On solitary wave breaking and impact on a horizontal deck

The impact of waves and bores generated by broken solitary waves on horizontal decks of coastal structures was studied by solving the Navier–Stokes equations. Solitary waves of different amplitudes were considered, and submerged ramps were used to bring the waves to the breaking point. The horizontal fixed deck was located downwave of the ramp and placed at various elevations above and below the still-water level. The results include the surface elevation of the wave and the bore-induced horizontal and vertical forces on the deck. The results were compared with laboratory measurements and those due to the bore generated by breaking a reservoir, and a discussion is provided on the relative magnitude of the loads. It is found that breaking solitary waves and dam-break provide reasonable loading conclusions for tsunamis events.<br/

Water current load on arrays of rectangular plates

Water current interaction with arrays of plates is studied by use of the computational fluid dynamics focusing on hydrokinetic energy production applications. Various configurations of arrays of equidistant rectangular plates are considered and the current-induced pressure and velocity distribution, and the hydrodynamic forces on the individual plates are computed. First, current interaction with a singe plate in a three-dimensional current tank is studied, and results are compared with laboratory measurements for which very good agreement is observed. Next, the velocity and the pressure fields around an array of plates are determined and the forces on individual plates are computed and compared with the empirical relations. It is found that the current-induced force on the leading plate in the array is substantially different from those on the downstream plates, which experience negative forces, due to the change of the flow field. In three parametric studies, the effect of plate spacing, the number of plates and the relative water depth on the current-induced forces is investigated. It is shown that the relative size of the plates, and the number of plates in an array play significant role on the current-induced loads. Finally, the relative direction of the plates and the incoming flow is changed and its effect on the hydrodynamic forces on the plates is studied in a three-dimensional computational tank. The current loads on an oriented set of plates is shown to be remarkably different, when compared with those perpendicular to the current direction. It is concluded that the current-induced loads on an array of plates cannot be estimated by empirical relations, and specific computations, similar to those shown here, or laboratory experiments are required to investigate the current load

Effect of currents on nonlinear waves in shallow water

Effect of various forms of currents on regular nonlinear waves in shallow water is investigated by use of a computational fluid dynamics approach. A range of wave conditions with different wave heights and wave periods are considered. Effect of three types of currents on these waves is investigated, namely (i) uniform current over the water depth, (ii) shear current from the seafloor to the still-water level, and (iii) a custom current profile that changes over the water depth. The current profiles are considered in both following and opposing directions of the incoming wave, forming in total 18 wave-current configurations. The Navier-Stokes equations for a laminar flow are solved computationally in two dimensions. A numerical wave-current maker is created to generate combined nonlinear waves and currents in shallow water. The effect of the currents on the change of the wave field, including quantitative change of the surface elevation, wave height, wavelength, horizontal particle velocity, and the velocity and pressure fields is presented and discussed. It is found that presence of the current can alter the wave field significantly, and the current profile and direction play a significant role in the change of the wave field. A following current in shallow water increases the peak of surface elevation, horizontal particle velocity and pressure, along with an increase in wavelength and wave height, while an opposing current reduces these. The change of wave height with current direction appears to be opposite to that observed in deep water in the literature. It is also concluded that a linear superposition of the undisturbed wave and current velocities can describe the horizontal particle velocity of the wave-current field for following currents (particularly under the wave trough) reasonably well, but larger differences are observed for opposing currents

Storm Wave Forces on Selected Prototype Coastal Bridges on the Island of Oahu

Submitted to: Hawaii Department of Transportation Coastal Bridge and Port Vulnerability to Tsunami and Storm Surge Project Project No: DOT-08-004, TA 2009-1RHydrodynamic study of storm wave loads on four selected coastal bridges (prototype scale) around the Island of Oahu is presented here. These include NewMakaha Stream bridge, New South Punaluu Stream bridge, Maili Stream (Maipalaoa) bridge and Kahaluu Stream bridge on the Island of Oahu. Maximum water level at the location of the selected bridges is determined under extreme conditions of a Category 5 Hurricane making landfall on the island. The maximum wave height and wave period are estimated theoretically based on the highest water level. Several different scenarios are considered for each of the selected bridges. The wave loads on the bridges are calculated by use of several theoretical methods. One is based on Euler’s equations coupled with the Volume of Fluid method, for which OpenFOAM, an open access computational fluid dynamics (CFD) package is used to perform the computations, and another one is based on the Green-Naghdi (Level I) nonlinear shallow water wave equations, and is applied to the cases in which the bridge is fully submerged. Existing theoretical and empirical relations, including the Long-Wave Approximation for a fully submerged bridge, developed based on the linear potential theory, and the empirical relations for an elevated bridge deck are also used. Re- sults are compared with each other. The condition that results in the maximum wave forces for each of the bridges is summarized at the end of the report.This work is partially based on funding from State of Hawaii’s Department of Transportation (HDOT) and the Federal Highway Administration (FHWA), grant numbers DOT-08-004, TA 2009-1R. Any findings and opinions contained in this paper are those of the authors and do not necessarily reflect the opinions of the funding agency