This study presents the 1-way coupling model between a phase averaging model and a phase resolving model in order to make use of their advantages. In this model, the technique of double connection boundaries is adapted. This method can expand an effective computational area efficiently and reduce the computation time consequently. The results of the present model are compared with those of the single boundary model or experimental measurements in some situations. As a result, this present model can predict the wave fields with sufficient accuracy in a shorter time.
A functional for variational problems of multilayer-fluid systems with vorticity was presented, after which a set of nonlinear equations were derived to simulate surface and internal waves considering both strong nonlinearity and strong dispersivity of waves. The linear dispersion relations for surface and internal waves were shown also for deep-wave conditions. Stable results of surface waves propagating over a submerged breakwater, as well as internal waves reciprocating inside a closed tank, were obtained using the numerical model, where two-layer stratification was treated below a fixed horizontal plate. The internal waves resulted by the present model had a different period from that through a Boussinesq-type model. The surface waves over a slope steepened further due to the assumed vorticity effect.
When the hydraulic model tests for wave propagation are done, the re-reflected waves caused at the wave generators also propagate to the experimental area. The absorption methods for the short-period waves are well known, but they are not useful for the reduction of long-period reflected waves. In this study, the analytical model for producing long-period waves using the pump-type wave maker is presented, and laboratory tests for the reduction of long-period re-reflected waves are carried out. In addition, the reduction of short-reflected waves using filter materials is also tested. The combination of these reduction methods for long-and short-period waves might be generally useful for the hydraulic model tests.
A Corrected Incompressible SPH (CISPH) method is proposed for accurate tracking of water surface in breaking wave and resultant splash-up. Corrective terms are derived based on a variational approach to ensure the angular momentum preservation of Incompressible SPH (ISPH) formulations. The proposed CISPH model is applied to simulate the breaking and post-breaking of solitary waves on a plane slope. The high precision of the CISPH model is confirmed through comparisons with experimental data of plunging breaker. The introduction of corrective terms significantly improves the capability and the accuracy of the ISPH model in the simulation of wave breaking and resultant splash-up.
We developed a new fluid solver that combines the advantages of both a Lagrangian scheme and an Eulerian scheme. The massless Lagrangian marker particles are put into the Eulerian grid and advected according to the velocity field to capture accurately the interface. The applicability of the present method is demonstrated for dam breaking, wave breaking in shallow water, impact pressure acting on a vertical wall and the interaction between some blocks and wave breaking. The efficiency and the accuracy are also investigated. The numerical results show good agreement with numerical and experimental results performed by other researchers.
A numerical model for transformation of short periodic waves is developed on the basis of hybridization of highly accurate finite difference scheme and TVD scheme. TVD scheme is highly dissipative when applied to oscillating solutions because it is not able to distinguish smooth extrema from discontinuity by its smooth indicator. To overcome the fatal shortcoming, TVD scheme is hybridized with a scheme with higher order accuracz. A switch function together with a discontinuous indicator is introduced to make the scheme TVD from breaking point to the shore. The model performance is verified through comparisons of model results with experimental data as well as existing empirical formulae. It is found that wave damping due to breaking is reproduced well by TVD scheme if an appropriate switch is employed.
The main purpose of this study is to newly develop a three-dimensional numerical model of multiphase flow “DOLPHIN-3D” using a CIP method and an extended SMAC method based on irregular mesh size grids, which introduces a DTM method of a highly accurate turbulence model based on the LES and the dynamic motion analysis of multiple rigid bodies. The validity of the model is verified by applying it to dynamic analysis of drifting bodies under wave actions and comparing with the laboratory experiments. The results reveal that the model is capable of simulating three-dimensional multiphase flows and time-changing wave pressures acting on drifting rigid bodies with high accuracy. The model would be, therefore, useful in discussing complex physical phenomena with solid-gas-liquid interaction.
