• Fire Science and Engineering
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• v.33 no.6
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• pp.186-189
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• 2019

NFSC 202 stipulates that if a loudspeaker or wiring on one floor of a building is shorted because of fire, it should not interfere with the fire notification on the other floors. To address this problem, this study proposes an ultrasonic transmitter/receiver consisting of an ADC, HPF, and LPF in an emergency broadcasting system that can operate regardless of the volume level of the amplifier output loudspeaker capacity. After transmitting the transmission frequency at -12 dB (110 kHz), it is received at -18 dB by transmitting -12 dB in case of short circuit depending on the frequency characteristics. Typically, depending on the loudspeaker capacity, it is received from -24 dB to -66 dB. In case of disconnection, it exceeds -66 dB and no data are received. It is also possible to check the track status during fire or general broadcasting. Thus, it was confirmed that the system is suitable for NFSC 202 regulations. Furthermore, as the current system is replaced, the inspection or test criteria should be amended or revised.

• Ocean and Polar Research
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• v.35 no.1
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• pp.15-26
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• 2013

The toxic, Harmful Algal Blooms (HABs) caused by the Cochlodinium polykrikoides have a serious impact on the coastal waters of Korea. In this study, the acoustic detection system was developed for rapid HABs detection, based on the acoustic backscattering properties of the C. polykrikoides. The developed system was mainly composed of a pulser-receiver board, a signal processor board, a control board, a network board, a power board, ultrasonic sensors (3.5 and 5.0 MHz), an environmental sensor, GPS, and a land-based control unit. To evaluate the performance of the system, a trail was done at a laboratory, and two in situ trials were conducted: (1) when there was no red tide, and (2) when there was red tide. In the laboratory evaluation, the system performed well in accordance with the number of C. polykrikoides in the received level. Second, under the condition when there was no red tide in the field, there was a good correlation between the acoustic data and sampling data. Finally, under the condition when there was red tide in the field, the system successfully worked at various densities in accordance with the number of C. polykrikoides, and the results corresponded with the sampling data and monitoring result of NFRDI (National Fisheries Research & Development Institute). From the laboratory and field evaluations, the developed acoustic detection system for early detecting HABs has demonstrated that it could be a significant system to monitor the occurrence of HABs in coastal regions.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.4
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• pp.338-344
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• 2010

A double rotation C-scanning system and a software program Under-Sodium MultiVIEW have been developed for the under-sodium viewing of a reactor core and in-vessel structures of a sodium-cooled fast reactor KALIMER-600. Double rotation C-scanning system has been designed and manufactured by the reproduction of double rotation plug of a reactor head in KALIMER-600. Hardware system which consists of a double rotating scanner, ultrasonic waveguide sensors, a high power ultrasonic pulser-receiver, a scanner driving module and a multi channel A/D board have been constructed. The functions of scanner control, image mapping and signal processing of Under-Sodium MultiVIEW program have been implemented by using a LabVIEW graphical programming language. The performance of Under-Sodium MultiVIEW program was verified by a double rotation C-scanning test in water.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.751-758
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• 2002

Boreholes that are drilled in soft or unconsolidated materials such as gravels and coals are prone to collapse. To maintain the hole, some kinds of casing pipes are needed. If thereby a plastic pipe e.g. PVC is used for the casing, Televiewer tool is still capable of detecting structural features such as fractures in the borehole wall behind the pipe, whereas other borehole-imaging logging devices such as BIPS (Borehole Image Processing System) and FMS(Formation Micro Scanner) won't provide any information about that. Televiewer's primary component is a piezoelectric transducer centered in the hole. It acts as both a transmitter and receiver, and sends an ultrasonic beam. That is reflected, in the same manner as the seismic wave propagation, from the both sides(inner and outer surfaces) of the casing pipe, transmits through the pipe and then reflected from the borehole wall. With an appropriate choice of time-windowing, it is possible to capture the returning signals from both the borehole wall and the outer side of casing pipe as well. A suite of laboratory tests were performed on various physical models composed of plastic pipes with different diameters. Although the amplitudes of returning signals were reduced to about half the usual value due to the transmission loss, the dynamic range of Televiewer tool was sufficient to observe the structural features behind the casing pipe. Besides, several representative case studies at various research areas in our country are presented. The results demonstrate the usefulness of the transmissivity of Televiewer acoustic km, which will assist in further structural interpretation.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.2
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• pp.219-226
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• 2020

