• Journal of the Korean Society for Marine Environment & Energy
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• v.13 no.2
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• pp.112-120
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• 2010

In this paper time series wave data measured continuously for 24 hours during a storm in Yura Sea Area are used to investigate statistical characteristics of nonlinear waves. The exceedance probability of wave height is compared using the Rayleigh distribution and the Edgeworth-Rayleigh (ER) distribution. Wave data which show stationary state for 10 hours contain 4600 waves approximately. The Gram-Chalier distribution fits the probability of wave elevation better than the Gaussian distribution. The Rayleigh ($H_{rms}$) distribution follows the exceedance probability of wave height in general and predicts the probability of freak waves well. The ER distribution overpredicts the exceedance probability of wave heights and the occurrence of freak waves. If wave data measured for 30 minute period which contains 250 waves are used, the ER distribution can predict the occurrence probability of freak waves well. But it overpredicts the probability of overall wave height If no freak wave occurs, the Rayleigh ($H_{rms}$) distribution agrees well with wave height distribution for the most of wave height ranges. The wave height distribution of freak waves of which height are less than 10 m shows similar tendency compared with freak waves greater than 10 m. The value of $H_{max}/H_{1/3}$ is related to the kurtosis of wave elevation. It seems that there exists threshold value of the kurtosis for the occurrence of freak waves.

• Journal of Fisheries and Marine Sciences Education
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• v.25 no.1
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• pp.1-11
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• 2013

The aim of this study was estimated the characteristics of the wave propagation by the water level conditions using a numerical modeling method at the Wando sea area. For three cases numerical simulation on the condition of incident and incoming of the deepwater design wave and the season normal wave, the spatial distribution of the incident wave at study area were investigated. And the calculated numerical modeling results were compared with measured field wave data. According to on-site wave data measured for 18 days, the range of the significant wave height and period were 0.10~1.14 m, 4.35~8.74 sec, respectively, and the maximum wave height were 0.15~1.66 m. From the results of numerical model for offshore design wave incident, the wave height attacked from Southern-East direction at this study area were over maximum 10.5 m because of rapidly change of water depth. Numerical modeling by three water level conditions of Approxmate Lowest Low Water Level(Approx. L.L.W), Mean Sea Level(M.S.L) and Approximate Highest High Water Level(Approx. H.H.W) were practiced. From the results for the case of Approx. H.W.L, variations of wave height at the back area of islands were about 1.6 m at maximum value for the case of deepwater design wave incoming. The significant wave heights of winter season were bigger than summer under normal wave condition, the incident wave height over 5.5 m decreased by shielding effect of islands. The change of maximum wave height at summer season were distinct than winter and was about 1.2 m and 0.8 m, respectively.

• Journal of Ocean Engineering and Technology
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• v.36 no.1
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• pp.1-10
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• 2022

Recently, as the offshore structures are operated in the deep-sea oil fields, interest in the analysis of relative wave elevation around platforms is increased. In this study, it is examined how the analysis results differ depending on the characteristics of the wave probe when interpreting the relative wave elevation in the model test. First, by conducting the wave probe comparison experiment in the two-dimensional wave tank, it is confirmed how the measured values differ according to the type of wave probe for the same physical phenomenon. Two types of wave probe are selected, the resistance type and the capacitance type, and the causes of the difference in measured values is studied. After that, the model test of the semi-submersible platform is conducted to investigate the relative wave elevation. Relative wave elevation is measured with the wave probes used in the wave probe comparison experiment and analyzed to estimate the asymmetric factor and the extreme upwell. The results between the two types of wave probes are compared, and qualitative study for the cause of the difference is conducted by photographing the physical phenomenon using a high-speed camera. Through the above study, it is confirmed that the capacitance type wave probe shows a larger measured value than the resistance type under the breaking-wave condition, and the same results are obtained for the asymmetric factor and the extreme upwell. These results is thought to be due to the difference in the measurement principle between wave probes, which is whether or not they measured water bubbles. This implies that the model test should be conducted using appropriate wave probes by considering the physical phenomenon to be analyzed.

• 한국해양학회지
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• v.28 no.3
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• pp.192-201
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• 1993

To reduce tsunami hazards, it is necessary to develope the methods which can simulate tsunami wave signals of coastal areas. In the present paper, it is attempted t use Sign Method for analyzing and simulating recorded tsunami signals. A tsunami record Y(t) can be represented as the convolution integral of a source evolution function E(t') and a wave propagation function K(t-t') Y(t)=.int. E(t')K(t-t')dt' A source function contains the peculiarities of a tsunami generator. A wave function is a kind of transfer function which contains the characteristics of a wave propagation path. The source functions and the wave function and the wave functions of 9 Korean coast points and 6 Japan coast points are estimated, and the tsunami wave signals are simulated by the convolution integrals of the source functions and the wave functions. According to the results of analysis, the Sign Method is an effective method for simulating tsunami wave signals of Korean coast points which are located far from tsunami source areas. Furthermore, if the source function of a neighboring point ad the wave function of an another tsunami are given, unrecorded tsunami wave also can be estimated.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.4
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• pp.401-412
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• 2008

