• Journal of the Society of Naval Architects of Korea
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• v.48 no.6
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• pp.544-551
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• 2011

The internal flows of moonpool usually causes huge added resistance on drillships, and those are very complex to analyze. Therefore, not only experimental approaches but also numerical simulations are required for better investigations when dealing with the hydrodynamic problems of moonpool. In the present research, numerical simulations are used to find out why the resistance increases by moonpool on a running drillship. That is, the three-dimensional numerical simulations and model tests are carried out to examine the characteristics of internal flow and added resistance by changing the section of the moonpool in both longitudinal and transverse directions. Finally, based on the present studies, an optimized shape of the moonpool is suggested, which effectively reduces added resistance, and that is confirmed with three-dimensional numerical simulations and model tests.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.2
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• pp.132-142
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• 2017

As the International Maritime Organization (IMO) recently introduced the Energy Efficiency Design Index (EEDI) for new ships building and the Energy Efficiency Operational Indicator (EEOI) for ship operation, thus an accurate estimation of added resistance of ships advancing in waves has become necessary. In the present study, OpenFOAM, computational fluid dynamics libraries of which source codes are opened to the public, was used to calculate the added resistance and motions of the KCS. Unstructured grid using a hanging-node and cut-cell method was used to generate dense grid around a wave and KCS. A dynamic deformation mesh method was used to consider the motions of the KCS. Five wavelengths from a short wavelength (${\lambda}/LPP=0.65$) to a long wavelength (${\lambda}/LPP=1.95$) were considered. The added resistance and the heave & pitch motions calculated for various waves were compared with the results of model experiments.

• Journal of the Korean Magnetics Society
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• v.5 no.3
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• pp.222-232
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• 1995

자기저항이란 외부 자기장에 의해 재료의 전기저항이 변화되는 현상을 일컫는다. Au와 같은 비자성도체 및 반도체 재료의 경우 외부에서 자기장이 가해지면 전도 전자가 Lorentz 힘을 받아 궤적이 변하므로 저항이 변화한다. 이러한 저항 변화 를 정상 자기저항(Ordinary Magnetoresistance, OMR)이라 하며 일반적으로 상당히 작은 저항의 변화를 나타낸다. 강자성도체 재료에서는 정상 자기저항 효과 외에도 부가적인 효과가 생긴다. 이는 스핀-궤도 결합에 기인한 효과로써 자기 저항은 강자성체의 자화용이축, 외부자계와 잔류간의 각도에 의존하며 이방성 자기저항(Anisotropic Magnetoresistance, AMR)이라 한다. AMR 비(%)는 일반적 으로 다음과 같이 정의된다. 즉 ${\Delta}{\rho}_{AMR}/{\rho}_{ave}=(\rho_{\|}-\rho_{T})/{\rho}_{ave}$로 여기서 $\rho_{\|}$는 자기장의 방향이 전류의 방향과 같을 때의 비저항 이고 $\rho_{T}$는 서로 수직일 때이며 ${\rho}_{ave}=(\rho_{\|}-\rho_{T})/3$이다. 기존의 MR 센서나 자기재생헤드(magnetic read head)에 사용되는 퍼머로이계 합금의 AMR 비는 상온에서 약 2% 정도의 저항변화를 보인다.

• Tuberculosis and Respiratory Diseases
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• v.52 no.3
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• pp.251-259
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• 2002

Background : Reduced lung compliance and increased lung resistance are the primary lung mechanical abnormalities in acute respiratory distress syndrome (ARDS). Although there is little information regarding the mechanisms responsible for the increases in the respiratory resistance of ARDS, bronchodilators have been frequently administered in mechanically ventilated ARDS patients. To determine the effect of a bronchodilator on the respiratory mechanics depending on the level of applied positive end-expiratory pressure (PEEP), the changes in the respiratory mechanics by salbutamol inhalation was measured under the variable PEEP level in patients with ARDS. Materials and Methods : Fifteen mechanically ventilated paralyzed ARDS patients (14 of male, mean age 57 years) were enrolled in this study. The respiratory system compliance, and the maximum and minimum inspiratory resistance were obtained by the end-inspiratory occlusion method during constant flow inflation using the CP-100 pulmonary monitor (Bicore, Irvine, CA, USA). The measurements were performed at randomly applied 8, 10 and 12 cm $H_2O$ PEEP before and 30 mins after administrating salbutamol using a meter-dose-inhaler (100ug${\times}$6). Results : 1) The maximum inspiratory resistance of the lung was higher than the reported normal values due to an increase in the minimal inspiratory resistance & additional resistance. 2) The maximum inspiratory resistance and peak airway pressure were significantly higher at 12cm $H_2O$ of PEEP compared with those at 10cm $H_2O$ of PEEP. 3) Salbutamol induced a significant decrease in the maximum and the minimum inspiratory resistance but no significant change in the additional resistance only was observed at 12cm $H_2O$ of PEEP(from $15.66{\pm}1.99$ to $13.54{\pm}2.41$, from $10.24{\pm}2.98$ to $8.04{\pm}2.34$, and from $5.42{\pm}3.41$ to $5.50{\pm}3.58cm$ $H_2O$/L/sec, respectively). 4)The lung compliance did not change at the applied PEEP and salbutamol inhalation levels. Conclusion : The bronchodilator response would be different depending on the level of applied PEEP despite the increased respiratory resistance in patients with ARDS.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.4
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• pp.75-86
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• 1992