Nondestructive testing is one of the most commonly used quality inspection methods for evaluating ship structures. However, accurate evaluation is dif icult because various composite materials, such as reinforcements, resin, and fiber-reinforced plastics (FRPs), are used in hulls, and manufacturing quality differences are likely to exist owing to the fabrication environment and the skill level of workers. This possibility is especially true for FRP ships because they are significantly thicker than other structures, such as automobiles and aircraft, and are mainly manufactured using the hand lay-up method. Because the density of a material is a critical condition for ultrasonic inspection, in this study, a hull plate was selected from a vessel manufactured using e-glass fiber, which is widely used in the manufacture of FRP vessels with the weight fraction of the glass content generally considered. The most suitable ultrasonic testing conditions for the glass FRP hull plate were investigated using a pulse-echo ultrasonic gauge. A-scans were performed with three probes (1.00, 2.25, and 5.00 MHz), and the results were compared with those of the hull plate thickness measured using a Vernier caliper. It was found that when the probe frequency was higher, the eco-pulse velocity of the receiver had to be lowered to obtain accurate measurement results, whereas fewer errors occurred at a relatively low probe frequency.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2004.04a
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• pp.235-242
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• 2004

In this study numerical and experimental studies are conducted to examine the wave screening effectiveness of trenches. The numerical study is based on a finite element model of a "sandbox" with Lysmer-Kuhlemeyer-type absorbing boundaries. Using the model, the screening effectiveness of trench is studied for different trench dimensions and distance from source and receiver to trench. The results of the numerical modeling are compared with the results of the ultrasonic experiment which is performed on a acrylic block with a drilled rectangular cut. These results show that the screening effectiveness of the trench is nearly equal if the depth of trench is lager than 60 % of the surface wave length. If is also shown that if the distance between the trench and the source is lager than twice the surface wave length, the thickness of the trench does not affect the screening effectiveness.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.4
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• pp.294-299
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• 1999

In this paper, the calibration system for contact transducer has been developed to improve the reliability of the inspection result of ultrasonic testing on rotors. This system consists of signal processing parts: (oscilloscope, spectrum analyzer, pulser/receiver), standard block, and user interface program. Signal processing for the calibration system was performed quickly with high accuracy. The developed system has been applied to a practical calibration of probe using the non-destructive testing on rotors, and demonstrated high sensitivity and precision.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1812_1813
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• 2009

This paper presents an accurate indoor localization method of a mobile robot using ultrasonic sensors. The coordinates of mobile robot are calculated by using trilateration which is using the distance between the transmitter and receiver. At this time, the distances can't be accurately calculated by containing noise. We propose Extended Kalman Filter(EKF) to improve estimation accuracy. The performance of proposed EKF is evaluated by simulation program. As a result, we confirm that the errors in estimate of mobile robot's position are eliminated from measured distance.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.258-263
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• 1999

In this study, the numerical and experimental investigations were conducted to understand ultrasonic wave propagation and to evaluate the degree of fiber waviness in thick composites nondestructively. The path, energy and traveling time of insonified wave were predicted by adopting the ray and plane wave theories. In the analysis, the composites were assumed to have continuous fiber with sinusoidal waviness in a matrix and were modeled as stacks of infinitesimally short length off-axis elements with varying fiber orientation along the length direction. From the experiments on the specially fabricated thick composite specimens with various degrees of uniform fiber waviness, the energy distributions of received wave were obtain for the various positions of transmitter. It was observed that the energy of wave was converged to the adjacent peaks of fiber waviness. The location where maximum energy of wave was detected from the experiments showed good agreement with the location obtained from theoretical predictions. Finally, the test procedure was Proposed to evaluate fiber waviness in thick composites by considering the energy of wave and relative distance between transmitter and receiver.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.33 no.3
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• pp.189-193
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• 1997

We make an ultrasonic system as a trial to measure the distance between trawl doors, and carried out a water tank ($24{\times} 24$m, water depth 1 m) experiment for confirming the practical use of the system in October 1996. This system calculates the distance between the pinger (50 kHz) and the transponder (50 kHz/70 kHz) attached each one on the trawl door by measuring the time-difference of receiving with two channels receiver on the trawler. This paper assums that both the length of the warp from the stern to the trawl door is same. At results the system shows a good relation between the distance and the time-difference of receiving while the location of the pinger is moved in variously in the water tank, and it was found that the method of measuring techniques on the prototype system could be applied to the measurement of the trawl door opening in the field experiment.