Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering)
Online ISSN : 1883-8944
Print ISSN : 1884-2399
ISSN-L : 1883-8944
Volume 67 , Issue 2
Showing 1-50 articles out of 279 articles from the selected issue
  • Wataru KIOKA, Masashi OKAJIMA, Toshikazu KITANO
    2011 Volume 67 Issue 2 Pages I_1-I_5
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    The characteristics of highly nonlinear waves reflecting from a vertical wall in water of finite depths are investigated both experimentally and theoretically. In this study, we re-examine nonlinear interaction phenomena with a vertical wall on a sloping beach as the effects of slope, i.e. changing in water depth are not included in any previous studies. The results of regular-wave experiments indicate that the wave periods of individual standing waves become slightly longer than those of progressive waves. The periods of reflecting wave groups become also longer than those of progressive wave groups. In both cases, amplitude modulations in the reflected wave field are very significant for higher wave steepness while no amplitude modulation occurs in the progressive wave field.
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  • Keisuke NAKAYAMA, Taro KAKINUMA, Hidekazu TSUJI, Masayuki OIKAWA
    2011 Volume 67 Issue 2 Pages I_6-I_10
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    To clarify the resonance of fully-nonlinear internal solitary waves which is one of the reasons for the occurrence of large amplitude internal waves, fully-nonlinear and strongly-dispersive internal wave equation model was applied, which attempted to investigate interaction of internal solitary waves in a two-dimensional plane. The 3rd order theoretical solutions for internal waves in a two-layer system was used for the initial conditions and progress of internal solitary wave was confirmed. Seven different incident wave angles were given, in which 'stem' was confirmed to appear when incident wave angle is less than critical angle. As a result, it is found that the amplified internal wave amplitude becomes about three times as much as the original amplitude.
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  • Tsunehiro SEKIMOTO, Sayaka NAKAJIMA, Hiroyuki KATAYAMA, Kenya TAKAHASH ...
    2011 Volume 67 Issue 2 Pages I_11-I_15
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Hydraulic model tests of wave deformation on the reef with steep forereef slope by using irregular waves were conducted. Two types of the reef topography were inspected. It is confirmed that wave deformation near the reef has very strong nonlinearity near the reef edge. Hydraulic jump at the wave front in times of buckrush and wave breaking in times of uprush coexist at the reef edge. Numerical model based on wave energy balance model developed by Takayama et al. (1991) was modified in order to estimate extreme wave condition inside and outside the reef. The comparison of the numerical simulation result with the experimental one demonstrates that Takayama's model improved in this study provides very good agreement with the experimental data.
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  • Yasunori WATANABE, Atsushi IWASHITA
    2011 Volume 67 Issue 2 Pages I_16-I_20
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    A novel numerical technique to fulfill dynamic interfacial boundary conditions on fixed Cartecian computing grids, based on interactive interpolations of velocity gradients to the both air and liquid phases, was proposed in this paper. The balances of the tangential shears across the interface and the normal pressure jump were able to be reasonably achieved in our method used in computations of the air-liquid interfacial flows. An early stage of wind wave generation, wavelets initiated from a still water horizontally blowing undisturbed wind was reasonably computed using the current technique
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  • Taro ARIKAWA, Minoru AKIYAMA, Noboru Yamazaki
    2011 Volume 67 Issue 2 Pages I_21-I_25
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    It is important to develop the Solid-Gas-Liquid coupling system for analyzing the mechanism of failure of structures on land by Tsunami. At first, the numeric wave tank, whose name is CADMAS-SURF/3D, is improved to correspond to two phase incompressible fluid. This two phase flow tank is applied to the impulsive wave pressure problem. As a result, it is confirmed that a numeric noise, which is called Spike Noise, is removed and the accuracy of the result is good agreement with the single phase model. Next step, the coupling system with DEM method is developed. The wall destruction test by fluid is conducted. The appearance of the wall destruction adjusted the large-scale experiment, and the validity of three phase coupling system is confirmed qualitatively.
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  • Chiemi HORI, Hitoshi GOTOH, Hiroyuki IKARI, Abbas KHAYYER
    2011 Volume 67 Issue 2 Pages I_26-I_30
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Simulating turbulence by the standard particle method is difficult due to its unphysical pressure fluctuation. However, the particle method has been improved so as to efficiently suppress such a fluctuation in our previous studies. In this paper, the refined particle method is combined with the sub-particle-scale (SPS) turbulence model. The SPS turbulence model is introduced for the Reynolds stress terms in the filtered Navier-Stokes equation. The standard Smagorinsky model is used in the present study. A spilling breaker is simulated and its turbulent characteristics are analyzed. By comparing with experimental data, a predictive validity of the present simulation is shown.
