• Journal of Theoretical and Applied Mechanics
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• v.2 no.1
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• pp.1-14
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• 1996

In this paper, breaking waves are generated in a 2-D wave tank and simulated by using a higher-order boundary element method. A piston-type wavemaker is operated by signals composed of elementary waves. The phase of elementary waves is determined by the linear theory such that they are focused to a prescribed position. Calculated plunging waves coincide well with experiment. A steel box with different plate thicknesses is installed at a predetermined position in the tank. Measured impulsive pressures due to breaking waves are found to be 0.8-1.2$\rho$C2, where $\rho$ corresponds to water density and C to wave celerity. The transverse displacement of the plate is described in terms of modal eigenfunctions. The natural frequencies measured by impact tests in air for thin plate coincide with the computational and theoretical values. The radiationpotential due to plate vibration is derived and the radiation force is expressed in terms of hydroelastic added mass and damping forces. Comparison of natural frequencies of plate in water proves that hydroelastic added mass and damping are properly considered. The measured strain due to regular waves supports the calculated one, but there are apparent discrepancies between theory and experiment in the impulsive case.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.2
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• pp.819-827
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• 2019

Bragg reflection of water waves by three kinds of surface-piercing fixed structures with rectangular, cosinoidal and triangular shapes is studied. Boundary element method is used to analyze the wave scattering by these structures based on the linear wave theory. Results of reflection and transmission coefficients are validated by comparing with those available in literature. These structures with proper configurations are proved to be effective in attenuating waves by using Bragg reflection, and the triangular structures are found to be the best choices among the structures with same width and same area. Systematic calculations are then carried out for the triangular structures by varying the number, the draft, the width, the gap and the combination of width and gap of the structures to analyze their influences on the characteristics of Bragg reflection. The results are of reference values for design of the structures to attenuate waves based on the Bragg reflection.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.4
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• pp.373-381
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• 2009

The running attitude of a high-speed planing craft may change significantly depending on its speed in seaway. Other variables that may influence its running attitude are its weight, center of gravity, sea conditions, and so on. In this paper, planing craft model tests were carried out with respect to above variables in SNU towing tank, and vertical motion responses of a planing craft in regular head waves were analyzed. The experimental results in regular waves were compared with those in calm water, and compared with the theoretical estimations. Finally, the effects of running speeds of a planing craft on its motion amplitudes are confirmed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.4
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• pp.258-265
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• 2015

Over the last 20 years, freak waves have attracted many researchers because of their unexpected behaviors and damages on offshore structures and vessels in the ocean and coastal waters. Despite many researches on the causes, mechanisms and occurrence of freak waves, we have not reached consensus on the results of the researches. This paper presents the occurrence probability of freak waves based on the analysis of wave records measured at coastal waters of Donghae harbor in the East Sea. Three freak waves were found which satisfied conditions of m and $H_S{\geq}2.5m$ and $H_m/H_S{\geq}2$. The occurrence probabilities of freak waves were estimated from extreme distributions by Mori, Rayleigh and Ahn, and found to be on the orders of O($10^{-1}$), O($10^{-2}$), and O($10^{-3}$), respectively. The occurrence probabilities of freak waves measured from waves records were estimated between O($10^{-2}$) and O($10^{-3}$), which were located between predictions by Rayleigh and Ahn's extreme probability distributions. However, we need more analysis of wave records obtained from diverse field conditions in order to verify the accuracy of the estimation of occurrence probability of freak waves.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.3
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• pp.161-169
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• 2020

Physical experiments have been performed in a wave basin to investigate change of the wave loading on the crown wall under obliquely incident wave conditions. The measurement was carried out with wave incidence angle of 0, 15, 30 and 45°. The pressure transducers were placed on the front and bottom face of the crown wall to obtain horizontal and uplift force as well. It was found that both the horizontal and vertical force decreases with the incidence angle. Based on the analysis of the experimental data, a formula was suggested to estimate the reduction rate of horizontal and vertical forces under obliquely incident waves.

