• Structural Engineering and Mechanics
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• 제54권1호
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• pp.105-119
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• 2015

Structural damage detection using modal strain energy (MSE) is one of the most efficient and reliable structural health monitoring techniques. However, some of the existing MSE methods have been validated for special types of structures such as beams or steel truss bridges which demands improving the available methods. The purpose of this study is to improve an efficient modal strain energy method to detect and quantify the damage in complex structures at early stage of formation. In this paper, a modal strain energy method was mathematically developed and then numerically applied to a fixed-end beam and a three-story frame including single and multiple damage scenarios in absence and presence of up to five per cent noise. For each damage scenario, all mode shapes and natural frequencies of intact structures and the first five mode shapes of assumed damaged structures were obtained using STRAND7. The derived mode shapes of each intact and damaged structure at any damage scenario were then separately used in the improved formulation using MATLAB to detect the location and quantify the severity of damage as compared to those obtained from previous method. It was found that the improved method is more accurate, efficient and convergent than its predecessors. The outcomes of this study can be safely and inexpensively used for structural health monitoring to minimize the loss of lives and property by identifying the unforeseen structural damages.

• Smart Structures and Systems
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• 제4권3호
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• pp.343-365
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• 2008

In this study, the frequency domain method which utilizes the evaluation of changes in the structural mode shape is adopted to identify regions which contain localized damages. Frequency response function (FRF) values corresponding to the modal frequency, analogous to the mode shape coefficients, are used since change in natural frequency of the system is usually insignificant for localized damage. This method requires only few sensors to obtain the dynamic response of the structure at specific locations to determine the FRF via fast-Fourier transform (FFT). Numerical examples of an aluminum plate, which includes damages of varying severity, locations and combinations of multiple locations, are presented to demonstrate the feasibility of the method. An experimental verification of the method is also done using an aluminum plate with two different degrees of damage, namely a half-through notch and a through notch. The inconsistency in attaining the FRF values for practical applications due to varying impact load may be overcome via statistical averaging, although large variations in the loading in terms of the contact duration should still be avoided. Nonetheless, this method needs special attention when the damages induce notable changes in the modal frequency, such as when the damages are of high severity or cover more extensive area or near the boundary where the support condition is modified. This is largely due to the significant decrease in the frequency term compared to the increase in the vibration amplitude. For practical reasons such as the use of limited number of sensors and to facilitate automation, extending the resolution of this method of identification may not be efficient. Hence, methods based on wave propagation can be employed as a complement on the isolated region to provide an accurate localization as well as to trace the geometry of the damage.

• Structural Engineering and Mechanics
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• 제74권6호
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• pp.789-807
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• 2020

Multiple earthquakes that occur during short seismic intervals affect the inelastic behavior of the structures. Sequential ground motions against the single earthquake event cause the building structure to face loss in stiffness and its strength. Although, numerous research studies had been conducted in this research area but still significant limitations exist such as: 1) use of traditional design procedure which usually considers single seismic excitation; 2) selecting a seismic excitation data based on earthquake events occurred at another place and time. Therefore, it is important to study the effects of successive ground motions on the framed structures. The objective of this study is to overcome the aforementioned limitations through testing a two storey RC building structural model scaled down to 1/10 ratio through a similitude relation. The scaled model is examined using a shaking table. Thereafter, the experimental model results are validated with simulated results using ETABS software. The test framed specimen is subjected to sequential five artificial and four real-time earthquake motions. Dynamic response history analysis has been conducted to investigate the i) observed response and crack pattern; ii) maximum displacement; iii) residual displacement; iv) Interstorey drift ratio and damage limitation. The results of the study conclude that the low-rise building model has ability to resist successive artificial ground motion from its strength. Sequential artificial ground motions cause the framed structure to displace each storey twice in correlation with vary first artificial seismic vibration. The displacement parameters showed that real-time successive ground motions have a limited impact on the low-rise reinforced concrete model. The finding shows that traditional seismic design EC8 requires to reconsider the traditional design procedure.

