• 한국정보과학회논문지:컴퓨팅의 실제 및 레터
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• 제9권6호
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• pp.674-682
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• 2003

선박 자율운항시스템(autonomous navigation system)이란 선박운항에 있어 항해계획을 수립하고 현재의 선박운항 상태를 파악하여 주변 상황변화를 예측하고 대처하는 항해 전문가의 능력을 전산화한 것이다. 선박 자율운항시스템은 항해, 충돌회피, 선체유지, 자료융합, 운동제어 그리고 이를 통합하는 아키텍처로 구성되어 있다. 운동제어시스템은 선박의 유체학적 특성을 고려하여 해도 상에 원하는 위치로 선박을 이동하기 위해서 추진 및 조타장치를 제어하는 시스템으로 자율운항제어시스템에 필수적인 구성 시스템 중에 하나이다. 본 논문은 운영플랫폼인 가상세계시스템을 기반으로 운영되는 선박자율운항시스템과 운동제어시스템의 연동과 구현에 관한 연구이다. 운동제어시스템은 충돌회피시스템으로부터 상위 레벨의 고수준제어 요구치를 전달받아 조타 및 추진치로 변환하고 조타장치와 추진장치를 제어하는 시스템이다. 본 논문에서 선박 운동 특성을 수학적으로 모방하는 Oldenburger의 제어 이론에 기반하여 선박운동제어기를 개발하고 성능검정을 위해 선박시뮬레이터에서 다양한 시나리오를 바탕으로 시뮬레이션 한다.

• 대한조선학회논문집
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• 제47권2호
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• pp.150-162
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• 2010

Assessment of hydrodynamic performance of a ship hull has been focused on a model ship rather than a full-scale ship. In order to design the propeller of a ship, model-scale wake is often extended to full-scale based upon an empirical method or designer's experience, since wake measurement data for a full-scale ship is very rare. Recently modern CFD tools made some success in reproducing wake field of a model ship, which implicates that there are some possibilities of the accurate prediction of full-scale wakes. In this paper firstly the evaluation of model-scale wake obtained by Fluent package was performed. It was found that CFD calculation with the Reynolds-stress model (RSM) provided much better agreement with wake measurement in the towing tank than with the realizable k-$\varepsilon$ model (RKE). In the next full-scale wake was calculated using the same package to find out the difference between model and full-scale wakes. Three hull forms of KLNG, KCS, KVLCC2 having measurement data open for the public, were chosen for the comparison of resistance, form factor, and propeller plane wake between model ships and full-scale ships.

• 한국해양공학회지
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• 제29권3호
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• pp.270-282
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• 2015

A submerged body moving near the free surface needs to maintain its attitude and position to accomplish missions. It is necessary to validate the performance of a designed controller before a sea trial. The hydrodynamic coefficients of maneuvering are generally obtained by experiments or computational fluid dynamics, but these coefficients have uncertainty. Environmental loads such as the wave exciting force and suction force act on the submerged body when it moves near the free surface. Thus, a controller for the submerged body should be robust to parameter uncertainty and environmental loads. In this paper, the six-degree-of-freedom equations of motions for the submerged body are constructed. The suction force is calculated using the double Rankine body method. An adaptive control method based on an artificial neural network and proportional-integral-derivative control are used for the depth controller. Simulations are performed under various depth and speed conditions, and the results show the effectiveness of the designed controller.

• 대한조선학회논문집
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• 제50권1호
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• pp.1-7
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• 2013

The high-skewed and/or composite propellers of current interests to reduce the ship vibration and to increase the acoustic performance are likely to be exposed to the unexpected structural problems. One typical example is that the added mass effect on the propellers working in the non-uniform wake field reduces the natural frequency of the propeller leading to the resonance with the low-frequency excitation of the external forces. To avoid this resonance problem during the design stage, the technique of fluid-structure interaction has been developed, but the higher-order effect of the blade geometry deformation is not yet considered in evaluating the added mass effects. In this paper the fluid boundary-value problem is formulated by the potential-based panel method in the inviscid fluid region with the velocity inflow due to the body deformation, and the structural response of the solid body under the hydrodynamic loading is solved by applying the finite element method which implements the 20-node iso-parametric element model. The fluid-structure problem is solved iteratively. A basic fluid-sturcture interaction study is performed with the simple rectangular plates of thin thickness with various planform submerged in the water of infinite extent. The computations show good correlation with the experimental results of Linholm, et al. (1965).

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권3호
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• pp.562-577
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• 2014

A reliable steady/transient hydro-elastic analysis is developed for flexible (composite) marine propeller blade design which deforms according to its environmental load (ship speed, revolution speed, wake distribution, etc.) Hydro-elastic analysis based on CFD and FEM has been widely used in the engineering field because of its accurate results however it takes large computation time to apply early propeller design stage. Therefore the analysis based on a boundary element method-Finite Element Method (BEM-FEM) Fluid-Structure Interaction (FSI) is introduced for computational efficiency and accuracy. The steady FSI analysis, and its application to reverse engineering, is designed for use regarding optimum geometry and ply stack design. A time domain two-way coupled transient FSI analysis is developed by considering the hydrodynamic damping ffects of added mass due to fluid around the propeller blade. The analysis makes possible to evaluate blade strength and also enable to do risk assessment by estimating the change in performance and the deformation depending on blade position in the ship's wake. To validate this hydro-elastic analysis methodology, published model test results of P5479 and P5475 are applied to verify the steady and the transient FSI analysis, respectively. As the results, the proposed steady and unsteady analysis methodology gives sufficient accuracy to apply flexible marine propeller design.

