Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering)
Online ISSN : 1883-8944
Print ISSN : 1884-2399
ISSN-L : 1883-8944
Volume 73 , Issue 2
Showing 1-50 articles out of 281 articles from the selected issue
Paper
  • Akihiro USUI, Shinichi AOKI, Koji KAWASAKI, Tomohiro SUZUKI
    2017 Volume 73 Issue 2 Pages I_1-I_6
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     After the 2011 off the Pacific coast of Tohoku Earthquake, the necessity of tenacious coastal/harbor structure has been suggested. However, it's necessary to examine experimentally its performance to make it in practical use. In this study, we proposed a theoretical modeal to generate an arbitrary waveform by self-propelled wavemaker device. When the wave generating tank is not long enough, multiple reflection occurs between the wall and the wavemaker. The theoretical model considering multiple reflection between the wall and wavemaker was developed and compared with the target waveform. In this study, arbitrary water level rise by a self-propelled wavemaker was examined using CADMAS-SURF/3D which is combined with the immersed boundary method. As a result, the generated wave showed good aggrement with the target waveform by considering waveform deformation, average water depth change, change in wavemaker position and interaction between reflected wave from the wall and wavemaker.
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  • Kenta SATO, Shunichi KOSHIMURA
    2017 Volume 73 Issue 2 Pages I_7-I_12
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     A non-hydrostatic free surface numerical model is required to perform a tsunami inundation simulation. It is, however, difficult to carry out large-scale tsunami simulation because of the iterative calculation of the Poisson equation in the invompressible flow model.
     In recent years, the Lattice Boltzmann Method (LBM) has attracted attention as a novel computational fluid dynamics to overcome the incompressible flow model problems. In this study, we developed a two-dimensional LBM for free surface simulation method based on Piecewise Linear Interface Reconstruction - Volume of Fluid (PLIC-VOF) method. The classical dam-break and reconstruction test is used to verify our approach enables to high accuracy free surface simulation compare to conventional LBM-VOF method.
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  • Tomohiro MORI, Takenori SHIMOZONO
    2017 Volume 73 Issue 2 Pages I_13-I_18
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     The non-hydrostatic pressure needs to be taken into account in depth-integrated modeling of levee overflows especially with a large overflow depth. A possible approach may be to employ the Boussinesq-type equations as model equations. However, conventional Boussinesq-type models tend to be unstable around the levee crest by oscilations introduced by the high-order terms when applied to overflow simulations. In order to enhance the model stability, we enhance the Boussinesq-type equations by adding a modification term with a free parameter. We investigate how the modification term affects model stability and accuracy and specify a possible range of the modification parameter through comparions of model results with experimental data
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  • Hiroyuki IKARI, Hitoshi GOTOH, Naoki TSURUTA, Yuji KOBAYASHI
    2017 Volume 73 Issue 2 Pages I_19-I_24
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     In a wave or flow simulation including a porous media, a drag force is given to a fluid inside a porous media to simulate flow resistance due to a porous body. However, in a case that a water surface exists inside a porous media such as a wave absorbing block area, a volume conservation cannot be satisfied without taking a porosity of a porous media into consideration. An apparent volume change of a fluid particle on the basis of the porosity is one way to solve this problem in a particle method. In this study, a wave analysis on a wave absorbing seawall is carried out using an improved multi-resolution MPS method. In this simulation, it is shown that an apparent volume change works very well to estimate a wave overtopping discharge more accurately and the calculated result for the case with volume change is in much better agreement with an experimental result than the one without volume change. Besides, it is found that the introduction of a turbulence model can be effective for a more accurate estimation of a wave overtopping discharge.
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  • Hitoshi GOTOH, Kojiro SUZUKI, Hiroyuki IKARI, Taro ARIKAWA, Abbas KHAY ...
    2017 Volume 73 Issue 2 Pages I_25-I_30
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     In recent years, a numerical design for the coastal engineering problem, namely, the so-called numerical wave flume is widely used and expected to expand its potential more as an ancillary or substitute tool for hydraulic experiments. However, for the time being, the numerical wave flume is limited in versatility for the actual engineering problems as the request level of coastal designs is increasing. In this study, a numerical wave flume based on the accurate particle method with a DEM coupling model, namely, parisphere is newly developed for accurate and stable simulations of the violent free-surface multiphase flows. First, a simple benchmark is performed by targeting a sedimentation of heavier particles in the water to examine the numerical accuracy of the model. The parisphere shows a good reproducibility in the motions of particles with an improvement of the energy conservation. Second, a simulation of a complex damaging process of a breakwater, which includes solid-liquid multiphase flows, is implemented. By comparing with the experimental results, it is found that parisphere can reproduces the complex phenomenon with satisfying the prudent requirements, that is, expression of solid-solid/solid-liquid interactions, porosity of the mound, drifting of rigid bodies and accurate pressure distributions.
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  • Keisuke NAKAYAMA, Takahiro SATO, Leon BOEGMAN, Kenji SHIMIZU
    2017 Volume 73 Issue 2 Pages I_31-I_36
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     In marginal seas and on continental shelves, interaction of tides and topography excites internal tides, which can degenerate into internal solitary waves (ISWs). Since the breaker type of ISWs is important for sediment resuspension and long-term transport of nutrients, plankton, and hypoxic water, it is needed to categorize the breaker types accurately. Previous studies on ISW breaking over a uniform slope in two-layer stratified fluids demonstrated four breaker types: fission, collapsing, plunging, and surging. The critical depth and density difference between the layers may be important factors, but they have not been considered in the categorization. Using the results of two-dimensional numerical simulations, this study aims to propose new indices for the categorization of ISW breaking, which take the critical depth and the density difference into account. The proposed three indices successfully categorize the four breaker types.
