Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering)
Online ISSN : 1883-8944
Print ISSN : 1884-2399
ISSN-L : 1883-8944
Volume 74 , Issue 2
Showing 1-50 articles out of 248 articles from the selected issue
Paper
  • Shino SAKAGUCHI, Keisuke NAKAYAMA, Thuy Thi Thu VU, Katsuaki KOMAI, Pe ...
    2018 Volume 74 Issue 2 Pages I_1-I_6
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     It was revealed that a solitary wave is highly reproduced by using Fully-nonlinerar and strongly Dispersive Surface wave equations (FDS equations) comparing with theoretical solutions. Furthermore, we improved the FDS equations by expanding velocity potential into a series of a power function of zμ instead of z. Dispersion relationship computed by the improved FDS equations agreed very well with the theoretical solution when we gave the number of expansion terms as 3 with μ=2. Also, we applied the improved FDS equations to a wave field over a bump. As a result, the improved FDS equations was found to reproduce time series of wave height and velocity of the laboratory experiments.
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  • Naoto HIGUCHI, Katsuya HIRAYAMA, Junya NAGANUMA
    2018 Volume 74 Issue 2 Pages I_7-I_12
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Because the ship waves generated by large ship navigation in a harbor may affect safe navigation and efficient cargo handling of small ships, they must be estimated in a harbor tranquility analysis. In this study, ship waves are generated through straight and curved navigation channel in an experimental horizontal shallow basin in order to verify calculation results reproduced by using a ship wave generation model expanded for setting horizontal 2D ship navigation channels. The ship shape approximated with the Lewis-form can reproduce wave profiles and maximum wave heights for various depth Froude numbers Fh, though it with the parabolic function overestimates except for Fh = 0.8 or less. On the other hand, both models tend to overestimate maximum wave heights generated by turning ship in outside of navigation channels. Therefore, improvement of the expanded ship wave generation model may be required in near future, considering the difference of ship waves generated inside and outside of turning ship.
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  • Yashiro AIDA, Katsuya HIRAYAMA
    2018 Volume 74 Issue 2 Pages I_13-I_18
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     In calculation of motions and forces of ship moored to a berth equipped in an oceanic island which is surrounded by much steep bathymetry from deep to shallow water, directional spreading and nonlinearity of offshore wave should be taken into account because the berth is not sheltered from them. In order to realize such calculation, a modeling of moored ship motions is conducted with expanding the CADMAS-SURF/3D, which is one of the computed fluid dynamics (CFD), to both the generation of deformed multi-directional irregular waves and the consideration of moored arbitrary shaped floating body. In this study, a coupling the CADMAS-SURF/3D with the NOWT-PARI, which is one of the Boussinesq-type wave transformation model, is conducted in order to reduce the calculation capacity and generate the deformed multi-directional irregular waves in the expanded CADMAS-SURF/3D. In this model, The moored floating body is expressed with porous media and moved by buouancy, mooring and external nonlinear wave forces.
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  • Yoshinao MATSUBA, Takenori SHIMOZONO, Yoshimitsu TAJIMA
    2018 Volume 74 Issue 2 Pages I_19-I_24
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     We constructed a 1-D Boussinesq model to reproduce previously observed infragravity waves developed on a barred beach on Hiratsuka Coast. We applied pressure gradient at sea surface for detection of wave-breaking and introduced numerical viscosity satisfying TVD condition to represent wave attenuation by wave-breaking. This model showed good agreements with both experiments and the observations. Modeled cross-shore distribution of wave spectra suggested development of long standing waves whose amplified frequency components had nodes/antinodes above the bar. We also confirmed gradual infragravity wave development which was inferred from the field observations.The model results suggested that 3rd order nonlinear interacton gives unignorable impacts on the development around the sand bar.
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  • Naoto OCHI, Taro KAKINUMA, Keisuke NAKAYAMA
    2018 Volume 74 Issue 2 Pages I_25-I_30
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     The internal solitary waves propagating from deep water to shallow water in the two-layer fluids, were numerically simulated by solving the set of nonlinear equations in consideration of both strong nonlinearity and strong dispersion of waves. The BO solitons propagated into the shallow-water regions, generating the KdV solitons, the characteristics of which depended on the positional relationship between the interface and the critical level. When the interface of the static internal waves was below the critical level in the shallow-water region, the disintegration of the internal solitary waves occurred remarkably. The wave height decreased when the internal wave traveled through the deep region after passing the shallow region.
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  • Yutaro NAKANISHI, Keisuke NAKAYAMA, Yasuyuki NAKAGAWA, Hirotada MOKI, ...
    2018 Volume 74 Issue 2 Pages I_31-I_36
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Seagrass in the shallow water areas are revealed to absorb large quantities of CO2 from the Earth's atmosphere, capture the carbon and store it at the sea bottom. Previous studies have demonstrated that coastal blue carbon ecosystems accumulate about 55 % of total capture of CO2 in the atmosphere due to photosynthesis. However, because of the complexities of the interaction between seagrass and flow field, it is difficult to clarify CO2 transport around seagrass. Therefore, this study aims to develop a new object-oriented seagrass model by taking into account the interaction between seagrass and flow field. As a result, we revealed residual current around seagrass meadows.
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  • Tetsuya KAKINOKI, Gozo TSUJIMOTO, Riki ISHIHARA, Tokuzo HOSOYAMADA, Da ...
