Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering)
Online ISSN : 1883-8944
Print ISSN : 1884-2399
Volume 65 , Issue 1
Showing 1-50 articles out of 295 articles from the selected issue
  • Takenori SHIMOZONO, Shinji SATO
    2009 Volume 65 Issue 1 Pages 1-5
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    Nonlinear dispersive wave equations are now widely used to simulate the propagation of shallow water waves. In recent years, it has been clarified that some equations accommodate wave breaking phenomena as well as steady wave solutions. In the present study, comparative studies of the Boussinesq-type equations with different sets of parameters are carried out to investigate the existence of wave breaking solutions. The behavior of solution over the breaking limit is numerically examined using a blowup profile as an indicator of wave breaking. It is found that the solution exhibits the blowup with most sets of parameters for cases with h/L<0.04, while only some specific sets of parameters realize it for shorter waves. Moreover, locations of the blow-up are shown to agree well with actual breaking points known from the empirical criteria.
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  • Yasunori WATANABE, Yasuo NIIDA, Ayumi SARUWATARI, Hiroshi SAEKI
    2009 Volume 65 Issue 1 Pages 6-10
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    Two-way stochastic subgrid bubble models to determine the number density and sizes of small air-bubbles entrained under circular jets and the advetion and diffusion process for Large Eddy Simulation (LES) are proposed in this paper. The proposing model has been applied to two simple air-water two phase flows - the bubble flow in still water as well as the aerated flow under circular jet flowing into still water. It was found that the bubble motion intensifies the turbulence, which enhances fluctuating bubble motion. This air-water energy tranfer via turbulent interaction is important factor to determine the near-surface fluid dynamics.
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  • Yasunori WATANABE, Shin-ichiro ISHIZAKI
    2009 Volume 65 Issue 1 Pages 11-15
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    A flip-through overtopping jet evolves into laterally deintegrated jets, so-called finger jets, at an early stage of the wave uprush on a vertical wall. The finger jets are vertically stretched to fragment into small multiple droplets or sprays. In this study, these fingering and fragmenting processes were visualized, and the shapes of the jets and sprays were quantitatively measured on the basis of novel level-set image detecting algorithm. The evolution of the size distributions and water volume fractions for the both jets and sprays were characterized via spectrum image analysis.
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  • Ayumi SARUWATARI, Yasunori WATANABE
    2009 Volume 65 Issue 1 Pages 16-20
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    Local surface deformations of the wave breaking jets were computed using a three-dimensional large eddy simulation. The typical counter-rotating vortices formed with the jet entrains the adjacent jet surface into inner fluid to penetrate the jet, forming a so-called finger jets. The tips of the fingers are fragmented into sprays. The breakup rate of the fingers and the volume fraction of the resulting sprays have also been statistically estimated in this paper. It has been found that local acceleration along the fingers determines the breakup rate as well as the fluid fraction.
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  • Hitoshi GOTOH, Abbas KHAYYER, Chiemi HORI
    2009 Volume 65 Issue 1 Pages 21-25
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    Particle methods, despite their inherent capabilities, have a few drawbacks including spurious pressure fluctuations. Several reasons are supposed to be behind this drawback. One of the important issues contributing to unphysical pressure fluctuations in a particle-based simulation of free-surface flows is related to an insufficient or a too simple criterion for assessment of free-surface particles. In this paper, we propose an auxiliary criterion for a more efficient and accurate assessment of free-surface in a particle-based calculation of incompressible free-surface fluid flows. The proposed criterion is based on the nearly symmetric arrangement of non-free-surface particles and its efficiency is demonstrated.
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  • Toshinori OGASAWARA, Shigetomo KIKUCHI, Shigeki SAKAI
    2009 Volume 65 Issue 1 Pages 26-30
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    For unreal pressure oscillation in fluid particles due to MPS method, two algorithms which corrected the source term in the Poisson equation are compared with original MPS method. In addition, wave boundary condition is improved to generate solitary wave by a wave maker with piston type. The incident wave heights are compared to experimental data. In dynamic analysis of fluid-structure interaction problems, the influence of pressure oscillation on the structure deformation and the fluid force is investigated in detail. As a result, although it was indicated that the two algorithms restrain the pressure oscillation, their coefficients suited to numerical conditions will be required. Further, we made clear that the oscillation of pressure strongly affects the structure deformation because the fluid force does not accurately act on the elastic body.
