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Koo O.H.,Republic of Korea Navy | Paik J.K.,Pusan National University
Marine Technology | Year: 2015

Lord Admiral Yi Sun Shin, born on April 28, 1545, transformed the Geobukseon, a class of turtle-shaped battleships into a formidable naval force. The newly redesigned ships measured 37 m in length and 6.8 m in width, weighing 150 tons and accommodating 130-150 crewmembers. They included 8-10 oars each on the port and starboard sides, and could be equipped with sails when needed. The ships had 12 rooms each on the port and starboard sides under the cannon deck, with two rooms used for sorting food and other cargo; three used for storing cannonballs, arrows, swords, spears, and so forth; and the remainder for crewmembers. One room for officers was placed on the cannon deck. In battle, most of the crewmembers were on the cannon deck, except for the rowers, who controlled the speed and direction of the ship. Each ship's main body was shaped like a turtle equipped with the head of a dragon. The roof was covered with sharp iron spikes, and the iron-covered body was designed to defeat gunfire attacks. Because the ship had an entirely closed roof, crewmembers could be protected from enemy attacks more easily than on standard warships with open battle decks. Aside from watch and cannon holes on the sides, the new Geobukseon design featured cannon holes on the back of the turtle Body. The Geobukseon were certainly powerful enough to defeat enemy fleets at long distances, but under Admiral Yi's skillful tactical directions, they did much more than that. Source


Yang D.,Korea University | Shin J.,Samsung | Kim J.,Republic of Korea Navy | Kim G.-H.,Dong - Eui University
Journal of Communications and Networks | Year: 2015

In opportunistic networks, it is difficult to predict when a node encounters others and how long it keeps in contact with another. Nodes continually attempt to explore neighbor nodes in the vicinity to transmit data. In battery-operated devices, this persistent exploration consumes a great deal of energy. In this paper, we propose an optimal energy-efficient neighbor discovery scheme (OPEED) that guarantees neighbor discovery within a delay bound. Through performance evaluation, we show that the OPEED scheme consumes 33%-83% less energy than other schemes. © 2015 KICS. Source


Visconti U.,Seoul National University | Eun W.J.,Seoul National University | Kang J.P.,Republic of Korea Navy | Lim J.H.,Samsung | And 2 more authors.
24th AIAA/AHS Adaptive Structures Conference | Year: 2016

The paper discusses the analyses implemented for the design improvement of the SNUF (Seoul National University Flap), a small-scaled flap-driving mechanism aimed at reducing vibratory loads in a helicopter rotor. Predictions of the hinge moment, both in steady and transient flow, were obtained through CFD (Computational Fluid Dynamics) calculations. When compared with results originating from theoretical formulation, it showed good correlation. Furthermore, the displacement occurring in the piezo-ceramic stack according to different frequencies was measured thanks to a further capable high-voltage amplifier able to span through the actuating frequency range, namely 0-65 Hz. Future proceedings aimed at verifying the effect of centrifugal loads in the SNUF, such as pulling test and contact analysis, are also illustrated. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA, All rights reserved. Source


Park S.-I.,Republic of Korea Navy | Lee S.-J.,Seoul National University | You G.-S.,Seoul National University | Suh J.-C.,Seoul National University
Journal of Ship Research | Year: 2014

Normally, tip vortex cavitation (TVC) is first observed at a certain location behind the tips of propeller blades. Therefore, TVC is important for naval ships and research vessels that require raising the cavitation inception speed to maximum possible values. The concepts for alleviating the tip vortex are summarized by Platzer and Souders (1979), who carried out a thorough literature survey. Active control of TVC involves the injection of a polymer or water from the blade tip. The main effect of such mass injection (both water and polymer solutions) into the vortex core is an increase in the core radius, consequently delaying TVC inception. However, the location of the injection port needs to be selected with great care to ensure that the mass injection is effective in delaying TVC inception. In the present study, we propose a semiactive control scheme that is achieved by attaching a thread at the propeller tip. The main idea of a semiactive control is that because of its flexibility, the attached thread can be sucked into the low-pressure region closer to the vortex core center. An experimental study using a scale model was carried out in the cavitation tunnel at the Seoul National University. It was found that a flexible thread can effectively suppress the occurrence of TVC under the design condition for a model propeller. Source


Shin K.,Seoul National University | Shin Y.,Seoul National University | Kang S.,Seoul National University | Kwon J.,Republic of Korea Navy
40th International Conference on Computers and Industrial Engineering: Soft Computing Techniques for Advanced Manufacturing and Service Systems, CIE40 2010 | Year: 2010

Due to the rapid changes in circumstances of cooperates such as globalization, technical innovation and competition, inter-dependence among cooperates which compose supply chain has been intensified. This make cooperates be exposed to various risk and even a small uncertainty can disrupt the balance of whole supply chain. Therefore, in this paper, the framework to develop alternative execution plan to minimize the total transportation cost and expected cost from risk has been devised. In order to model the relationship between risk factors and risk propagation effect, Bayesian Belief Network (BBN) has been applied. Moreover, with the simple and fast heuristic algorithm, Dijkstra, the alternative transportation plan can be found. The result of numerical experiment shows the cost effectiveness of the proposed framework. Source

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