Nonlinear wave loads on decks of coastal structures

Abstract

This dissertation is concerned with the theoretical calculations of two-dimensional nonlinear wave loads on a horizontal deck of the coastal structure located in water of finite depth. The deck may be fully submerged, partially inundated or fully elevated above the still-water level. Two different approaches are used to calculate the waveinduced horizontal and vertical forces and overturning moment. One is based on the theory of directed fluid sheets, namely the Green-Naghdi (GN) theory of water waves, and the other is based on Euler's equations. The forces on the deck are calculated by integrating the time-dependent pressure around the body. The Level I GN equations are used to obtain an unsteady solution of the problem of propagation of flow of an incompressible and inviscid fluid over a fully submerged thin horizontal plate, an idealized model of a horizontal deck. A theoretical formulation of the problem is provided, and the solution of the equations are approximated by finite-difference equations. Euler's equations are solved with a finite-volume formulation and an Euler scheme for time derivations to approximate the loads of the flow of an incompressible and inviscid fluid on the deck of a coastal structure, whether it is submerged or elevated. The free surface between the water and air is captured by an interface capturing approach, namely the Volume of Fluid method. The computations are performed by use of the InterFoam solver of the Computational Fluid Dynamic's program, OpenFOAM. The results section of this dissertation is mainly concerned with the loads due to nonlinear waves of solitary and cnoidal types. Results are compared with the available laboratory experiments, and with a linear solution of the problem. Comparisons of the results of the GN and Euler's equations show a close agreement between the two methods. The presence of girders, on a model of a bridge deck with girders, is studied by making a direct comparison with the flat plate, and by changing the number of girders on the model. It appears that the girders do not have any influence on the vertical force, and only a small influence on the horizontal force. The effect of formation of air pockets between the girders, in a model of an elevated bridge deck, is studied by adding air pressure relief openings to the deck of the structure. It is found that the entrapment of air pockets increases the vertical uplift force significantly. By use of the GN equations, a parametric study is performed to assess how the periodic wave loads on a submerged deck depend on the wave conditions (wave height, wave period and submergence depth) and deck geometry (deck width).