• Strategy21
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• 통권41호
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• pp.153-173
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• 2017

On 15 December 2015, China seized an underwater drone belonging to the U.S. in the South China Sea. The underwater drone was then about to be retrieved by the Bowditch, a U.S. naval ship.Although China returned the underwater drone to the U.S. on 20 December 2016, the incident resulted in the considerable controversy involving the use of underwater drones. The reason for this is that the seizure of the underwater drone happened in the exclusive economic zone (hereafter referred to as "EEZ") of the Philippines. Part XIII of the United Nations Convention on the Law of the Sea (hereafter referred to as "UNCLOS") governs the matters of marine scientific research (hereafter referred to as "MSR"). If a State intends to use an underwater drone in the EEZ of another coastal State for the purpose of MSR, the former has to obtain the consent of the latter in accordance with relevant provisions included in Part XIII of the UNCLOS. However, it is not obvious whether the consent of a coastal State should be required to launch an underwater drone in the EEZ of the State for the purpose of hydrographic surveying or military surveying. Maritime powers such as the U.S. regard hydrographic surveying or military surveying as part of "other internationally lawful uses of the sea related to these freedoms, such as those associated with the operation of ships, aircraft and submarine cables and pipelines" found in Article 58(1) of the UNCLOS, or part of the freedom of the high seas. This interpretation is not incompatible with the implications that the UNCLOS has. Nevertheless, Korea cannot accept this kind of interpretation that is supported by maritime powers. The freedom of hydrographic surveying or military surveying could imply that the EEZ of Korea would be full of underwater drones launched by China, Japan or even Russia. Hence, Korea should claim that the data collected for the purpose of MSR cannot be distinguished from that collected for the purpose of hydrographic surveying or military surveying. This means that hydrographic surveying or military surveying without the consent of a coastal State in the EEZ of the State should not be permitted.

• Journal of Advanced Marine Engineering and Technology
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• 제11권3호
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• pp.45-52
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• 1987

Generally the factors affected largely by the cold cracking sensitivity of the weld are the quantity of the diffusible hydrogen, the brittleness and hardness of the bond area and the tensile restraint stress. These factors have relation each other, and if we can reduce one of these factors, it becomes instrumental to the root cracks prevention of weld. This study deals with the gravity type-underwater-welding of KR Grade A-3 marine steel plate using E4303 welding electrode in order to compare wet-underwater-welding with in-air- welding, resulting in obtaining the tensile restraint characteristics, the hardness distribution, the quantity of diffusible hydrogen and the macro- and micro-crack properties in both underwater and in-air welds. The main results obtained are as follows: 1) The quantity of diffusible hydrogen measured for 48 hours is about 18cc/100g-weld-metal for the in-air-weld of one pass and about 48cc/100g-weld-metal for the underwater-weld of one pass which is about 3 times penetration of diffusible hydrogen compairing with the case of the in-air-weld. However, it was experimentally confirmed that, by the multi-pass welding of 2 to 5 passes, the diffusible hydrogen in the underwater weld metal can be reduced as much as 27 to 49%. 2) The hardness of the weld metal indicates the highest value in the heat affected zones of underwater weld for more rapid cooling rate, resulting in the higher sensitivity of cold cracking. So, it is desirable to soften the higher hardness in the HAZ by tempering effect such as the multi-pass welding in the underwater welding. 3) At the bond vicinity of the underwater weld HAZ, micro cracks were found as resulted by both more rapid cooling rate and more diffusible hydrogen and also by the stress corrosion cracking under the tensile restraint stress in the underwater. But this could be prevented by the tempering effect of the following weld bead such as the multi-pass welding.

• 수산해양기술연구
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• 제60권2호
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• pp.128-141
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• 2024

Fish resource surveys were conducted near Jeju Island in June, August and October 2021 using an underwater camera monitoring system, fish pots, and SCUBA diving methods. The efficiency of the methods used to survey fish resources was compared using the number of individuals compared to area per unit time (inds/m³/h) and the number of species compared to area per unit time (spp./m³/h). As a result of comparing the number of individuals compared to the area per unit time (inds/m³/h), the order was underwater camera 214.69, SCUBA diving 124.62, and fish pots 0.57 inds/m³/h. The number of species compared to area per unit time (spp./m³/h) is in the following order: SCUBA diving 0.85, underwater camera 0.38, and fish pots 0.01 spp./m³/h. The fish resource monitoring method using underwater cameras was found to be more efficient in individual counts, and the SCUBA diving method was found to be more efficient in species counts. When considering cost and survey efficiency, the fish resource survey method using underwater cameras was judged to be more effective. The results of this study are expected to be widely used in estimating the population density of fish, which is the core of future fisheries resource surveys.

• 대한조선학회논문집
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• 제57권5호
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• pp.271-277
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• 2020

Recoverability and vulnerability of navy ships under underwater explosion are critical verification factors in the acquisition phase of navy ships. This paper aims to establish numerical analysis techniques for the underwater explosion of navy ships. Doubly Asymptotic Approach (DAA) Equation of Motion (EOM) of primary shock wave and secondary bubble pulse proposed by Geers-Hunter was introduced. Assuming a non-compressive fluid, reference solution of the DAA EOM of Geers-Hunter using Runge-Kutta method was derived for the secondary bubble pulse phase with an assumed charge conditions. Convergence analyses to determine fluid element size were performed, suggesting that the minimum fluid element size for underwater explosion analysis was 0.1 m. The spherical and cylindrical fluid domains were found to be appropriate for the underwater explosion analyses from the fluid domain shape study. Because the element size of 0.1 m was too small to be applied to the actual navy ships, a very slender beam with the square solid section was selected for the study of fluid domain existence effect. The two underwater explosion models with/without fluid domain provided very similar results in terms of the displacement and stress processes.