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  • Naoto HIGUCHI, Katsuya HIRAYAMA
    2017 Volume 73 Issue 2 Pages I_37-I_42
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     In resent busy ports and harbors, their tranquility must be affected with not only storm waves propageted from outside but also harbor waves generated by inside ship navigation. In this study, a new ship wave generation method is developed and installed to a Boussinesq-type wave transformation model, considering expandability of setting of ship navigation channels and applicability for variable ship shape. For approximation of ship shape, not only the parabolic function but also the Lewis-Form are used. The Lewis model can reproduce results of past model experiments in over same accuracy on comparison with the parabolic model. However, improvement of dependency in spatial resolution for generating ship wave heights may be required in near future.
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  • Tomohiro YASUDA, Hiroshige UEYAMA, Hajime MASE
    2017 Volume 73 Issue 2 Pages I_43-I_48
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     This study proposes the empirical formula of wave height estimation over reefs in which the coefficients in the formula are determined using simulation results by the Boussinesq wave model that can simulate wave transformation in shallow sea. Seabed slope and gradient are not considered in the past studies, but they are considered by coefficients (α, B and A) in this study. The applicability of proposed formula was confirmed through comparison with the observations and simulated values by the KP equation model. The proposed empirical formula is able to employ to estimate the design wave height on reefs.
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  • Katsuya HIRAYAMA, Yasuhiro AIDA, Koji KAWAGUCHI, Hitoshi TAMURA, Hidek ...
    2017 Volume 73 Issue 2 Pages I_49-I_54
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     The storm waves missed in offshore wave observation are often estimated in wave hindcasting for extreme wave analysis. In this paper, the estimation errors on WAM and WWIII at NOWPHAS stations along Japan Sea coast are verified and especially they in Toyama Bay are revised through calculations of nonlinear wave transformation by NOWT-PARI. It is comfirmed that the hindcasting storm waves diffracted at the top of Noto peninsula should be compensated by observation data, and in addition, considering effect of wave nonlinearity is important at NOWPHAS Toyama station.
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  • Keisuke NAKAYAMA, Kenji SHIMIZU
    2017 Volume 73 Issue 2 Pages I_55-I_60
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     In stratified lakes and oceans, organic matter and nutrients tend to remain within the pycnocline for long time due to suppressed diapycnal mixing by the strong density gradient. Isopycnal mass transport due to Stokes velocity within the pycnocline can be important for long-term processes in the ecology and biogeochemistry. Previous studies have investigated mass transport velocity under sinusoidal internal waves, which exist stably under vertically symmetric stratification. However, studies on mass transport velocity under internal solitary waves, which exist stably under vertically asymmetric stratification, are scarce. This study investigates mass transport velocity due to both sinusoidal and solitary internal waves under three-layer stratification using a fully dispersive, fully nonlinear internal wave model. The model is validated using an analytical solution for mass transport velocity due to sinusoidal waves under vertically symmetric stratification. Mass transport velocity in the middle layer under internal solitary waves tends to be more positive than that under sinusoidal internal waves, and decreases as the top layer thickness increases.
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  • Yuki IMAI, Nobuhito MORI, Junichi NINOMIYA, Hajime MASE
    2017 Volume 73 Issue 2 Pages I_61-I_66
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     It is important to accurately estimate the wave-induced current, Stokes drift, in analysis of the ocean circulation. This study proposes a novel expression of Stokes drift on random waves for open ocean. Specifically, the Stokes drift could be calculated from wave directional spectra and that was inserted to a numerical model for performing a simulation of open ocean circulation. The Stokes drift velocity profile calculated by the numerical model could express high-frequency contribution that the Stokes drift could not penetrate deeper. The developed numerical model was validated through theoretical and experimental simulation. Finally we tried to perform simulation with the model on real bathymetry and analyze ocean surface current.
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  • Shoki HOMMA, Ayumi SARUWATARI, Makoto MIYATAKE
    2017 Volume 73 Issue 2 Pages I_67-I_72
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     A three-dimensional numerical simulation was conducted to characterize the density structure in the Tsugaru Strait during a stratified season. Relatively strong internal waves formed behind the sea knolls at the two necks of the strait was found to propagate and reflected in the topography, resulting in development of complex density oscillation inside and outside of the strait. Shear at the pycnocline was intensified by formation of a wind-driven current during a storm event in summer and maintained for a few days after the storm. The density stratification was confirmed to be one of the factors to cause seasonal variation of the flow in the strait.
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  • Yasunori WATANABE, Kazunao SUGIMURA
    2017 Volume 73 Issue 2 Pages I_73-I_78
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     This paper presents mechanical features of transitional air-water momentum and energy transfers in initial growing wind waves on the basis of the fluid flow statistics observed in wind-wave tunnel experiments. In the initial waves with short fetch, superpositions of capillary waves on the crest of gravity waves generate significant vorticity and transport it downward, resulting in a thick momentum boundary layer containing organized vortices. As the capillaries attenuate in growing wind-driven current via wave-current interaction, with increase of fetch, vorticity generation also attenuate and thus the thickness of the boundary layer decrease.
