To analyze the influence of vorticity on surface and internal waves, Kakinuma and Nakayama (2007) proposed a fully-nonlinear strongly-dispersive internal wave equation by taking into acount vorticity effects (FSI model). In this study, we made an attempt to apply the FSI model to reproduce the trochoidal waves in order to investigate the reliability of the FSI model in flow fields with vorticity. As a result, we obatained good agreement between the FSI model and the theoretical solutions. Furthermore, we applied the FSI model into solitary waves with positive vorticity, which results in the supression of wave celerity and wave height.
Nonlinear interaction between internal waves including very large amplitude waves has been numerically simulated using nonlinear internal-wave equations based on a variational principle. When an internal solitary wave is reflected at a vertical wall, the amplification factor of wave amplitude becomes lager as the ratio of the amplitude of incident wave to the limit amplitude of internal solitary wave is moderate, where the kinetic energy is predominant in the wave energy. As the amplitude of internal wave is close to the limit amplitude of internal solitary wave, the internal wave shows linear characteristics, such that the kinetic energy nearly equals to the available potential energy. Internal waves of very large amplitude propagating over an upslope or a downslope have also been examined, where the energy of the main wave is almost conserved.
Internal solitary waves propagating from deep water to shallow water in a two-layer fluid are numerically simulated by solving the set of nonlinear equations in consideration of both strong nonlinearity and strong dispersion of waves. As an internal solitary wave travels from deep water to shallow water, almost all its wave energy is transmitted from the deep- to the shallow-water regions. A BO soliton propagates into a shallow-water region, generating KdV solitons, the characteristics of which depend on the positional relationship between the interface and the critical level. In the case where the static interface is below the critical level in a shallow-water region, disintegration of an internal solitary wave occurs remarkably, after which the available potential energy of the wave train becomes larger than its kinetic energy.
We develop a tsunami simulator integrating a 3-D fluid simulation technology that runs on large-scale parallel computers using smoothed-particle hydrodynamics (SPH) method, together with a 2-D tsunami propagation simulation technique using a nonlinear shallow water wave model. We use the 2-D simulation to calculate tsunami propagation of scale of about 1000km from epicenter to near shore. The 3-D SPH method can be used to calculate the force that a tsunami can exert on a building, and to simulate flooding patterns in urban area of at most km scale. By applying the processing power of computers to the technologies resulting from this research, we seek to contribute to improved disaster preparedness and disaster mitigation through a better understanding of tsunami's mechanisms.
A numerical wave flume based on a particle method is a key tool for a design of coastal structure under the action of extremely large and strongly nonlinear wave forces. The SPH, which is the predominant method in the international research society, contains unphysical artificial viscosity due to its explicit algorithm. The ISPH method evades the artificial viscosity by introducing semi-implicit algorithm, however it suffers from another drawback, namely a pressure fluctuation. In this study, accurate schemes, which have been developed to enhance a stability of pressure in the MPS method, are applied to the ISPH method, with examining their applicability through some benchmark tests.
Surface tension plays a key role in splash generation. However, accurate modeling of surface tension is challenging due to the numerical difficulties in calculating the interface curvature. This paper presents a new surface tension model for macroscopic particle methods on the basis of Continuum Surface Force (CSF) concept. The new model is characterized by a novel formulation for curvature estimation using directsecond order derivatives of color function via a meticuluos and comprehensive discretization. The newmodel is referred to as Laplacian-based surface tension model which applies a high-order Laplacian schemeincluding the approximation of boundary integrals. A set of benchmark tests are considered for simple andcomprehensible verifications and then the model is applied to a water drop impact test to investigate itsappropriateness in calculation of splash generation. Comparisons are also made with two commonly appliedsurface tension models in the context of particle methods, namely, divergence-gradient based model and the arc fitting one.
The so-called numerical wave flume has rapidly advanced and increased its pragmatic application to coastal engineering problems. In application of the particle methods, incident waves as an input condition are reproduced by a similar way to the physical experiments by setting a wave paddle composed of moving particles and forcedly driven in accordance with the input condition. Despite its simple and convenient procedure, considering more comprehensive situations, some additional manners, e.g. dynamic bending plate, non-reflection function, control of the volume of fluid are required to reproduce more physical distribution of velocities of inlet flow. In this study, a novel moving boundary condition as a wave-making model for the Moving Particle Semi-implicit method is proposed by setting virtual wall particles. Its performance is verified through some benchmarks, e.g. reproduction of flap and piston motions of a wavemaker with showing its good adaptability.
