Journal of Waterway, Port, Coastal, and Ocean Engineering

The least-upper-bound (lub) theory recently proposed by Tayfun and Al-Humoud as a model for the statistical distribution of nonlinear wave crests is explored further. The theoretical distribution of the lub to the largest crest in N waves is also considered, deriving expressions for the associated mode, mean, and standard deviation. These provide a rational basis for describing the nature and occurrence of freak waves and outliers in observational data. The lub distribution and related statistics are then checked with additional measurements gathered during the peaks of two severe storms in the North Sea. The data comprise two hourly records and coincide with the extremes of more extensive measurements discussed by Forristall. Analyses of both records yield crest height distributions and statistics that compare with the lub model predictions quite well, thus confirming the validity of the lub theory convincingly. The theoretical expressions describing the statistics of the largest crest in N waves are then used to examine the nature of two exceptionally large waves recorded within the two hourly measurements. Although these waves display characteristics in apparent conformity with freak-wave occurrences, they are shown to be simple outliers that can be predicted well within the context of the extreme-value statistics derived here.

This paper reports the results of a new mathematical derivation for the transformation of a progressive wave propagating obliquely on a gentle slope. On the basis of the conservation principle of wave motion and in a wave-ray coordinate system, an explicit expression for the velocity potential of the wave field is derived as a function of the bottom slope α perturbed to a second order in an Eulerian coordinate system. Wave profile is then obtained in the Lagrangian system. Together, these enable the description of the features of wave shoaling and refraction in the direction of wave propagation from deep to shallow water, particularly, the process of successive deformation of a wave profile.

Nearshore dredging for construction aggregate or beach nourishment can result in a perturbation of natural littoral processes, changes in wave transformation patterns, and a net loss of sand from the littoral system. A method is described for estimating both direct and indirect effects of dredging on shoreline change. The direct effect results from infilling of the dredged pit via cross-shore sediment transport and is addressed statistically, assuming that the beach profile is in some arbitrary equilibrium shape. The indirect effect arises from project-induced wave transformation, which alters longshore sediment transport patterns, and is described using both spectral and monochromatic, numerical wave transformation models to provide input to a one-line model for shoreline change. Infilling of the pit is neglected when estimating the indirect effect, providing a worst-case estimate of the indirect effect. The methodology is applied to a site on the Turkish Black Sea coast, using hindcast wave data. The influences of pit location and geometry are investigated systematically, and recommendations regarding optimum pit dimensions and locations are made.

In this paper, the dual integral formulation is derived for solving the scattering problem of normal incident wave passing a thin vertical and inclined barrier with rigid boundary condition which is descending from the water surface to a depth. Absorbing and porous boundary conditions are both considered. The breakwater thickness is assumed to be zero since it is negligible in comparison with the water depth and the wavelength of the incident wave. Although the multidomain boundary element method (BEM) can solve boundary value problems with degenerate boundaries by dividing the interesting domain into two subdomains, the hypersingular formulation provides the key to solve the problem more efficiently in a single domain. To demonstrate the effects of the breakwater with rigid, absorbing, and porous boundary conditions for the energy dissipation by the barrier, the transmission and reflection coefficients of the scattering problem are determined by the developed dual BEM program. In addition, the results are obtained for the cases of wave scattering by the barrier with zero thickness in constant water depth and are compared with the analytical solutions, the multidomain BEM solution, and the experimental data.

This study presents a two-dimensional time-independent finite difference model to simulate tidal effects on the intrusion of seawater in either a confined or phreatic aquifer. The model considers a sloped beach face. The irregular beach face and varying ground water surface are mapped to a square domain and the time dependence of the moving boundary is removed by an appropriate coordinate transformation. The finite-difference expression of the governing equations is, therefore, written in a time-independent mesh system, and a time-independent finite difference scheme is established. The numerical technique is confirmed by the reported results of the traditional Henry’s and modified Henry’s problems. Idealized saltwater intrusion, known as Henry’s problem, was extended to simulate seawater intrusion on sloped beach faces accounting for tidal effects. Tidal effects enhance the migration of seawater. The dominant feature of a confined aquifer is that seawater intrudes inland during the flood tide. The saltwater continues to intrude further inland and reaches its furthest upstream position at ebb tide. In an unconfined aquifer, the tidal fluctuation causes the variation of the intrusion profile in the vertical direction only. The fluctuation of the water table oscillates according with the fluctuating tide with a time lag, but the influence of the tide is damped out with horizontal distance from the beach. The variation of the distance through which the seawater intrudes also oscillates with the tide, with a constant time lag of $0.25T\text{,}$ where T is the tidal period. The shape of the aquifer also affects the intrusion of saltwater and the velocity of intrusion. The rate of seawater intrusion and the distance through which the seawater intrudes increases with the slope of the bank.

This study reports an experimental investigation on vortex induced transverse vibrations of a highly flexible free hanging pipe. The experiment was carried out in a towing tank with a 6 m of long flexible rubber pipe, by exciting top end oscillations and measuring lateral displacements at nine points. The largest response amplitude of transverse vibrations occurs at the bottom part of the model for all excitation frequencies and amplitudes. Even though Kc numbers are different along the model length due to in-line response amplitude differences, transverse vibration frequencies are all the same along the model length. Transverse structural wave propagation is observed at the experiment and found in the measured data analysis. A transverse structural wave initiated at a particular point by vortex shedding propagates along the model length and resulting in all the response frequencies to be same.

Contraction scour in a firm-clay estuarine riverbed is estimated at an oil-unloading terminal at the Port of Haldia in India, where a scour hole attained a maximum depth greater than 5 m relative to the original bottom. A linear equation for the erosion flux as a function of the excess bed shear stress was semicalibrated in a rotating-cylinder device called SERF (Simulator of Erosion Rate Function) and coupled to a hydrodynamic code to simulate the hole as a clear-water scour process. SERF, whose essential design is based on previous such devices, additionally included a load cell for in situ and rapid measurement of the eroded sediment mass. Based on SERF’s performance and the degree of comparison between measured and simulated hole geometry, it appears that this device holds promise as a simple tool for prediction of scour in firm-clay beds.