• 한국항해항만학회지
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• 제34권5호
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• pp.325-330
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• 2010

선박의 조종성능 향상을 위해 적용되고 있는 쌍동타의 유체력 평가를 위해 $Re=1.5{\times}10^4$에서 쌍동타의 상 하부 러더 간격을 변화시켜 쌍동타 주위 유동을 계측하였다. 영각의 변화에 따른 쌍동타 주위에서 생성되는 와의 생성과 소멸 메커니즘을 이해하기 위해 속도 및 에너지 분포를 2-프레임 그레이레벨 상호상관 PIV기법을 이용하여 비교 분석하였다. 쌍동타의 상 하부 러더 간격 L=0.75C에서 물리적 한계영역으로 정의되었다.

• 대한조선학회논문집
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• 제57권1호
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• pp.35-44
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• 2020

Propeller cavitation extent, pressure fluctuation induced by cavitation, pressure distribution on propeller blade, total velocity distribution and nominal wake distribution for a MR Taker were computed in both conditions of model test and sea trial using a code STAR-CCM⁺. Then some of the results were compared with model test data at LCT and full-scale measurement (Ahn et al (2014); Kim et al (2014)] in order to confirm the availability of a numerical prediction method and to get the physical insight of local flow around a ship and propeller. The nominal wake distributions computed and measured by LDV velocimeter on the variation of on-coming velocity show the wake contraction characteristics proposed by Hoekstra (1974). The numerical prediction of propeller cavitation extent on a blade angular position and pressure fluctuation level on each location of pressure sensors are very similar with the experimental results.

• Tribology and Lubricants
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• 제34권6호
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• pp.247-253
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• 2018

Temperature rise due to viscous shear of the lubricating oil generates hydrodynamic pressure, even if the lubricating surfaces are parallel. This effect, known as the thermal wedge effect, varies significantly with film-temperature boundary conditions. The bearing conducts a part of the heat generated; hence, the oil temperature varies with the thermal conductivity of the bearing. In this study, we analyze the effect of thermal conductivity on the thermohydrodynamic (THD) lubrication of parallel slider bearings. We numerically analyze the continuity equation, Navier-Stokes equation, energy equation including the temperature-viscosity and temperature-density relations for lubricants, and the heat conduction equation for bearing by creating a 2D model of the micro-bearing using the commercial computational fluid dynamics (CFD) code FLUENT. We then compare the variation in temperature, viscosity, and pressure distributions with the thermal conductivity. The results demonstrate that the thermal conductivity has a significant influence on THD lubrication characteristics of parallel slider bearings. The lower the thermal conductivity, the greater the pressure generation due to the thermal wedge effect resulting in a higher load-carrying capacity and smaller frictional force. The present results can function as the basic data for optimum bearing design; however, the applicability requires further studies on various operating conditions.

• 한국해양공학회지
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• 제33권4호
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• pp.313-321
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• 2019

The prediction of the hydrodynamic performance of a planing hull vessel is an important and challenging topic for computational fluid dynamic (CFD) applications to naval hydrodynamics. In this paper, the resistance and planing attitude analysis for a Fridsma hull, which is a prismatic planing hull, in still water are numerically studied using OpenFOAM. OpenFOAM is an open source code package based on C++ libraries and the finite volume method (FVM) for the discretization of the RANS equation. The volume of fluid method (VOF) is used to capture the water-air interface and the SST ${\kappa}-{\omega}$ model is used for the turbulence simulation. The overset mesh method is used to capture the large motion of the hull at higher speeds. Before the extensive analysis, uncertainty analyses using various time steps and grid sizes were performed for one ship speed case of Fn = 1.19. The results of the present study are compared with those of a model test, other CFD research, and Savitsky's empirical formula. The results of the present study, following the trend of other CFD results, slightly over predict the resistance and under predict the sinkage and, more significantly, the trim.

• Tribology and Lubricants
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• 제35권2호
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• pp.123-131
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• 2019

This study characterizes the coastdown performances of two small electric motors supported on high-speed ball bearings (BBs) and gas foil bearings (GFBs), and it predicts their acceleration performances. The two motors have identical permanent magnetic rotors and mating stators. However, the shaft of the GFBs has a larger mass and polar/transverse moments of inertia than that of the BBs. Motor coastdown tests demonstrate that the rotor speed decreases linearly with the BBs and nonlinearly with the GFBs. A simple model for the BBs predicts a constant drag torque and linear decay of speed with time. The test data validate the model predictions. For the GFBs, the hydrodynamic lubrication model predictions reveal that the drag torque increases linearly with speed, and the speed decreases exponentially with time. The predictions agree very well with the test data in the speed range of 100-30 krpm. The boundary lubrication model predicts a constant drag torque and linear decay of speed with time. The predictions agree well with the test data below 15 krpm. Mixed lubrication occurs in the speed range of 30-15 krpm. Rotor acceleration performances are predicted based on the characteristics of deceleration performances. The GFBs require more time to reach 100,000 krpm than the BBs because of their larger shaft polar moment of inertia. However, predictions for the assumed identical polar moment of inertia reveal that the GFBs have a nearly identical acceleration performance to that of the BBs with a motor torque greater than $0.03N{\cdot}m$.