This paper presents a suspended-particle/liquid two-way coupling model integrated with conventional stochastic and subgrid stress models of a large eddy simulation. The model is applied to particle laden turbulent flows in a wave boundary layer developed over a flat sea bed for understanding dynamic effects of turbulence on the particle size, number density and the density. The turbulence intensification due to the presence of particles results in additional suspensions from the bed, featuring a recursive turbulence/suspension interaction process of the particle laden flow within the boundary layer.
Experiments have been carried out to investigate drag coefficients and response of wind waves under periodically fluctuating winds. Wind stresses estimated from momentum conservation law considering radiation stresses were compared with those estimated from vertical distribution of wind speed. It is found that the former stresses are much larger than latter ones and about twice of the latter in the case of breaking wind waves. Vertical distributions of time-averaged wind speed of periodically fluctuating winds were also compared with those of constant wind speed. The significant difference between them can not be found. However, in the case of periodically fluctuating winds long period waves with predominant period of fluctuating winds were exited unlike constant wind speed.
Field measurements at a sea observation tower were made to investigate the dependence of air-sea CO2 transfer velocity on swell conditions. Based on directional wave spectra, we classified swell conditions into three groups, i. e., Pure windsea, Swell-dominated sea and Cross swell. The present data show that the transfer velocity for Pure windsea increases monotonously with the wind speed, while the presence of swell contaminates the wind-speed dependence of the transfer velocity. Also, the transfer velocity for Cross swell seems to take larger values than the other conditions. Moreover, we examined how the transfer velocity nondimensionalized by the friction velocity depends on a nondimensional wave-energy dissipation rate. In such relations, there is no remarkable difference in three types of swell conditions. This means that the energy dissipation rate may be effective for the parameterization of the transfer velocity.
In this study, distributions of dissolved CO2 under breaking waves are experimentally measured using two-color Laser Induced Fluorescence (LIF). CO2 mainly dissolves on gas/water interfaces of the plunging waves and around bubbles entrained by successive plunging jets. vortices induced by the jets quickly diffuse downward the dissolved CO2 together with the bubbles. Undertow transport the dissolved CO2 offshoreward below the trough level for enhancing the CO2 concentration in a whole surf zone.
The two-phase flow measurements using imaging technique for two-dimensional bubble measurements, so called Bubble Tracking Velocimetry (BTV) and PIV were conducted to the surf zone breaking waves. The characteristics of air bubbles in the surf zone such as bubble distributions, bubble size spectra, and turbulent characteristics of fluid velocity were measured with highly temporal and spatial resolutions in the laboratory. The temporal transitions of bubble size spectra were measured and the relationship between the gas and liquid phases were analyzed for the surf zone breaking waves.
The structure of gas pressure during wave breaking has not been fully explained. In this study, the distribution of gas pressure during wave breaking for two breaker types was studied by conducting hydraulic experiments and numerical computations. Further, the effects of wave breaking on the gas pressure were considered. As a result, we found that the distribution of gas pressure became symmetric between the front and back of the wave crest when wave breaking does not occur. On the other hand, gas pressure was found to be asymmetric between the front and back of the wave crest when there was wave breaking. Specifically, isobaric contour intervals were found to be smaller in front of the wave crest.
In this paper, a fragmentation model of jets with free-surfaces, describing evolution of the size spectra of sprays during the fragmentation process is developed. A 3-D large eddy simulation reproduces amplification of free-surface disturbances of the jets induced by the counter-rotating vortices and the resulting jetting flows splitting into fingers and sprays. It is found that a probability density of the finger or spray size can be described by a log-normal distribution, and its evolution depends on Weber number. The present fragmentation model is capable of predicting the volume fraction of the jets at arbitrary time after the inception of fragmentation.
This report describes advanced deformation scheme for breaking waves, and the results of breaking wave simulation. A three-dimensional numerical wave tank was developed. This code is also adapted to the parallel computing system and multi grid size system, so that the problem is more efficiently solved. This code is called ‘CADMAS-SURF/3D’(SUper Roller Flume for Computer Aided Design of MAritime Structure in 3D). At first, the accuracy of prediction of breaking point was checked in the wave flume, and the validity was verified due to comparison of the Goda's breaking index. Then, the performance of 3 dimensional breaking problems was tried. Two types of submerged breakwater were installed in our Tank. Results were qualitatively good agreement with experiments.
