Αριθμητική και πειραματική μελέτη της υδροδυναμικής πλωτού κυματοθραύστη

Abstract

The hydrodynamic behavior of fixed and elastically moored floating breakwaters is studied in the present thesis, using a finite-difference, mathematical model based on the Boussinesq type equations. The flow under the floating breakwater is treated as confined flow separately. The pressure field beneath the floating structure is determined by solving implicitly the Laplace equation for the potential Φ of the confined flow using the appropriate boundary conditions. The dynamic equations of motion are solved with the consequent adjustments of the continuity equation in the case of elastically moored floating breakwaters. Numerical results, concerning the efficiency of fixed, heave motion and elastically moored floating breakwaters are compared to experimental results satisfactorily. The ability of the numerical model to predict the pressure field beneath the floating structure, the vertical force acting on it and the dynamic response of the breakwater is thoroughly examined by making comparisons of the numerical results with experimental data. The experimental part of the thesis was conducted in the CIEM flume of the Catalonia University of Technology, Barcelona. The influence of the incident wave characteristics (regular and irregular waves) and certain geometric characteristics such as the width and the draught of the structure on its efficiency are examined. Four different floating breakwaters configurations are examined: (a) fixed single floating breakwater, (b) heave motion floating breakwater, (c) fixed floating breakwater with attached front plate (impermeable and permeable) and (d) fixed double floating breakwater. Results related to transmission, reflection and energy dissipation of the incident (regular and irregular) waves on the structure are presented. A comparison of numerical and experimental results is also presented. For the single floating breakwater the efficiency of the structure is proportional to the width/wavelength and draught/water depth ratios. The fixed single floating breakwater operates in a highly reflective manner. On the other hand the heave motion floating breakwater operates in a dissipative manner with much lower reflection. The attached plate in the front part of the floating breakwater enhances significantly the efficiency of the structure. No great differences are observed between the impermeable and the permeable plate cases. Generally the most efficient configuration has been proven to be the double floating breakwater. However, with regard to cost effectiveness the configuration of the floating breakwater with the attached plate should be considered the most efficient for design purposes. The final goal is to study the hydrodynamics of floating breakwaters in shallow and intermediate waters.