    2018 Volume 74 Issue 2 Pages I_37-I_42
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     At the heavy rain in northern Kyushu in July 2017, a large number of reservoirs were damaged, and they were destroyed. Even in the sea area, lakes and reservoirs, waves are generated by sediment inflow due to slope collapse. The wave may cause damage to surrounding structures and people. Inflow sediments due to heavy rain into a sea area or a reservoir forms huge waves that cause serious disasters. Many laborator experiments and numerical simulations of water waves due to landslides have been carried out in order to clarify the process of wave genertion. However, there are a few studies which analysis of water waves due to inflow sediments into a small area of water. In this study, model experiments of debris flow were conducted in a two dimensional flume and numerical model based on shallow water equations integrated with the water depth have been performed in order to clarify the hydraulic characteristics of the waves. In conclusion, the experimental study has demonstrated that the flowing form of inflow sediments and the distributions of the flow velocity are not spatially uniform. It is found that the numerical results agree with the experiments by considering interface resistance between the inflow sediments layer and the water layer and Reynolds stress.
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  • Hiroyuki IKARI, Hitoshi GOTOH, Yuji KOBAYASHI, Kouta KONISHI
    2018 Volume 74 Issue 2 Pages I_43-I_48
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     This paper presents a numerical simulation of dumping sand in underwater from a split hopper barge using Incompressible SPH method. In the model, the defomation of sand media is calculated based on the constitutive law of an elastoplatic body, however, an isolated sand particle gives suspended sediment concentration to ambient fluid particles. The transport of suspended sediments is calculated using an advection-diffusion equation. The model is validated in comparison to previous experimental results associated with the deposition shape. The calculated results show good agreement with experimental ones.
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  • Badarch AYURZANA, Tokuzo HOSOYAMADA
    2018 Volume 74 Issue 2 Pages I_49-I_54
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     A novel free surface numerical calculation scheme based on LBM and immersed boundary method is developed as the numerical wave channel. The method is applied to wave–structure interaction and estimation of wave forces acting on a compsite type breakwater. Wave–breakwater interactions such are wave overtopping and transmission, and wave forces on the breakwater are analyzed with the method. The numerical scheme is extended to seepage flows in the rubble foundation. The results of wave forces and wave pressure distribution calculated in the numerical wave channel agreed well with those of Goda's formula even in wave-breaking condition, confirming that the proposed numerical model has a high potential applicability to estimation of wave action toward complex shape of breakwaters.
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  • Yuta MITOBE, Jun OCHIAI, Hitoshi TANAKA, Nguyen Xuan TINH, Shunsuke AI ...
    2018 Volume 74 Issue 2 Pages I_55-I_60
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     In order to obtain further understanding on the temporal variation of bottom boundary layer and bed shear stress under tsunami waves, hydraulic experiments on flow structures and boundary layer development under turbulent bores were conducted. PTV was applied to obtain 2D vertical distribution of velocity. Initial water depth in the channel was set as 0, 1, 3, and 5 cm to investigate different flow motion and process of boundary layer development under the bores. While wave forms measured in the same conditions show good repeatability, 3D turbulent structure near the surface induced difference of the values and phases of velocity measured in the surface layer. Higher momentum and turbulence are gradually transported to lower layer under still water level. Shear velocity estimated from the vertical profile of the horizontal velocity has a peak after the arrival of the bores and this peak cannot be explained by the law of resistance under steady flow.
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  • Soken KADOWAKI, Yasunori WATANABE
    2018 Volume 74 Issue 2 Pages I_61-I_66
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     This paper presents interface renewal processes of droplet impacts and the resulting interface transport on the basis of phase-field two-phase flow computations. Three-dimensional vortex structures organized with a vortex ring and vertical counter-rotating vortex pairs are formed in the both sides across the interface via a transient formation of surface cavity and concentric vertical jet. The interface boundary layer of the droplet is entrained in the vortices descending by self-induction effects, resulting in vortex-induced mass transport. This process may enhance exchanges of heat, gas and moisture across the water surface.
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  • Ayumi SARUWATARI, Ryota SAKAGAWA, Junichi OTSUKA, Yasuyuki BABA, Teruh ...
    2018 Volume 74 Issue 2 Pages I_67-I_72
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Whitecap coverage, marine aerosol concentration and air-sea heat exchange during storm events under fetch-limited conditions were investigated based on the field observation conducted at an offshore observatory in Tanabe Bay, Wakayama. Observed whitecap coverage and aerosol concentration under unsaturated wind waves were found to be smaller than that without fetch limitation. Vertical mixing in the surface layer associated with the whitecapping is shown to significantly affect the air-sea heat flux during a storm.
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  • Kent YAMASHITA, Yasunori WATANABE
    2018 Volume 74 Issue 2 Pages I_73-I_78
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     This paper presents mechanical effects of a sea-surface drag reduction under strong wind and the contribution of wind speeds and wave parameters to the reduction. The wind turbulent boundary layer flows over waves were computed and the drag actually acting on wave surface was calculated. They were found that distinctive vortex structures induced by wave conditions are developed with increase of wind speed and the drag change depends on the structures, and that there is a great difference between the actual drag and the drag from current models.
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  • Yoshiaki TANAKA, Yoshimitsu TAJIMA
    2018 Volume 74 Issue 2 Pages I_79-I_84
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     This study carried out laboratory experiments to investigate characteristics of the water surface fluctuation on the reef and to clarify how such water fluctuation on the reef affects the spatial distribution of the maximum runup height on the shore frtonted by a fringing reef. In the experiment, image-based analysis was applied to capture the spatio-temporal distributions of water level and shoreline location. Spectral analysis was performed on the obtained spatio-temporal fluctuations of the water level and on the time-varying shoreline profile. This result showed the clear evidence of the resonance not only in the cross-shore direction but also in the alongshore direction. The resulting long wave fluctuation, including the resonance, also showed strong correlation with the observed peak runup heights.
