• Journal of the Society of Naval Architects of Korea
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• v.42 no.3
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• pp.212-219
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• 2005

Real sea waves in a towing wave basin have been generated using random periodic motion of the segmented wave makers and the wave reflections of sidewalls. Theoretically, the real sea waves can be described by the superposition of many random oblique waves. This paper introduces numerical real sea wave generation in a rectangular wave basin using spectral method that uses a superposition of orthogonal functions which have to satisfy the Laplace equation. Oblique regular waves, long crested irregular waves and real sea waves were simulated and met the requirement of sidewall wave reflection and wave absorption. MLM (Maximum Likelihood Method) and Spatial Fourier Transform were used in order to obtain propagated wave direction characteristics. The estimated results proved the usefulness of the method and the performances showed reasonable directional patterns comparing with generating patterns.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.6
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• pp.531-552
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• 2020

In the previous study, both the wave characteristics at the tip of composite breakwater and on caisson were investigated by applying olaFlow numerical model of three-dimensional regular waves. In this paper, the same numerical model and layout/shape of composite breakwater as applied the previous study under the action of one directional irregular waves were used to analyze two and three-dimensional spatial change of wave force including the impulsive breaking wave pressure applied to trunk of breakwater, the effect of rear region, and the occurrence of diffracted waves at the tip of caisson located on the high crested rubble mound. In addition, the frequency spectrum, mean significant wave height, mean horizontal velocity, and mean turbulent kinetic energy through the numerical analysis were studied. In conclusion, the larger wave pressure occurs at the front wall of caisson around the still water level than the original design conditions when it generates the shock-crushing wave pressure in three-dimensional analysis condition. Which was not occurred by two-dimensional analysis. Furthermore, it was confirmed that the wave pressure distribution at the caisson changes along the length of breakwater when the same significant incident wave was applied to the caisson. Although there is difference in magnitude, but its variation shows the similar tendency with the case of previous study.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.317-322
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• 2003

The Sectional and Spatial failure modes are discussed using the experimental data with long crest wave and multi-directional waves considering the failure modes occurring around the rubble-mound breakwater. The spatial & sectional stability and failure mode around the rubble-mound structures with construction progress can be summarized as follows: 1) The rubble mound structures at basic construction step was occurred serious failures when ${\xi}$ was about 6.5. 2) It was clarified that the failure modes at the round head of detached breakwater are classified as failure by plunging breaking on the slope, failure by direct incident wave force and failure by scouring at the toe of the detached break water. 3) The failure mode was found in the lower wave height than the design wave by the breaker depth effect. 4) The failure on the slope were also developed at the lee side of the round head because diffracted wave propagated into the behind area by grouping effect of multi-directional irregular wave.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.2
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• pp.139-148
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• 2001

Phenomena induced by waves, such as overtopping, sediment transport, vibration/fluctuation and destruction of structures are highly influenced by the directionality of wave propagation. These phenomena are often dominated by non-linearity, and so hydraulic model experiments are widely adopted for stability analysis rather than numerical modeling, Thus, stability ofrubblc mound breakwaters(RMB) due to wavc directionality was experimentally investigated in this study. The incident wave angle $30^{\circ}$ was found more risky on the damage rate of RMB under directional regular waves, and the incident wave angle $40^{\circ}$ was found relatively risky under directional irregular waves. These results clarified the wave directionality effect on the stability ofRMB, These facts were found correspondent to the occurrence of the peak between $20^{\circ}$-$40^{\circ}$ with the directional frequency distribution of lIlO maximum water particle velocity.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.2
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• pp.77-82
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• 2017

Recently, the possibility of abnormal waves of which height is greater than design wave height have been increased due to the climate change, and therefore it has been urgent to secure the stability for harbor structures. As a countermeasure for improving the stability of conventional caisson breakwaters, a method has been proposed in which adjacent caissons are interlocked with each other to consecutively resist the abnormal wave forces. In order to reflect this research trend, the reduction effect of the maximum wave force resulted from introducing a long caisson has been presented in the revision to the design criteria for ports and fishing harbors and commentary. However, no method has been proposed to evaluate the stability of interlocking caisson breakwater. In this study, we consider the effect of the phase difference of the oblique incidence of the wave based on the linear wave theory and apply the Goda pressure formula for considering design wave pressure distribution in the vertical direction. Sliding stability assessment formula of an interlocking caisson breakwater is proposed for regular, irregular, and multi-directional irregular wave conditions.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.2 no.3
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• pp.119-127
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• 1990