A rubble mound or subjacent sand ground of a composite breakwater can be scoured by a tsunami overtopping. Hence, it is indispensable to examine a scouring due to overtopping water for making a damage prediction of composite breakwater. Although a particle method is suitable for simulating this scouring process, small conductivity in a sand layer at sea bottom can bring a numerical instability in an interaction term between fluid and sand. Therefore, in this study, the higher order Laplacian model has been improved for a more stable calculation, and the applicability of the model is examined through a numerical test on scouring process due to submerged impinging jet.
Sprays and air bubbles formed during wind wave breaking events under various wind conditions were simultaneously visualized using two high-speed video cameras and a back-light imaging technique. The shapes of the sprays and entrained bubbles were quantitatively measured on the basis of novel level-set image detecting algorithm. Spectrum slope of spray and bubble size were found to decrease from approximately 2.2 mm and 1.5 mm respectively. It was also found that the volume rate and wind-wave Reynolds number (RB), the number density and RB are both related to positive correlation.
We carried out a direct numerical simulation of open-channel flow with wind shear stress to investigate numerically the effect of the wind stress on the air-water gas transfer. The numerical results show the wind shear to affect significantly turbulent eddies close to the air-water interface. Spatial patterns of the surface divergence and the interfacial gas flux are stretched in the wind direction,and the similarity between both patterns is found to decrease with increase of the wind stress. The cross-correlation coefficients between the gas flux and the spanwise vorticity are also obviously changed by the presence of the wind stress. The gas transfer velocity in this case doesn't agree with the solution of the surface divergence model. This suggests that the other dynamical mechanism promotes the gas transfer at the wind-sheared interface.
This paper proposed an oxygen transfer model for bubble-laden turbulence generated by plunging jets. The proposing model has been validated through comparisons with experiments for bubble velocity, liquid velocity, liquid turbulence and oxygen flux. It was found dissolved oxygen concentrations in bubbly flows was determined by local bubble behaviors and turbulent flows modified around bubbles. This bubble-mediated gas transfer via mechanical interaction between bubbles and turbulence is important to understand air-sea gas exchange in the surf zone.
High speed infrared imaging measurements were performed for identifying mechanical factors to govern surface skin temperatures on wind waves under moderate to strong winds. Surface renewals owing to turbulent disturbances are found to predominantly determine the skin temperature amplitude and phase lags to surface elevation, which is parameterized by a so-called wind-wave Reynolds number (RB). The modulations of the skin temperature variations are observed at RB ~ 4 × 104, indicating governing dynamics to produce surface turbulence is altered at the boundary.
This paper presents a novel stochastic-LES hybrid model for favre averaged bubble-turbulence interactions in free-surface flows. The current model is found to be capable of computing local behaviors of dense bubble flows coupled with fluid turbulent motion, which is ensured by comparisons with experimental observations. The model is also applied to the flow at a planar jet impact onto a still water, as a model of overturning jets of breaking waves, which reasonably computed cavity deformation, air tube entrainment and bubble formations.
To understand the characteristics of the bottom boundary layer, movements of suspended particle material and its related radionuclide transport on Jyoban coast, the field measurement was conducted at the shallow water depth (30m) by using turbidity sensor, in-situ laser scattering type particle distribution measuring device and acoustic measuring instruments. The survey results have shown that large particles more than about 200μm appeared with the low turbidity in calms, though small particles covered with the high turbidity in storms. Furthermore, it was revealed that the increased turbidity ranged from the bottom to about 10m in height by using acoustic measuring instruments.
Effects of two-way wave-current interaction (WCI) on the surfzone-inner shelf circulations affected by submesoscale eddies and unsteady littoral currents are investigated with the ROMS-WEC model (Uchiyama et al., 2010) coupled tightly with a spectrum-peak wave model to account for both wave effects on currents (WEC) and current effects on waves (CEW) (e.g., Uchiyama et al., 2009). Eddy activity around the outer edge of the surfzone is enhanced when CEW is considered. The key mechanism to induce the surfzone-inner shelf dynamical interaction and enhancement of offshore eddy activity is considered to be CEW that weakens the offshore component of the littoral currents. In turn,offshore eddy activity is attenuated by WEC, demonstrating that WCI plays an essential role not only in the sufzone but also in the shelf region.
