• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.55 no.3
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• pp.273-283
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• 2019

The authors has predicted the maneuvering characteristics of a fishing vessel in deep water using Kijima's empirical formula in a previous study. Since the Kijima's empirical formula was developed by a regression analysis of merchant vessels which have dimensions ($C_b$, L/B, etc.) that are different from those of fishing vessels, it was possible to make a prediction approximately even with inaccurate estimation. In this study, the authors estimated the turning-motion characteristics of a model ship of fisheries training ship in shallow water based on the results of its previous study. The turning-motion characteristics of the model ship in shallow water was found out through quantitative analysis according to the water depth to ship draft ratio (H/d). In conclusion, the turning-motion characteristics of the model ship had significant changes immediately after an H/d 1.5, and this result will be helpful for sailing in shallow water.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.2
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• pp.106-121
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• 2020

In order to make harbor outskirt facilities robust using the reliability-based design, probabilistic models of wave heights at varying stage of shoaling process optimized for Korean sea waves are prerequisite. In this rationale, we numerically simulate the nonlinear shoaling process of random waves over the beach with a sandbar at its foreshore. In doing so, comprehensive numerical models made of spatially filtered Navier-Stokes Eq., LES [Large Eddy Simulation], dynamic Smagorinsky turbulence closure were used. Considering the characteristics of swells observed at the east coast of Korean Peninsula, random waves were simulated using JONSWAP wave spectrum of various peak enhancement coefficients and random phase method. The coefficients of probabilistic models proposed in this study are estimated from the results of frequency analysis of wave crests and its associated trough detected by Wave by Wave Analysis of the time series of numerically simulated free surface displacements based on the threshold crossing method. Numerical results show that Modified Glukhovskiy wave height distribution, the most referred probabilistic models at finite water depth in the literature, over-predicts the occurring probability of relatively large and small wave heights, and under predicts the occurrence rate of waves of moderate heights. On the other hand, probabilistic models developed in this study show vary encouraging agreements. In addition, the discrepancy of the Modified Glukhovskiy distribution from the measured one are most visible over the surf zone, and as a result, the Modified Glukhovskiy distribution should be applied with caution for the reliability-based design of harbor outskirt facilities deployed near the surf-zone.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.2
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• pp.77-89
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• 1991

Based on Boussinesq equation, the parabolic approximation equation is used to analyse the propagation of shallow water waves with currents over slowly varying depth. Rip currents (jet-like) occur mainly in shallow waters where the Ursell parameter significatly exceeds the range of application of Stokes wave theory. We employ the nonlinear parabolic approximation equation which is valid for waves of large Ursell parameters and small scale currents. Two types of currents are considered; relatively strong and relatively weak currents. The wave propagating over rip currents on a sloping bottom experiences a shoaling due to the variations of depth and current velocity as well as refraction and diffraction due to the vorticity of currents. Numerical analyses for a nonlinear theory are valid before the breaking point.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1950-1953
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• 2006

본 연구에서는 파랑의 방향에 따른 비대칭성을 고려한 방향 스펙트럼 식을 새로 제안하였다. 심해에서 생성된 다방향 불규칙 파랑이 등수심선에 대해 일정한 각도를 가지고 입사하는 경우, 각 방향의 파랑 성분의 굴절각의 차이에 의해 입사각에 대한 비대칭성이 발생하였다. 파랑의 굴절에 대해서는 Snell의 법칙을 이용하고 천수를 고려하여 해석적으로 계산하였으며, 이 결과와 새로 제안된 방향스펙트럼 식을 이용한 결과를 서로 비교하였다. 그 결과 비대칭성이 강한 천해역에서는 기존의 스펙트럼식에 비해 3배 이상 정확한 값을 재현하였다.

