• Journal of the Society of Naval Architects of Korea
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• v.56 no.3
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• pp.200-210
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• 2019

High-speed planing craft is generally smaller than commercial vessels, for which not only the roll motion but also the pitch and heave motions are relatively large during operation However, if seakeeping performance of high-speed planing craft is evaluated by assessment methods of commercial vessels considering roll damping only, it would get unreasonable results due to excessive magnitudes of motion. This research aims at developing a procedure to evaluate seakeeping performance of high-speed planing craft reasonably well by considering responses of roll, heave and pitch motions. In addition, we tried to combine advantages of the potential flow method and CFD in this procedure, a so-called hybrid method, which uses the 3D panel method for the analysis of seakeeping performance, and tunes the damping coefficient using CFD analysis at a specific frequency. Finally, we evaluated seakeeping performance of coastal rescue boat in operation by applying the proposed procedure, and analyzed the results referring to the seakeeping criteria.

• Ocean Systems Engineering
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• v.13 no.2
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• pp.173-193
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• 2023

Reliable prediction of the motion of FOWT (floating offshore wind turbine) and associated mooring line tension is important in both design and operation/monitoring processes. In the present study, a 5MW OC4 semisubmersible wind turbine is numerically modeled, simulated, and analyzed by the open-source numerical tool, OpenFAST and in-house numerical tool, Charm3D-FAST. Another commercial-level program FASTv8-OrcaFlex is also introduced for comparison for selected cases. The three simulation programs solve the same turbine-floater-mooring coupled dynamics in time domain while there exist minor differences in the details of the program. Both the motions and mooring-line tensions are calculated and compared with the DeepCWind 1/50 scale model-testing results. The system identification between the numerical and physical models is checked through the static-offset test and free-decay test. Then the system motions and mooring tensions are systematically compared among the simulated results and measured values. Reasonably good agreements between the simulation and measurement are demonstrated for (i) white-noise random waves, (ii) typical random waves, and (iii) typical random waves with steady wind. Based on the comparison between numerical results and experimental data, the relative importance and role of the differences in the numerical methodologies of those three programs can be observed and interpreted. These comparative-study results may provide a certain confidence level and some insight of potential variability in motion and tension predictions for future FOWT designs and applications.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.6
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• pp.614-619
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• 2015

In this study, a dynamics model was developed to predict the motion performance of an Autonomous Underwater Vehicle (AUV). The dynamics model includes basic dynamic state variables of the hull and force terms to determine the motion of the AUV. The affecting terms for the forces are hydrostatic force, added mass, hydrodynamic damping, lift and drag forces. The force terms can be calculated using analytical and Computational Fluid Dynamics methods. For the underwater motion simulation, a simple PD controller was used. Also, the AUV was tested in a water tank and near sea for the partial verification of the fluid drag force coefficients and way-point tracking motions.

• Journal of the Society of Naval Architects of Korea
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• v.40 no.4
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• pp.16-21
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• 2003

The very large container ships have been built recently and those ships have very small structural rigidity compared with the other conventional ships. As a result, the destruction of ship hull is occurred by the springing including to warping phenomena due to encounter waves. In this study, the solutions of hydrodynamic coefficients are obtained by solving the three dimensional source distribution method and the forward speed Green function representing a translating and pulsating source potential for infinite water depth is used to calculating the integral equation. The vessel is longitudinally divided into various sections and the added mass, wave damping and wave exciting forces of each section is calculated by integrating the dynamic pressures over the mean wetted section surface. The equations for six degree freedom of motions is obtained for each section in the frequency domain and stiffness matrix is calculated by Euler beam theory. The computations are carried out for very large ship and effects of bending and torsional ridigity on the wave frequency and angle are investigated.

• 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 Ocean Engineering and Technology
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• v.25 no.4
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• pp.7-11
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• 2011

The installation phase for a topside module suggested can be divided into 9 stages, which include start, pre-lifting, lifting, lifted, rotating, positioning, lowering, mating, and end of installation. The transfer of the topside module from a transport barge to a crane vessel takes place in the first three stages, from start to lifting, while the transfer of the module onto a floating spar hull occurs in the last three stages, from lowering to the end. The coupled multi-body motions are calculated in both calm water and in irregular waves with significant wave height (1.52m), with suggested force equilibrium diagrams. The effects of the hydrodynamic interactions between the crane vessel and barge during the lifting stage have been considered. The internal forces caused by the load transfer and ballasting are derived for the lifting phases. The results of these internal forces for the calm water condition are compared with those in the irregular sea condition. Although the effect of pitch motion on the relative vertical motion between the deck of the floating structure and the topside module is significant in the lifting phases, the internal force induced pitch motion is too small to show its influence. However, the effect of the internal force on the wave-induced heave responses in the lifting phases is noticeable in the irregular sea condition because the transfer mass-induced draught changes in the floating structure are observed to have higher amplitudes than the external force induced responses.

• 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.339-349
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• 2017

This paper is related to structural design evaluation of 19,000 TEU ultra large container ship, dealing with hydroelastic response, i.e. springing and whipping. It illustrates application of direct calculation tools and methodologies to both fatigue and ultimate strength assessment, simultaneously taking into account ship motions and her elastic deformations. Methodology for springing and whipping assessment within so called WhiSp notation is elaborated in details, and in order to evaluate innovative container ship design with increased loading capacity, a series of independent hydroelastic computations for container ship with mobile deckhouse and conventional one are performed with the same calculation setup. Fully coupled 3D FEM - 3D BEM model is applied, while the ultimate bending capacity of hull girder is determined by means of MARS software. Beside comparative analysis of representative quantities for considered ships, relative influence of hydroelasticity on ship response is addressed.

• 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.23 no.5
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• pp.9-14
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• 2009

The green water on deck has many harmful effects on the vessel in rough seas such as damages to hull structures, damages to cargos, increase of the downtime, decrease of the stability, and so on. Floating Production Storage and Offloading vessels (FPSOs) are operated in a specific location and are normally positioned to meet mostly head or bow waves in order to reduce the roll motions. But this makes FPSOs more vulnerable to green water around the bow region therefore the bow shape should be properly designed to mitigate the green water damage. In this paper, experimental results in regular head waves for three kinds of bow shapes are compared and some design considerations are proposed, with the building a database for computational fluid dynamics (CFD) validation in mind.