• Journal of Ocean Engineering and Technology
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• v.31 no.6
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• pp.379-387
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• 2017

In this study, a pile-guide mooring system (PGMS) was designed for an offshore liquefied natural gas bunkering terminal (LNG-BT), which is an essential infrastructure for large LNG-fuelled ships. The PGMS consisted of guide piles to restrict five motions of the floater, except for heave, as well as a seabed truss structure to support the guide piles and foundation piles to fix the system to the seabed. Singapore port was considered for a case study because it is a highly probable ports for LNG bunkering projects. The wave height, current speed, and wind speed in Singapore port were investigated to calculate the environmental loads acting on the hull and PGMS. A load and resistance factor approach was used for the structural design, and a finite element analysis was performed for design verification. The steel usage of the PGMS was analyzed and compared with the material usage of a gravity-based structure under similar LNG capacity and water depth criteria. This paper also describes the water depth limit and wave conditions of the PGMS based on estimation of the initial investment and the present value profit difference. It suggests a suitable LNG-BT support system for various design conditions.

• Journal of Advanced Marine Engineering and Technology
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• v.17 no.1
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• pp.55-65
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• 1993

Galvanic protection method is one the cathodic protection methods and is mostly used for corrosion prevention of heat exchangers and ship's hull. In this paper, it was investigated that how cathodic potential distribution was varied with according to the bare and painted steel plates in case of galvanic anode protection. The results obtained above were as follows. 1. Cathodic potential distribution of a painted steel plate was smoothed than that of the bare steel plate all over the cathodic surface area. 2. It was shown that polarization potential of the bare steel plate was somewhat shifted to negative potential, on the contrary that of the painted steel plate was somewhat shifted from negative potential to positive potential as time gone by beginning of galvanic anode method. 3. The applied current density in order to maintain constant protection potential(-770mv SCE) in the painted steel plate was less than that of the bare steel plate because of the high resistance polarization of the painted steel plate. 4. It was suggested that required number and life-time of anode for galvanic anode protection could be decided easily with corrosion prevention coefficient obtained by experimental data.

• Journal of Ocean Engineering and Technology
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• v.23 no.6
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• pp.71-76
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• 2009

This paper describes a statistical analysis method for predicting a coast fishing boat's effective horsepower. The EHP estimation method for small coast fishing boats was developed, based on a statistical regression analysis of model test results in a circulating water channel. The statistical regression formula of a fishing boat's effective horsepower is determined from the regression analysis of the resistance test results for 15 actual coast fishing boats. This method was applied to the effective horsepower prediction of a G/T 4 ton class coast fishing boat. From the estimation of the effective horsepower using this regression formula and the experimental model test of the G/T 4 ton class coast fishing boat, the estimation accuracy was verified under 10 percent of the design speed. However, the effective horsepower prediction method for coast fishing boats using the regression formula will be used at the initial design and hull-form development stage.

• Journal of Advanced Research in Ocean Engineering
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• v.3 no.2
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• pp.83-101
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• 2017

In this study, the added resistances of the large container ship in head and oblique seas are evaluated using a time-domain Rankine panel method. The mean forces and moments are computed by the near-field method, namely, the integration of the second-order pressure directly on the ship surface. Furthermore, a weakly nonlinear approach in which the nonlinear restoring and Froude-Krylov forces on the exact wetted surface of a ship are included in order to examine the effects of amplitudes of waves on ship motions and added resistances. The computation results for various advance speeds and heading angles are validated by comparing with the experimental data, and the validation shows reasonable consistency. Nevertheless, there exist discrepancies between the numerical and experimental results, especially for a shorter wave length, a higher advance speed, and stern quartering seas. Therefore, the accuracies of the linear and weakly nonlinear methods in the evaluation of the mean drift forces and moments are also discussed considering the characteristics of the hull such as the small incline angle of the non-wall-sided stern and the fine geometry around the high-nose bulbous bow.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.3
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• pp.292-304
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• 2017

High-speed vessels are prone to the surf-riding in adverse quartering seas. The possibility of mitigating the surf-riding of the ITTC A2 fishing vessel in the design stage is investigated using the 6-DOF weakly non-linear model developed for surf-riding simulations in quartering seas. The longitudinal position of the ship's center of buoyancy (LCB) is chosen as the design parameter. The adjusting of LCB is achieved by changing frame area curves, and hull surfaces are reconstructed accordingly using the Radial Basis Function (RBF). Surf-riding motions in regular following seas for cases with different LCBs and Froude numbers are simulated using the numerical model. Results show that the surf-riding cannot be prevented by the adjusting of LCB. However, it occurs with a higher threshold speed when ship's center of buoyancy (COB) is moved towards stem compared to moving towards stern, which is mainly due to the differences on wave resistance caused by the adjusting of LCB.