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  • Takatomo MIYAKE, Yoshiyuki UNO, Nobuyuki ONO, Toshiaki YUKIMARU, Toshi ...
    2018 Volume 74 Issue 2 Pages I_85-I_90
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     In Ibusuki port coast, a coastal improvement project is in progress applying the idea of integrated shore protection system combining jetties, offshore breakwaters, seawalls and beach nourishment. For the construction of these works, the local environment of the hot spring groundwater system named as “natural sand-steaming hot spring” should be carefully conserved, because that is an important tourism resource in the region. This study intends to estimate the impact of the beach nourishment on the hot spring groundwater. Comprehensive field observations continued for four seasonal periods on the groundwater levels and temperatures have been conducted to understand their fluctuating characteristics under the tidal motions. From the observation results of the groundwater levels and temperatures, their horizontal, vertical and temporal variations have been analyzed. The characteristic behaviors of the groundwater flows, such as a cold seawater mass penetrates into the hot groundwater flows during flood tide, a hot water mass seeps out on the surface of the sandy beach during ebb tide, have been confirmed.
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  • Yasuro OHTANI, Takaaki UDA, Yasuhiro OSAKI, Shingo NAGANUMA, Toshiro S ...
    2018 Volume 74 Issue 2 Pages I_91-I_96
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     The method developed by Lippmann and Halman, in which the imageries taken by a video or web camera are employed to observe water depth in the surf zone and the formation of a bar and trough, was applied to the observation around No. 29 artificial headland on the Hokota coast facing the Pacific Ocean. Typhoon No. 21 hit the coast with storm waves of H1/3 = 5.4 m, T1/3 = 15.4 s on October 23, 2017, and then calm wave condition continued. During this period, the direction of longshore channel, where longshore currents are developing, changed offshore to form a rip channel while cutting the bar, and a rip head was formed offshore of outer bar. Furthermore, it was found that a rip current always develops along the north side of No. 29 artificial headland because of its wave-sheltering effect.
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  • Takaaki UDA, Yasuro OHTANI, Shingo NAGANUMA, Yasuhiro OSAKI, Yasuhiro ...
    2018 Volume 74 Issue 2 Pages I_97-I_102
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Field investigation of rip current was carried out on the Hokota coast on November 29 and 30, 2017. Oblique photographs were taken from on top of sand dune. Also, photographs were taken using a drone from an elevation of 150 m above the surf zone together with tracing floats with a small GPS, which were thrown into the surf zone near No. 29 artificial headland. Wave field was calculated using the energy balance equation, and numerical simulation of nearshore current was carried out. The calculated flow pattern was compared with those measured. It was concluded that the development of rip currents in the area between artificial headland Nos. 29 and 30, and stationary development of rip current near No. 29 HL were successfully explained by numerical simulation.
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  • Takashi FUJIKI, Nobuhito MORI, Koji KAWAGUCHI, Fumikazu SUEHIRO
    2018 Volume 74 Issue 2 Pages I_103-I_108
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     As the spectral partitioning method, Wave Identification and Tracking System (WITS) developed for wave directional spectrum simulated by numerical wave model is widely used. In this study, we newly proposed spectral partitioning method based on Gaussian Mixture Model (Mixture). We validated the Mixture with the numerical simulation and presented that the Mixture showed the more accuracy on the partitioning of given spectrum than the WITS. We applied the Mixture to wave directional spectrum from two datasets, simulated by SWAN and in-situ observed, under typhoon condition. We confirmed the Mixture can detect only two or three peaks which can be interpreted as windsea and swell clearly, whereas the WITS tend to detect many peaks which seem difficult to interpret as practical wave systems rationally.
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  • Hitoshi TAMURA
    2018 Volume 74 Issue 2 Pages I_109-I_114
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     In this study, we propose a Swell Index (SI) to define the ocean swells quantitatively in the wave field. SI can be widely applied to decompose the measured wave spectra into windsea and swell components. Based on an analysis of wave fields in the Toyama bay, we show that the SI can clearly separate the swell energy from total one and the use of SI successfully explains the characteristic wave fields in the bay. We also examine wave ray pattern which is significantly modulated by the bottom-induced refraction. We conclude that SI is a useful metric to quantify the swells for practical purposes because of their simplicity and robustness.
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  • Ryusuke SAITO, Noriaki HASHIMOTO, Takashi FUJIKI, Koji KAWAGUCHI, Masa ...
    2018 Volume 74 Issue 2 Pages I_115-I_120
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     An upgraded submerged Doppler-type directional Wave Meter (DWM) can measure 31 wave quantities related to directional wave motions, i.e. water surface elevation, 3 components of water particle velocities at each layer of 10 different water depths ranging from shallow to deep. In this study, accuracy of directional spectrum estimation is investigated for various cases where directional spectra are estimated with various sets of different number of wave quantities measured with DWM. As a result, accuracy improvement is confirmed in some wave conditions when more quantities are applied to the estimations, compared with the cases where a few wave quantities are applied to the estimations. On the other hand, it was found that when the directional spectra are estimated by adding the water particle velocity components at the deep water depths, the energy concentration of the direction function tends to be estimated higher in proportion to the number of observation layers of the deeper water particle velocity components. Since this feature should be clarified in investigating characteristics of directional spectra observed with DWM, we will continue further investigation for morte accurate and reliable directional spectrum estimation.
