• 한국소음진동공학회논문집
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• 제25권12호
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• pp.830-842
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• 2015

This paper aims to develop a SI(structural identification) technique using the kinetic energy optimization technique(KEOT) and the direct matrix updating method(DMUM) to decide on optimal location of sensors and to update FE model respectively, which ultimately contributes to a composition of more effective SHM. Owing to the characteristic structural flexing behavior of cable bridges, which makes them vulnerable to any vibration, systematic and continuous structural health monitoring (SHM) is pivotal for them. Since it is necessary to select optimal measurement locations with the fewest possible measurements and also to accurately assess the structural state of a bridge for the development of an effective SHM, a SI technique is as much important to accurately determine the modal parameters of the current structure based on the data optimally obtained. In this study, the KEOT was utilized to determine the optimal measurement locations, while the DMUM was utilized for FE model updating. As a result of experiment, the required number of measurement locations derived from KEOT based on the target mode was reduced by approximately 80 % compared to the initial number of measurement locations. Moreover, compared to the eigenvalue of the modal experiment, an improved FE model with a margin of error of less than 1 % was derived from DMUM. Finally, the SI technique for long-span bridges proposed in this study, which utilizes both KEOT and DMUM, is proven effective in minimizing the number of sensors while accurately determining the structural dynamic characteristics.

• Journal of Radiation Protection and Research
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• 제41권4호
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• pp.333-338
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• 2016

Background: In case of radiation emergencies, internal exposure monitoring for the members of public will be required to confirm internal contamination of each individual. In-vivo monitoring technique using portable gamma spectrometer can be easily applied for internal exposure monitoring in the vicinity of the on-site area. Materials and Methods: In this study, minimum detectable doses (MDDs) for $^{134}Cs$, $^{137}Cs$, and $^{131}I$ were calculated adjusting minimum detectable activities (MDAs) from 50 to 1,000 Bq to find out the optimal in-vivo counting condition. DCAL software was used to derive retention fraction of Cs and I isotopes in the whole body and thyroid, respectively. A minimum detect-able level was determined to set committed effective dose of 0.1 mSv for emergency response. Results and Discussion: We found that MDDs at each MDA increased along with the elapsed time. 1,000 Bq for $^{134}Cs$ and $^{137}Cs$, and 100 Bq for $^{131}I$ were suggested as optimal MDAs to provide in-vivo monitoring service in case of radiation emergencies. Conclusion: In-vivo monitoring program for emergency response should be designed to achieve the optimal MDA suggested from the present work. We expect that a reduction of counting time compared with routine monitoring program can achieve the high throughput system in case of radiation emergencies.

• Smart Structures and Systems
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• 제15권2호
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• pp.355-373
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• 2015

An optimal sensor placement (OSP) method based on structural subsection technique (SST) and model reduction technique was proposed for modal identification of truss structures, which was conducted using genetic algorithm (GA). The constraints of GA variables were determined by SST in advance. Subsequently, according to model reduction technique, the optimal group of master degrees of freedom and the optimal objective function value were obtained using GA in a case of the given number of sensors. Correspondingly, the optimal number of sensors was determined according to optimal objective function values in cases of the different number of sensors. The proposed method was applied on a scaled jacket offshore platform to get its optimal number of sensors and the corresponding optimal sensor layout. Then modal kinetic energy and modal assurance criterion were adopted to evaluate vibration energy and mode independence property. The experiment was also conducted to verify the effectiveness of the selected optimal sensor layout. The results showed that experimental modes agreed reasonably well with numerical results. Moreover the influence of the proposed method using different optimal algorithms and model reduction technique on optimal results was also compared. The results showed that the influence was very little.

• 대한전기학회논문지
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• 제43권2호
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• pp.179-188
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• 1994

This paper deals with implementation of an expert system to obtain an optimal plan of load transfer for fault restoration with the capability of security monitoring and assessment in distribution systems. Based on the technique of load transfer tree analysis, the proposed expert system can afford to assist system operators in proposing an optimal plan of load transfer for fault restoration, In paticular, an application of the proposed ES to practical distribution systems yields an optimal load transfer plan which ensures system security by considering security assessment for contingency of feeders and main transformers in the knowledge based sense.

• 한국농공학회지
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• 제45권5호
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• pp.117-125
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• 2003

Since the recorded information used for operation of a catchment modelling system contain errors that influence the calibration of catchment modelling system control parameter values, the accurate estimation of these parameters is difficult. Despite these influences, existing traditional calibration approaches focus only on achieving the best "curve fitting" between simulated and recorded data, and not on generic evaluation of control parameter values. This paper introduces an Early Stopping Technique which is aimed at avoiding the procedure of curve-fitting through monitoring improvements in the objective function used for assessing the optimal parameter set. Application of this approach to the calibration of SWMM (Storm Water Management Model) on the Centennial Park catchment in Sydney, Australia is outlined. outlined.