This study focuses on the hydrodynamics in the opening of artificial reefs and the applicability of a quasi-three dimensional nearshore current model with the wave-current interaction. First, the characteristics of the waves and steady currents in the opening area were investigated using the wave flume under irregular wave conditions. Secondly, the numerical model was calibrated and verified by comparing with the experiment results. Finally, the numerical model was applied to the results of a field investigation conducted at Uradome Beach in Tottori, Japan. The computed wave and steady current fields in the opening of two artificial reefs were compared with the measured data. From the computed results, we found that the numerical model gives reliable results to the prediction of the hydrodynamics around the artificial reefs.
This study aims to investigate the characteristic behavior of severe wave inundation along the reef coast during typhoon event. Laboratory experiments were performed to represent storm waves transforming over shallow fringing reef. Image-based measuring technique was developed and applied to capture the wave characteristics as high-resolution data sets both in spatial and temporal domains. It was found through the obtained experimental data set that, besides significantly elevated mean water level, infragravity waves were generated and formed standing waves on the reef even though regular periodic waves were introduced to the flume. Amplitude of the observed resonant infragravity wave was highly dependent on the period of incident regular waves. Wave-induced radiation stress near the breaking point also had fluctuations with frequency of infragravity waves and the phase of this fluctuating radiation stress matched with that of estimated acceleration of horizontal velocity at the node of observed resonant infragravity waves. This wave-induced radiation stress near the breaking point may also change the period of infragravity wave or even vanish the evolutions of infragravity waves.
The relationship between skewness and kurtosis of surface elevation and slope of irregular waves was investigated using laboratory and field observations. The squared values of skewness were found to be proportional to kurtosis as estimated by using the Stokes wave model. The joint probability density functions of surface elevation and slopes were evaluated by applying the principle of maximum entropy. The effects of reflected waves on the joint distribution of the surface elevation and slopes were also investigated. The theoretical conditional distributions of p(η, ηx=0) based on a simple nonlinear wave model reproduced the dependence on the representative wave slope and were in good agreement with the laboratory observations.
This study aims at clarifying statistical properties of significant wave period T1/3 observed in 7 observatories along the Sea of Japan coast. Its conditional frequency distribution with H1/3 is roughly approximated by normal distribution. Data with H1/3/L1/3 > 0.03~0.04 in the distribution is very few. This may be brought by wave breakings. To realize breaking effect in the distribution, cut off distribution model is proposed in this study. Connecting the cut off model and the existing frequency distribution of H1/3 (Kimura et al. 2013), the combined frequency distribution between H1/3 and T1/3 is newly proposed. This study also discussed a combined distribution of zero-crossing wave height H and period T giving a model spectrum. Combined Rayleigh~Log-Normal distribution shows excellent adaptability.
Using season-separated data sets over 45 years of measured sea level pressures (pH, pL), pressure-based wind speeds(U) and hindcast-based wave heights(H) on the inner sea areas of Japan such as Tokyo Bay and the climate change indices(CCIs) on the global scale, their correlation, EOF, trend and jump analyses are conducted. The main results are as follows; 1)Statistically significant correlations are more or less detected among CCIs, but WP is a CCI correlated most weakly with the other CCIs. 2)The CCI yielding a significant correlation with any of summer or winter season-separated pH, pL, U and H data is WP, with the correlation stronger in winter season. 3)Statistically significant trends in each data set may be substantially replaced by jumps of mean value or both mean and variance values putting a turning year at around 1986-1987.
Measured and hindcasted wave data samples in the coastal area of the Japan Sea during a huge low pressure system in April 2012 are analyzed. The results are that 1) frequent occurrence of large wave heights in recent years gives rise to an increasing trend of low-induced annual maximum wave height data samples at many of the measurement stations and results in augmentation of the return wave heights and their standard deviations, 2) wave models such as SWAN and authors's YH3 reproduce well the time variations of wave heights and wave periods during the low, 3) the low may yield a maximum wave height slightly exceeding 13 m in the Japan Sea, which probably corresponds to the uppermost value in the past 70 years, 4) a Monte-Carlo simulation suggests the likely occurrence of greater wave heights.
