Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering)
Online ISSN : 1883-8944
Print ISSN : 1884-2399
ISSN-L : 1883-8944
Volume 71 , Issue 2
Showing 1-50 articles out of 292 articles from the selected issue
Paper
  • Keisuke NAKAYAMA
    2015 Volume 71 Issue 2 Pages I_1-I_6
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     Many investigations related to soliton resonance with the large initial amplitude of surface waves have been done in the previous studies by using numerical computaions and laboratory experiments. However, less attention has been paid to small intitial amplitude waves in the analysis of soliton resonance. Therefore, this study aims to investigate soliton resonance with the initial amplitude of 10 % of the total water-depth for surface waves by using the fully-nonlinear and strongly-dispersive wave model. As a result, the amplification rate was found to reach to 3.6 times as large as the initial amplitude. Also, the large amplification rate was found to appear when the initial shape of a solitary wave can be modeled by the KdV theory.
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  • Hiroki IKEZAWA, Takenori SHIMOZONO, Shinji SATO
    2015 Volume 71 Issue 2 Pages I_7-I_12
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     The 2011 Tohoku tsunami overflowed coastal levees and devastated their hinterlands in numerous coastal towns. The disastrous event highlighted the importance of coastal risk evaluation for extreme tsunami overflow while the effects of coastal levees are not well accounted for in existing flood models. The purpose of this study is to develop a 1D depth-integrated non-hydrostatic model for tsunami flooding over a levee with a trapezoidal cross section. The model is capable of simulating tsunami overflow seamlessly as the levee is simply treated as a steep topography. To confirm the model performance, a levee-overflow experiments are conducted in a current flume, and the model results are compared with the experimental data. It is concluded that hydrostatic models result in a significant underestimation of overflow discharge, whereas the present model, which accounts for the non-hydrostatic pressure due to vertical flow acceleration aroud the levee, performs much better especially when the overflow depth is large.
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  • Naoki TSURUTA, Hitoshi GOTOH, Kojiro SUZUKI, Kenichiro SHIMOSAKO, Abba ...
    2015 Volume 71 Issue 2 Pages I_13-I_18
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     For practical application of the numerical wave flume to the coastal engineering problems, considering the computational cost, the open boundary condition is required in order to reproduce the pseudo extension of the flume due to the limited computational domain. Regarding the particle method as one of the numerical wave flume, although it is widely used for the engineering problems thanks to its superiority of tracking the violent free-surface flow, its framework with the open boundary condition is not sufficiently studied particularly for the projection-based particle methods. The particle method is on the basis of the fully Lagrangian method, thus, it is difficult to apply the fixed open boundary condition with flow-in and flow-out of particles. To resolve the problem, in this study, a novel open boundary condition for the projection-based particle methods is developed by using the SPP scheme for the free-surface boundary condition and WPP scheme for the wall boundary condition, which were recently developed with the potential virtual particles. Its good performance for both the inlet boundary condition and outlet boundary condition is shown through some benchmarks.
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  • Hiroyuki IKARI, Hitoshi GOTOH, Tomoya TANBO, Tomoyuki EJIRI
    2015 Volume 71 Issue 2 Pages I_19-I_24
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     The paper presents an improved soil dynamics model and sub-particle-scale suspended load model for MPS-based simulation of scouring due to submerged vertical jet. In the soil model, the diffusive term with the diffusive coefficient depending on a stress and strain-rate based on the Mohr-Coulomb yield function is introduced. The soil model was validated through a dam-break simulation, and the calculated deposition shape is in good agreement with the experimental one. The suspended load model is applied to express pick-up of sub-particle-scale sand. These two models were used in the simulation of scouring due to submerged vertical jet, and the shape of scour hole in the simulation showed good agreement with the experimental one.
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  • Hitoshi GOTOH, Abbas KHAYYER, Hiroyuki IKARI, Yuma SHIMIZU
    2015 Volume 71 Issue 2 Pages I_25-I_30
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     The MPS (Moving Particle Semi-implicit) method is a Lagrangian meshfree method superior to simulate complicated violent flows with free surface, such as breaking wave or wave impact. 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 in improving the energy conservation properties of a profection-based particle method, namely, the MPS method by considering a set of wave simulations. It is shown that the most improved MPS, referred to as, MPS-HS-HL-ECS-GC-DS with Wendland kernel, provides the best energy conservation property.
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  • Ryosuke TERAOKA, Yuji SUGIHARA, Nobuhiro MATSUNAGA
    2015 Volume 71 Issue 2 Pages I_31-I_36
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     We carried out a direct numerical simulation of open-channel flow with free-surface fluctuation to investigate the effect of the fluctuation on the air-water gas transfer. The numerical results indicate that spatial patterns of the surface divergence agree with those of the surface elevation and the air-water gas flux. The relationship between the surface divergence and the gas flux is similar to the numerical result for the flat surface. This suggests that the gas transfer mechanism is closely connected with the surface divergence motion. The gas transfer velocity at high Froude number becomes relatively larger than the surface divergence model. The result shows the surface fluctuation to promote the gas transfer.
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  • Yasunori WATANABE, Takuya MAKITA, Haruhi OYAIZU
    2015 Volume 71 Issue 2 Pages I_37-I_42
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     In this study, local behaviors of cavities formed at impact of a steady planar jet onto still water were measured on the basis of a high-speed, high-resolution back-light imaging technique. The characteristic time and length scales to define deformation of the cavities, depending on the impact velocity, were analyzed to identify the mechanisms of the cavity growth. The both capillary and vortex-induced pressure are found to govern the local cavity behaviors.
