Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering)
Online ISSN : 1883-8944
Print ISSN : 1884-2399
ISSN-L : 1883-8944
Volume 72 , Issue 2
Showing 1-50 articles out of 295 articles from the selected issue
Paper
  • Keisuke NAKAYAMA, Taro KAKINUMA
    2016 Volume 72 Issue 2 Pages I_1-I_6
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     In many studies regarding surface wave field using vertically integrated wave equations, vorticity effect is often neglected. However, in the previous studies, it has been revealed that bulbous waves occur, which have more round shape, when surface waves progress over a mild slope on shear flows. On the other hand, trochoidal wave is considered one of the most typical surface waves with vorticity. Some previous studies proposed fully-nonliear and strongly-dispersive wave equations with vorticity, but it has not been confirmed whether the equations can be applied to analyze trochoidal waves qualitatively. Therefore, this study aims to investigate the applicability of the fully-nonliear and strongly-dispersive wave equations with vorticity by using the trochoidal wave theory. Also, bulbous waves are found to be reproduced by using the proposed equation.
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  • Keisuke NAKAYAMA, Kenji SHIMIZU, Taro KAKINUMA, Eiichi TSUJI
    2016 Volume 72 Issue 2 Pages I_7-I_12
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     It has been known that the resonance of an incident solitary wave and the reflected wave from a oblique boundary increases the wave amplitude by a factor of up to 3.7, which is close to the theoretically derived value, 4.0, by Miles. Although solitary wave train is induced by the deformation of Tsunami surge reaches a river bend, previous studies investigated the resonance of only two solitary waves. In this study, we investigate the interactions of four solitary waves as a first step towards understanding the resonance of solitary wave trains. As a result, the maximum amplification factor is revealed to reach up to 3.8. Also, we find that the interaction of reflected and incident solitary waves is not (3142)-type but always O-type, which demonstrates that it may be possible to analyze the interaction of solitary wave train easily by using the theory proposed in the study.
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  • Kei YAMASHITA, Taro KAKINUMA, Keisuke NAKAYAMA
    2016 Volume 72 Issue 2 Pages I_13-I_18
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     The numerical solutions, for the coexisting fields of surface and internal solitary waves, were obtained using the nonlinear wave equations, based on the variational principle. In the coexisting fields of the surface and internal solitary waves, the phase velocity of the surface-mode solitary wave, was smaller than that of the surface solitary wave for the corresponding one-layer fluid; conversely, the phase velocity of the internal-mode solitary wave, was smaller than that of the corresponding internal solitary wave without a surface wave. The maximum wave height of the internal-mode internal solitary wave, was larger than that of the corresponding internal solitary wave without a surface wave. The wave height ratio between the internal-mode surface and internal solitary waves, was smaller than the linear shallow water solution; their difference increased as the relative wave height of the internal-mode internal solitary wave increased.
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  • Masanobu HASEBE, Shigeru TABETA, Takuji WASEDA
    2016 Volume 72 Issue 2 Pages I_19-I_24
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     The applicability of hydrostatic approximation was studied by numerical simulations and theoretical speculations. By numerical simulations on tsunami propagation with soliton fission, it was found that the reproducibility of dispersive wave shape may be affected by horizontal grid size and non-hydrostatic pressure behind wave crest. Referring these results of numerical simulations, theoretical considerations were made based on theories about non-linier long-wave and finite amplitude wave. As a result, the conditions which can be applied hydrostatic approximation have been derived as δε<0.0087 and ε2<0.03 (here δ=Δz/Δx, ε=|w/u|) for numerical simulations on shallow water.
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  • Takuya UENO, Masatoshi YUHI, Masazumi AMAKATA, Shinya UMEDA, Takehisa ...
    2016 Volume 72 Issue 2 Pages I_25-I_30
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     This paper presents a numerical model based on a finite-volume Godunov-type high-resolution scheme and quadtree grids for tsunami inundation flow around coastal structures such as a triangular bump, a rectangular cylinder and a porous vertical barrier. The numerical model is developed based on a wellbalanced formulation of nonlinear shallow water equations and the HLLC Riemann solver. The use of quadtree grids enables the model to substantially reduce the computation time while preserving computation accuracy. The comparison between numerical results and experimental results indicate good agreement on free surface elevation, flow velocity, and water pressure including tsunami run-up, overflow and diffraction around structures. The model is able to accurately reproduce the flow characteristics and reduction effect on tsunami inundation flows behind a porous barrier.
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  • Akihiro USUI, Yusaku HIRATSUKA, Shinichi AOKI, Koji KAWASAKI
    2016 Volume 72 Issue 2 Pages I_31-I_36
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     After the 2011 off the Pacific coast of Tohoku Earthquake, the necessity of tenacious coastal/harbor structure has been pointed out. Although some investigations have been done experimentally, it is difficult to make waves similar to actual tsunami in hydraulic experiments. In this study, characteristics and feasibility of a self-propelled wavemaker is proposed and investigated using CADMAS-SURF/3D which is combined with the immersed boundary method. As a result, the following findings were obtained: 1) The magnitude of standing waves indued by the long-distance movement of a wave board in a water tank has approximately exponential relation with wave-making time, and the oscilallation with the natural frequency is predominant. 2) Regarding overflow phenomenon, it is possible to control overflow time and overflow depth by arbitrary movement of the wave board compared with the gate type generation. 3) When short period waves are made at the same time as water level rise, the period can be controlled by taking into account the Doppler effect. Consequently, it was shown that tsunami and storm surge experiments has more reality by the use of this wave generation system.
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  • Maya TAKAMURA, Kazunori TAKAHASHI, Christian N. KOYAMA, Keiko UDO, Mot ...