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  • Masaru KATSUMATA, Takenori SHIMOZONO, Akio OKAYASU
    2011 Volume 67 Issue 2 Pages I_31-I_35
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    A 2D numerical method with shock capturing properties was developed for Boussinesq-type equations in an attempt to describe wave-breaking phenomena. The model is based on hybridization of the 4th-order finite difference scheme and TVD method. The model tests were performed through comparison of model outputs with experimental data on two different problems; 2D solitary wave deformation over uneven bottom and wave deformations over submerged breakwaters. It was found that the model can simulate a wide range of 2D wave deformations without instability although it had a tendency to underestimate wave dissipations associated with wave breaking.
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  • Kwangho LEE, Norimi MIZUTANI
    2011 Volume 67 Issue 2 Pages I_36-I_40
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    In the present work, an algebraic interface capturing method called THINC is employed to track free-surface in computations of multi-phase flow simulations instead of geometrical-type methods such a VOF method. The THINC method uses a hyperbolic tangent functions to represent the surface, and compute the numerical flux for the fluid fraction functions. The main advantage of THINC is its easy applicability to incorporate various numerical codes because it does not require the extra geometric reconstruction needed in most of VOF-type methods. In order to verify the applicability of THINC to wave fields, several numerical simulations are performed based on the one-field model for immiscible two-phase flows (TWOPM). Comparisons are made between the numerical results and the experimental data, and good agreement is achieved.
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  • Mohammad BAGUS-ADITYAWAN, Hitoshi TANAKA
    2011 Volume 67 Issue 2 Pages I_41-I_45
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Higher order equation with advanced numerical scheme is able to provide realistic solution for breaking wave case, yet difficult to apply in practical application. Recent development has enhanced SWE, by coupling with k-ω model for better bed stress assessment, and applying FORCE-MUSCL shock capturing scheme to handle breaking wave. In this study, this enhanced SWE model is used to simulate and investigate bed stress accumulation under breaking solitary wave run up (canonical problem). Comparison of bed stress accumulation to the conventional Manning method shows similar general conclusion that bed stress is more significant during run down. Further comparison to non breaking wave case shows that bed stress during run down is greatly emphasize in the breaking wave case.
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  • Takenori SHIMOZONO
    2011 Volume 67 Issue 2 Pages I_46-I_50
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Laboratory experiments were performed to investigate characteristics of boundary layer flows under different types of bores. Temporal variations of nearbed velocity profile were measured by a PIV technique and compared with solutions of the boundary layer equation under upper boundary conditions given by the measured free-stream velocities. The results suggested that the boundary layer remained laminar at the bore front even for the case of a fully-developed turbulent bore. The bore-induced turbulence affected the boundary layer after a certain period of time and resulted in a significant rise in bed shear stress. It was also found that the bed-generated turbulence tends to be dominant during the late stage of bore propagation.
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  • Naoto KIHARA, Ko NAKAYA, Takaki TSUBONO, Masafumi MATSUYAMA, Hiromaru ...
    2011 Volume 67 Issue 2 Pages I_51-I_55
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Field measurements were carried out in the Tanabe bay by StUPA (Structure of Upper Ocean and Atmospheric Mixing) project in order to clarify structures in the upper ocean and the atmospheric surface layer. In this study the most important wave scale for the momentum transfer in the atmospheric surface layer over the bay with mixed states of developing wind-waves and swells is investigated. Momentum fluxes estimated by six empirical formulae for the drag coefficient and the roughness height with various wave scales are compared with measured ones. The results show that the saturation rate of wind-waves is most important index for the momentum transfer in the bay and there is a clear relationship between the drag coefficient and the saturation rate.
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  • Natsuki MIZUTANI, Masahiro KAJI, Masahiro MIYAJIMA
    2011 Volume 67 Issue 2 Pages I_56-I_60
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Occurrence frequency of air flow separations over wind waves was measured to investigate relationship between the air flow separation and a drag coefficient. The occurrence frequencies converged to a value of 10% with windsea Reynolds number, RB, ranging between 200 and 1000. In that condition, the drag coefficients also have a constant value. Under moderate wind speed and short fetch condition, the air flow separation controls momentum transfer from air side to water side without wave breaking. As a result, despite growth of wind speed, wave breaking probability and wave steepness are still kept constant. This process is considered as a self-regulation mechanism of wind waves without wave breaking.
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  • Yasunori WATANABE, Shinji TADAKI, Tomohito YAMADA
    2011 Volume 67 Issue 2 Pages I_61-I_65
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Deformations of air-water interfaces throughout a splash event of falling water drops on a still water surface were studied in this paper on the basis of back-light imaging measurements.A series of interfacial processes, formations of fine sprays shedding from crown tips, air bubbles released from the center of a cavity, secondary droplets fragmented from a centric jet, was parameterized with Froude and Weber numbers as well as relative densities of impacting and receiving liquids with the aim to develop a future model to describe local heat and moisture exchanges between atmosphere and ocean under rainfall.