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  • Yasunori WATANABE, Yuki OSHIMA
    2015 Volume 71 Issue 2 Pages I_43-I_48
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     In this study, imaging experiments for measuring free-surface shapes of run-up dambreak waves and fluid velocity distributions on the basis of Laser-Induced Fluorescence (LIF) and Super-Resolution Particle Imaging Velocimetry (SRPIV) were performed with aim to identify kinetic features of the run-up flows depending on slop angles. Organized patterns of the rotational shear flows are found to be formed in the bottom and surface boundary layers behind the wave front, which provides mechanical effects to provide typical blob-like surface shape in the wave front as well as wavy surface form behind it.
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  • Ayumi SARUWATARI, Yoshihisa OKA
    2015 Volume 71 Issue 2 Pages I_49-I_54
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     The effects of the bed conditions on a velocity field under an oscillating flow were experimentally investigated by visually measuring the flow fields with various bed conditions; (1) flat bottom, (2) movable granular bottom and (3) fixed permeable bottom. The flows over the granular and permeable bottoms are free from the ‘non-slip’ condition, which can induce attenuation of the bottom shear stress and generation of turbulence under the bottom. It was confirmed that the boundary-layer thickness and vorticity over the bottom decreased on the permeable and movable bottom conditions. Suspension of the bottom particles was found to contribute to transport turbulent energy to the entire flow field.
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  • Hiroki FUJIKAWA, Yoshimitsu TAJIMA, Ryo TAKEMORI, Yudai IWATSUKA, Take ...
    2015 Volume 71 Issue 2 Pages I_55-I_60
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     The coral beach shows unique characteristics of beach deformation because the beach is formed by coral gravels whose density and grain sizes are lighter and larger than silica sand grains on a general sandy beach. This study aims to investigate the characteristics of seepage and resulting accumulation process of coral grains on the coral beach through field observations and simple numerical analysis. This study first conducted a field survey at the ballast island which is located at the northside of Iriomoteshima island. Field survey revealed that coral gravels with relatively larger grain sizes were dominantly deposited on top of the ballast island while relatively smaller gravels were dominant around the swash zone at the daily water level. It was also found that certain amount of wave energy was transmitted to the seepage layer of coral bed and combination of measured water level change inside the seepage layer and numerical model revealed that swash zone of the coral beach has much higher permiability than that of general sandy beachs.
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  • Akihiko KIMURA, Taro KAKINUMA
    2015 Volume 71 Issue 2 Pages I_61-I_66
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     The conditions in which a takeoff is possible for a surfer to ride a wave have been discussed by generating numerical simulations considering wave breaking. In the horizontal direction, a surfer is required to achieve a sufficient horizontal component of paddling speed not to be overtaken by a wave peak. On the other hand, in regard to the vertical direction, a surfer needs to float at a position where the force on him along the wave front is downward when he stops paddling to try to take off. According to both of these conditions, the temporal changes of the required horizontal component of paddling speed are evaluated to take off on two different waves, which show the plunging and the spilling types of wave breaking.
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  • Shinji SATO, Keisuke MURAKAMI, Yoshio SUWA, Ryuichiro NISHI, Hiroki MA ...
    2015 Volume 71 Issue 2 Pages I_67-I_72
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     Field data of waves and nearshore currents were obtained in Miyazaki Coast due to 5 typhoons which consecutively impacted the coast in 2014. Strong northward currents as well as infragravity motions with periods 30-300 seconds were generated by typhoon waves incident mainly from the south. The characteristics of the motions were closely related to typhoon tracks. Longshore sand transport was estimated on the basis of breaker heights and longshore current velocities. The northward transport of more than 500,000m3 estimated by waves and currents was consistent with bathymetry surveys but in the opposite direction to the long-term southward transport. It was confirmed that the characteristics of sediment transport largely depended on the typhoon property. Alongshore rhythmic nearshore topography developed after 5 typhoons was suggested to be related to the edge waves propagating alongshore.
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  • Masataka YAMAGUCI, Hirokazu NONAKA, Yoshio HATADA, Kunimitsu INOUCHI, ...
    2015 Volume 71 Issue 2 Pages I_73-I_78
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     This paper discusses variability of the Toba constant BT(=0.062) or the variable Toba coefficient B in the 3/2 power law between significant wave height Hs and period Ts. Main conclusions are summarized below. (1)The Takagaki et al.(2012) equation has a reasonable accuracy for estimating roughness length z0 and may yield a proper evaluation of friction velocity u* and B. (2)The Takagaki et al.(2012) equation with Iwano et al.(2013) indicates a weak dependence of B on u* even in usual wind conditions and also the observation-based Kahma·Calkoen(1992) equation suggests an implicit dependence of B on both u* and Hs. (3)Estimates of observation-based B at 17 points in many inner sea areas are site-dependent, in cases where the mean value ranges from 0.0463 to 0.0679. (4)A significant variation of the observation-based B with both u* and Hs suggests that the Toba 3/2-power law may not hold in a strict sense. (5)In addition, estimates of observation-based B are drag coefficient(Cd) formula-dependent, in cases where the mean value ranges from 0.0586 to 0.0625 for each of 6 Cd formulae.
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  • Noriaki HASHIMOTO, Masao MITSUI, Koji KAWAGUCHI, Masaki YOKOTA, Keisuk ...