Simulations of three-dimensional numerical wave tank are performed to investigate wave force acting on a large cylindrical structure and consequent wave deformation, which are induced by bore after breaking waves. The numerical model is based on the three-dimensional Navier-Stokes equations with a finite-difference method combined with a volume of fluid(VOF) method, which is capable of tracking the complex free surface, including wave breaking. In order to promote wave breaking of the incident wave, the approach slope was built seaward of the structure with a constant slope and a large cylindrical structure was installed on a flat bed. The incident waves were broken on the approach slope or flat bed by its wave height. In the present study, all waves acting on the large cylindrical structure were limited to breaking bore after wave breaking. The effects of the position of the structure and the incident wave height on the wave force and wave transformations were mainly investigated with the concern of wave breaking. Further, the relations between the variation of wave energy by wave propagation after wave breaking and wave force acting on the structure were discussed to give the understanding of the full-linear wave-structure interactions in three-dimensional wave fields.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.4
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• pp.207-213
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• 2003

This study is to numerically investigate the characteristics of wave energy variations propagating over impermeable submerged breakwaters with irregular waves. Two-dimensional numerical wave flume based on the VOF method was used. VOF method is the most efficient capable of simulating free surfaces including wave breaking. From the computed frequency spectrum results, wave breaking play important role in ability of the submerged breakwaters to dissipate incident wave energy. In case of occurring wave breaking, our analysis shows that wave energy moves to short wave period on one-row impermeable submerged breakwater's lee side and is widely distributed not having peak period on two- row impermeable submerged breakwater's lee side.

• Journal of the Korean Society for Marine Environment & Energy
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• v.3 no.2
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• pp.49-59
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• 2000

Wave distribution in Jangjeon Harbour is numerically simulated for an optimum design of the harbour facilities. A deep-water design wave is estimated based on stochastic extreme wave analysis of wind data in the vicinity of the harbour, and it is applied to the boundary condition at open sea. Boussinesq wave theory that includes effects of frequency dispersion and nonlinearity is employed for the wave simulation. The porosity and sponge layer are adapted at beach to depict partial reflection and complete absorption of waves, respectively. The design wave for breakwater is computed in global domain with coarse grids and the wave distribution inside of wharf is simulated in local domain with fine grids.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.4
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• pp.933-945
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• 1994

A shock-wave in a supersonic flow can be theoretically determined by a given pressure ratio at upstream and downstream flowfields, and then the obtained shock-wave is stable in its position. Under the practical situation in which the shock-wave interacts with the boundary layer along a solid wall, it cannot, however, be stable even for the given pressure ratio being independent of time and oscillates around a time-mean position. In the present study, oscillations of a weak normal shock-wave in a supersonic diffuser were measured by a Line Image Sensor(LIS), and they were compared with the data of the wall pressure fluctuations at the foot of the shock-wave interacting with the wall boundary layer. LIS was incorporated into a conventional schlieren optical system and its signal, instantaneous displacement of the interacting shock-wave, was analyzed by a statistical method. The results show that the displacement of an oscillating shock-wave increase with the upstream Mach number and the dominant frequency components of the oscillating shock-wave are below 200 Hz. Measurements indicated that shock-wave oscillations may not entirely be caused by the boundary layer separation. The statistical properties of oscillations appeared, however, to be significantly affected by shock-induced separation of turbulent boundary layer.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.10
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• pp.2686-2697
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• 1994

When a railway train enters a tunnel at high speed, a compression wave is formed in front of the train and propagates along the tunnel. The compression wave subsequently emerges from the exit of the tunnel, which causes an impulsive noise. In order to estimate the magnitudes of the noises and to effectively minimize them, the characteristics of the compression wave propagating in a tunnel must be understood. In the present paper, the experimental and analytical investigations on the attenuation and distortion of the propagating compression waves were carried out using a model tunnel. This facility is a kind of open-ended shock tube with a fast-opening gate valve instead of a general diaphragm. One-dimensional flow model employed in the present study could appropriately predict the strength of the compression wave, Mach number and flow velocity induced by the compression wave. The experimental results show that the strength of a compression wave decreases with the distance from the tunnel entrance. The decreasing rate of the wave strength and pressure gradient in the wave is strongly dependent on the strength of the initial compression wave at the tunnel entrance.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.4
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• pp.213-220
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• 2005

An approach to calculate expected sliding distance of wave dissipating caisson breakwater is proposed. Time history of dynamic wave pressure for the calculation of sliding distance is made by extending conventional static wave pressure developed for the wave dissipating caisson breakwater. Construction of impact wave and standing wave was done by using duration time and maximum wave pressures of themselves. In the numerical analysis, the sliding distance for an attack of single wave and expected sliding distance for 50 years of wave dissipating breakwater by proposed method were compared with those by conventional method for uplift caisson breakwater. It was found that the sliding distance of wave dissipating breakwater by the proposed method is smaller than by conventional method.