• International Journal of Aeronautical and Space Sciences
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• 제15권1호
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• pp.20-31
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• 2014

This paper deals with the development of a realistic shape optimization of damaged columns that are subjected to conservative and non-conservative forces, using the Genetic Algorithm (GA). The analysis is based on the design of the most optimized shape of the column under the constraint of constant weight, considering the Static, Vibrational, and Flutter characteristics. Under the action of conservative and non-conservative longitudinal forces, an elastic column loses its stability. A numerical analysis based on FEM has been performed on a uniform damaged column, to compute the fundamental buckling load, vibration frequency, and flutter load, under various end restraints. An optimization search based on the Genetic Algorithm is then executed, to find the optimal shape design of the column. The optimized column references the one having the highest buckling load, highest vibration frequency, and highest flutter load, among all the possible shapes of the column, for a given volume. A comparison is then made between the values obtained for the optimized damaged column, and those obtained for the optimized undamaged column. The comparison reveals that the incorporation of damage in the column alters its optimal shape to only a certain extent. Also, the critical load and frequency values for the optimized damaged column are comparatively low, compared with those obtained for the optimized undamaged column. However, these results hold true only for moderate-intensity damage cases. For high intensity damage, the optimal shape may not remain the same, and may vary, according to the severity of damage.

• 한국해양공학회지
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• 제16권6호
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• pp.18-24
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• 2002

The vibrational system in this study consists of a cantilever pipe conveying fluid, the moving mass upon it, and an attached tip mass. The equation of motion is derived by using the Lagrange equation. The influences of the velocity and the velocities of fluid flow in the pipe have been studied on the dynamic behavior of a cantilever pipe using a numerical method. While the moving mass moves upon the cantilever pipe, the velocity of fluid flow and the nozzle angle increase; as a result, the tip displacement of the cantilever pipe, conveying fluid, is decreased. After the moving mass passes over the cantilever pipe, the tip displacement of the pipe is influenced by the potential energy of the cantilever pipe and the deflection of the pipe; the effect is the result of the moving mass and gravity. As the velocity of fluid flow and nozzle angle increases, the natural frequency of he system is decreased at the second mode and third mode, but it is increased at the first mode. As the moving mass increases, the natural frequency of the system is decreased at all modes.

• 한국기계가공학회지
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• 제11권1호
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• pp.76-81
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• 2012

Ultrasonic metal welding is one of the welding methods which welds metal by applying high frequency vibrational energy into specific area at constant pressure, avaliable in room temperature and low temperature. Ultrasonic metal welder is consisted of power supply, transducer, booster, and horn. Precise designing is required since each parts' shape, length and mass can affect driving frequency and vibration mode. This paper focused to horn design, its length L was set to 62mm by calculating vibration equation. By performing modal analysis with various shape variable b times integer, when length of b is 30mm the output was 39,599Hz at 10th mode. Also by performing harmonic response analysis, the frequency response result was 39,533Hz, which was similar to modal analysis result. In order to observe the designed horn's performance, about 4,000 voltage data was obtained from a light sensor and was analyzed by FFT analysis using Origin Tool. The result RMS amplitude was approximately 8.5${\mu}m$ at 40,000Hz, and maximum amplitude was 12.3${\mu}m$. Therefore, it was verified that the ultrasonic metal welding horn was optimally designed.

• 센서학회지
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• 제24권3호
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• pp.169-174
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• 2015

In this study, we developed a system to detect the various defects in the metallic objects using the phenomenon that the defects cause the changes of the natural resonant frequencies. Our system consists of a FFT Amp, an Auto Impact Hammer, a Hammer controller and a PC. Auto Impact Hammer creates vibrations in the metallic objects when tapped on the surface. These vibrational signals are converted to the voltage signals by an acceleration sensor attached to the metallic part surface. These analog voltage signals were fed into an ADC (analog-digital converter) and an FFT (fast fourier transform) conversion in the FFT Amp to obtain the digital data in the frequency domain. Labview graphical program was used to process the digital data from th FFT amp to display the spectrum. We compared those spectra with the standard spectrum to find the shifts in the resonant frequencies of the metal parts, and thus detecting the defects. We used PCB's acceleration sensor and TI's TMS320F28335 DSP (digital signal processor) to obtain the resolution of 2.93 Hz and to analyze the frequencies up to 44 kHz.

• 한국소음진동공학회논문집
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• 제15권11호
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• pp.1232-1240
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• 2005

The purpose of this paper is that investigates the dynamic behavior characteristic of W.T.S (wind turbine system) and carries out the evaluation analysis during operating W.T.S. To investigate the dynamic behavior characteristic of W.T.S, the experiments to measure vibration of the blade from the attached accelerometer on the flap and edge section of the blade that is one of the most important elements of dynamic characteristic of W.T.S are performed. Natural frequency and mode shape are calculated with commercial program ( ANSYS) using the measured vibration acceleration that receives the signal with F.F.T Analyzer from the accelerometer For validation of these experiments, the finite element analysis is performed with commercial F.E.M program (ANSYS) on the basis of the natural frequency and mode shape. The results indicate that experimental values have good agreements with the finite element analysis.