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  • Toshikazu KITANO, Yuki UEDA, Kouta KANEZAKI, Wenpeng ZHAO
    2018 Volume 74 Issue 2 Pages I_121-I_126
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Overlap of several hazards: storm surge, high waves, river runoff and flood etc. accumulates risk and its prediction will become troublesome. The importance of statistical distribution of joint occurence is now increasing in disaster risk reduction plan, but it is hard to say that bivariate GP distribution has been developed for those applications. Though GP distribution requires a suitable threshold to extract the extremes of hazard magnituides, the methods of threshold choice has not enough discussed for bivariate extremes. This reserch focuses on the correlation coefficient of occurrence rates, whose efficiency is examined through the observed data of wind velocities at two cities in Germany.
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  • Tomoya SHIMURA, Nobuhito MORI
    2018 Volume 74 Issue 2 Pages I_127-I_132
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Long-term high-resolution wave climate hindcast around Japan based on JRA-55 was conducted. The hindcast shows the good agreement with observations. Wave climate around Japan is represented by average of wave spectrum. The variability of monthly wave spectrum was analyzed by principal component (PC) analysis. The winter first PC mode of the Japan sea side, the eastern Japan Pacific side and the eastern Japan Pacific side can be characterized by the magnitude of wave development, the fluctuation of swell propagating from east and the fluctuation of swell propagating from the Aleutian Islands, respectively. In summer, the typhoon-generated swell has significant impacts on wave spectrum climate. Using average of wave spectrum, the corresponding large scale atmospheric condition is easily understood.
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  • Nobuhito MORI, Tomoya SHIMURA, Risako KISHIMOTO
    2018 Volume 74 Issue 2 Pages I_133-I_138
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Monthly mean wave heights gives significant impact on coastal morphology, harbor usage and coastal construction management. The variability of wave height is influenced by seasonal, annual and inter-annual changes in atmospheric and ocean variability such as ENSO or the other teleconnections. However, it is difficult to qualify the relation between wave climate and climate variability due to lack of data. This study analyzes monthly wave height variabilities considering local generated waves and remote swells based on statistical analysis by principal component analysis and multi-linear regression method using atmospheric analysis data, wave hindcasts and observations. The spatial and temporal characteristics of monthly wave heights are obtained around Japan.
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  • Yuhki TSURUDOME, Taro KAKINUMA, Tetsuya TANEDA
    2018 Volume 74 Issue 2 Pages I_139-I_144
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     The hydraulic experiments, for the tsunami generation due to seabed deformation, were performed using the wave basin, which consisted of both an outside, and an inside, tanks, with six segments composing part of the seabed. The water level was measured by utilizing three laser rangers. The obtained experimental results for the water surface displacement, were compared with the corresponding numerical results through a nonlinear shallow water model. The tsunami height increased, as the total displacement, the rise velocity, or the width, of the rise area in the seabed, was increased. The tsunami height also increased, as the still water depth was decreased. The experimental results for the water surface displacement, showed both large lifting speed, and short period oscillation, which were not reproduced by the numerical calculation, where the vertical motion was assumed to be relatively weak.
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  • Naoki FUJII, Masafumi MATSUYAMA, Hayato MORI
    2018 Volume 74 Issue 2 Pages I_145-I_150
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Tsunamis generated by submarine and subaerial landslides is less occurrence frequency than tsunamis caused by the fault movement, and its actual condition is not so clear. Experimental and analytical studies on submarine and subaerial landslide tsunami are conducted, but there were few cases of research compared to tsunamis caused by the fault movement. In this study, we carried out hydraulic model experiment using the plane water tank made of granular material and solid model simulating submarines and subaerial landslides, examined and organized the summarized tsunami water level and its propagation process. As a result, useful data for verifying the validity of the landslide tsunami calculation model could be acquired.
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  • Naoki TSURUTA, Abbas KHAYYER, Hitoshi GOTOH, Kojiro SUZUKI
    2018 Volume 74 Issue 2 Pages I_151-I_156
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     In recent years, the request level of the numerical design of the coastal engineering problems is increasing, and as a result, the more complicated situation is newly targeted. As a typical example, the scour process by a large tsunami is widely studied with mainly targeting breakwaters. This paper presents a simple and effective sedimentation model by the projection-based particle methods for a scour process to reproduce the accurate shapes of the changed mounds behind the target scour part. This new technique is easily applied to the recently developed particle-based numerical wave flume, namely, so-called “PARISPHERE”. Its applicability is shown through a benchmark targeting an experiment of the scour process. In addition, a simple benchmark is implemented with targeting a two-phase flow problem to show the fundamental applicability of PARISPHERE to the multiphase flow simulation. In the simulation by the standard ISPH, a problem related to unphysical motions of the particles are found. While, PARISPHERE shows a good performance of the physical motions of particles with good energy conservation.
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  • Hiroyuki IKARI, Hitoshi GOTOH, Ryotarou MATSUSHIMA, Genki NIWA
    2018 Volume 74 Issue 2 Pages I_157-I_162
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     In a particle-based elastoplastic model, it is difficult to eliminate numerical noise because of its explicit algorithm. Moving Least Square is one of the method to modify a physical quantity and based on the approximation that it can be described by the Taylor series expansion. In this study, MLS is introduced to modify a stress field that includes numerical noise. Moreover, Particle Shifting is also applied to obtain more accurate stress field. The present model is applied to a numerical simulation on a caisson breakwater failure due to tsunami overtopping. In a series of failure process of a caisson breakwater including a tsunami overtopping, a scouring of mound and soil foundation behind a caission and fall of the caisson into a scour hole, a calculation that stress noise does not emerge clearly is realized.