Trends analysis for the annual maximum storm water levels and significant wave heights was conducted using the Mann-Kendall trend test and the record-breaking test. The trend test revealed that the extreme vales of the storm water level at Toyama and Maizuru have an increasing trend. The extreme significant wave heights at Hachinohe also show a tendency to increase. It is found that the storm water levels and wave heights at Hachinohe have increasing breaks of record. The estimation method for evaluating the return values in non-stationary quasi-periodic extreme time series was developed in which the scale and location parameter in extreme distribution function are in a linear manner with time. The estimated 2-year, 5-year and 10-year return values showed moderately changes in accordance with the observed extreme data.
We investigated the spectral structure and source balance of short gravity waves,based on in situ observations of wavenumber spectra retrieved by air-sea interaction spar (ASIS) buoys. The observed wavenumber spectra showed the spectral power laws described by Toba  and Phillips  in addition to the characteristic nodal point at ~10 rad/m. The wave model reproduced the spectral form in the higher wavenumber domain using the nonlinear dissipation term. In the equilibrium range,nonlinear transfer played a major role in maintaining equilibrium conditions. On the other hand,in the saturation range,which starts at the upper limit of the equilibrium range, nonlinear transfer did not keep up with other source terms, and the dissipation term was in balance with wind input.
It is well known that a correlation between infragravity wave heights and the properties of wind waves observed in offshore harbor. Hirasihi et al (1997) have proposed a function of infragravity wave spectrum related to a function of wind wave spectrum by a boundary frequency estimated with parameter: αl. The αl can be estimated with the square root of ratio of infragravity wave energy to total wave energy: RL. In this study, a related function between αl and RL for JONSWAP spectrum is proposed and it is confirmed that an averaged value of αl estimated with spectra observed in storm conditions at each observation station may overestimate the infragravity wave heights in calm conditions. Moreover, the related function between Ursell number and αl proposed Hirayama et al (2014) can estimate them with good accuracy.
The strong typhoon Sanba crossed the east side of Japan in September, 2012. The minimum central pressure of the Sanba reached 900 hPa. The typhoon generated wind waves more than 15 m in the significant wave height and gave severe damages to coastal structures. This study analyzed observed wave records at 10 stations along the typhoon track. A series of numerical analysis was performed to understand the characteristics of extreme sea condition by the typhoon. The maximum wave heights were estimated based on the spectral wave model and the nonlinear short wave statistical theory. The observed data shows the nonlinear enhancement of maximum wave height slightly. The estimated maximum wave height by the nonlinear theory shows better agreement with the observed peak of maximum wave height than that by the linear theory.
Long waves are known to play a dominant role in the swash zone hydrodynamics during storms. Here an attempt to relate the wave properties of the incident long waves to those of offshore waves is carried out by using field data. Equivalent deepwater significant wave height of the incident long waves near the shoreline is shown to be expressed by an empirical formula with significant wave height and mean period at offshore. In addition, applicability of a separation method of incident and reflected waves for long waves on a sloping beach (SLSS) is discussed.
In order to examine the local effects for Abiki amplification in bay and ports, data analysis is performed using tide and atmospheric pressure time-series measured at 10 locations along the western coast of Kyushu Island during February 21 to 25, 2009. Abiki oscillations were defined by subtracting the predicted tide from measured tide levels. Using the threshold value of Abiki wave weight, zero-up and zero-down crossing methods, the durations of Abiki amplification are evaluated. Positive relationships (R2=0.44) between the wave height and duration of Abiki amplification are confirmed. Tidal motions of spring tide play an important role as for the local amplification factor after comparison with the time series between synoptic atmospheric pressure, predicted tide, slight atmospheric pressure change, and Abiki wave height.
Large seiches occurred in Kyushu and its peripheral areas in February and July, 2009. Nakai and Hashimoto(2011, 2012) reported that slight atmospheric pressure changes played very important roles for the seiches. Like the examples of 2009, seiches occur locally in limited areas in many cases. On the other hand, seiches occurred throughout Japan in November, 2004 and January, 2005. The authors analyzed the propagation direction and speed of slight atmospheric changes by F-K spectrum for these cases. Slight atmospheric changes propagated almost eastward and crossed the Japanese Islands quickly in 2009. But they propagated along the Japanese Islands to the northeast direction for a long time in 2004 and 2005. The propagation directions of slight atmospheric pressure changes affect the sea areas where seiches occur very much.
