• Earthquakes and Structures
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• 제22권2호
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• pp.185-201
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• 2022

Structural Health Monitoring (SHM) is used to provide reliable information about the structure's integrity in near realtime following extreme incidents such as earthquakes, considering the inevitable aging and degradation that occurs in operating environments. This paper experimentally investigates an integrated wireless sensor network (Wi-SN) based monitoring technique for damage detection in concrete structures. An effective SHM technique can be used to detect potential structural damage based on post-earthquake data. Two novel methods are proposed for damage detection in reinforced concrete (RC) building structures including: (i) Jerk Energy Method (JEM), which is based on time-domain analysis, and (ii) Modal Contributing Parameter (MCP), which is based on frequency-domain analysis. Wireless accelerometer sensors are installed at each story level to monitor the dynamic responses from the building structure. Prior knowledge of the initial state (immediately after construction) of the structure is not required in these methods. Proposed methods only use responses recorded during ambient vibration state (i.e., operational state) to estimate the damage index. Herein, the experimental studies serve as an illustration of the procedures. In particular, (i) a 3-story shear-type steel frame model is analyzed for several damage scenarios and (ii) 2-story RC scaled down (at 1/6th) building models, simulated and verified under experimental tests on a shaking table. As a result, in addition to the usual benefits like system adaptability, and cost-effectiveness, the proposed sensing system does not require a cluster of sensors. The spatial information in the real-time recorded data is used in global damage identification stage of SHM. Whereas in next stage of SHM, the damage is detected at the story level. Experimental results also show the efficiency and superior performance of the proposed measuring techniques.

• 한국해양공학회지
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• 제13권3호통권33호
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• pp.36-48
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• 1999

Fatigue life and crack retardation behavior after penetration were experimentally examined using surface pre-cracked specimens of aluminium alloy 5083. The Wheeler model retardation parameter was used successfully to predict crack growth behavior after penetration. By using a crack propagation rule, the change in crack shape after penetration can be evaluated quantitatively. Advanced, waveform-based acoustic emission (AE) techniques have been successfully used to evaluate signal characteristics obtained form fatigue crack propagation and penetratin behavior in 6061 aluminum plate with surface crack under fatigue stress. Surface defects in the structural members are apt to be origins of fatigue crack growth, which may cause serious failure of the whole structure. The nondestructive analysis on the crack growth and penetration from these defects may, therefore, be one of the most important subjects on the reliability of the leak before break (LBB) design. The goal of the present study is to determine if different sources of the AE could be identified by characteristics of the waveforms produced from the crack growth and penetration. AE signals detected in four stages were found to have different signal per stage. With analysis of waveform and power spectrum in 6061 aluminum alloys with a surface crack, it is found to be capabilities on real-time monitoring for the crack propagation and penetration behavior of various damages and defects in structural members.

• 한국생산제조학회지
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• 제22권4호
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• pp.658-664
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• 2013

In this paper, we present a case study of vibration suppression based on the application of active damping to the small boring process of a boring bar with diameter below ${\Phi}12$. The proposed active damping system consists of an acceleration sensor for real-time monitoring of the vibration signal, a driver for phase control in a computer program, and piezoelectric actuators for damping. In this system, the vibration signals are detected by the acceleration sensor and sent to the computer as an input. The phase shift parameter of the natural frequency of the input signal is sent to the data acquisition board in the computer and calculated by the phase control program. This study confirmed the effectiveness of this damping system, and it opens up the possibility of the development of active damping systems for small boring processes.

