• Journal of Soil and Groundwater Environment
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• v.21 no.6
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• pp.80-86
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• 2016

Earthquakes of M5.1, M5.8 and M4.5 occurred in September 12 and 19 respectively in Gyeongju, Gyeongbuk Province. Theses earthquakes inflated fears of people and highlighted necessity of detailed countermeasures because we have considered our country is safe to earthquakes. In the meanwhile, earthquake also impacts groundwater and thus it was recently reported that the Gyeongju Earthquakes affected groundwater there. This study evaluates daily groundwater data collected from five national groundwater monitoring stations (Geoncheon, Sannae, Oedong, Yangbuksin, Cheonbuk) in Gyeongju. The analysis revealed that only groundwater level of bedrock monitoring well hosted in andesite exhibited earthquake impact while no wells in the other four stations hosted in sedimentary rocks showed substantial responses to the earthquakes. This may be derived from the difference of seismic velocity of hosting rocks as well as epicenter distance. Special interest on groundwater monitoring is required to predict earthquakes as precursory phenomena.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2004.10a
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• pp.451-458
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• 2004

The caisson-type breakwaters have been widely used in the area of harbor construction. Because of the importance of the breakwaters, structural health monitoring in the breakwaters by using appropriate methods is of great needs. In this study, a caisson-type breakwater that has fatigue cracks due to wave-impact is investigated. First, a signal-based structural health monitoring method is proposed for the breakwaters structures. Excitation and sensor systems are designed on finite element model and monitoring categories are also selected. Structural health monitoring was realized by using measured dynamic response signals and analyzed information.

• Journal of Korean Society on Water Environment
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• v.22 no.3
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• pp.427-430
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• 2006

Uncertainty is one of the key issues of the water quality management. Uncertainty occurs in the course of all water quality management stages including monitoring, modeling, and regulation enforcement. To reduce uncertainties of water quality monitoring, manualized monitoring methodology should be developed and implemented. In addition, long-term monitoring is essential for acquiring reliable water quality data which enables best water quality management. For the water quality management in the watershed scale, fate of pollutant including its generation, transport and impact should be considered while regarding each stage of water quality management as an unit process. Uncertainties of each stage of water quality management should be treated properly to prevent error propagation transferred to the next stage of management for successful achievement of water quality conservation.

• Journal of the Korean Society of Safety
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• v.30 no.4
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• pp.174-180
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• 2015

This study developed a Safety Culture Impact Assessment Model (SCIAM) which consists of a safety culture assessment methodology and a safety culture impact quantification methodology. The SCIAM uses safety culture impact index (SCII) to monitor the status of safety culture of the NPPs periodically and it uses relative core damage frequency (RCDF) to present the impact of safety culture on the safety of the NPPs. As a result of applying SCIAM to the reference plant (Kori 3), the standard for the healthy safety culture of the reference plant is suggested. SCIAM might contribute to improve the safety of the NPPs (Nuclear Power Plants) by monitoring the status of safety culture periodically and presenting the standard of healthy safety culture.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.27-30
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• 2005

This paper studied the PVDF(polyvinylidene fluoride) and Acoustic Emission sensors characteristics of the laminated composite panels under the low velocity impact. The various impact test by changing impact height is performed on the instrumented drop weight impact tester. The STFT(short time Fourier transform) and WT(wavelet transform) are used to decompose the each sensor signals. A ultrasonic C-scan and digital scope are used to define damaged area in each case. The test result indicated that the individual sensor signals involve the damage initiation and development.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.3
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• pp.247-252
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• 2014

This paper presents a novel impact sensor which can be fabricated with smart paint made of grapheme. This smart nano paint can be easily installed on structures using a spray-on technique and that can make the sensor low cost and practical. The graphene effectively improves the piezoresistivity of the smart paint and that is available to achieve sensitive impact sensor with high gauge factor. The nano smart-paint can detect sufficient impact to cover the damaged energy range of the composite around 1~3J. The voltage outputs from the sprayed paints show fairly linear responses after signal processing. The impact makes deformation of the structure and it brings change of piezoresistivity of the paint and those converts into voltage output consequently by means of a simple signal processing system. The nano smart paint is lightweight and easily applied to the structural surface, and there is no stress concentration. The nano smart paint is expected to be a cost effective and sensitive multi-functional sensor for composites and other damage monitoring applications in the field of structural health monitoring.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.6
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• pp.55-62
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• 2015