• Journal of Electrical Engineering and Technology
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• 제13권5호
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• pp.1769-1777
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• 2018

This paper proposes a method for optimal placement of Phasor Measurement Units (PMUs) considering system configuration and its attributes during the planning phase of PMU deployment. Each bus of the system is assessed on four diverse attributes; namely, redundancy of measurements, rotor angle and frequency monitoring of generator buses, reactive power deficiency, and maximum loading limit under transmission line outage contingency, and a consolidated 'degree of criticality' is determined using Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). The major contribution of the proposed work is the development of modified objective function which incorporates values of the degree of criticality of buses. The problem is formulated as maximization of the aggregate degree of criticality of the system. The resultant PMU configuration extends complete observability of the system and majority of the PMUs are located on critical buses. As budgetary restrictions on utilities may not allow installation PMUs even at optimal locations in a single phase, multi-horizon deployment of PMUs is also addressed. The proposed approach is tested on IEEE 14-bus, IEEE 30-bus, New England (NE) 39-bus, IEEE 57-bus and IEEE 118-bus systems and compared with some existing methods.

• 한국구조물진단유지관리공학회 논문집
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• 제6권2호
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• pp.145-155
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• 2002

It is essential for health monitoring of a cable-stayed bridge to provide more accurate and enough information from the sensors. In experimental modal testing, the chosen measurement locations and the number of measurements have a major influence on the quality of the results. The choice is often difficult for complex structures like a cable-stayed bridge. It is extremely important a cable-stayed bridge to minimize the number of sensing operations required to monitor the structural system. In order to obtain the desired accuracy for the structural test, several issues must take into consideration. Two important issues are the number and location of response sensors. There are usually several alternative locations where different sensors can be located. On the other hand, the number of sensors might be limited due to economic constraints. Therefore, techniques such as methodologies, algorithms etc., which address the issue of limited instrumentation and its effects on resolution and accuracy in health monitoring systems are paramount to a damage diagnosis approach. This paper discusses an optimum sensor placement criterion suitable to the identification of structural damage for continuous health monitoring. A Kinetic Energy optimization technique and an Effective Independence Method are analyzed and numerical and theoretical issues are addressed for a cable-stayed bridge. Its application to a cable-stayed bridge is discussed to optimize the sensor placement for identification and control purposes.

• 한국구조물진단유지관리공학회 논문집
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• 제22권4호
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• pp.121-125
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• 2018

본 연구에서는 음향 방출 기법을 사용하여 강연선(7-wire strand)의 손상을 감지하기 위한 기초 실험을 수행하였다. 강연선은 주로 교량에 추가적인 인장력을 제공하기 위해 널리 사용되는 건설 자재이다. 프리스트레스 교량 또는 사장교가 대표적인 경우이다. 그러나 교량 노화가 급격히 진행되면서 강연선 부식 문제가 대두되고 있다. 이러한 이유로 케이블 점검을 위한 다양한 비파괴 방법이 연구되고 있고 현장 적용이 시도되고 있다. 비파괴 방법 ??중 하나인 음향 방출 기법은 케이블 손상 및 파단을 감지하는 효과적인 기술로 알려져 있다. 본 연구에서는 음향 방출 기법의 교량에 대한 적용 가능성을 평가하기 위해 강연선의 손상에 따른 음향 방출 신호 특성을 인장 실험을 분석 하고, 현장 적용을 위한 최적 센서 주파수 타입을 선정하였다. 결과적으로, 음향 방출 기법을 활용하여 향후 교량 케이블의 부식 파단 및 파단 징후를 감지 할 수 있다고 여겨진다.

• 한국구조물진단유지관리공학회 논문집
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• 제1권2호
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• pp.87-94
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• 1997

This research aims to develop an algorithm of optimal transducer placement using Kinetic Energy of the structural system. The structural vibration response-based health monitoring is considered one of the best for the system which requires a long-term, continuous monitoring. In its experimental modal testing, however, it is difficult to decide on the measurement locations and their number, especially for complex structures, which have a major influence on the quality of the results. In order to minimize the number of sensing operations and optimize the transducer location while maximizing the accuracy of results, this paper discusses about an optimum transducer placement criterion suitable for the identification of structural damage. As a criterion algorithm, it proposes the Kinetic Energy Optimization Technique (EOT), and then addresses the numerical issues which are subsequently applicable to actual experiment where a bridge model is used. By using the experimental data, it compares the EOT with the EIM (Effective Independence Method) which is generally used to optimize the transducer placement for the damage identification and control purposes. The comparison conclusively shows that the EOT algorithm proposed in this paper is preferable when a structure is to be instrumented with fewer sensors.

• 전산구조공학
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• 제10권3호
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• pp.157-165
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• 1997

이 연구의 목적은 대형 구조물의 상설 감지를 위한 감지기의 최적 위치의 알고리즘을 개발하는데에 있다. 구조물의 진동을 이용한 감지 시스템은 장기적으로 계속해서 구조물을 자동으로 감지하는데에 좋은 방법중의 하나이다. 하지만 구조물의 진동을 정확히 계측하기 위해서는 감지기의 위치나 감지기의 숫자에 큰 영향을 받는데, 이와 같은 일은 대형 구조물에 있어서 쉽지가 않다. 최적의 감지기 위치와 최소의 감지기로 가장 정확한 데이터를 획득하기 위하여 최적합한 감지기의 위치를 위한 알고리즘이 개발되어 수치적 그리고 실험적으로 유용성을 보인다. EOT가 개발되어 모형 교량에 적용하여 EIM과 비교 분석된다. 이들의 비교를 통하여, 이 연구에서 제안되어진 EOT가 적은 수의 감지기로 좋은 결과를 보여, 상설감지의 목적에 적합함을 보여준다.