• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.13 no.2
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• pp.1-18
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• 2017

Metal fatigue is an important aging mechanism that material characteristics can be deteriorated when even a small load is applied repeatedly. An accurate fatigue evaluation is very important for component structural integrity and reliability. In the design stage of a nuclear power plant, the fatigue evaluations of the Class 1 components have to be performed. However, operating experience shows that the design evaluation can be very conservative due to conservatism in the transient severity and number of occurrence. Therefore, the fatigue monitoring system has been considered as a practical mean to ensure safe operation of the nuclear power plants. The fatigue monitoring system can quantify accumulated fatigue damage up to date for various plant conditions. The purpose of this paper is to describe the fatigue monitoring procedure and to introduce the fatigue monitoring program developed by the authors. The feasibility of the fatigue monitoring program is demonstrated by comparing with the actual operating data and finite element analysis results.

• Nuclear Engineering and Technology
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• v.51 no.3
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• pp.867-876
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• 2019

Second harmonic generation using nonlinear ultrasonic waves have been shown to be an early indicator of possible fatigue damage in nuclear power plant components. This technique relies on measuring amplitudes, making it highly susceptible to variations in transducer coupling and instrumentation. This paper proposes an experimental procedure for in-situ surface wave nonlinear ultrasound measurements on specimen with permanently mounted transducers under high cycle fatigue loading without interrupting the experiment. It allows continuous monitoring and minimizes variation due to transducer coupling. Moreover, relations describing the effects of the measurement system nonlinearity including the effects of the material transfer function on the measured nonlinearity parameter are derived. An in-situ high cycle fatigue test was conducted using two 304 stainless steel specimens with two different excitation frequencies. A comprehensive analysis of the nonlinear sources, which result in variations in the measured nonlinearity parameters, was performed and the effects of the system nonlinearities are explained and identified. In both specimens, monotonic trend was observed in nonlinear parameter when the value of fundamental amplitude was not changing.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.385-389
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• 2004

Test facilities for the wind turbine performance monitoring and mechanical load measurements are installed in Vestas 100 kW wind turbine in Wollyong test site, Jeju island. The monitoring system consists of Garrad-Hassan T-MON system, telemetry system for blade load measurement, various sensors such as anemometer, wind vane, strain gauge, power meter, and etc. The experimental procedure for the measurement of wind turbine loads, such as edgewise(lead-lag) bending moment, flapwise bending moment, and tower base bending moment, has been established. Strain gauges are on-site calibrated against load cell prior to monitoring the wind turbine loads. Using the established monitoring system, the wind turbine is remotely monitored. From the measured load data, the load analysis has been performed to obtain the load power spectral density and the fatigue load spectra of the wind turbine.

• Structural Engineering and Mechanics
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• v.17 no.5
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• pp.655-670
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• 2004

This paper aims to evaluate the effect of typhoons on fatigue damage accumulation in steel decks of long-span suspension bridges. The strain-time histories at critical locations of deck sections of long-span bridges during different typhoons passing the bridge area are investigated by using on-line strain data acquired from the structural health monitoring system installed on the bridge. The fatigue damage models based on Miner's Law and Continuum Damage Mechanics (CDM) are applied to calculate the increment of fatigue damage due to the action of a typhoon. Accumulated fatigue damage during the typhoon is also calculated and compared between Miner's Law and the CDM method. It is found that for the Tsing Ma Bridge case, the stress spectrum generated by a typhoon is significantly different than that generated by normal traffic and its histogram shapes can be described approximately as a Rayleigh distribution. The influence of typhoon loading on accumulative fatigue damage is more significant than that due to normal traffic loading. The increment of fatigue damage generated by hourly stress spectrum for the maximum typhoon loading may be much greater than those for normal traffic loading. It is, therefore, concluded that it is necessary to evaluate typhoon induced fatigue damage for the purpose of accurately evaluating accumulative fatigue damage for long-span bridges located within typhoon prone regions.

• Journal of the Korean Solar Energy Society
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• v.29 no.6
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• pp.69-74
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• 2009

Monitoring system is an absolutely-required system for assessing a performance and fatigue load of the wind turbine in an on-shore wind energy experimental research complex. It was implemented for the purpose of monitoring the wind information measured from a meteorological tower at the monitoring house, and of utilizing the measured data(fatigue data and electric analyzing data of wind turbine)for the performance assessment, by using the LabVIEW program. Then, by adding the performance assessment-related data acquired from the wind turbine during the performance assessment and the data recorder for synchronizing the data of meteorological tower, the system(BusDAQ) was implemented. Because it transmitted the data by converting the output 'RS-232' of data logger which measures the wind condition into CAN protocol, the data error rate was minimized. Also, This paper is introduced to make the best use of the developed monitoring system and to explain about construct of the system and detailed data communication of its system.

