• Smart Structures and Systems
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• v.20 no.6
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• pp.769-780
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• 2017

Cable force monitoring is an essential and critical part of the safety evaluation of cable-supported bridges. A reasonable cable force monitoring scheme, particularly, sensor placement related to accurate safety assessment and budget cost-saving becomes a major concern of bridge administrative authorities. This paper presents optimal sensor placement for cable force monitoring by selecting representative sensor positions, which consider the spatial correlativeness existing in the cable group. The limited sensors would be utilized for maximizing useful information from the monitored bridges. The maximum information coefficient (MIC), mutual information (MI) based kernel density estimation, as well as Pearson coefficients, were all employed to detect potential spatial correlation in the cable group. Compared with the Pearson coefficient and MIC, the mutual information is more suitable for identifying the association existing in cable group and thus, is selected to describe the spatial relevance in this study. Then, the bond energy algorithm, which collects clusters based on the relationship of surrounding elements, is used for the optimal placement of cable sensors. Several optimal placement strategies are discussed with different correlation thresholds for the cable group of Nanjing No.3 Yangtze River Bridge, verifying the effectiveness of the proposed method.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.2
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• pp.439-446
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• 2017

Portable low-cost Kinect sensor was used to analyze standing balance ability of the elderly. Eighty subjects who can walk alone and have a normal cognitive level participated in this experiment. Based on Berg Balance scale (BBS) test with 52 points, subjects were divided into Healthy older (HO: 46 persons, BBS: $53.80{\pm}1.19$) and Impaired older (IO: 34 persons, BBS: $49.06{\pm}2.03$) group. Each subject performed 30 seconds four different standing balance tests (EO: Eyes Open, EC: Eyes Close, EOf: Eyes Open on foam, ECf: Eyes Close on foam). Five variables (Mean distance, Range of distance, Root mean square, Mean velocity, 95% ellipse area) were calculated from the hip joint center movement of Kinect sensor. Results showed that there were significant differences between groups for four different standing tests. Calculated variables from kinect sensor showed significant correlation with BBS score. Especially, mediolateral mean distance, mediolateral root mean square, mediolateral range of distance and 95% ellipse area showed discriminative ability for all tests. Mean values of variables of IO were higher than those of HO, which means the decreased balance ability in IO compared with HO. Therefore, it was possible to estimate simple balance assessment of the elderly using portable low-cost Kinect sensor.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3D
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• pp.461-467
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• 2006

To detect individual vehicular speed, double loop detection technique has been widely used. This paper investigates four methodologies to measure individual speed using only a single loop sensor in a traveling lane. Two methods developed earlier include estimating the speed by means of (Case 1) the slop of inductance wave form generated by the sensor and (Case 2) the average vehicle lengths. Two other methods are newly developed through this study, which are estimations by measuring (Case 3) the mean of wheelbases using the sensor installed traversal to the traveling lane and (Case 4) the mean of wheel tracks by the sensor installed diagonally to the traveling lane. These four methodologies were field-tested and their accuracy of speed output was compared statistically. This study used Equality Coefficient and Mean Absolute Percentage Error for the assessment. It was found that the method (Case 1) was best accurate, followed by method (Case 4), (Case 2), and (Case 3).

• Journal of the Korean Society of Safety
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• v.34 no.3
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• pp.96-101
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• 2019

Chemicals Control Act have been strengthened to control more safely hazardous chemicals from 2015. In particular, the standards for the installation and management of handling facilities was enhanced with specific regulations depending on type of the facilities and the hazardous chemicals. However, some standards for handling facilities caused difficulties in implementing the strengthened standards due to various field conditions, such as lack of physical space. The Ministry of Environment is implementing Safety Assessment System (SAS) to solve these problems since 2018. However, many plants have difficulties in preparing alternative methods to pass the safety evaluation. The purpose of this study was to review and analyze the SAS and to suggest alternative measures in terms of management and technical aspects through the case study of hydrochloric acid storage tanks. The following safety solutions were suggested for handling facilities that had insufficient the space and capacity for the retaining wall due to physical space. Firstly, insufficient space was resolved by introducing equipment relocation or demolition, and retaining wall expansion. Secondly, the wall of the surrounding buildings was used as an alternative to the retaining wall with additional chemical resistant treatment. Finally, sensor installation and facility inspection were suggested as ways to improve chemical safety. Therefore, improvement of chemical accident prevention system is required not only in terms of facilities supplementation but also management aspect. The results of this study are expected to be available for similar facilities and will be based on the preparation of additional safety assessment as alternatives measures in the future.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.17 no.3
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• pp.329-338
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• 2019

