• 비파괴검사학회지
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• 제21권1호
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• pp.54-61
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• 2001

웨이블릿 변환과 인공신경망을 이용하여 AE 신호를 분류하는 소프트웨어 패키지를 개발하였다. 웨이블릿 변환으로는 연속 웨이블릿 변환과 이산 웨이블릿 변환을 모두 고려하였으며, 인공신경망의 모델로는 오류 역전파 인공신경망을 사용하였다. 분류에 사용된 AE 신호는 용접부에 인공결함을 가진 시편의 3점 굽힘시험에서 발생한 신호이다. 개발된 소프트웨어 패키지를 이용하여 이 신호를 웨이블릿 변환시켜 생성된 시간-주파수 평면상에서 특징값을 추출하고 이를 인공신경망에 학습하여 인공신경망 분류기를 설계하고 검증하였다. 본 연구에서 개발된 소프트웨어 패키지를 이용한 AE 신호 분류법이 유용함을 보이고, 또한 연속 웨이블릿 변환과 이산 웨이블릿 변환에 의한 분류 결과를 비교하였다.

• 한국산학기술학회논문지
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• 제9권3호
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• pp.621-627
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• 2008

본 논문은 824-849MHz 주파수용 무선통신 단말기의 송신전력을 모니터링하는 역할을 위한 소형화된 LTCC(low temperature to-fired ceramics) 전력검출부에 대하여 기술한다. 제안된 LTCC 전력검출부는 검출기 다이오드, 정합회로를 위한 집중 소자들, 그리고 LTCC 스트립선로 방향성결합기로 구성된다. 소형화를 위하여 실제로 점유된 면적을 줄이기 위해서 다수의 벤드(bend) 소자를 지닌 스트립선로 방향성합기가 설계, 제작되며, 최소 손실과 고속 동작을 위하여 제로 바이어스 쇼트키 다이오드가 사용된다. 제작된 LTCC 전력검출부의 측정결과는 유효 RF 입력 전력영역에서 우수한 선형성을 지니며 예측 결과와 잘 일치한다.

• Steel and Composite Structures
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• 제29권4호
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• pp.527-544
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• 2018

The paper presents the study on a change in modal parameters and structural stiffness of cable-stayed Fiberline Bridge made entirely of Glass Fiber Reinforced Polymer (GFRP) composite used for 20 years in the fjord area of Kolding, Denmark. Due to this specific location the bridge structure was subjected to natural aging in harsh environmental conditions. The flexural properties of the pultruded GFRP profiles acquired from the analyzed footbridge in 1997 and 2012 were determined through three-point bending tests. It was found that the Young's modulus increased by approximately 9%. Moreover, the influence of the temperature on the storage and loss modulus of GFRP material acquired from the Fiberline Bridge was studied by the dynamic mechanical analysis. The good thermal stability in potential real temperatures was found. The natural vibration frequencies and mode shapes of the bridge for its original state were evaluated through the application of the Finite Element (FE) method. The initial FE model was created using the real geometrical and material data obtained from both the design data and flexural test results performed in 1997 for the intact composite GFRP material. Full scale experimental investigations of the free-decay response under human jumping for the experimental state were carried out applying accelerometers. Seven natural frequencies, corresponding mode shapes and damping ratios were identified. The numerical and experimental results were compared. Based on the difference in the fundamental natural frequency it was again confirmed that the structural stiffness of the bridge increased by about 9% after 20 years of service life. Data collected from this study were used to validate the assumed FE model. It can be concluded that the updated FE model accurately reproduces the dynamic behavior of the bridge and can be used as a proper baseline model for the long-term monitoring to evaluate the overall structural response under service loads. The obtained results provided a relevant data for the structural health monitoring of all-GFRP bridge.

• Coupled systems mechanics
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• 제4권4호
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• pp.279-295
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• 2015

The article presents a theoretical-experimental approach developed for modeling the coefficient of sliding friction in the dynamic system tool-workpiece in slide diamond burnishing of low-alloy unhardened steels. The experimental setup, implemented on conventional lathe, includes a specially designed device, with a straight cantilever beam as body. The beam is simultaneously loaded by bending (from transverse slide friction force) and compression (from longitudinal burnishing force), which is a reason for geometrical nonlinearity. A method, based on the idea of separation of the variables (time and metric) before establishing the differential equation of motion, has been applied for dynamic modeling of the beam elastic curve. Between the longitudinal (burnishing force) and transverse (slide friction force) forces exists a correlation defined by Coulomb's law of sliding friction. On this basis, an analytical relationship between the beam deflection and the sought friction coefficient has been obtained. In order to measure the deflection of the beam, strain gauges connected in a "full bridge" type of circuit are used. A flexible adhesive is selected, which provides an opportunity for dynamic measurements through the constructed measuring system. The signal is proportional to the beam deflection and is fed to the analog input of USB DAQ board, from where the signal enters in a purposely created virtual instrument which is developed by means of Labview. The basic characteristic of the virtual instrument is the ability to record and visualize in a real time the measured deflection. The signal sampling frequency is chosen in accordance with Nyquist-Shannon sampling theorem. In order to obtain a regression model of the friction coefficient with the participation of the diamond burnishing process parameters, an experimental design with 55 experimental points is synthesized. A regression analysis and analysis of variance have been carried out. The influence of the factors on the friction coefficient is established using sections of the hyper-surface of the friction coefficient model with the hyper-planes.