• Journal of Ocean Engineering and Technology
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• v.19 no.4 s.65
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• pp.21-27
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• 2005

Large welded structures, including ships and offshore structures, are normally in operation under cyclic fatigue loadings. These structures include many geometric discontinuities, as well as material discontinuities due to weld joints. The fatigue strength at these hot spots is very important for the structural performance. In the past, various Non Destructive Evaluation (NDE) techniques have been developed to detect fatigue cracks and to estimate their location and size. However, an important limitation of most of the existing NDE methods is that they are off line; the normal operation of the structure has to be interrupted, and the device often has to be disassembled. This study explores the development of a structural health monitoring system, with a special interest in applying the technique to welded structural members in ship and offshore structures. In particular, the impedance based structural health monitoring technique that employs the coupling effect of piezoceramic (PZT) materials and structures is investigated.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.1
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• pp.123-130
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• 1988

Two kinds of 16bit-personal computer-based fatigue testing automation and monitoring system were constructed; one is Single-System utilizing a personal computer, the other si Dual-System consisting of two personal computers. The system developed in this study permits to perform multi-step programmed loading and pseudo-random loading fatigue tests, three parameters such as load, total displacement and subtracted displacement can be measured simultaneously. For improvements in measurements of fatigue behavior, two kinds of signal noise reduction software was developed. In addition, a software was also designed to automatically measure the crack opening point and crack length using the unloading elastic compliance technique.

• Smart Structures and Systems
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• v.8 no.1
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• pp.93-105
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• 2011

This paper presents a flexible low-profile antenna sensor for fatigue crack detection and monitoring. The sensor was inspired by the sense of pain in bio-systems as a protection mechanism. Because the antenna sensor does not need wiring for power supply or data transmission, it is an ideal candidate as sensing elements for the implementation of engineering sensor skins with a dense sensor distribution. Based on the principle of microstrip patch antenna, the antenna sensor is essentially an electromagnetic cavity that radiates at certain resonant frequencies. By implementing a metallic structure as the ground plane of the antenna sensor, crack development in the metallic structure due to fatigue loading can be detected from the resonant frequency shift of the antenna sensor. A monostatic microwave radar system was developed to interrogate the antenna sensor remotely. Fabrication and characterization of the antenna sensor for crack monitoring as well as the implementation of the remote interrogation system are presented.

• International Journal of Contents
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• v.12 no.1
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• pp.44-48
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• 2016

Driver fatigue is a major cause of fatal road accidents and has significant implications in road safety. In recent years, researchers have investigated steering wheel grip force as an alternative method to detect driver fatigue noninvasively and in real time. In this study, a fatigue detection system was developed by monitoring the grip force and changes in the grip force were measured while participants' engaged in an interactive simulated driving task. The study also measured the participants' subjective sleepiness to ensure the validity of measuring grip force. The results indicated that while participants engaged in a driving task, steering wheel grip force decreased and subjective sleepiness increased concurrently over time. The possible applications of the driver fatigue detection system by steering wheel grip force and future guidelines are discussed.

• Korean Journal of Occupational Health Nursing
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• v.30 no.4
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• pp.145-155
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• 2021

Purpose: The purpose of this study was to examine the effects of customer violence experiences, protection systems, and monitoring systems on the subjective health status of salespersons and electronic machine repairers. Methods: A total of 934 persons were sampled nationwide, including 582 salespersons and 352 electronic machine repairers, from March 2~30, 2020 and asked to fill out a self-reported questionnaire. Results: The findings show that electronic machine repairers were more exposed to customer violence and had a weaker protection system than salespersons. They also experienced severe control from management through a monitoring system. The regression analysis revealed that verbal violence had a negative impact on the subjective health status of electronic machine repairers (p=.021). A worker protection system had significant effects on the improved subjective health status of salespersons (p=.009). Depression and fatigue had negative impacts on the subjective health status of both salespersons (depression: p<.001, fatigue: p<.001) and electronic machine repairers (depression: p<.001, fatigue: p=.002). Conclusion: These findings put a greater emphasis on the need for worker protection systems to prevent workplace violence and a health promotion program to manage depression and fatigue in workplaces.