Suction of unsaturated bentonite buffers is a very important input parameter for hydro-mechanical performance assessment and design of an engineered barrier system. This study analyzed suction measurement techniques and constitutive models of unsaturated porous media reported in the literature, and suggested suction measurement techniques and constitutive models suitable for bentonite buffer in an HLW repository. The literature review showed the suction of bentonite buffer to be much higher than that of soil, as measured by total suction including matric suction and osmotic suction. The measurement methods (RH-Cell, RH-Cell/Sensor) using a relative humidity sensor were suitable for suction measurement of the bentonite buffer; the RH-Cell /Sensor method was more preferred in consideration of the temperature change due to radioactive decay heat and measurement time. Various water retention models of bentonite buffers have been proposed through experiments, but the van Genuchten model is mainly used as a constitutive model of hydro-mechanical performance assessment of unsaturated buffers. The water characteristic curve of bentonite buffers showed different tendencies according to bentonite type, dry density, temperature, salinity, sample state and hysteresis. Selection of water retention models and determination of model input parameters should consider the effects of these controlling factors so as to improve overall reliability.

• Journal of Welding and Joining
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• v.30 no.6
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• pp.80-85
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• 2012

Fatigue cracks in structural components are the most common cause of structural failure when exposed to fatigue loading. In this respect, fatigue crack detection and structural health assessment are very important. Currently, various smart materials are used for detecting fatigue crack and measurement of SIFs(Stress Intensity Factors). So, this paper presented a measurement of SIFs using MFC(Micro Fiber Composite) sensor which is the one of the smart material. MFC sensor is more flexible, durable and reliable than other smart materials. The SIFs of Mode I(K I) as well as Mode II(K II) based on the piezoelectric constitutive law and fracture mechanics are calculated. In this study, the SIF values measured by MFC sensors are compared with the theoretical results.

• Structural Monitoring and Maintenance
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• v.7 no.2
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• pp.149-166
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• 2020

This paper presents the results of an experimental investigation on a vibration-based damage identification framework for a steel girder type and a truss bridge based on acceleration responses to operational loading. The method relies on sensor clustering-based time-series analysis of the operational acceleration response of the bridge to the passage of a moving vehicle. The results are presented in terms of Damage Features from each sensor, which are obtained by comparing the actual acceleration response from the sensors to the predicted response from the time-series model. The damage in the bridge is detected by observing the change in damage features of the bridge as structural changes occur in the bridge. The relative severity of the damage can also be quantitatively assessed by observing the magnitude of the changes in the damage features. The experimental results show the potential usefulness of the proposed method for future applications on condition assessment of real-life bridge infrastructures.

• Proceedings of the KSR Conference
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• 2003.10b
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• pp.483-488
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• 2003

Calibration and gauge factor readjustment process made for the health monitoring system installed in the railway bridges is reviewed and some findings are explained in this study: specifically, the calibrators made for this purpose are illustrated and the regression processes of the calibration on long-term displacement using water level sensor, longitudinal displacement using LVDT sensor, instantaneous displacement using LVDT sensors and accelerometer are described in details. Based on the regression results, new gauge factors are obtained from regression equation and another verification is made by performing another calibration again with new factors. From the second calibration, it was found that the suggested regression curves and their factors are appropriate and much better results are expected. Future work will be concentrated on the long-term analysis of the measurement data and on the database structures so that the assessment of the structure such as damage detection and remaining life estimation is possible.

• Speech Sciences
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• v.7 no.1
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• pp.39-52
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• 2000

The present study investigates the clinical applicability of a new device which objectively measures nasal resonating vibration via piezoelectric vibratory sensor from 10 normal volunteers, 10 patients with definite hypernasality and 10 nasal polyposis patients. For the assessment of the hypernasality, the ratio of 'ng' to 'a' as well as that of 'mama' to 'papa' passages were used. For the evaluation of hyponasality, the ratio of nasal vibration post- to pre-induced cul-de-sac resonation was calculated. In the control group, the ratio of ng/a and mama/papa passages was larger than 8, while in the hypernasality group, the ratio was markedly lower. The vibratory signals of 'a' and 'ng' increased markedly in the control group and the hypernasality group after inducing cul-de-sac resonation, while in the hyponasality group, the change was minimal.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.39 no.10
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• pp.1029-1036
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• 1990

This paper presents a systematic study for control loops in the induction motor drive system employing a load commutated current source inverter (LCCSI) which has appeared since the early 1980's, and their effects on the dynamic stability of the system. A set of dq equations which amalgamate the overall system is developed, and from the equations it is revealed that the steady state characteristics of the LCCSI-induction motor system are between VSI and ASCI. When the speed control loop is constructed without a speed sensor, the evaluation of the pole/zero locations and the assessment of the stability for the added loops are investigated. We also show that the V/F loop is essential in this type of drive without the speed sensor.