• Journal of Korea Multimedia Society
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• v.25 no.1
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• pp.61-71
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• 2022

When communication such as light, radio wave, or magnetic field is used underwater, the communication distance is very short, so sound waves are mainly used. However, by combining the strengths of each medium and communicating, stable communication may be possible. Underwater multi-media communication requires a protocol stack that supports it, which is very complex. To this end, this paper proposes a standard protocol stack and modeling technique to enable easy protocol stack modeling for the purpose. In fact, in this paper, a random model was created and analyzed through the proposal of modeling elements and similarity measurement methods, and as a result, it was analyzed that it was very helpful in creating a new model based on a standard model.

• Journal of Ocean Engineering and Technology
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• v.29 no.5
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• pp.392-397
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• 2015

An autonomous underwater vehicle (AUV) can perform flexible operations even in complex underwater environments because of its autonomy. Localization is one of the key components of this autonomous navigation. Because the inertial navigation system of an AUV suffers from drift, observing fixed objects in an inertial reference system can enhance the localization performance. In this paper, we propose a method of AUV localization using visual measurements of underwater structures. A camera measurement model that emulates the camera’s observations of underwater structures is designed in a particle filtering framework. Then, the particle weight is updated based on the extracted visual information of the underwater structures. The proposed method is validated based on the results of experiments performed in a structured basin environment.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.3
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• pp.645-653
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• 2004

The prediction and its visualization on fish behaviour in relation to fishing gear are carried out based on field detection and observation during fishing operation. However, field observation is very difficult due to variable underwater environments and accordingly due to complex, chaotic response of fish behaviour in the physiological and ecological points. Therefore simple graphic display in previous results was not enough to represent real underwater images of the fishing gear and fish behaviour. In this study more actual visualization technique was developed using by previous fish behaviour model with chaos theory in order to predict, evaluate or analyse complex and non-linear phenomena of response patterns in complex fish behaviour. In addition, display of the fish finder was also designed to simulate the underwater fish detection and distribution in fishing ground. This suggested visualization tool was very similar to the information of the fish movement in the field observation in visual underwater reality and useful to check up between simulations and observations.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.3
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• pp.243-251
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• 2016

Autonomous Underwater Vehicles (AUVs) generally work in complex marine environments. Any fault in AUVs may cause significant losses. Thus, system reliability and automatic fault diagnosis are important. To address the actuator failure of AUVs, a fault diagnosis method based on the Gaussian particle filter is proposed in this study. Six free-space motion equation mathematical models are established in accordance with the actuator configuration of AUVs. The value of the control (moment) loss parameter is adopted on the basis of these models to represent underwater vehicle malfunction, and an actuator failure model is established. An improved Gaussian particle filtering algorithm is proposed and is used to estimate the AUV failure model and motion state. Bayes algorithm is employed to perform robot fault detection. The sliding window method is adopted for fault magnitude estimation. The feasibility and validity of the proposed method are verified through simulation experiments and experimental data.

• Journal of information and communication convergence engineering
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• v.14 no.2
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• pp.78-83
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• 2016

In underwater acoustic communication, the transmitted signals are severely influenced by the reflections from both the sea surface and the sea bottom. As very large reflection signals from these boundaries cause an inter-symbol interference (ISI) effect, the communication quality worsens. A channel estimation-based equalizer is usually adopted to compensate for the reflected signals under the acoustic communication channel. In this study, a feed-forward equalizer (FFE) with the least mean squares (LMS) algorithm was applied to a quadrature phase-shift keying (QPSK) transmission system. Two different types of equalizers were adopted in the QPSK system, namely a real-coefficient equalizer and a complex-coefficient equalizer. The performance of the complex-coefficient equalizer was better than that of two real-coefficient equalizers. Therefore, a Hilbert transform was applied to the real-coefficient binary phase-shift keying (BPSK) system to obtain a complex-coefficient BPSK system. Consequently, we obtained better results than those of a real-coefficient equalizer.

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.493-500
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• 2018

This paper addresses a decentralized observer-based output-feedback formation control problem for multiple unmanned underwater vehicles (UUVs). The complex nonlinear model for a UUV is feedback-linearized. It is assumed that each UUV in the formation exploits only the information regarding itself and the immediate predecessor, which imposes structural constraints on the formation controller gain matrices. The design condition is presented as a two-stage linear matrix inequalities problem. The synthesized controller demonstrates its own advantages through a numerical example.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.5
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• pp.439-446
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• 2017

This paper deals with an experimental study of the dynamics of an underwater bubbles and shock waves, generated by rapid underwater release of highly compressed gas. Aribag inflators, which are used for automobile's airbag system, are used to generate the extremely-rapid underwater gas release. Experimental studies of the complex underwater bubble dynamics as well as underwater shock wave were carried out in a specifically designed cylindrical water tank. The water tank is equipped with a high-speed camera and pressure sensors. The high-speed camera was used to capture the expansion and collapse of the gas bubble created by inflators, while pressure sensors was used to measure the underwater shock propagation and magnitudes. The experimental results were compared against the results of explosion of pentolite explosive. Several physical phenomena that has been observed and discussed, which are different from the explosive underwater explosion.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.4
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• pp.328-334
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• 2012

Power flow finite element method(PFFEM) combining power flow analysis(PFA) with finite element method is efficient for vibration analysis of a built-up structure, and power flow boundary element method(PFBEM) combining PFA with boundary element method is useful for predicting the noise level of a vibrating complex structure. In this paper, the coupled PFFE/PFBE method is used to investigate the vibration and radiated noise of the unmanned underwater vehicle(UUV) in water. PFFEM is employed to analyze the vibrational responses of the UUV, and PFBEM is applied to analyze the underwater radiation noise. The vibrational energy of the structure is treated as an acoustic intensity boundary condition of PFBEM to calculate underwater radiation noise. Numerical simulations are presented for the UUV in water, and reliable results have been obtained.

• The Journal of the Acoustical Society of Korea
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• v.31 no.8
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• pp.551-560
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• 2012

Target detection by acoustic barrier method includes active and passive sonar technique and time reversal process whose theoretical background is already well defined. In this paper, the concept and theory of underwater detection by passive ocean time reversal is established. Also, the reason that this study was conducted was to investigate feasibility of complex mathematical modeling to provide some predictive capability for underwater acoustic barrier with passive time reversal. It may eventually lead to a useful predictive tool when designing underwater acoustic barrier detection system using the passive time reversal concept.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1174-1179
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• 2000

In recent years, the structural shock response to underwater explosion has been studied as much, or more, through numerical simulations than through testing for several reasons. Very high costs and sensitive environmental concerns have kept destructive underwater explosion testing to a minimum. Increase of simulation capabilities and sophisticated simulation tools has made numerical simulations more efficient analysis methods as well as more reliable testing aids. For the simulation of underwater explosions against, surface ships or submerged structures one has to include the effects of the explosive shock wave, the motion of the gaseous reactive products, the local cavitation collapse, the different nonlinear structural properties and the complex fluid-structure interaction phenomena. In this study, as benchmark step for the validation of hydrocode LS/DYNA3D and of technology of fluid-structure interaction problems, two kinds of cavitation problems are analyzed and structural shock response of floating ship model are compared with experimental result.