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Min K.-I.,Samsung | Jung C.-H.,Republic of Korea Navy | Hur K.,Yonsei University | Jeon I.-Y.,Invensys | Moon Y.-H.,Yonsei University
IFAC Proceedings Volumes (IFAC-PapersOnline) | Year: 2011

This paper presents a new governor control scheme based on an Output Feedback PID controller which guarantees the control stability associated with the feedback gain and improves damping of the generator. The proposed control scheme of speed governor is developed on the basis of the PID controller in the previous study. The differential feedback has been replaced by the nonlinear output feedback. The proposed output feedback control has two advantages: first, it guarantees the wide-range of stable region for any change in the frequency regulation droop R with differential and integral feedback gains chosen in some proper range, and second remarkably improves generator damping free from havoc by the differential feedback. This paper discusses the possibility that the proposed governor control can be utilized as one of the means for power system stabilization (PSS). The computer simulations have been conducted on three cases, which show that generator damping can be remarkably improved by the proposed frequency control scheme. © 2011 IFAC.

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.

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.

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.

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.

Shin K.,Seoul National University | Shin Y.,LG Corp | Kwon J.-H.,Republic of Korea Navy | Kang S.-H.,Seoul National University
Computers and Industrial Engineering | Year: 2012

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 backorder replenishment plan to minimize the total replenishment cost and expected risk cost has been devised. In order to model the relationship between risks and risk propagation, Bayesian Belief Network has been applied. Moreover, with the fast heuristic algorithm, breath first search and elementary stepwise system based reverse Dijkstra, the alternative backorder replenishment plan can be established. The numerical example shows how to apply the proposed framework and make dynamic backorder replenishment plan considering impact of risk. © 2011 Elsevier Ltd. All rights reserved.

Shin K.S.,Seoul National University | Shin Y.W.,Seoul National University | Kwon J.-H.,Republic of Korea Navy | Kang S.-H.,Seoul National University
Industrial Management and Data Systems | Year: 2012

Purpose - The purpose of this paper is to propose a novel risk assessment approach that considers the inter-relationship between supply chain risks and the structure of network at the same time. To reduce the impact of the supply chain risk and enhance the flexibility of transportation route finding during the product delivery, the authors propose a way to model the risk propagation and how to integrate it with the supply chain network using Bayesian Belief Network (BBN). The key risk indicators (KRI) of each vertex and edge of the supply chain network which are measured or computed by the proposed approach can be utilized to develop the optimal transportation route in the execution phase. Design/methodology/approach - BBN is utilized to illustrate the relations among supply chain risks which may take place in a certain vertex. To apply the BBN to the supply chain network, the authors develop the framework to integrate BBN and the supply chain network by using the general functions that describe the characteristics of the risk factors and inter-relationships between vertices. Findings - By using the proposed risk assessment and dynamic route-finding approach, it is possible to reduce the unexpected cost from the supply chain risk and overcome the limitations of previous risk management strategies which focus on developing counter plans and assume the independency of supply chain risks. Practical implications - The proposed approach describes how to develop KRI-BBN to model the risk propagation and to integrate the KRI-BBN and supply chain network. The KRIs directly measured or computed by KRI-BBN in real time can be utilized to alternate supply chain execution plans such as inventory management, demand management and product flow management. Transportation problem considering risk is developed to show how to apply the proposed approach and numerical experiments are conducted to prove the cost effectiveness. Originality/value - The contribution of this paper lies in the way of developing KRI-BBN to assess the supply chain risk and modelling of the risk propagation by integrating KRI-BBN with supply chain network. With the proposed risk assessment approach, it is able to alternate the transportation route to minimize the unexpected cost and transportation cost simultaneously. © Emerald Group Publishing Limited.

Hwang J.-S.,Seoul National University | Kim J.-W.,Seoul National University | Nam H.-U.,Republic of Korea Navy | Park G.-C.,Seoul National University
Nuclear Technology | Year: 2011

A major safety factor in marine reactor design, critical heat flux (CHF), is assessed using the MARS system analysis code under heaving conditions. As gravity acceleration changes, the CHF is affected by the thermal hydraulics in the reactor through inlet flow fluctuations. Performing the analysis with the MARS code, which uses the properties of water for the working fluid, requires applying the CHF experimental data using fluid-to-fluid (FTF) scaling because most CHF experiments are conducted with Freon (R-113) as the working fluid. The FTF scaling methods suggested by Ahmad, Katto, and Coffield are adopted and compared. Otsuji et al.'s experiment, which was conducted using mass flow rate oscillation, is applied to evaluate the capability of MARS for heaving conditions. According to the calculations the FTF methods of Ahmad, Katto, and Coffield show good agreement (within an error of ±10.73% for Otsuji et al.'s experiment) for inlet flow rate oscillation corresponding to gravity acceleration in a vertical direction. In addition, variation of the acceleration affects the flow conditions, such as the mass flow rate and the void fraction. Thus, MARS has a noteworthy ability to predict the CHF for heaving conditions by simulating inlet flow rate oscillation.

Cho Y.,Republic of Korea Navy | Smith J.S.,Auburn University | Smith A.E.,Auburn University
2010 IEEE World Congress on Computational Intelligence, WCCI 2010 - 2010 IEEE Congress on Evolutionary Computation, CEC 2010 | Year: 2010

An agent location optimization model for military mobile ad-hoc networks is described. A mobile ad-hoc network (MANET) is a self-configuring network of autonomous agents designed to continuously support users who change the topology of the network dynamically and independently. The autonomous agents are controlled to maximize the connectivity of user nodes that move within the target region considering tactical military aspects. The primary objective of the agent location model is to maximize the connectivity and quality of communication between user nodes and a control node. To support military applications, a new approach, the Pre-deployed Agent Level (PAL) is introduced and a particle Swarm Optimization (PSO)-based heuristic with PAL is developed to solve the problem under three user mobility models. The focus of the paper is to determine the effect of PAL on the communication quality in the network. © 2010 IEEE.

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.

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