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  • Hironori HIGASHI, Yasuo FURUSHIMA, Naoki FURUICHI, Tatsuo FUKUHARA
    2017 Volume 73 Issue 2 Pages I_79-I_84
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     We carried out in-situ measurement of deep-sea turbulence in Sagami Bay and hydrodynamic simulation using three vertical mixing schemes (standard k-ε model, Mellor (2001) model, and Furuichi et al. (2012) model) to investigate their reproducibility performances. One of four measurements indicated that dissipation rate of turbulent kinetic energy reached 10-6m2s-3 near deep seabed at about 1000 m depth, and that thickness of bottom mixing layer with 10-7m2s-3 was approximately 150 m. All simulated results underestimated the mixing layer thickness. Among them, Furuichi et al. (2012) model was able to simulate relative large thickness without depending on bottom boundary conditions. It is suggested that Furuichi et al. (2012) model might be expected to be improved by modifying parameterization of turbulence length scale.
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  • Naoki FURUICHI, Hironori HIGASHI, Koichi SUGIMATSU, Hideaki MAKI, Hiro ...
    2017 Volume 73 Issue 2 Pages I_85-I_90
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     Field surveys of the particulate matter concentration for each particle size were carried out. We found that (1) the particulate matter concentration for each particle size under stratied condition can be significantly decreased above the the BBL compared to within the BBL, and (2) the concentration can be almost uniformely distributed in uniform density fields. The mean turbulence dissipation rates measured by microstructure profiler for case (1) were larger by a factor of 2-3 than the mean turbulence when particulate matter concentraton did not significantly decrease above the the BBL. Our results were consistent with previous numerical study on the effects of turbulent process around the bottom boundary layers (BBLs) on suspended particulate matter dynamics, suggesting that the BBL thickness and the turbulence intensity variation are among the important parameters for determing the distribution of particulate matter concentration.
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  • Yasunori WATANABE, Atsuki SUZUKI
    2017 Volume 73 Issue 2 Pages I_91-I_96
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     A novel experiment of free-surface deformation in a rotating circular cylinder is proposed in this study, which physically models an air-tube fragment observed in a plunging wave breaking. It is found during the experiment that the fragment is induced by unstable anti-symmetric rotating flows around air-tube affected by centrifugal force, surface tension, buoyancy and drag force. Overall features of the fragment wave-number and critical rotation frequency can be described in terms of Froude and Weber numbers.
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  • Hirokazu SUMI, Takashi YAMAZAKI, Naoya MIYAUCHI, Tomoaki NAKAMURA, Tak ...
    2017 Volume 73 Issue 2 Pages I_97-I_102
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     In this study, the form and conditions of obliquely descending eddy (ODE) formation were examined. Sediment transport due to ODEs was also studied. The results of this study newly confirmed the formation of four ODEs, whereas the previous studies have shown the formation of three ODEs in the on-offshore direction. Conditions of ODE formation were found to be controlled by Breaker type index (Bt) and Reynolds number (Re). Sediment was transported by ODEs, leaving tongue-shaped erosion. Tongue-shaped erosion matched an ODE's contact point with the sea bottom topography. Therefore, sediment erosion is thought to occur as a result of an ODE reaching the sea bottom topography.
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  • Yoshinao MATSUBA, Takenori SHIMOZONO, Yoshimitsu TAJIMA
    2017 Volume 73 Issue 2 Pages I_103-I_108
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     We counducted a UAV-based field survey focusing on nonlinear wave-wave interactions of wind waves and swells during propagation and swash processes. Shoreline evolution was detected from UAV images and was analysed together with offshore wave data. We found through spectral and bispectral analyses that nonlinear interactions of the two wave components occurred through wave breaking over an offshore bar, generating longer waves of a difference frequency. The resulting long waves further interacted with swells in shallower water to characterize the spectral structure of shoreline evolution.
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  • Takashi FUJIKI, Koji KAWAGUCHI, Satosi SAKURABA, Noriaki HASHIMOTO
    2017 Volume 73 Issue 2 Pages I_109-I_114
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     Although swell can be the dominant source for the coastal process, there is not enough research on directional wave spectrum of swell. We analyzed wave data recorded on the Pacific coast in Tohoku and Kanto region for a year to investigate such swell. We selected wave data under the moderate wave and meteorological condition for pure swell, and identified swell and wind sea with the criteria of inverse wave age. We confirmed the validity of our identification swell and wind sea with 3/2 power-low on characteristic wave height and period for wind sea. We showed the peculiar properties for swell directional spectrum which concentrated and isolated energy partition and shape of directional spectrum modified for swell. We concluded that the parameter for local wave fields such as wave steepness and inverse wave age is insufficient for populating the swell directional spectrum which is affected mainly by the remote source.
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  • Nobuhito MORI, Tomoya SHIMURA, Mark HEMER, Xiaolan WANG
    2017 Volume 73 Issue 2 Pages I_115-I_120
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     Projections of wave climate change have been conducted targeting climate change impact on coastal zone since the Fifth Assessment Report (AR5) of IPCC in 2012. Although the many projections are available for mean wave climate, the projections for extreme waves are not well conducted since IPCC AR5. This study conducts multi-GCM and multi-wave-model ensemble experiments changing radiative forcing, GCMs and wave models. The uncertainty of projection is discussed and characteristics of wave climate change in different ocean basins are examined in detail. Future change of extreme wave heights shows similar spatial distribution to mean wave heights but tropical cyclone plays important role at particular areas.
