Coastal Engineering Journal

To investigate the near-field and far-field hydrodynamic conditions along the Jiangsu Coast in large scale, a two-dimensional tidal wave model which covers the Bohai Sea, the Yellow Sea and the East China Sea is developed and validated. After a brief review of previous models, some influencing factors, such as tide generating force, river discharges as well as shoreline changes due to land reclamation, are examined in this study. We suggest that whether these factors should be considered in the model depends on the different purposes and geographical regions of interest. Then, a series of experiments are designed to further investigate the previously proposed important factors of influence [i.e. local bathymetry and the role of Shandong Peninsula (SDP)] on the tidal motions in the Yellow Sea. The numerical experimental results show that the interaction between the tidal wave system in the northern Yellow Sea and the incoming tidal wave plays a main role on the formation of the rotating tidal wave system in the southern Yellow Sea, whereas the role of geometric position of the SDP is secondary. With respect to the tidal current, it is found that the radial shape of it is independent of the local bathymetry, but may be generated by the convergent tidal wave formed by the meeting of the rotating tidal wave in the southern Yellow Sea and the incoming tidal wave from the East China Sea. Furthermore, a certain water depth is crucial for the intensity of current velocity to generate the special topography of radial sand ridges.

The effect of submerged vertical breakwater dimension on wave hydrodynamics and vortex generation around the breakwater is investigated with numerical modeling via two dimensionless parameters: the breakwater dimensionless submergence depth (a/H_i; a-the breakwater depth of submergence) and the Keulegan–Carpenter number (KC = H_iπ/L_bw; H_i-incident wave-height and L_bw-breakwater width). In the numerical model, Reynolds Averaged Navier–Stokes (RANS) equations with a standard k–ε turbulence closure model were implemented; the free surface was traced using the VOF method. A total of 10 different simulations with different KC number and breakwater submergence depth were conducted for this study. The results revealed that the transmission coefficient increases with increasing a/H_i and KC number, but that the effect of the KC number is not linear like the relation to a/H_i. For the waves modeled, the transmission coefficient increases dramatically with increasing the KC number until the KC number reaches a critical value, this critical value is observed when breakwater width is equal to a quarter of wavelength. This gives a hint in design of breakwater width. Turbulence intensity decreases with increasing a/H_i and KC on the seaside of the breakwater while it increases especially near the bed on the leeside of the breakwater; this can increase scour risk on the leeside of the breakwater. The optimum a/H_i for both, high-energy dissipation rate and low risk of scour tends to 3.5 for KC ≈ 1.0.

Crown heights of seawalls should be designed to suppress overtopping discharge to a permissible level. The permissible level is determined from viewpoints of the structure types of coastal seawalls and hinterland use. It is usually difficult to design the crown heights of seawalls, especially in the present time where climate change due to global warming is expected. This study analyzes climate change effects such as sea level rise (SLR) and increase of waves and surges on the failure probability of seawalls under various conditions of crown height, toe depth and slope by using a Level III reliability analysis. It was found that the difference of SLR trends (fast, medium or low) has less impact on overtopping rates than the differences in wave height change for a seawall at a target location.

In this paper, we provide a technical note for the implementation of a symbolic Euler–Lagrange transformation on nonlinear progressive water waves. By the implementation, the solution of nonlinear steady waves in the Eulerian description can be obtained and then transformed to the corresponding solution in the Lagrangian description automatically. We consider four closure conditions in a single symbolic implementation to derive both the Eulerian and Lagrangian solutions. In order to accomplish an automatically symbolic computation, we propose trigonometry-polynomial transformations to convert the hierarchical system of differential equations of different orders into a system of algebraic ones. During the symbolic computation, the solutions of a user-prescribed order can be automatically obtained via multiple loops. For example, the fifth- and seventh-order Euler–Lagrange solutions are obtained within 7 min and 3.5 h, respectively.

