• Ocean Systems Engineering
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• v.10 no.3
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• pp.333-357
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• 2020

International Maritime Organisation (IMO) regulations insist on reduced emission of CO₂, noxious and other environmentally dangerous gases from ship, which are usually let out while burning fossil fuel for running its propulsive machinery. Contrallability of ship during sailing has a direct implication on its course keeping and changing ability, and tries to have an optimised routing. Bad coursekeeping ability of a ship may lead to frequent use of rudder and resulting changes in the ship's drift angle. Consequently, it increases vessels resistance and also may lead to longer path for its journey due to zigzag movements. These adverse effects on the ship journey obviously lead to the increase in fuel consumption and higher emission. Hence, IMO has made it mandatory to evaluate the manoeuvring qualities of a ship at the designed stage itself. In this paper a numerical horizontal planar motion mechanism is simulated in CFD environment and from the force history, the hydrodynamic derivatives appearing in the manoeuvring equation of motion of a ship are estimated. These derivatives along with propeller thrust and rudder effects are used to simulate different standard manoeuvres of the vessel and check its parameters against the IMO requirements. The present study also simulates these manoeuvres by using numerical free running model for the same ship. The results obtained from both these studies are presented and discussed here.

• Journal of Ocean Engineering and Technology
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• v.31 no.2
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• pp.155-163
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• 2017

Submerged bodies moving underwater behave differently based on their type and assigned mission. This paper describes the dynamic characteristics, including the stability, turning ability, and operational ability, of submerged bodies in relation to design parameters such as the tail cone angle, shape of the control plate, and length of the parallel middle body. A submerged body operated in other countries is adopted as a reference for the dynamic characteristics, its principal dimensions and the shape of the bare hull and appendages are used for comparison. This paper suggests a few candidate hull forms based on changes in the typical design parameters. Finally, the dynamic characteristics for these candidate hull forms are defined.

• Journal of Ocean Engineering and Technology
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• v.35 no.1
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• pp.13-23
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• 2021

Since the introduction of the mandatory energy efficiency design index (EEDI), several studies have been conducted on the maneuverability of waves owing to the decrease in engine power. However, most studies have used the mean wave force during a single cycle to evaluate maneuverability and investigated the turning performance. In this study, we calculated the external force in accordance with the angle of incidence of the wave width and wavelengths encountered by KVLCC2 (KRISO very large crude-oil carrier) operating at low speeds in regular waves using computational fluid dynamics (CFD). We compare the model test results with those published in other papers. Based on the external force calculated using CFD, an external force that varies according to the phase of the wave that meets the hull was derived, and based on the derived external force and MMG control simulation, a maneuvering simulation model was constructed. Using this method, a weather vaning simulation was performed in regular waves to evaluate the course-keeping ability of KVLCC2 in waves. The results confirmed that there was a difference in the operating trajectory according to the wavelength and phase of the waves encountered.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.466-477
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• 2021

There are three different well-known methods for predicting the manoeuvrability of ships: (1) free running model test, (2) direct manoeuvring simulation using CFD and (3) system-based manoeuvring simulation. In this paper, the manoeuvrability of the KVLCC2 was estimated using CFD with rigid body motion and body force propeller method. The free running manoeuvre at the different time steps were also simulated. The yaw checking ability and the turning ability of KVLCC2 were predicted using CFD and could have been confirmed that the IMO criteria was satisfied. When the results were compared with the model test and system-based method, the free running simulation showed better agreement to that of the model test. It could also be confirmed that the results vary depending on the time step. Overall, the CFD results using the body force propeller method estimated most accurately the test results.