• 한국음향학회지
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• 제38권3호
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• pp.334-339
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• 2019

차량 점용접 부위에서 BSR(Buzz, Squeak, Rattle) 소음 발생 가능성을 국부 진동을 사용하여 비파괴적으로 추정하는 진동기반 계측법을 제시한다. 용접부에 부착된 구조물에 의한 점용점 부위의 국부적인 진동을 유발하고 진동전달 특성을 파악한다. 관측된 진동 특성으로부터 국부 구조의 굽힘강성값을 도출하였다. 강성값의 변화로부터 점용접의 상태 강건성을 파악하였다. 제시되는 방법의 검증을 위해 부분적으로 용접품질이 변화된 시편을 제작하였다. 제작된 시편에서 계측된 진동 특성을 분석하였다. 용접 강건성에 의해 변화하는 특정 주파수 대역을 파악하였다. 구조별, 위치별 계측을 통해 제시된 방법으로 분별이 가능한지 검증하였다. 국부 진동 평가방법은 구조물의 용접 강건성을 생산 현장에서 파악하게 하는 평가방법으로써 BSR발생 가능성을 저감하기위한 생산 품질 확보에 사용될 수 있다.

• 대한토목학회논문집
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• 제30권2A호
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• pp.149-159
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• 2010

본 연구에서는 전두께 프리캐스트 바닥판을 적용한 CFT 트러스 거더 합성형교의 구조거동을 평가하기 위한 실험적 연구를 수행하였다. 모형교량의 지간장은 20 m이고, CFT 트러스 거더의 상현재와 하현재는 콘크리트 충전강관 단면이다. CFT 트러스 거더 합성형교의 구조특성을 평가하기 위해 정적 및 동적실험을 수행하였다. 실험 및 해석에 의해 산정된 고유진동수가 잘 일치함을 확인하였고, 해석결과에서 거더간에 설치되는 브레이싱은 CFT 트러스 거더 합성형교의 고유진동수에 거의 영향을 미치지 않는 것으로 나타났다. 정적 휨 실험을 통해서 CFT 트러스 거더 합성형교의 항복강도 및 변형특성을 평가하였다. 또한, 실험결과를 통해서 프리캐스트 바닥판을 통한 등분포 전단연결재의 배치는 CFT 트러스 거더의 합성형교에 적용 가능함을 확인하였다.

• Structural Engineering and Mechanics
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• 제88권4호
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• pp.389-403
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• 2023

In order to explore the influence of tooth root cracks on the dynamic characteristics of multi-stage planetary gear transmission systems, a concentrated parameter method was used to construct a nonlinear dynamic model of the system with 30-DOF in bending and torsion, taking into account factors such as crack depth, length, angle, error, time-varying meshing stiffness (TVMS), and damping. In the model, the energy method was used to establish a TVMS model with cracks, and the influence of cracks on the TVMS of the system was studied. By using the Runge- Kutta method to calculate the differential equations of system dynamics, a series of system vibration diagrams containing cracks were obtained, and the influence of different crack parameters on the vibration of the system was analyzed. And vibration testing experiments were conducted on the system with planetary gear cracks. The results show that when the gear contains cracks, the TVMS of the system will decrease, and as the cracks intensify, the TVMS will decrease. When cracks appear on the II-stage planetary gear, the system will experience impact effects with intervals of rotation cycles of the II-stage planetary gear. There will be obvious sidebands near the meshing frequency doubling, and the vibration trajectory of the gear will also become disordered. These situations will become more and more obvious as the degree of cracks intensifies. Through experiments, the theoretical results are in good agreement with experimental results, verifying the correctness of the theoretical model. This provides a theoretical basis for fault diagnosis and reliability research of the system.

