• 한국해양공학회지
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• 제11권4호
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• pp.169-179
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• 1997

This paper presents a discrete-time sliding mode control of an autonomous underwater vehicle with parameter uncertainties and long sample interval based on discrete variable structure system. Although conventional sliding mode montrol techniques are robust to system uncertainties, in the case of the system with long sample interval, the sliding control system reveals chattering phenomenon and even makes the system unstable. This paper considers the AUV which acquires position informations from a surface ship through an acoustic telemetry system with a certain discrete interval. The control system is designed on the basis of a Lyapunov function and a sufficient condition of the switching gain to make the system stable is give. Each component of the switching gain can be determined separately one another. The controller is robust to the uncertainties, and reaching condition of the control system is satisfied for any initial condition. This control law is a generalized form of the discrete sliding mode control and reduce the chattering problem considerably. Motion control of the AUV in the vertical plane shows the effectiveness of the proposed technique.

• 한국기계가공학회지
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• 제16권1호
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• pp.51-57
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• 2017

In the present study, the long-pitch roller-chain of a continuous ship unloader is studied. It is the vertical excavating and transporting the cargo has carried in bulk amount. The size of the pitch in the long-pitch roller chain is about 350 mm. The finite element technique is used for the structural safety of the roller chain. The objective of the study is to perform a dynamic analysis of the load at the point of contact with the sprocket of the roller chain, and analyze each point in the stress of the chain's components by using load. From the tooth sprocket optimization analysis, the results show an optimal design. Static structural analysis was safe. Contact analysis results show the greatest stress on the sprocket. By increasing the tooth size, the stress was reduced.

• 한국항해항만학회지
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• 제36권9호
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• pp.707-714
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• 2012

Recently, tug boats are widely used for towing a barge which transports building materials, a large block of a ship, offshore crane, and so on. In order to simulate the dynamics of the coupled towing system correctly, the dynamics of the towline should be well modeled. In this paper, the towline was modeled as the multiple finite elements, and each element was assumed as a rigid cylinder which moves in five degrees of freedom except roll. The external tension and its moment acting on each element of the towline were modeled depending on the position vector's direction. Tugboat's motion was simulated in six degrees of freedom where wave and current effects were included, and towed barge was assumed to move in the horizontal plane only. In order to confirm the mathematical models of the coupled towing systems, standard maneuvering trials such as course changing maneuver, turning circle test and zig-zag test were simulated. In addition, the same trials were simulated when the external disturbances like wave and current exist. As the result, it is supposed that the results might be qualitatively reasonable.

• 한국해양학회지
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• 제23권3호
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• pp.97-109
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• 1988

한국 동해의 wind stress와 wind-stress curl의 값을 수산진흥원 정선관측 바람자료를 근거로 하여 계산하였다. 바람에 의한 해수 이용을 염두에 두고 주로 지속적이고 강한 바람을 취해서 구한 월평균 wind stress 값들은 동해 전체에서 구한 기존의 값들과 거의 같았으나 wind-stress curl의 경우는 그 값이 훨씬 크게 나타났다. 이는 동해가 국지적으로 지형적인 영향을 받은 것으로 판단된다. 한편 바람에 의한 상층수의 이동으로 울릉도 부근에는 계절에 관계없이 난수괴(warm core)가 존재 하나 그 위치는 고정되어 있지 않다.

• 대한기계학회논문집B
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• 제29권7호
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• pp.805-813
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• 2005

The thermal performance of a flat-strip heat pipe with inner grooves and the screen mesh cover was investigated experimentally. The heat pipes were made of 2024 aluminum alloy of which the dimensions were 30 (W) $\times$ 4 (T) $\times$ 150 (L) mm. The cross sectional dimensions of inner groove were 0.4$\times$0.9 mm and the space between grooves was 0.6 mm. To enhance the capillary force, foe screen meshes were attached to cover the grooved inner surface. In the grooved heat pipes without screen mesh cover, the maximum thermal load of 180 W (12 W/$cm^2$) was achieved for operating temperature below $130^{\circ}C$ at horizontal position. The heat pipes with screen mesh cover showed the thermal resistances less than one third of those without screen mesh cover, and showed less fluctuation in the thermal resistance values. Furthermore, the thermal performance of the former exhibited less dependence on the tilt angle and the fill charge ratio.

