• Progress in Superconductivity and Cryogenics
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• 제18권4호
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• pp.25-29
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• 2016

The high temperature superconducting (HTS) contra-rotating propulsion (CRP) systems comprise two coaxial propellers sited on behind the other and rotate in opposite directions. They have the hydrodynamic advantage of recovering the slipstream rotational energy which would otherwise be lost to a conventional single-screw system. However, the cooling systems used for HTS CRP system need a high cooling power enough to maintain a low temperature of 2G HTS material operating at liquid neon (LNe) temperature (24.5 - 27 K). In this paper, a single thermo-syphon cooling approach using a Gifford-McMahon (G-M) cryo-cooler is presented. First, an optimal thermal design of a 1.5 MW HTS motor was conducted varying to different types of commercial 2G HTS tapes. Then, a mono-cryogenic cooling system for an integration of two 1.5 MW HTS motors will be designed and analyzed. Finally, the 3D finite element analysis (FEA) simulation of thermal characteristics was also performed.

• Journal of Ocean Engineering and Technology
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• 제20권6호
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• pp.123-129
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• 2006

The mechanical properties of bellows, such as the extensibility and the strength can be changed depending on the shape. For the shipbuilding material, it is desirable that the fatigue life is long due to the elastic property and the reduction of thermal stress in piping system. Nowadays, the domestic production and design of bellows are based on the E.J.M.A. Code. Therefore, the design standard is in need because of much errors and lack of detailed analysis. In this study, it is attempted to find out the optimal shape of U-type bellows using the finite element analysis. The design factors, mountain height, length, thickness, and the number of convolutions are considered and the proper values are chosen for the simulation. The results shaw that as the number of convolutions reduces, the volume decreases while the stress increases. However, as the number of convolutions increases, the volume increases above the standard volume and the stress obviously increases. In addition, the effect of the thickness of bellows on the stress is very large. Both of the mass and stress are decreasing at a certain lower value region. Also, we investigated shape optimization with considering maximum stress distribution tendency.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제34권8호
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• pp.971-980
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• 2010

In this paper, we present a navigation control algorithm for mobile robots that move in environments having static and moving obstacles. The algorithm includes a global and a local path-planning algorithm that uses $D^*$ search algorithm, a fuzzy logic for determining the immediate level of danger due to collision, and a fuzzy logic for evaluating the required wheel velocities of the mobile robot. To apply the $D^*$ search algorithm, the two-dimensional space that the robot moves in is decomposed into small rectangular cells. The algorithm is verified by performing simulations using the Python programming language as well as by using the dynamic equations for a two-wheeled mobile robot. The simulation results show that the algorithm can be used to move the robot successfully to reach the goal position, while avoiding moving and unknown static obstacles.

• Journal of Information Technology and Architecture
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• 제9권2호
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• pp.143-154
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• 2012

With the realization of the importance of the NWI, iterated by the Cheonan Ship sink and the YP-Do shelling, this thesis separates the NWI from the peninsula, regarding it separate from the Korea Theater of Operations, and suggests the method to establish NCOE with consideration to the characteristics of separated theater as well as the current situation. Although the NWI holds strategic value, systematical NCOE of surveillance and reconnaissance system, command and control system, and precision strike system is not yet established. Pertaining to this issue, Architecting was utilized to identify improvement measures and of the identified improvement measures, improvement on the "strike on nK hardened artillery sites with K-9 Self-Propelled Artillery in correlations with theater ISR" shows greatly improved strike effects when conducting simulations based on the Operation-Plan Analysis Model. Such a method of NCOE establishment will serve as a standard model for military force building and operation execution system for separated theater operations such as the NWI.

• Journal of Advanced Marine Engineering and Technology
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• 제39권9호
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• pp.935-939
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• 2015

This paper describes sensorless speed control of brushless DC motors by using direct torque control. Direct torque control offers fast torque response, robust specification of parameter changes, and lower hardware and processing costs compared to vector-controlled drives. In this paper, the current error compensation method is applied to the sensorless speed control of a brushless DC motor. Through this control technique, the controlled stator voltage is applied to the brushless DC motor such that the error between the stator currents in the mathematical model and the actual motor can be forced to decay to zero as time proceeds, and therefore, the motor speed approaches the setting value. This paper discusses the composition of the controller, which can carry out robust speed control without any proportional-integral (PI) controllers. The simulation results show that the control system has good dynamic speed and load responses at wide ranges of speed.

