• Ocean and Polar Research
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• v.29 no.2
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• pp.113-121
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• 2007

The sound wave in the sea propagates under the effect of water depth, sound speed structure, sea surface roughness, bottom roughness, and acoustic properties of bottom sediment. In shallow water, the bottom sediments are distributed very variously with place and the sound speed structure varying with time and space. In order to investigate the seasonal propagation characteristics of low-frequency sound wave in the Yellow Sea, propagation experiments were conducted along a track in the middle part of the Yellow Sea in spring, summer, and autumn. In this paper we consider seasonal variations of the sound speed profile and propagation loss based on the measurement results. Also we quantitatively investigate variation of bottom loss by dividing the propagation loss into three components: spreading loss, absorption loss, and bottom loss. As a result, the propagation losses measured in summer were larger than the losses in spring and autumn, and the propagation losses measured in autumn were smaller than the losses in spring. The spreading loss and the absorption loss did not show seasonal variations, but the bottom loss showed seasonal variations. So it was thought that the seasonal variation of the propagation loss was due to the seasonal change of the bottom loss and the seasonal variation of the bottom loss was due to the change of the sound speed profile by season.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.210-215
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• 2001

CD-ROM Drives Rotating high speed as 10000 rpm cause serious noise and vibration problems. At the high speed, dominant noise is Air Borne Noise produced from high-speed airflow and Structure Borne Noise produced from structural vibration. In this research, vibration and sound characteristics in CD-ROM Drive were studied by the use of experimental analysis and computational simulation. Sound intensity techniques and ODS(Operational Deflection Shape) techniques are applied to identify the acoustic noise source of CD-ROM drive. And Computational simulation using SYSNOISE is conducted for describing the noise behavior.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.326-331
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• 2011

Aluminum extruded panel used in a high speed train shows high stiffness, however, its sound insulation performance is remarkably decreased by local resonance phenomena. In this paper, improvement strategy of the sound insulation performance is proposed for the floor extruded panel used in HEMU-400x, 400km/h class next generation high speed train under development, and the improvement effect is verified by experiment. Aluminum extruded panel specimen for the floor is manufactured and urethane foam is installed in the core of the panel. Based on ASTM E2249-02, intensity transmission loss is measured and the improvement effect in local resonance frequency band is verified. Finally, improvement effect of the sound insulation performance is estimated on the layered floor structure including the foamed aluminum panel.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.680-690
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• 2020

In ocean environment, the sound speed gradient of seawater has an important influence on far field sound propagation. The FEM/BEM is used to decouple the vibroacoustic radiation of the spherical shell, and the Green function of the virtual source chain is adopted for decoupling. For far field radiated Sound Pressure Level (SPL), the Beam Displacement Ray normal Mode (BDRM) is employed. The vibration and near-/far-field radiated SPL of spherical shell is analyzed in shallow sea uniform layer, negative/positive gradient, negative thermocline environment, and deep-sea sound channel. Results show that the vibroacoustic radiation of spherical shell acted at 300Hz can be analogous to dipole. When the radiated field of the spherical shell is dominated by large-grazing-angle waves, it can be analogous to vertically distributed dipole, and the far field radiated SPL is lower; while similar to horizontally distributed dipole if dominated by small-grazing-angle waves, and the far field SPL is high.

• Proceedings of the KSR Conference
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• 2009.05b
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• pp.457-462
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• 2009

In a high speed train, aluminium extruded panel is widely used in floor, side wall and roof structures for high bending stiffness and weight reduction. However, with some inevitable reasons, aluminium extruded panel shows inferior sound insulation performance compared with the flat panel having same weight. Especially, occurrence of local resonance modes in the particular frequency band, is one of the main reason in the deterioration of the sound insulation performance. Local resonance modes are generated in the structure which consists of periodic unit structure, such as the aluminium extruded panel. The local resonance frequency is determined by the specification of the unit structure. In this study, we predict the local resonance frequency band on the aluminium extruded panel used for the high speed train, and investigate how the design modification in the unit structure influences the local resonance frequency band and panel bending stiffness. The purpose of the study is to provide the design information for the effective unit structure in order to improve the sound insulation performance of the aluminium extruded panel.

