• Journal of Ship and Ocean Technology
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• v.10 no.1
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• pp.1-9
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• 2006

The resistance reduction by an air lubrication effect of a large air cavity covering the hull bottom surface and the similarity relations involved have been investigated with a series of towing tank tests of three geometrically similar models. The test results of geometrically similar models have indicated that a large air cavity was formed beneath the bottom having a backward-facing step by artificially supplying air is effective for resistance reduction. The areas of air cavity and the required flow rates of air are directly related to the effective wetted surface area. The traditional extrapolation methods seem to be applicable to the estimation of the resistance in the tested range if corrections are made to account the changes in the frictional resistance caused by the changes in the effective wetted surface area. To investigate the effectiveness of air lubrication in improving the resistance performance of a practical ship, a small test boat having a backward-facing step under its bottom has been manufactured and speed trials in a river have been performed. Air has been supplied artificially into the downstream region of the bottom step to form a large air cavity covering the bottom surface. The results have confirmed the practical applicability of air lubrication for the resistance reduction of a small high-speed boat.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.5
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• pp.513-522
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• 2008

In this paper, one of the widely-used ice resistance prediction methods, introduced by Spencer(1992) of the Institute for Ocean Technology, Canada, is reviewed. Spencer's component-based scaling system for ship-ice model tests is analysed to estimate the ice resistance of various types of icebreaking vessels (Canadian MV Arctic, Terry Fox, R-Class icebreaker, US icebreakers Polar Star and Healy, Russian SA-15 cargo ships, Japanese PM Teshio and a model ship). The general form and the non-dimensional coefficients in ice resistance prediction formula are obtained using the published ice model test and full-scale sea trial data. The applicability of Spencer's method on R-Class icebreaker is discussed to estimate ice resistance for the larger icebreaking cargo vessels. Additional parameters to account for the difference in hull forms of icebreakers and cargo vessels are recommended to be included in the Spencer's original ice resistance prediction formula.

• Journal of Ocean Engineering and Technology
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• v.19 no.6 s.67
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• pp.16-21
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• 2005

In the design of super tankers or LNG carriers, which transport a large amount of liquid in the cargo tanks, the structural d11mage due to liquid sloshing is an important problem. The impact pressure from sloshing is most violent when the liquid motion of a partially filled tank is in resonance with the motion of a ship. In this study, the sloshing natural periods of a baffled tank, often installed to reduce liquid motion, is analyzed. A variational method is adopted to estimate the sloshing natural periods for a prismatic cargo tank with baffles of arbitrary filling depth of liquid; the results are compared with Lloyd's Register regulations on sloshing periods. In this study, using an effective liquid-fill-depth concept, sloshing periods for a baffled tank can be expressed by the same form as rectangular prismatic tanks without baffles. In contrast to Lloyd's Register regulations, which can be applicable only to cargo tanks with constant baffle size and distribution, the present results can be applicable to cases of variable baffle size and distribution.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.3
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• pp.117-124
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• 1992

Waves around a practical hull form and a series 60 model are computed by rectangular variable spacing and staggered flesh systems based on MAC(Marker and Cell) method. As a governing equation, the Euler equation is adopted. The comparison indicates that the computed waves are in good agreement with the measured results and that the MAC method is useful. On the other hand, a critical condition for the appearance of sub-breaking waves derived from the in viscid instability analysis is applied to the calculated flow field around a blunt bow. It is confirmed that the derived condition detects well the appearance of sub-breaking waves.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.2
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• pp.723-735
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• 2019

This paper employs computational tools to investigate the cause of resistance reductions in calm water and waves of the sharp bow form compared to the blunt bow in 66,000 DWT bulk carriers. A more slender shape at the fore-shoulder without a bulbous bow is a prominent feature of the sharp bow. The blunt bow incorporates a bulbous shape. A two-phase unsteady Reynolds averaged Navier-Stokes equations have been solved; and a realizable k-ε model has been applied for the turbulent closure. The free-surface is obtained by solving a VOF equation. The computational results have been validated with model tests carried out at a towing tank. The pressure component of resistance in the sharp bow is reduced by 8.9% in calm water, and 6.4-12.7% in regular head waves. The frictional components of resistance in the sharp and blunt bows are largely the same.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.5
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• pp.396-408
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• 2014