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  • Abbas KHAYYER, Hitoshi GOTOH, Chiemi HORI
    2009 Volume 65 Issue 1 Pages 31-35
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    The paper presents particle-based simulations of a dam break on a wet bed by standard and improved versions of three particle methods, namely, MPS, ISPH and WCSPH methods. The improved versions of the three mentioned methods are CMPS-HS, CISPH-HS and WCSPH-MLS methods. Direct comparisons of experimental photos and their corresponding simulation snapshots have been made in terms of the reproduced free-surface profile as well as the simulated mixing processes. In order to obtain further improved simulations, in this paper, we propose a new viscosity reduction function in WCSPH-MLS calculation, and apply a frictional force term in CMPS-HS method.
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  • Hidemi MUTSUDA, Koji YUTO, Yasuaki DOI
    2009 Volume 65 Issue 1 Pages 36-40
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    This paper describes a numerical method for elastic-plastic deformation of structure caused by impact pressure. Both fluid and solid phases are represented by SPH (Smoothed Particle Hydrodynamics), which is a typical particle method. We employed the artificial stress and coefficient of collapsing parameter, and also proposed the fluid structure interaction model in the original SPH. Our numerical results are in good agreement with the experimental data and the previous numerical results. Especially, we also compared the internal strain field with the numerical results. Furthermore, we also applied to some practical problems, such as collapsing of a concrete wall and steel flame structure.
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  • Hitoshi GOTOH, Abbas KHAYYER, Hiroyuki IKARI, Chiemi HORI
    2009 Volume 65 Issue 1 Pages 41-45
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    The paper presents a 3D-CMPS method for refined simulation of a plunging breaking wave and resultant splash-up. The Corrected MPS (CMPS) has been extended to three dimensions and 3D-CMPS method has been developed on the basis of 3D-MPS method. To enhance the computational efficiency of the calculations, the parallelization of 3D-CMPS method has been carried out with two different solvers of simultaneous linear equations corresponding to the Poisson Pressure Equation (PPE). The parallelization has been performed based on a dynamic domain decomposition strategy for an optimized load balancing among the processors.
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  • Hiroyuki IKARI, Hitoshi GOTOH, Hidefumi YODOSHI
    2009 Volume 65 Issue 1 Pages 46-50
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    In order to simulate an occurrence process of tsunami induced by a slope failure due to an earthquake, it is required to treat an elastoplastic analysis for slope failure, fluid analysis and fluid-elastoplastic interaction in the numerical model. Therefore, in this study, by using the particle method which is suitable for an analysis on large deformation of soil and complicated water surface change, the fluid-elastoplastic hybrid model is developed to simulate a complicated process of a slope failure induced tsunami. In this model, an elastoplastic analysis including large deformation of soil and a fluid analysis are unified.
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  • Hidemi MUTSUDA, Takehiro KURIHARA, Takayuki KUROKAWA, Kenta KAWAKAMI, ...
    2009 Volume 65 Issue 1 Pages 51-55
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    We have developed a new numerical scheme that combines a Eulerian scheme with Lagrangian particles to compute fluid-structure interaction caused by impact pressure. The proposed numerical model was applied to several problems such as water entry problems with splashing in 2D and 3D, impact pressure problems caused by breaking and interaction between an elastic structure and water wave. The present model can reproduce not only impact pressure acting on a vertical wall but also deformation, vibration, stress and strain. We validated an internal strain field of structure due to wave force by using a piezoelectric sensor. We showed the flexible sensor developed is useful to measure an internal stain and solid deformation.
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  • Takeru ARAKI, Shunichi KOSHIMURA
    2009 Volume 65 Issue 1 Pages 56-60
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    The Lattice Boltzmann Method (LBM) has been developed as a new and robust numerical model to solve the fluid dynamics. In this study, we applied LBM for free surface flow, which Shallow-water approximation cannot provide accurate estimation. LBM was tested in some benchmark problems and laboratory experiment. The model results are in good agreement with dam-break experiment, including the movement of free surface of water body, splash against the upper wall, and a wave traveling back to the other side of the tank. Through the model validation, we found that LBM can be applied to simulate the complex behavior in tsunami wave front.
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  • Shuji ISHIHARA
    2009 Volume 65 Issue 1 Pages 61-65
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    In this paper, a direct extension of the multi-directional ghost-cell immersed boundary method to free-surface flow was proposed. This method allow us to represent a sharp interface with appropriate boundary condition. The numerical method is based on a finite-volume approach on a collocated Cartesian grid together with a implicit HSMAC method for coupling of velocity, pressure and free-surface elevation. A series of numerical experiments have beed conducted to verify the accuracy of this method. Good agreements are obtained when numerical results are compared to available analytical, experimental, and other numerical results.
