• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.6
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• pp.613-619
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• 2017

Recently, the size of container ships has been progressively increasing, and much attention is required for safe navigation in shallow areas such as coastal waters and ports due to increases in draft. It is necessary to understand the characteristics of ship motion not only in still waters but also with waves. Especially in shallow regions, squat due to the vertical movement of the ship can be an important evaluation factor for the safe navigation, and wave drift force acting in the horizontal direction can have a great influence on the maneuverability of a ship. In this study, a numerical simulation using computational fluid dynamics has been performed for the wave exciting force acting in the vertical direction and the wave drift force acting in the horizontal direction for a very large container vessel sailing in shallow zone. As a result, it was found that total resistance in still waters greatly increased in shallow water. Wave drift force was shown to decrease given longer wavelengths regardless of water depth. It was observed that the wave exciting force in shallow water was considerably larger than at other water depths. As wave height against the central part of the ship lowered, the aft side rose.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.2
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• pp.202-209
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• 1998

A three-dimensional numerical method based on the Green's integral equation is developed to predict the motion response and drift force in waves for the ocean monitoring facilities. In this method, we use source and doublet distribution, and triangular and rectangular eliments. To eliminate the irregular frequency phenomenon, the method of improved integral equation is applied and the time-mean drift force is calculated by the method of direct pressure integration over the body surface. To conform the validity of the present numerical method, some calculations for the floating sphere are performed and it is shown that the present method provides sufficiently reliable results. As a calculation example for the real facilities, the motion response and the drift force of the vertical cylinder type ocean monitoring buoy with 2.6 m diameter and 3,77 m draft are calculated and discussed. The obtained results of motion response can be used to determine the shape and dimension of the buoy to reduce the motion response, and other data such as the effect of motion reduction due to a damper can be predictable through these motion calculations. Also, the calculation results of drift force can be used in the design procedure of mooring system to predict the maximum wave load acting on the mooring system. The present method has, in principle, no restriction in the application to the arbitrary shape facilities. So, this method can be a robust tool for the design, installation, and operation of various kinds of the floating-type ocean monitoring facilities.

• Journal of Korean Society of Steel Construction
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• v.29 no.6
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• pp.401-410
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• 2017

This study deals with dynamic instability of a tendon moored submerged floating tunnel (SFT) due to tendon slack. In general, environmental loadings such as wave and current govern SFT design. Especially, the wave force, whose amplitude and direction continuously change, directly induces the dynamic behavior of the SFT. The motion of the floating tube, induced by the wave force, leads dynamic response of the attached tendons and the dynamic change of internal forces of the tendons significantly affects to the fatigue design as well as the structural strength design. When the severe motion of the SFT occurs due to significant waves, tendons might lose their tension and slack so that the floating tube can be transiently instable. In this study, the characteristics of dynamic instability of the SFT due to tendon slack are investigated performing hydrodynamic analysis. In addition, the effects of draft, buoyancy-weight ratio, and tendon inclination on tendon slack and dynamic instability behavior are analytically investigated.

• Bulletin of the Society of Naval Architects of Korea
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• v.11 no.2
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• pp.23-40
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• 1974

Semisubmersible 해양석유시추선의 기본설계에 필요한 파랑중(波浪中)에서 운동(運動)을 계산(計算)하는 이론적방법(理論的方法)을 제시하고 "MOHOLE"과 "SEDCO 1350-F" 석유시추선들의 운동(運動)을 해석하였다. 이 규칙파에서 운동계산을 불규칙해양파(波)에 적용하는 응용해석을 보여주었다. 현재 이론적 방법으로는 6자유도(自由度)의 운동을 해양파의 어떤 방향에 대해서도 정확히 계산할 수 있으며 계산의 정확성은 수조(水槽)에서의 모형선의 운동측정치와 실선(實船)의 운동측정치와 비교하여 증명되었다. 또 현재의 방법은 종전에 개발된 방법보다 더 일반적(一般的)인 경우를 다룰 수 있으며 결과치도 더 정확하다. 극소운동특성을 갖는 해양석유시추선과 부체(浮體)해양구조물의 설계는 경비가 비싸고 시간이 많이 드는 모형실험보다는 유체역학적(流體力學的) Parameters를 신속 정확히 자주 변경 검토해야 하는 기본설계단계에서는 정확한 이론적인 전자계산기에 의한 계산방법이 절실히 필요하다. 예상(豫想)과 같은 부가질량(附加質量)과 감쇠력(減衰力)은 Resonance 운동주기에서만 운동에 영향을 준다. 해양구조물에 작용하는 파력(波力)은 Froude-Krilov force, 부가질량(附加質量) 및 감쇠력(減衰力)과 Restoring force로 구성했으며 규칙파(規則波)에서의 6자유도(自由度) 운동방정식은 본 논문에 제시된 실험측정치(値)와 실험으로 정확도가 증명된 이론치(値)의 부가질량과 감쇠력 계수(係數)를 써서 풀었다. 규칙파(規則波)에서의 계산된 운동을 Pierson Moskowitz 해양파(海洋波) 스펙트럼과 linear superposition principle에 의해 불규칙해양파(不規則海洋波)에서의 운동을 계산하는데 사용했다. 불규칙파(不規則波)에서의 운동은 운동스펙트럼과 통계적 운동치로 나타냈다. 현재의 계산방법은 실제 기본설게에 사용되어 왔으며, 다른 응용분야는 파랑중(波浪中)에서의 파면(波面)과 Deck간(間)의 Clearance, 계류선(係留線)의 동장력(動張力)계산의 기본 Data 및 기본설계의 Draft 등 Parameters를 통(通)한 Optimum Design 등(等)이다. 파(波)의 한 방향(方向)에 대(對)한 전자계산기(電子計算機)(IBM 370 또는 CDC 6400)에 의한 운동계산은 10초(秒)미만밖에 안걸린다. 또 현재의 계산방법은 해양석유시추선뿐 아니라 이와 비슷한 부체(浮體)해양구조물과 Pipe-laying선(船) 또 Supply Boat설계(設計)에도 쓰여지고 있다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.381-384
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• 2011