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  • Toshikazu KITANO, Wataru KIOKA, Kenzo KUMAGAI
    2017 Volume 73 Issue 2 Pages I_121-I_126
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     Two-level design for the protection of coastal zone is a well-worn but worthwhile approach in civil engineering, and it is usually characterized as high/low occurrences of those natural hazards, though it does not convince us of the real scales. Once in a thousnad years against the L2 hazards will be beyond our individual understanding in comparison with the frequent occurrence of the L1 hazards. We propose here a new interpretation of those levels: L2 as the prediction of the coming maximum in the future; L1 as the estimation of the return level, whose impotant key is to employ a single common period for both levels, with an example demonstarated.
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  • Yoshio HATADA, Kazuya SEKIYA
    2017 Volume 73 Issue 2 Pages I_127-I_132
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     Characteristics of spatial changes of annual maximum wave heights and annual maximum storm surge deviations in the inland sea and inner bay areas are discussed based on 45 years of hindcasts data on 1km regularly spaced grids at three locations, the Western Seto Inland Sea, Ise Bay and Tokyo Bay. Correlation coefficient of the annual maximum values between a focus point and the other compared points and Taylor diagram are used to illustrate the spatial changes around a point. Ratio of standard deviation σfocus pt.comp. pt. is used instead of σcalculationobservation in the diagram. Distribution of numbers at each point on all grids which have a high correlation (ρ>0.9) to the other points is estimated in order to facilitate understanding of spatial changes by locality of the annual maximum values. Main results are as follows: 1) Annual wave heights at the focus point show a narrow high correlation area with a long axis of the small sea area surrounding the point. 2) Annual storm surge deviations at the focus point show a larger and more rounded high correlation area than those of wave heights. 3) A contour map of σfocus pt.comp. pt. is useful to define real position of the plotted points in Taylor diagram. 4) Numbers at each point with high correlations of storm surge deviations are 3 to 4 times larger than those of wave heights, and high number areas appear in different locations than waves.
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  • Shunichiro NAKAMURA, Yoshimitsu TAJIMA, Masahiro KAMBARA
    2017 Volume 73 Issue 2 Pages I_133-I_138
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     Tropical islands located in Southern Pacific Ocean are exposed to severe coastal hazard due to stormy waves but insufficient record or experience of the past disaster events make it difficult to statistically evaluate various hazard levels at each region. This study newly develops a stochastic typhoon model focusing on its application to cyclones migrating around these tropical islands located around the lower latitude and applies the developed model for statistical evaluation of offshore wave heights with different return periods.
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  • Hajime MASE, Tracey H. A. TOM, Ai IKEMOTO, Koji KAWASAKI
    2017 Volume 73 Issue 2 Pages I_139-I_144
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     Wave models of WAVEWATCH III and WAM are developed and extended from ocean to nearshore sea; on the other hand, SWAN is developed for nearshore sea to ocean region. From the developed process, WAVEWATCH and WAM had better to be employed for the ocean wave prediction and SWAN for the nearshore region. In actual fact, IOOS (Integrated Ocean Observing System) is operated to forecast waves using WAVEWATCH for ocean and SWAN for nearshore sea. There are still few reaserch to examine the validity or accuracy of wave prediction when using the WAVEWATCH III and SWAN; that is, which wave model is better for the wave prediction. This study carried out the inter-comparioson of the accuracy of wave predictions using the WAVEWATCH III and SWAN against the observed wave data by NOWPHAS.
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  • Takuto HAGA, Katsumi SEKI, Taro ARIKAWA
    2017 Volume 73 Issue 2 Pages I_145-I_150
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     GSM (Global Spectral Model). A climate distribution data set by JMA (Japan Meteorological Agency) is applied to the wave and storm surge estimation for explosive cyclones and typhoons. Wind and atmospheric pressure conditions for the wave and storm surge estimation are obtained using two methods involving the GSM data set. One way is that the GSM data set is linearly interpolated while another is an empirical typhoon model based on the data set. The main results are summarized as follows; when linear interpolation is used in estimations of meteorological fields, it shows high correlation with long-term waves due to bomb low pressure. On the other hand, when using a typhoon model to estimate the weather field, it was confirmed that this method yields high accuracy to the peak value of local typhoon-generated waves.
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  • Muneo TSUDA, Yoshiharu MATSUMI, Sooyoul KIM, Nobuhiko MATSUDA, Mikiko ...
    2017 Volume 73 Issue 2 Pages I_151-I_156
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     The present study describes an artificial neural network(ANN)-based real time wave forecast system in order to manage maritime construction works. This system forecasts wave heights, periods and directions up to the lead time of 168 h (7 days) at a construction site using input parameters of wind, sea level pressure and wave. These input data are obtained automatically every hour from websites of public wave data, meteorological stations and wave construction sites. Furthermore, the motion of working vessel and suspended load is predicted using the forecasted wave information. The developed ANN-based real time wave forecast system is applied to a construction site and the forecasted data on the website can be accessed by personal computers and mobile phones.