• Steel and Composite Structures
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• 제50권4호
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• pp.375-382
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• 2024

The network theory studies interconnection between discrete objects to find about the behavior of a collection of objects. Also, nanomaterials are a collection of discrete atoms interconnected together to perform a specific task of mechanical or/and electrical type. Therefore, it is reasonable to use the network theory in the study of behavior of super-molecule in nano-scale. In the current study, we aim to examine vibrational behavior of spherical nanostructured composite with different geometrical and materials properties. In this regard, a specific shear deformation displacement theory, classical elasticity theory and analytical solution to find the natural frequency of the spherical nano-composite structure. The analytical results are validated by comparison to finite element (FE). Further, a detail comprehensive results of frequency variations are presented in terms of different parameters. It is revealed that the current methodology provides accurate results in comparison to FE results. On the other hand, different geometrical and weight fraction have influential role in determining frequency of the structure.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2023년도 가을학술발표대회논문집
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• pp.227-228
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• 2023

A floating floor generally consists of mortar bed separated from the structural RC slab by a continuous resilient layer. It is known that the floating floors are a type of vibration-isolation system to improve the impact sound insulation performance. However, some researchers have demonstrated that the amplification of vibration response at a specific range of frequencies results in an increase in the impact sound level. This study carried out the forced vibration tests to obtain the frequency response function (FRF) of a floating floor compared with a bare RC slab. Test results shows that the additional peak occur in vibrational spectrum of the floating floor except natural vibration modes of the bare RC slab. This is because the relatively flexible resilient material and mass of the mortar bed offer an additional degree of freedom in the structural system. Therefore, it could be efficient for reduction of floor impact vibration and noise to control the additional mode frequency and response of floating floors.

• 대한기계학회논문집
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• 제15권1호
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• pp.366-375
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• 1991

본 연구에서는 보 이론(beam theory)의 변위함수(displacement function)를 도입하고 전달행렬법을 이용하여 각 배관요소의 경계조건에 대한 고유 진동수와 배관 의 불안정성을 일으키는 유체의 임계속도(critical velocity)를 계산 평가하고, 실험 으로 입증된 Blevins의 결과치와 비교하였다.

• 한국강구조학회 논문집
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• 제27권2호
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• pp.181-193
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• 2015

심미성과 기능성이 현대 건축의 중요한 요소로 대두되면서 최근 비교적 경량의 고진동수 계단의 활용처가 점차 증가하고 있다. 하지만 국내의 실정 상 고진동수 계단의 진동성능을 평가하기 위한 방법이 전무한 실정이다. 유럽강구조학회의 지침의 경우 등가임펄스하중 개념을 도입하여 고진동수 바닥의 응답예측 및 진동성능 평가에 활용하고 있으나, 이는 서행보행에 대한 실험치를 토대로 제안한 값으로 2.2Hz 이상의 속보 가진에 대한 응답을 과대평가하는 한계를 지니고 있다. 이에 본 연구에는 1.4~4.5Hz의 다양한 가진진동수에 대한 가속도 응답의 실측값을 바탕으로 서행 및 속보 가진 시의 응답을 합리적으로 예측할 수 있는 등가임펄스 식을 제안하였다.

• Korean Chemical Engineering Research
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• 제53권6호
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• pp.808-813
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• 2015

해수 중에 보론은 주로 붕산(boric acid, $B(OH)_3$)으로 존재하며 그 크기가 역삼투압(RO, reverse osmosis) 공정의 막의 공칭공경(nominal pore size)만큼 작아 이를 제거하기가 쉽지 않다. 이에 본 연구에서는 수용액 중 보론 화합물의 크기를 역삼투압 공정에서 제거가 용이하도록 키우기 위한 방법으로 $B(OH)_3$가 폴리올과 착화합물을 형성하는 원리를 이용하고자하며 착화합물의 형성 여부를 라만 분광학 연구를 통해 확인하고자 하였다. 먼저 $B(OH)_3$와 붕산염(borate ion, ${B(OH)_4}^-$) 이온의 대칭(symmetric) B-O 신축운동 모드(stretching vibrational mode)의 진동수를 확인하기 위하여 pH를 증가시키며 라만 스펙트럼을 측정한 결과 $877cm^{-1}$에서 $730cm^{-1}$으로 피크의 이동이 관찰되었다. 이는 수용액 중의 $B(OH)_3$가 pH가 증가하면서 ${B(OH)_4}^-$로 전환됨을 나타내고 이러한 피크의 이동은 진동수 계산(frequency calculation)에 의한 예측과 정확하게 일치하였다. 반면 $B(OH)_3$ 수용액에 폴리올을 첨가한 경우 pH가 증가하여도 ${B(OH)_4}^-$의 특성 진동수인 $730cm^{-1}$가 나타나지 않았으며 이는 $B(OH)_3$가 ${B(OH)_4}^-$로 전환되는 것이 아니라 폴리올과 착화합물을 형성함을 간접적으로 보여주고 있다.