A review is made on the statistical features of breaking waves in the nearshore waters. The bed slope effect in the breaker index formula by Goda (1973) is reduced in a newly revised formula. The breaker index of regular waves should be treated as a statistical variable with the coefficient of variation ranging from 5% to 14%. The significant wave height rarely exceeds 0.6 times the local water depth. The wave nonlinearity as expressed in the form of skewness and the ratios of one-third and one-tenth highest wave height to the energy-based significant wave height increases toward the middle of surf zone, but it is destroyed by wave breaking process and disappears near the shoreline. Changes of characteristic wave heights across the surf zone are also exhibited.
This paper reports the cross-shore variations of a pressure gradient on a fixed barred beach. The data sets were obtained as part of large-scale laboratory experiments. The cross-shore variation of the pressure gradient showed that the maximum value of the pressure gradient appeared in the wave breaking area, and the pressure gradients were considered to be influenced by the fluctuation of water surface elevation. The spatial variation of pressure gradient and water surface elevation showed a good correlation from offshore to onshore in both regular and irregular wave cases. The exceedance probabilities of the pressure gradient were also analyzed and found that the distribution of the exceedance probability of the pressure gradient could be evaluated by the Weibull distribution.
A practical form of the joint distribution of wave heights and periods is proposed in this paper. It is traditionally inevitable to employ the approximation of local-height and local-period in sense of simplicity. The ambiguous relation in the previous studies is pointed out, which is the doubtful assumption between the angular velocity and real-period, and then an altanative relation is introduced newly. It is an advantage in this study that the marginal distribution of wave height is obtained as the Rayleigh distribution. The proposed joint distribution is so adaptable that the effect of nonlinearity and wave-breaking will be easily taken into account.
Quasi-resonant four-wave interactions may influence the statistical properties of deep water surface gravity waves such as a freak wave. The freak wave prediction method developed by Mori and Janssen (2006) based on the quasi-resonant wave theory is compared with Europian Centre for Meidum Range Weather Forecasts wave analysis data. Mori and Janssen (2006) model shows low correlation with the observed wave data.To improve the forecasts score, the directional effects are considered by using a series of the Mote Carlo simulations of cubic Nonlinear Schrodinger equation. The broad band spectrum effects are also considered in the prediction method.
This paper presents an estimate of probable maximum wave height (PMWH) generated by typhoons and low pressure systems on the Northwestern Pacific Ocean and the Japan Sea. Typhoons and lows are generated over a period of 100, 000 years using a Monte-Carlo simulation model, and the wind and wave computations are conducted for each of a large number of selected intense typhoons and lows. The analyses show that the typhoon-generated PMWH exceeds 26 m at a sea area near Shikoku Island facing the Pacific Ocean and that the low-pressure- generated PMWH is above 26 m at an eastern sea area far from East Japan. Those PMWHs are 7 to 13 m greater than the maximum wave heights generated by historical typhoons and lows in the recent decades.
This paper presents a wave hindcast system for estimating climatic characteristics of waves over 23 years at an arbitrary point in a quasi-closed basin that is partly connected to an open ocean such as the Seto Inland Sea. A data set of hourly over-sea wind distribution is made using measured wind data acquired at many coastal and sea stations. A wave computation at each of the wave measurement stations is conducted using a backward ray tracing wave model on a grid with high spatial resolution. Comparison between calculated and measured wave data shows that the system yields a reasonable estimate of long-term wave characteristics and that the present system has a higher ability in a long-term wave estimation than previous systems.