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  • Bahareh KAMRANZAD, Nobuhito MORI, Tomoya SHIMURA
    2017 Volume 73 Issue 2 Pages I_157-I_162
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     In order to estimate the wave climate in a specific region for different purposes such as climate change impact assessment, wave energy assessment, etc., it is important to consider the long-term variations in the range of 10-100 years. Since a specified amount of error in wind modeling (as forcing for numerical wave model) results in a greater amount of error in the wave modeling, two globally available wave analysis data, i.e., ERA-Interim and JRA-55 were considered to discuss about their performance in the study area, where the lack of sufficient wave data exists. The results showed that JRA-55 wave field yields more accurate results than ERA-Interim waves. The regional wave downscaling was carried out using SWAN and two approaches were considered; the local model with locally wind generated wave conditions in lateral boundaries in which, the southern boundary of the computational domain was considered around the Equator, and nested model with a smaller domain, in which, the boundary conditions are given by global model of WW3. The regional downscaling results show that the local model underestimates the wave heights comparing to the measurements and the tuning the physical parameters is required. In order to evaluate the results in the spatial domain, the monthly mean significant wave heights were compared to the satellite monthly mean data by the altimeter. The results showed that the monthly variations by the nested model give reasonable agreement with the satellite data. It can be concluded that the nested model from WW3 to SWAN represents accurate results both in the domain (spatial distribution), and in comparison with high temporal resolution wave data.
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  • Masataka YAMAGUCHI, Hirokazu NONAKA, Kunimitsu INOUCHI, Mikio HINO, Yo ...
    2017 Volume 73 Issue 2 Pages I_163-I_168
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     A conventional linear analysis(LA) and circular analysis(CA) are conducted for hindcasts-based and measurements-based one or two hourly wave direction data samples over 12 years at 43 onshore and off-shore stations around Japan. The main findings are as follows: 1) Both LA 1 auxiliarily using the CA-based mean value and LA 2 directly using the mean approximate CA-based statistics such as not only mean value but also standard deviation, skewness and kurtosis for either hindcasts or measurements, in cases where closer agreement is obtained for lower order statistics. 2) The above-mentioned results also hold for the statistics on hindcast-measurement difference-based error. 3) The error for mean value of wave direction is less than ±10 degrees at each of almost all stations, which suggests a higher accuracy of the hindcasts.
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  • Renshi KITTE, Satoshi GORYO, Takeshi IZAKI, Tetsuya TANEDA, Akio NAGAY ...
    2017 Volume 73 Issue 2 Pages I_169-I_174
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     This study investigates characteristic changes of edge waves by a topographic obstacle like a cape experimentally and numerically. The experiments were conducted in a small wave tank with setting a step-type shelf to measure two dimensional water surface fluctuations. The dispersion relationships and on-offshore wave heights of the edge wave components are found to be consistent with those described by the edge wave theory. In the numerical analysis where a concentric circle topography for the shoreline and shelf edge was set, characteristics of edge wave propagation and on-offshore distributions of edge wave height were analyzed. These results are found to reproduce the characteristics expressed by the edge wave theory. The characteristic changes of edge wave celerity and plane wave height distribution by a topographic obstacle are discussed based on the experimental and numerical results by changing experimental conditions and dimension of a model obstacle systematically.
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  • Tomonori SAITA, Masahiro HAYATA, Toru YAMASHIRO
    2017 Volume 73 Issue 2 Pages I_175-I_180
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     Secondary undulations caused by meteorological disturbances over the East China Sea are frequently observed in sea areas around the west coast of Kyushu Island. In this study, numerical analyses were carried out to figure out a relationship between propagation paths of atmospheric pressure wave over the East China Sea and characteristics of sea level fluctuation off the west coast of Kyushu Island. As the result, it is clarified that a behavior of water surface waves caused by atmospheric pressure disturbances strongly depends on incident position and angle of a pressure wave to the Okinawa Trough. A propagation path of the pressure wave also exerts a significant influence on timing that peaks of sea level fluctuation arise in the sea area off Meshima Island, Uji Island, Nagasaki, Kami-Koshiki and Makurazaki. In particular it is possible that a peak of sea level fluctuation in nearshore area off Kyushu Island comes around 4 hours before that around Meshima island located on the west side of the Okinawa Trough.
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  • Sooyoul KIM, Kenzou KUMAGAI, Hajime MASE
    2017 Volume 73 Issue 2 Pages I_181-I_186
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     In the present study, the effects of the drag stresss at sea surface (Cd) and bottom (fc) induced by surge and wave interaction on the inundation depth of Typhoon Haiyan were investigated. The error between observations and predictions is estimated up to 90 % when using Cd and fc in comparison to the only Cd and the empirical relation-based drags of sea surface and bottom. In addition, the wave and current interaction-induced sea surface drag leveled off at 25 m/s wind speed is appropriciate when using using Cd and fc. In this condition, it is found that the average Manning number converted from fc corresponds to 0.02.
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  • Toshiaki NARAZAKI, Seiji FUJIMARU, Naoki SHIMAZOE, Noriaki HASHIMOTO, ...
    2017 Volume 73 Issue 2 Pages I_187-I_192
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     Genkai-nada Sea coast is the north coast of Fukuoka Prefecture including Fukuoka city which is the largest city in Kyushu. Although typhoons sometimes strike the northern part of Kyushu, the coast has never experienced severe storm surge disasters over a long period of time. Thus very few protective structures against the storm surges have been installed along the coast. In 2015 the Flood Protection Law has been revised, and consequently a guide book for the hazard map of storm surge inundation was issued by the relevant ministries and agencies. In this study, a lot of numerical simulations were performed to examine the maximum possible storm surge inundation along the Genkai-nada Sea coast on the basis of the guide book. From the simulation results, this paper proposes a rational manner to set the worst typhoon track, and discusses the influence of sea surface drag coefficient under the strong wind.