• The Journal of the Acoustical Society of Korea
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• 제27권3E호
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• pp.104-111
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• 2008

Recently, a method for robust time reversal focusing has been introduced to extend the period of stable focusing in time-dependent ocean environments [S. Kim et al., J. Acoust. Soc. Am. 114, 145-157, (2003)]. In this study, concept of focal-size broadening based on waveguide invariant theory in an ocean time reversal acoustics is described. It is achieved by imposing the multiple location constraints. The signal vector used in multiple location constraints are found from the theory on waveguide invariant for frequency band corresponding the extended focal range. The broadening of foci in an ocean waveguide can play an important role in the application of time reversal processing, particularly to the underwater acoustic communication with moving vehicles. The proposed method is demonstrated in the context of the underwater acoustic communication from the transmit/receive array (TRA) to a slowly moving vehicle.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2001년도 춘계종합학술대회
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• pp.769-773
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• 2001

해양에 있어서 음향은 수심의 계측, 정보의 전달 등 다양한 분야에서 활용되고 있다. 최근에 들어 와서는 어업에 있어서도 음향을 적극적으로 활용하여 산업에 이용하고자 하는 노력을 하고 있다. 특히 기르는 어업분야에 있어서 식이음(먹이를 먹을 때 나는 소리)등을 이용하여 어류의 행동을 제어하는 기술을 개발하고 있다. 본 연구는 어류의 방성음에 관한 기초적 연구의 일환으로, 우리 나라 남해안에서 주로 서식하고 있는 참돔과 조피볼락을 대상으로 그들이 내는 방성음을 수록하고, FFT분석을 통하여 특성을 파악하였다.

• 한국정밀공학회지
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• 제10권4호
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• pp.118-127
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• 1993

A nonlinear control design method called the QJQG/LTR method is presented for the depth control of underwater vehicles with the deadzone of the flow control valve. And, it is shown how the design plant model can be formulated in the QLQG/LTR depth control system design for underwater vehicles which have the triple integrator. In order to show the effectiveness of this control system, the linear LQG/LTR control system neglected the deadzone effect and the nonlinear QLQG/LTR control system considered it are compared. It is found that the QLQG/LTR control system is relatively insensitive to the input magnitude, even if there exists a hard nonlinearity in the plant.

• Journal of information and communication convergence engineering
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• 제14권3호
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• pp.200-206
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• 2016

Images can be obtained by collecting rays from objects. The characteristics of electromagnetic wave propagation depend on the medium. In particular, in an underwater imaging system, the interface between air and water must be considered. Further, reflection and transmission coefficients can be found by using electromagnetic theory. Because of the fact that the values of these coefficients differ according to the media, the recorded light intensities will change. A color image sensor has three different color channels. Therefore, the reflection and transmission coefficients have to be calculated individually. Thereafter, by using these coefficients, we can compensate for the color information of underwater objects. In this paper, we present a method to compensate for the color information of underwater objects by using electromagnetic wave propagation theory. To prove our method, we conducted optical experiments and evaluated the quality of the compensated image by a metric known as mean square error.

• 한국음향학회지
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• 제31권2호
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• pp.107-113
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• 2012

본 연구에서는 수중 채널환경에서 측정을 수행하고 측정 데이터를 분석하여 수중 채널의 공간 다이버시티 특성을 연구하였다. 측정 데이터 분석 결과 정지채널의 경우 페이딩에 의한 영향은 크지 않았으며, 서로 이격된 센서에 수신된 신호의 페이딩 특성은 송신단과 수신단의 거리에 의한 영향도 적어서 수신 센서의 간격이 반송파의 10파장 이상 이격하여야 최적의 공간 다이버시티이득을 얻을 수 있었다. 그리고 이동 채널 환경의 경우에는 센서 간의 거리가 8파장이상일 때 공간 상관계수 값이 0.3 보다 작아서 최적의 공간 다이버시티 이득을 얻을 수 있는 것으로 분석 되었다. 향후 이 연구결과를 바탕으로 수중 이동 채널 환경에서의 MIMO 채널 모델링 및 성능 분석을 할 예정이다.

• 전기전자학회논문지
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• 제26권3호
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• pp.396-400
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• 2022

본 연구에서는 해저에서 발견한 인체를 해수면까지 운반하는 인양백을 기반으로 수중구조를 위한 ICT 기반 수중통신 모니터링 장치를 구현한다. 인양백은 에어를 주입하는 리프트백, 사이드백, CO₂ 카트리지 등으로 패키지화 되어 있다. 모니터링 시스템은 휴대하기 용이한 구조로 모바일 방식으로 개발한다. 수중 초음파 센서 신호는 USB 포트를 사용하여 공급되며, O/S는 리눅스로 구성한다. 수중통신동시험은 동해안에서 수심 6m~40m까지 실시간으로 측정 시험을 진행한다. 초음파 음향센서는 2,400bps로 변환되어 2원화에 따라 전송오차를 검증한다. 센서에서 모니터링까지 통신속도는 115,200bps, 제어기에서 수신부까지 통신속도는 2,400bps를 사용한다. 리프팅 장치의 상용화 단계에서 로우엔드 타입 개발이 용이하고 호환성이 넓도록 한다.