    2016 Volume 72 Issue 2 Pages I_37-I_42
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     The GPR exploration is used to analyze underground structures by transmitting electromagnetic waves and record reflections where the propagation characteristics change. The depth of reflection planes is calculated from the traveling time with the velocity of electromagnetic wave. In most cases, the velocity of electromagnetic wave is determined by the water content ratio of soil. In this study, we employed the common-mid-point (CMP) method and estimated the velocity to be 0.06 m/ns to recalculate the depth. Comparing with the CMP method, we found the method using the water content ratio presented a margin of error of approximately 0.7 m depending on the accuracy of ratio. We also analyzed soil properties such as water content ratio, relative magnetic permeability, grain size and density of soil particles of boring core, and compared with GPR data. The relative permittivity calculated from the water content ratios ranged from 5 to 66 and relative magnetic permeability from 1.00 to 1.02, indicating that the GPR captured the changes of relative permittivity underground. In addition, we found the water content ratios corresponding to relative permittivity show a linear relationship with the density of soil particles. This study suggests the necessity of paying attention to the possibility of a large margin of error when we use the water content ratio of soil to measure the depth of reflection planes.
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  • Wataru KIOKA, Kousuke KURONO, Shintaro YAMAUCHI, Shinichiro FUJISAWA
    2016 Volume 72 Issue 2 Pages I_43-I_48
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     A lattice Boltzmann model (LBM) for simulating weakly compressible binary fluids with density contrast is proposed based on the lattice Boltzmann equations (LBE) presented by He et al. (1999). The present LBM is developed combining the LBE proposed by Zheng et al. (2006) and slightly modified by Zu and He (2013) for interface capturing with the LBE of He et al.(1999) for simulating the velocity and pressure fields. The combined LBE is capable of simulating multiphase flows with moderate density ratios. The dynamics of high-speed air flow and pressure fluctuation inside the fixed cylindrical oscillating water column chamber are then simulated numerically using the density ratio of 20. The behaviors of air flow and pressure fluctuation agree well with the experimental results.
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  • Naoki TSURUTA, Hitoshi GOTOH, Kojiro SUZUKI, Abbas KHAYYER, Kenichiro ...
    2016 Volume 72 Issue 2 Pages I_49-I_54
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     States of impact wave pressures under violent flows would be sensitively changed depending on their boundary conditions, and as a result, it is difficult to measure the pressure in hydraulic experiments. The particle method corresponding to a numerical wave flume has potential to resolve it with a numerical robustness for tracking large deformation of free surface and an accuracy in reproduction of fluid advection by its fully Lagrangian algorithm. Its performance has been increasingly enhanced by a recently developed free-surface boundary model (Space Potential Particles: SPP). However, SPP was developed on the basis of the lower-order kernel function. Moreover, its validation has not been studied sufficiently. In this study, a higher-order kernel function corresponding to the Wendland kernel is newly introduced into the SPP scheme. Its good performance is firstly shown through analysises with a simple benchmark about its applicability to the Pressure Poisson Equation. Second, a benchmark targeting a sloshing flow shows effective enhancements of numerical stability and accuracy by the proposed model through comparison with an experimental result.
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  • Hitoshi GOTOH, Abbas KHAYYER, Yuma SHIMIZU
    2016 Volume 72 Issue 2 Pages I_55-I_60
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     The ISPH (Incompressible Smoothed Particle Hydrodynamics) method is a Lagrangian meshfree method, which is superior to simulate complicated violent flows with free surface including fragmentation and coalescence of water. Despite its advantages, however its energy conservation properties have not been examined rigorously. This paper aims at examining the effect of a few enhanced schemes for improving the energy conservation properties of a projection-based particle method, namely, the ISPH method by considering a set of wave simulations. It is shown that the most improved ISPH method, referred to as, CISPH-HS-HL-ECS-GC-DS with Wendland kernel, provides the best energy conservation property.
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  • Hiroyuki IKARI, Hitoshi GOTOH, Ryotaro MATSUSHIMA
    2016 Volume 72 Issue 2 Pages I_61-I_66
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     In a scouring simulation by a particle method, it is necessary to apply a larger particle than the actual sand size to save a computational cost; however, this coarse graining can cause deterioration of the accuracy of scouring speed. Hence, it is required to consider the behavior of sub-particle-scale sand grain. In this study, the performance of a turbidity transport model on the basis of the SPH method is examined. A numerical simulation on a turbidity flow into water is carried out and calculated results by three types of models are compared with a previous experimental result. The model with the effect of fluid acceleration and grain size distribution shows the best agreement with the experiment.
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  • Yasunori WATANABE, Risa SASAKI, Haruhi OYAIZU, Takuya MAKITA, Koichi M ...
    2016 Volume 72 Issue 2 Pages I_67-I_72
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     This paper presents the boundary condition model, based on empirical contact angle model, for free-surfaces on moving contact lines of run-up waves. The inundation process on an urban topographic model composed of streets and impermeable blocks, which models urban floods observed in Kamaishi city affected by the 2011 Tohoku tsunami, was computed in this study. We find unsteady bores are consecutively formed under steady overflows from a tide wall and propagate along streets, which causes unsteady wave forces on urban buildings for long time.
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  • Akio NAGAYAMA, Naoyuki INUKAI, Keita MATSUSHIMA, Toshiyuki ASANO
    2016 Volume 72 Issue 2 Pages I_73-I_78
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     This study aims to clarify the cause of a water accident; 5 people were drown at jyogehama beach in 2014, by field observations and numerical analysis. The beach was topograhically characterized by the small beach cusps and steep slope foreshore zone. The present study sets a hypothesis that the swash currents associated with the cusp topography would generate strong currents and affect the water victims. Our field observations have found that the wave heights at the accident were higher than usual, and incident waves were running up wider in the swash zone, then drew back offshore concerntrating into the lower areas of the cusps. Whereas, the numerical analysis using OpenFOAM have revealed the similar characteristics of water surface fluctuations and three dimensional velocity structures. The water mass conveyed by run-up and run-down waves are found to be concentracted in some regions under the effects of cusp topography, and as the results strong velocities are generated there. Such characteristic flows may provide great possibility to cause the water accident.