Given the importance of ports to immediate disaster relief operations after a major tsunami, breakwaters are necessary to sustain a minimum level of functionality required to carry out port operations. However, most breakwaters that protect fishery or industrial ports are not designed to withstand a tsunami. For this reason, many of these breakwaters were destroyed by the 2011 Great East Japan Earthquake and Tsunami. However, some breakwaters withstood the tsunami, which facilitated the rapid resumption of port operations. In this study, 67 ports were investigated by using satellite images to identify the percentage of breakwaters that suffered damage due to the 2011 tsunami and how the tsunami height and breakwater width influenced the degree of breakwater damage. Because tsunami heights were not measured at the breakwaters, they were estimated by interpolating the data observed at nearby locations with a Gaussian weighting function at a reasonable accuracy. Possible drawbacks of this simplified method are also discussed because a certain degree of estimation error is inevitable. Breakwaters less than 8 m wide were quantitatively demonstrated to inevitably experience extensive damage when the tsunami height exceeded 14 m. In contrast, breakwaters that were more than 14 m wide, exposed to tsunami heights of less than 6 m, or both were not greatly damaged. An examination of the effectiveness of armor blocks also revealed that their placement could substantially reduce breakwater damage due to a tsunami. The results suggest a simplified method, particularly for assisting local fishery administrators or other authorities concerned, to practically estimate the risk of a port suffering damage because of future tsunamis. The proposed method should contribute to prioritizing the protection of ports in order of their likelihood of failure.

In this paper, the pressure field on a circular cylinder oscillating close to a plane bed in still water is investigated to assess the effects of proximity of the cylinder to the bed. The range of Keulegan–Carpenter (KC) numbers of the oscillatory cylinder in the present study is between 15 and 40. The flow is in the subcritical regime since the Reynolds number of oscillating cylinder was between 9 500 and 26 000. Two different gaps between the cylinder and the plane expressed as ratios of the diameter of the cylinder are 0.1 and 1.0. The cylinder and the plane bed are both smooth. The frequency spectra of pressure measured at 36 positions around the cylinder have been obtained for the different KC numbers and the gap ratios. A wavelet analysis is used for the simultaneous time–frequency representation of the pressure fluctuations in order to identify the flow induced transitory characteristics. Such a representation shows clearly the abrupt changes in the pressure distribution that are attributed to vortex shedding. The results show that changes in the pressure variations are not at the same phase with the velocity fluctuations indicating the inability of pressures to respond to velocity variations simultaneously.

From Tuesday, 16 December 2014, until Thursday, 18 December 2014, Hokkaido was battered by strong winds and high sea waves caused by a passing low pressure system intensified to typhoon levels. In the city of Nemuro, a rise in sea level influenced by the storm surge which exceeded quay height in port areas was observed from predawn Wednesday, 17 December 2014. Flooding was experienced in areas of central Nemuro, the Nemuro Port and estuaries of rivers. This technical note provides a comprehensive meteorological analysis and the results of a local flood survey carried out by the authors from 19 to 21 December 2014, and summarizes the characteristics of the 2014 Nemuro storm surge disaster.

A computational framework for probabilistic tsunami risk assessment due to a mega-thrust subduction earthquake is developed and is applied to the 2011 Tohoku Tsunami from retrospective viewpoints. The uncertain tsunami source characteristics are represented by multiple source inversion models and their stochastic variations that are generated using the spectral analysis and synthesis method. By conducting Monte Carlo tsunami simulation, stochastic inundation depth maps can be developed, which are subsequently integrated with tsunami fragility curves to develop stochastic tsunami risk maps. The stochastic tsunami risk maps display spatial variability of tsunami damage probabilities for a building portfolio, reflecting not only possible tsunami scenarios but also uncertain tsunami resistance of buildings. The numerical results indicate that both stochastic tsunami risk maps and risk curves are affected by the local terrain features, proximity to major tsunami sources, and building characteristics (material type and story number). Consideration of different reference tsunami source models in probabilistic tsunami risk assessment are identified as one of the critical contributors to the overall uncertainty of the tsunami risk predictions. Therefore, in determining critical scenarios for tsunami evacuation and risk mitigation, a wide range of possible tsunami scenarios should be considered in light of the current limited seismological knowledge for the mega-thrust subduction earthquake.