A sample of typhoon-generated annual maximum wave height (TG-AMWH) of 10, 000 years is produced for the East China Sea using a Monte-Carlo simulation model. Then, an extreme value analysis of this very large sample of TG-AMWH yields an estimate of the parent distribution of the TG-AMWH which is expressed as a Weibull distribution for nearly the entire sea. Next, a similar extreme value analysis is separately conducted for each of 200 sample sets, each with a size of 50. The investigation, based on a sample of return wave height with a size of 200 leads to the conclusion that the identification of the parent distribution of the TG-AMWH may significantly decrease the confidence interval of the return wave height. Also, this may be true of the historical typhoon case.
Wave hindcastings for 16 strong typhoons in the recent 16 years are conducted separately in the 3 sea areas of the Seto Inland Sea to estimate the maximum wave height in the Sea. A wave model is driven by one-hourly winds obtained with a spatial interpolation of measurement data at many coastal and sea stations and using inflow directional spectra calculated on the boundary that is open to the Pacific Ocean. The wave hindcasts are validated by a close agreement with the measurements at many stations. Brief conclusions are that the maximum wave heights of 4 to 7 m in the northern area of the Sea are caused by either Typhoon 9119 or 0418 and that the wave heights of 4 to 5 m in the southern area are generated by either Typhoon 0423 or 0310.
The Weibull distribution of three parameters has been frequently employed in the extreme wave height analysis. The value of shape parameter is pre-required in estimating the location and scale parameters by the least-square fit. Goda (1988) recommands the four values of shape parameter in point of view of the statistical properties of Weibul distribution. This study shows that the values selected by Goda and an additional new value interpret the dynamical properties of wind-waves, and it demonstrates the estimation method based on the extreme value theory for a practical data of wave heights.
Recently, the third generation wave models are widely employed in many countries. However, the examination of their estimation accuracy in an inland sea is not necessarily sufficient due to insufficient wave observation data and difficulty of estimating accurate wind field around the area In this paper, therefore, we applied a modified WAM to Seto Inland Sea with the wind data estimated for Typhoon 0514 with MM5 and Typhoon Bogus. The estimation accuracy of wind and waves were investigated with the data observed at a few stations. Several energy source functions that had been proposed so far were examined in the modified WAM. In addition, ADWAM (Adjoint WAM) was also applied for the data and its applicability and usefulness were discussed.
In late years 3 dimensional non-linear wind prediction model that a result of high precision is provided are put to practical use. When we predict wave, it is often that we adopt SMB method in a closedown sea area like a bay. It is the fact that sea surface wind of that case converts AMEDAS data of a neighborhood by a simple coefficient by a geographical condition. However, an observation spot of wind in the inland strongly takes influence of the neighboring topography. Therefore, it is thought that it becomes a cause to lose precision of wave prediction to use a uniform coefficient. If a place of wind is correct, as for the wave prediction by SMB method, practical precision is provided. Thus, We suggest a method to predict sea surface wind in 3 dimensional non-linear wind prediction model.
This study investigated about the continuity of momentum flux through an air-water interface. We conducted to measure air-flow and water-flow very close to a water surface in a wind wave tank using PIV technique. To evaluate of the continuity of momentum flux calculating from the friction velocity was very difficult, because we could not detect exact a mean water level to fit a log-law profile for the experimental data. The viscous stress affected not only the viscous sub layer but also the turbulent boundary layer. The ratio of the viscous stress in water-flow is from several percent to about ten percent. We deduced that the continuity of momentum flux calculating from the total stress was strongly affected by three-dimensional turbulent water-flow.
Ocean wave database around Japanese islands for 45 years is build based on the meteorological dataset ERA-40, ECMWF 40 Years Re-Analysis. Since the ERA-40 is coarse for the wave hindcasting in the target domain, the mesoscale meteorological model MM5 was applied to evaluate the sea-surface wind at higher resolution; and, the wave model SWAN was employed to compute the long-term wave fields. The computed wave fields were successfully improved by applying the wind fields evaluated with MM5. The comparison of the wave database with the field observed data shows good agreement, and leads to the conclusion that the database is highly accurate.