Meteotsunamis have frequently been excited in bays and harbors along west coast of Kyushu during early spring time. Makurazaki harbor has also been suffered by meteotsunami disturbances, although its mouth does not open east wards. The present study investigates the possibility of a resonant coupling between atmospheric disturbance and geometric edge waves trapped on the continental shelf. A field observation was conducted by deploying three tidal gauges along the coast. The measured predominant spectral peaks and phase patterns were discussed by referring the theoretically predicted ones for the trapped waves on the shelf.
The 2011 Tohoku Earthquake Tsunami attacked the northern Pacific coast of Japan, ran up along the rivers and overflew the river levee. Video images of tsunami run-up recorded in this catastrophic event enabled us to quantitatively estimate various hydrodynamic features of tsunami and it was found that existing numerical models tend to underestimate the tsunami run-up velocity along the river. This study performed several numerical experiments and compared the results with video-image analysis around the Kido River Mouth. It was found through the analysis that discretization schemes of advection term and other computational conditions such as profiles incident tsunami and detailed geography of the river including levee are essential factors for accurate predictions of tsunami run-up along the river.
To simulate landslide induced tsunami, we proposed an integrated model including landslide and tsunami models. The model was derived based on the two layer-model assuming the Coulomb theory. The numerical model was verified by the simulation of 1792 Ariake-Kai tsunami caused by Mayuyama collapse, which killed 15,000 people. The numerical result was approximately consistent with the measured data of deposition area. To further validate the model, we compared measured tsunami heights with computed results. The results was satisfied with JSCE's K and κ values (K=0.96, κ=1.37). These findings confirm that the model can be used with confidence to investigate 1792 Ariake-Kai tsunami. According to our results, the tsunami was reflected by Kumamoto area and the waves were trapped on Shimabara peninsula.
Some well-engineered reinforced concrete buildings collapsed due to the tsunami in the Tohoku-Pacific Coast Earthquake on March 11th, 2011. Understanding the tsunami forces and damage mechanisms of these buildings has become an urgent issue that demands prompt action from the tsunami resistant building design. In this study, a tsunami simulation using VOF method has been conducted to reproduce the tsunami in Onagawa city, Miyagi prefecture. Calculated tsunami elevations and inundation on shore showed good agreement with the recorded results. Tsunami loads acting on a collapsed building in the Onagawa port area were also discussed under considering the damaged situations of the building foundation and its piles in order to clarify the falling mechanism of the building.
This paper presents a study on influences of computational conditions on numerical simulation of the building shape, collapse and drift in Tateyama city. The conventional tsunami simulation presents the influence of the building as a roughness. In this study, we studied in consideration of a shape, the collapse and drift of the building. The conventional tsunami simulation underestimates the inundation and velocity in some fronts and rear place of building group. Even if the shape of building is considered in the simulation, inundation is underestimated behind the building, when collapses of buildings are not taken into consideration. In this study, the consideration of the condition of the building is important and cannot ignore the influence of collapse and drift on calculating Tsunami simulation.
After the Great East Japan Earthquake Tsunami of 2011, we became deeply concerned about estimating the supposed maximum tsunamis. Authors investigated the volcanic tsunamis in the northern part of Kagoshima bay which is conceived as one of the most serious disasters in our region. In the calculated results for the real basin, effects of the local topography and bathymetry were so large that the common nature of the volcanic tsunamis in closed basins was not necessarily clarified. The present study aims to find universal characteristics inherent in volcanic tsunamis in the closed basin using an idealistic basin model.
Numerical simulation of distant tsunamis traveling through the sea on the plate or over the mantle has been performed, where it is assumed that the upper layer of mantle under the crust is a fluid, while the plate is an elastic thin plate floating between the sea and mantle. Internal-mode tsunamis progressing more slowly than the surface-mode ones appear because of the existence of the mantle, i.e., the lower layer of fluids. In several cases, where the parameters are the density and static depth of the upper layer of mantle, as well as the flexural rigidity of plate, the internal-mode tsunamis show an appropriate time lag of peak time from that of tsunamis propagating through the sea without the mantle, after the travel between Chile and Japan.
