• Bulletin of the Society of Naval Architects of Korea
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• v.12 no.1
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• pp.47-58
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• 1975

The effect of the bow shape on the ship motion response among longitudinal regular waves, is investigated employing the strip theory. The two dimensional hydrodynamic forces such as added mass and damping are calculated by the integral equation method for arbitrary sections. Nine ship models are selected for investigation. They are U, UV and V bow ship forms of different block coefficient of 0.6, 0.7 and 0.8 with constant after body. The heave amplitude of the V bow ship is smaller than that of the U bow ship in the whole range of wave length except extremely short wave as were stated by the earlier investigators. This results holds also in the case of bow vertical motions such as vertical relative displacement, velocity and acceralation. As to the pitch amplitudes, the V bow ship gives smaller value in long waves but larger value in short waves. However, heave and pitch phase angles are practically not influenced by the form of the fore body sections. In the bow motions, a little difference in phase angle is appeared in the vicinity of the wave which has same ship length. With respect to the wave exiting force and moment unfovourable effects could be expected in V bow ships. And these tendency hold also in the wave bending moment.

• Ocean Systems Engineering
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• v.6 no.3
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• pp.233-244
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• 2016

Tension Leg Platform (TLP) is a floating structure that consists of four columns with large diameter. The diffraction theory is used to calculate the wave force of floating structures with large dimensions (TLP). In this study, the diffraction and Froude-Krylov wave forces of TLP for surge, sway and heave motions and wave force moment for roll, pitch degrees of freedom in different wave periods and three wave approach angles have been investigated. From the numerical results, it can be concluded that the wave force for different wave approach angle is different. There are some humps and hollows in the curve of wave forces and moment in different wave periods (different wavelengths). When wave incidents with angle 0 degree, the moment of diffraction force for pitch in high wave periods (low frequencies) is dominant. The diffraction force for heave in low wave periods (high wave frequencies) is dominant. The phase difference between Froude-Krylov and diffraction forces is important to obtain total wave force.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.711-722
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• 2020

An optimization framework using genetic algorithms has been developed towards an automated parametric optimization of the Octabuoy semi-submersible design. Compared with deep draft production units, the design of the shallow draught Octabuoy semi-submersible provides a floating system with improved motion characteristics, being less susceptible to vortex induced motions in loop currents. The relatively large water plane area results in a decreased natural heave period, which locates the floater in the wave period range with more wave energy. Considering this, the hull design of Octabuoy semi-submersible has been optimized to improve the floater's motion performance. The optimization has been conducted with optimized parameters of the pontoon's rectangular cross section area, the cone shaped section's height and diameter. Through numerical evaluations of both the 1st-order and 2nd-order hydrodynamics, the optimization through genetic algorithms has been proven to provide improved hydrodynamic performance, in terms of heave and pitch motions. This work presents a meaningful framework as a reference in the process of floating system's design.

• Korean Journal of Computational Design and Engineering
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• v.16 no.3
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• pp.227-235
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• 2011

Ship handling simulator should have capabilities of calculating ship motions (heave, pitch, and roll) at given sea state and displaying the calculated motions through a real-time 3D visualization system. Motion solver of a ship handling simulator generally calculates those motions in addition to position for an own ship, a main simulation target, but provides only position information for traffic ships. Therefore, it is required to simulate real-time traffic ship and buoy motions coupled with ocean waves in a ship handling simulator for the realistic visualization. In the paper, the authors propose a simple dynamics model by which ship and buoy motions are calculated with the input data of wave height and discuss a method for the implementation of a ship and buoy motions calculation module.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.2
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• pp.149-159
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• 2017

In this study, the numerical investigation of ship motions and added resistance at constant forward velocity of KVLCC2 model is presented. Finite volume CFD code is used to calculate three dimensional, incompressible, unsteady RANS equations. Numerical computations show that reliable numerical results can be obtained in head waves. In the numerical analyses, body attached mesh method is used to simulate the ship motions. Free surface is simulated by using VOF method. The relationship between the turbulence viscosity and the velocities are obtained through the standard ${\kappa}-{\varepsilon}$ turbulence model. The numerical results are examined in terms of ship resistance, ship motions and added resistance. The validation studies are carried out by comparing the present results obtained for the KVLCC2 hull from the literature. It is shown that, ship resistance, pitch and heave motions in regular head waves can be estimated accurately, although, added resistance can be predicted with some error.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.3
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• pp.700-714
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• 2014