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  • Yasuo NIIDA, Yasunori WATANABE
    2011 Volume 67 Issue 2 Pages I_66-I_70
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    This paper presents fundamental properties of concentrations of oxygen dissolved from air-bubbles pumped into water with the aim to understand aeration effects to oxygen supply in the surf zone. Fluorescence imaging experiments were performed to identify relations of the local transfer of oxygen and the bubble size distribution. It has been found that the both of spatial distributions and temporal variations of dissolved oxygen were described by the number densities of small bubbles less than 2.0 mm.
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  • Yuji SUGIHARA, Daisuke NAKAGAWA, Koji SHIONO
    2011 Volume 67 Issue 2 Pages I_71-I_75
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    A direct numerical simulation is made to investigate the gas transfer at the air-water interface in an open channel flow. The numerical results show the interfacial gas flux to increase intensively in large positive surface divergence regions. This means that the surface divergence model is effective for evaluating the gas transfer velocity at the air-water interface. Scaling relations for turbulence controlling the gas transfer are examined from view points of the surface divergence model. The scale of the surface divergence can be expressed by the Taylor microscale, not macro turbulent scales. We found a dimensionless gas transfer velocity to depend on the -1/4 power of a turbulent Reynolds number. The divergence model shows formally the same Reynolds number dependence as the small eddy model based on the Kolmogorov scaling.
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  • Bambang WINARTA, Hitoshi TANAKA
    2011 Volume 67 Issue 2 Pages I_76-I_80
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    A wave flume is commonly used in solitary wave boundary layer research. However, it is hard to reproduce near-bed hydrodynamic and sediment transport phenomena at a realistic scale. Latterly, an oscillating water tunnel has been utilized to examine turbulent solitary wave boundary layer (Sumer et al. 2010). Both of experimental facilities actually have main difficulty to achieve reliable ensemble average. In this study, a new generation system for solitary wave boundary layer which enables to do measurement under single and periodical motion is proposed. As a result, single and periodical measurements confirm a good agreement. It is concluded that the new generation system is able to investigate solitary wave boundary layer and applicable for sediment transport experiment by facilitating ensemble averaging.
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  • Tetsunori INOUE, Ronnie GLUD
    2011 Volume 67 Issue 2 Pages I_81-I_85
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Three approaches; eddy-correlation (EC), turbulent kinetic energy (TKE), and inertial dissipation (ID) methods were compared to evaluate their potential for estimation of shear velocity in a protected coastal region. As an independent assessment parameter we used simultaneous oxygen recordings in the vicinity of the sediment-water interface that were compared with theoretical distribution as derived from the respective shear velocity estimates. Overall differences from measured oxygen concentration were 0.2% for EC method, 9.8% for TKE method, and 0.7% and 4.6% for ID method using vertical and longitudinal velocity components, respectively. The results revealed that the EC method appeared to be the best approach though not significantly different from the ID method using vertical velocity component at the study site.
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  • Yuta MITOBE, Yasunori WATANABE
    2011 Volume 67 Issue 2 Pages I_86-I_90
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Three-dimensional breaking wave shapes of typical breaker types were measured using our proposing image technique with a PC projector and digital camera. Surface curvature of the wave fronts was found to characterize the deformations of the breaking waves, which depends on the Surf Similarity Parameter. The current technique is useful for identifying transient breaking wave process in terms of geometrical features of the surface forms.
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  • Junichi OTSUKA, Yasunori WATANABE
    2011 Volume 67 Issue 2 Pages I_91-I_95
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Suspended sediment velocity and flux in a surf zone were experimentally measured using an Ultrasonic Velocity Profiler (UVP) and an optical concentration meter for understanding the transport process of suspended sediment under breaking waves. The concentration near the bed increased when a breaking wave front passed. The time-averaged horizontal flux was offshore-direction owing to the undertow, and the time-averaged vertical flux was downward owing to the settling effect. The pick-up coefficient evaluated from the mean concentration and the wave energy flux dissipation rate was 406 on the average. The pick-up coefficient acquired in this small-scale experiment was much higher than that in the large-scale experiments and field observations.
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  • Yusuke UCHIYAMA, James C. MCWILLIAMS
    2011 Volume 67 Issue 2 Pages I_96-I_100
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Littoral flows are analyzed with an Eulerian-averaged primitive equation for slowly-evolving oceanic flows based on a vortex-force formalism coupled with a WKB spectrum-peak wave model (ROMS-WEC; Uchiyama et al., 2010). Two surf zone problems on a realistic topography are analyzed: 1) shear instability associated with longshore currents driven by obliquely incident waves, and 2) normal mode instability of offshore-directed rip currents under a near-normal incident condition. The coupled wave-current model successfully reproduces 3-D shear waves during the SandyDuck field measurement. We found in 3-D rip-induced coherent eddies that littoral currents have significant depth dependency leading to vorticity stretching/titling effects and to faster decay of enstrophy and kinetic energy than 2-D rip eddies.