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  • Taro KAKINUMA, Kei YAMASHITA, Keisuke NAKAYAMA
    2009 Volume 65 Issue 1 Pages 66-70
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    Internal waves propagating over a submerged breakwater in a two-layer system are numerically simulated using a set of nonlinear internal-wave equations derived on the basis of a variational principle without any assumptions concerning wave nonlinearity and dispersion. When an internal-wave crest starts wave disintegration after passing over an offshore shoulder of submerged breakwater, both the horizontal velocity and dynamic pressure below the internal-wave crest show a remarkable distribution or a remarkable curvature of distribution in the vertical direction with wave dispersion. Over a submerged breakwater where the width of the breakwater crown is short or the lower-layer depth is deep over the breakwater crown, the crests of internal waves do not show wave disintegration.
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  • Mohammad BAGUS ADITYAWAN, Bambang WINARTA, Hitoshi TANAKA, Hiroto YAMA ...
    2009 Volume 65 Issue 1 Pages 71-75
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    The Manning equation is commonly used in assessing the bed stress and also in modeling the wave propagation and run up. Nevertheless, this method might lead to an inaccurate estimation of the bed stress. In the present study, we will discuss the application of wave boundary layer in wave modeling. The free stream velocity at several cross sections is obtained from numerical simulation of solitary wave run up on a sloping beach. The wave propagation is calculated using the depth averaged equation with conventional Manning approach. The 1D vertical k-ω model will be used to assess the bed stress in wave propagation and run up. The velocity will be used as an input for the 1D model at the corresponding cross section.
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  • Natsuki MIZUTANI, Cowen Edwin A., Masahiro MIYAJIMA
    2009 Volume 65 Issue 1 Pages 76-80
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    We carried out the visualization experiment on air-flows over wind waves to investigate an occurrence frequency of an air-flow separation behind a wind wave crest. An air-flow separation behind a wave crest strongly depends on a local wave shape around the wave crest, but the occurrence frequency of the air-flow separation can be explained by the wave steepness. Physical surface roughness (significant wave height) grows as wind speed increases. However, the surface roughness length, z0, doesn't grow. If the air-flow separation occurs over wind waves, the air-flow travels from the wave crest to the next wave crest. Then, the air-flow doesn't sense as physical surface roughness as significant wave height. Therefore, the surface roughness length doesn't grow as wind speed increases.
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  • Takuya ANDO, Koji SAKURAGI, Yuji SUGIHARA, Shigeatsu SERIZAWA, Hiroshi ...
    2009 Volume 65 Issue 1 Pages 81-85
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    Estimations of the drag coefficient over the ocean surface were made by means of the eddy correlation and inertial dissipation methods. The variation of the drag coefficient with the wave age and swell conditions was investigated by using data set, showing good agreements between both methods. On the basis of directional wave spectra, we classified swell conditions into five groups, i.e., Pure windsea, Swell-dominated sea, Cross, Following and Counter swells. The present data show that the drag coefficient increases obviously with decreasing the wave age under same wind speeds, whereas the dependence of the drag coefficient on the swell conditions is unclear in comparison with that on the wave age. This suggests that the drag coefficient depends strongly on microstructures of the wave field, not lower-frequency structures for swells.
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  • Tomokazu MURAKAMI, Jun YOSHINO, Takashi YASUDA
    2009 Volume 65 Issue 1 Pages 86-90
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    This study aims at development of the bursting-layer model which enables us to describe correctly Reynolds stress in a non-logarithmic layer (bursting-layer) generated under the strong winds affected sea surface. The Reynolds stress in the non-logarithmic layer was separated into a low-frequency Reynolds stress that originates from the mean shear flow and a high-frequency Reynolds stress that originates from wind-wave breakers. The thickness of the non-logarithmic layer, the vertical distribution of the horizontal mean velocity, the low-frequency eddy viscous coefficient and so on were formulated to describe the low-frequency Reynolds stress and the high-frequency Reynolds stress. Furthermore, validity of both the Reynolds stress described with the bursting-layer model was verified by performing comparisons with experimental results.
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  • Junichi OTSUKA, Yasunori WATANABE
    2009 Volume 65 Issue 1 Pages 91-95
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    Three dimensional vortex structures involving pairs of longitudinal vortices are produced in breaking waves. Distributions of lateral velocities induced by the vortices were experimentally measured in small- and large-scale wave flumes using an Ultrasonic Velocity Profiler with the aim to identify the scaling law to describe the length, temporal and velocity scales of the longitudinal vortices. The rates of diffusion and surface replacement owing to the vortices were characterized for spilling and plunging breakers. It was also found fundamental features of local lateral flows with diffusion in the surf zone were subjected to Froude scaling law.