Numerical simulation of tsunamis in two bays in Kagoshima Prefecture was performed: Shibushi Bay and Kagoshima Bay. The former, which faces the Hyuganada connected to the Pacific, has been attacked by Hyuganada earthquake tsunamis, as well as Nankai earthquake tsunamis. In the present study, the tsunamis due to both 1968 and 1970 Hyuganada earthquakes were simulated to study the properties of tsunamis around the southern part of Kyushu including the inside of Shibushi Bay. On the other hand, although the bay mouth of the latter is not directed to the sources of these tsunamis, tsunamis have been generated by submarine volcanic eruption in the bay. We supposed the value of scale index for submarine eruption concerning tsunami generation and then simulated tsunamis due to submarine volcanic eruption in Kagoshima Bay.
We proposed to take several wave boundaries which make possible multi-way incident into three dimensional analytical boundary and then we made three dimensional tsunami analysis over wide area based on the result of two dimensional analysis. By this proposed technique, the propagation movement of two dimensional tsunami was reflected in three dimensional analysis boundary, and the continuous generation of the tsunami simulation that comprised a macroscopic evaluation of the tsunami and a microscopic evaluation in the vicinity of the site could be shown. This analysis of the continuous generation of tsunami can be expected as a technique to be able to achieve the flood simulation in high accuracy as well as being able to make the evaluation of the power of tsunami load that affects on embankments, bridges, and buildings.
Imaging measurements of runup dam-break waves over sloping beds were performed for identifying kinematic features of wave propagation and free-surface transition. It has been found that typical blob like front shapes with transverse undulations were developed during propagation especially on highly sloping beds. The rolling motion of the wave front at the bed contact was observed to entrain air beneath the water layer behind the front, which becomes mechanically unstable to be fragmented into bubbles and to affect the wave forms.
The design to strengthen coastal defence structures with their ductility is going to be employed. This study applies three different numerical models; CADMAS-SURF2D-OpenFOAM and MPS, to verify their accuracy compared with the hydraulic experiments of breakwaters under tsunami load and to clarify their applicability for ductility design. In case that tsunamis overflow crown heights of breakwaters extremely, it was suggested that tsunami velocity behind breakwaters could not be simulated accurately by CADMAS-SURF2D, while OpenFOAM and MPS had good agreement with experimental results. It was also found that numerical results may lead to underestimate necessary weights of armor blocks.
A Hierarchical Bayes model of tsunami source inversion is proposed in this study. The model makes possible simultaneously to estimate unknown parameters and unknown hyper parameters that define the weight of constraints on the solution of unknown parameters. A quantitative analysis of uncertainty on unknown parameters was conducted on the basis of the proposed model. It allows us to obtain not only point estimation but also interval estimation. A simulation-based validation and verification were conducted on the test case of a tsunami generated by a uniform slip of a rectangular reverse fault.
This study aims at the estimation of tsunami wave force due to the 2011 Tohoku earthquake tsunami. Field survey in Ryori, Iwate Prefecture, suggested multiple mechanisms for the collapse of 8.6 m high coastal dikes. Numerical tsunami simulation based on the nonlinear dispersive wave theory revealed the concentration of tsunami-induced flow to the northern area which is considered to develop severe scour of the foundation. The model also simulated the large wave force was exerted to the dike due to the tsunami overflow as well as the impulsive breaker force due to 10m high short period wave generated at the wave front. The estimated wave force was consistent with the collapse of the parapet observed in the field study.
A fast tsunami simulation system was developed which utilized the superposition of point source computations stocked as a database. The single point source was represented by the Gaussian distribution with s=5 km. The propagation of the point source was computed by using the linear Boussinesq theory. The accuracy of the model was discussed in representing the actual tsunami source profile as well as in the dispersive tsunami propagation. The system was applied to a hypothetical Japan Sea tsunami used in the disaster mitigation planning of Tottori Prefecture. The system successfully displayed the sensitivity of local tsunami height to the tsunami source location and thus demonstrated the performance to assist specific evacuation planning in individual towns and cities.
Waveform analysis using data by the 2010 Chilean tsunami obtained in Tokyo Bay were carried out. Numerical experiments using single sine wave with various periods in and around the bay were also carried out. Then we conclude that a tsunami in Tokyo Bay is characterized by a tsunami originated from the Seiche excited in Sagami Bay; the Seiche in Sagami Bay is efficiently excited from offshore tsunami whose period is 30 min or more.
