• Journal of the Korea Society for Simulation
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• v.20 no.4
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• pp.157-166
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• 2011

As underwater environment monitoring system's interest has increased, the research is proceeding about underwater acoustic sensor network. Underwater sensor network can be applicable to many fields, such as underwater environment monitoring, underwater resource exploration, oceanic data collection, military purposes, etc. It is essential to define the PHY-MAC protocol for revitalization of the underwater acoustic sensor network which is available utilization in a variety of fields. However, underwater acoustic sensor network has to implement by consideration of underwater environmental characteristics, such as limited bandwidth, multi-path, fading, long propagation delay caused by low acoustic speed. In this paper, we define frequency of adjusted PHY protocol, network topology, MAC protocol, PHY-MAC interface, data frame format by consideration of underwater environmental characteristics. We also present system configuration of our implementation and evaluate performance based on our implementation with test in real underwater field.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.5
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• pp.645-652
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• 2015

In underwater, such as fish farm and sea, turbidity is increased by water droplets and various suspended, therefore light attenuation occurs depending on the depth also caused by the scattering effect of light float. In this paper, in order to improve the visibility of underwater images obtained from these aquatic environment, we propose a visibility enhancement method using a haze removal method based on dark channel prior and a trained color transform model. In order to train a color transform model, we used underwater pattern images captured from Pohang and Yeosu, and to measure the performance of the proposed method, we carried out experiment of visibility enhancement using underwater images collected from Yeosu, Geomundo and Philippines. The results show that the proposed method can improve the visibility of underwater images of various locations.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.2
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• pp.309-314
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• 2012

In this paper, we present surface-to-underwater visible light communication systems using white LEDs. Pulse position modulation (PPM)-based analogue data communications and on-off keying-based digital data communications systems are developed. Inexpensive and commercial power-LEDs and photo-diodes are used to construct two types of systems. We report the experimental results obtained from the prototype systems to show the possibility of an optical underwater visible light transceiver as a basis for short range underwater wireless network. Their performance deteriorates more than the atmosphere's one because of attenuation and scattering of the light in water, but these results are promising for the potential to create more robust network interface that improve medium performance such as a LED modulation and a photo-detector demodulation.

• The Journal of the Korea institute of electronic communication sciences
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• v.12 no.6
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• pp.997-1002
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• 2017

Underwater communication, which is used acoustic channel of 1500[m/s] speed being different of wireless electric wave in terrestrial communication, is sensitive on water temperature and salinity and also affected from 3D underwater space. 3D underwater communication is sensitive on propagation loss of acoustic wave and underwater noise with complexity of communication space. In this paper, transmission performance with consideration of these characteristics of 3D underwater communication environments is measured and analyzed on MANET operated on 3D underwater communication environments. Some underwater MANET operation conditions will be suggested. Computer simulation with underwater simulator based on NS-2 will be used for performance measure, performance parameter like as throughput, transmission delay, packet loss rate and consumed energy will be used in simulation for performance measure.

• Journal of the Korean GEO-environmental Society
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• v.13 no.6
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• pp.41-50
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• 2012

In general, it is critical that grout consistency permit the complete filling of void space without segregation of ingredients. Recently, the antiwashout agent is used on underwater grout materials for preventing the grout from the segregation in water. This study introduces a new type of antiwashout underwater and flowable grout material using viscous modifiers and its characteristics comparing with conventional grout materials in fresh and sea water. It is found that the antiwashout underwater grout both in fresh and sea water has enough strength and good resistance to segregation.

• Explosives and Blasting
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• v.31 no.1
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• pp.11-22
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• 2013

This study compared and analysed ground vibration, size of underwater background noise in fish farms and underwater object noise of blasting and obtained ground vibration prediction equation through a regression analysis and correlation equation between underwater object noises in order to predict degrees of underwater noise in blasting and organize underwater noise control regulations. Before the study, when background noise of fish and shellfish farms with different conditions was measured, levels of background noise were different according to environmental characteristics of each farm. Ground vibration which causes underwater noise was measured to obtain a correlation equation between ground vibration and underwater object noise. Therefore, if underwater noise is predicted for each construction with a use of a correlation and permissible standards appropriate for each condition are applied for design and construction, financial loss from damages to fish and shellfish caused by development of insufficient technological and engineering logic can be prevented and successful construction with safety of underwater creatures guaranteed can be achieved.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.131-136
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• 2017