An importance of infrastructures' protection against crash or blast loading has been an emerging issue as structures are becoming much bigger and population densities in downtown are growing up. However, there exists no such a standard to evaluate the protection performance of construction material itself. Prior to building standards for protection assessment techniques, this study performed gas-gun propelled projectile impact tests with series of contact-type monitoring systems to investigate the applicability of each sensing type. Through the impact tests, failure modes and protection performances of both normal concrete and UHPC (Ultra High Performance Concrete) reinforced by steel fibers were also evaluated. The results showed that LVDT could be applicable for the impact test among contact-type sensors and UHPC with fibers had a remarkable potential to improve protection against impact loading.

• Nuclear Engineering and Technology
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• v.53 no.9
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• pp.3068-3084
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• 2021

Investigations of large commercial aircraft impact effect on nuclear power plant (NPP) buildings have been drawing extensive attentions, particularly after the 9/11 event, and this paper aims to experimentally assess the damage and vibrations of NPP buildings subjected to aircraft crash. In present Part I, two shots of reduce-scaled model test of aircraft impacting on NPP building were carried out. Firstly, the 1:15 aircraft model (weighs 135 kg) and RC NPP model (weighs about 70 t) are designed and prepared. Then, based on the large rocket sled loading test platform, the aircraft models were accelerated to impact perpendicularly on the two sides of NPP model, i.e., containment and auxiliary buildings, with a velocity of about 170 m/s. The strain-time histories of rebars within the impact area and acceleration-time histories of each floor of NPP model are derived from the pre-arranged twenty-one strain gauges and twenty tri-axial accelerometers, and the whole impact processes were recorded by three high-speed cameras. The local penetration and perforation failure modes occurred respectively in the collision scenarios of containment and auxiliary buildings, and some suggestions for the NPP design are given. The maximum acceleration in the 1:15 scaled tests is 1785.73 g, and thus the corresponding maximum resultant acceleration in a prototype impact might be about 119 g, which poses a potential threat to the nuclear equipment. Furthermore, it was found that the nonlinear decrease of vibrations along the height was well reflected by the variations of both the maximum resultant vibrations and Cumulative Absolute Velocity (CAV). The present experimental work on the damage and dynamic responses of NPP structure under aircraft impact is firstly presented, which could provide a benchmark basis for further safety assessments of prototype NPP structure as well as inner systems and components against aircraft crash.

• 제어로봇시스템학회:학술대회논문집
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• 1998.10a
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• pp.295-300
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• 1998

In this paper, a real time diagnostic algorithm fur estimating the impact location by loose parts is proposed. It is composed of two modules such as the alarm discrimination module (ADM) and the impact-location estimation module(IEM). ADM decides whether the detected signal that triggers the alarm is the impact signal by loose parts or the noise signal. When the decision from ADM is concluded as the impact signal, the beginning time of burst-type signal, which the impact signal has usually such a form in time domain, provides the necessary data fur IEM. IEM by use of the arrival time method estimates the impact location of loose parts. The overall results of the estimated impact location are displayed on a computer monitor by the graphical mode and numerical data composed of the impact point, and thereby a plant operator can recognize easily the status of the impact event. This algorithm can perform the diagnosis process automatically and hence the operator's burden and the possible operator's error due to lack of expert knowledge of impact signals can be reduced remarkably. In order to validate the application of this method, the test experiment with a mock-up (flat board and reactor) system is performed. The experimental results show the efficiency of this algorithm even under high level noise and potential application to Loose Part Monitoring System (LPMS) for improving diagnosis capability in nuclear power plants.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.27 no.2
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• pp.148-154
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• 2017

This paper discussed design for resonance avoidance of sensor plates of loose-parts monitoring systems (LPMS) in nuclear power plants (NPP). An LPMS monitors impact of loose parts in primary loop of NPP by using accelerometers, which is mounted on sensor plates. Resonance of the plates may cause false alarms at frequencies over 10 kHz, which can be misunderstood as impact signals of loose parts with small mass and cause unnecessary response of NPP operators. Modal analysis was carried out for the existing sensor plate and design parameters affecting natural frequencies were chosen. Frequency response functions of plates were analyzed by changing the parameters and the optimized plate design for avoiding resonance was determined. Experiments was carried out for the plate specimen with improved design and verified the proposed approach and design.