Journal of Waterway, Port, Coastal, and Ocean Engineering

The velocity characteristics of a solitary wave shoaling in the prebreaking zone and near the breaking point are investigated experimentally. The study focuses on the near-bottom and boundary layer flows on a 1:10 slope, with the incident wave steepness varying from 0.133 to 0.384. Both a flow visualization technique (FVT) with thin-layered dye as well as particle image velocimetry (PIV) with a high-speed camera were used. Results from FVT reveal that laminar boundary layer flow occurs not only in the prebreaking zone during the shoaling phases, but also in the postbreaking zone during the run-up and run-down phases. However, the laminar boundary layer disappears soon after breaking but before the run-up motion, and immediately after the flow separation followed by hydraulic jump during the later stage of the run-down motion. Results from the PIV measurement show that the maximum horizontal velocity appears under the wave crest and increases during the shoaling process. Flow reversal is observed after the passage of the wave crest. Three unique similarity profiles are then obtained for the velocity distributions in the acceleration phases and in the layers of flow reversal with overshooting, as well as for the maximum onshore and offshore velocities in the boundary layer. In addition, the nondimensional time for the beginning of flow reversal at each measuring section is found to be exponentially proportional to the dimensionless distance to the slope origin, but nearly independent of the incident wave steepness. This study also investigates the lead-time effects of the horizontal velocity at different heights in the boundary layer and at different measuring sections along the slope. The maximum value of the nondimensional lead time, occurring very close to the sloping bottom, decreases linearly with the dimensionless distance to the toe of the slope.

It is well known that, for a series of submerged artificial bars uniformly distributed in the coastal region parallel to the coastline, if the wavelength of the incident wave train is twice that of the bar distance, Bragg resonant reflection occurs. In this paper, three closed-form analytical solutions for linear long-wave reflection for bars with triangular shape, rectified cosinoidal shape, and idealized trapezoidal shape are presented. These analytical solutions show that the magnitude of the peak Bragg resonant reflection still depends on three bar parameters, which are the bar number, the dimensionless bar height, and the dimensionless bar width. Based on intensive analysis of the relations among these parameters, three sets of optimal curves to determine the optimal collocation of the three types of artificial bars are established, which may be very significant in the study of Bragg resonance and in the fundamental design of Bragg breakwaters.

Particle trajectories under a solitary wave are studied using the high-level Irrotational Green-Naghdi (IGN) equations. The steady IGN equations are solved using the Newton-Raphson method. It is determined that the IGN-2 model provides the converged IGN results of the velocity predictions, and the particle trajectories calculated by the IGN-2 model agree well with the available experimental data.

A two-dimensional numerical model is developed to study the propagation of a solitary wave in the presence of a steady current flow. The numerical model is based on the Reynolds-averaged Navier-Stokes (RANS) equations with a $k\text{-}\epsilon$ turbulence closure scheme and an internal wave-maker method. To capture the air-water interface, the volume of fluid (VOF) method is used in the numerical simulation. The current flow is initialized by imposing a steady inlet velocity on one computational domain end and a constant pressure outlet on the other end. The desired wave is generated by an internal wave maker. The propagation of a solitary wave traveling with a following/opposing current is simulated. The effects of the current velocity on the solitary-wave motion are investigated. The results show that the solitary wave has a smaller wave height, larger wave width, and higher traveling speed after interacting with a following current. Contrariwise, the solitary wave becomes higher with a smaller wave width and lower traveling speed with an opposing current. The regression equations for predicting the wave height, wave width, and traveling speed of the resulting solitary wave are for practical engineering applications. The impacts of the current flow on the induced velocity and the turbulent kinetic energy (TKE) of a solitary wave are also investigated.

A two-dimensional (2D) porous model was developed to investigate the accumulation of pore pressure in marine sediments in which the volume-averaged Reynolds-averaged Navier-Stokes (VARANS) equations were used as the governing equations for the wave motion and the Biot consolidation theory was used for the porous seabed. Unlike most of the previous investigations on the accumulation of pore pressure in which the amplitude of the shear stress over the wave period was used in the source term, in this study, the source term was redefined as a time-dependent function using the phase-resolved oscillatory shear stresses. Overall good agreement of both the oscillatory and residual pore pressures with previous analytical solutions and experimental data demonstrated the reliability of the model for the prediction of wave-induced pore-pressure accumulation. For the case with progressive wave loadings, the liquefaction zone related to the initial incident of the wave phases was formed as a 2D pattern during the first liquefaction wave period. This 2D pattern became one-dimensional after one wave period, decreasing progressively to a constant value after a number of wave cycles. For the case with standing wave loadings, a 2D liquefaction zone occurred first in the region where the shear strains are highest. Eventually, this 2D pattern becomes continuous, which implies that even the soil in the antinode section can be liquefied. Compared with the seabed response under linear wave loading, the pore pressure more easily accumulates to a higher value under nonlinear wave loading because of the higher peak in the shear strains. Parametric studies indicate that both the wave characteristics and soil properties affect the maximum relative liquefaction depth ($z_L/h$) significantly. In general, the maximum liquefaction depth increases as the wave height and wavelength increase in shallow water within the seabed, which has a lower permeability and lower relative density.

Impact on a column by an idealized 1:5-scale shipping container propelled by tsunami flow was modeled in a large-scale wave flume. Results from hydraulic experiments were compared with corresponding data from in-air impact experiments using the same experimental configuration to assess the hydrodynamic effects on impact force and duration. Experiments were conducted by varying flow conditions, velocity, and nonstructural mass. An aluminum specimen was tested empty and with the addition of nonstructural mass to simulate partially loaded shipping containers. The measured peak impact forces from the longitudinal test in water were observed to have an increase no greater than 17% of the corresponding measured peak impact forces from the longitudinal test in air. The impact duration measured from the in-air test provided a lower bound for the impact duration measured for the in-water tests. Hydraulic effects were shown to increase the impact duration by an average of 20%. The additional nonstructural mass was shown to have no significant impact on the measured peak impact force, but was shown to increase the overall impulse on the column, as expected.