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Qu, K.; Sun, W.Y.; Ren, X.Y.; Kraatz, S., and Jiang, C.B., 2021. Numerical investigation on the hydrodynamic characteristics of coastal bridge decks under the impact of extreme waves. Journal of Coastal Research, 37(2), 442–455. Coconut Creek (Florida), ISSN 0749-0208. Extreme waves, such as freak waves or rogue waves, occur unexpectedly in the ocean and have extremely large wave heights. Extreme waves often are attributed to the process of wave focusing. Coastal structures such as bridges are highly susceptible to extreme waves and have caused substantial damage to coastal infrastructure in the past. Although impacts of various types of waves on coastal bridges have been studied in the past, hydrodynamic loads on bridge deck under the impact of extreme waves have not yet been investigated. This work adds to the existing body of work by systematically carrying out numerical investigations on the hydrodynamic characteristics of coastal bridge decks under the impact of extreme waves generated by wave focusing. Simulations were carried out by creating a numerical wave tank (NWT) using the open-source flow solver REEF3D, which numerically solves the governing equations of the incompressible two-phase flow on a staggered mesh and captures the interface between air and water using a high-resolution level-set method. The NWT was validated for the case of focused waves and wave impact loads on a two-dimensional (2D) rectangular cylinder in a straight channel and compared to experimental measurements. The NWT was then used to study the hydrodynamic loads of a coastal bridge deck by considering the effects of four prominent factors, i.e. submersion depth, wave height, wave period, and water depth. The findings made in this paper enhance the understanding of the damage mechanisms of coastal bridges under the impact of extreme waves. [ABSTRACT FROM AUTHOR]

In recent years, excavating materials from the reef flat gradually becomes the main source of sand and aggregate for the coral-lined coasts in tropical and subtropical regions, especially the low-laying atoll islands. These artificial excavation pits are bound to have significant impacts on the wave hydrodynamics over the fringing reefs. However, effects of the excavation pit on the hydrodynamic characteristics of tsunami-like wave over the fringing reef are few studied. To fill the knowledge gap of previous research, effects of artificial excavation pit on the transformation and runup processes of tsunami-like wave over the fringing reef have been systematically investigated in this study based on a high-resolution two-phase flow model. Effects of several main factors are carefully discussed. Research results indicate that the presence of excavation pit can have noticeable influences on the wave transformation and runup processes of tsunami-like wave over the fringing reef. Complex interactions between the breaking surge bore and the water body in the excavation pit can be observed. The complicated flow field in the pit can dissipate more wave energy and result in a lower maximum wave runup height. However, the local wave height near the pit in most situations can be amplified. It is hoped that the research findings can broaden the understandings on the wave hydrodynamics over the fringing reef with the artificial excavation pit. • Effects of artificial excavation pit on the transformation and runup processes of tsunami-like wave over the fringing reef are investigated by applying a two-phase numerical model. • Influences of main factors, such as wave height, water depth, pit location, pit depth and width, forereef and backreef slopes, and reef-flat length are discussed in detail. • Results indicates that the presence of artificial excavation pit can significantly influences the hydrodynamic characteristics of tsunami-like wave over the fringing reef. [ABSTRACT FROM AUTHOR]

To protect the coastal communities and infrastructures from the devastating damages caused by the extreme ocean surface waves during the severe weather conditions, many coastal defense structures, such as seawall, have been widely constructed along the coastline. In fact, huge ocean surface waves and strong onshore winds coexist in the real harsh coastal environment. Hence, it is of significant necessity to accurately evaluate the overtopping characteristics of coastal defense structures under the combined impact of waves and onshore wind. In this paper, overtopping characteristics of the coastal seawalls under the combined impact of onshore wind and solitary wave are numerically studied. Influences of some main factors, such as onshore wind speed, water depth, wave height, beach slope, and seawall slope, are discussed in detail. The results show that the presence of onshore wind can greatly affect the runup and the amount of overtopping water of seawall under the action of solitary wave. It is hoped that the results of this paper will further deepen our understanding of the overtopping characteristics of seawalls during the severe weather conditions. • ▪Transformation and overtopping properties of solitary wave over the seawall under the influence of onshore wind are investigated by applying a two-phase numerical wind-wave tank. • ▪Effects of prominent factors, such as wind speed, wave height, water depth, beach slope, and side slope of the seawall are discussed in details. • ▪Results indicates that the existence of onshore wind can significantly enhance the impacting loads and increase the overtopping water of the seawall under solitary wave. [ABSTRACT FROM AUTHOR]