• 한국항공우주학회지
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• 제38권1호
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• pp.80-86
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• 2010

본 논문은 현재 KAIST 인공위성연구센터(SaTReC)에서 개발하고 있는 과학기술위성3호 (STSAT-3) 위성본체의 S대역 통신채널 중 송신기 개발에 관하여 서술하고 있다. STSAT-3의 통신시스템은 위성제어 및 상태정보 전송을 위하여 S대역을 사용하며 임무수행용 통신채널로는 X대역을 사용하고 있다. S대역 송신기(S band Transmitter, STX)는 변조기, 주파수 합성기, 파워 앰프, 전력공급기 로 구성되어 있다. 변조 방법으로는 주파수 천이방식(Frequency Shift Keying, FSK)을 사용 하며 위성체와는 RS-422통신 방식을 이용한다. STSAT-3의 STX는 모듈화에 근거하여 설계 및 제작 되었으며 1.5W(31.7dBm) 송신 출력에 1E-5 비트오율(BER) 성능을 만족한다. 현재 성능시험, 환경시험(진동시험, 열진공시험)을 성공적으로 마쳤다.

• 한국생활과학회지
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• 제21권5호
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• pp.989-1004
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• 2012

The purpose of this study was to investigate the characteristics of the pigment and the dyeability of juniperus chinensis needles, berry, bark and heartwood extracts using distilled water, methanol, normal butanol and ethyl acetate as a solvent. Ultraviolet-visible absorption spectrum bands of the extracts were measured at around 280nm to 320nm in all the solvent extracts. The maximum absorption wavelength was able to determine tannin. All the solvent extracts except for distilled water extracts were able to confirm the presence of chlorophyll. Infrared absorption spectra (FT-IR) of all parts of the extracts showed broad absorption bands of OH due to phenolic-OH, benzene CH peak of phenol chemical structure, ether-based stretching vibration peak and the peak of flavonoid compounds that appeared in all the solvent extracts. The yield of juniper needles and heartwood in distilled water and methanol extraction were effective. Extraction of berry yields in distilled water was also effective. The yield of ethanol extraction from the bark showed better efficiency. As a result of using distilled water for the dye solution, the color of the fabrics dyed with all extracts of the needles and Y series berries generally showed light Y progression with a strong red tinge. By using a mixture of 20% ethanol and 80% distilled water for the dye solution, the color of the fabrics dyed with needles and berry extracts showed Y series dominantly. The color of the fabrics dyed with Bark and heartwood extracts were dominantly R series.

• 한국멀티미디어학회논문지
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• 제16권6호
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• pp.689-699
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• 2013

로봇 원격조종 방법은 1:1, 1:N, N:1, 그리고 N:N의 다양한 방법이 있다. 오퍼레이터가 원격지 로봇을 제어하기 위해서는 로봇의 주변 상황, 모바일 장치의 충돌 가능성, 그리고 매니퓰레이터의 힘을 인지할 수 있어야 한다. 원격조종에서는 데이터 통신과 처리에 소요되는 시간에 따른 지연이 발생하는데, 이 시간 지연은 로봇의 충돌과 햅틱 기반 제어에 있어 양방향 힘 반영에 따른 매니퓰레이터의 바이브레이션과 과도한 힘 반영을 초래할 수 있다. N:N 제어 방식은 근래 개발 중인 조종 기술로 멀티 오퍼레이터가 멀티 로봇을 스위칭하면서 제어하는 구조를 가진다. 이 구조를 구현하기 위해서는 오퍼레이터가 어떤 로봇을 제어할 것인지, 또는 그 로봇의 어떤 장치를 제어할 것인지에 대한 스위칭 기능이 필요하며, 다수의 오퍼레이터가 함께 원격조종을 수행할 때에는 이 스위칭 알고리즘이 반드시 필요하다. 또한 오퍼레이터의 성향에 따라 조종 성향이 달라지므로 이를 일반화하기위한 방안도 요구된다. 본 논문에서는 다수의 로봇과 다수의 오퍼레이터가 원격으로 로봇들을 제어하여 작업을 수행할 수 있는 햅틱 기반 제어 환경을 구축하는 방안과 구현에 대하여 기술한다.

• Wind and Structures
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• 제17권2호
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• pp.163-184
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• 2013

An accurate identification of the aerodynamic characteristics of vehicles and the bridge is the premise for the coupled vibration analysis of a wind-vehicle-bridge system. At present, the interaction of aerodynamic forces between the road vehicles and bridge is ignored in most previous studies. In the present study, an experimental setup was developed to measure the aerodynamic characteristics of vehicles and the bridge for different cases in a wind tunnel considering the aerodynamic interference. The influence of the wind turbulence, the wind speed, the vehicle interference, and the vehicle position on the aerodynamic coefficients of vehicles, and the influence of vehicles on the static coefficients of the bridge were investigated, based on the experimental results. The variations in the aerodynamic characteristics of vehicles and the bridge were studied and the measured results were validated according to the results of surface pressure measurements on the vehicle and the bridge. The measured results were further validated by comparing the measured results with values derived numerically. The measured results showed that the wind turbulence, the vehicle interference, and the vehicle position significantly affected the aerodynamic coefficients of vehicles. However, the influence of the wind speed on the aerodynamic coefficients of the studied vehicle is small. The static coefficients of the bridge were also significantly influenced by the presence of vehicles.