    2015 Volume 71 Issue 2 Pages I_79-I_84
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     An ultrasonic Doppler type directional Wave Meter (DWM) has been used for directional wave observations since 1990's in Japan. In those days, due to poor computer power, directional spectra were estimated by using four time series data of water surface elevation and oblique components of three water particle velocities measured at an upper layer in water. Recently, we carried out 31 components measurements of water surface elevation and 30 oblique components of water particle velocities at 10 layers. In this case, since hundreds of simultaneous integral equations can be used for estimating directional spectra, estimation accuracy of directional spectra can be certainly evaluated quantitatively by using various combinations of the hundreds of equations. In this study, first, we examined the estimation accuracy through numerical simulations for DWM with Bayesian Directional spectrum estimation Method (BDM), Extended Maximum Entropy Method (EMEP), and Extended Maximum Likelihood Method (EMLM). Then the results were verified with the filed data observed by DWM. Various combinations of simultaneous integral equations observed by DWM were solved by BDM, EMEP, and EMLM. According to the results of the filed observations, the estimates by BDM and EMEP using information of water surface elevation and water particle velocities in all the layers, compared with EMLM, yield directional spectra with sharp and narrower directional spreading, and thus an accuracy improvement of the directional spectrum estimation can be expected by BDM and EMEP. These results are agree well with the results of the numerical simulations, where the estimates by BDM, EMEP, and EMLM were compared with the true directional spectra.
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  • Katsuya HIRAYAMA, Hiroaki KASHIMA, Minoru ITSUI, Tatsunori NARUKE
    2015 Volume 71 Issue 2 Pages I_85-I_90
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     For the last decade, coastal disasters caused by swell which is higher than design wave on breakwaters and seawalls have often occurred in Japan. However, it is still rare to expect the occurrence of such extreme swells on the design or reconstruction procedure of structures, because the period of design wave is usually estimated with the relationship to the extrame wave height. Therefore in this study, the extreme value distributions for swells are estimated and characteristics of their regional distribution are considered, using the extreme swells separated from observed strom waves with the criteria proposed for long-period NOWPHAS dataset. Moreover, nonlinear wave transformations in shallow water are calculated from offshore to coastal line. As a conclusion, the extreme swell with the same return period to the design wave can raise the higher maximum wave height in front of structures due to wave refraction, shoaling and breaking on bathymetry in the Paciffic ocean side.
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  • Hiroshi TAKASHIMA, Yukitomo TSUBOKAWA, Toshio ENDO, Yasuhiro TAKAHASHI ...
    2015 Volume 71 Issue 2 Pages I_91-I_96
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     In recent years, damage of port structures caused by long period swell is increasing, and induces the needs of study about the evaluation method of offshore design wave for the breakwater that demonstrate appropriate function especially during high waves in the future as an adaptation measures of global warming. In this study, we analyzed the wave properties that caused the disaster, and clarified the needs of offshore design wave considering long period swell. The long period swell was defined as under 0.025(wave steepness) for the estimation of the offshore design wave. The main conclusions are as follows. (1) The caisson width shows a tendency to increase in accordance with the increase of the wave period. (2) Variable parameter which brings greater resultant force of wave pressure among conventional design wave and design wave for long period swell after performing the wave deformation calculation is adopted for designing performance of breakwater. Such a reasonable performance design of the breakwater which provides improved performance against wave action, ensuring of harbor tranquility, and continuous exhibition of port functions contributes to the logistics and human distribution of associated area, industrial activities, and prevention/reduction of disaster to improve the living environments.
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  • Toshikazu KITANO, Wataru KIOKA
    2015 Volume 71 Issue 2 Pages I_97-I_102
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     In making decision based on statistical hypothesis testing, two types errors are inevitable. Thus the most important but difficult thing to do in facing a real problem, e.g. adaptation to the climate change, is balancing the probabilities of both errors. False positive, or type 1 error, is to ommit the unnecessary worry while false negative, or type 2 error, is to miss the risk without awareness. The latter error have not been examined even for the general analyses of extremes, but it should be treated more extensively to discuss the provisions against the coastal disasters. An example is demonstrated to show how to calculate and balance these probabilities.
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  • Nobuhito MORI, Tomoya SHIMURA, Hirotaka KAMAHORI, Arun CHAWLA, Tomohir ...
    2015 Volume 71 Issue 2 Pages I_103-I_108
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     This study examined long-term wave hindcasts forced by JRA-55 reanalysis released by Japan Meteorological Agency. The wave hindcasts were performed by new version of WAVEWATCHIII 4.18 with two different configurations, ST2 and ST4 forced by sea surface winds of JRA-55. The mean and extreme significant wave heights show good agreement with observed data by buoys and satellite altimeter. The results of wave hindcasts based on JRA-55 performs better than existing wave reanalysis as ERA-40 and ERA-interim. The extreme value analysis for wave heights are agree with observed data in the mid-latitude except active tropical cyclone regions.
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  • Hirokazu NONAKA, Masataka YAMAGUCHI, Kunimitsu INOUCHI, Mikio HINO, Yo ...
    2015 Volume 71 Issue 2 Pages I_109-I_114
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     A wave hindcasting system, which consists of one hourly MSM(meso-scale model)-based sea winds distribution data set with high space-time-resolution provided by JMA(Japan Meteorological Agency) and the third generation wave model SWAN developed by Booij et al.(1999) or the second generation wave model YH3 developed by Yamaguchi et al.(1984) is applied to the wave estimation in the Japan Sea for each of the 8 selected intense low pressure systems over the period from 2003 to 2012. The comparison between hindcasts and measurements for the time variations of wave heights and for those of wave periods at many stations deployed along the coastal areas of not only Japan but also Korea facing the Japan Sea is conducted respectively and both the wave heights-based and wave periods-based error statistics such as correlation coefficient and mean slope value in a correlation diagram for each storm are obtained. In the end, a spatial distribution of the largest value HmaxM in the 7 storm-dependent maximum wave heights is investigated. The main results are summarized as follows; 1)the system has a significant ability for reproducing not only remarkably severe wave conditions in the Japanese coastal areas of the Sea but also swell-like high waves in the eastern coastal areas of Korea except for the December, 2003 storm case with less accurate estimates of winds, 2)the SWAN-based system with its near-latest version reveals a slightly better accuracy than the YH3-based system, 3)the estimate of the largest maximum wave height HmaxM, which is extracted at every grid point from the 7 cases of a storm-generated maximum wave height HmaxM is over 13 m in the offshore area of the Tohoku region of Japan and more than 9 m in the northern offshore area of the east coast of Korea.