This study investigates the land subsidence in Miyagi Coast caused by The Great East Japan Earthquake of 2011 by analyzing water level measurement and tidal data. The continuous water level measurement data at Kobama, Nobiru, Onagawa, and Fukuchi were compared to the tidal level. It was found that before the earthquake, the recorded water level coincide well with the tidal level. The land subsidence caused vertical dislocation of the water level measurement device. Therefore,the measured water level elevation deviates from the astronomical tide. The land subsidence at each location was estimated based on this deviation. The estimated subsidence from the water level analysis at each location correlates well with the reported subsidence by the Geospatial Authority of Japan (GSI).
This study estimated the storm surge and wave distributions of Typhoon Haiyan in Central Philippines by using a 2D parametric typhoon model, a one-layer long-wave-based fluid model, and SWAN. The simulation led at Tacloban that the storm surge waveform began with a trough due to north wind at the front of the typhoon and subsequently showed a quick rise up to 4m due to the suction-induced crest and the drift by south wind while the maximum significant wave height was about 2m. The spatial resolution can be critical in wave generation simulations for the typhoon with a very low central pressure and a small radius of maximum wind speed. The simulation with T1330-base model typhoons in Visayas showed that the storm surge can exceed 3m not only around Tacloban and Estancia.
The present study conducts a series of hindcast simulations for Typhoon Haiyan storm surges and waves using a coupled model of surge and wave (SuWAT) with changing typhoon radius in 30 km, 40 km, 50 km, 70 km, 80 km, and satellite observation as well as wind velocity limit for the wave dependent drag coefficient. The hindcast results indicate that the radiuses of 50 km and 70 km are reasonable to calculate the typhoon Haiyan storm surges along Leyte Gulf. The 30 m/s wind speed limit for the wave dependent drag coefficient is acceptable in comparison with the field survey results. Further study, which includes inundation modeling, is required to assess the Haiyan storm surges more accurate.
Field measurements and numerical simulations are used to assess the resons for different types of water-related structural damage observed in Tacloban and Eastern Samar. Coastal Tacloban saw heavy damage due to wind waves riding atop storm surge, while inland Tacloban experienced much lighter damage because wind waves were not present (though inundation by surge soiled structures). Eastern Samar experienced little wind-induced or pressure-induced setup, but breaking-wave-induced setup over the reef combined with wave runup and infragravity motions caused heavy damage along the coast.
The catastrophic typhoon “Yolanda” on Nov. 2013 invoked storm surge in the coastal area of the Philippines. The storm surge made the coastal regions to the devastation and maximum water height reached 5m in the Tacloban area. This paper presents the comparison between storm surge simulated results from atmospheric - storm surge- wave- tide coupled model and the observation measured by The 2013 Philippines Storm Surge Joint Survey Group headed up by Prof T. Shibayama. In this study, the TC-Bogus scheme is used in order to simulate accurate typhoon. The simulated storm surge results reached almost 5m in the Tacloban area. The coupled model including TC-Bogus scheme gives accurate simulations for estimating storm surge.
The east coast of eastern Samar in the Philippines faces to the Pacific Ocean and suffered significant damage due to storm waves caused by Typhoon Haiyan. The coast has various characteristic features such as fringing coral reef, varying beach slopes, pocket beaches and well-developed mangrove forest especially inside Matarinao bay. This paper aims to investigate how this characteristic coast was affected by the catastrophic typhoon event mainly through observations of satellite images. Various types of optical satellite images were utilized to capture the changes before and after the typhoon event. Comparisons of satellite observations and numerically computed wave height distributions along the coast clearly showed that the coast inside the bay was strongly protected by sand spit with fringing reefs and thus mangrove strip inside the bay was less damaged. It was also found that estimated penetration distance of wave runup on the beach showed certain correlation with the local width of fringing coral reefs.
Typhoon Haiyan, which struck the Philippines and nearby areas in November 2013, was an extremely intense tropical cyclone that had a catastrophic impact. A series of numerical analyses indicated that the maximum storm surge level was 5-6 m in Tacloban. The numerical experiments show the coherent structure of the storm surge profile due to the specific bathymetry of Leyte Gulf and the Philippines Trench as a major contributor to the storm surge disaster in Leyte Gulf. Based on the comparisons of forecasts and hindcasts, it was difficult to predict the storm surge a few days in advance, quantitatively.