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  • Hajime SHIROZU, Shinji SASSA, Makoto MIYATAKE
    2016 Volume 72 Issue 2 Pages I_79-I_84
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     Laboratory experiments were performed in order to investigate effects of suction dynamics induced by wave run-up within foreshore sediment. Then, the sediment strengthning as a consequence of cyclic elastoplastic contraction due to suction dynamics was formalized and the strenghning process was merged into a physics-based beach profile model.
     Validity and evaluation of the modified numerical model considering suction dynamic effects was conducted by comparing results of simulaton with measured values of the experiment under the condition with/without the effects of suction dynamics. The predicted results with the suction dynamics effects incorporated compare favorably with the measured morphological change, demonstrating their important role in suppressing the sediment transport rate in the foreshore zone of a sandy beach.
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  • Naoyuki INUKAI, Kazuki KOMIYA, Masatake FUKUMOTO, Yoshio ISHINO, Ryosu ...
    2016 Volume 72 Issue 2 Pages I_85-I_90
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     Uchinada beach locats the north-east from the Port of Kanazawa. The many accident due to the rip current occurred in this area in the past years. Firstly, this study got the archives about the beach accident from the Japan Coast Guard, and concerned the situation when the accident occurred with comparing the wave conditions. Secondaly, this study conducted the horizontal field survey with ADCP that was set on the water scooter, to obtain the current condition and the topography at the area. Finally, this study extract the component of the rip current from the observed data. Furthermore, this study calculated the interval space of the rip current, and compared with the observed data.
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  • Hitoshi TAMURA, William M. DRENNAN
    2016 Volume 72 Issue 2 Pages I_91-I_96
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     In this study, we investigated the structure of turbulent air flow over ocean waves. Observations of wind and waves were retrieved by air-sea interaction spar (ASIS) buoys during the shoaling waves experiment (SHOWEX) in Duck, NC in 1999. It is shown that the turbulent velocity spectra and co-spectra for pure wind sea conditions follow the universal forms estimated by Miyake et al. [1970]. In the presence of strong swells, the wave boundary layer was extended and the universal spectral scaling of uw broke down [Drennan et al., 1999]. On the other hand, the use of the peak wave frequency (fp) to reproduce the “universal spectra” succeeded at explaining the spectral structure of turbulent flow field. The uw co-spectra become negative near the fp, which suggests the upward momentum transport (i.e., negative wind stress) induced by ocean waves. Finally, we show the importance of short gravity waves to decide the the structure of turbulent air flow over ocean waves.
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  • Junichi OTSUKA, Yasunori WATANABE
    2016 Volume 72 Issue 2 Pages I_97-I_102
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     Spatio-temporal variation of dissolved carbon dioxide (DCO2) concentration and air-water turbulent flow field in a surf zone were measured in a wave flume using a LIF system, a PIV system and a LED back-light system. We observed entrained bubbles and strong turbulence locally enhanced the gas dissolution into water in the transition region. However DCO2 concentration could not totally increase in the region since the strong turbulence extensively diffused the DCO2 in a short time. DCO2 concentration in the bore region increased with time and reached the high level earlier than the transition region. The high concentrated DCO2 in the bore region was transported in a whole surf zone due to the undertow. Therefore, to estimate the gas transfer velocity in a surf zone, we need to evaluate the undertow effect on the DCO2 transport in addition to the breaking wave effects, such as the aeration effect and the turbulence intencity.
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  • Haruhi OYAIZU, Yasunori WATANABE
    2016 Volume 72 Issue 2 Pages I_103-I_108
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     In this study, back light imaging measurements were performed for estimating bubble size distributions and simultaneous bubble velocity for electolytically-generated bubbles. We find that the bubble sizes are well approximated by a log-normal distribution with empirical parameters uniquely determined by the current density of electrolysis, and the motions of bubbles formed at high number density become unstable owing to a so-called clustering effect. The statistical analyses for the measured bubble and fluid velocities provide novel empirical models of the rise velocity and drag force for clustered micro-bubbles, which may be applicable to bubbly flows under breaking waves.
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  • Katsuya HIRAYAMA, Yasuhiro AIDA, Koji KAWAGUCHI, Takashi FUJIKI, Koji ...
    2016 Volume 72 Issue 2 Pages I_109-I_114
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     For an isolated island surrounded deep sea in ocean, offshore waves come in any direction due to its peculiar bathymetry. In this study, an applicable method to conduct both wave hindcasting and calculation of wave transformation efficiently is suggested in order to estimate the design waves for each berth in such isolated islands. Moreover, the calculation accuracy is verified with some data observed near a coast.
     It is better that topography of isolated islands is neglected in calculation grid for wave hindcasting because offshore waves in all direction can be estimated without wave diffraction due to neighbor islands. A Boussinesq model coupled on to a spectral method can reproduce both wave transformation from offshore to coast and wave overtopping on a berth, though wave heights are little underestimated to observed data.