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  • Yuki KUTSUZAWA, Nguyen Xuan TINH, Kazuya WATANABE, Hitoshi TANAKA
    2018 Volume 74 Issue 2 Pages I_163-I_168
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     The 2011 Great Earthquake and Tsunami has caused huge morphological changes along the coastal areas in the Tohoku region. One of the key parameters causing these dramatical damages is the tsunami bottom shear stress acting on the sea bottom. In general, the tsunami wave is a longwave and the steady flow resistance method have been practically used in many tsunami numerical models to estimate the bottom shear stress by mean of using the depth-averaged velocity and friction coefficient (Method 1). However, the actual tsunami waves are unsteady flow conditions, so the application of Method 1 may inappropriate. Therefore, the EFDC vertical turbulent model is applied to take into account the effect of complex boundary layer development under unsteady tsunami condition (Method 2). In this study, these both methods are applied to calculate the tsunami bottom shear stress and compare between them. The shape of vertical velocity distribution results from the Method 2 are similar to the wave friction method. And bottom shear stresses by Method 2 are overall larger compared to the Method 1 under tsunami wave impacts.
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  • Yuki KAJIKAWA, Nobuhiko MATSUDA, Masahide TAKEDA, Mikiko EGUCHI, Yamat ...
    2018 Volume 74 Issue 2 Pages I_169-I_174
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     In the presented study, the authors investigated improvement of calculation accuracy of a 1D nonlinear dispersive model in order to reproduce complex tsunami bore generated by an electric sluice gate with high accuracy. In the investigation targeting a small scale experiment, by introducing both alteration of dispersive term and correction of artificial amplification method of the first dispersive wave height into the model, the improved model could reproduce the measured dispersive waveform with high accuracy. Moreover, in the investigation targeting a large scale experiment, the improved model could reproduce the experimental results well by introducing a proposed compensation equation of gate discharge into the model.
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  • Kenta SATO, Shunichi KOSHIMURA
    2018 Volume 74 Issue 2 Pages I_175-I_180
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Free surface flow problems occur in numerous disaster simulations, such as tsunami inland penetration in urban area. Simulation models for these problems require non-hydrostatic, three-dimensional and highly resolved because of the higher-order physical phenomena. The lattice Boltzmann method (LBM) is an alternative simulation tool that is attracting as a fully explicit and efficient approach.In this regard, the LBM is considered to have an advantage over other methods when executing high-performance three-dimensional tsunami simulations. On the other hand, 2D-3D hybrid tsunami simulation method is required in a huge area. In the current study, we verified the weak-compressibility of the MRT-LBM for three-dimensional free surface models in classical benchmark problems. Moreover, we developed the 2D-3D hybrid tsunami simulation method considering the compressibility. Through the experiments, we substantiated that the weak-compressibility can be controlled with in the order of the Mach number squared. Besides, we demonstrated the proposal model can calculate 3D phenomena efficiently and accurately such as flows around obstacles by the classical dam-break benchmark.
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  • Kenya TAKAHASHI, Takeshi NISHIHATA, Duc Thang CHU
    2018 Volume 74 Issue 2 Pages I_181-I_186
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Numerical simulation of hydraulic model tests for tsunami that is air-water two-phase flow in the underground pipeline was performed by OpenFOAM, and the applicability of OpenFOAM and the influence of gas phase were verified by comparing the calculation results with the hydraulic model test results. As a result, it was confirmed that the advantage of OpenFOAM in the case of pipeline or gas phase calculation target, and that the initial state inside the pipeline influences flow and pressure distribution. Also, not only the water surface elevation at the exit of the pipeline and flooding depth, but also the air mass in the pipeline and the gas phase velocity was reproduced well. However, large pressure fluctuations associated with the air hammer phenomenon were not reproduced. In order to reproduce the overflow phenomenon at the time of the arrival of the tsunami, it is necessary to consider the air-water two-phase flow in the underground pipeline. In order to further improve the reproduction accuracy, a method such as calculating a compressive fluid can be considered.
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  • Nobuki FUKUI, Nobuhito MORI, Katsuichiro GODA
    2018 Volume 74 Issue 2 Pages I_187-I_192
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Numerical simulation of tsunami using ultra high-resolution topography (resolution is less than 1m) enables to consider the effect of structures on wave run-up. However, numerical simulation with medium resolution (resolution is around 100m) is still used and important for practical use due to computational cost. This study develops Drag Force Model (DFM) as upscaled urban roughness parameterization to obtain acceptable accuracy in medium resolution tsunami model based on physical modeling. Survey results by The 2011 Tohoku Earthquake Tsunami Joint Survey (TTJS) Group are used for its validation with previous models. The model differences give little difference in terms of the maximum inundated depths and inundated area. However, DFM estimates larger resistance forces corresponding to the existence of structures (in particular a group of structures in nearshore area) than other models and the momentum fluxes decrease about twice.
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  • Yoshimichi YAMAMOTO, Maiki HAYAKAWA, S Masihullah AHMADI
    2018 Volume 74 Issue 2 Pages I_193-I_198
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     When the calculation grid interval of a numerical simulation is enlarged for flood prediction in a large domain, the flood from a land gate broken by an earthquake or the crossing tunnel in the banking road effective as a wall against a tsunami cannot be taken into consideration. Moreover, only the flood from the coastline attracts attention and the risk of the flood from a river is often neglected.
