• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.12
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• pp.1511-1519
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• 2012

Pipe structures contain many welded zones, and ultrasonic tests are increasingly being performed by using automated testing devices in order to evaluate the weld integrity. An electromagnetic acoustic transducer (EMAT) is a noncontact transducer that can transmit or receive ultrasonic waves without a couplant. Furthermore, it can easily generate specific guided waves such as SH (shear horizontal) or Lamb waves by altering the design of the coil and magnet. Therefore, an EMAT should be useful for application to an automated ultrasonic inspection system. In this study, SH waves generated using an EMAT were applied to inspect the pipe-weld zone. To analyze the specific SH mode (SH0) from the SH wave signals, wavelet transform was applied. It was found that flaws could be detected precisely because the intensity of the $SH_0$ mode-frequency, which is analyzed by using wavelet transform, is proportional to the length of the flaw.

• Geophysics and Geophysical Exploration
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• v.1 no.3
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• pp.183-187
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• 1998

Seismic waveform estimation is based on the assumption that the seismic trace tying a well is one dimensional convolution of the propagating seismic waveform and the reflectivity series derived from well logs (sonic and density). With this assumption, the waveform embedded in a seismic trace can be estimated using a Wiener match filter. In this paper, I experimented a preprocessing procedure that applies both on the seismic trace and on the reflectivity series. The procedure is based on the assumption that the travel time can be estimated better from the seismic trace and that the instantaneous reflectivity values can be measured better on the well log. Thus the procedure is, 1) start-time adjustment and dynamic differential stretches are applied on the sonic log, and 2) seismic amplitudes are balanced such that the low frequency part of the seismic are matched to that of the reflectivities derived from well logs.

• Journal of the Korean Institute of Intelligent Systems
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• v.20 no.6
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• pp.831-836
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• 2010

In real system application, the path planning and following system for the coordinated control of heterogeneous marine robots based on the underwater acoustic communication has the following problems: surface and underwater robots have different maneuvering properties, an underwater robot requires more effective operating, it has a limited communication range because of the transmission loss (TL) of acoustic wave, it has a communication error because of the Doppler distortion of acoustic wave, and further, it requires an easy design procedure in terms of its structures and parameters. To solve these problems, an intelligent path planning algorithm using the evolution strategy (ES) and the fuzzy logic controller (FLC) based on system modeling, is proposed. To verify the performance of the proposed algorithm, the path planning and following of an underwater robot is performed according to the maneuvering of a surface robot. Simulation results show that the proposed algorithm effectively solves the problems.

• Journal of the Korean Geotechnical Society
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• v.19 no.3
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• pp.83-91
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• 2003

The electrokinetic technique has been applied to remove mainly the heavy metal and the ultrasonic technique to remove mainly organic substance in contaminated soil. In this study, the combined electrokinetic and ultrasonic remediation technique was studied far the removal of heavy metal and organic substance in contaminated soils. This study emphasized the coupled effects of electrokinetic and ultrasonic techniques on migration as well as remediation of contaminants in soils. The laboratory soil flushing tests combining electrokinetic and ultrasonic technique were conducted using specially designed and fabricated devices to determine the effect of both of these techniques. A series of laboratory experiments involving the simple, electrokinetic, ultrasonic, and electrokinetic & ultrasonic flushing test were carried out. A soil admixed with sand and kaolin was used as a test specimen, and Pb and ethylene glycol were used as contaminants of heavy metal and organic substance. An increase in out flow, permeability and contaminant removal rate was observed in electrokinetic and ultrasonic flushing tests. Some practical implications of these results are discussed in terms of technical feasibility of in situ implementation of electrokinetic ultrasonic remediation technique.

• The Journal of the Acoustical Society of Korea
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• v.41 no.2
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• pp.131-142
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• 2022

In order to examine the possibility of horizontal simulations of acoustic waves on the environments of big water depth variations, this study introduces a 3-dimensional model based on the pababolic equation. The model gives approximated solutions by separating the cross- and non cross-terms in the equation. Assuming artificial bathymetry (25 km × 4 km) with a source frequency 75 Hz, the simulations give clear horizontal refractions on the transmission loss distributions. The degree of refractions shows non-linear increase along the propagating range and proportional increase with water depth along the cross range. Another simulations with the real bathymetry (25 km × 8 km) also give clear horizontal refractions. The horizontal distributions present little difference with the depth resolution variations of the same data source because the model gives interpolations over the depth data before simulations. Meanwhile, the horizontal distributions show big difference with those of different data sources.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.233-233
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• 2021

