• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.10
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• pp.150-158
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• 2003

In the beam pattern synthesis problem using line source, the relationship between source distribution function and beam pattern may be represented by Fourier transform pair. In this paper, a general method to synthesize the line source distribution for a desired lobe-like beam pattern is presented by developing the nonlinear inversion method based on an iterative sampling technique. This method can be applied to the synthesis of continuously distributed dielectric constants satisfying the desired inverse scattering coefficient patterns when illuminating by TE-polarized and TM-polarized plane waves to arbitrary dielectric material. Furthermore this method can also be applied to the synthesis of transmission line with arbitrary reflection coefficient patterns. Some bandstop spatial filter and dispersive transmission line filter are illustrated for generality.

• Journal of the Society of Naval Architects of Korea
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• v.35 no.2
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• pp.38-50
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• 1998

In order to understand the characteristics of floating breakwaters we planned series of experimental and numerical investigations and completed the first stage which is the experiment with fred pontoons near the free surface. As controlling parameters the draft and breadth of pontoon were varied and the wave frequency and steepness were also varied. Wave transmission and forces exiled on the breakwater were experimentally investigated and compared with the results computed based on linear potential theory. Discussions made are on the effect of draft and wave length on the wave transmission and force in fixed pontoon case. The predicted and measured results show quantitatively good agreement both in forces and transmission coefficient. The effect of separation distance between two pontoons on the wave transmission and force in array case is also examined.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.3
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• pp.45-56
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• 2000

An experimental and numerical investigation was made to examine the characteristics of pontoon type floating breakwaters(FBW) in regular waves. Motion responses of FBW and wave transmission coefficients are observed and compared with the results based on the linear potential theory. The linear potential theory is found to be a successful tool to investigate the characteristics of the floating breakwaters. We confirm that there exists a minimum wave transmission coefficient which is a function of wave-length/beam and beam/draft ratio. As beam/draft ratio increases the value of wave-length/beam ratio where the minimum, wave transmission coefficient occurs increases. Excessive mooring stiffness can deteriorate the performance of the floating breakwaters.

• Computational Structural Engineering
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• v.9 no.1
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• pp.55-64
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• 1996

Sloshing frequencies of the fluid in rectangular tanks with a bottom-mounted rectangular block are determined by linear water wave theory. Velocity potential is decomposed into those for the wall-induced waves, and the reflected, transmitted, and scattered waves by the block. The reflection and transmission coefficients are determined using the continuity conditions of mass flux and energy flux on the common vertical boundaries of the fluid regions, and the boundary conditions on the both sides of the block. The analysis results indicate that the sloshing frequencies reduce, as the block becomes tall and vade and as the block moves toward the center. The variations of the sloshing frequencies due to the block are found to be more sensitive in broad thanks than is tall tanks.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.2
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• pp.196-208
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• 2009

In this paper, wave responses of buoyant flap-typed storm surge barriers was studied numerically. Wave motions were modeled by using a linear potential wave theory, and behaviors of structures were represented as a Newton's 2nd law of motion. The near field region of the fluid was discretized as conventional quadratic iso-parametric elements, while the far field was modeled as infinite elements. Comparisons with the results from hydraulic model tests show that the present model gives good results. By using the model, the applicability of a buoyant flap-typed storm surge barrier in Masan bay was investigated considering field environmental conditions.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.6 s.150
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• pp.638-646
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• 2006

In this paper a new hull-panel generation algorithm named 'Panel Cutting Method' was developed to solve the flow phenomena around a ship advancing on the free surface with a constant speed. In this algorithm the non-linearity of the free surface boundary conditions was taken into account using the iterative method and the raised panel was used at each iteration step. Numerical calculations were performed to investigate the validity of the developed algorithm using the series $60(C_B=0.60)$ hull The wave resistance coefficients, the wave patterns and the wave heights were compared between the computed and the experimental results at Fn=0.25 and 0.316. The comparison showed good agreement between computation and experiment.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.3
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• pp.41-50
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• 1993

