• The Journal of the Acoustical Society of Korea
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• v.23 no.2
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• pp.134-145
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• 2004

The study aims to develop the underwater wireless telephone system. The system is designed based on the underwater acoustic communication channel parameters such as ambient noise, multipath effect and diver breathing noise. The system adopts SSB modem and its carrier frequency is about 33 kHz in which ambient noise level is low and therefore a high S/N ratio is easily obtained. The source level of the transmitter is designed as 131 dB re 1μPa. Its intelligibility index of sentence shows as 80% or mure in the range of less than 300m in the sea trial.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.377-384
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• 2014

The requirement of acoustic material which is used in underwater environment more increases. The material is used to reduce acoustic signature and radiate noise for underwater vehicle. Underwater acoustic material was made by viscoelastic material such as a rubber and a polyurethane etc. The mechanical and acoustic characteristics of these material change with hydrostatic pressure. In order to increase an acoustic performance according to hydrostatic pressure, several kinds of scatterers were added to viscoelastic material. In this paper, acoustic modelling and analysis techniques of underwater acoustic material with hydrostatic pressure were introduced and proposed. The specimens for pulse tube test were made and echo reductions were calculated and measured with hydrostatic pressure. Also the characteristics of echo reduction of the specimens with hydrostatic pressure were obtained and discussed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.11
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• pp.868-875
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• 2014

The requirement of acoustic material which is used in underwater environment more increases. The material is used to reduce acoustic signature and radiate noise for underwater vehicle. Underwater acoustic material was made by viscoelastic material such as rubber and polyurethane etc. The mechanical and acoustic characteristics of these material change with hydrostatic pressure. In order to improve an acoustic performance according to hydrostatic pressure, several kinds of scatterers were added to viscoelastic material. In this paper, acoustic modelling and analysis techniques of underwater acoustic material with hydrostatic pressure were introduced and proposed. The specimens for pulse tube test were made and echo reductions were calculated and measured with hydrostatic pressure. Also the characteristics of echo reduction of the specimens with hydrostatic pressure were obtained and discussed.

• The Journal of the Acoustical Society of Korea
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• v.40 no.4
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• pp.314-319
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• 2021

The measurement of the Underwater Radiated Noise (URN) for the underwater vehicle should consider both the acoustic interference due to the surface reflection and the calculation of the Closet Point of Approach (CPA). In this paper, I tried to analyze the underwater vehicle's URN using the Lloyd's mirror effect. First, the theoretical Lloyd's mirror pattern was compared with the sea trial result, and the sea trial results corresponded well with the theoretical predicted pattern. And then the CPA distance could be estimated by the Lloyd's mirror pattern. As a results, acoustic source level shows the spectral fluctuation due to the acoustic interference of the Lloyd's mirror effect.

• The Journal of Korea Robotics Society
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• v.14 no.1
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• pp.14-21
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• 2019

In the ground environment, mobile robot research uses sensors such as GPS and optical cameras to localize surrounding landmarks and to estimate the position of the robot. However, an underwater environment restricts the use of sensors such as optical cameras and GPS. Also, unlike the ground environment, it is difficult to make a continuous observation of landmarks for location estimation. So, in underwater research, artificial markers are installed to generate a strong and lasting landmark. When artificial markers are acquired with an underwater sonar sensor, different types of noise are caused in the underwater sonar image. This noise is one of the factors that reduces object detection performance. This paper aims to improve object detection performance through distortion and rotation augmentation of training data. Object detection is detected using a Faster R-CNN.

• The Journal of the Acoustical Society of Korea
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• v.42 no.4
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• pp.313-319
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• 2023

In this paper, a time series machine learning model, Long Short Term Memory (LSTM), is applied into the bubble flow noise data and the underwater projectile launch noise data to predict missing values of time-series underwater noise data. The former is mixed with bubble noise, flow noise, and fluid-induced interaction noise measured in a pipe and can be classified into three types. The latter is the noise generated when an underwater projectile is ejected from a launch tube and has a characteristic of instantaenous noise. For such types of noise, a data-driven model can be more useful than an analytical model. We constructed an LSTM model with given data and evaluated the model's performance based on the number of hidden units, the number of input sequences, and the decimation factor of signal. It is shown that the optimal LSTM model works well for new data of the same type.

• 대한공업교육학회지
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• v.33 no.2
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• pp.273-286
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• 2008

Underwater acoustic sensor array can detect acoustic signal in underwater and the sensor array can be mounted in each left, right or front side of the UUV(Unmanned Underwater Vehicle). The sensor array could be conformal array and effected turbulent boundary layer flow noise. Therefore, in this paper numerical simulations were performed to know the how the outer flow noise affect the hydrophone which embedded in the elastomer. Corcos wall pressure model was used as turbulent boundary layer flow noise and this model was applied to the frequency density function. Characteristics of transfer function according the kx wave number were simulated and design parameters were thickness of elastomer, density, and modulus of elasticity. Based on the simulation results when increasing the thickness of elastomer noise reduction was increased. This results can be applied to the design of conformal array of UUV.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.2
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• pp.93-101
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• 2014

Underwater radiated noise is the key in acoustic stealth performance of modern naval ships. The underwater radiated noise predicted by the hull vibration with radiation efficiency cannot always give the information of radiation pattern which is essential to analyze of detection probability by enemy and to improve the operational performance of the naval ship. The radiation pattern of underwater radiated noise is able to be obtained with radiation efficiency and radiation directional coefficient. In this paper, a new method to extract the radiation efficiency and radiation directional coefficient is suggested and proved with the simulation and experiment by using cylindrical shell of 70 cm diameter in air.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.21 no.1
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• pp.7-11
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• 1985

Underwater ambient noise in the depth 5m to 200m layers was measured at 14 point from the 24th of July to 2nd of August, 1984, in the Korean east sea areas. The underwater ambient noise pressure level was depended upon configuration of the sea bottom and sea condition, which was formed type of prevaling noise at a long distance from coast and type of intermittent and regional noise at a short distance from coast.

• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.3
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• pp.392-403
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• 2013

For the analysis of radiating noise problems in medium-to-high frequency ranges, the Energy Flow Boundary Element Method (EFBEM) was developed. EFBEM is the analysis technique that applies the Boundary Element Method (BEM) to Energy Flow Analysis (EFA). The fundamental solutions representing spherical wave property for radiating noise problems in open field and considering the free surface effect in underwater are developed. Also the directivity factor is developed to express wave's directivity patterns in medium-to-high frequency ranges. Indirect EFBEM by using fundamental solutions and fictitious source was applied to open field and underwater noise problems successfully. Through numerical applications, the acoustic energy density distributions due to vibration of a simple plate model and a sphere model were compared with those of commercial code, and the comparison showed good agreement in the level and pattern of the energy density distributions.