• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.155-160
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• 2002

In this paper, a compliant buoy mooring system of a floating cylindrical structure in shallow water depth is studied experimentally. The compliant buoy mooring system consists of four buoys, vertical mooring legs and horizontal mooring lines. A series of model test were carried out at KRISO ocean engineering basin for various mooring parameters; line length, pretension of mooring leg and mooring layouts and environmental conditions; regular and irregular waves combined with current and wind. The mooring line tensions and 6-DOF motions of the floating structure were measured using water-proof load cells and 3 CCD camera system. The results of a series of model tests were discussed on nonlinear motion behaviors of the floating structure and characterisitics of cumulative distributions of mooring line peak tensions.

• Journal of Ocean Engineering and Technology
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• v.29 no.3
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• pp.217-223
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• 2015

In order to predict the motions of a planing hull in waves, it is necessary to accurately estimate the force components acting on the hull such as the hydrodynamic force, buoyancy, and friction, as well as the wave exciting force. In particular, based on strip theory, hydrodynamic forces can be estimated by the summation of the forces acting on each cross-section of the hull. A non-linear strip method for planing hulls was mathematically developed by Zarnick, and his formula has been used to predict the vertical motions of prismatic planing hulls in regular waves. In this study, several improvements were added to Zarnick's formula to predict the vertical motions of warped planing hulls. Based on calm water model test results, the buoyancy force and moment correction coefficients were modified. Further improvements were made in the pile-up correction. Pile-up correction factors were changed according to variations of the deadrise angles using the results found in previous research. Using the same hull form, captive model tests were carried out in other recent research, and the results were compared with the present calculation results. The comparison showed reasonably good agreements between the model tests and present calculations.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.3
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• pp.193-204
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• 2011

To develop more robust oil boom which is vulnerable to various failure mode under severe weather condition, highly accurate wave model is developed using Spatially filtered Navier-Stokes Eq., LDS (Lagrangian Dynamic Smagorinsky model) for residual stresses, SPH (Smoothed Particle Hydrodynamics). To clarify the hydraulic characteristics of floating type oil boom, we numerically simulate the behavior of oil spill around oil boom under very energetic progressive waves. At the first stage, we firmly anchored the oil boom, and then, allowed the excursion of the oil boom. It turns out that oil boom with skirt of enough length (longer than 30% of depth) effectively confines the oil spill even against very energetic waves. We can also observe obliquely descending vertical eddies between y = 1~2 m as horizontal vortices shedding at the interface of oil spill and water are diffused toward the bottom, which is believed to be the birth, growing and break-down of Kelvin-Helmholz wave.

• Ocean and Polar Research
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• v.30 no.4
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• pp.453-466
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• 2008

In order to examine the generation mechanism of long ocean waves along the west coast of Korea and to understand the amplification process of the long ocean waves, sea level, atmospheric pressure and wind data observed every minute from 2007 March 29 to 2007 April 1 were analyzed and onedimensional numerical ocean model experiments were performed. An atmospheric pressure jump propagated southeastward from Backryungdo to Yeonggwang along the west coast of Korea with speed of $13{\sim}27\;m/s$ between 2007 March 30 23:00 and 2007 April 1 1:30. Average magnitude of pressure jump was 4.2 hPa. As a moving atmospheric jump propagated from north to south along the coast, long ocean waves were generated and the sea level abnormally rose or fell at Anheung, Kunsan, Wido and Yeonggwang. Average amplitude of sea level rise (or fall) was about 113.6 cm. In a one-dimensional numerical ocean model, nonlinear shallow water equations were numerically integrated and a moving atmospheric pressure jump with traveling speed of 24 m/s was used as an external force. While the atmospheric pressure jump travels over 60 m depth ocean, a long ocean wave is generated. Because the propagation speed of the atmospheric jump is almost equal to that of the long ocean wave, Proudman resonance occurs and the long ocean wave amplifies. As the atmospheric pressure jump moves into the coastal area shallower than 60 m, the speed of the long ocean wave decreases and Proudman resonance effect decreases. However, the amplitude of the long ocean wave increases and wave length becomes shorter because of shoaling effect. When the long ocean wave hits the land boundary, amplitude of the long ocean wave drastically amplifies due to reflection. Data analysis and numerical experiments suggest that the southeastward propagation of an atmospheric pressure jump over the shallow ocean, which is a necessary condition for Proudaman resonance, generated the long ocean waves along the west coast of Korea on 2007 March 31 and the ocean waves amplified due to shoaling effect in the coastal area and reflection at the shore.

