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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of the Society of Naval Architects of Korea
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Journal DOI :
The Society of Naval Architects of Korea
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Volume & Issues
Volume 50, Issue 6 - Dec 2013
Volume 50, Issue 5 - Oct 2013
Volume 50, Issue 4 - Aug 2013
Volume 50, Issue 3 - Jun 2013
Volume 50, Issue 2 - Apr 2013
Volume 50, Issue 1 - Feb 2013
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The Sloshing Effect on the Roll Motion and 2-DoF Motions of a 2D Rectangular Cylinder
Kim, Yun-Ho ; Sung, Hong-Gun ; Cho, Seok-Kyu ; Choi, Hang-Shoon ;
Journal of the Society of Naval Architects of Korea, volume 50, issue 2, 2013, Pages 69~78
DOI : 10.3744/SNAK.2013.50.2.69
This study is constructed to investigate the sloshing effect on the motions of a two-dimensional rectangular cylinder experimentally and numerically. The modes of motion under consideration are sway and roll, and also experimental cases are divided by two categories; 1-DoF roll motion and 2-DoF motion (Coupling sway and roll). It is found that the sway response is considerably affected by the motion of the fluid, particularly near the sloshing natural frequency, while the roll response changes comparatively small. The dominant mode of motion is analyzed for 2-DoF experiments as well. The measured data for 1-DoF motions is compared with numerical results obtained by the Multi-modal approach. The numerical schemes vary in detail with the number of dominant sloshing modes; i.e. there is a single dominant mode for the Single-dominant method, while the Model 2 method assumes that the first two modes are superior. For the roll motion, numerical results obtained by the two different methods are relatively in good agreement with the experiments, and these two results are similar in most wave frequency range. However, the discrepancies are apparent where the fluid motion is not governed by a single mode. But both of numerical methods over-predict the motion at the vicinity of the sloshing natural frequency. In order to correct the discrepancy, the modal damping needs to be investigated more precisely. Furthermore, another multi-modal approach, such as the Boussinesq-type method, seems to be required in the region of the intermediate liquid.
Analysis of Added Resistance using a Cartesian-Grid-based Computational Method
Yang, Kyung-Kyu ; Lee, Jae-Hoon ; Nam, Bo-Woo ; Kim, Yonghwan ;
Journal of the Society of Naval Architects of Korea, volume 50, issue 2, 2013, Pages 79~87
DOI : 10.3744/SNAK.2013.50.2.79
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.
Effects of Trim on Resistance Performance of a Ship
Park, Dong Woo ; Lee, Sang Bong ; Chung, Sung Seob ; Seo, Heung Won ; Kwon, Jae-Woong ;
Journal of the Society of Naval Architects of Korea, volume 50, issue 2, 2013, Pages 88~94
DOI : 10.3744/SNAK.2013.50.2.88
The primary objective of the current work is to obviously analyze regarding effects of trim conditions of a ship on resistance performance using model test and CFD. Model tests at a towing tank are conducted to investigate resistance for trim conditions at the given same displacement. Measured resistance shows small but distinct differences according to trim conditions. However, these differences are difficult to be clarified by measured physical quantities and wave pattern analysis from model tests. CFD is employed for the assessment of resistance performance according to trim conditions. The flow computation is conducted considering free surface and dynamic trim using a commercial CFD code (STAR-CCM+). The initiative of the present work is to systematically demonstrate pressure resistance acting on each region of divided finite zones of ship surface along the length and draught direction of surface when pressure distribution on the ship is interpreted. Also, a standard to assess the pressure resistance applied on the divided regions of a ship is established.
Numerical Prediction of Running Attitude and Resistance of Planing Craft
Oh, Gwangho ; Yoo, Jaehoon ;
Journal of the Society of Naval Architects of Korea, volume 50, issue 2, 2013, Pages 95~103
DOI : 10.3744/SNAK.2013.50.2.95
Prediction of the running posture is important to evaluate the resistance by the numerical calculation for a high speed vessel. Especially for a planing craft having a large variation of running attitude it becomes more essential, but it can not be obtained easily because the running posture and the hydrodynamic forces including the resistance are interacted with each other. So iterative calculation to obtain the dynamic forces according to the changes in attitude is necessary, in this study, considering the calculated hydrodynamic force at the assumed draft as the additional buoyancy the corrected draft is calculated through satisfying the equilibrium between the buoyancy and the hull weight. To verify the derived method three kinds of hull forms were used with the results of model tests, R/V ATHENA and 150 tons class guide vessel for middle-speed semi-planing crafts, 28 feet fast boat for a high-speed planing boat. For all cases with several iterations the converged value of draft can be obtained, lastly the resistance and flow around hull were simulated by using VOF method.