ADCP(Acoustic Doppler Current Profiler)는 유수의 흐름을 방해하지 않으면서 수중에 발사된 음파의 도플러 효과를 이용하여 3차원 유속 측정이 가능한 초음파 유량측정장비이다. 2009년부터 다양한 하천에서 ADCP 사용량이 증가하면서 ADCP를 이용한 유량측정 기법과 현장 적용상의 문제, 자료처리 과정에서의 문제점들이 발생하고 있다. 이런 문제점들을 분석한 결과 다음과 같은 사례들이 나타났다. 첫 번째 하상이 매우 불규칙한 단면의 부적절한 측정 사례, 두 번째 하안 수직벽 존재에 따른 단면의 부적절한 측정 사례, 세 번째 수심 오측이 다수 발생한 측정 사례, 네 번째 유속 프로파일 결측이 다수 발생한 측정 사례, 다섯 번째 통신문제로 인한 주기적인 결측이 발생한 측정 사례, 여섯 번째 홍수기 고농도 유사로 인해 결측이 발생한 사례, 일곱 번째 수중식생의 영향으로 수심 및 유속 프로파일 오측이 발생한 측정 사례, 여덟 번째 이동상 조건이 발생한 측정 사례 등 많은 문제들이 발생하였다. 본 연구에서는 수중식생의 영향으로 수심 및 유속 프로파일 오측이 발생하는 사례에 대해 개선할 수 있는 방안을 연구하였다. ADCP에서 수중에 발사한 음파 중 식생에 부딪친 강한 반사파의 노이즈로 side-lobe현상에 의한 오측 및 결측이 발생한다. 현재 오측 및 결측 자료는 ADCP 제조사별 자료 취득 소프트웨어의 기능에 의존 하거나, USGS의 OSW(Office of Surface Water) Hydroacoustics의 QRev를 이용하여 후처리 과정을 거쳐 측정 자료로 정리하고 있다. 이에 본 연구에서는 노이즈로 인한 side-lobe 현상을 물리적인 방법으로 제거하기 위해 음향 녹음 과정에서 노이즈를 물리적인 방법으로 제거하는 윈드실드와 팝 필터를 고려한 ADCP필터를 개발하여 적용하였다. 이번 연구의 대상지점은 원주시(지정대교)수위관측소로 5월 이후 수중에 식생이 성장하는 지점이다. 먼저 ADCP필터를 제거한 상태에서 측정을 실시하고, 이후 ADCP필터를 장착하여 측정을 실시하였다. ADCP필터 적용의 측정성과에서는 노이즈에 의한 오측 및 결측이 다수 발생하는 것을 볼 수 있고, ADCP필터를 적용한 측정성과에서는 노이즈가 제거되어 오측 및 결측이 개선되는 결과를 볼 수 있었다. 본 연구에서는 수중식생 영향으로 강한 반사파에 의한 노이즈로 side-lobe현상에 의한 ADCP측 정성과의 오측 및 결측을 ADCP필터를 적용하여 물리적인 방법으로 노이즈를 제거 할 수 있다는 결과를 얻었다.

• The Journal of the Acoustical Society of Korea
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• v.25 no.8
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• pp.395-402
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• 2006

When an active SONAR works in the subsurface. its detection Performance is limited by the reverberation. The winds Play a primary role in the Production of bubbles in the ocean. And the bubbles as efficient scatters contribute to the reverberant field. In this Paper the effects of wind-generated bubbles on sound propagation in the subsurface are investigated as a mid-frequency Hull-mounted SONAR works. The active signal excess is calculated at source depths 3. 5. and 10m considering bubble layer for frequencies 5. 7.5, and 10kHz. The change of the near-surface sound speed tend to increase surface reverberation levels and change the active signal excess. In the 10m/s winds. the maximum detection range reduces over 3km through the near-surface . The reason is the upper refraction due to the wind-generated bubbles.

• Journal of the Korean Academy of Clinical Electrophysiology
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• v.1 no.2
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• pp.31-38
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• 2003

This study was to compared the effectiveness of piroxicam gel phonophoresis with conventional ultrasound therapy in knee osteoarthritis. Eighteen patients with a means age of $55.7{\pm}5$ years were randomly assigned to phonophoresis or ultrasound groups. Continuous ultrasonic waves of 1 MHz frequency and $1\;W/cm^2\;SATA_i$ were applied for 5 minutes to the target knee joint. This study indicated their pain level by marking on a visual analog scale(VAS) at the start of treatment and at the end of 3day. Osteoarthritis VAS scores, pain on rest state, non weight bearing range of motion, 20 meters walking, and walking step by the patients were evaluated before and after therapy. Both therapeutic modalities were found to be effective and generally well tolerated after 3 therapy sessions. But piroxicam phonophoresis was not superior to conventional ultrasound in patients with knee osteoarthritis.

• The Journal of the Acoustical Society of Korea
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• v.7 no.4
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• pp.110-116
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• 1988

The thermal front over the shallow coastal seas of Korea during the winter season provides very unique acoustic media such that wave equation is easily separable and the solutions turn out to be very simple and well known. In steady of using the WKB method to solve the radial equation the mode technique have been applied to obtain the solution. The radial propagation is rather weakly influenced by the presence of the thermal front that causes the horizontal variations of the sound speed. The physical description of the sound propagation is also presented in terms of ray tracing.

• Journal of the Korean Academy of Clinical Electrophysiology
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• v.2 no.1
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• pp.39-48
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• 2004

The study was to determine the effect of local anesthetics phonophoretic. Emla 5%(lidocaine+prilocaine) cream make use of medicines. Phonophoretic the application of a ultra sound(I group), application an ointment(II group). Forty college student between the age of man $22.85{\pm}3.31$ woman $21.05{\pm}2.12$, weight of man $70.70{\pm}9.43\;kg$ woman $50.65{\pm}5.13\;kg$, height of man $17.6{\pm}5.43\;cm$ woman $161.20{\pm}4.34\;cm$ were in this study. The results was as follows. There was statistical difference between I group($49.25{\pm}10.83$) and II group($58.90{\pm}10.83$) for the timing of local anesthetics(p<.05).