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  • Mamoru ARITA, Ichiro DEGUCHI, Yusuke IRIE, Takurou MATUMOTO, Takayuki ...
    2011 Volume 67 Issue 2 Pages I_101-I_105
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Mean water level around the rip channel in Uradome Beach in Tottori was measured by the stereo image analysis of the two video images. It is found that the mean sea level along the rip current was slightly higher than those in the region along each side of the rip current. A series of numerical simulations of wave-induced currents and mean sea levels were also carried out on the bottom profile measured at Uradome Beach. The numerical results show that rip current come up through the place where the wave height is low that just corresponds to the place where the mean water level is higher than the surrounding region.
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  • Katsuya HIRAYAMA, Hiroaki KASHIMA
    2011 Volume 67 Issue 2 Pages I_106-I_110
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    The coastal disaster due to wave overtopping was occurred in the Shimoniilawa coast faces to the Toyama bay in northern part of Japan in 2008. Several technical studies on the mechanism and the way of countermeasures have been justly reported. However, their consideration to wave transformations for over 14 seconds-period swell seem to be limited because they are based on a small model test using the simplified bathymetry or an ideal numerical simulation omitting hydrodynamics around submerged and detached breakwaters. In this paper, the large scale model test is carried out in the large basin set up the bathymetry model as fine as possible. The results indicate that the long period oscillations of water surface along the coast can make increase the wave overtopping and a coastal jetty can reduce the amplitude of them.
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  • Masashi OCHI, Makoto MIYATAKE, Katsutoshi KIMURA
    2011 Volume 67 Issue 2 Pages I_111-I_115
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    The effect on beach unstabilization due to the runup wave-induced coastal seepage is investigated through the experiment and the numerical modelling. The groundwater flow is estimated by using the orbit of fluorescent paint injected into sandy beach model. As the result, the steep slope of phreatic surface is made the seaward and upward directed groundwater flow to accelerate. The numerical modelling simulates the interacting runup wave motion and groundwater flow. The exfiltration flux on backwash shows that beach face leads to unstable condition caused by the uplift seepage force. This seepage force is made to increase the unstable region while the phreatic surface is rising.
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  • Hiroaki KASHIMA, Katsuya HIRAYAMA, Nobuhito MORI
    2011 Volume 67 Issue 2 Pages I_116-I_120
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Nonlinear four-wave interactions influence the statistical properties of deep-water extreme waves such as a freak wave. However, it is still not clear the characteristics of deep-water generated freak wave shoaling to shallow water region. In this study, the experiments with several bathymetry model are conducted to uni-directional random waves. The maximum wave height increases with an increase in kurtosis by third-order nonlinear interactions in deep water. The dependence of the kurtosis on the freak wave occurrence weaken by second-order nonlinear interactions associated with wave shoaling when the dimensionless depth kh < 1.36.
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  • Nobuhito MORI, Takeru MICHIMAE, Hiroaki SHIMADA, Hajime MASE
    2011 Volume 67 Issue 2 Pages I_121-I_125
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    A linear envelope assumption and quasi-resonant four-wave interactions for deep-water random waves may influence the statistical properties of deep-water surface gravity waves. As a consequence, the exceedance probability of wave height substantially deviates from the expected distribution obtained by assuming linear narrow banded spectrum waves. Here the occurrence probability of maximum wave heights is compared with ocean wave measurements during the yearsd 2001-2005 around Japan. The maximum wave height distribution and probability of occurrence of freak waves are compared with theoretical expectations and are adjusted by the measured data. The proposed distribution well predicts extreme waves in nonlinear random wave fields.
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  • Yoshio HATADA, Masataka YAMAGUCHI, Hirokazu NONAKA, Manabu OHFUKU
    2011 Volume 67 Issue 2 Pages I_126-I_130
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Shallow water wave hindcasting for each of 29 strong typhoons selected carefully in the 1918-1960 year period was conducted in 3 sea areas of the Seto Inland Sea, in cases where sea wind distributions were estimated by applying a method developed by Yamaguchi et al.(2009) to the wind data sets acquired at land stations located around the Inland Sea. Then, combining these hindcastings with the data samples of wave height during the 1961-2005 year period estimated in our previous study, the largest wave height during the 88 years ranging from 1918 to 2005 and 100-year return wave height were re-evaluated in the Inland Sea. An important conclusion is that a practicable extension of the data year period may be required for more proper estimation of the return wave height.
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  • Masataka YAMAGUCHI, Yoshio HATADA, Hirokazu NONAKA, Manabu OHFUKU, Mik ...