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  • Takashi FUJIKI, Noriaki HASHIMOTO, Koji KAWAGUCHI, Satoshi SAKURABA
    2016 Volume 72 Issue 2 Pages I_115-I_120
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     Although swell can be dominant for damage of coastal structures, there is not enough research on directional wave spectrum of swell for design use. We improved Bayesian Directional Method (BDM) to calculate more precise estimator for directional spectrum using Non Negative Least Square method (NNLS) for optimization. We examined the estimation accuracy of directional wave spectrum of swell using the data obtained submerged Doppler-type directional wave meter (SDDWM) for the extended maximum liklihood method (EMLM), Bayesian Directional Method (BDM), Bayesian Directional Method with NNLS (BDM-NNLS). Provided directional spectrum from Bretschneider-MITSUYASU spectrum and MITSUYASU directional function, we simulated the data obtained from SDDWM. As a result, BDM-NNLS showed the best agreement for the estimation accuracy of directional wave spectrum of swell.
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  • Takashi IZUMIYA, Yuta KIKUCHI, Kunihiko ISHIBASHI
    2016 Volume 72 Issue 2 Pages I_121-I_126
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     Microseisms were measured on the Niigata West Coast by using broadband seismometer in order to reveal the features and the origin of them. The observed microseism contained a predominant fluctuating component with the period of 3s to 4s, which is about a half of the significant wave period. There exists a predominant direction of the propergation of microseism that is pointing northward, the northeastern part of the sea of Japan where larger waves are generating. Using the theory of the generation of microseisms by Longuet-Higgins(1950) and Hasselmann(1963), the bottom pressure spectrum was calculated and compared with the spectrum of microseisms. It was found that the peak frequency and shape of the pressure spectrum agree well with those of the spectrum of microseisms. It means that observed microseisms were generated by the bottom pressure fluctuations with a frequency of 2fp.
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  • Akira KIMURA, Takao OTA
    2016 Volume 72 Issue 2 Pages I_127-I_132
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     Wave climate statistics is a major concept including overall statistical properties of continuously observed waves through many years. This study aimed at clarifying wave climate characteristics of the Pacific Ocean coastal areas of Japan. The statistical models are proposed according to the investigated results on wave climate data at 8 observatories in the area. In this area wave climate is characteristic of the typhoon influence. Since, it is quite different from ordinary waves, the modeling was conducted respectively and the results are added together. Finally, Monte Carlo simulations are conducted to show the effectiveness of the present model.
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  • Hirokazu NONAKA, Masataka YAMAGUCHI, Yoshio HATADA, Kunimitsu INOUCHI, ...
    2016 Volume 72 Issue 2 Pages I_133-I_138
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     A long-term wave hindcast system which consists of a sea winds data set and a backward ray tracing wave model is revised by replacing the ECMWF or NCEP/NCAR reanalysis winds data set with the MSM(Meso Scale Model)-based winds data set opened to the public domain by JMA(Japan Meteorological Agency). The new winds data set is produced with a much higher time and space resolution than the previous one. The revised system is applied to a 12-year wave hindcasting at each of 15 coastal stations and 3 northern offshore stations in the Japan Sea and accuracy of the system is investigated based on a comparison between hindcasts and measurements for wave heights or wave periods. Main results are as follows: 1)In the semi-closed Japan Sea where local wind-generated waves are dominant, introduction of the MSM winds data set into the system leads to a more accurate evaluation of the long-term wave conditions, even if a more advanced wave model is not used. In this connection, mean value of the correlation coefficient for wave heights is 0.95 and that for wave periods is 0.85. These values are 0.04-0.08 larger than the previous values. 2)Area-dependency of wave hindcasts is not detected to an improved degree, and the effect of annual step-wise sophistication of the MSM on the accuracy of evaluated waves may not be clear.
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  • Risako KISHIMOTO, Nobuhito MORI, Tomoya SHIMURA, Tomohiro YASUDA, Haji ...
    2016 Volume 72 Issue 2 Pages I_139-I_144
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     A statistical model of global wave heights prediction was developed based on the JRA-55 reanalysis data. The previous version of the statistical model estimates global wave heights from wind velocities, sea level pressures and their gradients. This study implemented results from a principal component analysis(PCA) of sea level pressures in the statistical model. The PCA method does better in swell, so the error decreased especially in the area where the previous model failed to estimate wave heights properly. The proposed model significantly improves the underestimation of monthly wave height from local wind and pressure model (the previous model): a positive bias in summer and a negative bias in winter in northern hemisphere.
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  • Yoshio HATADA, Kyohei SHIRAKAMI
    2016 Volume 72 Issue 2 Pages I_145-I_150
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     Variability in long periods of typhoon generated 50-year return wave height H50 in the Northwestern Pacific Ocean was estimated by wave hindcasts. The wave hindcasts are conducted from a period of 80 years using a parametric typhoon wind and wave prediction model in deep water. To estimate the variability of return wave height, H50 was estimated for each of six 30-year sets of annual maximum wave height data obtained between 1934 and 2013, with a 10-year forward shift for the beginning of each data set. Five sets of annual maximum wave height data from periods of 40 years were also used to compare with the H50 for the 30-year period data. Trend indices of annual maximum wave heights are estimated over a 65-year period when the annual values are obtained continuously. Main results are as follows: 1) H50 obtained from the 30-year periods shows no remarkable yearly increase or decrease over the large area. H50 obtained from the 40-year periods shows the same trend with less yearly change than that of the 30-year periods. 2) Trend indices of annual maximum wave heights show that no significant increase or decrease is detected in the area. 3) As far as the last 80 years is concerned, H50 shows no remarkable increase of decrease in the Northwestern Pacific Ocean.
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  • Hirokazu NONAKA, Masataka YAMAGUCHI, Kunimitsu INOUCHI, Yoshihiro UTSU ...