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  • Yoshio HATADA, Ryutaro YANO
    2015 Volume 71 Issue 2 Pages I_115-I_120
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     Taylor diagram was tested to investigate accuracy of wave hindcasted results in Tokyo Bay, Ise Bay and the Seto Inland Sea. This diagram is illustrated in polar coordinates with correlation coefficient for azimuthal direction and ratio of standard deviation σcal.obs. for radial direction. Pattern correspondence of a time series between hindcasts and measurements of a storm is plotted on a diagram. Hindcasted significant wave heights, wind speeds and directions are compared with measurements over 10-120 storms at 30 sights. The results are summarized as follows: 1) A storm case with low accuracy of hindcasting is found with ease using this diagram. 2) Accuracy of hindcasts at inland sights are higher than those of sights facing open sea in Tokyo Bay. A systematic difference between inland sights and sights facing open sea is not seen in Ise Bay and the Seto Inland Sea. 3) Hindcasting accuracy is higher at Ise Bay sights than the Seto Inland Sea sights, and that of Tokyo Bay is higher than Ise Bay. 4) Taylor diagram has become a useful tool for evaluation of accuracy of the wave hindcastings.
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  • Kohei UCHIYAMA, Koji KODAMA, Masaru MIZUGUCHI
    2015 Volume 71 Issue 2 Pages I_121-I_126
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     Long waves in shallow water are known to be one of the causes of the coastal disasters such as overtopping, coastal erosion, and so on. We made an attempt to theoretically elucidate the relationship between the wave height of incident long waves near the shoreline and the wave properties of offshore waves on the basis of experimental data. We show that the wave period of short waves have no effect on the separation of bound and free long waves at the wave breaking point, and wave height of incident long waves observed near the shoreline (after breaking) is proportional to bound long waves at wave breaking point. Finally, we devised a semi empirical relation between the incident long wave height and the offshore wind wave height and period.
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  • Kojiro SUZUKI, Yukitomo TSUBOKAWA
    2015 Volume 71 Issue 2 Pages I_127-I_132
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     The sea surface currents induced by the storm surges and the seiches in Tokyo Bay were investigated using HF radar data. According to the tide data at Harumi, the number of storm surges larger than 50 cm was 15 from 2005 to 2014. Among these surges, the number of seiches larger than 10 cm was 8 (53%). The period of these seiches was 6-7 hrs. Using harmonic analysis, residual current was obtained from HF radar's sea surface current data. The phase of residual current is 2 hrs earlier than that of the seiches. Therefore, it is possible to predict the occurrence of the seiches 2 hrs in advance from HF radar's data. The seiche has the characteristics of the damped oscillation whose minimum and maximum peaks ap-pear much earliear than those of the undamped oscillation.
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  • Shunpei MATSUO, Toshiyuki ASANO
    2015 Volume 71 Issue 2 Pages I_133-I_138
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     Every early spring, west coasts of Kyushu have suffered from meteo-tsunami disaster locally called “Abiki”. The generation and development of meteo-tsunami is governed by barometric wave - ocean surface wave resonance when both moving speeds nearly coincide. This study has conducted wide range numerical simulations and compared the results with the observed secondary undulations for the greatest class meteo-tsunami event occurred in February, 2009. When the barometric waves propagate from exact eastwards, the numerical results are found to reproduce the order of the occurrence and the magnitude of the observed meteo-tsunamis pretty well. If the propagation direction shifted only 10 degree from the west to south-east wards, the significant refraction effect by the deep area of Okinawa trough arises, as the results, the numerical results do not explain the order of the occurrence of the observation results.
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  • Kanako HASUMI, Yukinobu ODA, Takahide HONDA
    2015 Volume 71 Issue 2 Pages I_139-I_144
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     It is reported that long-period waves with more than 30s wave period sometimes cause interruptions in marine works. The long-period wave could be induced by a typhoon, and the relations between long-period-waves and typhoons were examined. In this study, three parameters, maximum wind speed and ra-dius of strong wind area of a typhoon and propagation distance between typhoon location to observation point, were investigated as the dominant parameters to the long-period wave height at the observation point, and the estimation model of long-period waves were proposed. In the analysis, the propagation times from the typhoon location to the observation point were taken into account. As a result, the strong relation between the long-period waves and the three above-mentioned parameters was confirmed by con-sidering the propagation time. Among the three parameters, the propagation distances affect to the long-period waves the most. The possibility that long-period waves can be estimated with the three above-mentioned parameters was presented.
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  • Kenta SATO, Shunichi KOSHIMURA
    2015 Volume 71 Issue 2 Pages I_145-I_150
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     Lattice Boltzmann Method (LBM) has been developed as a new, robust and efficient model to solve the fluid dynamics. In this study, we stabilize LBM on free surface flows applying incompressible model which is simple low cost. The model was verified in the dam-break flow experiment over a 3-D isolated block. The model results are in good agreement with the experimental data, including the movement of free surface of water body, and splash against the block. Through the model verification, we found that our model can be applied to simulate three dimensional behavior of tsunami inland penetration.
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  • Souki FUKAZAWA, Yoshimitsu TAJIMA
    2015 Volume 71 Issue 2 Pages I_151-I_156
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     While numerical prediction of tsunami run up along the river is important for evaluation of expanded risks of inundation from the river, verifications of the models are not yet sufficientlty conducted due to lack of the detailed data. Video footage of tsunami running up along the Kido river under the 2011 Tohoku Earthquake Tsunami indicated that widely-used tsunami runup model tends to underestimate observed runup speed of tsunami along the river. This study analyzed the influence of numerical discretization schemes on tsunami run-up velocity. The case study of the experiment of bore wave showed that non-conservative schemes tend to underestimate the runup speed of tsunami bore while conservative ones yield reasonable predictive skills. Similar trend was also observed in the case study of 1 dimensional river run-up and indicates the importance of choince of numerical scheems for predictions of runup speed of tsunami along the river.