• 한국근적외분광분석학회:학술대회논문집
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• 한국근적외분광분석학회 2001년도 NIR-2001
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• pp.1284-1284
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• 2001

The transesterification of molten ethylene/vinylacetate (EVA) copolymers by octanol as a reagent and sodium methoxide as a catalyst in an extruder has been monitored by on-line near infrared (NIR) spectroscopy. A total of 60 NIR spectra were acquired for 37 minutes with the last spectrum recorded 31 minutes after the addition of octanol and catalyst was stopped. The experimental spectra show strong baseline fluctuations which are corrected for by multiplicative scatter correction (MSC). The chemometric methods of orthogonal projection approach (OPA) and multivariate curve resolution (MCR) were used to resolve the spectra and to derive concentration profiles of the species. The detailed analysis reveals the absence of completely pure variables that leads to small errors in the calculation of pure spectra. The initial estimation of a concentration that is necessary as an input parameter for MCR also presents a non-trivial task. We obtained results that were not ideal but applicable for practical concentration control. They enable a fast monitoring of the process in real-time and resolve the spectra of the EVA copolymer and the ethylene/vinyl alcohol (EVAL) copolymer to be very close to the reference spectra. The chemometric methods used and the decomposed spectra are discussed in detail.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2013년도 전력전자학술대회 논문집
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• pp.126-127
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• 2013

In industry, Supervisory Control and Data Acquisition (SCADA) system plays critical role to ensure production is monitored and controlled rigorously and in timely manner. Having a cost saving yet still effective SCADA system would be much desired by Industry. SCADA itself is a field with constant development and research like how this paper investigates on creating an extremely low cost device, which can be adapted to many different SCADA applications through some very basic programming when combined with relevant peripherals. Much of the process in some expensive SCADA application based on smartphone application is due to specialized communication infrastructure. This paper addresses the needs by developing low cost and integrated wireless SCADA system. The system features capability on accessing the performance of remotely situated device parameter, such as temperature, control analog or digital input output on real time basis. We use existing mobile network capability through Bluetooth communication channel.

• 한국전자통신학회논문지
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• 제5권4호
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• pp.379-384
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• 2010

최근 이슈가 되고 있는 IPTV 서비스의 성공적인 정착과 관련된 중요한 이슈로 서비스 품질을 들 수 있다. 현재 IPTV 서비스의 품질에 영향을 미치는 상당히 많은 파라미터들이 알려져 있다. 그럼에도 불구하고 실시간으로 모든 파라미터를 전부 감시하고 관리한다는 것은 현실적으로 거의 불가능한 일이다. 따라서 IPTV 서비스에 미치는 영향의 정도가 큰 몇몇 핵심 파라미터를 선정하는 것이 필요하게 되었다. 이러한 목적을 위하여 본 논문에서는 IPTV 서비스의 품질을 감시하고 측정하는 실제 환경을 구성하고 각 파라미터가 이에 미치는 영향을 분석하고자 한다. 특히 MPEG-2 전송 스트림 계층에서 측정되는 Continuous Count Error(CCE)에 주목하여 이의 영향이 다른 파라미터에 비해 매우 큼을 보인다.

• 응용통계연구
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• 제34권5호
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• pp.735-744
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• 2021

제품의 수명을 유지시키는 것은 품질관리의 주요 목표 중 하나이다. 실제 공정에서는 시간 및 비용의 문제로 인해 모든 표본의 수명을 측정할 수 없는 경우가 많이 발생하기 때문에, 대부분 중도절단된 자료를 포함시켜 표본을 구성한다. 이 논문에서는 제1형의 우측중도절단된 수명 자료가 로그정규분포를 따르는 경우, 제품 수명의 평균을 모니터링하는 두 가지 누적합 관리도 절차를 제안한다. 하나는 우도비에 기초한 누적합 관리도이고, 다른 하나는 이항분포에 기초한 누적합 관리도 절차이다. 모의실험을 통해 평균런길이를 비교하는 방법으로 제안된 두 관리도 절차의 성능을 비교하였다. 모의실험 결과, 중도절단율이 낮은 경우, 형상모수값이 작은 경우, 평균의 감소 변화량이 큰 경우에는 우도비 누적합 관리도가 더 효율적이며, 반대로 중도절단율이 높은 경우, 형상모수값이 큰 경우, 평균의 감소 변화량이 적은 경우에는 이항 누적합 관리도가 더 효율적인 것으로 나타났다.