• Journal of Electrical Engineering and Technology
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• v.12 no.6
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• pp.2378-2387
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• 2017

Violinists learn to make better sounds by hearing and evaluating their own playing though numerous practice. This study proposes a new method of auditory feedback, which mimics this violinists' step and verifies its efficiency using experiments. Making the desired sound quality of a violin is difficult without auditory feedback even though an expert violinist plays. An algorithm for controlling a robot arm of violin playing robot is determined based on correlations with bowing speed, bowing force, and sound point that determine the sound quality of a violin. The bowing speed is estimated by the control command of the robot arm, where the bowing force and the sound point are recognized by using a two-axis load cell and a photo interrupter, respectively. To improve the sound quality of a violin playing robot, the sounds information is obtained by auditory feedback system applied Short Time Fourier Transform (STFT) to the sounds from a violin. This study suggests Gaussian-Harmonic-Quality (GHQ) uses sounds' clarity, accuracy, and harmonic structure in order to decide sound quality, objectively. Through the experiments, the auditory feedback system improved the performance quality by the robot accordingly, changing the bowing speed, bowing force, and sound point and determining the quality of robot sounds by GHQ sound quality evaluation system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.457-462
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• 2011

The sidewall of the HEMU-400x consists of two parts. One is the multi-layered structure including aluminium extruded panel and the other is the double glazed window. When the train runs in a tunnel, the equivalent sound insulation performance of the side wall significantly influences the internal noise levels. In aspect of the sound insulation strategy, it is important to make two parts have similar performance. In this study, the intensity sound transmission loss (ITL) is measured on the specimens of the two parts. Mass law deviation (MLD) is considered in order to compare the sound insulation performance of the two parts in respect of the weight. Contribution of each part to the sound insulation is analyzed and the sound insulation strategy is investigated to reduce the interior noise.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.42.2-42.2
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• 2011

Noise generated from wind turbines has been predicted by numerical methods. Sound pressure level(SPL) on the turbines is predicted after aerodynamic analysis is carried out by Wind Turbine Flow, Aeroacoustics and Structure analysis (WINFAS) code. The level of each panel of acoustic sphere is determined by the sum of tonal, turbulence ingestion and airfoil self noise. With the noise source database, the acoustic sphere, SPL on the ground is calculated using the model based on acoustic ray theory. The model has been designed to consider the effects on the condition of terrain and atmosphere. The variations of SPL on the ground occur not only because of the different source level but also because of the nonuniform distributions of the sound speed along the height. Hence, the profile of an effective sound speed which is the sum of the contribution of sound speed to a temperature gradient and a wind speed variation is used by the theory based on atmospheric stability. With the integrated numerical method, the prediction of sound propagation on the wind farm is carried out with the states of the atmospheric stability.

• The Journal of the Acoustical Society of Korea
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• v.37 no.5
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• pp.276-283
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• 2018

The purpose of the study is to identify a sound generating organ that has a major influence on the central frequency of the cicadas with the Helmholtz resonator structure for the first time. The sound of cicadas Cryptotympana atrata and Hyalessa fuscata were recorded and analyzed, then the motion of the tymbals was analyzed with a high-speed camera to compare the relationship between the frequency of sound and the motion of the tymbals. As a result, there was little difference in the frequency distribution of calling song and scream for two species. The tymbals of C. atrata oscillated in three vibration modes, while those of H. fuscata oscillated in one mode. There was no difference in the frequency of both tymbals of both cicadas, and three vibration modes of C. atrata generated sound with different frequency bands. The frequency band of tymbals and the central frequency band of calling song were very similar. In conclusion, it is presumed that the frequency of the cicadas with the Helmholtz resonator structure was determined by mode frequency of the tymbals than resonance condition of the abdomen.

• Journal of Power System Engineering
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• v.12 no.4
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• pp.46-51
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• 2008

Honeycomb panel has a constructive advantage because it is constructed with a honeycomb core, so it has relatively higher strength ratio to weight. Therefore honeycomb panel has been used as the light weight panels in the high-speed railway technology and high-speed ship like as cruise yachts. Also it has been used in the aircraft and aerospace industry as a structural panel because light weight structure is indispensible in that field of industry. Recently, the honeycomb panel is embossed in the viewpoints of high oil prices as the lightweight panel of the transport machine, however the sound insulation capacity of the honeycomb panel is poorer than those of uniform and another sandwich panels. In this paper a method to improving the sound absorption coefficient of a honeycomb panel Is studied by using the Helmholtz resonator. The sound absorption coefficients for some kinds of honeycomb cores are demonstrated by the normal incident absorption coefficient method.