     So, by this research, for coasts where there is possibility of hitting a great huge tsunami and cannot disregard the flood from rivers, we examined the above subjects by simulating tsunami floods. Furthermore, in order to evaluate the scour in the land side of a dike by the tsunami and the durability of a refuge mound, we proposed a method for getting suitable coefficients of bed load rates based on hydraulic experiments on the scour and tried improvement about a prediction method of the scour by the tsunami.
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  • Yoshimi KUSUHARA, Taro KAKINUMA, Akihiko KIMURA
    2018 Volume 74 Issue 2 Pages I_199-I_204
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     The tsunamis ascending the rivers, were simulated using a three-dimensional numerical model. The tsunami height, which is the maximum water-surface displacement at each point, increased, as the width of rivers was decreased. When the soliton disintegration occurred in the rivers with a narrow width, the tsunami height increased in the tsunami ascent. Conversely, when no soliton disintegration occurred in the rivers with a wide width, the tsunami height decreased through the tsunami propagation, after the peak of the tsunami height appeared. In the cases determining the tsunamis ascending the rivers with a compound channel, the direction of tsunami propagation became inclined. In the present cases, the tsunami height was lower over the flood plain than the incident tsunami height. If the width of rivers is decreased upstream, the tsunami height increased owing to both the contraction in the river width, and the soliton disintegration.
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  • Yusuke OISHI, Takashi FURUMURA, Fumihiko IMAMURA, Kei YAMASHITA, Daisu ...
    2018 Volume 74 Issue 2 Pages I_205-I_210
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Characteristics of tsunami oscillation in Tokyo, Sagami and Suruga Bays were investigated regarding the estimated Nankai-Trough megathrust earthquake models. In the cases where there is a large fault slip in the Nankai area, the oscillation of 76 minutes period was commonly excited in the three bays. In the cases with a large slip area in the Tokai or Tonankai area, the 68-minute component was excited only in Suruga and Tokyo Bays. The tsunami tended to be prolonged in the three-bay oscillation mode. The tsunami in the Keihin Canal in Tokyo Bay tended to be strengthened when the oscillation of the entire Tokyo bay include the components that are close to the characteristic period of the canal (30 min). In considering the continuity or amplification of tsunamis of canals in Tokyo bay, it is useful to focus on the macro-scale tsunami oscillation mode among the three neighboring bays.
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  • Kiyoshi HASHIMOTO, Yoshitomo SUZUKI, Hitoshi TANAKA
    2018 Volume 74 Issue 2 Pages I_211-I_216
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Along the Sendai Bay Coast in Miyagi Prefecture, there are historical canals such as Teizan Canal, Tona Canal and Kitakami Canal connecting the Abukuma River and the Old Kitakami River mouths with a total length of 49km. The mitigation effect of these exting canals during the 2011 devastating tsunami has already been investigated by the authors. In addition, it has been reported that the number of the broken coastal embankment was fewer in the northern area of the Abuluma River as compared with the southern area where canal system does not exist. This study investigates the possibility of a new canal construction as a part of multiple defense system in the southern area of the Abukuma River along Sendai Coast. Using 2-D tsunami numerical analysis, it is found that a new canal has reduction effect of tsunami disaster with respect to tsunami arrival time, inundation height, tunami-induced velocity, etc.
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  • Shuhei ONO, Tetsuya HIRAISHI, Ryoukei AZUMA, Hideaki HANDA, Tadao ITO
    2018 Volume 74 Issue 2 Pages I_217-I_222
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Tsunami hazards cause the wide inundation in the innermost area with law ground heights as well ports and coastal areas. Such the inundation hazard become remarkable in case that the tsunami run up along a river. A river gate may become an effective tool to prevent the tsunami–run up in the river. The gate, which is originally designed for storm surge mitigation, is capable to stop the tsunami-penetration into the river mouth but it's strenrthen is not endurable against the tsunami impulsive pressures. A tsunami energy dissipater becomes necessary to reduce the tsunami energy acting the river gate.
     The paper proposes application of the hydro-plane type removable breakwater as the tsunami energy dissipater. A series of model experiments with a scale of 1/33 are conducted employing a visor-gate type river one and hydro-plane type breakwater changing the height of drift from 0 to 1.2 times higher than the initial water level. The effect of tsunami energy dissipating becomes the highest when the breakwater is adjusted to drift up until the initial water surface level. Meanwhile the dissipating effect increased as the initicial tsunami height increased. The distance between the breakwater and gate became an important parameter to determine the dissipating effect. Two experimental formuals representing the water level and wave pressure variation respectively were derived from dimensionless wave heights, water depth, distance and breakwater height. The formula reproducesed the experimental results well except of the case that incident tsunami overtopped the standing breakwater.
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  • Yuta MITOBE, Koyuki ABE
    2018 Volume 74 Issue 2 Pages I_223-I_228
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Effects of tsunami energy reduction by local scour at landward toes of coastal dykes induced by overflow were discussed through a numerical experiment. In order to include development of the scour and the energy reduction, empirical formulas were derived from the results of some movable-bed experiments. Final scour width normalized by the height of the dyke can be decided by normalized overflow depth. Based on the trend of the increase rate of the width, also the tempral variation of the scour width was formulated with related to its rate to the final scour width. Scour depth was calculated with the empirical rate between the scour depth and width, and used for estimation of its energy reduction rate. The models of the development and the energy reduction rate of the scour were coupled with shallow water equation model to conduct the numerical experiment. The effect of the scour on velocity and fluid force behind the dykes was discussed with simple model topography and solitary waves. Due to the time required for the development of the scour to have mean effect to reduce the tsunami energy, the peaks of the velocity and the fluid force appeared before appearance of the effect of the scour. In the case with initial scour width, the peak values were effectively reduced and this implied availability of artificial pools at the landward toe.
