1s에너지 스캔 방식 광전자회절을 이용하여 Ni(111)$(2\times2)$-O/CO에 공동 흡착된 CO의 흡착구조를 시편의 준비 온도에 따라 연구하였다. 실온근방에서 준비한 시편의 경우 표면진동분광결과와 잘 일치하는 결과인 atop 흡착을 얻었으나, 저온시편의 경우 atop흡착 외에 상당량의 CO가 hollow 흡착으로 해석되었다. 일부분의 hollow 흡착 CO는 미리 흡착된 산소의 precoverage가 적거나 없는 곳에 흡착된 곳으로 해석된다. 유사한 결과가 C 1s와 O 1s를 통행 얻은 고 분해능 XPS에서 얻은 흡착위치에서도 확인되었다.