This study aims to identify the relations between seakeeping characteristics and hull form parameters for YTU Gulet series with cruiser stern. Seakeeping analyses are carried out by means of a computer software which is based on the strip theory and statistical short term response prediction method. Multiple regression analysis is used for numerical assessment through a computer software. RMS heave-pitch motions and absolute vertical accelerations on passenger saloon for Sea State 3 at head waves are investigated for this purpose. It is well known that while ship weight and the ratios of main dimensions are the primary factors on ship motions, other hull form parameters ($C_P$, $C_{WP}$, $C_{VP}$, etc.) are the secondary factors. In this study, to have an idea of geometric properties on ship motions of gulets three different regression models are developed. The obtained outcomes provide practical predictions of seakeeping behavior of gulets with a high level of accuracy that would be useful during the concept design stage.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.6
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• pp.617-622
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• 2013

The sloshing of liquid inside an ocean floater is caused by disturbances due to waves. For the analysis of sloshing impact within the floater and that of waves on the floater, the coupled analysis method is used. The Stokes $5^{th}$ order non-linear wave theory equations were adapted for wave making. Furthermore, Navier-Stokes equation and Shear-Stress Transport (SST) turbulent model were used to Computational Fluid dynamics, where the ocean floater motions are considered the heave and the pitch motion. The results obtained confirms the mutual relationship between the rigid body motions and that of sloshing, where the sloshing behaviour within the floater is characterized by the wave effects on the floater.

• Bulletin of the Society of Naval Architects of Korea
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• v.17 no.3
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• pp.1-4
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• 1980

It is well known that discrepancies between measured and predicted ship motions are significant in the range of low frequencies. In this paper, the vertical ship motions in regular longitudinal waves in a shallow water are briefly discussed. The investigation is focussed on the role of wave exciting forces and moments to the motion responses in these low frequencies. It is confirmed that diffraction forces are in general small in a shallow water as one may expect. Furthermore the wave exciting forces and moments on a displacement-type ship will be larger practicularly in low frequencies, when the contribution of the diffraction effect is neglected. As a result of this fact theoretically predicted responses for the pitch motion becomes closer to the experimental one. The discrepancies for the heave motion, however, are still apparent.

• Journal of Ocean Engineering and Technology
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• v.28 no.2
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• pp.119-125
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• 2014

A vertical planar motion mechanism(VPMM) test was used to increase the prediction accuracy for the maneuverability of an underwater glider model. To improve the accuracy of the linear hydrodynamic coefficients, the analysis techniques of a pure heave test and pure pitch test were developed and confirmed. In this study, the added mass and damping coefficient were measured using a VPMM test. The VPMM equipment provided pure heaving and pitching motions to the underwater glider model and acquired the forces and moments using load cells. As a result, the hydrodynamic coefficients of the underwater glider could be acquired after a Fourier analysis of the forces and moments. Finally, a motion control simulation was performed for the glider control system, and the results are presented.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.3
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• pp.320-329
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• 2017

In this research, we have calculated characteristics of wave-piercing high-speed planing hull, by using a RANS solver and overset grid method, for comparing with experimental measurements of that and simulating with several appendages, since the computed results of commercial CFD code look reasonable for the prediction of the performances of planing hulls on calm water in planing conditions. As a result, it is confirmed that the dynamic instability phenomena in pitch and heave motions (porpoising) occurred after a certain $Fn_V$, and effectively suppressed using some of appendages, especially the 0.5L spray rail is suppressed to 24-55 % in the pitch motion and 33-55 % in the heave motion. In spray phenomenon, 1L hard chine suppress spray effectively and it is effective to set the angle of appendages to be less than $0^{\circ}$ in order to suppress wave.