• International Journal of Aeronautical and Space Sciences
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• 제17권1호
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• pp.37-44
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• 2016

Optical fiber temperature sensing systems have incomparable advantages over traditional electrical-cable-based monitoring systems. However, the fiber optic interrogators and sensors have often been rejected as a temperature monitoring technology in real-world industrial applications because of high cost and over-specification. This study proposes a multiplexed fiber optic temperature monitoring sensor system using an economical Optical Time-Domain Reflectometer (OTDR) and Hard-Polymer-Clad Fiber (HPCF). HPCF is a special optical fiber in which a hard polymer cladding made of fluoroacrylate acts as a protective coating for an inner silica core. An OTDR is an optical loss measurement system that provides optical loss and event distance measurement in real time. A temperature sensor array with the five sensor nodes at 10-m interval was economically and quickly made by locally stripping HPCF clad through photo-thermal and photo-chemical processes using a continuous/pulse hybrid-mode laser. The exposed cores created backscattering signals in the OTDR attenuation trace. It was demonstrated that the backscattering peaks were independently sensitive to temperature variation. Since the 1.5-mm-long exposed core showed a 5-m-wide backscattering peak, the OTDR with a spatial resolution of 40 mm allows for making a sensor node at every 5 m for independent multiplexing. The performance of the sensor node included an operating range of up to $120^{\circ}C$, a resolution of $0.59^{\circ}C$, and a temperature sensitivity of $-0.00967dB/^{\circ}C$. Temperature monitoring errors in the environment tests stood at $0.76^{\circ}C$ and $0.36^{\circ}C$ under the temperature variation of the unstrapped fiber region and the vibration of the sensor node. The small sensitivities to the environment and the economic feasibility of the highly multiplexed HPCF temperature monitoring sensor system will be important advantages for use as system-integrated temperature sensors.

• 한국산학기술학회논문지
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• 제6권6호
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• pp.560-565
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• 2005

본 논문은 8각 아웃렛 박스 제조용 수동 금형을 2벌의 금형으로 자동화한 것에 관한 연구이다. 8각 아웃렛 박스는 건축물의 전선관용 스위치 박스 또는 배선 연결용 박스이다. 이 박스를 제조 할 때는 제 1차 프레스에서 성형하고 제 2-6차 프레스로 8각 아웃렛 박스의 4측면 가공과 벤딩을 하게 되므로 프레스 6대, 금형 6벌, 작업자 7명을 필요로 한다. 이 때문에 인건비 과다발생, 생산속도 저조, 불량률 $10\%$ 이상 발생, 제조원가 상승의 요인이 되고 있으며, 프레스의 굉음과 진동 및 안전사고의 위험 등으로 작업자들이 직무를 기피하고 있다. 이러한 현상을 없애기 위해 금형 5벌을 1벌의 금형에 통합시킨 캠금형 개발과 자동이송장치를 개발하였다. 그 결과 프레스 2대와 금형 2벌로 무인화 작업을 할 수 있게 되어 직무기피요인을 해소하게 되고 제조원가 절감효과를 얻게 되었다.

• 한국터널지하공간학회 논문집
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• 제6권4호
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• pp.345-356
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• 2004

지하구조물을 축조하는 공법으로 기존에 가장 많이 사용해 온 것이 개착식 공법이나, 지상교통 흐름을 방해하고 공사소음 및 주변 지반의 침하로 인한 민원 발생 등 많은 문제점을 야기해 왔다. 많은 경우에 있어 지중에 매설된 상수도관 하수도관 도시가스관 고압 전력구 통신 케이블 등 지중 매설물의 위치가 정확하게 파악되지 않아서 안전한 시공에 어려움이 크고, 개착공사 시 지하지장물의 이설로 인한 공지지연 및 추가공사비가 소요될 것으로 판단되다. 따라서 본 논문에서는 기존 지하구조물 축조공법을 개선하여 슬래브강관과 PC벽체 트렌치를 이용한 터널축조공법 (T.R.c.M.)을 서울지하철 현장에 적용한 시공사례를 소개하고자 한다. 연구결과, T.R.c.M.공법은 진동과 소음을 최소화하여 주변환경과 교통의 흐름에 전혀 지장을 주지 않고 안정적으로 터널을 축조할 수 있는 공법임을 알 수 있었다.

• Wind and Structures
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• 제29권6호
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• pp.417-430
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• 2019

To study the wake influence of an upstream bridge on the wind-resistance performance of a downstream bridge, two adjacent long-span cable-stayed bridges are taken as examples. Based on wind tunnel tests, the static aerodynamic coefficients and the dynamic response of the downstream bridge are measured in the wake of the upstream one. Considering different horizontal and vertical distances, the flutter derivatives of the downstream bridge at different angles of attack are extracted by Computational Fluid Dynamics (CFD) simulations and discussed, and the change in critical flutter state is further studied. The results show that a train passing through the downstream bridge could significantly increase the lift coefficient of the bridge which has the same direction with the gravity of the train, leading to possible vertical deformation and vibration. In the wake of the upstream bridge, the change in lift coefficient of the downstream bridge is reduced, but the dynamic response seems to be strong. The effect of aerodynamic interference on flutter stability is related to the horizontal and vertical distances between the two adjacent bridges as well as the attack angle of incoming flow. At large angles of attack, the aerodynamic condition around the downstream girder which may drive the bridge to torsional flutter instability is weakened by the wake of the upstream bridge, and the critical flutter wind speed increases at this situation.

