• 한국소음진동공학회논문집
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• 제12권6호
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• pp.437-444
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• 2002

This paper is to provide the basic way of a acoustical evaluation and efficient control noise by investigating the limits of perceptual loudness of living environment and by finding out any correlation between Physical characteristics of noise and psychoacoustic parameters. The limits of perceptual loudness were selected by the subjects in a chamber for residential and working environment. And the noise sources were analyzed to find out whether there is any correlation with Zwicker parameters and ACF factors. In this study especially, to set up the domestic evaluation grade about floor impact noise. we'd like to suggest the loudness Perception research result as fundamental resource for setting up the evaluation grade through the result that is based on annoyance. In the result of this research, upper limit of heavy-weight impact noise was L-60, and lower limit of it was L-50. On the other hand, upper limit of light-weight impact noise was L-70, and lower limit of it was L-55. It seemed that the loudness of noise from vacuum cleaner noise does not affect its perceived noisiness. Noises implicated In human such as floor walking noise and talking sound, are the most irritating noise in office environment.

• 비파괴검사학회지
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• 제30권5호
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• pp.437-443
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• 2010

최근 재료, 생물의학(biomedicine), 음향, 전자 등 다양한 분야에서 나노 구조를 갖는 박막 기술이 도입되면서 박막 계면의 수명과 내구성 확보를 위한 초고주파수의 초음파현미경을 이용한 정량적인 비파괴적 접합평가에 관한 연구가 큰 이슈가 되고 있다. 본 연구에서는 초음파의 집속, 누설탄성표면파의 발생과 V(z) 곡선의 시뮬레이션 그리고 초고주파수 음향 이미징 기법을 이용하여 나노 스케일 구조를 갖는 박막 시험편의 접합계면을 평가하였다. V(z) 곡선의 컴퓨터 시뮬레이션을 통하여 접합계면에 존재하는 미세 결함(디라미네이션 등)의 검출 감도를 추정할 수 있었으며, 1 GHz의 초고주파수 디포커싱 모드로 박막 시험편의 접합계면에 존재하는 나노 스케일의 미세 결함을 음향 이미지로 가시화 할 수 있어 나노 구조를 갖는 박막의 접합계면의 비파괴평가에 초음파현미경이 매우 유용함을 알 수 있었다.

• 수산해양기술연구
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• 제52권1호
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• pp.36-41
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• 2016

Changes in target strength (TS) values of sandfish when sandfish was alive and dead were investigated using ex-situ at 120 kHz. TS values measured by tilt angles with -50~+50 degrees showed ranges from -71.0 to -53.3 dB for live sandfish, -63.1~-46.3 dB for thawed sandfish, and -70.0~-50.4 dB after 24 hours from thawed, respectively. It was shown that while TS values were similar between the case of live and the case of after 24 hours from thawed, mean TS values were higher by approximately 5 dB in the case of immediate thawed sandfish. It was also seen that TS values were similar between the case of thawed sandfish and the case of after 21 hours from live. The results showed that TS values of live sandfish were different from those of frozen sandfish. It implies that when estimating TS of frozen fish, the influx of bubbles and changes of body should be considered.

• 수산해양기술연구
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• 제51권3호
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• pp.405-413
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• 2015

Acoustic target strength (TS) measurement and theoretical acoustic scattering models were applied to estimate the TS for assessing the fish biomass. TS measurement was made of ex situ sailfin sandfish Arctoscopus japonicus at 70 and 120 kHz, and then compared to backscatter model prediction. The live sandfish was tethered in seawater using monofilament lines. Measurements were made versus incidence angle, $-50^{\circ}$ to $50^{\circ}$ relative to dorsal aspect directions. Distorted wave Born approximation (DWBA) model was used to calculated TS pattern. The TS values of sandfish (body length: 16.2 cm) at 70 and 120 kHz were -66.94 dB and -64.45 dB, respectively, and were about 20 dB lower than TS of other fishes in Korea waters. These TS levels were distributed within the range of the theoretical TS. Ex situ measurement and theoretical TS may be applied to improve acoustical detection and biomass estimation of the sandfish, and is necessary to measure with various lengths.

• 수산해양기술연구
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• 제47권1호
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• pp.27-36
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• 2011

Squid by-product like viscera has just been recognized as one of the serious pollutants on the surrounding marine environment in Ulleung island of Korea. The effect as a marine pollutant, however, has not been examined and evaluated properly. It was carried out the comprehensive examination of the marine pollution by disposing squid by-products. The sediments and water qualities were investigated in several positions, including the dumping position around Ulleung island. It is also estimated a spreading of by-product in terms of estimating the sinking speed and evaluating the attracting characteristics as a feed. As a result, There were no significant pollutions of the sediment and water quality. The spreading of by-product by the local current was 2-2.5 times of the depth, and it will become longer in spring tide. It was confirmed that the squid by-product has attracting ability for local fish by acoustical survey. Furthermore, it can be useful for the local fish species as feeds.

• 수산해양기술연구
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• 제49권3호
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• pp.270-281
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• 2013

Hydro-acoustic surveys with scientific echo sounder were carried out to estimate the total density and distribution of the juvenile cod in Jinhae bay, Korea. The surveys were conducted 4 times from May to June using 2 frequency method (38kHz and 120kHz) and beam trawl were used to investigate the species composition. Also the catch amounts of juvenile cod were compared with the cod density estimated by the hydro-acoustic method. It was confirmed that the juvenile cod was stayed in Jinhae bay in early June and There was the relationship between catch of juvenile cod and the estimated density by hydro-acoustic survey. The number of juvenile cod was consequently about 365,000 fish (CV 12.9%) in May and 113,000 fish (CV 9.2%) in May based on the hydro-acoustic data.

