• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.3
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• pp.227-236
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• 2003

Leaks in underground pipelines can cause social, environmental and economical problems. One of relevant countermeasures against leaks is to find and repair of leak points of the pipes. Leak noise is a good source to identify the location of leak points of the pipelines. Although there have been several methods to detect the leak location with leak noise, such as listening rods, hydrophones or ground microphones, they have not been so efficient tools. In this paper, acoustic emission (AE) sensors and accelermeters are used to detect leak locations which could provide all easier and move efficient method. Filtering, signal processing and algorithm of raw input data from sensors for the detection of leak location are described. A 120m-long pipeline system for experiment is installed and the results with the system show that the algorithm with the AE sensors and accelerometers offers accurate pinpointing of leaks. Theoretical analysis of sound wave propagation speed of water in underground pipes, which is critically important in leak locating, is also described.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.472-482
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• 2019

This paper describes the stabilization of underwater TAS winch system Deploy/Recover operation performance. TAS winch installed on the stern of submarine performs to deploy/recover sensor, towing cable and rope tail which is deployed from the stern and separated from submarine itself. Also TAS winch provides transmission path of power to the sensor and data transmitting/receiving path which data are acquired from underwater environment like sound, depth and temperature. At the step of TAS winch evaluation test, sporadic standstill and rotating speed oscillation phenomenon were occurred. Winch motor provides the available torque to deploy/recover TAS and root cause analysis to the winch motor was done to find exact reason to sporadic malfunction. When winch motor was disassembled, eccentricity of rotor, slip-ring and the other composition part for winch motor were found. These might cause magnetic field distortion. To make TAS winch system more stable and block magnetic field distortion, this paper suggests methods to enhance fixing status installed in winch motor. For reliable data acquisition for TAS winch operation, the deploy/recover function of the improved type of TAS winch was verified in LBTS making similar condition with sea status. At the end of stage, improved type of TAS winch was tested on some functions not only deploy/recover function, but sustainability of TAS operation on specific velocity, steering angle of submarine in the sea trial. Improved type of TAS winch was verified in accordance with design requirement. Also, validity of suggested methods were verified by the sea trial.

• Journal of Internet Computing and Services
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• v.22 no.6
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• pp.33-40
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• 2021

Automatic Speech Recognition(ASR) is a technology that analyzes human speech sound into speech signals and then automatically converts them into character strings that can be understandable by human. Speech recognition technology has evolved from the basic level of recognizing a single word to the advanced level of recognizing sentences consisting of multiple words. In real-time voice conversation, the high recognition rate improves the convenience of natural information delivery and expands the scope of voice-based applications. On the other hand, with the active application of speech recognition technology, concerns about related cyber attacks and threats are also increasing. According to the existing studies, researches on the technology development itself, such as the design of the Automatic Speaker Verification(ASV) technique and improvement of accuracy, are being actively conducted. However, there are not many analysis studies of attacks and threats in depth and variety. In this study, we propose a cyber attack model that bypasses voice authentication by simply manipulating voice frequency and voice speed for AI voice recognition service equipped with automated identification technology and analyze cyber threats by conducting extensive experiments on the automated identification system of commercial smartphones. Through this, we intend to inform the seriousness of the related cyber threats and raise interests in research on effective countermeasures.

• The Journal of the Acoustical Society of Korea
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• v.39 no.6
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• pp.524-532
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• 2020

In this study, noise radiated from a high-speed fan-motor unit for a cordless vacuum cleaner is reduced by designing splitter blades on the existing impeller. First of all, in order to investigate the flow field through a fan-motor unit, especially impeller, the unsteady incompressible Reynolds-Averaged Navier-Stokes (RANS) equations are numerically solved by using computational fluid dynamic technique. With predicted flow field results as input, the Ffowcs Williams-Hawkings (FW-H) integral equation is solved to predict aerodynamic noise radiated from the impeller. The validity of the numerical methods is confirmed by comparing the predicted sound pressure spectrum with the measured one. Further analysis of the predicted flow field shows that the strong vortex is formed between the impeller blades. As the vortex induces the loss of the flow field and acts as an aerodynamic noise source, supplementary splitter blades are designed to the existing impeller to suppress the identified vortex. The length and position of splitter are selected as design factors and the effect of each design factor on aerodynamic noise is numerically analyzed by using the Taguchi method. From this results, the optimum location and length of splitter for minimum radiated noise is determined. The finally selected design shows lower noise than the existing one.