• Smart Structures and Systems
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• 제3권3호
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• pp.341-356
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• 2007

A good understanding of normal modal variability of civil structures due to varying environmental conditions such as temperature and wind is important for reliable performance of vibration-based damage detection methods. This paper addresses the quantification of wind-induced modal variability of a cable-stayed bridge making use of one-year monitoring data. In order to discriminate the wind-induced modal variability from the temperature-induced modal variability, the one-year monitoring data are divided into two sets: the first set includes the data obtained under weak wind conditions (hourly-average wind speed less than 2 m/s) during all four seasons, and the second set includes the data obtained under both weak and strong (typhoon) wind conditions during the summer only. The measured modal frequencies and temperatures of the bridge obtained from the first set of data are used to formulate temperature-frequency correlation models by means of artificial neural network technique. Before the second set of data is utilized to quantify the wind-induced modal variability, the effect of temperature on the measured modal frequencies is first eliminated by normalizing these modal frequencies to a reference temperature with the use of the temperature-frequency correlation models. Then the wind-induced modal variability is quantitatively evaluated by correlating the normalized modal frequencies for each mode with the wind speed measurement data. It is revealed that in contrast to the dependence of modal frequencies on temperature, there is no explicit correlation between the modal frequencies and wind intensity. For most of the measured modes, the modal frequencies exhibit a slightly increasing trend with the increase of wind speed in statistical sense. The relative variation of the modal frequencies arising from wind effect (with the maximum hourly-average wind speed up to 17.6 m/s) is estimated to range from 1.61% to 7.87% for the measured 8 modes of the bridge, being notably less than the modal variability caused by temperature effect.

• Structural Engineering and Mechanics
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• 제67권6호
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• pp.643-658
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• 2018

In this paper, we introduce a new framework for running the finite element (FE) packages inside an online Loop together with MATLAB. Contrary to the Hardware-in-the-Loop techniques (HiL), in the proposed Software-in-the-Loop framework (SiL), the FE package represents a simulation platform replicating the real system which can be out of access due to several strategic reasons, e.g., costs and accessibility. Practically, SiL for sophisticated structural design and multi-physical simulations provides a platform for preliminary tests before prototyping and mass production. This feature may reduce the new product's costs significantly and may add several flexibilities in implementing different instruments with the goal of shortlisting the most cost-effective ones before moving to real-time experiments for the civil and mechanical systems. The proposed SiL interconnection is not limited to ABAQUS as long as the host FE package is capable of executing user-defined commands in FORTRAN language. The focal point of this research is on using the compiled FORTRAN subroutine as a messenger between ABAQUS/CAE kernel and MATLAB Engine. In order to show the generality of the proposed scheme, the limitations of the available SiL schemes in the literature are addressed in this paper. Additionally, all technical details for establishing the connection between FEM and MATLAB are provided for the interested reader. Finally, two numerical sub-problems are defined for offline and online post-processing, i.e., offline optimization and closed-loop system performance analysis in control theory.

• 한국음향학회지
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• 제31권8호
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• pp.561-568
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• 2012

본 연구는 등가 종 모델을 이용하여 한국종의 맥놀이 주기를 조절하는 방법을 제시한다. 한국종이 갖고 있는 미세한 비대칭성은 하나의 원주 모드를 미세한 주파수의 차이를 갖는 모드 쌍으로 분리시키는데, 이 모드 쌍의 상호간섭에 의해서 진동과 음향의 맥놀이가 발생한다. 등가 종은 축대칭 종에 등가 집중질량을 부착시킨 미소 비대칭 구조물로, 실제 종의 모드 쌍과 동일한 모드 특성을 갖는다. 등가 종 모델은 회전 쉘 이론을 근거로, 유한요소해석을 통해서 구성된다. 맥놀이 특성을 변화시키기 위하여 국부적으로 요소 두께를 감소시킬 때, 등가 종을 이용하여 맥놀이 주기를 예측한다. 예측 결과는 시험 종에 대한 실험을 통해 그 타당성을 확인한다. 본 방법은 대형 종의 맥놀이 주기 조절에 소요되는 시간을 크게 줄일 수 있을 것이다.