    2016 Volume 72 Issue 2 Pages I_151-I_156
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     A wave hindcasting system(MSM/SWAN), which consists of hourly sea wind distributions made using MSM(Meso Scale Model) and the third generation wave model SWAN is applied on the Northwestern Pacific Ocean with a space resolution of 0.1 degree for 10 storms such as 4 low depressions and 6 typhoons and additional 3 typhoons. Comparison between hindcasts and measurements for the time variations of (significant) wave height H and wave period T and the maximum wave height Hmax is conducted at each of 12 GPS buoy stations deployed along 10 to 20 km offshore areas from the northern area to the western area of the Japanese Pacific coasts. The main findings are summarized as follows: (1)For wave height, hindcasts are in reasonable agreement with measurements and for wave period, a similar result is obtained to a lesser degree. (2)In a detailed comparison, hindcasts yield a tendency of overestimation for wave heights during a typhoon, because hindcasts indicate an earlier growth and a slower decay than measurements. (3)Error statistics suggest relatively close agreement between hindcasts and measurements at northern stations during low depressions and hindcasts slightly greater than measurements at western stations during typhoons. (4)For the maximum wave height during a storm at any of the buoy stations, hindcast is in overall agreement with measurement, in cases where absolute relative error is less than 20 %. (5) The authors' second generation model YH3 yields a similar level agreement with SWAN for the evaluation of Hmax under the same conditions for winds and computation domain.
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  • Masataka YAMAGUCHI, Hirokazu NONAKA, Kunimitsu INOUCHI, Mikio HINO, Yo ...
    2016 Volume 72 Issue 2 Pages I_157-I_162
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     In recent years, the data sets of MSM(Meso-Scale Model)-based analysis winds and prediction winds with a high space resolution have been opened to the public domain by JMA(Japan Meteorological Agency), but validation for the accuracy of sea winds in the data sets may not be satisfactory due to the lack of observed sea winds data used in the comparison. This study investigates the accuracy of MSM winds data using measurement data over about 10 years at 4 buoys extensively deployed in the offshore areas of the Pacific coasts of Japan. The main findings are as follows: 1)MSM winds are in reasonable agreement with buoy-based measurement winds, although the relatively wide scatter of the data in lower wind speed cases becomes smaller with increasing wind speed. 2)The accuracy of MSM winds has become slightly higher in more recent years, probably due to some improvement in computational conditions. 3)Time-varying MSM winds in each of 36 storm cases follow well the corresponding measured winds and the degree of agreement becomes better in the case of stronger storms. 4)On the whole, it can be said that the accuracy of MSM winds is significantly high in not only normal winds but also severe winds.
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  • Masaki YOKOTA, Keiske ODA, Ryusuke SAITO, Noriaki HASHIMOTO, Masao MIT ...
    2016 Volume 72 Issue 2 Pages I_163-I_168
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     Directional spectrum represents the energy distribution of irregular sea waves as a function of frequency and propagation direction. It is one of the most fundamental physical quantities of sea waves. Therefore, it is very important to know the characteristics of the directional wave spectra, not only for the research purposes but also for the plan, design, and construction of ports and their related facilities. The spreading parameter Smax is an important parameter to describe the degree of the energy concentration in propagation direction. The investigation of the spreading parameter has not been conducted well, whereas the accuracy of wave period and wave height which obtained from wave prediction model is sufficient. Although the spreading parameter can be calculated based on wave observation, but response characteristics to disturbance are not clarlfied since the survey sites are limited. In this study, we analyzed the wave data measured with Doppler-type directional spectra wave meters to estimate directional spectra and to investigate the occurrence characteristics of Smax, an energy concentration parameter in direction, around the Japanese coastal area. Also, a fundamental study about the appearance characteristics of spreading parameter was done by using wave prediction model. We investigate the response characteristics of Smax with one direction wind, model typhoon, and GPV wind data. As a result of the statistical analyses on the directional spectrum, the calculated Smax show rapid change in every 2 hours and the clear correlation was not confirmed between the wave period or the significant wave heights and Smax. At Naoetsu, the value of Smax calculated from the mean directional spectrum during one violate wave term is about 14 which is a little higher than the value generally used for the wind waves. On condition with one direction wind, Smax is increased with the increase of the decrement distance. Smax is low at the center of typhoon, Smax is increased with the increase of the distance from the center of typhoon. In wave prediction model, Smax is decreased with the increase of the wave steepness. Comparison of wave observation data and wave prediction data shows that Smax which calculated using wave prediction model is bigger than those calculated using wave observation data.
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  • Yuki NISHIMURA, Tomonori MATSUURA
    2016 Volume 72 Issue 2 Pages I_169-I_174
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     It is difficult to obtain instantaneously two-dimensional physical-parameters of surface waves from the wave gauge observations such as NOWPHAS. Therefore, we estimated wave parameters (significant wavelength, wave direction and significant wave height) from two ALOS-2/PALSAR-2 satellite images. The satellite images were taken at 12:35 on 2 December 2014 over Tsuruga and Fukui in Hokuriku region of Japan. The significant wavelength and wave direction was estimated by Fast Fourier Transform (FFT) for wave-crest lines in the image. We focused our analysis object on swells of more than wave periods 10s for FFT analysis. For the estimated wavelength distribution, the wavelength of swells has changed combined with wind wave generation. In addition, the wavelength is drastically shortened from a depth of 50m shallower. This is consistent with the theoretical value obtained from a small amplitude wave theory. For the wave direction distribution, the wave ray of swells changes at cape and bay due to wave convergence at cape and wave divergence in bay. Finally, the significant wave height was calculated from the significant wave period. As a result, the wave height in Tsuruga is lower than Fukui because coastline topography shields the incident of the waves.
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  • Takehisa SAITOH, Genki KOKUBO, Hajime MASE
    2016 Volume 72 Issue 2 Pages I_175-I_180
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     Long swell prediction around Japan Sea is examined using artificial neural network. In this artificial neural network, meteorological data around the generation point of long swell is adopted as input data, and wave data of prediction point is used as output data.