Wave drag reduction due to the repetitive laser induced energy deposition over a flat-nosed cylinder is experimentally conducted in this study. Irradiated laser pulses are focused by a convex lens installed in side of the in-draft wind tunnel of Mach 1.94. The maximum frequency of the energy deposition is limited up to 80. Time-averaged drag force is measured using a low friction piston which was backed by a load cell in a cavity as a controlled pressure. Stagnation pressure history, which is measured at the nose of the model, is synchronized with corresponding sequential schlieren images. With cylinder model, amount of drag reduction is linearly increased with input laser power. The power gain only depends upon the pulse energy. A drag reduction about 21% which corresponds to power gain of energy deposition of approximately 10 was obtained.

• Journal of Ocean Engineering and Technology
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• v.28 no.4
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• pp.274-279
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• 2014

This paper investigates the line dynamic forces connecting tugs and a floater, where the planar motion of the floater is due to the weather criteria during the position keeping of the offshore structure by tugs. The analysis situation consists of the position keeping states for the seabed mooring line connection work of the offshore structure at the offshore site. Specifically, the decision about the tug power capacity for the position keeping is essential and depends on the weather criteria, line characteristics, length of line, etc. The planar motion of the structure is constrained by the interference of the installation vessel's operational range, behavior of the underwater fairlead, and other surrounding structures. In this paper, the tug line forces and planar motion of an offshore structure are summarized dependent on the tug line length and line material characteristics in the states fora given floater draft and weather criteria. The tug line dynamic forces and planar motion evaluated here will be used to determine the proper tug power and clearance of an offshore structure.

• 한국HCI학회:학술대회논문집
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• 2009.02a
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• pp.384-389
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• 2009

In general, gestures can be utilized in human-computer interaction area. Even though the acceleration information is most widely used for the detection of user’s intention, it is hard to use the information under the condition of zero or small variations of gesture velocity due to the inherent characteristics of the accelerometer. In this paper, a natural interaction method which does not require excessive gesture acceleration will be described. Taking advantages of the gravity, the system can generate various types of signals. Also, many problems such as initialization and draft error can be solved using restorative uprighting force of the system.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.4
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• pp.282-290
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• 2015

In this study, a latching control technology, proposed by Sheng et al.(2015), was applied in order to maximize the extraction efficiency of WEC (Wave Energy Converter), which is the heaving buoy coupled with linear electric generator. The latching control is the phase-control technique for improving the wave energy conversion with appropriate latching duration of keeping the buoy fixed. From the time-domain analysis in regular waves, the latching control technology can significantly improve the heave velocity and extracted power, even though the resonance condition is not satisfied. By using the latching control technology, the draft of buoy as well as the required PTO damping force can be significantly reduced along with increased extracted power, which is a big advantage in manufacturing the WEC.

• THE INTERNATIONAL COMMERCE & LAW REVIEW
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• v.13
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• pp.83-103
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• 2000

Through the this paper, a conclusion could be derived from CISG PICC MISC made by UNIDROIT, UNCITRAL, ICC of representative system making out a draft for uniform law, convention, trade usages. (1) In short, like most int'l sales rules applicable to commercial contracts, these rules play a supporting role, supplying answers to problems arising from transaction between the parties. (2) Though every one has in its own way a special feature, use of MISC made on the basis of actual facts which the parties are faced with their daily transactions, CISG and Incoterms being now in force, is desirable. (3) In case of use of MISC similar to a system of Incoterms, as PICC, it is necessary for MISC to set forth definitions about important terminology which is possible to give concerned parties confusion. (4) In a sense, PICC has a character complementing problems which CISG can not solve, therefore, if int'l agreement is given, it is desirable to adopt revised PICC adding specials conditions (A) of MISC as appendix of PICC such as Llouyd's Form in an appendix to MIA, as int'l convention.

• Journal of Biosystems Engineering
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• v.27 no.6
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• pp.521-528
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• 2002

Rotary and plow implements are mainly utilized for the tillage operation in Korea, and a implement control system for agricultural tractors was designed and fabricated to improve the working accuracy and efficiency. The control system was composed of three units: 1) sensors fur detection of angle of liftarm, draft force, engine rpm, tillage depth and so on, 2) a controller, and 3) hydraulic circuits, which included solenoid valves and so on, for operation of three point linkage and implements. The control system can control the speed(high and low speed) of implements by adjusting input flow rates of the hydraulic cylinder which was controled by two speed valve, which was composed of a solenoid valve and a orifice. Indoor experiments were conducted to evaluate response characteristics of the designed implement control system under experimental conditions of various engine nm, two kinds of input flow rates of the cylinder and some input frequency. The results of experiments showed the response characteristics sufficient to use as the implement control system fur agricultural tractors.