• Transactions of Materials Processing
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• v.6 no.4
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• pp.300-310
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• 1997

A finite element inverse method is introduced for direct prediction of blank shapes, strain distributions, and reliable intermediate shapes from desired final shapes in axisymmetric multi-step deep drawing processes. This mothod enables the determination of process disign. The approach deals with the Hencky's deformation theory. Hill's second order yield criterion, simplified boundary conditions, and minimization of plastic work with constraints. The algorithm developed is applied to motor case forming, and cylindrical cup drawing with the large limit drawing ratio so that it confirms its validity by demonstrating resonably accurate numerical results of each problem. Numerical examples reveal the reason of difficulties in motor case forming with corresponding limit diagrams.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.4 no.4
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• pp.225-230
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• 1992

An attempt is made to assemble and synthesize recent publications which may contribute to our capability for understanding the transformation of wave spectra in finite-depth water or in the presence of current. This review is limited essentially to the effects of shoaling and current on one-dimensional transformation of wave spectra and examining the adequacy of the approximation of irregular waves by a monochromatic wave in modeling of wave transformation in coastal areas.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.177-188
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• 1991

The littoral drift in the nearshore zone occurs mainly due to wave action and nearshore currents. Beach topotraphical evolution model presented in this study shows the possibility which can be applied to the prediction of beach deformation over short time interval, associated with the construction of coastal structures. The 3-dimensional beach evolution model, based on Watanabe's equation and Deguchi's flux model, is developed and consists of three submodels of wave transformation, rip-currents, and beach deformation. This model is applied to the several cases with different conditions and compared with the results of Watanabe's numerical model. In addition, the effects of parameters involved are discussed.

• Journal of the Korean Society for Marine Environment & Energy
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• v.20 no.2
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• pp.91-99
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• 2017

The parametric study was performed for performance enhancement of wave energy converter(WEC) using a submerged pendulum plate. The wave exciting moment and hydrodynamic moment were obtained by means of eigenfunction expansion method based on the linear potential theory, and then the roll response of a pendulum plate and time averaged extracted power were investigated. The optimal PTO damping coefficient was suggested to give optimal extracted power. The peak value of optimal extracted power occurs at the resonant frequency. The resonant peak and it's width increase, as the height and thickness of a pendulum plate increase. The mooring line installed at the end of the pendulum plate is effective for extracting wave energy because it can not only induce the resonance with the waves of the installation site but also increase the restoring moment in case of PTO-on. The WEC using a rolling pendulum plate suitable for the shallow water acts as breakwater as well as energy extraction device.

• Journal of the Society of Naval Architects of Korea
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• v.32 no.1
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• pp.70-82
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• 1995

A multi-layer simulation program is developed to estimate the ocean current considering sea bottom geometry. The so-called $\sigma$ coordinate system is introduced in vertical direction to describe sea bottom topography more accurately and effectively. Leapfrog scheme combined with Euler backward scheme is used to reduce computation error which may be possibly accumulated in time evolution by Leapfrog scheme alone. In this paper, very simple examples of rectangular basins with various bottom geometries were taken and the effect of sea bottom geometry on vertical structure of the ocean tidal current and its direction were investigated. Through comparisons between the present three dimensional calculation in which bottom topography is directly taken into consideration and the two dimensional calculation in which depth average concept is employed, it was found that magnitude of surface current and its direction could be largely affected by the sea bottom topography, particularly in shallow region with complex bottom shape.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.5
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• pp.484-491
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• 2007

Numerical experiments using a numerical wave tank have been performed to verier the nonlinear interaction between monochromatic waves and a submerged horizontal plate. As a model for numerical wave tank, we used a higher-order Boundary Element Method(BEM) based on fully nonlinear potential flow theory and CADMAS-SURF for solving Navier Stokes equations and exact free surface conditions. Both nonlinear models are able to predict the higher harmonic generation in the shallow water region over a submerged horizontal plate. CADMAS-SURF, which involves the viscous effect, can evaluate the higher harmonic generation by flow separation and vortices at the each ends of plate. The comparison of reflection and transmission coefficients with experimental results(Patarapanich and Cheong, 1989) at different lengths and submergence depths of a horizontal plate are presented with a good agreement. It is found that the transfer of energy from the incident fundamental waves to higher harmonics becomes larger as the submergence depth ratio decreases and the length ratio increases.