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  • Makoto NEMOTO, Tadashi KITO, Masaki OSADA, Kenji HIRATA
    2015 Volume 71 Issue 2 Pages I_157-I_162
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     The 2011 Tohoku earthquake (M9.0) generated a huge tsunami and its tsunami waveforms were recorded at the huge-tsunami meters deployed by the Japan Meteorological Agency (JMA) along the Pacific coast of the Tohoku region. Relatively short-period water oscillation was observed between the origin time and the arrivals of main tsunami waves. In this study, synthetic tsunami waveforms were calculated using horizontal crustal displacement of the neighboring ocean-bottom topography to explain the cause of the observed water oscillation. A comparison of observed tsunami waveforms and synthetic ones indicates that the observed water oscillation may be generated by the horizontal displacement near the Pacific coast in the Tohoku region due to faulting of the 2011 Tohoku earthquake. This result suggests that great earthquakes such as the 2011 Tohoku earthquake can produce such large crustal deformation near the coast and lead to tsunami near the coast just after the earthquake.
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  • Yuji KOZONO, Tomoyuki TAKAHASHI, Masaaki SAKURABA, Kazuya NOJIMA
    2015 Volume 71 Issue 2 Pages I_163-I_168
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     Tsunami flow and structures such as buildings interact with each other. Influence of buildings on numerical simulation of tsunami inundation was studied in this paper. The three kind of methods to consider the effect of building on tsunami flow were adapted in Kesennuma city where serious damage occurred by the 2011 Tohoku tsunami. By comparison of computed inundation with measured, the wave force threshold that causes building collapse and washed-away was determined. A simulation considering the collapse of the building by using the threshold showed the influence of buildings washed-away is necessary to simulate accurate tsunami inundation.
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  • Takuya MIYASHITA, Nobuhito MORI, Daniel COX, Tomohiro YASUDA, Hajime M ...
    2015 Volume 71 Issue 2 Pages I_169-I_174
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     The 2011 Tohoku Earthquake Tsunami showed complex behavior especially in urban areas. To minimize casualties and damage from future events, simulations that can understand the local behavior are required. This study examines a series of numerical simulations by quasi-3D model and 2D model to estimate characteristics of surface elevation and velocity of tsunami in a real city condition. The quasi-3D model agreed well with the experiment on the strait street from shorelines, but it differed with the experimental data at the points behind buildings. The 2D simulation tended to be smaller in comparison with the quasi-3D model because 2D model allows friction to be vertically uniform. There can be large differences of the inundation area between the 2D and quasi-3D models.
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  • Ryo YOSHIKAWA, Taro KAKINUMA, Aya OYAMA, Tsunakiyo IRIBE, Shoichiro YO ...
    2015 Volume 71 Issue 2 Pages I_175-I_180
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     Numerical simulations using an MPS method have been generated to study tsunamis due to a landslide or a sector collapse. In the cases the initial position of the fluid, which falls down a slope and flows into the water, is the same, the tsunami height becomes larger as the density of the fluid is larger, although the tsunami height is not so large when the fluid changes the shape to a flat form on the slope before flowing into the water. On the other hand, in the cases the falling object is a rigid body, the tsunami height becomes larger as the initial potential energy of the rigid body is larger, though the tsunami height is not so large when the wave holds a bore at its front in the propagation after showing a plunging wave. If the specific gravity of the falling fluid is one, the tsunami height near the shore becomes larger as the offshore still water depth is shallower, while in the case the density of the falling rigid body is larger than that of the water, the tsunami height near the shore becomes larger as the offshore still water depth is deeper.
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  • Daiki MATSUI, Tatsuhiko UCHIDA, Kento NAKAMURA, Atsushi HATTORI, Shoji ...
    2015 Volume 71 Issue 2 Pages I_181-I_186
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     For simulation of tsunami run-up in rivers and inundation, a numerical computation method which can evaluate three dimensional flows is required to simulate several phenomena integrally. In this study, we developed a non-hydroststic quasi-3D tsunami simulation model based on the general BVC method, newly considering the unsteady term of vertical velocity and the vertical pressure gradient term on water surface. First, the present model was applied to the tsunami run-up experiments. The model was validated through the comparisons with the experimental results. Then, we applied it to the 2011 Tohoku Tsunami in the Kitakami River. Altough calculated water levels were higher than observed ones, the model reproduced water levels of tsunami traces and the arrival time.
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  • Takumi OSHIRO, Eizo NAKAZA, Kento INAGAKI, Md. Mostafizur Rahman, Syo ...
    2015 Volume 71 Issue 2 Pages I_187-I_192
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     The 3.11 Tohoku-region huge tsunami revealed that the canal and coastal forest barriers acted to reduce velocity and delay the arrival time of tsunami. However, since most of the trees in the coastal forest were knocked down and displaced by the tsunami, the integrated barrier functions of coastal forest and canal against tsunami have not been thoroughly understood. The main purpose of this experimental research is to ensure the function of a canal as a barrier against tsunami, by placing the canal ahead of the vegetation. The results show the efficient composite effects of both a canal and vegetation. For example, tsunami arrival time was delayed, heigt of reflected tsunami was increased, transmited discharge by tsunami was decreased.