• 대한기계학회논문집A
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• 제30권2호
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• pp.202-209
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• 2006

As the economic power is improved and the customer's demand is hard to please, the noise and vibration is the most important yardstick that can determine the quality of the product. Especially, as the airconditioner's demand increase suddenly, the product of quality and the noise is becoming a decisive factor of determining whether purchase the product or not. Therefore, every manufactory is investing a lot of money and research to cut down the unpleasantness induced from noise and vibration. And they are emphasizing their product's difference by advertising a silence very actively. With these reason, the demand of a silent indoor air-conditioner is the essential research filed when the product is develop(:d. In this study, the noise and vibration is visualized in the space and frequency domain by using experimental methods such as operational deflection shape (ODS), modal testing and sound intensity. Also the location of noise source and its characteristic is analyzed in an acoustical point of view to reduce the structure borne noise that come from the fan motor, and the pertinent control method is suggested. Furthermore, the most suitable shape of the motor bracket is suggested by applying FEM and DOE (Design of experiments) in the noise and vibration point a view.

• 대한기계학회논문집B
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• 제25권10호
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• pp.1327-1336
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• 2001

The structural modes driven by the low wave-number components of smooth elastic wall pressure provide a relatively weak coupling between the flow and the wall motion. If the elastic thin plate has any resonant mode whose wave-number of resonance coincides with $\omega$/U$\sub$c/, the power will be transmitted to those modes of vibration by the flows. We examine the problem in which the elastic thin plate is subject to pressure fluctuations under turbulent boundary layer. Measurements are presented of the frequency spectra of the near- and far-field pressures and radiated sound contributed by the various wave modes of the thin elastic plate. Dispersion equation for wave motions of elastic plate is used to investigate the effect of bending waves of relatively low wave number on radiated sound. The low wave-number motion of elastic plate is observed to have much less influence on the low-frequency energy of wall pressure fluctuations than that of the rediated sound. High amplitude events of the wall pressure are observed to weakly couple with high-frequency energy of radiated sound for case of low tension applied to the plate. The sound source localization is applied to the measurement of radiated sound by using acoustic mirror system.

• 수산해양기술연구
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• 제52권3호
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• pp.276-280
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• 2016

This study investigated luring distributions by water layer of common squid which were targeted by angling fishing vessels equipped with LED and metal-halide lamps using a scientific echosounder with a 120 kHz frequency in order to develop energy-effective underwater fish aggregation devices. In the analysis, angles of a transducer were changed from $0^{\circ}$ to $45^{\circ}$ and were rotated every $10^{\circ}$ horizontally. It was shown that common squid were densely distributed from the surface to 40 m and they were also distributed in directions of $10^{\circ}{\sim}+30^{\circ}$, $-30^{\circ}{\sim}-60^{\circ}$, and $-120^{\circ}{\sim}-130^{\circ}$with the head of vessel as the center. Comparative results of angles of transducer on acoustical densities of common squid distributing in 21~40 m water depth showed an average $101.8m^2/nm^2$ in vertical direction of $0^{\circ}$, $12.3m^2/nm^2$ in angle of $30^{\circ}$, and $42.4m^2/nm^2$ in angle of $45^{\circ}$, respectively. It implied that more considerations on acoustic scattering strength by incidence angle direction of the transducer and swimming oriental angle direction of common squid would be required.

• 말소리와 음성과학
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• 제3권3호
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• pp.133-140
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• 2011

Muscle misuse dysphonia (MMD) is defined as a behavioral voice disorder resulting from inappropriate contractions of intrinsic and/or extrinsic laryngeal muscles. The purpose of this study was to investigate the effect of motor learning guided laryngeal motor control therapy (MLG-LMCT) which is designed to improve an existing LMT and further the effective voice treatment on people with muscle misuse dysphonia. Forty-six people with MMD (M:F=16:30) participated in this study. The voice samples of the participants were recorded to investigate the effect of MLG-LMCT before and after the voice therapy. Voice samples were analyzed via electro-glotto-graph (EGG). Contact quotient (CQ), speed quotient (SQ), and waveform were reported. In addition, perceptual and acoustical evaluation were conducted to determine the change of voice improvement after treatment. The experimenter massaged the tensioned muscles around the neck. In order to find more proper phonation the experimenter showed the subjects their EGG wave forms as to whether or not they are moving the vocal folds to the appropriate position. Therefore, the EGG wave forms were used as a type of visual feedback. With the wave form, the experimenter helped subjects move the vocal folds and laryngeal muscles to find more proper voice production. The sensory stimuli from the experimenter gradually faded out. A paired dependent t- test revealed that there was significant differences in CQ between pre- and post-therapy. Perceptually, overall, rough, breathy, strain, and transition were significantly reduced. Acoustically, there were significant differences in Fo, jitter, shimmer, and NHR. After using MLG-LMCT, most of the subjects showed improvements in voice quality. The results from this study led us to the following conclusions: Motor learning guided laryngeal motor control therapy (MLG-LMCT) has reduces muscle misuse dysphonia. These results may occur because a visual feedback from EGG wave form can maintain the effect of the muscle tension reduction from laryngeal manual therapy. In case of people with MMD who reduced muscle tension from the therapy (LMT) but, not appropriately manipulating the location of larynx or adducting the vocal folds, MLG-LMCT might be an alternative therapy approach.