This study makes an experimental study on hydrodynamics and sediment driven by dam-break waves in swash zones of three sandy beaches. The experiment adopts three beaches: a 1:10 uniform-sand beach, a 1:10 non-uniform-sand beach, and a 1:35 non-uniform-sand beach. This paper reports its measurements on swash water depth, morphology, bedload, and migration of sand particles. It also analyzes the hydraulic jump and sandbar, sorting and sedimentology characteristics, and fractal dimension of bedform. The analysis indicates that the uniformness of sand particle sizes plays an important role in hydrodynamic behaviors, bedform evolution, bedload transport, and migration of sand particles. The fractal dimension of beach profiles lies between 1.15 and 1.25 after swash action, despite changes in bed profiles. [ABSTRACT FROM AUTHOR]

When hydrodynamic loads of the bridge deck exerted by extreme surges and waves exceed the restraining capacity of the superstructure and substructure, bridge deck will be pushed off from the substructure. However, before the final failure of coastal bridge deck, its dynamic behavior can be idealized as a mass-spring-damper system. In the harsh ocean environment, extreme surges and waves coexist. It is their joint impact that has finally caused the damages of the coastal bridges. In previous studies, only the damage effect of ocean surface waves on the movable bridge deck was considered, and the influence of background current was not considered. In this study, hydrodynamic characteristics of movable coastal bridge deck under joint impact of solitary wave and current have been well investigated. Effects of the wave height, water depth, submersion depth, background current speed, and lateral stiffness on the hydrodynamic characteristics of movable coastal bridge deck were systematically analyzed. The results indicate that the existence of background current can significantly influence the hydrodynamic characteristics and dynamic responses of movable bridge deck under the action of solitary wave. The effective wave celerity gradually increases with background current speed, which eventually enhances the horizontal load and lateral displacement of the movable bridge deck, and it finally increases the potential risk of bridge damage. • Hydrodynamic characteristics of movable bridge deck under the joint impact of solitary wave and current have been investigated considering the effects of wave height, water depth, submersion depth, background current speed, and lateral stiffness. • ▪Results indicate that the existence of background current can significantly influence the hydrodynamic characteristics of movable bridge deck under the impact of solitary wave, increasing the potential risk of bridge damage. • ▪Although the lateral stiffness of the bridge deck has significant impact on the lateral displacement, it has limited influences on the peak values of both horizontal and vertical loads of the movable bridge deck. [ABSTRACT FROM AUTHOR]

In harsh ocean environment, there are complex interactions between extreme surge waves and strong wind during hurricanes. Coastal infrastructures, such as coastal bridges, ineluctably need to withstand the joint action of waves and wind. During past few decades, many researchers have carried out a lot of theoretical, experimental, and numerical simulation work to study the damage mechanism of coastal bridges during extreme weather events. According to the authors' knowledges, hydrodynamic characteristics of the coastal bridge deck under the joint action of surge waves and onshore wind have been largely ignored in previous researches. As one of the preliminary attempts, a series of numerical simulations have been performed to systematically investigate the hydrodynamic characteristics of coastal bridge deck under joint action of regular waves and onshore wind by considering the effects of prominent factors, such as wind speed, wave height, submersion depth, and water depth. The results indicates that the existence of the onshore wind can significantly distort the incident wave profile, enhance the intensity of wave impacting bridge deck, and generate the suction effects over the bridge deck, which will finally affect the hydrodynamic characteristics of the coastal bridge deck under the impact of regular waves. It is hoped that findings drawn from this study can further enhance our understanding on damage mechanism of coastal bridge decks during extreme weather events. • Hydrodynamic characteristics of bridge deck under the joint impact of regular waves and onshore wind have been investigated by considering the effects of wave height, wind speed, submersion depth and water depth. • Results indicate that the existence of the onshore wind can significantly distort the incident wave profile, enhance the intensity of wave impacting bridge deck, and generate the suction effects over the bridge deck. • When the wind speed is low, effects of onshore wind on the hydrodynamic loads of bridge deck are very limited. Only when the wind speed is large enough, effects of the existence of onshore wind become apparent. [ABSTRACT FROM AUTHOR]