• Ocean Systems Engineering
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• v.4 no.4
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• pp.327-342
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• 2014

The tension leg platform (TLP) is one of the compliant structures which are generally used for deep water oil exploration. With respect to the horizontal degrees of freedom, it behaves like a floating structure moored by vertical tethers which are pretension due to the excess buoyancy of the platform, whereas with respect to the vertical degrees of freedom, it is stiff and resembles a fixed structure and is not allowed to float freely. In the current study, a numerical study for square TLP using modified Morison equation was carried out in the time domain with water particle kinematics using Airy's linear wave theory to investigate the effect of changing the tether tension force on the stiffness matrix of TLP's, the dynamic behavior of TLP's; and on the fatigue stresses in the cables. The effect was investigated for different parameters of the hydrodynamic forces such as wave periods, and wave heights. The numerical study takes into consideration the effect of coupling between various degrees of freedom. The stiffness of the TLP was derived from a combination of hydrostatic restoring forces and restoring forces due to cables. Nonlinear equation was solved using Newmark's beta integration method. Only uni-directional waves in the surge direction was considered in the analysis. It was found that for short wave periods (i.e., 10 sec.), the surge response consisted of small amplitude oscillations about a displaced position that is significantly dependent on tether tension force, wave height; whereas for longer wave periods, the surge response showed high amplitude oscillations that is significantly dependent on wave height, and that special attention should be given to tethers fatigue because of their high tensile static and dynamic stress.

• Journal of Advanced Research in Ocean Engineering
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• v.1 no.2
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• pp.85-93
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• 2015

The nonlinear time-domain analysis method was implemented to carry out a series of integrated simulations for a deep-water crane vessel system composed of four sub components, including a floating vessel, lifted equipment, hoisting cable and dynamic positioning (hereinafter DP) system. The analysis of the coupled dynamics consists of the crane vessel and equipment connected using the crane wire, and the DP is modeled according to the wind, wave and current conditions. The DP systems were numerically implemented using a classical PD feedback controller, and various simulations of the deepwater installation were conducted using different conditions in order to evaluate the global performance of the floating crane vessel combined with the DP system.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2005.03a
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• pp.110-117
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• 2005

This paper deals the shaking table tests with 1/100 scaled model followed by Scott & Iai(1989)'s similitude law for OO dam main desging section to understand nonlinear behavior characteristics of concrete dam body by earthquake wave. As earthquake wave, Hachinohe and Elcentro waves were used and acceleration and displacements are measured to analyze behaviors of dam body. For ground maximum acceleration range ($0.3^{\sim}0.9g$), the results showed linear behavior regardless of ground maximum acceleration and secured safety of structure. To analyze the behavior of dam after tension cracking, 3cm-notch was placed at the critical section of over-flowing section. As results of applying Hachinohe wave(0.8g), Even though tension cracks were formed at over-flowing section by Hachinohe wave(0.8g), it showed that the dam is stable for supporting upper stream part of water tank of dam.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.7 s.100
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• pp.806-812
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• 2005

This paper adresses the shaking table tests with 1/100 scaled model followed similitude law for OOdam main designing section to understand nonlinear behavior characteristics of concrete dam body by ground motion. As earthquake wave, Hachinohe and El Centre waves were used and acceleration and displacements are measured to analyze behaviors of dam body. For maximum ground acceleration range $(0.3\~0.9 g)$, the results showed linear behavior regardless of maximum 9round acceleration and secured safety of structure. To analyze the behavior of dam after tension cracking, 3 cm-notch was placed at the critical section of over-flowing section. As results of applying Hachinohe wave(0.8 g), Even though tension cracks were formed at over-flowing section by Hachinohe wave(0.8 g), it showed that the dam is stable for supporting upper stream Part of water tank of dam.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.10 no.4
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• pp.204-210
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• 1998

This paper presents the development of the probability density function applicable for wave heights (peak-to-trough excursions) in finite water depth including shallow water depth. The probability distribution applicable to wave heights of a non-Gaussian random process is derived based on the concept of the maximum entropy method. When wave heights are limited by breaking wave heights (or water depth) and only first and second moments of wave heights are given, the probability density function developed is closed form and expressed in terms of wave parameters such as $H_m$(mean wave height), $H_{rms}$(root-mean-square wave height), $H_b$(breaking wave height). When higher than third moment of wave heights are given, it is necessary to solve the system of nonlinear integral equations numerically using Newton-Raphson method to obtain the parameters of probability density function which is maximizing the entropy function. The probability density function thusly derived agrees very well with the histogram of wave heights in finite water depth obtained during storm. The probability density function of wave heights developed using maximum entropy method appears to be useful in estimating extreme values and statistical properties of wave heights for the design of coastal structures.

• Journal of Ocean Engineering and Technology
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• v.19 no.6 s.67
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• pp.35-43
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• 2005

Recently, various-shaped coastal structures have been studied and developed. Among them, the submerged breakwater became generally known as a more effective structure than other structures, bemuse it not only serves its original function, but also has the ability to preserve the coastal environment. Most previous investigations have been focused on the wave deformation and energy dissipation due to submerged breakwater, but less interest was given to their internal properties and dynamic behavior of the seabed foundation under wave loadings. In this study, a direct numerical simulation (DNS) is newly proposed to study the dynamic interaction between a permeable submerged breakwater aver a sand seabed and nonlinear waves, including wave breaking. The accuracy of the model is checked by comparing the numerical solution with the existing experimental data related to wave $\cdot$ permeable submerged breakwater $\cdot$ seabed interaction, and showed fairly nice agreement between them. From the numerical results, based on the newly proposed numerical model, the properties of the wave-induced pore water pressure and the flow in the seabed foundation are studied. In relation to their internal properties, the stability oj the permeable submerged breakwater is discussed.