     As a result, it is found that atmospheric pressure and velocity are suitable for the factor of input data, and the occurrence of long swell at prediction point is possible to estimate using half a day before meteorological data as input data
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  • Sota NAKAJO, Ryuta YAMAGUCHI, Takaomi HOKAMURA, Sooyoul KIM
    2016 Volume 72 Issue 2 Pages I_181-I_186
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     Real-time prediction of unusual sea level fluctuation, called as ”Abiki”, is important from viewpoint of disaster prevention. Atmospheric pressure fluctuation with small amplitude is regarded as one of important factor of Abiki. However, actual real-time prediction of the distribution is difficult. In this study, we developed neural network model for prediction of Abiki and investigated the relationship between the reproducibility and parameters of our basic model. It was shown the importance of information of pressure fluctuation and wind direction from our model again. Then the potential of improvement of our model by using multispot measurement was also shown.
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  • Kenji TANAKA, Daiki ITO, Shun SHOJI
    2016 Volume 72 Issue 2 Pages I_187-I_192
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     We conducted the numerical experiments on propagation and enhancing process of meteotsunami using multi-nested model based on the Priceton Ocean Model (POM). The meteotsunami generated in the middle or west sector of the East Chia Sea propagated slower than the atmospheric disturbance. However , the Okinawa trough made the meteotsunami propagating much faster than that of the atmospheric disturbance. As a result, it is possible that the preceding wave reaches the west coast of Kyushu 30 - 60 minutes before landing the pressure disturbance. The single abrupt pressure jump revealed that the travelling orientation of the pressure disturbance played an important role in amplifying the oscillation with the period range of 24 - 30 minutes. Even though the horizontal scale of the each pressure wave itself was so small, it is possible that the meteotsunami can hit widely after travelling the East China Sea via Okinawa trough.
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  • Kohei MAKINO, Hisamichi NOBUOKA
    2016 Volume 72 Issue 2 Pages I_193-I_198
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     The purposes of this study are considering to reduce the statistical variability of the region to target storm surge disaster for the prediction of that probabilistic storm surge inundation area by using the regional frequency analysis in coastal areas. It was possible to select a function that summarized variation between adjacent tide level observation points by using regional common distribution. Considering the regional classification of five points from Onahama port to the Chiba port including Ibaraki Prefecture coast in Japan by the regional frequency analysis. The results of extreme statistical analysis for various storm surge showed us that it was possible to reduce the statistical variability of the extreme value data at Oarai Port and Choshi Port by using the regional frequency analysis. The results of the probabilistic inundation area for each return period by using an numerical simulation of storm surge, also showed that it was possible to restrain the local variation by the regional frequency analysis and to predict average inundation in the Ibaraki Prefecture coast.
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  • Koji KAWASAKI, Masaki NIMURA, Shinnya SHIMOKAWA, Satoshi IIZUKA, Takah ...
    2016 Volume 72 Issue 2 Pages I_199-I_204
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     Due to rising sea temperatures caused by the global warming, there has been growing concerns about the attack of huge typhoon and its-induced storm surge. Sophistication of storm surge model and real time prediction are, therefore, important to prevent and mitigate storm surge disaster. In this study, we developed a storm surge simulation system using Finite Volume Community Ocean Model (FVCOM), MSM data of Japan Meteorological Agency and the Ocean Tidal Model NAO.99Jb so as to predict storm surge in real time. The validity and applicability of the system were verfieid by calculating storm surge caused by previous typhoon and comparing with the field observation. As a result, the numereical results showed that the system is able to reproduce the maximum value and peak time of storm surge. The system was also confirmed to be applicable to real time storm surge prediction by conducing MPI parallel computation on high-performance computer system.
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  • Masaru YAMASHIRO, Akihiro YURINO, Masaki YOKOTA, Mitsuyoshi KODAMA, No ...
    2016 Volume 72 Issue 2 Pages I_205-I_210
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     Recently, some coastal circulation models, e.g. Princeton Ocean Model (POM), Regional Ocean Modeling System (ROMS), etc. are applied to the storm surge simulations for enabling more accurate estimations. Among these existing models, Finite Volume Coastal Ocean Model (FVCOM) developed by Chen et al. (2003) has an advantage in that it employs unstructured grid system so as to compute tidal currents in complicated inner bays with high accuracy. In this study, for the purpose of understanding the applicability of the model to numerical simulations of storm surge inundation, numerical simulations of storm surge in the innermost part of the Ariake Sea were performed. First, a computational mesh with high spatial resolution was created, and the roughness factors on the surface of land were determined considering the land-use classification. Next, the numerical simulations were performed including the river discharges and the astronomical tides. The simulation results show that the numerical model with unstructured grids is sufficiently effective for numerical simulations of storm surge inundation.
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  • Koji KAWASAKI, Shinya SHIMOKAWA, Tomokazu MURAKAMI
    2016 Volume 72 Issue 2 Pages I_211-I_216
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     The intensification of typhoon and sea rise level which are caused by the global warming have been feared in recent years, and it is important to examine the influence of huge typhoon which exceeds Ise Bay typhoon. In other words, it is essential to predict the potential maximum typhoon scale and its-induced storm surge disaster. This study, therefore, examined inundation characteristics at the head of Ise Bay due to huge typhoon by conducting storm surge inundation calculation for virtual Muroto typhoon with the same course as Ise Bay typhoon, and potential typhoon based on the present climate or the SRES A1B scenario of IPCC. The numerical results revealed that the bay head area below sea level has high risk for human and property and early evacuation is of importance to mitigate catastrophic storm surge disaster.