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  • Yusuke MATSUO, Nobuhito MORI, Takaaki SHIGEMATSU, Shohachi KAKUNO
    2009 Volume 65 Issue 1 Pages 96-100
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    The characteristics of bubble entrainment process in the surf zone are discussed. The two-phase flow measurements using two-dimensional imaging technique for bubble measurements, so called Bubble Tracking Velocimetry (BTV) were conducted in the laboratory wave tank. The horizontal and vertical distributions of void fraction and characteristic bubble size were measured and analyzed in detail. The relationship between the void fraction and wave energy dissipation are proposed for the surf zone breaking waves.
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  • Hirokazu SUMI, Takemori NOZAKI, Toshiyuki TAKAE
    2009 Volume 65 Issue 1 Pages 101-105
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    The mechanical properties of bottom shear stresses in the surf zone is still uncertain. This study has investigated the temporal and spatial distributions of the bottom shear stresses in the surf zone. The experiments have indicated that the temporal and spatial distributions of the bottom shear stresses varies, depending on the water surface level and flow velocity. The time variations of the bottom shear stresses and velocity in the same phase of the water surface level changes. Thus, the water surface level changes in the same phase of the velocity in the surf zone. The maximum bottom shear stresses have shifted from the peak of the water surface level. The bottom shear stresses under the peak of waves tend to be larger than those under the trough of waves.
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  • Hirokazu SUMI, Takemori NOZAKI, Toshiyuki TAKAE
    2009 Volume 65 Issue 1 Pages 106-110
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    Horizontal and obliquely descending eddies due to breaking waves tend to have three-dimensional phenomena. There are a few studies on experimental observations of three-dimensional velocity distributions under the breaking waves. Thus, the formation of the horizontal and obliquely descending eddies are not completely explained at present. This study has experimentally found the generation condition of the horizontal and obliquely descending eddies and the three-dimensional velocity distribution under the wave breakings. As a result, the generation condition of the obliquely descending eddies is dependent on the breaking type index (Bt) and Reynold's number. Still more, the lateral velocity distribution has been found to be random in time and space.
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  • Kwang-Ho LEE, Toshiaki FUJII, Norimi MIZUTANI
    2009 Volume 65 Issue 1 Pages 111-115
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    The purpose of this study is to investigate the application of soft computing method for predicting the breaking wave height and water depth, considering the effects of the groundwater table. An artificial neural network, fuzzy inference system and an adaptive-network based fuzzy inference system are chosen as a soft computing method. The predicted results by the soft computing method show the good agreement with the experimental results and are more accurate than those obtained by existing empirical schemes. Moreover, an adaptive-network based fuzzy inference system is a most useful tool for predicting the breaking wave height and water depth.
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  • Takeshi INAGAKI, Keiko UDO, Akira MANO
    2009 Volume 65 Issue 1 Pages 116-120
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    For investigation of beach processes, it is necessary to consider wave-driven sand transport. Hydrodynamics in the wave run-up area should be estimated accurately in order to predict the beach processes, however, the accuracy of existing numerical models regarding moving shoreline change are insufficient for the prediction of the shear stress and the sediment transport. This study developed theoretical-based moving shoreline model using shallow water equation. The wave run-up heights obtained from numerical results of this model were approximately proportional to the values calculated from Hunt (1959) formula. This theory-based model can simulate the moving shoreline change accurately.
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  • Kenji KASAHARA, Koji FUJIMA, Yoshinori SHIGIHARA
    2009 Volume 65 Issue 1 Pages 121-125
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    Wave damping in case of plunging breakers and breaking bores was examined by hydraulic experiments. Wave amplification to wave breaking point was reproduced by numerical simulation by nonlinear dispersive theory, and wave breaking point was estimated by the authors' method accurately. However, an existing wave-breaking model underestimated the wave damping, because that was established by experiments of spilling breakers. A proper model to reproduce the wave damping in plunging breakers and breaking bores was proposed through numerical tests. If we can estimate the breaker type, the maximum error of highest water level becomes 5 to 6 % by selecting the proper model. Even if we cannot estimate the breaker type, the maximum error is round 10 % by using the intermediate model.
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  • Taro KAKINUMA, Shizuka OHISHI, Youhei YAMAMOTO, Kazuo NAKAMURA, Yoshis ...
    2009 Volume 65 Issue 1 Pages 126-130
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    Seepage velocity in a breaker zone was measured with dye for visualization. Pressure sensors were also installed to obtain pore water pressure. Three cases of different incident wave periods were treated in laboratory experiments. The time-averaged pore water pressure was higher nearer to the shore, resulting in seepage flows, whose velocity was larger as the incident wave period was longer, generally running from onshore to offshore. The penetrated water flowed out from the permeable seabed at a bar top or on the rather offshore side of the bar top if a bar was remarkably developed. The pore water pressure in the breaker zone showed time variation depending on the wave phase including wave breaking and bore propagation. There was a phase where the pore water pressure decreased locally below the bar.