• Smart Structures and Systems
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• 제15권3호
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• pp.665-682
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• 2015

Structural identification or St-Id is 'the parametric correlation of structural response characteristics predicted by a mathematical model with analogous characteristics derived from experimental measurements'. This paper describes a St-Id exercise on Humber Bridge that adopted a novel two-stage approach to first calibrate and then validate a mathematical model. This model was then used to predict effects of wind and temperature loads on global static deformation that would be practically impossible to observe. The first stage of the process was an ambient vibration survey in 2008 that used operational modal analysis to estimate a set of modes classified as vertical, torsional or lateral. In the more recent second stage a finite element model (FEM) was developed with an appropriate level of refinement to provide a corresponding set of modal properties. A series of manual adjustments to modal parameters such as cable tension and bearing stiffness resulted in a FEM that produced excellent correspondence for vertical and torsional modes, along with correspondence for the lower frequency lateral modes. In the third stage traffic, wind and temperature data along with deformation measurements from a sparse structural health monitoring system installed in 2011 were compared with equivalent predictions from the partially validated FEM. The match of static response between FEM and SHM data proved good enough for the FEM to be used to predict the un-measurable global deformed shape of the bridge due to vehicle and temperature effects but the FEM had limited capability to reproduce static effects of wind. In addition the FEM was used to show internal forces due to a heavy vehicle to to estimate the worst-case bearing movements under extreme combinations of wind, traffic and temperature loads. The paper shows that in this case, but with limitations, such a two-stage FEM calibration/validation process can be an effective tool for performance prognosis.

• Wind and Structures
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• 제27권6호
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• pp.399-416
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• 2018

In order to reveal the independent relationship between track irregularity and wind loads, the stochastic characteristics of train-bridge coupling systems subjected to wind loads were investigated by the multi-sample calculation. The vehicle was selected as 23 degrees of freedom dynamical model, and the bridge was described by three-dimensional finite element model. It was assumed that the wind loads were random processes with strong spatial correlation, while the track irregularities were stationary random ones. As a case study, a high-speed train running on a cable-stayed bridge subjected to wind loads was studied. The effect of rail irregularities was deemed to be independent of the effect of wind excitations on the coupling system in the same wind circumstance for the same project, leading to the conclusion that the effect of wind loads and moving vehicle could be calculated separately. The variance results of the stochastic responses of vehicle-bridge coupling system under the action of wind loads and rail irregularities together were equivalent to the sum of the variance of the responses induced by each excitation. Therefore, when one of the input excitations is different, only the effect of changed loads needs to be assessed. Moreover, the new calculated results were combined with the effect of unchanged loads to present the stochastic response of coupling system subjected to the different excitations, reducing the cost of computations. The stochastic characteristics, the CFD (cumulative distribution function) of the coupling system with different wind velocities, vehicle speed, and vehicle marshalling were studied likewise.

• Smart Structures and Systems
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• 제30권1호
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• pp.75-88
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• 2022

Engineering structures in operation essentially belong to time-varying or nonlinear structures and the resultant response signals are usually non-stationary. For such time-varying structures, it is of great importance to extract time-dependent dynamic parameters from non-stationary response signals, which benefits structural health monitoring, safety assessment and vibration control. However, various traditional signal processing methods are unable to extract the embedded meaningful information. As a newly developed technique, variational mode decomposition (VMD) shows its superiority on signal decomposition, however, it still suffers two main problems. The foremost problem is that the number of modal components is required to be defined in advance. Another problem needs to be addressed is that VMD cannot effectively separate non-stationary signals composed of closely spaced or overlapped modes. As such, a new method named generalized adaptive variational modal decomposition (GAVMD) is proposed. In this new method, the number of component signals is adaptively estimated by an index of mean frequency, while the generalized demodulation algorithm is introduced to yield a generalized VMD that can decompose mode overlapped signals successfully. After that, synchrosqueezing wavelet transform (SWT) is applied to extract instantaneous frequencies (IFs) of the decomposed mono-component signals. To verify the validity and accuracy of the proposed method, three numerical examples and a steel cable with time-varying tension force are investigated. The results demonstrate that the proposed GAVMD method can decompose the multi-component signal with overlapped modes well and its combination with SWT enables a successful IF extraction of each individual component.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1998년도 Proceedings ICPE 98 1998 International Conference on Power Electronics
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• pp.961-965
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• 1998