Design of Hull Residual Life Prediction System Considering Corrosion and Coating
Park, Seong-Whan ; Lee, Han Min ;
Journal of the Society of Naval Architects of Korea, volume 50, issue 2, 2013, Pages 104~110
DOI : 10.3744/SNAK.2013.50.2.104
In this paper, the design procedure and results for 'Residual Life Prediction System Considering Corrosion and Coating' are explained, which is one module of 'Life-cycle Management System of Ship and Offshore Plant's' Operation. This 'Residual Life Prediction System' has two main functions; one is residual life prediction function based on probability processing using corrosion measurement data of ship's major structural members, and another is rust rate prediction function based on visual image processing of inspection photos. The analysis of system user requirements and functions are introduced, and the structure and environment of the developed system are explained.
Natural Frequency of 2-Dimensional Heaving Circular Cylinder: Frequency-Domain Analysis
Lee, Dong-Yeop ; Lee, Seung-Joon ;
Journal of the Society of Naval Architects of Korea, volume 50, issue 2, 2013, Pages 111~119
DOI : 10.3744/SNAK.2013.50.2.111
The concept of the natural frequency is useful for understanding the characters of oscillating systems. However, when a circular cylinder floating horizontally on the water surface is heaving, due to the hydrodynamic forces, the system is not governed by the equation like that of the harmonic one. In this paper, in order to shed some lights on the more correct use of the concept of the natural frequency, a problem of the heaving circular cylinder is analyzed in the frequency domain. Previously, it was thought that the theory of Ursell (1949) could not be used to get the added mass and wave-making damping for short waves, however, they were obtained by applying an accurate collocation method to the theory in this study. Using the so developed numerical method, we found the added mass and wave-making damping of the circular cylinder for the entire range of the frequency. Then, the MCFR(Modulus of Complex Frequency Response) was used to locate the frequency corresponding to the local maximum of MCFR and we define it as the natural frequency. Comparing our results with the previous investigation, we found that the pressure distribution on the cylinder gets close asymptotically to that of a cylinder in infinite fluid OR close to that of the cylinder, that the approximation of the natural frequency by Lee (2008) is different from our new value only by 0.64%, and that the approximation of the heaving system by an equivalent damped harmonic oscillation is not proper by the reason that is clearly shown from the comparison of the shape of the corresponding MCFRs.
Study on the Effect of Density Ratio of Gas and Liquid in Sloshing Experiment
Ahn, Yangjun ; Kim, Sang-Yeob ; Kim, Kyong-Hwan ; Lee, Sang-Woo ; Kim, Yonghwan ;
Journal of the Society of Naval Architects of Korea, volume 50, issue 2, 2013, Pages 120~128
DOI : 10.3744/SNAK.2013.50.2.120
This paper presents the results of sloshing experiments having different fluids in model tanks with various density ratios. The experimental model consisting water and air at ambient, which has been commonly used, is not consistent in density ratio with that of an actual LNG cargo tank. Therefore, an advanced experimental scheme is developed to consider the same density ratio of LNG and NG by using a mixed gas of sulfur hexafluoride (
) and nitrogen (
). For experimental observation, a two-dimensional model tank of 1/40 scale and a three-dimensional model tank of 1/50 scale have been manufactured and tested at various conditions. Two different fillings with various excitation frequencies under regular motions have been considered for the two-dimensional model tank, and three different filling levels under irregular motions have been imposed for the three-dimensional model tank. The density ratio between gas and liquid varies from the ratio of the ambient air and water to that of the actual LNG cargo container, and the different composition of gas is used for this variation. Based on the present experimental results, it is found that the decrease of sloshing pressure is predicted when the density ratio increases.