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  • Yoko SHIBUTANI, Sota NAKAJYO, Sooyoul KIM, Nobuhito MORI, Hajime MASE
    2016 Volume 72 Issue 2 Pages I_217-I_222
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     Impact of climate change on tropical cyclones has been assessed for coastal disasters. In this study, we have carried out a sensitivity tests of storm surge simulations to climate change considering typhoon characteristics and sea level rises in the Osaka bay. The results indicated that the maximum surge height with the worst track is 1.0m higher than the 2nd Typhoon Muroto maximum surge height with the 2nd Muroto track. There are less flooding compared to that of the original track, but the the inundation area is increased signifisantly under the future climate condition. The changes of inundation area due to climate change will be increased about 160 % in comparison with historical run. In addition, we estimated its return period as 21 years based on stochastic tropical cyclone model.
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  • Jun YOSHINO, Risa TAKASHIMA, Tomonao KOBAYASHI
    2016 Volume 72 Issue 2 Pages I_223-I_228
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     In this study, we evaluate the long-term variability of the maximum potential storm surge height induced by a mature typhoon reaching to the maximum potential intensity (MPI), with considering the radius of maximum wind speed (RMW). Two cases of the maximum potential storm surge height in Ise Bay are analyzed using HadCM3 in the CMIP3 multi-model dataset. In CASE1, the change of MPI is only included, and in CASE2, the changes of both MPI and RMW are considered. The evaluated 100-year trends in the 21st century are +2.5m for B1 scenario and +3.2m for A2 scenario in CASE1, and +3.2m for B1 scenario and +3.9m for A2 scenario in CASE2. The results suggest that an appropriate setting of RMW in a mature typhoon especially makes much difference in predicting the long-term variability of the maximum potential storm surge height under the future climate.
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  • Tetsuya TAKESHITA, Kazuki HIMENO, Minoru ITSUI, Yuho TOMINAGA, Kenichi ...
    2016 Volume 72 Issue 2 Pages I_229-I_234
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     In this study, we present the results of a sensivity analysis for maximum water height prediction based on the difference between the assumed typhoon and low pressure courses and the depression data used for high tide prediction calculations.
     The results confirm that the typhoon courses which generate the highest tides are forecasted through the coast direction, the shore topography, and the wind direction. The forecast accuracy is further improved using a sensitivity analysis. In the case of a low pressure field that excludes the typhoon effect, we present a method for calculating the depression data using a natural neighbor interpolation. The estimated high tide values using this model were in good agreement with those of measured tides. Finally, we present the sensivity analysis considering not only parallel moving of the center of depression but also the shore topography, and the wind direction is necessary for the setting of low pressure course.
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  • Tetsuya TAKESHITA, Kazuki HIMENO, tatsuya NIWA, Thuy Thi Thu MAI, Mako ...
    2016 Volume 72 Issue 2 Pages I_235-I_240
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     This study has two aims. The first aim is to confirm the necessity of considering time variation of astronomical tides in the estimation of storm surge inundation in a low-lying area. Therefore, we conducted a simulation on the Noubi Plain in the Chubu region, Japan. The second aim is to check the need for considering the change in sea level in the estimation of inland flood inundation in a coastal area where rain water is directly drained into the sea. Therefore, we carried out inland flood inundation calculations, when high tides and rains simultaneously occur, on Nemuro city in the Hokkaido region.
     We confirm the following: The estimation of maximum inundation area and water quantity in a storm surge is sufficient with a fixed high tide level, but the fluctuation of astronomical tides must be considered to calculate the duration of an inundation. In estimating inland flood inundation, considering the tidal record is very important according to the simulation of a flooded area in October, 2015.
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  • Katsuyuki SUZUYAMA, Naoto HIGUCHI, Hidenori SHIBAKI
    2016 Volume 72 Issue 2 Pages I_241-I_246
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     In examining the inundation damage due to storm surge, it is important to accurately estimate the overtopping and overflowing over the seawall and coastal dike. Two-dimensional Navier-Stokes equations by the VOF method, CADMAS-SURF, could be applied to the estimation. However, it requires enormous computation time.
     In this study, we propose a simple estimation method which is an alternative to CADMAS-SURF. This method is easily incorporated into a numerical simulation model for storm surge inundation, by which the flow rates in the transition, from the overtopping to the coexisting situation with the overflowing, can be continuously calculated with a high accuracy in a short time.
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  • Ayumi SARUWATARI, Toshihiro TAKEE, Yasunori WATANABE
    2016 Volume 72 Issue 2 Pages I_247-I_252
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     Explosively developing extratropical cyclones are becoming one of the important factors to cause a storm surge in winter. This study statistically evaluates risk of storm surge based on 3D flow fields under developing storm surge computed for various meteorological conditions. Vertical structure of the flow in the Nemuro Bay driven by the strong wind and wind-induced surface gradient showed characteristics different from that in the open ocean forming a typical Ekman spiral. Surge height and event duration are sensitive to the cyclone trajectory. The results of this study also shows the highest surge level in the Nemuro Bay had a risk to increase more than 1.5 times as high as the highest surge of the storm event in 2014.
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  • Kenta SATO, Shunichi KOSHIMURA
    2016 Volume 72 Issue 2 Pages I_253-I_258
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     Lattice Boltzmann Method (LBM) is the one of the efficient Computational Fluid Dynamics (CFD) solvers. It has become an alternative powerful method with the other conventional CFD solvers. In this study, we developed a free surface simulation model of LBM with the multiple relaxation time collision operator for high calculation accuracy. The model was verified in the still water simulation and the dambreak flow. The model results are in good agreement with the experimental data, including the movement of free surface of water and solid wall boundary condition. Through the model verification, we found that our model can be applied to simulate the complex behavior of free surface flows.
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  • Yuta MITOBE, Neetu TIWARI, Kazuya WATANABE, Hitoshi TANAKA, Yasunori W ...