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  • Katsuya HIRAYAMA, Hiroaki KASHIMA, Keiji NAKAI, Masanobu KUDAKA
    2009 Volume 65 Issue 1 Pages 131-135
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    Generally, a joint distribution of significant wave height, period and direction outside a harbor is analyzed with assumption that a single-peaked spectrum is observed in each time. However, the significant wave periods should be underestimated when double-peaked spectra are observed, and that seems to affect wave height exceedance within the harbor. In this paper, the occurrence frequency of the double-peaked spectrum is estimated by using newly proposed method. Moreover, the estimation of the probability of wave height exceedance within the harbor is carried out with considering both the separated significant periods of wind wave and swell from the double-peaked spectrum. On a berth in the target harbor, it reduces 0.1% when the number of underestimation of significant wave periods is 2% in whole observed spectra.
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  • Masataka YAMAGUCHI, Hirokazu NONAKA
    2009 Volume 65 Issue 1 Pages 136-140
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    Two kinds of surface elevation data with a diverse form of spectrum are analyzed to investigate the effect of spectral form on a ratio of the surface elevation-based statistics to the spectrum-based statistics of wave height and period. One is generated by use of a Monte-Carlo simulation and the other is acquired from in-situ measurements. Main conclusions are 1) a proper evaluation for the parameter characterizing the spectral form requires a highly-resolved estimate of spectrum 2) wave height ratio is most closely related to the spectral peakedness parameter Qp and each of the wave period ratios to the spectral width parameter v and 3) the simulation-based ratio indicates an explicit dependency on double-peakedness of the spectrum but the measurement-based ratio shows a weak dependency due to statistical variability.
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  • Nobuhito MORI, Masahiro YOSHIGI, Hiroaki SHIMADA, Tomohiro YASUDA, Haj ...
    2009 Volume 65 Issue 1 Pages 141-145
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    A series of data set of ocean wave records from the Pacific Ocean and the Sea of Japan is analyzed for understanding freak wave characteristics in lights of wave height statistics, frequency and directional spectrum parameters, and nonlinear statistical parameters. In addition, measured maximum wave heights are compared with predicted ones by a nonlinear wave theory, and the relation of freak wave occurrence with weather condition is made. It was found that observed data shows a weak correlation between maximum wave heights and kurtosis of free surface elevation and that freak waves at peak of storm are observed under migratory low atmospheric pressures.
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  • Hajime MASE, Nobuhito MORI, Tomohiro YASUDA, Junichiro SAKUNAKA, Tomoa ...
    2009 Volume 65 Issue 1 Pages 146-150
    Published: 2009
    Released: February 09, 2010
    JOURNALS FREE ACCESS
    A system to determine a design wave was proposed for a site selection of floating type wind power farm by utilizing wave analysis data in the North Pacific for 54 years. The wave analysis database was made from WAM's output calculated using NCEP/NCAR wind data. Even for a site of floating type wind power farm, the wave analysis database is not able to be employed directly as an offshore design wave since the site is not so far from a coast and it has insufficient spatial resolution. A procedure how to utilize the wave analysis databasae was shown in this study. Following this procedure, a design wave is assessed in any offshore site for a short time.
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  • hirokazu NONAKA, Masataka YAMAGUCHI, Yoshio HADATA
    2009 Volume 65 Issue 1 Pages 151-155
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    Station by station wave computation on the Pacific coasts of Japan for typhoons generated over a period of either 20,000 years or 100,000 years is conducted using a Monte-Carlo simulation system. The system consists of a stochastic generation model of a parameterized typhoon and a backward ray tracing-based wave model on a nested grid with high space resolution. Extreme value analyses of typhoon-generated annual maximum wave height samples reveal that the simulation-based 50-year return wave heights on the coasts are in reasonable agreement with the measurement-based ones and that the probable maximum wave height deduced from 100,000-year wave simulation may be around 10 m greater than the maximum wave height measured in the recent several decades to the best degree.
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  • Takashi IZUMIYA, Hitoshi SHIBUYA
    2009 Volume 65 Issue 1 Pages 156-160
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    A weighted least squares method for extreme statistics has been developed to estimate the parameters of candidate distribution functions. The method employs variances of the order statistics of extreme data, which are analytically evaluated by virtue of asymptotic distributions of the order statistics. A new criterion for goodness-of-fit in extreme statistics has been proposed to select a distribution function best fit to the parent distribution. Monte Carlo simulations with 5,000 and 10,000 samples have been carried out to verify an applicability of the new criterion for goodness-of-fit. The simulations show that the present criterion can select a correct distribution function for the case of FT-I type and generalized extreme value distributions, and Weibull distributions with the shape parameters of 0.75 and 1.0.
