R. Cengiz Ertekin

On the hydroelastic behavior of two-dimensional articulated plates

The hydroelastic behavior of two-dimensional articulated plates is investigated analytically within the scope of linear theory. The connectors are modeled by singular line loading and its derivatives. The velocity potential under the free surface and plate is obtained by use of a wave-maker theory. The characteristics of large displacements at the upstream and downstream edges of the plate and the connectors are obtained from the closed-form solutions. It is also shown that the hydroelastic properties are strongly dependent on the stiffness of the connectors and incoming wave frequency. Finally, the method is used to solve for the response of a multi-module articulated plate.

A numerical study of nonlinear wave interaction in regular and irregular seas: irrotational Green–Naghdi model

Abstract The irrotational Green–Naghdi model for nonlinear wave propagation in deep water is developed to simulate the irregular sea surface of a given directional wave spectrum. The model is derived from Hamiltons principle with a depthwise approximation to the flow field. The nonlinear boundary conditions are exactly satisfied on the actual free surface, and the continuity equation is satisfied exactly within the fluid domain. The ‘level’ of approximation in the depthwise direction is optimally chosen to simulate a given wave spectrum accurately with minimum computational effort. Several numerical techniques also are introduced to cut the computational cost further. Numerical results for two-dimensional nonlinear waves are presented.

PRELIMINARY ASSESSMENT OF THE WAVE-ENERGY RESOURCE USING OBSERVED WAVE AND WIND DATA

The first step in determining the feasibility of a wave-energy conversion device is to assess the available wave energy in a given area. We show the estimation of wave energy from observational wave and wind data. A total of five different methods of wave-energy estimation are presented. One of these methods, which is introduced for the first time, is the estimation of wave energy from observational wind data using the Weibull distribution. This new method of wave-energy assessment is applied to an area near the Hawaiian Islands and compared with other available results. The comparisons show that the theory based on observational wind data produces results that are in overall agreement with previous calculations based on the measured spectral-density of waves, as well as on observational wave- and wind-data.

Review of Wave Loads on Coastal Bridge Decks

Recent natural extreme events, such as Hurricane Ike in the U.S. (2008), Tohoku tsunami in Japan (2011), and Typhoon Haiyan in Southeast Asia (2013), have caused significant damage to the decks of coastal bridges. The failure of the structure occurs when wave-induced loads on the decks of coastal bridges exceed the bridge capacity, resulting in partial removal or a complete collapse of bridge decks. Tsunami, storm waves, and storm surge are known to be the ultimate agents of such failures. An understanding of the failure mechanism and possible solutions require a better knowledge of the destructive loads on the structure. Interaction of surface waves with the bridge deck is a complex problem, involving fluid–structure interaction, wave breaking, and overtopping. Possible submergence of the deck and entrapment of air pockets between girders can increase destructive forces and add to the complexities of the problem. In recent years, remarkable progress has been made on this topic, resulting in some new findings about the failure mechanism and the destructive wave loads. A review of the key studies on wave loads on the coastal bridge decks, including those in the past and very recently, is presented here. Emphasis is given to the pioneering works that have significantly improved our understanding of the problem. Challenges associated with the existing solutions are highlighted, and suggestions for future studies are provided.

On the Reverse Flow Beneath a Submerged Plate Due to Wave Action

A water wave, passing over a horizontal plate submerged beneath the free surface, would experience above the plate both a change in wave height and wavelength. On leaving the plate, the wave, in general, encounters a reduction in wave height as compared to the incident wave. The reduction in the wave height depends upon the wavelength, the plate length and its position below the free surface, i.e., the submergence depth, as well as the water depth. Depending on the particular flow configuration, a pulsating reverse flow can occur beneath the plate, in a direction opposite to that of wave propagation. This pulsating two-dimensional flow field has been proposed by others as a method to convert wave energy into electrical energy. The main objective of this paper is to study the reverse flow beneath a submerged plate by surface wave action in finite water depth. A 2-D numerical model that uses the boundary-element method is developed to simulate this physical event by solving the linear equations of motion for waves in an ideal fluid. In addition, the Reynolds-Averaged Navier-Stokes equations are used to solve the nonlinear equations of motion for waves in a viscous fluid by use of the Fractional-Step Method. The numerically obtained linear and nonlinear results are compared with the available experimental data.Copyright