• 한국안전학회지
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• 제38권5호
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• pp.1-7
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• 2023

This study analyzes the operational characteristics of 311 aged and non-aged residual current circuit breakers (RCCBs) in low-voltage consumer contexts. It investigates the influence of external temperature and harmonics based on the rated current multiples. To simulate temperature variations, a convectional oven was used around the circuit breakers. Additionally, the generation of harmonic reference signals and data measurement for overcurrent experiments were conducted using NI SCXI, myDAQ, and LabVIEW. An observation revealed that as the ambient temperature increased, the operating time of RCCBs decreased in the time delay region. This was attributed to the faster response or bending of the bimetal, which is the tripping element. However, aged RCCBs encountered challenges with tripping outside the protective curve. The operating time of the circuit breakers exhibited an acceleration influenced by the order and content of harmonic currents, potentially leading to malfunctions. Aged RCCBs demonstrated faster operating times than their non-aged counterparts. However, the difference in operating time varied based on the manufacturer's and operating environment of the RCCBs. Frequent malfunctions of RCCBs can result in power outages. In cases where these circuit breakers fail to operate, they can lead to secondary damages, including electrical fires and shocks. Consequently, it is imperative to consider the operating environment of RCCBs and provide appropriate replacement cycles to mitigate these risks.

• Steel and Composite Structures
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• 제50권3호
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• pp.347-362
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• 2024

Controlling vibrations and noise in steel box girders is important for reducing noise pollution and avoiding discomfort to residents of dwellings along bridges. The fundamental approach to solving this problem involves first identifying the main path of transmission of the vibration energy and then cutting it off by using targeted measures. However, this requires an investigation of the characteristics of flow of vibration energy in the steel box girder, whereas most studies in the area have focused on analyzing its single-point frequency response and overall vibrations. To solve this problem, this study examines the transmission of vibrations through the segments of a steel box girder when it is subjected to harmonic loads through structural intensity analysis based on standard finite element software and a post-processing code created by the authors. We identified several frequencies that dominated the vibrations of the steel box girder as well as the factors that influenced their emergence. We also assessed the contributions of a variety of vibrational waves to power flow, and the results showed that bending waves were dominant in the top plate and in-plane waves in the vertical plate of the girder. Finally, we analyzed the effects of commonly used stiffened structures and steel-concrete composite structures on the flow of vibration energy in the girder, and verified their positive impacts on energy regionalization. In addition to providing an efficient tool for the relevant analyses, the work here informs research on optimizing steel box girders to reduce vibrations and noise in them.

• 감성과학
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• 제18권4호
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• pp.25-34
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• 2015

본 연구에서는 전도성 직물을 기반으로 동작 센서로 구현하여 팔의 굽힘, 폄 동작에 따른 센서의 전기저항의 변화를 측정, 분석함으로써 관절 동작을 효과적으로 측정 할 수 있는 직물 센서의 요건을 탐색하였다. 이를 위해 두 가지 편직물인 'L'직물과 'W'직물 양면에 Single Wall Carbon Nano-Tube(SWCNT) 코팅을 한 후 이를 다양한 형태로 후가공하여 직물 센서를 개발하고 암 밴드에 부착하였다. 직물 센서는 코팅용 바탕 직물의 종류(2가지), 센서의 부착 방법(2가지), 센서의 layer 수(2가지), 센서의 길이(3가지), 센서의 너비(2가지)의 총 48개로 구성되었다. Con-Trex MJ에 48개의 암 밴드를 입힌 인체 모형 팔을 대상으로 직물 동작 센서의 성능을 평가하였다. 인체 모형 팔에 입혀진 총 48개의 암 밴드 각각에 대해서 frequency: 0.5Hz, ROM: $20^{\circ}{\sim}120^{\circ}$ 에서 굽힘과 폄 동작을 반복하도록 조정하였고, 48개 각 사례 당 세 세트(set)씩 반복 측정한 전압값을 기록하였다. 전압값을 peak-to-peak voltage(Vp-p)의 base line의 균일성, 동일 세트 내 Vp-p의 균일성, 세 세트 간의 Vp-p의 균일성을 기준으로 평가하고 분석한 결과, SWCNT 코팅된 'L' 직물을 두 겹으로 구성하여 열고정 방식으로 부착한 $50{\times}5mm$, $50{\times}10mm$, $100{\times}10mm$ 크기의 직물 센서와, SWCNT 코팅된 'W' 직물을 두 겹으로 구성하고 열고정 방식으로 부착한 $50{\times}10mm$ 크기의 직물 센서가 전체 변화율 5%이내의 가장 균일하고 안정적인 신호값을 나타내었다. 이상의 연구 결과를 통해 SWCNT 코팅 소재를 다양한 형태로 가공해 직물 센서로 구현했을 때 인체의 사지 동작을 측정할 수 있는 센서로서 적합함을 확인하였고, 최적의 센서 형태를 규명하였다.