In this study, uncertainty analysis based on ITTC(International Towing Tank Conference) Recommended Procedures is carried out in the towing-tank experiment for motion responses and added resistance. The experiment was conducted for KVLCC2 model in head sea condition. The heave, pitch and added resistance were measured in different wave conditions, and the measurement was repeated up to maximum 15 times in each wave condition in order to observe the uncertainty of measured data. The uncertainty analysis was carried out by adopting the ISO-GUM(International Organization for Standardization, Guide to the Expression of Uncertainty in Measurements) method recommended by ITTC. This paper describes the details about the analysis method, uncertainty and the measured uncertainty for each source. The uncertainty analysis results are summarized as a tabular form. To validate the accuracy of the present measurement, the experimental results are compared with the results of numerical computation and other experiment. From the present uncertainty analysis, the main sources of uncertainty are identified, which can be very useful to improve the accuracy for added resistance experiment.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.2
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• pp.210-224
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• 2010

The aim of the present study is to investigate the buckling strength of plates and stiffened panels with opening under transverse thrust and shear actions. It is observed that the existing design formulation for critical-buckling strength of plates are not valid for perforated plates, because the current design formulation trends can significantly overestimate or underestimate the load-carrying capacity of plates when plates have large opening and/or are thick. A series of eigen value and elastic.plastic large deflection finite element analyses are carried out with varying the aspect ratio of plate, the opening size and location on plate until and after the ultimate strength is reached. Based on the results obtained from the present study, closed-form design formulations for the elastic buckling strength of plates and stiffened panels with opening are derived. The derived design formulations are considered plasticity correction of the material and verified by experimental tests and results of nonlinear finite element computations.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.2
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• pp.54-65
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• 1993

In computing the wave resistance numerically, satisfying the boundary condition(BC) on the body surface is not so difficult, and then what form of the BC on the free surface(FS) be used is a crucial question. To shed some light on this, we examine the various BC's on the FS, namely, the Poisson's[1], the Ogilvie's[2] and the Dawson's[3] BC, using the same panel method for submerged bodies in two-dimension. We also show the performance of the Poisson's BC for a submerged sphere and the Wigley hull. It seems that we are still in need of a theory which gives a BC on the FS more accurate than those tested, and more practically applicable than the exact nonlinear BC.

• Journal of Navigation and Port Research
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• v.36 no.3
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• pp.157-162
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• 2012

A planing craft is designed specifically to achieve comparatively high speed on the surface of the water. The frictional resistance of planing craft can be reduced further by injecting air to the craft's bottom. In this paper, the resistance characteristics of high speed planing crafts with & without air injection at the bottom were compared by sea model-test method. As a result, we conformed that planing craft with air injection has much greater the effect of resistance reduction.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.1
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• pp.67-77
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• 2014

In this study, Explicit Algebraic Reynolds Stress Model (EARSM) which is based on the existing ${\kappa}-{\omega}$ model has been applied to the flow field analysis around ship hulls. Existing transport equations for the turbulent kinetic energy and the dissipation rate are used in almost the same form and anisotropy terms of Reynolds stresses are newly considered. The well-known KVLCC2 and KCS hull forms are selected as validation cases, which were also used in 2010 Workshop on CFD in Ship Hydrodynamics. In case of KVLCC2 double model, comparison of mean velocity distribution, turbulent kinetic energy, and Reynolds stresses near the propeller plane has been carried out and wave elevation and wave profiles have been additionally studied for KCS and KVLCC2 with free surface models. Some improved results for mean velocity distribution at the propeller plane have been obtained while there is little change in free surface wave profiles.