Estimation of friction coefficient for double walled permeable vertical breakwater

The present study deals with the derivation of an empirical formula for determining the friction coefficient of a double walled permeable vertical breakwater. The formulation is achieved in terms of variables representing the porosities of seaward side and shoreward side vertical walls, gap between the walls and depth of water. This formula is derived based on the results of experimental and theoretical studies carried out on a structure consisting of two vertical porous walls separated by some space. The theoretical model is developed by employing the method of eigenfunction expansion, which aids the prediction of such hydrodynamic coefficients as transmission, reflection, and energy dissipation coefficients. The values of friction coefficient are calculated by means of a best fit between the predicted and experimental values of hydrodynamic coefficients. The validity of the proposed formula is evaluated by conducting experiments and by comparing with published results. The results indicate that the proposed empirical formula can be effectively applied for the direct estimation of the friction coefficient of a double walled permeable vertical breakwater within the specified range.