Coral reefs are abundant in tropical and subtropical coastal regions. Besides their important role to ecosystems, coral reefs also act as natural buffers that help protect coastal regions from impacts of extreme surge and waves, such as those generated during hurricanes and tsunamis. Recent studies revealed that the bottom of coral reef has very similar properties as porous media. This paper investigates the hydrodynamic characteristics of the transformation and runup processes of tsunami-like wave impinging on a permeable fringing reef by applying a nonhydrostatic numerical wave model (NHWAVE). Effects of prominent factors, such as wave height, water depth, and thickness, median diameter and porosity of the permeable layer of fringing reef, on the hydrodynamic characteristics of tsunami-like wave over permeable fringing reef are discussed in detail. Results show that when the friction effects of the bottom of fringing reef are modelled using the classical quadratic friction law, the protective function of fringing reefs can be grossly underestimated. Research findings drawn from this study can further broaden our understanding on the hydrodynamic characteristics of fringing reefs under the impact of extreme surges and waves. • Transformation and runup processes of solitary wave over the permeable fringing reef are numerically investigated by applying a nonhydrostatic wave model. • Effects of prominent factors, such as wave height, water depth, thickness, median diameter and porosity of the permeable layer of coral reef are discussed in details. • Results indicates that if the friction effects are modelled by applying the classical quadratic friction law, the protection function of coral reef to the coastal regions can be grossly underestimated. [ABSTRACT FROM AUTHOR]

Attributed to the processes of wave focusing, extreme waves often occur unexpectedly with huge wave height in both deep and shallow water regions, which can cause serious damages to the coastal infrastructures, and threaten the intactness of coastal communities. Field observations after extreme weather events have revealed that as a type of natural barrier, coastal vegetations can effectively attenuate the intensity of extreme surges and waves and thus play a good role in naturally protecting the coast. Usually, focused wave is used as a typical extreme wave model to study the great impact of extreme waves on the coast. To numerically evaluate the wave attenuation of extreme waves by the emergent rigid vegetation patch, a high-resolution numerical wave tank has been established by applying the nonhydrostatic numerical wave model (NHWAVE), where both 2nd-order crest and trough focused waves can be generated by considering wave-wave interactions. The efficiencies of the rigid emergent vegetation patch in mitigating the maximum wave amplitude and total wave energy of both crest and trough focused waves as function significant wave height, peak wave period, water depth, vegetation density and width have been well analyzed and discussed. The results indicate that the emergent rigid vegetation patch can effectively reduce the maximum wave amplitude of focused wave by averagely 31% and the total wave energy by averagely 45%, thus, showing that coastal vegetation can effectively protect the coast from extreme waves. It is hoped that the research findings drawn from this study can further broaden our understanding on the wave attenuation of extreme waves by coastal vegetations. • Interactions between extreme waves and emergent rigid vegetation patch are investigated as function of parameters such as significant wave height, peak wave period, water depth, vegetation density and width. • ▪Results indicate that the emergent rigid vegetation patch can effectively reduce the maximum wave amplitude of focused wave by averagely 31% and the total wave energy by averagely 45%, thus, can effectively protect the coast from extreme waves. • The wave energy loss caused the bottom friction is much smaller compared to the energy dissipated by the vegetation patch, hence can be ignored. [ABSTRACT FROM AUTHOR]