• Explosives and Blasting
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• v.33 no.3
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• pp.21-28
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• 2015

The objective of this study is to develop a method for monitoring continuously the combustion propagation behavior of commercial thermite reaction mixtures using conventional continuous VOD (velocity of detonation) system. In order to monitor the combustion front propagation with elapsed time during thermite reaction, the VOD system employs two types of commercial VOD probes and one self-made probe: VOD PROBEROD-OS, VOD PROBEROD-HS and VOD PROBEROD-ES, respectively. Among the probes, the only self made VOD PROBEROD-ES successfully demonstrates the velocity of combustion propagation (VOC) with elapsed time. It was found that VOC of the thermite reaction mixture inside a steel tube has been reached around 200m/s within 100mm distance from the ignition and dramatically increased up to about twice the speed of sound in the range between 100mm and 300mm distance. Finally the VOC reached up to around 800m/s. This results imply that it is necessary to use over 300mm long cartridge of thermite reaction mixture in order to achieve normal VOC of the mixture.

• 대한공업교육학회지
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• v.36 no.1
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• pp.115-130
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• 2011

When the hollow cylinder structure moves in underwater with high speed structural can be propagated from the end of the structure to the front side. This noise can reduce the sensitivity of the conformal array which installed in the surface of the cylinder. To reduce this noise propagation it is suggested to install two self-reduction rings at the surrounding of the cylinder which is 500mm in diameter and 840mm in length. The places of the two noise reduction rings are 120mm and 240mm point from the end of the structure. Two noise reduction rings reduced 10.1 % of maximum stress. When outside noise frequency applied to the structure from the 4kZ to 6kHz, 20dB noise reduction was calculated using 6 order polynomial equation. When outside noise frequency also applied to the structure with 200Hz, 500Hz, 900Hz, maximum sound pressure level point moved to the end of the structure. Most conformal sensors are fabricated at the front side of the structure. Based on the simulation results proposed two rings can be reduced noise propagation from the tail of the structure effectively.

• Restorative Dentistry and Endodontics
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• v.15 no.1
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• pp.107-119
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• 1990

The purpose of this study was to evaluate the marginal adaptability of the amalgam restorations in applying the cavity varnish (Copalite$^{(R)}$) and dentin bonding agent (Scotchbond 2$^{(R)}$) under the scanning electron microscope. For this study, eighteen sound extracted human molars were selected. Class I cavities in 12 teeth and class V cavities in 6 teeth were prepared using an air turbine with No. 701 tungsten carbide bur and finished using a low speed handpiece with No. 557 fissure bur. The prepared specimens were then divided into three groups including 4 class I cavities and 2 class V cavities in each group and restored as follows ; Group I. All the prepared cavities were restored with amalgam only (Control). Group II. Two layers of Copalite$^{(R)}$ cavity varnish were applied to the cavities with a gentle stream of air after each application and cavities were restored with amalgam. Group III. The enamel cavity margins were etched with 37% phosphoric acid gel for 60 sec., rinsed for 30 sec. and dried. One layer of visible lightcured Scotchbond Dental Adhesive$^{(R)}$ was applied and immediately cured for 20 seconds with visible light-cure unit and cavities were restored with amalgam. All the specimens were cut at the neck of the teeth and the occlusal halves of specimens were sectioned buccolingually in the longitudinal axis centering the amalgam restorations, using the disk. The cut specimens were ground with sandpapers (400, 600, 800, 1000 grit), and cleaned for 5 minutes in the ultrasonic cleaner (Brason Co. U.S.A.). In the cut surfaces, the amalgam - tooth interfaces were examined under the scanning electron microscope (JSM, 35C type, JEOL). The obtained results were as follows ; 1. The amalgam-tooth interfaces were reduced more significantly in the Copalite$^{(R)}$ and Scotchbond 2$^{(R)}$ application group than in the control group. 2. In the class I cavities, the Scotchbond 2$^{(R)}$ application group showed the findings similar to the Copalite$^{(R)}$ application group in the cavity floor, and the marginal adaptability was better in the side wall than in the cavity floor. 3. In the class I cavities, the Scotchbond 2$^{(R)}$ application group showed better marginal adaptability in the occlusal margin than in the gingival margin. 4. The marginal adaptability was in the order of the Scothbond 2$^{(R)}$ application group, the Copalite$^{(R)}$ application group and the control group.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.6
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• pp.538-544
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• 2000