Large horizontal motion of moored large vessels and breaks of mooring ropes are mainly induced by long period waves traveling into harbor. One of the most popular countermeasures is the construction of breakwaters. Meanwhile they say the construction of hard breakwater may disturb the seawater exchange between the outside and inside of a harbor. A permeable breakwater becomes suitable if it becomes effective to reduce the long period wave in the harbor. An experiment studying the wave transmission coefficient in the permeable breakwater for long swells and a numerical simulation estimating that in long period waves is carried out in this paper. The harbor tranquility for long period waves in the target port increases when the long period wave transmission coefficient becomes about 0.1 to 0.4.
Three model spectral shapes on long period waves, which can be used as incident wave spectra for more accurate numerical estimations of long period wave fields in harbors, were proposed. Using continuously measured wave data at a point far outside and at two points inside Shibushi harbor in Kagoshima prefecture, Japan, the validity of the three proposed different spectral shapes, a) BS type, b) Exponential type, c) Triangular type, together with Hiraishi's flat shaped spectra, were examined. It was found that for a relatively long period of 80 to 120s, Hiraishi's flat type spectra largely underestimate the observed wave spectra, but for a relatively short period of less than 50s, all spectral shapes give practically the same spectra as the observed one.
In order to estimate sediment transport near a river mouth and a narrow inlet, it may be important to investigate the behavior of the long-period waves with periods of several minutes generated by wave groups in the sea. In this study, characteristics of the long-period waves and associated flows near Tenryu river mouth and the inlet of Hamana Lake are discussed based on the field data. Long-period waves are developed almost linearly to both significant wave heights and periods outside the inlet, but they are reduced about half in the inlet. The long-period fluctuation in the flow seems to consist of two components; one is associated with the long-period waves and the other is generated by tidal currents.
The characteristics of wave groups propagating over the continental shelf toward the coastal region are investigated using the envelopes computed by the Hilbert transform from field observations and related to the evolution of the amplitude and phase modulations. The measurements are performed by 3 wave gauges located over a few lengths of typical wind wave groups, in water of relatively shallow water depths. During the observation period, the significant wave height exceeds 3m for four days due to the passing of typhoon. It has been observed that the distribution of waves in a group approaching a shore becomes more uniform at the wave growth and wave decay stages of these high waves. During these periods the significant wave height tends to decrease with approaching the coastal zone.
Tsunami from the mega-thrust earthquake off the Kuril Islands on 15 November 2006 was observed by the offshore long-term observatory off Hokkaido, Japan. About one hour later, a series of the tsunami signal was observed by three bottom pressure sensors. Tsunami amplitudes observed offshore were approximately 5 cm, while those observed at the coast were a few tens of centimeters. An acoustic Doppler current profiler (ADCP) at the ocean-bottom, however, could not record any current anomaly by the tsunami propagation. In the present study, the tsunami computation has been also done, and its results have been compared to the observations.
Focusing on the scattering of tsuanmi energy by the seamounts, this study aims to discuss the effect of Emperor seamounts on the tsunami propagation of the 2006 Kuril Island tsunami, using a finite difference method. The model results suggest that the contribution of Emperor seamounts on the maximum tsunami energy along the Pacific coast of Japan is as much as 50 % or more. Also, the spectral analysis of the observed tsunami records in Japan indicates that the scattering waves from Kinmei seamount dominate the wave components of 8-20 minutes in its wave period, which is consistent with the theory of Longuet-Higgins (1967).
The purpose of this paper was to make clear relationships between tsunami generating and its propagating and a seabed deformation. In particular, we have studied how the deformation velocity and the deformation width affect the process of tsunami propagation. For the purpose of our work, numerical simulations of tsunami generated by the seabed deformation were carried out in three kinds of seabed deformations. As a result, when the width of seabed deformation became to more than 100 km, tsunami heights decayed to about 40% than its tsunami maximum heights. Further, it was found that the decay rate of tsunami height of negative waves is lower than that of positive waves. Moreover, the negative wave propagated with the wave height almost equal to the maximum tsunami height.
