• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.473-474
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• 2011

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.2
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• pp.117-125
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• 2000

The waveform and spectrum analysis of Tursiops truncatus(bottlenose dolphin) sonar signals were carried out on the basis of data collected during the dolphin show at the aquarium of Cheju Pacificland from October 1998 to February 1999. When greeting to audience, the pulse width, peak frequency and spectrum level from the five dolphins'sonar signals were 3.0ms, 4.54kHz and 125.6dB, respectively. At the time of warm-up just before the show, their figures were 5.0㎳, 5.24kHz and 127.0dB, respectively. During the performance of dolphins, with singing, peak frequency ranged 3.28∼5.78kHz and spectrum level ranged 137.0∼142.0dB. With playing ring, pulse width, peak frequency and spectrum level were 7.0㎳, 2.54kHz and 135.9dB, and when playing the ball, the values were 9.0㎳, 2.78kHz and 135.2dB, respectively. The values determined from the five dolphins during jump-up out of water were : pulse width 2.0㎳, peak frequency 4.50kHz and spectrum level 126.8dB. When they responded to trainer's instructions, the values were 2.25㎳, 248kHz and 148.7dB, respectively, and greeting to audience, the peak frequency and spectrum level were 5.84kHz and 122.5dB. During swimming under water, peak frequency and spectrum level were determined to be 10.10kHz and 126.8dB. It was found that there exited close consistencies in pulse width, frequency distribution and spectrum level between whistle sounds and dolphin's sonar signals. Accordingly, the dolphins can be easily trained by using whistle sound based on the results obtained from the waveform and spectrum of the dolphin's sonar signals.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.797-803
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• 2000

Recently, the singing phenomenon was encountered during the sea trials of high speed catamaran and 46,000 TDW product carrier and remedied after various treatments, which were based on the reduction of vortex shedding strength and the avoidance of resonance, respectively. And, the numerical approach for structure-acoustical problem like singing phenomenon was established using MSC/NASTRAN and SYSNOISE. In this paper, the effectiveness of numerical approach was verified through the control of singing noise. And the results according to the modification were also discussed. Finally, the future works were described to enhance the numerical approach pattern for singing phenomenon.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.5
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• pp.343-348
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• 2013

When a natural frequency of the trailing edge of a wing is close to a vortex shedding frequency, an amplitude of the edge oscillation becomes maximal; it makes intensive noise called singing. Motion of the trailing edge may also feedback to the vortex shedding so that self-sustained oscillation appears, and a resonant frequency is locked in some interval of the speed of the incident flow. In this study, we first evaluate main features of oscillating characteristics of the wing. Second we simulate fluid-structure interaction of the wing with a flap using a commercial code, ANSYS-CFX, and investigate lift characteristics in a frequency domain.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.753-756
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• 2013

The demand for sailing yacht is increasing in consonance the improvement of people's live. These yachts can be dually propelled by wind and by diesel engine power. A singing (humming, whistling) phenomenon induced on the propeller was discovered on a 55-foot catamaran sailing yacht. As a result, an increase in the structural vibration of the stern tube room and propulsion system with abnormal noise was detected due to this flow. In this study, the cause of the phenomenon is investigated and its possible countermeasures proposed.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.3
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• pp.233-237
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• 2011

In the present experiments, vortical structures behind the hydrofoil trailing edge are visualized and analyzed as an elementary study for propeller singing phenomena. Two sorts of hydrofoil are selected for the measurement of shedding vortices. One was KH45 hydrofoil section and the other is KH45 with the truncated trailing edge that is positioned at X/C = 0.9523(C=chord length). Assuming the Strouhal number of 0.23, the shedding frequencies of vortices are extracted by analyzing the boundary layer thickness and the flow speed. The frequency distribution of shedding vortices is obtained with the variation of angle-of-attack while the flow speed is fixed to 8m/s. The truncation of the trailing edge makes the frequency of shedding vortices about 120Hz lower than that of original trailing edge and makes the vorticity value higher than the original trailing edge.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.2
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• pp.121-127
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• 2011

As considerable interests in noise emission from a ship have been increased, the need for localization of noise sources of the marine propeller generating cavitation and singing noise is looming large. In many practical cases, cavitation and singing noise occur on a particular position of the certain blade of the propeller. It is so important to know the position of noise source correctly in order to eliminate or suppress unwanted noise. In this study, we develop "noise source localization technology" using TDOA method. Experimental measurements carried out at the circulating water channel and towing tank show that noise source can be clearly identified and localized using TDOA method.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.3
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• pp.59-64
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• 1994

A study was conducted to investigate the propeller singing place of an 86, 000 ton Deadweight Crude Oil Tanker. In preliminary study, proper use of finite element analysis was verified by comparing with the result of hammering test in the air. Then the finite element analysis was carried out for the blade in the water and compared with the noise measurement during sea trial, which enabled to confirm the local resonances of blade structure. Result of the study showed that the singing occurred most probably at trailing edges on the blade tip over 95% of propeller diameter. Owing to edge cutting of a successfoul remdial action, the singing excitation forces seemed to be reduced whereas the vibration characteristics of the blade was not changed.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.43 no.3
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• pp.206-211
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• 2007

The sciaenid species, which has swimbladder, generates sounds by vibrating in its length wards when spawning or getting stimulus from something else. This research analyzed on sound frequency characteristics relatives to their swimbladder length of three sciaenid species, yellow croaker(Larimichthys polyactis), brown croaker(Miichthys miiuy), and white flower croaker(Nibea albiflora). As results, the dominant frequency for yellow croaker ranged over 38.08 to 141.60Hz in wide frequency band, and the averaged pulse duration expressed in $280.3{\pm}156.0ms$. For brown croaker, the dominant frequency ranged in 49.80 to 59.57Hz, and the averaged pulse duration was $129.1{\pm}36.9ms$. Moreover, the dominant frequency of white flower croaker ranged in 73.24 to 86.91Hz, and the averaged pulse duration was $88.0{\pm}15.9ms$, it has shorter pulse duration than any two species. Therefore, the dominant frequency relatives to swimbladder length of sciaenidae showed that it had widely resonant characteristics and long pulse duration as in shorter swimbladder length. Additionally, for white flower croaker, we could confirm their behavior and sounds in response to production of recorded sounds using underwater speaker.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.51 no.2
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• pp.195-202
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• 2015

Hundreds of Steller sea lions, Eumetopias jubatus, migrate from Sakhalin and the northern Kuril Islands to Hokkaido in Japan every winter. During this migration, they may use their roaring sounds to navigate and to maintain their groups. We recorded the roars of wild Steller sea lions that had landed on reefs on the west coast of Hokkaido, and those of captive sea lions, while making video recordings. The fundamental frequency ($F_0$), Formant frequency ($F_1$), pulse repetition rate (PRR), and duration of syllables (T) were analyzed using a sonagraph. $F_0$, $F_1$, and PRR of the roars emitted by captive sea lions increased in the order male, female. By contrast, the $F_1$ of wild males was lower than that of females, while the $F_0$ and PRR of wild males and females did not differ statistically. These results suggest regional differences between the five groups showed that.