Tsunami Wave Profile Research Articles

Dynamics of a moored submerged floating tunnel under tsunami waves

This paper investigates the dynamic behavior of a moored submerged floating tunnel (SFT) under tsunami-like waves. A hydro-elastic numerical study is conducted with the time-domain dynamics simulation model that considers structural deformability through 1D line elements. Tsunami-like waves (solitary wave, 2011 Tohoku-tsunami, and 2005 Indian-Ocean-tsunami) are applied to the numerically modeled dynamic system to demonstrate the effects of tsunami wave profiles on the hydro-elastic behavior of the SFT and mooring-line tensions. After setting the numerical model, systematic sensitivity tests are conducted concerning various design parameters, such as drag coefficient, wave height, buoyancy-weight ratio, and water depth. The results show that SFT dynamics and mooring tensions can significantly depend on those design parameters. The SFT system is generally more vulnerable to shorter-duration and higher-elevation tsunamis due to greatly enlarged SFT transient motions and mooring snap loadings—a shorter-duration solitary wave results in 2.5 times higher maximum lateral SFT motions than longer-duration combined waves. Also, a three times larger full lateral movement is observed when tsunami elevation is doubled in combined waves. The results highlight the roles of those design factors and tsunami patterns so that they can be applied to the design of future SFTs in tsunami-prone regions.

Hazard and Risk-Based Tsunami Early Warning Algorithms for Ocean Bottom Sensor S-Net System in Tohoku, Japan, Using Sequential Multiple Linear Regression

This study presents robust algorithms for tsunami early warning using synthetic tsunami wave data at ocean bottom sensor (OBS) arrays with sequential multiple linear regression. The study focuses on the Tohoku region of Japan, where an S-net OBS system (150 pressure sensors) has been deployed. To calibrate the tsunami early warning system using realistic tsunami wave profiles at the S-net stations, 4000 stochastic tsunami simulations are employed. Forecasting models are built using multiple linear regression together with sequential feature selection based on Akaike Information Criterion and knee-point method to identify sensors that improve the accuracy most significantly. The study considers tsunami wave amplitude at a nearshore location and regional tsunami loss for buildings to develop hazard-based and risk-based tsunami warning algorithms. The models identify an optimal configuration of OBS stations and waiting time for issuing tsunami warnings. The model performance is compared against a base model, which only uses the earthquake magnitude and epicenter location. The result indicates that estimating the tsunami amplitude and loss via S-net improves accuracy. For the hazard-based forecasting, adding six sensors from the S-net improves the accuracy of the estimation most significantly with an optimal waiting time of 3 min. For the risk-based forecasting, a longer waiting time between 5 and 10 min is suitable.

Numerical study on hydrodynamic load of real-world tsunami wave at highway bridge deck using a coupled modeling system

In this study, a tsunami wave profile observed during the 2011 Japan Tsunami has been parameterized and applied for predicting hydrodynamic characteristics of coastal highway bridges under the impact of tsunami surge waves. The propagation of tsunami waves from the open sea to the inshore bridge site and its final impact at coastal highway bridge are typical multiscale coastal flow phenomena, whose integral simulation is beyond the reach of most existing numerical models. To simulate such multiscale flow phenomena, a newly developed coupled modeling system named the SIFUM-FVCOM system has been applied to study the tsunami wave impact at a coastal highway bridge deck. The effects of three dominant factors, particularly distance to the shoreline, clearance height, and tsunami wave height, on the resultant hydrodynamic loads at the bridge deck have been numerically investigated. The findings of this paper are believed to be instructive to improve our understandings on the hydrodynamic characteristics of coastal highway bridge under the impct of real-world tsunami wave and their future design.

Rapid tsunami loss estimation using regional inundation hazard metrics derived from stochastic tsunami simulation

This study explores the development of rapid tsunami loss estimation approaches that are based on regional inundation hazard metrics, such as representative inundation height and inundation area. In post-tsunami situations, these inundation hazard metrics can be inferred from remotely-sensed images. Using a probabilistic tsunami loss model for the Tohoku region of Japan, rapid tsunami loss estimation models are developed by regressing predicted tsunami losses against regional inundation hazard parameters, which are derived for coastal cities and towns in Miyagi Prefecture from 4000 stochastic tsunami simulations. Using numerous earthquake sources of moment magnitudes between 7.5 and 9.1 facilitates the robust development of a quick tsunami loss estimation tool. Special considerations are given in investigating the effects of coastal topography (plain versus ria) and the potential bias due to errors in estimating inundation heights and areas on tsunami loss. Performances of the new approaches are compared with conventional methods that are based on earthquake magnitude, source-to-site distance, and offshore tsunami wave profiles. The loss models based on regional inundation area outperform other approaches and thus are recommended for regional tsunami loss estimation.

