• Journal of the Korean earth science society
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• v.28 no.3
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• pp.367-373
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• 2007

A geoacoustic modeling has been developed to predict sound transmission through the submarine layers of sediment and rock. It demands a geoacoustic model with the measured, extrapolated, and predicted values of geoacoustic parameters controlling acoustic propagation. In the coastal areas of Okgye and Bukpyeong, the East Sea, the marine succession consists of Quaternary/Tertiary deposits and acoustic basement. The basement of Okgye coastal area is indicative of siliciclastics of the Pyeongan Group in Paleozoic, and the average velocities of P-wave and S-wave are 4276 m/s and 2400 m/s, respectively. The basement of Bukpyeong coastal area is indicative of limestone of the Joseon Supergroup in early Paleozoic, and the average velocities of P-wave and S-wave are 5542 m/s and 2742 m/s, respectively.

• Journal of the Korean Society for Marine Environment & Energy
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• v.19 no.4
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• pp.247-258
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• 2016

Physical and acoustic properties of sediment on the southwestern Taean Penisula, the Yellow Sea, were studied using eight piston cores. The sediments in the study area are largely composed of sand which has been deposited with sea-level change after LGM(Last Glacial Maximum). After the sea-level rise, fine-grained sediments discharged from Keum River and neighboring coast area were deposited as muddy sand or sandy mud. Results of these sedimentary environment in this area, the texture of sediments are different from place to place with variable horizontal and vertical distribution of physical and acoustic properties. Correlations among the physical, geoacoustic properties, and mean grain size show slight deviations from those of the South Sea in spite of similar pattern. This is probably due to the differences in sedimentary environment, mineral composition, and measurement system.

• The Journal of the Acoustical Society of Korea
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• v.15 no.6
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• pp.52-58
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• 1996

Using the acoustic resonances and oscillatory pulsations considered as the branch of wave technologies, the concept of the acoustic resonance diffusers for waste water treatment which maximize the oxygen transfer efficiency in gas-liquid two phase medium have been proposed, and studies for the principles and performance tests were accomplished. Besides, the design concepts for the low pressure Helmholtz resonator, cylinder and annular type reflection resonator and combined type resonance system have been implemented. The acoustic resonance energy which can speed up the mass transfer process increase the oxygen transfer efficiency, and periodic pulsations generated from the instability of air jet from nozzle make very small air bubbles. Then, the annular type jet resonator(AJR) applying these two principles successfully was evalulated as the most promising device and also the efficiency showing $20{\sim}30%$ better than conventional diffusers has been verified experimentally.

• The Journal of the Acoustical Society of Korea
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• v.34 no.3
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• pp.184-191
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• 2015

In this paper, a normal mode reverberation model for a range-independent environment of shallow water is proposed to calculate the reverberation level in the low-frequency range. Normal mode is used to calculate the acoustic energy propagating from the source to the scattering area and from the scattering area to the receiver. Each mode is decomposed into up and down going waves to consider scattering strength at the scattering area. The scattering functional form combines Lambert's law with a Gaussian-like term near the specular direction based on Kirchhoff approximation considering bottom condition. For verification of the suggested model, the result is relatively compared to several solutions of the problem XI and XV in the Reverberation Modeling Workshop I sponsored by the US Office of Naval Research.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.4
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• pp.892-898
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• 2008

3D rapid prototyping is the manufacturing technology to fabricate a prototype with the data stored in a computer, which differs from conventional casting technology in terms of an additive process. Various 3D rapid prototyping techniques such as stereolithograpy. fused deposition modeling. selective laser sintering, laminated object manufacturing have been developed but among them, 3D inkjet printing has a unique feature that materials could be jetted to directly form the body of a prototype, which could be a finished product functionally and structurally. However, this needs ink with a high solid content, which tends to increase the dynamic viscosity of ink. The increase of ink viscositytends to restrict the jettable range of ink and hence the jetting conditions should be optimized. The intrinsic speed of sound in a hot melt ink with ceramic nanoparticles dispersed is one of key components to determine the jettable range of ink. In this paper, the way to measure the intrinsic speed of sound in a hot melt ceramic ink is proposed and its influence on the jetting condition is discussed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.5
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• pp.1259-1268
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• 2015