• 터널과지하공간
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• 제18권6호
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• pp.480-490
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• 2008

천공탐사는 암반 굴착시 점보드릴의 유압착암기로부터 계측되는 기계량들인 천공데이터를 분석하여 암반의 특성을 평가하는 기법이다. 천공탐사는 발파공 또는 록볼트공 천공시 실시간으로 계측할 수 있기 때문에 암반을 신속하고 정량적으로 예측 및 평가할 수 있는 장점이 있다. 현재까지도 천공데이터에 관한 다양한 연구가 수행되어져오고 있지만, 암반 특성을 평가하기 위한 천공파라미터들의 항목 선정과 기 계량들의 수치적인 정량화가 정립되어 있지 않은 실정이다. 따라서 본 연구에서는 암석 및 지반 특성을 평가할 수 있는 천공파라미터의 항목 선정 및 천공시 천공데이터들 간의 관계를 파악하기 위해 균질 모형 암석 시험편을 제작하여 천공데이터를 획득하였고, 획득된 천공데이터를 이용하여 천공파라미터들의 상관관계 분석을 수행하였다. 분석 결과를 통해 유압착암기의 굴착능력은 타격에 의해 가장 큰 영향을 받음을 확인하였다.

• Smart Structures and Systems
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• 제16권1호
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• pp.163-181
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• 2015

This research investigates the structural health monitoring of nonlinear structures after a major seismic event. It considers the identification of flag-shaped or pinched hysteresis behavior in response to structures as a more general case of a normal hysteresis curve without pinching. The method is based on the overall least squares methods and the log likelihood ratio test. In particular, the structural response is divided into different loading and unloading sub-half cycles. The overall least squares analysis is first implemented to obtain the minimum residual mean square estimates of structural parameters for each sub-half cycle with the number of segments assumed. The log likelihood ratio test is used to assess the likelihood of these nonlinear segments being true representations in the presence of noise and model error. The resulting regression coefficients for identified segmented regression models are finally used to obtain stiffness, yielding deformation and energy dissipation parameters. The performance of the method is illustrated using a single degree of freedom system and a suite of 20 earthquake records. RMS noise of 5%, 10%, 15% and 20% is added to the response data to assess the robustness of the identification routine. The proposed method is computationally efficient and accurate in identifying the damage parameters within 10% average of the known values even with 20% added noise. The method requires no user input and could thus be automated and performed in real-time for each sub-half cycle, with results available effectively immediately after an event as well as during an event, if required.

• Geomechanics and Engineering
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• 제34권2호
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• pp.155-171
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• 2023

Aiming at the grouting treatment of water inflow in karst conduits, a visualized experiment system for conduit-type grouting blocking was developed. Through the improved water supply system and grouting system, and the optimized multisource information monitoring system, the real-time observation of diffusion and deposition of slurry, and the data acquisition of pressure and velocity during the whole process of grouting were realized, which breaks through the problem that the monitoring element is easy to fail due to slurry adhesion in conventional test system. Based on the grouting experiments in static and flowing water, the diffusion and deposition behavior of the quick-setting slurry under different working conditions were analyzed. The temporal and spatial variation behavior of the pressure and velocity were studied, and the blocking mechanism of the grouting were further revealed. The results showed that: (1) Under the flowing water condition, the counter-flow diffusion distance of slurry was negatively correlated with the flow water velocity and the volume ratio of cement and sodium silicate (C-S ratio), and positively correlated with the grouting volume. The slurry deposition thickness was negatively correlated with the flowing water velocity, and positively correlated with the grouting volume and C-S ratio. (2) The pressure increased slowly before blocking of the flowing water and rapidly after blocking in karst conduits. (3) With the continuous progress of grouting, the flowing water velocity decreased slowly first, then significantly, and finally tended to be stable. According to the research results, some engineering recommendations were put forward for the grouting treatment of the conduit-type water inflow disaster, which has been successfully applied in the treatment project of the China Resources Cement (Pingnan) Limestone Mine. This study provided some guidance and reference for the parameter optimization of grouting for the treatment projects of water inflow in karst conduits.