• Journal of Advanced Marine Engineering and Technology
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• 제39권9호
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• pp.918-922
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• 2015

As international environmental regulations for pollutant and greenhouse gas emissions discharged from ships are being reinforced, it is drawing attention to use LNG as ship fuel. This paper compares the explosion risk potential in the LNG fuel gas supply systems of two types used in marine LNG fuelled vessels. By selecting 8500 TEU class container ships as target, LNG storage tank was designed and pressure conditions were assumed for the use of each fuel supply type. The leak hole sizes were divided into three categories, and the leak frequencies for each category were estimated. The sizes of the representative leak holes and release rates were estimated. The release rate and the leak frequency showed an inverse relationship. The pump type fuel gas supply system showed high leak frequency, and the pressure type fuel gas supply system showed high release rate. Computational fluid dynamics simulation was applied to perform a comparative analysis of the explosion risk potential of each fuel supply system.

• Journal of Advanced Marine Engineering and Technology
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• 제39권9호
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• pp.967-972
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• 2015

Because of recent interests in energy conservation and prevention of environmental pollution, research related to these topics is increasing. The U.S. Navy has started to study the HED (hybrid electric drive) system in order to improve the COGAG propulsion system's fuel efficiency in AEGIS destroyers. (This ship's fuel consumption is 40% of the total fuel consumption of the U.S. Navy.) In addition, the Korean Navy is considering applications of the HED system in AEGIS destroyers. The purpose of this study is to analyze the U.S.A.'s HED system and to simulate its generating mode energy saving rate using LabVIEW. The results confirmed that the fuel savings are about 700 kg/h.

• Journal of Navigation and Port Research
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• 제29권1호
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• pp.83-90
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• 2005

Intra-block remarshalling is the task of rearranging into some target bays those containers which are scattered around within the block, so that the containers can be loaded onto the ship efficiently. However, if we rearrange the containers without considering the container loading sequence, excessive rehandling work will be required at the time of loading because the containers to be fetched are often stacked under other containers. Therefore, the remarshalling should be done by moving the relevant containers in an appropriate order. This paper presents an efficient heuristic search technique for finding an appropriate container moving order during remarshalling to avoid rehandling at the time of loading. Simulation experiments have shown that the proposed method can generate rehandling-free solutions in real time.

• Journal of Navigation and Port Research
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• 제28권1호
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• pp.23-29
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• 2004

This paper deals with Reed-Solomon Coding for EUROFIX system EUROFIX is an integrated navigation and communication system, which combines Differential GNSS and Loran-C EUROFIX transmits DGNSS(Differential Global Navigation Satellite Systems) (data by pulse position modulation of Loran-C pulses. Loran-C system is regarded as a satellite backup system in recent. And now, it is important to detect and correct much errors in communication systems. Error corrections or correction algorithm is actively studied nowadays because of this. In this paper, we study and design encoder and decoder of Reed Solomon Code using Finite Galois Field Fourier Transformation for error corrections in EUROFIX data transmission. Through extensive simulation, the designed Reed Solomon code is shown to be effective for error correction in EUROFIX data transmission.

• Journal of Navigation and Port Research
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• 제30권8호
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• pp.617-622
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• 2006

Gamcheon Harbor was developed to cope with increased freight demand of Busan port and supplement function of the north port. Because container wharf is opened to 1997 as well as general wharf, present maximum 50,000DWT class containerships have been incoming and outgoing. However, In Gamcheon port, small size ships such as fishing boats, miscellaneous boats account for 50 percent of the traffic and a public marine products wholesale market that is building on the north wharf will open in 2008. Therefore, it needs to grasp future year traffic volume before establishing operation plan for port management. Also, analysis on crossing situation risk is required because the breakwater entrance in Gamcheon Harbor is narrow and the crossed passing of ship is ever-present at breakwater front. Thus the traffic volume in the future was presumed and quantitative analysis was achieved on crossing situation though simulations with the traffic volume.