Effect of Entrapped Air on Solitary Wave Forces on a Coastal Bridge Deck with Girders

AbstractRecent tsunami and hurricane-caused destruction, and the possibility of both tsunami inundation and storms of even greater magnitude and frequency making landfall in the future, has focused attention on the vulnerability of coastal structures, and bridges in particular. Findings from a series of experiments measuring forces on a 1:35 scale bridge model impacted by a solitary wave with varying percentages of air relief openings (AROs) between girders are presented here. A range of water depths, wave amplitudes, and elevations of the model above the still-water level (SWL) are considered. Results show significant reduction of vertical uplift forces when AROs are added to the bridge model, particularly when the girders are fully elevated above the SWL or only slightly submerged, but relatively little effect on horizontal forces in the direction of wave propagation is observed. Buoyancy calculations show added hydrostatic force does not alone contribute to uplift forces, but rather a combination of hy...

Vulnerability assessment of coastal bridges on Oahu impacted by storm surge and waves

Vulnerability assessment of four selected prototype coastal bridges on the island of Oahu, Hawaii, to the combination of storm surge and waves is presented. The maximum storm surge condition is estimated by considering an extensive series of simulated hurricanes making landfall on the island of Oahu, where the bridges are located. For the given extreme environmental conditions, wave loads on the deck of the selected bridges are calculated by use of several theoretical and computational approaches, including Euler’s equations (OpenFOAM), the Green–Naghdi nonlinear equations, linear long-wave approximation and existing simplified, design-type force equations. Multiple scenarios of the relative location of the bridge deck and the still-water level are studied to determine the maximum possible wave loads on the bridge decks. Vulnerability of the coastal bridges to storm wave loads is determined by comparing the capacity of the bridge to the wave-induced loads on the structure.

Experimental Investigation on the Role of Entrapped Air on Solitary Wave Forces on a Coastal Bridge Deck

Recent devastations caused by tsunami and hurricanes and the inevitability of future hurricanes making landfall have focused attention on the need to assess the vulnerability of coastal structures, and bridges in particular. Findings from a series of experiments conducted on an 1:35 scale bridge model with girders under a solitary-wave flow are presented here. Side panels are added to the bridge model to trap air pockets between the girders. A range of elevations is considered, including cases where the bottom of the deck is just above the water surface and girders are submerged, to where girders are fully elevated above the water surface. Wave parameters tested include four water depths and five wave amplitudes. A qualitative comparison is made between results for forces on the trapped-air model and results from the same set of wave parameters on a model where the side panels are removed and air is allowed to escape. Results show effects of water particle velocity, buoyancy, air compression and sloshing all have effects on both horizontal forces in the direction of wave propagation and vertical uplift forces. In particular, in the case where air is trapped between girders and cannot escape, uplift forces are considerably larger when bridge elevation is such that the girders are fully elevated above the still water level or are slightly submerged.Copyright

A Comparative Study of Nonlinear Shallow-Water Wave Loads on a Submerged Horizontal Box

This paper is concerned with calculations of the two-dimensional nonlinear vertical and horizontal forces and overturning moment due to the unsteady flow of an inviscid, incompressible fluid over a fully-submerged horizontal, fixed box. The problem is approached on the basis of the Level I Green-Naghdi (GN) theory of shallow-water waves. The main objective of this paper is to present a comparison of the solitary and cnoidal wave loads calculated by use of the GN equations, with those computed by Euler’s equations and the recent laboratory measurements, and also with a linear solution of the problem for small-amplitude waves. The results show a remarkable similarity between the GN and Euler’s models and the laboratory measurements. In particular, the calculations predict that the thickness of the box has no effect on the vertical forces and only a slight influence on the two-dimensional horizontal positive force. The calculations also predict that viscosity of the fluid has a small effect on these loads. The results have applications to various physical problems such as wave forces on submerged coastal bridges and submerged breakwaters.Copyright

Low-power autonomous wave energy capture device for remote sensing and communications applications

Ocean remote sensing techniques often rely on autonomous buoys to measure and transmit real-time oceanographic and meteorological data. The operating lifetime, payload capacity, and sampling rate of such platforms are limited by onboard battery power. Here, we describe a rotary-drive, wave energy conversion device which utilizes the heaving motion of a surface buoy to generate power over a broad range of sea-states†. The device was demonstrated to generate over 50W of power in moderate seas at the Kilo Nalu Nearshore Reef Observatory.