This paper reports theoretical and experimental investigation into the added resistance of SWATH ships in waves. It was revealed from the experimental investigations on various SWATH models that the resistance of the SWATH models in waves is considerably reduced over part of the speed range as the wave height increases. As a first step to Identify it, the first and second order wave forces have been investigated barred on a linearised 3-D diffraction theory together with simplified boundary conditions and same results are reported herein. Also, the speed performance of SWATH ships in rough seas is compared with those of equivalent monohulls as well as with those of advanced high speed marine vehicles.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.6
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• pp.459-479
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• 2014

This paper considers experimental and numerical studies on added resistance in waves. As the numerical methods, three different methods, strip method, Rankine panel method and Cartesian-grid method, are applied. The computational results of vertical motion response and added resistance are compared with the experimental data of Series 60($C_B=0.8$) hull, S175 containership and KVLCC2 hull. To investigate the influence of above-still water hull form, a Rankine panel method is extended to two nonlinear methods: weakly-nonlinear and weak-scatterer approaches. As nonlinear computational models, three ships are considered: original KVLCC2 hull, 'Ax-bow' and 'Leadge-bow' hulls. Two of the three models are modified hull forms of original KVLCC2 hull, aiming the reduction of added resistance. The nonlinear computational results are compared with linear results, and the improvement of computational result is discussed. As experimental approach, a series of towing-tank experiment for ship motions and added resistance on the three models (original KVLCC2 hull, 'Ax-bow' and 'Leadge-bow') are carried out. For the original KVLCC2 hull, uncertainty analysis in the measurement of vertical motion response and added resistance is performed in three waves conditions: ${\lambda}/L=0.5$, 1.1, 2.0. From the experimental results, the effects of hull form on added resistance are discussed.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.6
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• pp.471-477
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• 2015

When a ship sails in a seaway, the resistance on a ship increases due to incident waves and winds. The magnitude of added resistance amounts to about 15–30% of a calm-water resistance. An accurate prediction of added resistance in waves, therefore, is essential to evaluate the performance of a ship in a real sea state and to design an optimum hull form from the viewpoint of the International Maritime Organization (IMO) regulations such as Energy Efficiency Design Index (EEDI) and Energy Efficiency Operational Indicator (EEOI). The present study considers added resistance problem of AFRAMAX-class tankers with the conventional bow and Ax-bow shapes. Added resistance due to waves is successfully calculated using 1) a three-dimensional time-domain seakeeping computations based on a Rankine panel method (three-dimensional panel) and 2) a commercial CFD program (STAR-CCM+). In the hydrodynamic computations of a three-dimensional panel method, geometric nonlinearity is accounted for in Froude-Krylov and restoring forces using simple wave corrections over exact wet hull surface of the tankers. Furthermore, a CFD program is applied by performing fully nonlinear computation without using an analytical formula for added resistance or empirical values for the viscous effect. Numerical computations are validated through four degree-of-freedom model-scale seakeeping experiments in regular head waves at the deep towing tank of Hyundai Heavy Industries.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.2
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• pp.79-87
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• 2013

In this paper, an Euler equation solver based on a Cartesian-grid method and non-uniform staggered grid system is applied to predict the ship motion response and added resistance in waves. Water, air, and solid domains are identified by a volume-fraction function for each phase and in each cell. For capturing the interface between air and water, the tangent of hyperbola for interface capturing (THINC) scheme is used with a weighed line interface calculation (WLIC) method. The volume fraction of solid body embedded in a Cartesian-grid system is calculated by a level-set based algorithm, and the body boundary condition is imposed by volume weighted formula. Added resistance is calculated by direct pressure integration on the ship surface. Numerical simulations for a Wigley III hull and an S175 containership in regular waves have been carried out to validate the newly developed code, and the ship motion responses and added resistances are compared with experimental data. For S175 containership, grid convergence test has been conducted to investigate the sensitivity of grid spacing on the motion responses and added resistances.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.1
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• pp.62-68
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• 2016

A simple calculation tool for added resistance in waves is developed to utilize for initial design or embedded module for navigation support system. In order to select an appropriate calculation method for added resistance in waves, three methods (drift method, integrated pressure method, radiated energy method) based on strip method are applied to Wigley I and KVLCC2. The methods for added resistance in waves give the underestimated results because it is difficult to consider nonlinear effects due to reflected wave. We apply asymptotic (Faltinsen's method) and empirical formula (NMRI's method) to improve the accuracy for short wave length region. In comparison with experimental results, the combination of radiated energy method and short wave correction method of NMRI is the most reasonable. However, a simple sum of results calculated by two methods gives rise to the overestimation of added resistance for short wave length region because added resistance of radiated energy method exits in total reflection region. To overcome this problem, modified radiated energy method is proposed using correction coefficient defined by reflection coefficient of NMRI's method. Finally, added resistance in regular waves is composed of added resistance of modified radiated energy method and that of short wave correction method of NMRI. Estimated added resistance in regular waves is validated by comparison with experimental results of other research groups.

• 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.