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  • Yoshimi GODA, Masanobu KUDAKA, Hiroyasu KAWAI
    2009 Volume 65 Issue 1 Pages 161-165
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    The L-moments method is applied for the POT storm wave data at eight stations around Japan, which have the record length of 27 to 38 years. The formulas of the L-moments of the Weibull distribution are newly derived for estimation of the shape, scale and location parameters from a sample. A new index called TUD (Twenty-Up Deviation) is developed for judgment of the degree of goodness of data fitting to a candidate distribution. Among eight stations, two stations show the best fitting to the Weibull distribution, four to the General Pareto (GPA) distribution, and two to the General Extreme-Value (GEV) distribution. At two stations fitted to the GPA distribution, the theoretical upper bounds of extreme wave heights are only 7% to 11% greater than the observed maximum wave height.
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  • Toshikazu KITANO, Wataru KIOKA, Rinya TAKAHASHI
    2009 Volume 65 Issue 1 Pages 166-170
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    It is important to detect the incremental tendency of extremal sea phenomena (sea level, wave height and so on) in recent short record and to predict the future's return level by extrapolating the trend line. It is noted that the extrapolation is adopted here in double senses: one is the extension of regression relation in time domain, another is that of rare occurence in probability domain. For the statistical uncertainty accompanied with those extrapolations, the degree of experience is introduced and executed for two types of return periods based on the instantaneous and mean occurence rates.
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  • Noriaki HASHIMOTO, Koji KAWAGUCHI, Katsuyuki SUZUYAMA, Masaru YAMASHIR ...
    2009 Volume 65 Issue 1 Pages 171-175
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    For the purpose of improving estimation accuracy of swell with the third generation wave models, the effectiveness of EDIA (Extended Discrete Interaction approximation) was discussed for various directional spectra. Then, numerical simulations were carried out to confirm the fact that EDIA can lead to accuracy improvement of swell with long decay distance. Finally the method was applied to simulate an actual case of 'Yorimawari-Nami'. It turned out that the accuracy improvement of simulating Yorimawari-Nami was not led only by the improvement of nonlinear energy transfer with EDIA. Some other improvement is still necessary. One of the possibilities is considered to be the improvement of computation accuracy of wave energy propagation scheme.
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  • Wataru KIOKA, Hiroyuki KATOH, Toshikazu KITANO
    2009 Volume 65 Issue 1 Pages 176-180
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    The turbulent air flow over water waves with varying wave slope, wave age and the Reynolds number is investigated using LES at both relatively low and high Reynolds numbers. For the present study, attention will also be paid to the case where waves propagate away from a storm into areas of lighter winds. The wave growth rates for the slow moving waves are found to depend strongly on wave slope while the decay rates for the fast moving waves are almost independent of wave slope. The critical value of wave age that marks this transition increases at the high Reynolds number.
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  • Noriaki HASHIMOTO, Masaki YOKOTA, Koji KAWAGUCHI, Kentarou YOSHIMATSU, ...
    2009 Volume 65 Issue 1 Pages 181-185
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    The sea surface drag coefficient used in the energy transfer function is simply described as a linear function of wind speed extrapolated from weak wind to strong wind condition. Accordingly, the accuracy of estimated waves under strong wind conditions seems to be unreliable. To deduce appropriate drag coefficient in high speed winds, the data assimilation method is considered to be a powerful tool, and is applied to WAM. Then the validity of the new method was examined by numerical experiments. As a result, it is confirmed that the drag coefficient deduced by the model is accurate when the observation data is enough. It is also confirmed that the accuracy of the deduced coefficient can be improved by adding a priori condition if the observation data is not enough.
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  • Masataka YAMAGUCHI, Manabu OOFKU, hirokazu NONAKA, Yoshio HADATA, Miki ...
    2009 Volume 65 Issue 1 Pages 186-190
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    Using the SDP(Surface Data Point) wind data measured at on-land branches of the Japanese Meteorological Agency which are located around the Kanto Sea area, Ise Bay and the Seto Inland Sea, a data set of hourly sea wind distribution on the concerned sea areas is made over a period of 45 years from 1961 to 2005. For that, the wind data interpolated from the SDP data at each of the coastal and sea measurement stations on the concerned areas is transformed into an equivalent of the wind data measured at each station by utilizing close correlation between two kinds of wind data at the same location. Then sea wind distribution is estimated through a spatial interpolation of the equivalent wind data. One finding is that a whole-year averaged wind distribution yields a reasonable approximation of climatic behavior.
