• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 추계학술발표대회 논문집
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• pp.190-193
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• 2005

The purpose of the present study is to design a 500W-class micro scale composite wind turbine blade. The blade airfoil of FFA-W3-211 was selected to meet Korean weather condition. The skin-spar-f Dam sandwich type structure was adopted for improving buckling and vibration damping characteristics. The design loads were determined at wind speed of 25m/s. and the structural analysis was performed to confirm safety and stability from strength. buckling and natural frequency using the finite element code. NISA II [6]. The prototype was manufactured using the hand-lay up method and it was experimently tested using the sand bag loading method. In order to evaluate the design results. it was compared with experimental results. According to comparison results. the estimated results such as compressible stress. max tip deflection natural frequency and buckling load factor were well agreed with the experimental results.

• Journal of Mechanical Science and Technology
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• 제17권2호
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• pp.197-206
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• 2003

It is intended to retrieve the time history of displacement from measured acceleration signal. In this study, the word retrieving means reconstructing the time history of original displacement signal from already measured acceleration signal not just extracting various information using relevant signal processing techniques. Unlike extracting required information from the signal, there are not many options to apply to retrieve the time history of displacement signal, once the acceleration signal is measured and recorded with given sampling rate. There are two methods, in general, to convert measured acceleration signal into displacement signal. One is directly integrating the acceleration signal in time domain. The other is dividing the Fourier transformed acceleration signal by the scale factor of - $\omega$$^2$and taking the inverse Fourier transform of it. It turned out both the methods produced a significant amount of errors depending on the sampling resolution in time and frequency domain when digitizing the acceleration signals. A simple and effective way to convert the time history of acceleration signal into the time history of displacement signal without significant errors is studied here with the analysis on the errors involved in the conversion process.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 I
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• pp.335-340
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• 2001

Dynamic stability of a rotary oscillating cantilever beam is presented in this study. Using the stretch deformation instead of the conventional axial deformation, three linear partial differential equations are derived from Hamilton's principle and transformed into dimensionless forms. Stability diagrams of the first order approximate solutions are obtained by using the multiple scale perturbation method. The stability diagrams show that relatively large unstable regions exist near the combination of the first chordwise bending natural frequency and the first stretch natural frequency. This result is verified by using the generalized-${\alpha}$ method.

• Computers and Concrete
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• 제25권2호
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• pp.133-144
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• 2020

This paper aims to study vibration characteristics of chiral and zigzag double-walled carbon nanotubes entrenched on Donnell shell model. The Eringen's nonlocal elastic equations are being combined with Donnell shell theory to observe small scale response. Wave propagation is proposed technique to establish field equations of model subjected to four distinct end supports. A nonlocal model has been formulated to explore the frequency spectrum of both chiral and zigzag double-walled CNTs along with diversity of indices and nonlocal parameter. The significance of scale effect in relevance of length-to-diameter and thickness- to- radius ratios are discussed and displayed in detail. The numerical solution based on this nonlocal Donnell shell model can be further used to predict other frequency phenomena of double-walled and multi-walled CNTs.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제36회 춘계학술대회논문집
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• pp.69-72
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• 2011

추력 75톤급 액체로켓엔진용 가스발생기의 초기 검증을 위한 세 번째 축소형 모델에서 연소시험이 수행되었다. 본 논문에서는 세 번째 축소형 가스발생기 모델의 연소시험 중 발생한 저주파 연소불안정에 대한 분석 결과를 기술하였다. 이러한 저주파 압력섭동은 연소실 압력, 산화제/연료 분사기의 차압과 연관된 것으로 판단된다.

• Advances in materials Research
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• 제7권3호
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• pp.163-174
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• 2018

This article studies the free and forced vibrations of the carbon nanotubes CNTs embedded in an elastic medium including thermal and dynamic load effects based on nonlocal Euler-Bernoulli beam. A Winkler type elastic foundation is employed to model the interaction of carbon nanotube and the surrounding elastic medium. Influence of all parameters such as nonlocal small-scale effects, high temperature change, Winkler modulus parameter, vibration mode and aspect ratio of short carbon nanotubes on the vibration frequency are analyzed and discussed. The non-local Euler-Bernoulli beam model predicts lower resonance frequencies. The research work reveals the significance of the small-scale coefficient, the vibrational mode number, the elastic medium and the temperature change on the non-dimensional natural frequency.

• 한국컴퓨터정보학회논문지
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• 제24권1호
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• pp.225-230
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• 2019

The purpose of this study is to provide basic data that mother's smart phone overdependence prevention education are needed by confirming the relationship between mother' s smartphone overdependence and parent role intelligence. The research subjects were 220 mothers of 0-2 years old who are attending 15 day care centers in Cheong-ju, Chung-buk. The research tool used smartphone overdependence scale, and parent role intelligence scale. For the analysis of the study, frequency analysis, Pearson's Ratio correlation and regression analysis were performed. The results showed that mother's smartphone overdependence was negatively correlated with parental role intelligence and negatively correlated with developmental stimulation, parenting, support, and management. The multiple regression analysis showed that there was a significant negative effect on the smartphone overdependency, parent role intelligence, and sub factors. This suggests that smartphone overdependence prevention education for mother should be needed for nurturing of desirable infants.

• Wind and Structures
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• 제20권6호
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• pp.793-810
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• 2015

Tests were conducted at the Florida International University (FIU) Wall of Wind (WOW) to investigate the susceptibility of Variable Message Signs (VMS) to wind induced vibrations due to vortex shedding and galloping instability. Large scale VMS models were tested in turbulence representative of the high frequency end of the spectrum in a simulated suburban atmospheric boundary layer. Data was measured for the $0^{\circ}$ and $45^{\circ}$ horizontal wind approach directions and vertical attack angles ranging from $-4.5^{\circ}$ to $+4.5^{\circ}$. Analysis of the power spectrum of the fluctuating lift indicated that vertical vortex oscillations could be significant for VMS with a large depth ratio attached to a structure with a low natural frequency. Analysis of the galloping test data indicated that VMS with large depth ratios, greater than about 0.5, and low natural frequency could also be subject to galloping instability.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.585-590
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• 2000

Problems involved in the numerical analysis on the forced oscillation of nonlinear oscillators such a microbubble oscillation under ultrasound and Duffing oscillator were discussed. One of the problems is proper choice of the time scale of the driving force. which is related to the numerical artifacts due to the mismatch between the natural frequency of an oscillator(or bubble) and the characteristic frequency of the applied force. Such problem may occur in a nonlinear oscillator whose behavior is crucially dependent on the frequency of the applied force. The artificial resonance problem during the numerical evaluation of such nonlinear systems was also discussed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 추계학술대회 논문집 전력기술부문
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• pp.167-170
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• 2002

This paper presents a mode estimation for the analysis of small signal stability in power system. The low frequency oscillation mode estimation is based on Prony method that is able to accurately compute the modal parameters (frequency and damping) of oscillation mode from time series. The time series or time domain data is obtained in TSA process. The method applied to a large scale power systems and compared on the eigenanalysis results.