The sonic layer depth (SLD) variability is important for understanding the acoustic properties of the upper ocean that influence acoustic communications, acoustic tomography, and naval operations related to searching and detecting marine underwater vessels. Generally, the SLD is the acoustical equivalent of the mixed layer depth (MLD), although they are defined differently. In this study the SLD was compared with the MLD over the annual cycle in the East Sea using an available set of temperature-salinity observation profiles. For the comparison, various definitions and methods of the MLD had applied. As a result, the SLD in the East Sea is slight similar to the curvature method applied MLD, but the other MLD have severe differences with the SLD. Futhermore, a parabolic equation transmission model is used to evaluate the cutoff frequency trapped in surface duct. It follow that there is an optimum frequency for propagation at which the loss of sound is minimum.

• The Journal of the Acoustical Society of Korea
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• v.23 no.8
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• pp.576-582
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• 2004

A computer code that is based on the Pseudo-spectral finite difference algorithm using staggered grid is developed for the wave propagation modeling in the time domain. The advantage of a finite difference approximation is that any geometrically complicated media can be modeled. Staggered grids are advantageous as it provides much more accuracy than using a regular grid. Pseudo-spectral methods are those that evaluate spatial derivatives by multiplying a wavenumber by the Fourier transform of a pressure wave-field and performing the inverse Fourier transform. This method is very stable and reduces memory and the number of computations. The synthetic results by this algorithm agree with the analytic solution in the infinite and half space. The time domain modeling was implemented in various models. such as half-space. Pekeris waveguide, and range dependent environment. The snapshots showing the total wave-field reveals the Propagation characteristic or the acoustic waves through the complex ocean environment.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.24 no.5
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• pp.289-302
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• 1991

Laboratory determination of acoustic property for unconsolidated sediment of Kwangyang Bay was carried out. The compressional wave velocity was correlated to other physical properties and sediment textures to establish a geoacoustic model of the bay. The model was compared to the North Pacific continental terrace sediment. Velocity of the bay is systematically lower(0.02-0.04km/s) than that of the North Pacific. Average velocity of the bay is 1.521km/s. The lowest velocity is measured at the southwestern part of the bay. This area coincides with high amount of fine-grained sediment related to slower circulation. The overall tendency is, however, similar to the North Pacific continental terrace sediment.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.8
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• pp.1465-1471
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• 2007

The electro-magnetic wave propagates through the air in the terrestrial communications, but the acoustic wave propagates through the seawater in the underwater acoustic communication(UAC). It makes the differences between the UAC link and the well hon air communication links. In this paper, we have studied path loss, absorption and ambient noise of the ocean as a medium for UAC. We have analyzed the absorption coefficient and ambient noise level of the coastal area of South Korea and suggested a strategy for the selection of the frequency band by considering the absorption coefficient and ambient noise level. Also, we present an illustrative example of a link budget for the QPSK UAC system which has carrier frequency 25kHz, bit rate 10kbps, range 1km and BER $10^{-3}$ in the shallow water environment with an ideal AWGN assumption.

• The Journal of the Acoustical Society of Korea
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• v.28 no.4
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• pp.328-335
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• 2009

Phase variance of the acoustic signals has to be investigated with the research of the medium, because the phase of the acoustic signals carries the information of the medium. The phase compensation of the received signals is required for the signal processing of SAS (Synthetic Aperture Sonar) and underwater communication. In this paper, the phase variance of the acoustic signals was studied depending on the micro-scale-turbulence of ocean. The turbulence strength of the locally isotropic and homogeneous turbulence was calculated, and the phase variance affected by the turbulence strength was computed along the ray paths. The CTD and ADCP data were acquired from a buoy system near the Mukho port in the East Sea of Korea and the ray paths were calculated by the Bellhop algorithm. As a result, the turbulence strength was mainly determined by the variation of temperature and flow speed, changing the phase variance of the received signals. Hence, we thought the phase variance should be considered in the sonar operating system.