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  • Kenzo KUMAGAI, Sooyoul KIM, Daiki TSUJIO, Hajime MASE, Takahito Tsuji
    2017 Volume 73 Issue 2 Pages I_193-I_198
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     Because storm surges and waves on the east coast of Hokkaido generated due to the Explosive Cyclone (EC) 2014, coastal damage occurred on the Nemuro coast. When the low pressure system comes to the east of Hokkaido, it is possible that abnormal surges and waves occur due to the eastern high wind speed prior to the passage of low pressure systems. In the present study, the EC 2014 surge and wave simulations were conducted using a coupled model of surge and wave and validated with observations. The simulation results show that the simulated surge and wave levels are well matched to the observed surge and wave ones. In addition, it is found that leveling off at 25 and 20 m/s wind speeds is appropriate for the surge and wave, respectively.
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  • Keiji NAKAI, Shoji SASA, Shoji IWASAKI, Nobuyuki TAKAHASHI, Yoshihiro ...
    2017 Volume 73 Issue 2 Pages I_199-I_204
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     It is known well that the main causes of storm surges in inner bay areas are atmospheric pressure drop and strong wind towards the inner parts of bays. But, other causes may be important in sea areas other than inner bay areas.
     A survey has been carried out on the characteristics of storm surges observed at seven tidal stations in the Hokuriku District in 2016. When remarkable storm surges are generated, southwestern wind which is along the shore often blows. Isozaki(1968) showed the Ekman transport by southwestern wind generated storm surges at stations along the Hokuriku coasts in the period of Typhoon 14 in 1959. This example is not a special one and similar phenomena are often observed in this area. The southernwestern wind is very important and essential for generating storm surges in the coastal area of the Hokuriku District. When the northeastern wind blows, the sea levels may decrease by the Ekman transport to the contrary.
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  • Sho MINAMI, Keita KUDOU, Kazuki YAGISAWA, Koji HASHIMOTO, Yasunori WAT ...
    2017 Volume 73 Issue 2 Pages I_205-I_210
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     Typhoon Lionlock (2016) followed a complicated route that was different from the conventional typhoon. Lionlock moved northwest of the Tohoku region, and proceeded to the Sea of Japan . the typhoon caused large fishery damage due to windward flow and strong winds in Hokkaido's Uchura Bay.it is very important to calcurate tide deviation occured by typhoon that followed a characteristic course. Therefore, in this study, numerical experiments using a typhoon model and nonlinear longwave model were performed. Using the Lionlock typhoon as a model, we calculated the storm surge of eight possible tracks, clarified the occurrence characteristics of the tide deviation in Uchiura Bay and estimated the damages along each track. Further, we made calculations for creating a tidal flooded immersion area map (Ministry of Land, Infrastructure and Transport), and obtained knowledge on measures to use against storm surges along the coast of Uchiura Bay in the future.
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  • Sota NAKAJO, Hideyuki FUJIKI, Sooyoul KIM, Gozo TSUJIMOTO
    2017 Volume 73 Issue 2 Pages I_211-I_216
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     The different temporal trend of tropical cyclone properties by each latitude has been shown based on analysis of representative value in each latitudinal band. Some variations of tropical cyclone properties are correlated to two oscillation indices of atmosphere and ocean interaction. The data of tropical cyclone was divided into two groups based on these results. Then representative scenarios for boundary conditions of storm surge simulation were estimated by using statistical approach. The phase change of tropical cyclone is not so large around three major bay, therefore the phase change of storm surge was also small. However, the change of tropical cyclone track caused local change of storm surge event in each bay.
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  • Masaya TOYODA, Jun YOSHINO, Tomonao KOBAYASHI
    2017 Volume 73 Issue 2 Pages I_217-I_222
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     In order to compare the future change and its uncertainty of typhoon intensity and storm surge between Super Typhoon Haiyan (2013) and Melor (2009) due to the differences of global warming scenarios (SRESs) and general circulation models (GCMs), two kinds of pseudo-global warming ensemble experiments are conducted using the high-resolution typhoon model and storm surge model. In the case of Typhoon Haiyan (2013), the peak intensities averaged in SRESs and GCMs are weaken by +3.7hPa and +7.9hPa, respectively. The uncertainty (standard deviation) of peak intensities in GCMs is greater than that in SRESs. In the case of Typhoon Melor (2009), the peak intensity averaged in SRESs is intensified by -5.4hPa, and the one averaged in GCMs is also intensified by -20.1hPa. The averaged landfalling intensities are strengthen in both SRESs and GCMs. The storm surges at Mikawa Bay as a result follow the same pattern in the landfalling intensities. It is concluded that tyhphoon intensities and storm surges in the future climate have larger uncertainties at the mid-latitude than at the low-latitude, due to larger uncertatinties of the vertical wind shear seen in a westerly jet at the mid-latitude.
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  • Jung-A YANG, Hajime MASE, Nobuhito MORI
    2017 Volume 73 Issue 2 Pages I_223-I_228
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     This study conducted a series of storm surge height simulations using historical typhoons for the south-eastern coast of the Korean Peninsula having complex terrain and verified the accuracy of a numerical model. The computational error of storm surge heights is related to the distance from typhoon center to target point and to the terrain complexity. We proposed a bias correction method considering coastline complexiry to reduce systematic numerical error. The bias correction method considering the terrain complexity improves the model's accuracy by 14% to 23%. In addition, projection of storm surges is examined based on a large ensemble projection (d4PDF) over 5,000 years. For the long-term assessment of storm surge heights, the numerical result were modified using the bias correction method which is proposed this study. The projected future changes of extreme storm surge heights with 100 years return period indicate both positive and negative sign and have a strong regional dependency.