Numerical Study on the Hydrodynamic Characteristics of Submarine Pipelines under the Impact of Real-World Tsunami-Like Waves

Submarine pipelines have been extensively used for marine oil and gas extraction due to their high efficiency, safety, and low price. However, submarine pipelines are vulnerable to extreme waves (i.e., tsunami waves). Previous research has often used solitary waves as a basis for studying the impacts of tsunami waves on submarine pipelines, although the hydrodynamic characteristics and wave properties drastically differ from those of real-world tsunami waves. This paper numerically investigates the hydrodynamic characteristics of tsunami waves interacting with submarine pipelines, but instead uses an improved wave model to generate a tsunami-like wave that more closely resembles those encountered in the real-world. The tsunami-like wave generated based on a real-world tsunami wave profile recorded during a 2011 tsunami in Japan has been applied. Given the same wave height, simulation results show that peak hydrodynamic forces of the tsunami-like wave are greater than those of the solitary wave. Meanwhile, the duration of the acting force under the tsunami-like wave is much longer than that of the solitary wave. These findings underline the basic reasons for the destructive power of tsunamis. It is also noted that the hydrodynamic forces of the pipeline under the tsunami-like wave increase with wave height, but will decrease as water depth increases. In addition to the single pipeline, the complicated hydrodynamic characteristics of pipelines in tandem arrangement have been also numerically studied. It is believed that the findings drawn from this paper can enhance our understanding of the induced forces on submarine pipelines under extreme tsunami waves.

Wave Profiles of a Virtual Extreme Tsunami in the Northern Region of South China Sea

Tsunami wave profile is one of the important inputs for evaluating impacts of the tsunami on coastal and offshore structures. To understand the tsunami wave patterns along the northern coastal regions of South China Sea, we simulate the tsunami propagation in the South China Sea generated by a hypothetical earthquake of magnitude [Formula: see text] in Manila trench. The Boussinesq equations are adopted to account for the nonlinear and dispersive effects on the propagation and deformation of tsunami wave propagating over the continental shelf. Focusing on several locations in the northern region of South China Sea, the nested grids with gradually higher spatial resolution are used to ensure computational accuracy. Numerical results reveal that undular bores and several soliton-like waves may develop in shallow water in regions where water depth is less than 100[Formula: see text]m. The shallow continental shelf length and the steepness of wavefront are the two dominant variables that determine the development of undulation.

Numerical analysis of tsunami-like wave impact on horizontal cylinders

During the past few decades, several tsunami events have caused tremendous devastation to onshore and offshore infrastructures. Although the tsunami waves have been studied with solitary waves since 1970s, the wave profile differences between solitary and tsunami waves directly result in the significant differences in their energy carrying capability and potential destructive impacts. In this study, a tsunami-like wave profile has been adopted by using a composition of solitary waves to simulate a real tsunami wave profile. A two-phase flow model was numerically resolved with the finite volume method with the volume of fluid method to track the free surface. The numerical model was first validated against the experimental and theoretical studies with the solitary wave. And then, the impact of tsunami waves at submerged horizontal cylinders was numerically studied. The hydrodynamic differences between the solitary wave and tsunami-like wave passing the submerged cylinders have been discussed, which shows the significant differences on the punching forces and the velocity field evolution around the cylinders. Moreover, the effects of wave height and submersion depth on the hydrodynamic loads were considered, and the influence of the spacing distance on the interactions between cylinders in a tandem arrangement was also investigated.