The rapid development of small-scale (1-10 MJ) Superconducting Magnetic Energy Storage Systems (SMES) can be explained by real perspective of practical implementation of these devices in electro power nets. However the serious problem of all high mechanically stressed superconducting coils-problem of training and degradation (decreasing) of operating current still exists. Moreover for SMES systems this problems is more dangerous because of pulsed origin of mechanical stresses-one of the major sources of local heat disturbances in superconducting coils. We investigated acoustic emission (AE) phenomenon on model and 0.5 MJ SMES coils taking into account close correlation of AE and local heat disturbances. Two-coils 0.5 MJ SMES system was developed, manufactured and tested at Russian Research Center in the frames of cooperation with Korean Electrical Engineering Company (KEPCO) [1]. The two-coil SMES operates with the stored energy transmitted between coils in the course of a single cycle with 2 seconds energy transfer time. Maximum operating current 1.55 kA corresponds to 0.5 MF in each coil. The Nb-Ti-based conductor was designed and used for SMES manufacturing. It represents transposed cable made of Nb-Ti strands in copper matrix, several cooper strands and several stainless steel strands. The coils are wound onto fiberglass cylindrical bobbins. To make AE event information more useful a real time instrumentation system was used. Two main measured and computer processed AE parameters were considered: the energy of AE events (E) and the accumulated energy of AE events (E ). Influence of current value in 0.5 MJ coils on E and E was studied. The sensors were installed onto the bobbin and the external surface of magnets. Three levels of initial current were examined: 600A, 1000A, 2450 A. An extraordinary strong dependence of the current level on E and E was observed. The specific features of AE from model coils, operated in sinusoidal vibration current changing mode were investigated. Three current frequency modes were examined: 0.012 Hz, 0.03 Hz and 0.12 Hz. In all modes maximum amplitude 1200 A was realized.

• 대한토목학회논문집
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• 제30권3A호
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• pp.297-307
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• 2010

최근 토목, 건축 구조물의 유지관리 기술에 대한 관심이 커지고 있으며 구조물의 성능저하 및 노후화 등으로 구조적 안전성의 검토가 요구되는 구조물의 수가 급증하고 있는 실정이다. 그리고 구조물의 노후화 및 부재의 균열 등으로 인하여 강성이 저하되면 구조물의 동특성에 변화가 나타나게 되며 구조물의 실제 거동상태에서 동특성을 분석하여 손상부위와 손상정도를 정확히 판단하는 것은 중요한 문제이다. 구조물 모니터링에 사용되는 대표적 계측장비가 동적계측기이다. 기존의 동적계측기는 측정 센서와 장비를 연결하는 케이블 길이가 길어질 경우 신뢰할 수 있는 데이터를 얻기 힘들고 각 센서와 계측기를 1:1로 연결하는 방식을 취하고 있어 비경제적이다. 따라서 센서를 부착하지 않고 원거리에서 진동을 측정하는 방법이 필요하다. 구조물의 진동을 계측하기 위하여 적용 가능한 비접촉식 방법으로는 레이저의 도플러효과, GPS를 이용하는 방법 및 영상처리기법 등이 대표적이다. 레이저의 도플러효과를 이용하는 방법은 정확도가 상대적으로 높지만 비경제적이며, GPS를 이용하는 방법은 장비가 고가이고 신호 자체의 오차와 데이터 취득속도의 제약이 있는 단점이 있다. 그러나 영상신호를 이용하는 방법은 간편하고 경제적이며 접근이 어려운 구조물의 진동 및 동특성 추출에 적합하다. 기존에도 센서를 대신하여 카메라의 영상신호를 이용하는 연구가 수행되기도 하였으나, 기존의 방법은 구조물에 부착된 표적의 한 지점을 기록한 후 영상처리기법을 이용하여 진동을 측정하는 방법으로서 측정 대상이 비교적 국한적일 수 있다. 그러므로 본 연구에서는 영상처리기법을 이용하여 구조물의 다중 변위응답을 측정할 수 있는 방법의 타당성을 검증하기 위하여 진동대 실험 및 현장재하실험을 수행하였다.

• 한국강구조학회 논문집
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• 제16권2호통권69호
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• pp.285-293
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• 2004

사회 기반 특수 시설로서 케이블을 이용한 현수교는 완공 후에 일반적인 교량 보다 더 신중한 안전점검 및 유지관리가 필요하다. 그러나, 교량의 설계 및 유지관리를 위한 구조해석은 구조체의 단순화된 기하학적 형상만을 고려하고 있다. 특히 강상판을 포함한 교량 구조물의 해석 모델링은 쉽지 않다. 본 논문에서는 완성계 현수교에 대한 행거 부재의 고유진동수와 전산해석을 통해 구조적 거동과 성능을 평가하였다. 전산해석의 정확도를 높이기 위해 해석 모델에 뼈대 구조물과 강상판을 고려하였다. 또한, 측정된 행거 장력과 상시 진동시에 측정된 구조물의 고유진동수 및 차량 재하시험 결과를 해석에 적용하였다. 결과로서, 제안된 알고리즘에 의한 예상 구조거동은 실제 구조물에서 측정된 자료와 매우 유사한 결과를 보였다. 또한, 내륙에 상륙한 태풍 매미에 의해 측정된 자료를 적용한 결과, 해석모델이 구조물의 예비설계 및 유지관리에 효과적으로 적용될 수 있음을 확인하였다.