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  • Ryuji NIKAIDO, Yusuke IGARASHI, Masanobu JIMBO, Shintaro OKAMOTO, Shin ...
    2017 Volume 73 Issue 2 Pages I_229-I_234
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     There are two methods to consider effects of buildings in numerical simulation of inundation due to storm surges and high waves. One of the method is to include effects of buildings in roughness, and the other is to introduce occupancy rate and drag forces of buildings in the basic equations. The purpose of this study is to assess the two different methods by comparing the numerical outputs. We first performed numerical simulations of simplified virtual terrain with different overtopping rate and building occupancy rate. Thereby, we showed that inundation depth of the method using building occupancy rate is larger near the position of overtopping. They also indicated that the inundation process is affected by both overtopping rate and building occupancy rate. We then performed numerical simulations in Fuji coast. We showed that results obtained by the method using building occupancy rate had wider inundation area and espisially deeper inundation depth in most of the area.
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  • Koki KAWAI, Katsumi SEKI, Makoto KOBAYASHI, Taiichi OOKAWA, Hiroshi IN ...
    2017 Volume 73 Issue 2 Pages I_235-I_240
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     The purpose of this study is to clarify how much vertical telescopic breakwater affects water level reduction in the event of a storm surge for the development of an evaluation method by using CADMAS-SURF/3D and STOC-ML. The velocity flow between the breakwaters corresponds to the theoretical value, which is evaluated based on water level difference. Therefore, the result indicates that the aperture can be reduced by around 1.0% when analyzing the breakwater with 7.2% aperture using STOC-ML. Because of this study, it is possible to obtain approximate water level reduction using dimensionless quantities including the conditions of wave, breakwater, and harbor.
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  • Tomohiro YASUDA, Shota HIRAI, Katsuhito IWAHARA, Daiki TSUJIO
    2017 Volume 73 Issue 2 Pages I_241-I_246
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     In the event of disaster, the risks of disaster are intertwined, and there is an occurrence possibility of simultaneous damage in multiple areas. This study assesses aggregate risk of storm surge by typhoons which attack Ise and Mikawa bay, and employs synthetic typhoon datasets made by the stochastic typhoon model. Storm surges in Ise and Mikawa bay are calculated by an empirical formula and a nonlinear shallow water equation model. Parameters of empirical formula to estimate storm surge in Mikawa bay is also derived, and applicability is confirmed. The study estimates loss function in Mikawa bay using the results of inundation simulation, and calculates damage using asset map. Event curve is estimated by the relationship of annual exceedance probability and aggregate loss.
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  • Yoshihiro UTSUNOMIYA, Masafumi MIYATA, Tomotsuka TAKAYAMA, Hiroyasu KA ...
    2017 Volume 73 Issue 2 Pages I_247-I_252
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     The technical standards and commentaries for port and harbor facilities in Japan have proposed to make new assumption of two different tsunamis of largest and frequent ones, but they have proposed no new procedures for waves and storm surges. Taking into account the new assumption for tsunamis, it is necessary to introduce the largest classes of waves and storm surges predicted by the biggest scenario typhoon into the design procedures of the port and harbor structures. The present paper has discussed the technical problems which will be encountered at the estimation of the largest wave and storm surge in scenario typhoons and at the application of them to stability check of the structures.
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  • Tomohiro YASUDA, Katsuhito IWAHARA, Shota HIRAI, Sota NAKAJO, Soo Youl ...
    2017 Volume 73 Issue 2 Pages I_253-I_258
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     Design procedure of coastal embankment compares tsunami height and storm surge height and employs higher value as a crown level. Estimation of tsunami or storm surge height is usually based on the historical maximum record or the assumed maximum value. This study proposes probabilistic evaluation procedure of storm surges employing stochastic typhoon model and applies to Suruga Bay. Typhoon tracks passed the target area were extracted from the synthetic typhoon tracks dataset for 5000 years. Storm surge simulation and inundation simulation were conducted by nonlinear shallow water models, and occurrence probabilities of storm surge height were estimated along coasts in Suruga Bay. Statistical analysis estimated a return period of the current design storm surge height at Suruga coast is about 270 years.
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  • Masahiro KAMBARA, Yoshimitsu TAJIMA, Shunichiro NAKAMURA, Takenori SHI ...
    2017 Volume 73 Issue 2 Pages I_259-I_264
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     The worst storm surge hazard by cyclone Nargis caused 140,000 of casualities in Myanmar in the year of 2008. Since Myanmar has less number of experiences of such severe storm surge disasters, it is difficult to estimate the statistic characteristics of such storm surge hazard. The delta area in the southern part of Bago City, in addition, has dense network system of canals and these canals may have significant impact on inundation characteristics aroud the delta. This study developed a Stochastic Typhoon Model at the eastern part of Indian Ocean and estimated the return period of the severe event of storm surge inundation. The developed inundation model accounted for the impact of canal networks. These developed models were then applied to the south eastern part of Myanmar delta and statistical characteristics of storm-surge-induced inundation hazard were investgated.