Numerical investigation of tsunami-like wave hydrodynamic characteristics and its comparison with solitary wave

Solitary waves have been commonly used as an initial condition in the experimental and numerical modelling of tsunamis for decades. However, the main component of a tsunami waves acts at completely different spatial and temporal scales than solitary waves. Thus, use of solitary waves as approximation of a tsunami wave may not yield realistic model results, especially in the coastal region where the shoaling effect restrains the development of the tsunami wave. Alternatively, N-shaped waves may be used to give a more realistic approximation of the tsunami wave profile. Based on the superposition of the sech2(*) waves, the observed tsunami wave profile could be approximated with the N-shaped wave method, and this paper presents numerical simulation results based on the tsunami-like wave generated based on the observed tsunami wave profile measured in the Tohoku tsunami. This tsunami-like wave was numerically generated with an internal wave source method based on the two-phase incompressible flow model with a Volume of Fluid (VOF) method to capture the free surface, and a finite volume scheme was used to solve all the governing equations. The model is first validated for the case of a solitary wave propagating within a straight channel, by comparing its analytical solutions to model results. Further, model comparisons between the solitary and tsunami-like wave are then made for (a) the simulation of wave run-up on shore and (b) wave transport over breakwater. Comparisons show that use of these largely different waveform shapes as inputs produces significant differences in overall wave evolution, hydrodynamic load characteristics as well as velocity and vortex fields. Further, it was found that the solitary wave uses underestimated the total energy and hence underestimated the run-up distance.

TSUNAMI-TIDE INTERACTION IN THE SETO INLAND SEA, JAPAN

Tsunami-tide interactions in the Seto Inland Sea (SIS) were investigated by taking into account the effects of tidal currents on the tsunami propagation in terms of the arrival time and the run-up heights along the coast of SIS. The initial tsunami wave profile was introduced by the possible Tokai-Tonankai-Nankai Earthquake of the magnitude Mw9.0, which is equivalent to that of 2011 Tohoku Earthquake. Numerical experiments with four different tidal phases, flood, ebb, high, and low, reveal that the water depth changes due to tides affect the tsunami propagation in terms of heights and arrival time. During high tides, the tsunami propagates faster and reaches higher than during the low tides. In addition, during the flood tides with rising water level, tsunami propagates faster than during the ebb tides. Further investigation also shows that the tsunami-tide interaction changes the tsunami signal such that the tsunami-only spectra shifts the spectral peaks after considering the tsunami-tide interactions. Local oscillation modes characterized by local bathymetry and topography shift to higher frequency modes due to the non-linear tsunami-tide interaction. To reduce the uncertainties involved in tsunami predictions and coastal defenses and management, it is strongly recommended to simulate tsunamis together with tides in shallow water environments.

Sensitivity of tsunami wave profiles and inundation simulations to earthquake slip and fault geometry for the 2011 Tohoku earthquake

In this study, we develop stochastic random-field slip models for the 2011 Tohoku earthquake and conduct a rigorous sensitivity analysis of tsunami hazards with respect to the uncertainty of earthquake slip and fault geometry. Synthetic earthquake slip distributions generated from the modified Mai-Beroza method captured key features of inversion-based source representations of the mega-thrust event, which were calibrated against rich geophysical observations of this event. Using original and synthesised earthquake source models (varied for strike, dip, and slip distributions), tsunami simulations were carried out and the resulting variability in tsunami hazard estimates was investigated. The results highlight significant sensitivity of the tsunami wave profiles and inundation heights to the coastal location and the slip characteristics, and indicate that earthquake slip characteristics are a major source of uncertainty in predicting tsunami risks due to future mega-thrust events.

漂流物対策として防衝工を配置した津波避難ビルに作用する津波波力に関する水理実験

Refuge facilities are required to save human life from a tsunami. Fender piles around a refuge facility could be a countermeasure to protect the facility from tsunami driftage. Hydraulic physical model tests were conducted to investigate tsunami wave force on a refuge facility with fender piles. Although it was found that fender piles had potential of wave force reduction, it was strongly depended on a tsunami wave profile. Visibility of a refuge facility should be high for evacuees. But there is a possibility that fender piles could bring it to deterioration. So, relationship between the layout of fender piles and the visibility was studied qualitatively. It was deduced that straight layout of fender piles would give safety feeling to refugees in a refuge facility and staggered layout would provide it to evacuee approaching toward a refuge facility.

