Αποτελεσματικός σχεδιασμός πλωτών κυματοθραυστών

Abstract

The purpose of the doctoral thesis is the extended analysis of the flow around a Floating Breakwater, (FB), fixed on the free surface, and the investigation of the parameters that are related with the structure’s efficiency. Such a study requires a numerical model that accounts for complicated hydrodynamics mechanisms that are developed near the structure, such as viscous and turbulence effects, vorticity generation. For this reason, a Reynolds Averaged Navier Stokes (RANS) solver is used in the numerical part of the thesis. The efficiency of the FB is evaluated through the calculation of the hydrodynamic coefficients, the transmission, reflection and dissipation coefficients, Ct, Cr and Cd respectively. The effects of the structure parameters, such as the draught, dr and the width, W, of the FB and the wave parameters, wavelength, L and wave steepness, Hi/L as well as the wave overtopping, on the efficiency of the FB are investigated. The effect of an attached plate at the seaward side of the FB on the efficiency of the structure is also investigated. Also an empirical formula that relates the hydrodynamic coefficients Ct, Cr and Cd with the above parameters is developed for operational reasons. In addition to the numerical investigation, an experimental study of the effect of wave overtopping on the hydrodynamic field and the efficiency of a fixed FB is performed in the wave flume of the Laboratory of Hydraulics, Department of Civil Engineering, Aristotle University of Thessaloniki. Measurements of the free surface and overtopping variation are performed by applying video image processing on video recorded data obtained by High Definition (HD) video cameras. Wave height measurements, free surface variation at several locations landward and above the deck of the FB together with the variation of Ct, Cr and Cd are compared against the numerical results, and an analysis of the detailed velocity field in the vicinity of the structure is performed. Finally, the efficiency of various types of FBs, alternative to the typical box pontoon, is investigated. The FBs examined, under regular monochromatic waves, are a double FB, a catamaran FB and a trapezoid with inclined faces of 45o. Detailed hydrodynamic characteristics such as velocity, turbulent kinetic energy and vorticity are also considered for improving the design of such structures.