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  • Eizo NAKAZA, Ryo TOKUYAMA, Kento INAGAKI
    2015 Volume 71 Issue 2 Pages I_193-I_198
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     After explaining the overview of characteristics of each of the huge tsunami boulders scattered in the southwestern islands, their original positions have been estimated in field surveys. Despite the existing views that seven major tsunami events occurred historically, the results show that only the Meiwa tsunami had affected the region. These discussions are in conjunction with the findings in excavation surveys by Nakaza. By experimentally examining the movement mechanisms of these giant tsunami boulders, it is shown that the generation of a shock wave pressure may cause the failure of a coastal cliff to break off into massive boulders, which are then drawn away from their original location after being fully submerged by the tsunami inundation depth.
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  • Sota NAKAJO, Hideyuki FUJIKI, Sooyoul KIM, Nobuhito MORI, Yoko SHIBUTA ...
    2015 Volume 71 Issue 2 Pages I_199-I_204
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     By using about 80 years historical data of tropical cyclone which passed through near Tokyo Bay area, this paper has estimated the potential of extreme storm surge event. Temporal variation of minimum central pressure and translation speed of along tropical cyclone tracks which will cause severe storm surge event has been determined from envelope curve of historical data, although tropical cyclone tracks themselves were assumed to same to those of original. Physical process of storm surge was simulated by the nonlinear shallow water equation. As a result, expected maximum storm surge at Tokyo was estimated about 1.8 m. This study clarified that northward cyclone tracks are especially dangerous for Tokyo bay because wind induced surge, rapid wind direction change, and harbor oscillation affect significantly.
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  • Shin-ichi AOKI, Tomokazu INUI, Tomoya ISHINO
    2015 Volume 71 Issue 2 Pages I_205-I_210
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     The typhoon No. 0918 yielded large storm surge in the head of Mikawa Bay. The departure was almost the same as the record by the Isewan Typhoon (Typhoon Vera) in 1959. Based on the authors' research, the key factors to the development of large departure in Mikawa Bay are the preceding strong east wind which gives large wind setup in Ise Bay and quick change in wind direction from east to west which causes water mass transport into Mikawa Bay as a free long wave.
     In this study, the development mechanism of such a large storm surge was investigated based on the numerical simulations using a typhoon model for the recent three events of storm surge. The typhoon model tended to predict large wind speed after the typhoons passed over the bay. The calculated departure showed lower wind setup in Ise Bay compared with the observed one, which does not enhance wave propagation from Ise to Mikawa bays after the inversion of wind direction. A simple 2D analysis indicates that the density stratification may increase wind setup in Ise Bay.
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  • Yusuke UCHIYAMA, Hiroaki TADA
    2015 Volume 71 Issue 2 Pages I_211-I_216
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     Typhoons alter the upper ocean dynamics and thermal structure, giving rise to feedback on the atmosphere. Intense ocean surface wind and barometric effects induce rough waves and storm surges that occasionally cause severe coastal disasters. For rigorous oceanic modeling under typhoon conditions, we implement the inverse barometer effect and the COAMPS bulk formula into ROMS. A submesoscale eddypermitting oceanic modeling is configured at a horizontal resolution of 2 km based on the JCOPE2-ROMS downscaling system forced by the JMA GPV-MSM atmospheric reanalysis. A retrospective, synoptic reanalysis is carried out with a particular focus on the two consecutive super typhoons Phanfone (#1418, Category 4, the lowest pressure was 935 hPa) and Vongfong (#1419, Cat. 5, 900 hPa) in the fall 2014. These typhoons abruptly amplify the volume outflux from the Seto Inland Sea (SIS) at the Bungo Channel, leading to the pronounced counter-clockwise circulation that opposes the clockwise overall SIS circulation under the normal condition. The model also successfully reproduces increased eddy kinetic energy below the typhoons with intense cyclonic positive vorticity driven by torque of the wind stress curl, not only at surface but also at depth down to about 100 m deep. These cyclones are cold-core mesoscale eddies with SST decrease by about 3°C associated with prominent mixed layer deepening.
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  • Tetsuya TAKESHITA, Katsuyuki SUZUYAMA, Yoshio SUWA, Kazuki HIMENO
    2015 Volume 71 Issue 2 Pages I_217-I_222
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     In Japan, storm surge hazard maps were made in some areas. But only few attempts had so far been made at the estimation of storm surge inundation depending on several typhoon scales and the consideration of lead time in order to evacuate from the typhoon. The purpose of this study is to estimate storm surge inundation corresponding to typhoon scales and intensities announced by the Japan Meteorological Agency and to consider the lead time for evacuation at the Tokyo Bay area and its surrounding area.
     As a result, the assumption typhoon which had a central atmospheric pressure of 910 hectopascals and was called “the Muroto typhoon grade” corresponded to “a very strong typhoon”. The typhoon's inundation became larger than any other typhoon scales of this study. The radius of the maximum cyclostrophic wind speed was the longer, a typhoon course which had the highest tidal level was the more westerly. Sequential wind velocity distribution was made in the process of the estimation of storm surge inundation. Using the wind velocity distribution, the arrival time of the strong winds area more than wind velocity 15 m/s was calculated as information to help setting of the refuge completion time.
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  • Sooyoul KIM, Yoshiharu MATSUMI, Yujiro IZUTA, Hajime MASE, Nobuhito MO ...
    2015 Volume 71 Issue 2 Pages I_223-I_228
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     In the present study, we examine and develop storm surge forecasting models at Sakai Minato and Hamada using artificial neural network (ANN). The storm surge forecasting model aims to forecast a time series of surge levels with the 3 hrs to 30 hrs leadtime ahead every 3 hrs interval at one station. For training data, we gathered the five historical typhoons and their data, which are storm surge levels, sea level pressures, depression rate of sea level pressures and typhoon positions. In addition, those were collected from storm surge simulations using projected typhoons under the past and future climate change experiment. In order to investigate the accuracy of the forecasting models, we changed the number of hidden units in the ANN from 13 to 130 with every 13 interval. We showed that the 30 hrs forecasting model can predict a time series of storm surge levels with the correlation coefficient of 0.97 and the root mean square error of 0.029 m.