Physical modeling of tsunamis generated by three‐dimensional deformable granular landslides

Tsunamis generated by deformable granular landslides are physically modeled in a three‐dimensional tsunami wave basin based on the generalized Froude similarity. The dynamic landslide impact characteristics were controlled by means of a novel pneumatic landslide generator. The wave amplitudes, periods, and wavelengths are related to the landslide parameters at impact with the landslide Froude number being a dominant parameter. Between 1 and 15% of the landslide kinetic energy at impact is converted into the wave train energy. The wave amplitudes decay in radial and angular directions from the landslide axis. The first wave crest mostly travels with speeds close to the theoretical approximation of the solitary wave speed. The measured tsunami wave profiles were either of the nonlinear oscillatory or nonlinear transition type depending primarily on the landslide Froude number and relative slide thickness at impact. The generated waves range from shallow to deep water depth regimes, with the majority being in the intermediate water depth regime. Wave characteristics are compared with other two‐ and three‐dimensional landslide tsunami studies and the results are discussed.

Behavior of the 2011 Tohoku Earthquake Tsunami and Resultant Damage in Tokyo Bay

The behavior of the 2011 Tohoku earthquake tsunami in Tokyo Bay and its resultant damage to the coasts are studied using a field survey, an analysis of observed tsunami wave profiles and numerical hindcasting using FVCOM and Delft3D-Flow. The field survey reveals that the tsunami caused several fishery ports to overflow, and unexpectedly large inundation and run-up heights of 2.84 m and 2.91 m were recorded in Funabashi Fishery Port and Shin-Futtsu Fishery Port, respectively. Examining the observed tsunami wave profiles, the tsunami wave entered the bay with a maximum height of approximately 0.9 m for the second wave and a period of approximately 60 min, propagating along the major axis of the bay with almost uniform height. Numerical hindcasting results using both the models are fairly consistent with the measurements, revealing that the tsunami wave heights are locally amplified in ports because of wave reflection, water accumulation due to their narrow and enclosed shape, and, to some extent, the harbor resonance. Heavy damage to seaweed farming was also observed, especially around the Futtsu Cape and the northern part of the Banzu tidal flat, which numerical analysis attributes to the appearance of large hydraulic resistance on seaweed net.

2011年東北津波の東京湾内での伝播特性と被害状況

Characteristics of the 2011 Tohoku Earthquake tsunami and resultant damage on the coast of Tokyo Bay were studied using a field survey, an analysis of observed tsunami wave profiles and numerical hindcasting using FVCOM. The tsunami was found to overflow in several fishery ports, leading to unexpectedly high inundation and runup heights of 2.84 m and 2.91 m in Funabashi Fishery Port and Shin-Futtsu Fishery Port, respectively. The observed tsunami wave profiles indicated that the tsunami wave entered the bay with a period and a maximum height of approximately 60 min and 0.9 m, respectively, and propagated along the major axis with nearly uniform height, while the wave was amplified in ports, which characteristics were successfully reproduced by numerical hindcasting.

Proposal of Hybrid Tsunami Monitoring Network System Consisted of Offshore, Coastal and On-Site Wave Sensors

Development and improvement of the International Tsunami Monitoring Monitoring System is getting more important after the 2004 Sumatra-Off-Earthquake Tsunami disaster. Till now, tsunami monitoring system has been developed and established based no observation net-work of strong ground motion only. Nevertheless, earthquake vibration data may give us incorrect tsunami forecasting, for the strength of the vibration and the tsunami-wave profile basic design of the future tsunami monitoring system using newly developed GPS buoy system and other coastal and on-site sensors. Method of real-time tsunami data processing system is also introduced.

Tsunami asymptotics

By applying the technique of uniform asymptotic approximation to the oscillatory integrals representing tsunami wave profiles, the form of the travelling wave far from the source is calculated for arbitrary initial disturbances. The approximations reproduce the entire profiles very accurately, from the front to the tail, and their numerical computation is much faster than that of the oscillatory integrals. For one-dimensional propagation, the uniform asymptotics involve Airy functions and their derivatives; for two-dimensional propagation, the uniform asymptotics involve products of these functions. Separate analyses are required when the initial disturbance is specified as surface elevation or surface velocity as functions of position, and when these functions are even or odd.‘There was an awful rainbow once in heaven’ (John Keats, 1820)