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  • Masataka YAMAGUCHI, Yoshio HADATA, Manabu OOFKU, hirokazu NONAKA, Miki ...
    2009 Volume 65 Issue 1 Pages 191-195
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    A long-term wave hindcast system applicable for the wave computations over a 45-year period at an arbitrary location of Tokyo Bay area is reconstructed. Hourly sea wind distributions estimated by making use of an analogy between land-based SDP wind measurement data and coast- and sea-based wind measurement data are given on the coastal sea area and those made by recompiling the NCEP/NCAR reanalysis surface wind product on the open ocean. Wave computation is based on a backward ray tracing model on a nested grid with very high space resolution. Comparison between hindcasts and measurements for wave height over a long period of 10 to 23 years at 5 stations situated inside and outside of Tokyo Bay verified a reasonable performance of the system.
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  • Takahide HONDA, Yukinobu ODA, Kazunori ITO
    2009 Volume 65 Issue 1 Pages 196-200
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    For a prediction of wave field where wave observation data do not exist, numerical wave estimation models such as SWAN are effective. For these models, global meteorological databases provided by ECMWF or NCEP can be used as wind input data; however these data may be coarse for wave hindcasting. In this study, to evaluate the fine wind field data for the wave hindcasting, the mesoscale meteorological model MM5 was applied. By applying the wind fields evaluated by MM5 to SWAN, the wave hindcasting was available with good accuracy. Moreover, for high waves produced by typhoon, it is well known that typhoon bogussing is effective, while wind field calculation at higher resolution without bogussing gave good estimations of wave fields as well.
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  • Yoshio HADATA, Masataka YAMAGUCHI, Manabu OOFKU, hirokazu NONAKA
    2009 Volume 65 Issue 1 Pages 201-205
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    Shallow water wave hindcastings are conducted in Osaka Bay and Kii Channel for not only the 3 large typhoons in the early 1960s, which caused an enormous amount of damage to Osaka Bay areas, but also the most recent 5 strong typhoons with the sea wind distribution properly evaluated using land-based wind measurement. A good agreement between abundantly-acquired wave measurements and the corresponding hindcasts for the recent typhoons may guarantee to some extent a reasonable accuracy of the wave hindcasts for the 3 typhoons in the 1960s which are performed with the sea wind distribution evaluated by the same method. It is deduced that wave heights generated by the 3 typhoons may change greatly 50-year return wave heights in Osaka Bay estimated using the wave hindcasts for intense storms in the recent 30 years.
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  • Tomoaki KOMAGUCHI, Han Soo LEE, Takao YAMASHITA
    2009 Volume 65 Issue 1 Pages 206-210
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    Hindcasts of three abnormal wave events in the central Japan/East Sea in winter in 1991, 2003, and 2008 were conducted by using a meso-scale meteorological model (MM5) and a third generation spectral wave model (WW3) to make clear the generation mechanism of the abnormal waves caused by winter monsoons. It is reported that coastal damages due to winter depression in 2008 were more serious than those in 1991 and 2003 and major damages of coastal structures in Toyama Bay in 2008 were caused by large wave-overtopping with a high sea level due to superposition of diffractive waves (form NW) and swells (from NE). It is clear in this study that the superimposition of developed wind waves and swells in the offshore region of the central Japan/East Sea makes the characteristics of abnormal high waves.
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  • Yoshimitsu TAJIMA, Hiroaki ISHIZASHI, Shinji SATO
    2009 Volume 65 Issue 1 Pages 211-215
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    This study aims to investigate physical mechanisms of locally concentrated nearshore hydrodynamic forces under interactive fields of waves and currents on sharply changing coastal bathymetries. Laboratory experiments were first performed to represent the focusing phenomena and a newly developed measuring system based on image analysis techniques successfully obtained quantitative high-resolution data of locally concentrated wave fields. Numerical analysis were finally performed to further investigate the physical mechanisms of the observed features and it was found that, among the other various possible factors, the slowly varying wave-induced nearshore currents have one of the most significant impacts on local concentrations of waves around the sharp edge of bathymetry.