The 2006 Chishima-Islands-off Earthquake was generated around 20: 14 on November 15 in 2006 in Japanese standard time (JST). It was reported by the Japan Meteorological Agency (JMA) that the magnitude of the earthquake was 7.9, and the hypocenter was at off-Chishima-Islands Pacific side coast, with the latitude of N46.7°, the longitude of E154° and 30km deep under the seabed. Two months after the earthquake, 2007 Chishima-Islands-off Earthquake was generated around 13: 23 on January 13 in 2007 (JST) with the magnitude of the earthquake 8.2 and the hypocenter of the latitude of N46.3°, the longitude of E154° and 10km deep. This paper introduces the observed tsunami profiles by the Nationwide Ocean Wave information network for Ports and Harbour S (NOWPHAS).
As tsunami information, not only issuing but also canceling is important for emergency management. Although tsunami database and real time observation data recorded at stations are available, those are not used for canceling to estimate the tsunami attenuation. This study evaluate the attenuation for 6 hours by using the tsunami database in Sanriku coast with the 394 faults models assumed. The index of the tsunami attenuation for 6 hours is proposed and estimated along the coast and sea regions, which can be used for canceling of tsunami warning after the tsunami wave heights are predicted.
It is very important for tsunami disaster prevention in the coastal area of Shikoku Island to clarify a mechanism of tsunami propagation in the Seto Inland Sea. Especially, a resonance of tsunami is a dominant factor in such a narrow inland sea. In this study, numerical simulation of tsunami propagation is executed to estimate tsunami height and characteristic period in the Seto Inland Sea. According to the numerical analysis, a tsunami height does not decline during about 10 hours and a characteristic period of Harima-nada is about 60 minutes. The tsunami continued to be resonated for more than 20 hours in the Seto Inland Sea.
The present paper has discussed how to improve our real-time tsunami prediction method by the inverse analysis of tsunami profile observed at offshore points. The inverse analysis of the offshore tsunami data estimates the initial displacements of water surface in the segmented tsunami sources. The estimated initial displacements predict tsunami profiles at inshore points of interests. Our prediction method is tried to improve by the introduction of correlation factors with surrounding segmented sources, the supplement of another observation point, or the employment of wider segmented source area. The paper also confirms that the real-time prediction can be applied to predict the tsunami at Shimotsu Port in Wakayama Prefecture as well as in Osaka Bay.
This study examines the validity to use an artificial neural network (ANN) for the prediction of tsunami magnitudes at several locations in the Osaka Bay by using observed water surface elavations of 20 minumites, at the tower of Shirahama Oceanographic Observatory. The tsunami data used as training and test data for ANN were simulated for different fault models considering tsunami source non-uniformity. The linear activation function was found to be a good choice for output units and the tangent sigmoid function for hidden layer's units. For the training of ANN the Levenberg-Marquardt method with Bayesian regulation were employed. Outputs from the trained network such as the first and the second sea surface falls and rises agreed well with the results of tsunami simulations at each location and all five locations.
An aim of our research is to develop a new tsunami detection system by using an ocean radar. In this study, a back scattering strength is proposed as the new detection index. The index is examined by using the ocean radars data observed in Ishigaki Island and Yonaguni Island. There were 46 earthquakes occurred from April 1, 2004 to March 31, 2006. For the M6.5 earthquake, the back scattering strength became larger rapidly around its epicenter when the main shock occurred. However, the M6.5 is not large for tsunamigenic earthquakes. Then, larger sea surface disturbance due to Typhoon Matsa in 2005 are also analyzed. Accordingly, it is confirmed that the back scattering strength became larger when it passed over the ocean radar observation region.
The earthquake off the west coast of Northern Sumatra and the resultant giant tsunami in the Indian Ocean in 2004 caused enormous damages in coutries around the Indian Ocean. As one of them, it was reported that a girder bridge crossing a river was washed away. In this study, numerical simulations by the particle method, which is suitable to treat a moving object and track a water surface, were carried out to examine the relation of a tsunami velocity and motion of a girder bridge. The calculated results showed good agreement with ones in a previous hydraulic experiment. In addition, in the case of a tsunami with drift woods and a bridge with handrail, the washed process of a girder bridge was simulated.