• 한국데이터정보과학회:학술대회논문집
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• 2005.04a
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• pp.155-163
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• 2005

This paper applies Support Vector Regression (SVR) to estimate and forecast nonlinear autoregressive integrated (ARI) model of the daily exchange rates of four currencies (Swiss Francs, Indian Rupees, South Korean Won and Philippines Pesos) against U.S. dollar. The forecasting abilities of SVR are compared with linear ARI model which is estimated by OLS. Sensitivity of SVR results are also examined to kernel type and other free parameters. Empirical findings are in favor of SVR. SVR method forecasts exchange rate level better than linear ARI model and also has superior ability in forecasting the exchange rates direction in short test phase but has similar performance with OLS when forecasting the turning points in long test phase.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.6
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• pp.80-89
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• 1998

Back rake angle of tool is one of the fundamental effects to the cutting ability. In this paper, for several back rake angle of lathe tool (-5$^{\circ}$ , 0$^{\circ}$ , 5$^{\circ}$ , 10$^{\circ}$ , 15$^{\circ}$ ), we experimentally examine cutting forces via orthogonal cutting. Using measured cutting forces, a formula for specific cutting resistance is derived according to the variation of tool angle. Also, the measured cutting forces are analyzed in both time and frequency domain. Cutting parameters are obtained by measuring the thickness of chip, and the effect of the back rake angle of tool is manifested. This study maintains the predicted cutting model with improved accuracy.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.925-928
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• 2004

The application of focused ion beam (FIB) technology in micro/nano machining has become increasingly popular. Its use in micro/nano machining has advantages over contemporary photolithography or other micro/nano machining technologies such as small feature resolution, the ability to process without masks and being accommodating for a variety of materials and geometries. This paper was carried out some experiments and verifications of mechanism on FIB-CVD using SMI8800 made by Seiko. FIB-CVD has in fact proved to be commercially useful for repair processes because the beam can be focused down to 0.05$\mu\textrm{m}$ dimensions and below and because the same tool can be used to sputter off material with sub-micrometer precision simply by turning off the gas ambient. Recently the chemical vapour deposition induced ion beam has been required more deposition rate and accurate pattern because of trying to manufacture many micro and nano parts. Therefore this paper suggested the optimization parameters and discussed some mechanism of chemical vapour deposition induced ion beam on FIB-CVD for simple pattern.

• Journal of the Korean Institute of Navigation
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• v.24 no.5
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• pp.397-403
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• 2000

Since very large and high-speed ships have been appeared in marine transportation from 1970s, these ships with poor maneuverability have made large-scale accidents frequently all over the world. The IMO(International Maritime Organization) recommended that ship designers should evaluate various maneuvering performance at initial stage and serve them to ship operators when they deliver a new ship. Meantime, it is expected that ships with large and wide superstructure would have poor maneuverability when they are affected by strong wind. Therefore, car carrier ship with large superstructure was selected to confirm how the ship responds to the external wind forces in this paper. The lateral and transverse projected areas above the water level were considered and ship behaviors were checked by change of rudder angles under severe wind conditions of different directions. In addition, hydrodynamic derivatives and coefficients were predicted from ship particulars and numerical calculations were carried out with the mathematical model of low speed maneuvering motions.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.4 s.148
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• pp.399-413
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• 2006

Mathematical model for coupled motions of Manta-type Unmanned Undersea Vehicle(UUV) moving with six degrees of freedom, is formulated. Furthermore, a calculation method for estimating the linear hydrodynamic derivatives acting on UUV, is proposed, and some of the estimated linear hydrodynamic derivatives are compared with results of captive model experiment. Based on linear dynamic model of UUV, a study was made to examine dynamic stability and turning ability in horizontal plane. And directional stability and required elevation rudder angles for neutrally operating in vertical plane, are also discussed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.529-532
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• 2003

Machining technique for optical crystals with single point diamond turning tool is reported in this paper. The main factors influencing the machined surface quality are discovered and regularities of machining process are drawn. Optical crystals have found more and more important applications in the field of modern optics. Optical crystals are mostly brittle materials of poor machinability. The traditional machining method is polishing which has many shortcomings such as low production efficiency. poor ability to be automatically controlled and edge effect of the workpiece. The purpose of our research is to find the optimum machining conditions for ductile cutting of optical crystals and apply the SPDT technique to the manufacturing of ultra precision optical components of brittle materials. As a result. the surface roughness is good when spindle speed is 200m/min. and teed rate is small. The influence of depth of cut is very small.