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  • Kentaro IMAI, Yuta HIRAKAWA, Shunsuke AITA, Yuta MITOBE, Tomoyuki TAKA ...
    2015 Volume 71 Issue 2 Pages I_229-I_234
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     The tsunami deposit is tend to be preservable in a coastal lake. In this research, the hydraulic experiment on tsunami rushing into a coastal lake was carried out with fixed bed condition.
     The experimental results showed that hydraulic jump occurred according to inundated flow flooding into the lake, and the state of flow changes complicatedly with the lapsed time. The changing flow state was depending on a lake scale. Furthermore, the water level and the flow velocity on the bottom became maximum near the dune back, and the maximum flow velocity was decreased when lake depth deeper. The results could give important knowledge for the depositional process of tsunami deposit in a coastal lake.
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  • Yuta MITOBE, Kentaro IMAI, Yuta HIRAKAWA, Shunsuke AITA, Tomoyuki TAKA ...
    2015 Volume 71 Issue 2 Pages I_235-I_240
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     Understanding of characteristics of morphology change induced by tsunamis is necessary for estimation of magnitudes of historical tsunamis. In this study, morphology change in coastal lakes caused by tsunami intrusion is discussed through a hydraulic model experiment. A horizontal open channel with 1/100 model of a coastal lake was used for a movable bed experiment. Temporal variation of bed shapes under dam-break flow is extracted from video images recorded from the side by a high-speed camera. And three dimensional bed shapes before and after the experiment are measured by an image measurement technique to get horizontal distributions of bed level changes. In this technique, object surfaces under color dot illumination from a PC projector are recorded by a digital camera, and three-dimensional coordinates of the color dots reflected on the surfaces are determined with geometrical relationship between the camera and the projector.
     Local scour was developed around seaward end of the lake model by the dam-break flow in all cases. While the erosion was limited in the area near the seaward end of the lake, deposition was observed in wider area behind the scour. With higher wave condition, the scour behind the mound was deeper and wider. While the deposition area behind the scour was also wider with the higher waves, maximum thickness of the deposit layer was smaller. It is found that a rate of increase of the scour depth is almost same among the cases with different wave conditions and hense duration of higher velocity is more important factor to increase the scour depth.
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  • Tatsuki IIDA, Shuichi KURE, Keiko UDO, Akira MANO, Hitoshi TANAKA
    2015 Volume 71 Issue 2 Pages I_241-I_246
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     The 2011 Tohoku Tsunami left many spots of deep and wide scouring near coastal structures such as levees, tidal gates, buildings, etc. The scouring caused major damage to the structures. There are two known scouring mechanisms; erosion by bottom shear stress and liquefaction by pore-pressure. The former is established; however, the latter has not been quantified. We advanced a quasi-3D numerical model by a finite volume method to simulate the flow and sediment transport. Temporal and spatial porepressure calculation under the ground was newly developed to find liquefaction. We applied the model to the breached spot of the coastal levee at Fujituka on the Sendai Bay Coast where the levees with gaps were assumed as the initial condition. We found the depth of liquefaction reached 28% of the maximum erosion depth by the bottom shear stress. We concluded that although erosion by the shear stress is the major process, liquefaction by the pore-pressure is also significant.
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  • Kentaro IMAI, Daisuke SUGAWARA, Tomoyuki TAKAHASHI, Shunji IWAMA, Hito ...
    2015 Volume 71 Issue 2 Pages I_247-I_252
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     A large-scale topographical variation occurred in Kitakami river mouth due to the 2011 Tohoku-oki earthquake tsunami. Land use is often developed in river mouth areas in Japan. As a variation by tsunami can be a factor of impediment to post-disaster recovery and reconstruction, it is important to clarify the process of a topographical change by tsunami in river mouth area.
     In this research, numerical simulations for tsunami sediment transport were carried out in Kitakami river mouth and the numerical results explain that 1) the erosion of the sandbar near the river mouth was proceeded by tsunami run up, 2) sediment was deposited in rice field of upper stream, and 3) sediment transport close to offing of the river mouth was caused by tsunami back wash.
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  • Takayuki OIE, WANG Dong, Takeshi TAKATANI, Kazuhiro ARAKI, LI Shaowu ...
    2015 Volume 71 Issue 2 Pages I_253-I_258
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     At The 2011 off the Pacific coast of Tohoku Earthquake, many seawalls were damaged by Tsunami overflow. Some previous studies indicated that if the foundation of structures was scoured, the stability of structures seriously declined, but the relationship between scouring depth and overflow hasn't been well understood and prediction method hasn't also established. In this study, the scouring depth caused by tsunami overflow was calculated by using numerical simulation based on accurate ISPH method and the results were compared with the physical model tests. The results of this study are as follows; 1) There is a high proportional relationship between scouring depth and the overflow depth, 2) The scouring behind the seawall can be reproduced and the maximum scouring depth can be evaluated by accurate ISPH method.
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  • Tomoyuki TAKABATAKE, Yukinobu ODA, Kazunori ITO, Takahide HONDA
    2015 Volume 71 Issue 2 Pages I_259-I_264
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     When tsunami comes to seaside industrial areas, sea water will come into water channels and the sur-face of water will go up. If water surface reaches ceilings of the water channels, pressure will act on the ceilings. In this study, characteristics of the pressures and its evaluation methods are investigated through hydraulic experiments and numerical simulations. Experimental results show that when air is enclosed between the water surface and the ceiling, the maximum impulsive pressure becomes lower compared with the case where water surface touches directly the ceiling. The existing methods, usually used to estimate uplift pressures on bridge decks, are tested against experimental data. It is found that although the methods require some modifications, the maximum impulsive pressure can be estimated relatively well by using the methods. Furthermore, experimental results are compared with the simulation results from OpenFOAM. The comparisons show that OpenFOAM can successfully simulate the experimental results.