• 대한조선학회논문집
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• 제53권1호
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• pp.10-17
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• 2016

When a planing hull straightly runs and turns, its floating position and pitch angle are changed depending on its speed, and large transient motion happens. In this paper, six degrees of freedom(6 DOF) equations of motion, which could simulate the motion of a planing hull, are established. Static and dynamic forces in vertical plane are modeled using pre-calculated displacements and metacentric heights depending on various draft, lift under bottom, and vertical damping coefficients which are used to tune the final motion. Hydrodynamic coefficients in horizontal plane at various equilibrium state are calculated by using Lewandowski's empirical formula and the speed-dependent equilibrium state are calculated beforehand by Savitsky's formula. The speed effects are considered by curve-fitting the coefficients at various speed to the polynomials. Accelerating, decelerating and backing, turning, and zig-zag are simulated and compared with the sea trial results, and it is confirmed that the speed reduction, roll, and pitch during such maneuvers of sea trial and simulation are well consistent.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권2호
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• pp.858-864
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• 2019

The increasing demands of lifting lugs can be attributed to the rapid advancement of shipbuilding and offshore-structure production technologies and an exponential increase in the size of the block units of ship structures. Therefore, to ensure safety during the transportation and turnover of large blocks, it is important to determine the structural integrity and position of lifting lugs. However, because the manufacturing cost and availability of lugs are important considerations, low cost and easily obtainable steel compositions of grades different from those of the blocks are often used as alternatives. The purpose of this study is to investigate the effect of a lifting-lug metal on the physical properties of a base metal in a dissimilar welding between the base metal and lifting lug. The effect was evaluated by observing the metal microstructures and determining the hardness and dilution values on the cross-sectional surface of the lifting lug. According to the results of the metal microstructures, impact, hardness, and emission spectrochemical analysis at the surface from where the lug was removed confirmed that the chemical composition of the lifting-lug metal did not influence the physical properties of the base metal.

• 한국해양환경ㆍ에너지학회지
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• 제2권2호
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• pp.31-37
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• 1999

본 논문에서 저자들은 선박의 자동 인식 시스템(AIS: Automatic Identification System)을 이용한 광역 해상 교통 관제 시스템의 개념과 현재의 추세를 소개하면서 동시에 초기 개발을 시도하였다. 이를 위해서 무궁화 위성을 AIS 개발을 위하여 사용하였다. 즉 해상에서 GPS에 의해 얻어지는 선박의 위치가 무궁화 위성을 통하여 관제 센터에 인력의 개입 없이 자동으로 보고되는 시스템을 구축하였다. 이와 같은 시스템은 레이더를 이용하는 기존의 관제 시스템보다 더욱 넓은 영역을 통제할 수 있으며 정보의 불확실성도 매우 감소한다. 본 연구에서 개발된 시스템의 시험 관제 결과는 인공위성과 AIS를 이용한 광역 해상 교통 관제 시스템의 충분한 가능성을 보여주고 있다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2015년도 추계학술대회
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• pp.43-44
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• 2015

AIS-ASM은 AIS의 고유 기능인 선박의 위치 정보 외에 다양한 해양안전정보를 제공하기 위한 연구 중 하나로, 2004년부터 관련 규정을 정비하여 진행 중이다. 본 연구는 여객선의 출항에서 입항까지 안전항해를 위해 필요한 국내 여객선 항해사의 의무보고 내용을 조사하고 업무 부하를 줄이기 위해 자동화 할 수 있는 부분을 차세대 해상디지털통신 기술인 ASM2.0을 활용하여 자동화 하는데 목적이 있으며, 국내 여객선 운항 관련 법규를 조사하여 상호 교환해야하는 정보를 도출하고 국제적으로 사용하고 있는 AIS-ASM 메시지 분석을 통해 ASM2.0에서 활용하기 위한 프로토콜을 설계하고 프로토타입을 구현하였다.

• 대한조선학회지
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• 제19권4호
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• pp.39-45
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• 1982

A floating rig, which has been used to develop the ocean resources has a common characteristics with the catamaran ship that it is composed of the two simple hulls. So the motion responses of the floating rig can be predicted theoretically with the aid of the strip method as those of the catamaran. And for the strip method, the two-dimensional hydrodynamic coefficients are the most important inputs to predict the results accurately. In this report, a theoretical method is proposed for calculating two-dimensional hydrodynamic forces and moments acting upon arbitrary shaped twin-hull cylinders, which are forced to make a heaving, swaying and rolling oscillation about their mean position on the free surface of a finite depth water. The theoretical results by making use of the singularity distribution method are presented. The accuracy of the coefficients was confirmed to be reasonable by the comparison with the Ohkusu's results for two circular cylinders in an infinite depth water. The depth effects on two-dimensional hydrodynamic coefficients for two circular cylinders are also checked. In some range of wave numbers, large differences in the behavior of hydrodynamic coefficients between for a finite depth and for an infinite depth are shown.