Journal of Waterway, Port, Coastal, and Ocean Engineering

A fully coupled hydrodynamic and morphologic numerical model was utilized for the simulation of wave-plus-current scour beneath submarine pipelines. The model was based on incompressible Reynolds-averaged Navier–Stokes equations, coupled with k-ω turbulence closure, with additional bed and suspended load descriptions forming the basis for seabed morphology. The model was successfully validated against experimental measurements involving scour development and eventual equilibrium in pure-current flows over a range of Shields parameters characteristic of both clear-water and live-bed regimes. This validation complements previously demonstrated accuracy for the same model in simulating pipeline scour processes in pure-wave environments. The model was subsequently utilized to simulate combined wave-plus-current scour over a wide range of combined Keulegan–Carpenter numbers and relative current strengths. The resulting equilibrium scour depths and trends were shown to be in accordance with existing experimentally based expressions from the literature. The variety of scour profile types emerging under various flow conditions is detailed and reconciled with experimental observations. The resulting matrix of scour depth time series was systematically analyzed, resulting in a new generalized expression for the scour time scale in combined wave-plus-current flow environments. This expression is fully consistent with existing experimentally based relations at both pure-current and pure-wave limits and is appropriate for engineering use.

The turbulent flow induced by regular and irregular waves on a steep rock-armored slope of 1:3 was studied experimentally. The armor layer consisted of two rows of stones with a median weight of 0.925 N. Four cases of incident waves, whose heights satisfied the hydraulic stability criterion for the armor layer, were tested. The measured wave reflection coefficients were in accordance to values in the literature. Flow measurements were performed using an underwater particle image velocimetry (PIV) system to record instantaneous velocity fields in the region seaward of the breaking point on the slope. In all cases, a return current toward deep water developed, and its magnitude was stronger for the regular than the irregular waves. The vertical profile of the current was approximately linear, and it compared well with a semianalytical model in the literature, which was modified for the present application. The generation of turbulence was enhanced mainly by flow separation resulting from the rough geometry of the armor layer and secondarily by local outflow/inflow resulting from the porosity of the armor layer, and it was correlated to ejection and sweep events. For the regular waves, the relative contributions of the streamwise, transverse, and vertical velocity fluctuations to the mean turbulent kinetic energy were 0.44, 0.28, and 0.28, respectively. The behavior of the phase-averaged velocity field for the regular waves demonstrated that the armor layer behaved as a rough impermeable surface rather than a true porous medium because of the small number (two) of rows of stones.

The interaction of plunging breaking waves with a pair of cylinders placed in tandem is investigated using an open-source computational fluid dynamics (CFD) model. The model is validated using experimental data for total wave forces and free surface elevations for breaking-wave interaction with a single cylinder. Wave interaction with tandem cylinders is investigated for four different wave impact scenarios on the first cylinder and six different distances between the cylinders in each scenario. Wave forces on the upstream cylinder are generally found to be less than the forces on a single cylinder for a particular scenario. The force on the downstream cylinder is lower than the force on the upstream cylinder when the breaker tongue impacts the first cylinder. Under conditions in which the breaker tongue impacts the downstream cylinder around the wave crest level, the wave force on the downstream cylinder is higher than the force on the upstream cylinder. The wave forces experienced by the tandem cylinders is highly influenced by the location of the breaking point with respect to the cylinders and the distance between the cylinders.

A new model for assessing the behavior of sediment clouds due to open-water disposal from barges is presented. The model takes into account the realistic physical condition in which the disposed sediments, due to the large and finite amount of sediments typically carried by the barge, will initially descend as a sediment plume (as if from a continuous release) and then transit into a discrete sediment cloud (as if from an instantaneous release) after the barged sediments are fully discharged. These aspects are not represented in existing models so far. The model also includes the geometrical factors of the barge, which can significantly affect the source conditions and thus the subsequent descent process. Two types of predictions are provided by the model: (1) qualitative predictions of the flow regimes of the sediment clouds along the descending path in the water column, and (2) quantitative predictions of the gross characteristics, such as the penetration rate and growth size of the sediment clouds due to entrainment. An experimental study was also carried out for model verification. The comparison between experimental data and model predictions was satisfactory, whereas predictions with the existing models were found to be inadequate due to their oversimplified representations. Similar conclusions were also drawn in the comparison between available field data and model predictions.

This paper presents more precise evidence on the existence of infragravity waves at a dissipative coastal segment of the Baltic Sea in Poland. The waves were identified with recorded water levels from four gauges in close shoreline proximity, and detailed analyses focused on the output and patterns obtained through the use of discrete wavelet transform (DWT) and cross-correlation functions. As a result, two infragravity waves could be identified: a progressive wave with a period of 34 s, wavelength of 96 m, and a modal number (n = 2); and a standing wave with a period of 130 s, and a wavelength of 252 m, and a modal number (n = 0). The combination of DWT and traditional cross-correlation analysis can serve as a universal tool for nearshore hydrodynamic investigations. Also, this methodology can be applied by extending instrumentation and placing two more wave gauges to form a line of five devices; this potential follow-up research should determine the wavelengths and modal numbers with more precision. This study provides the spatial scales needed to place such additional devices.

Standard strategies for dealing with the Sommerfeld condition in elliptic mild-slope models require strong assumptions on the wave field in the region exterior to the computational domain. More precisely, constant bathymetry along (and beyond) the open boundary, and parabolic approximations–based boundary conditions are usually imposed. Generally, these restrictions require large computational domains, implying higher costs for the numerical solver. An alternative method for coastal/harbor applications is proposed here. This approach is based on a perfectly matched layer (PML) that incorporates the effects of the exterior bathymetry. The model only requires constant exterior depth in the alongshore direction, a common approach used for idealizing the exterior bathymetry in elliptic models. In opposition to standard open boundary conditions for mild-slope models, the features of the proposed PML approach include (1) completely noncollinear coastlines, (2) better representation of the real unbounded domain using two different lateral sections to define the exterior bathymetry, and (3) the generation of reliable solutions for any incoming wave direction in a small computational domain. Numerical results of synthetic tests demonstrate that solutions are not significantly perturbed when open boundaries are placed close to the area of interest. In more complex problems, this provides important performance improvements in computational time, as shown for a real application of harbor agitation.

During tsunami inundation, coastal structures are subject to hydrostatic and hydrodynamic forces from the run-up and rundown and to impact forces from floating debris that is picked up by the flow. A new chapter in the upcoming revised U.S. design load standard covers these loads. To illustrate the application of this methodology for impact loading, it is applied to the determination of shipping-container impact loads for locations in Hilo, Hawaii. The steps include identification of the tsunami design zone, computation of the shipping-container impact hazard region, and computation of the design flow velocity and depth within that region. The flow velocity is used to determine the design impact force for the structure, and the depth is used to define up to what height impact must be considered. The standard provides a new, relatively simple “energy grade line” method that can be used to obtain estimates of these quantities. Because the method has not been widely validated within the archival literature, the results of the method are compared with results from a two-dimensional tsunami-inundation simulation. A simple extension that can improve the results of the energy grade line is proposed. This paper is meant to provide a reference for those applying these provisions in practice and to indicate areas for improvement.