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  • Sohei MARUYAMA, Tomotsuka TAKAYAMA, Kenichiro SHIMOSAKO, Akihiko YAHIR ...
    2015 Volume 71 Issue 2 Pages I_265-I_270
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     A series of hydraulic model experiments were performed to verify the effect of armoring concrete blocks on the tsunami pressure reduction in the state of soliton fission. Applicable ranges for Tanimoto and modified Tanimoto formulas of wave pressure acting on a caisson have been determined in terms of the ratio of tsunami height for water depth. The estimation formula for the tsunami pressure reduction factor of the armoring blocks was proposed in the result of the comparison of tsunami force between the states without and with the armoring blocks. The calculated tsunami forces acting on the caisson armored with the blocks well agree with the corresponding experimental ones. The sufficient stability of the armoring blocks against the tsunamis has been confirmed by the experiments.
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  • Yukari FUKUSHIMA, Kenji EBISU, Sota NAKAJYO, Takaomi HOKAMURA, Gozo TS ...
    2015 Volume 71 Issue 2 Pages I_271-I_276
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     This work aims to investigate the impact of a surge-like wave front on urban structures by performing physical experiments. Flume experiments are being conducted to test the hydrodynamic impact of surge on urban structures, with a particular interest to assess the role of an embankment-like structure in reducing hydrodynamic loadings. Since the onshore wave front induced by a tsunami or storm surge commonly propagates as a hydraulic bore, its hydrodynamic features are similar to those of a dam-break flow. Therefore, it is feasible to use a dam break to mimic an onshore tsunami or surge wave in laboratory, which is much straightforward to be implemented in practice. The laboratory measurements provide data for understanding the physics of the underlying processes of surge-structure interaction and for validating numerical tools.
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  • Song HEO, Yoshinori SHIGIHARA, Tsuyoshi TADA, Kenjiro HAYASHI
    2015 Volume 71 Issue 2 Pages I_277-I_282
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     We performed hydraulic experiment of a number of vessels drifting and stranding by tsunami and analyzed drifting tendencies of vessel. Also we verified the accuracy of the numerical model. In the hydraulic experiment, we founded the existence of certain patterns of drifting by initial position of vessels, furthermore we confirmed that there were variability caused by complexity of flow and collision between vessels.
     We investigated the influences due to difference of the numerical model of vessel drifting, based on the rigid model, about drag and inertia forces acting on objects. When evaluating the drift of certain vessels, we have to use drag forces model considered the flow velocity distribution; on the contrary when evaluating the diffusion status of the whole vessel, influence by the difference of the model is small. Also we founded that it is necessary to consider the bottom friction in reproduction of stranding. From the above results, except the case caused by grater uncertainty, it was shown that it is possible to evaluate the drift of vessels and range of strand by the rigid model when the tsunami occurred.
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  • Kazuya NOJIMA, Masaaki SAKURABA, Yuji KOZONO
    2015 Volume 71 Issue 2 Pages I_283-I_288
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     This paper presents the proposal of an applicative tsunami wreckage simulation with the capture effect by using the tsunami barrier. For the presented study, the tsunami wreckage simulation and damage estimation of Genroku Kanto Quake was carried out. The validity of applicative damage estimation for tsunami wreckage was presented in this paper.
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  • Yuuki KIMURA, Takenori SHIMOZONO, Shinji SATO
    2015 Volume 71 Issue 2 Pages I_289-I_294
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     Severe devastation by the 2011 Tohoku Tsunami highlited the importance of a robust and redundant coastal dike against a low-frequency extreme tsunami. To discuss its effectiveness, we need to clarify how coastal dike failure affects damages in its hinterland at the occurrence of significant overflows. The paper presents results of case studies of the 2011 tsunami event in which the impact of dike failure is analysed using a high-resolution flood simulation at two sites with different topographic features. The dike failure significantly increases flood intensity and thereby human and bulding damages on a vast coastal plain of the southern Sendai coast, while its impact is relatively small in narrow low-lying areas of Otsuchi located on ria coast. The model results describe flood impacts better when the dike failure is accounted for in the southern Sendai coast. We also analyse local scouring behind coastal dikes which may trigger the dike failure and show that it can be related with local flow velocity from the high-resolution flood model.
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  • Tomohiro YASUDA, Takuma MARUYAMA, Katsuichiro GODA, Nobuhito MORI, Haj ...
    2015 Volume 71 Issue 2 Pages I_295-I_300
    Published: 2015
    Released: November 10, 2015
    JOURNALS FREE ACCESS
     In 2012, the Central Disaster Management Council of the Cabinet Office proposed 11 slip distributions (scenarios) of the future Nankai Trough Earthquake. However, since only one critical scenario is defined for each region, it is difficult to evaluate the uncertainty of tsunamis. In this study, we develop stochastic slip distributions to explore a wide range of possible tsunami scenarios for the Nankai Earthquake. A series of procedure, i.e. stochastic slip generation, initial tsunami profile determination, and numerical simulation of tsunami propagation, is defined as stochastic tsunami model. The simulated tsunamis are basis to assess uncertainty and variability of tsunami wave profiles and characteristics. As a case study, two regions (Wakayama and Kochi) are focused upon for tsunami hazard assessment. The results indicate that the maximum tsunami height at a specific location is sensitive to the details of the tsunami sources and the dispersion of the maximum tsunami height is significant. The earthquake slip distribution also affects the time of tsunami arrival greatly. Therefore, it is important to take into account tsunami source uncertainty in developing tsunami hazard maps for coastal cities and towns in Wakayama and Kochi.
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