High speed under water vehicle by using solid rocket motor, which is a natural cavitation type, was tested. The vehicle's speed and running distance was measured, and pressure sensors installed on the surface of the vehicle show pressure-time history of pressures according to the development of the supercavitation. Underwater cameras installed on the wall of the test pool recorded whole processes from the onset of the supercavitation to fully developed one. CNU-SuperCT based on 2-dimensional inviscid theoretical analysis was used to simulate the test result. In consideration of CNU-SuperCT does not include the control fins of the vehicle, simulation results agree with test results very well. Also, pictures from underwater cameras support the test results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.9
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• pp.4507-4513
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• 2013

The developing unmanned underwater equipment can be used for underwater construction site such as underwater leveling works. If a optical camera is applied to the unmanned underwater equipment, recognition in underwater can be gone to low due to high turbidity in working field. To overcome this problem, a sonar will be installed to the unmanned underwater equipment. In this study, the resolution of the sonar and the quality test of the sonar image under high turbidity environment were conducted. And the method to indicate the boundary of the underwater construction site was proposed. By these results, the basic performance of the sonar was evaluated.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.101-101
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• 2015

1986년 한강종합개발사업으로 대규모 준설이 실시되고, 수위가 낮아지면서 발생한 문제점을 해결하고자, 1988년 김포대교 직하류 지점에 신곡수중보를 건설하였다. 당시 수중보의 설치목적은 취수시설 유지를 위한 수위유지가 주요기능이었으나, 30년이 지난 지금 생활용수 취수시설은 잠실 수중보 상류로 모두 이전하였고, 농업용수와 일부 공업용수 등의 일부 시설만이 남아 있어 신곡수중보 시설의 필요성 및 현재 기능에 대한 재평가가 필요한 시점이다. 신곡수중보 철거시 변화하는 한강 본류의 수위를 모의하기 위해 수리학적 모형인 HEC-RAS를 이용한 부정류 모의를 실시하였다. 모형의 보정을 위해 저수기를 대표하는 2014년 4월부터 5월까지 45일간과 풍수기를 대표하는 2014년 8월부터 9월까지 45일간을 모의하였다. 조위영향을 받고 있는 강화대교 관측수위를 기점수위로 선정하고, 팔당댐 유량을 유량조건으로 모의하였으며, 본류구간의 전류, 행주대교, 한강대교 지점의 실측수위와 모의결과는 잘 일치하는 것으로 나타났다. 신곡수중보 철거시 평가를 위해 팔당댐 방류량이 최소가 되는 조건과 한강의 갈수량, 저수량, 계획홍수량 등 유량조건 변화에 따른 한강 본류수위를 비교하였다. 보 철거시 서해안의 조위영향이 잠실수중보 직하류지점까지 영향을 미치고, 일시적인 수위하강 현상이 발생하는 것으로 모의되었다. 보 철거에 의해 감조하천으로 변화되는 구간에서는 전반적인 유속이 증가하여, 현재 문제가 되고 있는 신곡수중보 직상류 및 지천 합류부 주변의 퇴적문제와 수질 문제개선에 도움을 줄 것으로 예상된다. 또한 신곡수중보 상류지역에서 잠실수중보 하류까지 발생하는 수위변화와 수면폭변화는 간조대 형성에 유리한 조건을 제공하여 한강변의 퇴적지 면적 증가 및 생태계 서식처 제공에 도움을 줄 것으로 기대된다. 다만 신곡수중보 하류지역의 수위는 현재보다 전반적인 상승이 예상되어 장항습지 면적이 일부 감소할 것으로 예상되지만, 홍수시 침식 및 퇴적이 가장 활발히 발생하므로 하상변동 등에 대한 면밀한 평가가 필요하다. 또한 홍수기 신곡수중보 구조물에 대한 평가 결과에서는 철거 시 한강 본류의 하천 수위가 일부 하강하는 것으로 모의되어 하천을 횡단하는 구조물이 홍수위 상승에 기여한다고 판단되므로 대안마련을 위한 종합적인 평가가 필요하다.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.4
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• pp.12-17
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• 2018

A natural cavitation-type high-speed underwater vehicle with solid rocket motor is tested, and its speed and running distance are measured. The outputs from pressure sensors on the surface of the vehicle reveal a pressure-time history reflecting the development of supercavitation. Underwater cameras installed on the wall of the test pool record the entire process from the onset of supercavitation to its full development. CNU-SuperCT, based on two-dimensional inviscid theoretical analysis, is used to simulate test results. Considering CNU-SuperCT does not include the control fins of the vehicle, simulation results agree with test results very well. Additionally, pictures from underwater cameras support the test results.