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  • Takumu IWAMOTO, Tomohiro TAKAGAWA
    2017 Volume 73 Issue 2 Pages I_265-I_270
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     The 6hr seiche factor at Tokyo Bay was evaluated. Numerical simulation of storm surge at Tokyo Bay caused by Typhoon No. 18 and No. 19 in 2014 was conducted by using Regional Oceanic Modeling System(ROMS) and MSM-GPV. The both results agreed well at the 5 observation points of Tokyo Bay. The result of Typhoon No. 18 showed that 6hr seiche was well reproduced, also the result of Typhoon No. 19 showed the good reproducibility. Power spectrals, coherences and phase differences at the 5 observation points were obtained by spectral analysis of observed and simulated waveforms. For the case of Typhoon No. 18, the phase-difference between the bay mouth and innermost part of Tokyo Bay was little, and coherence was almost one. However, for the case of Typhoon No. 19, coherence was relatively small around the fundamental period of 6 hours. Furthermore, EOF analysis was conducted to analyze the space and time variability of Typhoon No. 18 and No. 19. The result of Typhoon No. 18 showed that the space variability of atmospheric pressure seems essential for causing water level distribution which strongly corresponds with the first oscilation mode of Tokyo bay with a fundamental period of 6 hours. Considering the balance of meteorological loading and gravitational force, the rapid time variability of atmospheric pressure may also be important.
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  • Yuki KAJIKAWA, Nobuhiko MATSUDA, Masahide TAKEDA, Hiroaki IWAMOTO, Mik ...
    2017 Volume 73 Issue 2 Pages I_271-I_276
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     The authers have been developing a tsunami generator using an electric sluice gate which can generate various tsunami wave profiles. However, in order to obtain the control data of tsunami wave profile we targeted, we must carry out the calibration under the various experimental conditions. Accordingly, in this study, in order to develop an efficient method of the creating control data for tsunami bore generated by the electric sluice gate, we proposed a tsunami bore generation control model in which the control data is created from a repeat calculation of 1D nonlinear dispersive model. The control model was able to output the control data under which the first dispersive wave height and the tsunami bore wave height could be reproduced in the experiment from input of the targeted wave profile.
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  • Taro KAKINUMA, Takuya GOTO, Tetsuya TANEDA
    2017 Volume 73 Issue 2 Pages I_277-I_282
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     The hydraulic experiments, for the tsunami generation due to seabed deformation, were performed using the wave basin, which consisted of both an outside, and an inside, tanks, with six segments composing part of the seabed. The water level was measured utilizing three laser rangers, to obtain the tsunami height change through the propagation of the generated tsunamis. The tsunami height increased, as the total displacement, the rise velocity, or the width, of the rise area in the seabed was increased. The tsunami height increased owing to the effective movement of the seabed rise position, even if both the total displacement, and the total width, of the rise area in the seabed were equal.
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  • Masatoshi YUHI, Takuya UENO, Akinori YAMAMOTO
    2017 Volume 73 Issue 2 Pages I_283-I_288
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     A numerical model was developed for the tunami generation and evolution induced by submarine landslide. The numerical model is developed based on a finite-volume Godunov-type high-resolution scheme for a well-balanced formulation of nonlinear shallow water equations with a source term arising from bottom motion. The comparison with vertically two-diensional experimental results indicate that the model is able to accurately reproduce the wave height distribution and time history of free surface elevation. The influence of the geometry of landslide is then investigated. The results for a series of numerical computations revealed that the proper setting of initial depth and shape of landslide is important. The comparison with horizontally two-dimensional experiments demonstrated that the numerical results well reproduced the leading depressive wave. The influence of two-dimensionality was shown to be stronger when the model width is smaller.
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  • Ryoichi YAMANAKA, Kosuke NAKAGAWA, Yasunori KOZUKI, Toshitaka BABA
    2017 Volume 73 Issue 2 Pages I_289-I_294
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     A tsunami simulation with a ground liquefaction was conducted for the evaluation of an effect on the variability of the tsunami inundation process caused by the ground deformation. We developed a new correction method to calculate a change of ground elevation by a ground liquefaction using the result of the simplified method and the result of FEM by FLIP. The tsunami simulation was conducted by JAGRUS. As a result, the inundation process and the arrival time of Tsunami were changed by a ground liquefaction around small rivers and banking structures because the tsunami runs up through small rivers and is trapped by roads and rail tracks. There were areas where the arrival time of the tsunami reached at most 10 minutes earlier. The numerical results suggested that ground conditions could change the tsunami prediction result drastically and we should start to escape disaster as soon as possible.
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  • Akifumi HISAMATSU, Fumihiko IMAMURA, Ritsuko S. MATSU'URA
    2017 Volume 73 Issue 2 Pages I_295-I_300
    Published: 2017
    Released: October 17, 2017
    JOURNALS FREE ACCESS
     The Conical Fault Model that reproduces self-similar rupture growth and ununiformity of final slip distribution with a few fault parameters was developed. Using this model, the sea-bottom surface deformation due to the 2011 Off the Pacific Coast of Tohoku Earthquake and offshore tsunami waveform at the coasts of Iwate, Miyagi and Fukushima Prefectures was calculated and reproduction accuracy of observation data was evaluated. On the other hand, the same evaluation was conducted for a conventional fault model that assumes uniform slip in a rectangular fault plane. In order to explore the relationship between the number of unknown fault parameters and reproducing accuracy of tsunami waveform, single and multiple faults were considered in both model. As a result, the new model reproduced tsunami waveform with higher accuracy and with less parameter than the conventional fault model. Furthermore, moment rate function of the new model was similar to those that were obtained based on inversion for teleseismic and strong motion data. Thus, the Conical Fault Model is useful to reproduce tsunami waveform of earthquakes when observation data is limited.
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