A series of numerical studies of the December 26, 2004 Indian Ocean tsunami had been carried out using dispersive wave models i. e. weakly and fully nonlinear Boussinesq-type equations and nondispersive wave models i. e. linear and nonlinear shallow water equations. Numerical model results are compared each other or with field measurements. General features of tsunami propagation agree well in all numerical results. Numerical results of water level distribution calculated by dispersive and nondispersive wave models showed important differences especially in development of wave front. Discussion of free surface spatial distribution concluded that the dispersion mechanism is important for tsunami propagation in deep sea region, whereas nonlinearity is important in shallow water region.
The 3-D dynamic tsunami simulation procedure developed by the authors takes into account the dynamic seabed displacement resulting from seismic faulting and acoustic effects of seawater. Some new techniques have been developed for upgrade of the existing procedure, which include the so-called nesting of the mesh size and extension for run-up to coastal areas. Practicality of the upgraded procedure has been successfully validated by, for example, simulation of the dynamic generation of a near-field tsunami followed by the propagation and run-up.
Inundated flow with floating bodies was videotaped in Banda Aceh at the time of the 2004 Indian Ocean Tsunami, and attracted public attention. In light of the circumstances, this study presents a model for estimating the moving velocity of floating bodies, i. e., the current velocity of inundated flow with floating bodies in a steady state. The model adopts the notion of the bore theory regarding the floating bodies as a hypothetical fluid, and takes account of the resistance due to the floating bodies piling up at the surge front of inundated flow. Experiments are carried out to grasp the behavior of floating bodies at the surge front. Through examinations of the experimental results and the solutions of the model, it is concluded that the model is useful to estimate the inundated flow with floating bodies.
Sometimes tsunami transports large boulders (tsunami boulders). The movement of tsunami boulders could have directly related to the hydraulic force of tsunami. Our field observations clarified that long axes of boulders at Pakarang Cape, Thailand, which had been transported by the 2004 Indian Ocean tsunami, were likely to be vertical against the tsunami flow direction. Moreover, our hydraulic experiment revealed that boulder movement is affected by their initial long axes orientations, suggesting that shapes and long axes orientations of boulders must be considered in the numerical simulation.
There are high risks that tsunamis may cause containers stored in ports to drift into sea/land areas. In this study, a simulation model for container drift behavior was constructed to enable accurate prediction of the drift behavior of containers and its collision force. The applicability of the model was confirmed by calculations reproducing previous container drift experiments. The results showed that it is possible to reproduce the collision force when containers drift and collide with walls at the back of the container storage area due to differences in the container weight, container length and rigidness of the wall for the supercritical flows on an apron.
It is important to evaluate the damage on structures due to the drifting bodies with tsunami. However drifting behavior is very sensitive to tsunami velocity and its force. The purpose of the present study is to investigate the variability in the drifting bodies due to tsunami. First, experimental tests are carried out. As a result, tsunami turbulent diffusivity that occurred by breaking waves was related to variability in drifting behavior. Second, calculation is carried out using the diffusion coefficient provided by the experiment. Finally, an evaluation method is proposed which can predict the behavior of drifting bodies by tsunami.
We investigated the damage of mangroves by the 2004 Indian Ocean tsunami at Banda Aceh, Indonesia. We clarified that no mangroves could have survived in the west of Banda Aceh affected by more than 10m height of tsunami, although more than 50% of mangroves with 20-25cm stem diameter could have survived in the east of Banda Aceh affected by 5-7m height of tsunami. We simulated the 2004 Indian Ocean tsunami to investigate the impact on mangroves. Based on our field observation and numerical simulation, we estimated the destruction limit of mangroves using the relationship between the stem diameter and computed-tsunami bending moment. Furthermore, we evaluated the potential mitigating effect of mangroves at Banda Aceh using the numerical model with the destruction limit considered.