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  • Yoshiya IGARASHI, Takehito ZAHA, Norio TANAKA, Hajime SATO, Hiroyuki T ...
    2018 Volume 74 Issue 2 Pages I_229-I_234
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Coastal forest has some advantages like a trapping of floating debris and/or reducing a tsunami energy, on the other hand, it also has a risk to increase the damage to houses behind forest when trees are broken and driftwoods are produced. However, if the breaking type of trees is an overturn, driftwoods are not produced and a forest still has an effect of trapping debris. If the tree trunk diameter at breast height is thick, the tree trunk is hard to be broken. Therefore, for the proper management of forest, thinning procedure of trees is needed to be periodically conducted. This study uses the characteristics of black pine in Hokkaido and numerical model which includes the tree breaking, and aims to clarify the effect of tsunami mitigation under breaking situation of the trees. To prevent the tree breaking, thinning procedure of trees should be held periodically to promote each tree growth. However, to reduce the tsunami energy through the forest, the density should be high and tree crown height should be small.
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  • Akihiro HAYASHI, Kei YAMASHITA, Fumihiko IMAMURA
    2018 Volume 74 Issue 2 Pages I_235-I_240
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     In this research, we proposed a method to quantitatively evaluate tsunami damage category of individual buildings in consideration of the distribution of coastal forests in the coastal plain, topographic conditions, and hydraulic parameters of the tsunami. In constructing the quantitative evaluation method, we used the building damage data at the Great East Japan Earthquake in 5 municipalities in Miyagi prefecture in the Sendai plain area. In this area, it was confirmed to reduce the tendency of the affected section of each structure type depending on the forest belt width of the coastal forest. Furthermore, we have constructed the quantitative evaluation formula using dimensionless variables expressing the presence of coastal forest, tsunami external force at building site, location / terrain gradient of each building, attenuation rate of tsunami force, which data is from the actual damage data and the tsunami numerical analysis. And we confirmed its statistical validity. By this method, we can quantitatively estimate the category of individual building damage even in other plain areas by obtaining target building structure, forest belt width of coastal forest, building altitude, tsunami hydraulic parameters.
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  • Yukinobu ODA, Teppei OMATA, Kanako HASUMI, Katsuyuki SAKASHITA
    2018 Volume 74 Issue 2 Pages I_241-I_246
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     In the tsunami safety assessment for a land-structure, not only tsunami pressure but also its deformation should be considered. It is generally considered that tsunami pressure consists of the bore pressure, which is the initial impact pressure, and the following quasi-steady pressure. Because the effective duration of the bore pressure is quite short, the deformation of the structure might be small in comparison with that by the quasi-steady pressure. In this study, the experimental model tests for the tsunami pressure and the deformation of the vertical wall structure were conducted to investigate the deformation characteristics depending on the tsunami pressure variation.
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  • Kentaro IMAI, Kentaro NAKAI, Toshihiro NODA, Nobuo ARAI, Shunji IWAMA, ...
    2018 Volume 74 Issue 2 Pages I_247-I_252
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     In this study, the subsidence amount of a body structure caused by a strong motion at the Nankai Trough great earthquake was evaluated by GEOASIA numerical simulation. We investigated the influence on the tsunami inundation process and area incorporating the numerical results of the structural vulnerability appeared by the strong motion. The numerical results show that the tsunami inundation area was extended by subsidence of body structures and collapse of an upright dike. It proves the importance of not only earthquake resistance but also vulnerability evaluation of coastal and river-side structures due to a strong motion during the process of tsunami hazard evaluation.
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  • Jiro ENDO, Yoshiyuki ISOZAKI, Yoshihiro OHMURA, Manabu KOBAYASHI, Naok ...
    2018 Volume 74 Issue 2 Pages I_253-I_258
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Open-type wharves on vertical piles may be effective to prevent and reduce the damage due to earthquake and tsunami. However, performance verification method for the structure has not been established. In this study, we conducted three-dimensional numerical analysis on the open-type wharves under steady flow condition. Based on the calculated results, we tried formulation of horizontal force acting on the pier. The model reproduced the experimental results well and showed that numerical analysis is applicable to the calculation of tsunami-induced forces including pressure. After understanding the wave pressure distribution acting on the deck block in detail, the horizontal forces were formulated using water depth, flow velocity and structural parameters, and the validity was shown from the relationship with measurement forces. In practice it can be calculated assuming the drag coefficient constant.
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  • Akio NAGAYAMA, Tomotaka TANAKA, Ryouga SAKAGUCHI, Ryoudai SUEYOSHI, To ...
    2018 Volume 74 Issue 2 Pages I_259-I_264
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Conventionally, for the estimation of a wave pressure to a structure by a tsunami, a method assuming hydrostatic pressure has been proposed. The method is adopted as a design guideline for the tsunami evacuation building. However, the method was targeted to the wall surface of a single structure. Verification under the condition that a plurality of structures are arranged is not sufficient. From this background, this study covers regularly arranged cylinder groups. The relationship between the installation interval of the cylinder, the generated wave pressure and the specific energy was studied by numerical calculation and model experiment. As a result, it was found that the wave pressure characteristics to the cylinder in the grid-arranged column group are strongly influenced by the lattice spacing.