    2016 Volume 72 Issue 2 Pages I_259-I_264
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     In order to improve the accuracy of numerical simulation on morphological changes caused by tsunamis, Simultaneous Coupling Method (SCM), which couples 2 dimensional shallow water equation model and boundary layer equation model, was applied to numerical simulation of tsunami runup in Kitakami River. Under the front of the tsunami wave, steep peak of bed-shear stress was observed, while the variation of bed-shear stress was similar to the variation of bed-shear stress based on manning's law, which has been commonl applied for standard model for tsunami propagation.
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  • Yuki KAJIKAWA, Masamitsu KUROIWA, Hisanari NAKAYAMA
    2016 Volume 72 Issue 2 Pages I_265-I_270
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     In this paper, a 2D numerical model using the high order WENO (Weighted Essenciallty Non-Oscillatory) scheme was proposed in order to predict a topography change in a harbor due to Tsunami. In this model, the FAVOR (Fractional Area/Volume Obstacle Representation) method was introduced into the governing equations. We applied the model to the small-scale experiment and the large-scale actual phenomenon in order to verify the validity of the model. Consequently, although the model was not able to reproduce local scouring around a breakwater where three dimensional flow was developed, it was clarified that the model can reproduce the topography change well by contracted flow.
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  • Yuta MITOBE, Kazuya WATANABE, Hitoshi TANAKA, Neetu TIWARI, Yasunori W ...
    2016 Volume 72 Issue 2 Pages I_271-I_276
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     In this study, a numerical experiment on water level change in river induced by tsunamis were conducted to discuss the mechanism of longer duration of high water level in rivers than the period of tsunami, which was observed in 2011 tsunami event. Wave conditions which has 5~100 % of wave heights of 2011 tsunami were made based on the simulated wave form of 2011 tsunami, and the characteristics of water level change with the different magnitude of tsunamis were tested through numerical simulation in Kitakami River. It is found that increase of tsunami height induce larger discharge across the river mouth for both of incoming and outgoing flow, while the increase rate is larger for incoming flow. And that results in the transition of the condition to keep higher water level in longer period with higher waves. This characteristics were observed for many simulated historical tsunami events. And tsunami period does not have significant effect to cause the difference on characteristics of the flow across the river mouth.
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  • Hiroshi NAGASHIMA, Nozomu YONEYAMA
    2016 Volume 72 Issue 2 Pages I_277-I_282
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     The Nankai Trough Earthquake Tsunami is predicted to occur in the near future in Japan. One of the countermeasures to be taken against the tsunami attack is to predict how long salt water carried by a river-runup tsunami would stay in the river to prevent a water purification plant from taking in salt water.
     In this study, a 2DH simulation from wave source, a 3D simulation around Yodogawa Estuary Barrage using the 2DH calculation result as its boundary condition, and a 2DH-3D hybrid simulation from wave source in two conditions of river flow rate and barrage were conducted, and 3D and hybrid simulation results were compared with 2DH simulation result. It was shown that free surfaces and overflow volume of the barrage were similar between 2DH and hybrid simulations whereas they were different between 2DH and 3D simulations, and significant vertical distributions of the density were present in the 3D region of hybrid simulation. This indicated that applicability of a 2DH-3D Hybrid model to salt water behavior caused by a river-runup tsunami around the barrage area.
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  • Yasunori WATANABE, Hitoshi TANAKA, Yuta MITOBE, Kazuya WATANABE
    2016 Volume 72 Issue 2 Pages I_283-I_288
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     This paper presents the novel semi-Lagrangian computational model for estimating comprehensive tsunami run-up process on high resolution topographical data under Adaptive-Mesh-Refinement environment. The model was applied to the experimental and numerical flooding cases on Kitakami river for the 2011 Tohoku tsunami models. The computational and topographical resolutions significantly affect timings and locations occurring overflow over embankments and spreading velocity of the floods. The current model has advantages to precisely compute divergence of the bed load flux, resulting from local gradients of the bottom shear, leading to reasonable estimates of the local deposition and erosion.
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  • Ryosuke AKOH, Shiro MAENO, Yoshitake TAKAHASHI, Kenta KUDAI, Keisuke Y ...
    2016 Volume 72 Issue 2 Pages I_289-I_294
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     Southern part of Okayama city is a low elevation area and has a great risk of liquefaction. Therefore coastal dike may possible subside due to the Nankai Trough earthquake and inundation just after quake is supposed to occur. In this study, we predicted the process of inundation in Okayama city caused by the dike subsidence, using the tsunami simulator that reproduced the layout of the city area in detail. Furthermore, evacuation routes and time to designated evacuation sites were evaluated by using the walking speed under the flooding conditions. The results show that many evacuation routes are changed by the inundation on the roads and the evacuation time of senior person becomes 1.6 times on average. This suggests that it is important for the evacuation planning to consider the water depth and the flow speed on the road. The present model is useful to investigate the evacuation time characteristic under the inundation conditions.
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  • Mutsuki Ota, Takashi IZUMIYA
    2016 Volume 72 Issue 2 Pages I_295-I_300
    Published: 2016
    Released: November 15, 2016
    JOURNALS FREE ACCESS
     We use Monte Carlo simulation to assess an accuracy of quantile and its standard deviation estimated by a maximum likelihood method to annual maximum data with historical information. The historical information is categorized into three classes: “censored” data where the seismic magnitudes are known, “binominal” data, where only threshold exceedance information is available and “range” data, where the seismic magnitudes of historical seismic data have error within predetermined range. The exponential distribution for annual maximum data of seismic magnitude in the eastern margin of the Japan Sea is selected as a candidate distribution. The extreme values and its standard deviation are estimated for the seismic magnitude with historical information. The introduction of historical information in the extreme value analysis can produce quantile estimates with higher accuracy when a proper evaluation of historical information is made.
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