    2011 Volume 67 Issue 2 Pages I_131-I_135
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Shallow water wave hindcastings are conducted in the Seto Inland Sea, Ise Bay and Tokyo Bay for each of the so-called 3 giant typhoons in the Showa Era (Muroto Typhoon in 1934, Makurazaki Typhoon in 1945 and Isewan Typhoon in 1959). The computations follow the spatial distribution of time-dependent wave height and maximum value. The sea wind distributions given as the driving forces are estimated using a method which transforms the land-based measurement wind data into the wind data at sea or coastal stations and applies a spatial interpolation technique to the data. The main conclusion is that any of the typhoons may have generated the largest wave height over the past 90 years in the sea area of the typhoon path.
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  • Hiroyasu KAWAI, Makoto SATOH, Koji KAWAGUCHI, Katsumi SEKI
    2011 Volume 67 Issue 2 Pages I_136-I_140
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    This study has estimated the monthly-mean significant wave height and period, most frequent wave direction, wave power, and wave and wind calmness ratio at the GPS buoys and their nearby coastal wave gauges on the Tohoku to Shikoku Coast, Japan. There is a similar seasonal variation in the monthly wave statistics among the seven GPS buoys on Tohoku Coast. The spatial variation among these GPS buoys is smaller than the yearly variation. The wave height at the coastal wave gauge is smaller than that at the GPS buoy owing to the surrounding bathymetry. The wave power is generally larger and the calmness ratios are lower at the GPS buoy sites than at the coastal wave gauge sites. The GPS buoys observed high waves near the typhoon center and the wave generation and propagation owing to a low-pressure system.
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  • Yoshimi GODA, Masanobu KUDAKA, Hiroyasu KAWAI
    2011 Volume 67 Issue 2 Pages I_141-I_145
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Return wave heights at eleven NOWPHAS stations along the Japan Sea coast were estimated through the regional frequency analysis with the L-moments method. Several plotting position estimators have been examined through large-scale Monte Carlo simulations, and the estimator with α = 0.45 and β = 0 has been recommended for application. Eleven stations were divided into two regions to maintain homogeneity of the data within the regions. The wave data in the two regions were well fitted by the Weibull distribution with the scale parameter of 1.202 and 1.224. The 100-year significant wave height H100 varied from 8.37 m at Tottori to 10.74 m at Sakata. The Generalized Pareto (GPA) distribution also exhibited good fitting to the wave data with the estimated H100 varying from 7.68 m at Tottori to 9.84 m at Sakata, but H100 at five stations (Setana, Fukaura, Sakata,Niigata, and Hamada) was lower than the maximum significant wave height observed there.
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  • Nobuhito MORI, Ryo TANAKA, Sota NAKAJO, Tomohiro YASUDA, Hajime MASE
    2011 Volume 67 Issue 2 Pages I_146-I_150
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Since ship captured accidents have been frequently occurred around Japan, it is sometimes regarded as freak wave as a cause of these accidents. Generally effects of swell are not well considered for wind wave modeling and their contributions to wave height statistics are unknown. A series of the wind-wave experiments was carried out using a wind-wave tunnel and numerical experiments using spectral wave model were also conducted. The energy growth of pure windsea and swell-windsea fields are analyzed in detail. The swell effects on the wave statistics, such as kurtosis and skewness are investigated. The effects of swell enhace the extreme waves if the windsea energy is close to the swell.
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  • Takashi IZUMYA, Yuki YOKOYAMA, Kunihiko ISHIBASHI
    2011 Volume 67 Issue 2 Pages I_151-I_155
    Published: 2011
    Released: November 09, 2011
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    The evolution of wind waves and swells in an opposing and following winds is investigated through laboratory experiments. The fluctuations of air pressures and water surface elevations under the coexistence of wind waves and swell were measured to evaluate an energy flux from the wind to the waves. The power spectra and the cross spectra between the wind-induced pressure and the surface elevation were calculated using the laboratory data. It was found that the energy flux from wind to swells in an opposing wind were negative for the period of swell longer than 1.2 s, but positive for the periods shorter than 1.2 s. For a following wind, the swell with the shorter period can be easily amplified. The significant wave heights of an opposing swell were found to be amplified when the wind waves effectively grew.
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  • Taro KAKINUMA, Kousuke FUKITA
    2011 Volume 67 Issue 2 Pages I_156-I_160
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    The generation of long waves due to atmospheric-pressure variation was numerically simulated in East Chine Sea, where the atmospheric-pressure wave was assumed to travel in the eastern direction. The height of long waves is larger as the moving velocity of the atmospheric-pressure wave is near to the celerity of shallow-water waves. Before attenuation of the harbor oscillation in Urauchi Bay, Kamikoshiki Island, the incidence of long waves can continue because of the oscillation system between the main island of Kyushu and Okinawa Trough. The atmospheric pressure was classified into four patterns based on the Grid Point Value pressure data. The long incident waves causing the largest harbor oscillation in Urauchi Bay on Feb. 25, 2009 was simulated with the estimated atmospheric-pressure pattern.