• Journal of Ocean Engineering and Technology
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• v.34 no.4
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• pp.245-252
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• 2020

Wave run-up is an important phenomenon that should be considered in ocean structure design. In this study, the wave run-up of a surface-piercing circular cylinder was calculated in the time domain using the three-dimensional linear and fully nonlinear numerical wave tank (NWT) techniques. The NWT was based on the boundary element method and the mixed Eulerian and Lagrangian method. Stokes second-order waves were applied to evaluate the effect of the nonlinear waves on wave run-up, and an artificial damping zone was adopted to reduce the amount of reflected and re-reflected waves from the sidewall of the NWT. Parametric studies were conducted to determine the effect of wavelength, wave steepness, and the draft of the cylinder on the wave run-up of the cylinder. The maximum wave run-up value occurred at 0°, which was in front of the cylinder, and the minimum value occurred near the circumferential angle of 135°. As the diffraction parameter increased, the wave run-up increased up to 1.7 times the wave height. Furthermore, the wave run-up was 4% higher than the linear wave when the wave steepness was 1/35. In particular, the crest height of the wave run-up increased by 8%.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.4
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• pp.338-348
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• 2015

In this study, the added resistance of ships in short waves is systematically studied by using two different numerical methods - Rankine panel method and Cartesian grid method – and existing asymptotic and empirical formulae. Analysis of added resistance in short waves has been preconceived as a shortcoming of numerical computation. This study aims to observe such preconception by comparing the computational results, particularly based on two representative three-dimensional methods, and with the existing formulae and experimental data. In the Rankine panel method, a near-field method based on direct pressure integration is adopted. In the Cartesian grid method, the wave-body interaction problem is considered as a multiphase problem, and volume fraction functions are defined in order to identify each phase in a Cartesian grid. The computational results of added resistance in short waves using the two methods are systematically compared with experimental data for several ship models, including S175 containership, KVLCC2 and Series 60 hulls (C_B = 0.7, 0.8). The present study includes the comparison with the established asymptotic and empirical formulae in short waves.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.2
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• pp.103-115
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• 2018

This paper performs a numerical computation of ship maneuvering performance in waves. For this purpose, modular-type model (MMG (Mathematical Modeling Group) model) is adopted for maneuvering simulation and wave drift force is included in the equation of maneuvering motion. In order to compute wave drift force, two different seakeeping programs are used: AdFLOW based on Wave Green function method and SWAN based on Rankine panel method. When wave drift force is calculated using SWAN program, not only ship forward speed but also ship lateral speed are considered. By doing this, effects of lateral speed on wave drift force and maneuvering performance in waves are confirmed. The developed method is validated by comparing turning test results in regular waves with existing experimental data. Sensitivities of wave drift force on maneuvering performance are, also, checked.

• Journal of Navigation and Port Research
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• v.41 no.5
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• pp.329-336
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• 2017

This study suggests a general process of analyzing the mooring and cargo handling limit waves, which is an incident to the new energy port under long wave agitation. To reduce damages of ships and harbor structures due to strong wave responses, it is necessary to predict the change of wave field in the mooring berth to make the proper decision by dock master. The berthing area at a new LNG port in the east coast of Korea in this study is frequently affected by oscillations from waves of 8.5~13s periods in the wintertime. The long period waves give difficulties on port operation by lowering the annual berthing ratio. It needs to find the event waves from the real time offshore wave records, which cause over the mooring limits. For that purpose, the wave records from field measurement and offshore wave buoy were analyzed. From numerical simulation, the response characteristics of long period waves in the berthing area were deduced with or without breakwater expansion plan, analyzing the offshore field wave data collected for two years. Some event wave cases caused over the cargo handling and mooring limits as per the standard Korean port design guideline, and those were used for the decision of port operation by dock master, comparing with the real time offshore wave observations.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1995.10a
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• pp.75-80
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• 1995

The model for the combined refraction and diffraction of water waves, the so-called mild-slope equation, was first developed by Berkhoff (1972) and has been studied by many coastal engineers because the model is able to consider the combined effect of refraction and diffraction of water waves and eliminate the problem of ray crossing which may happen in the previously developed ray theory. (omitted)