• Journal of Ocean Engineering and Technology
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• v.12 no.2 s.28
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• pp.97-110
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• 1998

The numerical damping and dispersion error characteristics associated with difference schemes and a panel shift method used for the calculation of steady free surface flows by a panel method are an analysed in this paper. First, 12 finite difference operators used for the double model flow by Letcher are applied to a two dimensional cylinder with the Kelvin free surface condition and the numerical errors with these schemes are compared with those by the panel shift method. Then, 3-D waves due to a submerged source are calculated by the difference schemes, the panel shift method and also by a higher order boundary element method(HOBEM). Finally, the waves and wave resistance for Wigley's hull are calculated with these three schemes. It is shown that the panel shift method is free of numerical damping and dispersion error and performs better than the difference schemes. However, it can be concluded that the HOBEM also free of the numerical damping and dispersion error is the most stable, accurate and efficient.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.3
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• pp.254-258
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• 2014

Field trial in ice-covered sea is one of the most important tasks in the design of icebreaking ships. To correctly estimate ice load and ice resistance on ship's hull, It is essential to understand the material properties of sea ice during ice field trials and to perform the proper experimental procedure by gathering sea ice data. A measurement of sea ice properties was conducted during February and March of 2012 with the Korean Icebreaking research vessel "ARAON" in the Amundsen Sea, Antarctica. This paper describes a test procedure to obtain sea ice data which provide basic information to estimate ice loads and icebreaking performance of the ship. The data gathered from sea ice field trials during the 2012 Antarctic voyage of the ARAON includes ice temperature/salinity/density and the compressive/flexural strength of sea ice. This paper analyses the gathered Antarctic sea ice material properties comparing with the previous data obtained during ARAON's Arctic and Antarctic voyages in 2010.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.4
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• pp.308-316
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• 2011

Although a yacht sails operate with large displacement due to very thin thickness, many studies for flow around yacht sails have not considered the sail deformation. The sail deformation not only caused a change in the center of effect(CE) on the sail but also a change in the thrust of the sail. The change of the CE and thrust affects the center of lateral resistance(CLR) and side forces of the hull, and the balance of the yacht. These changes affect the motion of the yacht which changes the velocity of the yacht. Thus, when analyzing the flow around yacht sails, the sail deformation should be considered. In the present study, fluid-structure-interaction(FSI) analysis of a two dimensional section of yacht sails was performed to consider the effects of sail deformation on the lift and drag performance. FSI and moving mesh methods were studied. Computational methods were verified using benchmark test cases such as the flow around horizontal and vertical cantilever beams. Shape deformation, pressure distribution, lift forces and separation flow were compared for both rigid and deformable sail.

• Journal of Ship and Ocean Technology
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• v.6 no.1
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• pp.27-33
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• 2002

Recently, the application of the electric propulsion system becomes popular because of its advantage over conventional propulsion. However, the complicated flow mechanism and interaction around the azimuth thruster are not fully understood yet, and the studies on the powering performance characteristics with azimuth/pod thrusters are now in progress. The experimental method developed in KRISO(Korea Research Institute of Ships & Ocean Engineering) is introduced and the results of the powering performance tests, consisting of resistance, self-propulsion and propeller open water tests for a cable layer with two azimuth thrusters are presented. For the analysis of powering performance with azimuth thrusters, it is necessary to evaluate the thrust/drag for components of a thruster unit, Extrapolation results could differ according to the various definitions of the propulsion unit; that is the pod, thruster leg and/or nozzle can be treated as hull appendages or as part of propulsion unit, The powering performances based on several definitions are investigated for this vessel. The results of the measurements for the 3-dimensional velocity distribution on the propeller plane are presented to understand the basis of the difference in propulsion characteristics due to the propeller rotational directions.

• Journal of the Society of Naval Architects of Korea
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• v.40 no.6
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• pp.1-11
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• 2003

For an accurate shock response analysis of a floating structure such as a naval surface ship subjected to an UNDEX(UNDerwater Explosion), the cavitation effects due to reflected wave at free surface and wetted structural surface should be considered. In this study, for the consideration of cavitation effects an effective method using LS-DYNA/USA and its theoretical background were presented. Through the application of the analysis of bulk cavitation phenomena in the free field, it could be confirmed that almost the same results were obtained between LS-DYNA/USA code and the analytical method. for the investigation of cavitation effects from the structural shock response characteristics, three dimensional UNDEX shock response analysis of an idealized ship model was also carried out It could be found that the cavitation Phenomena gave significant effects on the structural shock response characteristics, and especially that the shock loadings calculated at the installed location of shipboard equipment were underestimated in the case of no consideration of the cavitation effects, which might cause the severe mistake in its shock-resistance design.