A phased array ultrasonic nondestructive inspection system is being developed to obtain images of the interior of steel structures by modifying a medical ultrasound imaging system. The medical system consists of 64 individual transceiver channels that can drive 128 array elements. Several modifications of the system were required mainly due to the change of sound speed. It was necessary to fabricate array transducers for steel structure and to obtain A-scan signal that is necessary for the nondestructive testing. Boundary diffraction wave model was used for the prediction of radiation beam field from array transducers, which provided guidelines to design array transducers. And a RF data acquisition board was fabricated for the A-scan signal acquisition along a selected un line within an image. For the proper beam forming in the transmission and reception for steel structure, delay time was controlled. To demonstrate the performance of the developed system and fabricated transducers, images of artificial specimens and A-scan signals for selected scan lines were obtained in a real time fashion.

• Journal of the Korean Society for Railway
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• v.20 no.1
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• pp.76-84
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• 2017

Recently, the 'Ecological Network Restoration Project at Chupungnyeong' has been placed; this project is located at the center of the Baekdu mountain spine, the core of the ecological network of the Korean Peninsula. In the process of industrialization since the early 1900s, this area has been under railroad and road construction; as such, wildlife movements have been interrupted and many cases of road-kill have been found. The investment in railroads has increased because railroads are an environmentally sound means of transportation. Single track railways have been converted to double track electric railways and track reforming projects are underway in order to speed up the current railway system. This study suggests to take land use as a standard for assessing the ecological weaknesses of the domestic geo-spaces that are to be affected by rapid extension of railway lines. The land cover map issued by the Ministry of Environment was overlapped with the Korean Railway Line Map for analysis. The results showed that five items were high in sensitivity: paddy fields, fields, deciduous forests, bare land, and inland waters. It seems to be necessary to set weights for highly sensitive land use types; also, specific evaluation criteria need to be reestablished.

• Journal of the korean academy of Pediatric Dentistry
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• v.40 no.4
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• pp.247-252
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• 2013

Pit and fissure sealant prevents biofilm accumulation, plays a role in forming a barrier to acidic substance made by the bacteria. The Surface reaction-type pre-reacted glass ionomerI(S-PRG) filler was developed in 1999. S-PRG filler releases fluoride continuously and does not decompose under wet conditions. The aim of this study was to test the microleakage and anticariogenic effect to adjacent enamel of S-PRG filler-containing pit and fissure sealant. Sound premolars and molars were used in this study. A S-PRG filler-containing pit and fissure sealant, Beautisealant$^{(R)}$(Shofu, Japan) was used for this experiment, the composite resin sealant Concise$^{(R)}$(3M ESPE, USA) was used as control. For the microleakage test, all teeth surface were double coated with finger nail varnish, with the exception of a 1.0 mm window around the restoration margins. The teeth were immersed in 2% methylene blue solution for 24 hours and then rinsed in tap water. For the anticariogenic effect evaluation, all tooth were immersed in artificial carious solution for 9 days and rinsed with tap water. Each tooth was embedded in orthodontic acrylic rein and subsequently sectioned longitudinally in a bucco-lingual direction with a low-speed diamond saw. The cut sections were examined using a stereomicroscope. Differences in microleakage between the two groups were not different significantly. But the S-PRG filler-containing pit and fissure sealant showed higher anticariogenic effect than that of flowable resin sealant.