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  • Taro KAKINUMA, Taishi TOYOFUKU, Taisuke INOUE
    2009 Volume 65 Issue 1 Pages 216-220
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    A numerical model based on nonlinear shallow-water equations is applied to study oscillations in harbors of different shapes represented in 'L'-type, triangle, 'I'-type with different width, 'I'-type with a narrow strait, and 'C'-type. The second mode shows a higher amplification ratio at the head of an L-type harbor as its bending position is nearer to the harbor mouth. As a narrow strait is located nearer to the mouth of an I-type harbor, amplification ratios of the first and second modes at the harbor head are lower and higher, respectively. A C-type harbor shows rather complicated amplification ratios because the phase difference between waves propagating through two harbor mouths depends on the position inside the harbor. Harbor oscillations in I-type harbors where the still water depth is distributed are also simulated.
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  • Takashi IZUMIYA, Makoto KANAI
    2009 Volume 65 Issue 1 Pages 221-225
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    A stochastic forcing model has been developed to estimate the heights of infragravity waves excited by short gravity surface waves. The model includes a wave equation for infragravity waves with the external force term due to pressure disturbances by short gravity waves. The analytical solution of the wave equation was obtained, and the root-mean-square value of the surface elevation of infragravity waves was estimated. The rms value is proportional to the square root of the spectral moment of -2 order, m-2, of short gravity waves, which is also proportional to the product of the wave height and the peak wave period or the significant wave period of short gravity waves. The estimated rms heights of infragravity waves are compared with the observed data compiled by NOWPHAS and show good agreements with them.
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  • Keiji NAKAI, Noriaki HASHIMOTO
    2009 Volume 65 Issue 1 Pages 226-230
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    Nakai and Hashimoto(2008) defined "longevity of infragravity waves" and showed characteristics of longevities of various frequency components in The Pacific Ocean and The Sea of Japan. And they showed that the longest component whose period is more than 600s sometimes develops even when shorter components and wind waves do not develop. In this paper, we calculated longevities of wind waves and compared them with those of infragravity waves. And we analyzed the relationship between development of the longest component of infragravity waves and the atmospheric pressure. When the longest component starts developing, the atmospheric pressure starts decreasing in the synoptic scale and the variation of atmospheric pressure whose period is less than one hour increases at the same time.
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  • Kazuyuki OTA, Akinori YOSHIDA, Masaru YAMASHIRO, Naoki KOBAYAKAWA, Yas ...
    2009 Volume 65 Issue 1 Pages 231-235
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    Sufficient computation time to obtain stationary results for long wave oscillations in harbors by Boussinesq model was investigated. For different data lengths (computation times), wave spectra and significant wave heights of long waves were computed with a model harbor and several incident wave spectra. It was found that the length of the computation time to obtain stationary values are significantly influenced by frequency characteristic of amplification factor of water surface oscillations and the periods of the beats consisting of adjacent components of the incident random waves, and that the time length is generally much longer than that which is expected from random wave statistics.
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  • Sayaka NAKAJIMA, Kaori OHSHIMA, Kouichirou ANNO, Masahito TSURU, Shige ...
    2009 Volume 65 Issue 1 Pages 236-240
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    We have developed the long-period wave absorption structure by the experimental studies. On planning to apply it to actual fields, we propose the advanced type structure adding to upright wave absorbing blocks to dissipate not only long-period waves but also short-period one. The hydraulic performance such as reflection rates is verified through experiments. Furthermore, we reproduce the hydraulic performance of the structure with the numerical analysis based on the non-linear shallow water theory and demonstrate that it is useful for practical design of the structures.
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  • Nobuhito MORI, Rie TAKADA, Tomohiro YASUDA, Hajime MASE, Soo Youl KIM
    2009 Volume 65 Issue 1 Pages 241-245
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    Since major driving forces of storm surge are pressure depressions and wind stresses, a set of depth integrated equations is widely used for storm surge simulations. However, there are several phenomena should be take into consideration. This study estimates effects of wave radiation stress, vertical mixing models and boundary conditions at ocean upper layers on storm surge. The three dimensional hydro-static model is used to predict the sea surface elevation in the storm surge. The numerical results show that the wave radiation stress and the turbulent flux significantly influence on the surface elevation and the current, respectively.
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  • Nobuhiko HARA, Tadashi YAMADA, Hidenori SHIBAKI
    2009 Volume 65 Issue 1 Pages 246-250
    Published: 2009
    Released: February 23, 2010
    JOURNALS FREE ACCESS
    A surge-flood coupling model was developed for numerical analysis of the disaster phenomena in river and coastal areas. In the coastal area, the basic equations of storm surge model are the multi-level continuity and momentum equations integrated for each layer. The shear stresses and the pressure gradients are taken into consideration in the momentum equations. A general coordinate system is used due to its advantageous for the modeling the watercourse of complex shape of rivers. In the river areas, the basic equations of flood model are then two dimensional unsteady flow ones. The developed surge-flood coupling model is applied in this study for the analysis of the river current and the water level in the Tokyo Bay.
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