This paper compares various potential based panel methods for the analysis of two-dimensional hydrofoil. The strength of singularity on each panel is assumed to be constant or linear. Robin boundary condition as well as Neumann and Dirichlet boundary conditions are applied to various formulations to evaluate the accuracies of the methods. Pressures and lifts are computed for various two-dimensional hydrofoil geometries and are compared with the analytic solutions. Extensive studies are performed on the local errors near the trailing edge, known to be sensitive to the foil geometry with sharp trailing edge and high camber. Robin boundary condition with the perturbation velocity potential formulation shows the best accuracy and convergence rate.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.1
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• pp.25-37
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• 1993

This paper describes the use of the J-integral, a one parameter of the non-linear fracture mechanics(NLFM), as a means to measure toughness of steel fiber reinforced concrete. This parameter can be conveniently evaluated from experimentally determined load-deflection curves from flexural tests when a maximum-load failure criterion is employed. And, for high strength concrete which was reinforced steel fiber, with two different fiber length in the form of notched beams, were tested under 3-point bending, and $J_{IC}$, as well as the linear elastic fracture mechanics(LEFM) parameters $K_{IC}$ and $G_{IC}$ were evaluated. The results suggest that $J_{IC}$ is a promising fracture criterion for all of these. while $K_{IC}$(or $G_{IC}$) almost certainly are not. Also it was found that a fiber addition of less than 0.5% did not improve the fracture toughness of the high strength concrete. However, at more than 1.0% in fiber contents, $J_{IC}$ showed significant increases. reflecting the changed character of the concrete; $K_{IC}$ and $G_{IC}$ did not.

• Journal of Navigation and Port Research
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• v.29 no.10 s.106
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• pp.853-858
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• 2005

Recently, various novel numerical models based on Navier-Stokes equation have been developed for calculating wave motions in the sea with coastal or ocean structures. Among those models, Volume Of Fluid (VOF) method might be the most popular one, and it has been used for numerical simulations of wave motions including complicated phenomena of wave breakings. VOF method, however, needs enormous computation time and large computational storage memories in general, thus it is practically difficult to use this method for calculations in the case of random waves because long and stable computation (e.g for more than 100 significant wave periods) is required to obtain statistically meaningful results. On the other hand if the wave motion is potential motion, Boundary Element Method (BEM), which is a much faster and more accurate method than VOF method, can be effectively used. The aim of this study is to develop a new efficient model applicable to calculations of wave motion and/or wave-structure interactions under random waves. To achieve this, a strictly combined BEM-VOF model has been developed by making the best use of both methods' merits; VOF method is used in a restricted fluid domain around a structure where complicated phenomena of wave breakings may exist, and BEM is used in the other domains far from the disturbance where the wave motion may be assumed to be potential. The verification of the model was performed with numerical results for Stokes' 5th order wave propagation and a random wave propagation.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.4
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• pp.467-474
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• 2018

The purpose of this study is related to automatic hull-form design for ships operating at two speeds. Research was conducted using a series 60 ($C_B=0.6$) ship as a target, which has the most basic ship hull-form. Hull-form development was pursued from the viewpoint of improving resistance performance. In particular, automatic hull-form design for a ship was performed to improve wave resistance, which is closely related to hull-forms. For this purpose, we developed automatic hull-form design software for ships by combining an optimization technique, resistance prediction technique and hull-form modification technique, appling the software developed to a target ship. A sequential quadratic programming method was used for optimization, and a potential-based panel method was used to predict resistance performance. A Gaussian-type modification function was developed and applied to change the ship hull-form. The software developed was used to design a target ship operating at two different speeds, and the performance of the resulting optimized hull was compared with the results of the original hull. In order to verify the validity of the program developed, experimental results obtained in model tests were compared with calculated values by numerical analysis.