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  • Masaki MIMURA, Masanori ISHIMOTO, Youji KIKUCHI, Yoshihiro UTSUNOMIYA
    2011 Volume 67 Issue 2 Pages I_161-I_165
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    The moored ship motion induced by the long-period waves causes troubles in the cargo handling before the completion of the breakwater at Misato district in Kochi port. The Takamatsu Research and Engineering office for Port and Airport has developed "Long-period wave forecasting system of Kochi port" to predict the long-period waves, which affect the cargo handling. To promote the accuracy of the prediction the system introduces the disaster prevention information of the Japan Meteorological Agency and accepts the opinion of cargo handling traders. A result of the test run could confirm the validity of the system in the long-period wave forecast.
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  • Keiji NAKAI, Noriaki HASHIMOTO
    2011 Volume 67 Issue 2 Pages I_166-I_170
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    A survey has been carried out on the spatial and temporal characteristics of slight atmospheric pressure changes concerning the seiches which developed in wide areas of Kyushu in February in 2009. The dominant periods of slight pressure changes are about 100 minutes, and on the other hand, those of seiches depend on local conditions around tidal stations. The time series data of slight pressure changes of some stations are often very similar even if they are distant. By using the characteristics, we estimated the propagation speed and direction of slight pressure changes with FK spectrum analysis. The slight pressure changes propagated almost eastward in conjunction with the passage of the low pressure. The propagation speed of the slight pressure changes is 2.3 km/min and is more than that of the low pressure.
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  • Tomonori SAITA, Toshiyuki ASANO
    2011 Volume 67 Issue 2 Pages I_171-I_175
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Secondary undulations locally called "Abiki" are frequently observed in Urauch Bay in Koshiki Islands. A meteorological disturbance over the East China Sea has been pointed out as the cause of the secondary undulations. In this study, response characteristics of the East China Sea to propagating pressure waves and the oscillation property of Urauch Bay were evaluated by numerical analyses. As the result, it is clarified that pressure waves with phase velocity of 80-140 km/h and spatial scales of 10-40km lead to large fluctuations of water level which have the periods close to the natural period of Urauch Bay. The waves close to the natural period not only set up resonance in the bay but also produce oscillations with a half period of incident waves in Urauch Bay.
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  • Toshiyuki ASANO, Toru YAMASHIRO, Akira TAKESHITA, Hiroaki SAKAMOTO, No ...
    2011 Volume 67 Issue 2 Pages I_176-I_180
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    A long term field observation was conducted on the secondary undulations locally called "Abiki" occurred in Urauchi-bay, Kami-Koshiki Island. A comprehensive observation deployment for the sea level, current and barometric pressure was taken covering not only inside and nearby Urauchi-bay but also offshore field in the East China Sea. Vigorous secondary undulations greater than 150cm were happened over 5 days during 82 days' observation period. Just before the Abiki events, the atmospheric disturbances were found to travel eastward or north-eastward at a speed around 140km/h, which was resonantly coupled with the ocean wave in the offshore site. The observed Abiki heights can roughly be explained by the forced resonance in the offshore and the amplification after entering the bay.
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  • Hiroyuki KATAYAMA, Hiroyuki KATO, Yuichi TANJI, Akiyoshi NAKAYAMA, Tos ...
    2011 Volume 67 Issue 2 Pages I_181-I_185
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    The previous highest Abiki occurred in the range centering on Kagoshima Prefecture in February, 2009. The damage by the Abiki, such as a fishing boat overthrow and flood under a floor, generated at Ojima fishing port in Urauchi bay of Kamikoshiki island, Kagoshima. Authors (2010) investigated about the propagation characteristic of Abiki by numerical simulation using non-linear long wave theory. However, the problem was in the accuracy of the submarine topography originated in calculation mesh size, and investigation about the magnification of Abiki inside the Urauchi-bay was inadequate. In this research, the numerical simulation using three-step nesting bottom topography data was carried out, and the validity of the calculation technique was checked as compared with local observation data. Furthermore, the effect of Abiki countermearsures was analyzed.
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  • Hiroaki ISHIZASHI, Shinji SATO, Yoshimitsu TAJIMA, Tomohiro TAKAGAWA
    2011 Volume 67 Issue 2 Pages I_186-I_190
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Laboratory experiments were conducted to investigate the effect of edge wave on wave overtopping in a nearshore zone with abruptly changing bathymetry. Experiments demonstrated that the presence of standing edge wave would produce local increase in wave run-up. Detailed measurements of water surface elevations and velocities were conducted in a large wave basin in which nearshore bathymetry in front of Ashizaki district, one of districts damaged by the giant wave in 2008, was reproduced with a scale of 1/100. It was found in the experiments that standing edge wave with periods in a range 10s to 13s was developed in the narrow channel between the seawall and a group of detached breakwaters. The development of the standing edge wave was found to increase the wave overtopping rate by about 30%.