Wave directional spectrum estimation methods for irregular waves were considered in this study. Until now, the Longuet-Higgins Method (LHM) initiated by Longuet-Higgins et al. (1963) has been widely used, but resolutions of the estimation were found to be low. Kobune's Maximum Entropy Method (MEM) for the estimation of wave directional spectrum, bas-ed on the entropy Principle showed higher resolutions comparing with the LHM . If the wave directional spectrum is of Delta functions, the MEM is exact in its estimation. It was also found that for a unimodal spectrum, if the Mitsuyasu's spreading coefficient is above 5, the estimation resolutions were high. In bimodal spectrum, as the angle difference between the two peaks increased, the resolution improved. The energy seems to transfer to the smoother peak in the smoothing of peak's peakedness. LHM has a tendency to estimate bimodal spectrum as a unimodal spectrum ； thus, except for its computational speed, the resolution of LHM falls far below that of MEM.

• Journal of Ocean Engineering and Technology
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• v.17 no.4
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• pp.1-7
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• 2003

A virtual reality technology for multipurpose numerical simulation is developed to reproduce and investigate a variety of ocean environmental problems in a 3D Numerical Wave Tank(NWT). The governing equations for solving incompressible fluid motion are Navier-Stokes equation and continuity equation. The Marker-Density function technique is adopted to implement the fully nonlinear freesurface kinematic condition. The marine environmental situations, i.e., waves, currents, etc., are reproduced by use of multi-segmented wavemakers on the basis of the so-called ″snake-principle″. In this paper, some numerical reproduction techniques for regular, and irregular waves, multi-directional waves, Bull's-eye wave. wave-current, and solitary wave are presented, and a model test in motion with large amplitude of roll angle is conducted in the developed 3D-NWT, using a overlaid grid system.

• Journal of Ocean Engineering and Technology
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• v.7 no.2
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• pp.114-120
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• 1993

Responses of marine vehicles and ocean structures in a seaway can be predicted by applying the probabilistic approach. When we consider a linear system, the responses in a random seaway can be evaluated through spectral analysis in the frequency domain. But when we treat nonlinear system in irregular waves, it is necessary to get time history of waves. In the previous study we introduced one-directional waves (long crested waves)as wave environment and carried out calculations and experiments in the waves. But the real sea in which marine vehicles and structures are operated has multi-directional waves (short crested waves). It is important to get a simulated random sea and analyse dynamic problems in the sea. We need entire sample function or probabillty density function to infer statistical value of random process. However if the process are ergodic process, we can get statistical values by analysis of one sample function. In this paper, we developed the simulation technique of multi-directional waves and proved that the time history given by this method keep ergodic characteristics by the statistical analysis.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.1
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• pp.70-86
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• 2015

Short crested waves play an important role for planning and design of harbours. In this context a numerical simulation is carried out to evaluate wave tranquility inside a real harbour located in east coast of India. The annual offshore wave climate proximity to harbour site is established using Wave Model (WAM) hindcast wave data. The deep water waves are transformed to harbour front using a Near Shore spectral Wave model (NSW). A directional analysis is carried out to determine the probable incident wave directions towards the harbour. Most critical threshold wave height and wave period is chosen for normal operating conditions using exceedence probability analysis. Irregular random waves from various directions are generated confirming to Pierson Moskowitz spectrum at 20m water depth. Wave incident into inner harbor through harbor entrance is performed using Boussinesq Wave model (BW). Wave disturbance experienced inside the harbour and at various berths are analysed. The paper discusses the progresses took place in short wave modeling and it demonstrates application of wave climate for the evaluation of harbor tranquility using various types of wave models.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.174-180
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• 2002

A virtual reality technology for multipurpose numerical simulation is developed to reproduce and investigate a variety of ocean environmental problems in a 3D-Numerical Wave Tank. The governing equations for solving incompressible fluid motion are Navier-Stokes equation and continuity equation, and the Marker-Density function technique is adopted to implement the fully-nonlinear free-surface kinematic condition. The marine environmental situations, i.e. waves, currents, wind, etc., are reproduced by use of multi-segmented wavemaker on the basis of the so-called "snake-principle". In this paper, some numerical reproduction techniques for regular and irregular waves, multi-directional waves, Bull's-eye wave, wave-current, and solitary wave are presented, and a model test in motion with large amplitude of roll angle is conducted in the developed 3D-NWT, using a overlaid grid system.