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  • Hideo MATSUTOMI, Hayato OKADA, Tomohiro KUBOTA, Fumiko KONNO
    2018 Volume 74 Issue 2 Pages I_265-I_270
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     The dependency of the tsunami load (horizontal force Fx and vertical force Fz) on RC building on the density ρ of tsunami inundation water is examined through a small-scale hydraulic experiment using inundation flow with and without sediment (fresh water) for the advancement of the tsunami load evaluation. Although the experimental cases using the inundation flow with sediment, and the comparison and examination method for the results obtained by the experiments using the inundation flow with and without sediment are limited, it is verified that the tsunami load on the building depends on the density of tsunami inundation water and revealed that (1) when the inundation depth h at the front of the building or the ratio h/hiup where hiup is the incident inundation depth is the same, the horizontal force caused by the inundation flow with sediment is larger than that without sediment and the higher the density, the larger the horizontal force, (2) the vertical force is affected by the deposit sediment around the building and the vertical force caused by the inundation flow without sediment could be larger than that with sediment.
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  • Junpei MORIOKA, Takenori SHIMOZONO, Azumi KADO, Masayuki FUDO, Yoshimi ...
    2018 Volume 74 Issue 2 Pages I_271-I_276
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Evaluation of wave force acting on breakwaters due to tsunami oveflows has been an important issue after the devastating 2011 tsunami event. A few studies, however, have targeted on wave force exerted on different sections of breakwaters such as head and corner sections which are likely to be weak to tsunami attacks. In this research, physical tests were conducted in a wave basin to investigate characteristics of wave pressure on different sections of a model breakwater under unsteady tsunami overflows. The results of the experiments suggested that the maximum wave force occurs around a timing of the higherst water level at each section and it is larger at a corner section due to local wave concentration and smaller at a head due to horizontal flow development than that exerted on a trunk of the breakwater. The effect of vertical flow acceleration is found to be significant especially in upper part of the breaktwater where the wave pressure tends to be 10-20 percent lower than hydrostatic pressure estimated from instantaneous water level.
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  • Tsuyoshi IKEYA, Takahiro OTSUKA, Daisuke INAZU, Akio OKAYASU
    2018 Volume 74 Issue 2 Pages I_277-I_282
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Hydraulic model experiments and numerical analysis were carried out with the purpose of clarifying the influence of the existence of the piers on the tsunami force acting on the superstructures. In the hydraulic model experiment, the inundation depth and the impediment rate by bridge piers were varied as parameters, and the tsunami deformation around the pier and the tsunami force acting on the superstructure were measured. In the numerical analysis, we modeled the bridge piers as porous media and reproduced the tsunami deformation experiment by the VOF method. As a result, it became clear that as the impediment rate increases, the maximum flooding depth increases, and the vertical force acting on the superstructure also increases. In particular, when the inundation depth is large, it was found that the vertical force acting on the superstructure becomes larger than the buoyancy due to the reflected wave generated from the piers.
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  • Yoshihiro OHMURA, Manabu KOBAYASHI, Naoki FURUICHI, Koichi SUGIMATSU, ...
    2018 Volume 74 Issue 2 Pages I_283-I_288
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Physical model tests were conducted using a wave flume to investigate the characteristics of tsunami-induced pressures and forces acting on open-type wharves on vertical piles under sine wave conditions. It was confirmed that the wave pressure difference in the faces at the top and the bottom of the deck block brings lift and that the vertical force excels the horizontal force of the wharves. The wave pressures and forces acting on the wharves were different depending on presences of connection plates. We also found the occurrence of the impact pressure during the initial action of waves on wharves, which causes the maximum wave force. The impact pressure can be estimated by employing Tanimoto formula. It was revealed that the non-dimensionalized wave pressure variation at the maximum water level is smaller than that at the maximum vertical force occurs. The variation of wave pressure and drug & lift coefficients at the maximum water level under sine wave condition may be larger compared with that under steady flow condition.
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  • Kuniaki OI, Hiroshi YAGI, Tsuyoshi TADA, Yoshinori SHIGIHARA, Kenjirou ...
    2018 Volume 74 Issue 2 Pages I_289-I_294
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     This study inspects the damage of armor blocks which cover the port side rubble mounds of breakwater for the overflow in tsunami. The pattern of damage is classified as “All blocks slip”, “One block falls”, “One block rises” and “Materials constituting a mound collapse (blocks are stable)”. In this study, attention is paid to “One block falls”. The force and bending moment acting on an armor block covering port-side rubble mounds of breakwater were directly measured by using a load cell. The velocity distributions around armor blocks were measured by two components laser doppler anemometer. The damage of block occurs when the Falling moment due to fluid forces acting on a block exceeds the Resisting moment due to the weight of a block.
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  • Jun MITSUI, Shin-ichi KUBOTA, Akira MATSUMOTO
    2018 Volume 74 Issue 2 Pages I_295-I_300
    Published: 2018
    Released: November 10, 2018
    JOURNALS FREE ACCESS
     Stability of armor blocks covering high mound composite breakwaters against tsunami overflow was examined. A series of hydraulic model experiments revealed that the main failure mode is the sliding of all the blocks on the slope integrally due to the fast flow along the mound. Installing large blocks at the toe of the mound was effective for improving stability. It was also confirmed that the seepage flow reduces stability of the blocks. Numerical analysis revealed that large hydraulic forces act on the blocks above the harbor-side water level while small forces act on the blocks below the water level. This fact means that the height of the harbor-side water level greatly affects the stability of the blocks. Finally, an evaluation of the stability was performed based on the balance of total forces acting on the blocks on the mound.
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