• Journal of the Korean Society of Marine Environment & Safety
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• v.3 no.2
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• pp.13-21
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• 1997

This paper describes the effectiveness of laser pulse shaping in eliminating weld defects such as porosity, cracks and undercuts in pulsed Nd:YAG Laser welding. A large porosity was formed in a keyhole mode of deep penetration weld metal of any stainless steel. Solidification cracks were present in Type 303 with about 0.3%s. The conditions for the formation of porosity were determined in further detail in Type 316. With the objectives of obtaining a fundamental knowledge of formation and prevention of weld defects, the fusion and solidification behavior of a molten puddle was observed during laser spot welding of Type 310S. through high speed video photographing technique. It was deduced that cellular dendrite tips grew rapidly from the bottom to the surface, and consequently residual liquid remained at the grain boundaries in wide regions and enhanced the solidification cracking susceptibility. Several laser pulse shapes were investigated and optimum pulse shapes were proposed for the reduction and prevention of porosity and solidification cracking.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.11a
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• pp.217-218
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• 2017

Residential apartment underground structures are being utilized for many purposes such as parking lots, community centers, fitness centers, etc. for efficient use of space. However, there are increasing problems of leakage due to various environmental and deterioration conditions. This paper proposes the development of an information network system which can serve as a base to provide solutions, alternatives and technical information for leakage prevention and effective design at the beginning of the construction stage.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.3 s.96
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• pp.208-214
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• 1999

The purpose of this paper is to develop a profile modification technique of spur gears and its computer program for the prevention of gear tooth overlap. In the gear system, tooth overlap produces an impact at the initial contact of some tooth pairs. In this analysis, contact surface was assumed to be unbonded and frictionless under small deformation and stain. The problem is formulated by a variational statement with inequality constraint. Tooth load sharing is obtained by the application of contact theory, and overlap is known by the analysis of deformation. After carrying out the profile modification of gear tooth, we verified the reasonable results.

• Radioisotope journal
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• v.21 no.4
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• pp.46-54
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• 2006

Biocompatible and biodegradable hydrogels based on carboxymethyl cellulose(CMC) and polyethyleneglycol(PEG) were prepared far physical barriers for preventing surgical adhesions. These interpolymeric hydrogels were synthesized by a gamma irradiation crosslinking technique. The 1Scmxl.Scm of cecal serosa and adjacent abdominal wail were abraded with bane burr until tbe serosal surface was disrupted and hemorrhagic but not perforated. and the serosa of tbe cecum was sutured to the abdominal wall in 5mm apart from the injured sire. The denuded cecum was covered with either CMC/PEG hydrogels or solution from CMC/PEG hydrogel. Control rat serosa was not covered. Two weeks later. the rats were sacrificed and adhesion was scored on a 0-5 scale. No treatment showed the significantly higher incidence of adhesions than either CMC/BEC hydrogels or solution from CMC/PEG hydrogel. In conclusion, these studies demonstrate that CMC/BEG hydrogels have a function of prevention of intra abdominal adhesion in a rat model.

• Proceedings of the KIPE Conference
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• 2018.11a
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• pp.9-11
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• 2018

This paper studies on the development of an electric fire prevention system with the detection and alarm in case of parallel arc fault occurrence in low voltage distribution lines. The proposed detector has the characteristics of high speed operation responsibility and superior system reliability from composition using a large number of semiconductor devices. The line voltage is always feedback, and when an arc or a spark occurs, these are detected by the microcomputer. In addition, we design and develop algorithms using high speed and high precision microcomputer. A new conceptual control technique is adopted that RCD cuts-off by forming a forced short circuit between the phase voltage and ground in the event of an electrical accident. Some experimental tests of the proposed system also confirm practicality and the validity of the analytical results.

• Journal of the Korean Society of Industry Convergence
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• v.27 no.3
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• pp.581-590
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• 2024

This study aims to extract key topics through text mining of incident records (incident history, post-incident measures, preventive measures) from construction safety accident case data available on the public data portal. It also seeks to provide fundamental insights contributing to the establishment of manuals for disaster prevention by identifying correlations between these topics. After pre-processing the input data, we used the LDA-based topic modeling technique to derive the main topics. Consequently, we obtained five topics related to incident history, and four topics each related to post-incident measures and preventive measures. Although no dominant patterns emerged from the topic pattern analysis, the study holds significance as it provides quantitative information on the follow-up actions related to the incident history, thereby suggesting practical implications for the establishment of a preventive decision-making system through the linkage between accident history and subsequent measures for reccurrence prevention.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.3
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• pp.246-254
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• 2007

The scanning laser source (SLS) technique is a promising new laser ultrasonic tool for the detection of small surface-breaking defects. The SLS approach is based on monitoring the changes in laser-generated ultrasound as a laser source is scanned over a defect. Changes in amplitude and frequency content are observed for ultrasound generated by the laser over uniform and defective areas. The SLS technique uses a point or a short line-focused high-power laser beam which is swept across the test specimen surface and passes over surface-breaking or subsurface flaws. The ultrasonic signal that arrives at the Rayleigh wave speed is monitored as the SLS is scanned. It is found that the amplitude and frequency of the measured ultrasonic signal have specific variations when the laser source approaches, passes over and moves behind the defect. In this paper, the setup for SLS experiments with full B-scan capability is described and SLS signatures from small surface-breaking and subsurface flaws are discussed using a point or short line focused laser source.

• Journal of Electrical Engineering and Technology
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• v.6 no.4
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• pp.439-446
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• 2011

Frequency is an important operating parameter for the protection, control, and stability of a power system. Thus, it must be maintained very close to its nominal frequency. Due to the sudden change in generation and loads or faults in a power system, however, frequency deviates from its nominal value. An accurate monitoring of the power frequency is essential for optimum operation and prevention of wide area blackout. Most conventional frequency estimation schemes are based on the DFT filter. In these schemes, the gain error could cause defects when the frequency deviates from the nominal value. We present an advanced frequency estimation technique using gain compensation to enhance the DFT filter-based technique. The proposed technique can reduce the gain error caused when the frequency deviates from the nominal value. Simulation studies are performed using both the data from EMTP-RV software and the user-defined arbitrary signals to demonstrate the effectiveness of the proposed algorithm. Results show that the proposed algorithm achieves good performance under both steady state tests and dynamic conditions.

• Proceedings of the Korean Geotechical Society Conference
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• 2007.09a
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• pp.465-477
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• 2007

Recently a number of research has been performed for the combination of new high technologies in order to find the solutions for various problems in civil engineering research field. Various high-tech measuring instruments have been applied to the geotechnical engineering field, and many attempts have also been performed for the more accurate measurements. Especially, the researches using image on the digital photogrammetry technique are gradually extending nowadays. The computer program developed using the digital photogrammetry technique and the case studies are explained and presented in this paper. Therefore, it could be considered that not only the measurement with high-accuracy but the disaster prevention should be available through the practical use of digital photogrammetry technique. The applicability would also be increased in the measurement of both the geotechnical engineering field as well as other research fields.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.3412-3420
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• 2015

Smartphone has become an essential element in our daily life and built-in sensors of the smartphone can be utilized in order to recognize of user's situation. However, it is lack of research for safety and accident prevention by dynamic situation recognition. In this paper, we propose a technique that can be recognized risk situation dynamically using accelerometer, microphone and GPS sensor of mobile device. We propose an architecture and process for sensing techniques of Dynamic Recognition Technique, and develop the mobile application for verifying the suitability of the architecture.