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  • Takayuki MATSUBARA, Masahiro SEKIJIMA, Noriaki KANDA, Fumihiko IMAMURA
    2011 Volume 67 Issue 2 Pages I_191-I_195
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    The mechanism of tsunami generation due to sector collapse modeled with solid and semi-oval objects, beads, and sands was studies by hydraulic experiments. The profiles of mass flow due to the sector collapse flow with several conditions are designed. The thickness, velocity, and apparent density at the point where the mass plunged into the water surface were measured by laser displacement meters on the slope. Wave height and period of tsunami were measured by four wave gages. As a result, we found the two types of the tsunami generation influenced by the apparent density in case of beads and sands. When the density is high, the objects go deep along the slope. When the density is low, the objects stop near plunging point, and generate tsunami like a wave making plate.
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  • Hitoshi GOTOH, Hiroyuki IKARI, Takayuki MATSUBARA, Takashi ITO
    2011 Volume 67 Issue 2 Pages I_196-I_200
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Tsunami due to sector collapse with volcanic activity does not occur frequently, however, has caused enormous damages. Because density of soil collapse distributes widely depending on its cause of generation, a process of impact into water which drives a tsunami is not simple. In this paper, experiments, in which particles with two kinds of density fall down on a slope and impact with a still water surface, are carried out, and two defferent processes of tsunami generation are confirmed. On the other hand, a solid-liquid two-phase flow model based on an accurate particle method are developed to execute numerical simulations for reproduction of these phenomena.
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  • Masafumi MATSUYAMA, Kazumasa HASHI, Tsutomu SAKAKIYAMA, Yoshihito TANA ...
    2011 Volume 67 Issue 2 Pages I_201-I_205
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Effect of barrier concerning tsunami flow over hill was simulated by using 2D numerical system CADMAS-SURF/2D. Numerical area included sea shallower than 10m depth, 10m high hill on land, 12m high tsunami barrier, and hinterland. Input condition was 6.5m height wave with half of period 600s. It was found that the tsunami barrier reduced duration of high velocity more than 5m/s to about 10s around the top of hill. However, without the barrier, the high velocity continued for more than 40s there. The maximum tsunami force on the barrier occurred at tsunami flow overflowing. The profile of pressure distribution is similar to a right triangle like hydrostatic pressure.
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  • Atsushi FURUTA, Kazunori ITO, Yukinobu ODA
    2011 Volume 67 Issue 2 Pages I_206-I_210
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    This paper studies about flood disasters via drainage channels caused by tsunami, which may occur even if high seawalls protect coastal land area from tsunami. The flood could make loss of evacuation routes and be an obstacle to the safety measures, thus considering the countermeasures is important for industrial facilities from the points of view of business continuity. It was found that two phases numerical analysis consisting of water and air is applicable to simulate the flood disasters via drainage channels caused by tsunami comparing with that hydraulic physical model tests.
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  • Hideomi GOKON, Shunichi KOSHIMURA, Kentaro IMAI
    2011 Volume 67 Issue 2 Pages I_211-I_215
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    The tsunami that accompanied with a magnitude-8 earthquake attacked the Samoan and northern Tongan islands on 29 September 2009. Since the event occured, two scenarios ascertain the mechanism of the earthquake that a series of normal and thrust faults caused the large earthquake and tsunami. However, it is still uncertain which one was the first rupture. In this paper, the authors focus on the tsunami waveforms of Deep-ocean Assessment and Reporting of Tsunamis(DART), and proposed the tsunami source scenario that is the most consistent with the observed tsunami. The scenario is that, the rise time of the thrust fault rupture is 480 seconds, which starts from 3 minutes before the normal fault rupture, and the rise time of the normal fault rupture is 60 seconds.
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  • Yutaka HAYASHI, Shunichi KOSHIMURA, Fumihiko IMAMURA
    2011 Volume 67 Issue 2 Pages I_216-I_220
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    In order to evaluate and forecast the decay process of far-field tsunamis, we have constructed a time-dependent decay model of MRMS tsunami amplitudes. This model is based on the decay features of near- and far-field earthquake tsunamis around Japan and on the assumption that the propagation of tsunami energy is expressed by convolution operations with three effects (source, path, and site effects) and some parameters. Computed examples show that with suitable parameters, this model has the potential to duplicate various real MRMS tsunami waveforms. Through this study, we successfully mitigated issues related to the timely cancellation of tsunami warnings; the problem we are still facing on the issue is to determine parameters and functions of three effects for the proposed decay model of MRMS tsunami amplitudes.
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  • Makoto NEMOTO, Hideharu SUGINO, Shiro TAKASE, Yoko IWABUCHI, Akio YAMA ...
    2011 Volume 67 Issue 2 Pages I_221-I_225
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    A waveray method has been used in past studies in order to evaluate tsunami hazards. Though this method is useful for it's convenience, it is difficult to predict quantitative tsunami heights because of the problems of calculating method, such as divergences of refraction coefficient in the cross-section areas of waverays. In this study, to be able to use waveray method for tsunami height prediction, (1) we modeled the shape of wave sources and investigated the relationship between fault parameters, (2) we improved the method of calculating the refraction coefficient with waveray method.
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  • Takashi IZUMIYA, Yuichi KOBAYASHI, Mikako. SAKAI
    2011 Volume 67 Issue 2 Pages I_226-I_230
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    The elevation of the free surface from the undisturbed level by tsunami generation is expressed as the convolution of the Green's function and the vertical velocity of the bottom deformation integrated over the source area. The cross correlation of the waveforms at two observation stations is shown to yield the Green's function between these positions. The trans-ocean tsunami waveforms are computed with the Green's function retrieved by cross correlating tsunami records. The waveforms at the stations near the Japan coast which are estimated with the Green's function between the two observation stations are compared with the observed records. The agreement between the observed and computed waveforms shows fairly good.
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  • Tomoyuki TAKAHASHI, Takahiro KUROKAWA, Masataka FUJITA, Hiroaki SHIMAD ...
    2011 Volume 67 Issue 2 Pages I_231-I_235
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    Tsunamis generate a large amount of bed load and suspended load in shallow water region because of large tractive force and turbulence. The sediment transport causes serious damages in coastal region. Many various basic formulae have been proposed for sediment transport. In this study, a sand grain size is assumed to be dominant parameter for the difference among the formulae and a hydraulic experiment is conducted. The experiment uses a closed rectangular channel with a wavemaker. In the channel, there is movable bed section and sand of 0.166, 0.267 or 0.394 mm in median diameter is spread there. At the downstream end, two types of trap for sand are installed and sediment transport rate is measured. Finally, formulae for bed load and rising load are proposed. Both coefficients of the formulae vary with sand grain size.
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  • Shin-ichi YANAGISHIMA, Satoshi NAKAMURA, Masayuki BANNO, Masahito YAMA ...
    2011 Volume 67 Issue 2 Pages I_236-I_240
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    The tsunami traces and the topography survey in the Hazaki coast in southern part of Ibaraki Prefecture facing the Pacific Ocean were carried out after the tsunami caused by the 2011 off the Pacific coast of Tohoku earthquake. The tsunami run-up characteristic and topography change before and after tsunami raid on the sandy open coast were examined. In the survey area, the highest tsunami run-up reaches D.L.+10.10 meters, where the beach slopes of sand dune front and surfzone are both steep. The topography change by the tsunami is small because of two factors that the tsunami run-ups do not cross the top of dune and that the beach is not saturated with seawater by only ten times tsunami run-ups.
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  • Ryozo SHIOMI, Tsuyoshi HARAGUCHI, Tomoyuki TAKAHASHI, Akira HAYASHIDA, ...
    2011 Volume 67 Issue 2 Pages I_241-I_245
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    In 2008 and 2009, we made seismic survey in Kesennuma Bay, Miyagi Prefecture, where sedimentation of the tsunami deposits associated with the 1960 Chilean Earthquake caused significant modification of the bay bottom topography. Visual and X-ray CT analysis of lithology, measurements of magnetic susceptibility and its anisotropy, and diatom fossil analysis of piston cores recovered from 3 sites revealed that relatively thick tsunami deposits occur near the narrow segment of the Bay. Abundant occurrence of freshwater diatom suggests a possibility that the tsunami waves transported river sediments into the Kesennuma Bay.
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  • Kousuke KAYANE, Min ROH, Hitoshi TANAKA, Xuan Tinh NGUYEN
    2011 Volume 67 Issue 2 Pages I_246-I_250
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    By analyzing the detailed water measurement data sets outside/inside of rivers in Tohoku District which were caused by the 2010 Chilean Tsunami, the influences of this tsunami event are estimated. Based on the topographical river mouth, the relationship between river characteristics and tsunami wave height reduction can be derived empirically. This study indicates that the tsunami propagation distance into the river upstream is not only depended on the river mouth geographical features such as river mouth width and depth but also on the tidal level. The larger river entrance, the easier tsunami intrudes. In some narrow and shallow river mouths, the tsunami can only pass through the entrance during the high tide. The empirical relationship between tsunami height and river width has a correlation to the Green's Law
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