Abstract
      The present Doctoral Thesis proposes new formulas to estimate the coefficient of reflection for single- and double-perforated chambers in Jarlan-type breakwaters valid for regular and random waves.
      After having carried out a review of state of art, it has been necessary to obtain a new model based on an expanded experimental data base. This semi-empirical model is based on a potential flow theoretical model which was modified with specific empirical formulas to take into account the nonlinear relationships between the structural and wave climate parameters and the Jarlan-type breakwater reflectivity. 
      The new formulas were tested with 1500 regular wave and 160 random wave runs conducted at the Laboratory of Ports and Coasts of Universidad Politécnica de Valencia (LPC-UPV) during research projects ”Study of perforated caisson for quay walls and vertical breakwaters: MUDIVAR” (2002-2005) and “Study of overtopping and stability of low reflectivity vertical breakwaters: REDIVAR” (2007-2009); as well as, by the results of project “Study of perforated caisson for quay walls: MUCAR” (2008-2010) and “Design and adaptability of caisson production facility for low reflectivity vertical breakwaters and quay walls: CADIMA” (2008-2011), which are considered different JTB typologies with different porosities.
      Perforated wall typology, porosity and the number of chambers are structural variables were taken into account in the experiments. In addition to the wavelength, other climate variables, such as wave height, must be considered to explain the phenomenon of reflection in JTB. The results of these tests show, consistent with other authors who have performed similar experiments, that the Reflection Coefficient (CR) on JTB depends on the relative width of the perforated chamber (B/L), but wide dispersion of estimated CR shows that this variable is not sufficient to explain the observed results of CR. In the other hand, it has been observed that the porosity has a significant influence on the variation of the CR, however, it is difficult to know what is their relationship with the rest of variables.
      Analytical models proposed by Fugazza and Natale (FN0) and Williams et al. (W0) was modified for single- and double-chamber JTBs to improved the agreement with experimental observations for both FN0 and W0 models. FN0 model included the basic theoretical foundation of the phenomenon of wave reflection on JTBs, and W0 model introduces the wave dissipation term by damping within the chamber.
      The comparison between the results of both empirically modified models shows that the fit is better with the Fugazza model modified (FN1). However, the disagreement between certain experimental observations and the estimation of Reflected Energy (RE) by the FN1 and W1 models show high errors. Pruned Neural Network (NN) models with Evolutionary Strategies (ES) were used to identify an explicit empirical modification of the FN1 model for a better agreement with the experimental data. The ESs have proved to be very effective optimizing both the topology and parameters of pruned NN models, facilitating the process of finding the relationships captured by the NN models. Thus, the new formulas are similar to those of the NN model, but the obtained equations are explicit and therefore more robust and easier to use than the NN models. 
      Numerical simulations and graphic representations facilitated the search for simple empirical equations to modify FN1. As a result, an empirical relationship between wall porosities and RE or CR was found to significantly improve the FN1 model. The new semi-empirical model provides an estimation of RE with a low relative MSE; rMSE< 35% for regular wave tests and rMSE< 10% for random wave tests and double chamber JTB.  
      When compared with experimental data given by other authors, the new model provides an estimation of the reflection coefficient (CR) errors were similar for regular wave tests and slightly higher (rMSE< 13.5%) for random wave tests. Therefore, it can be stated that this semi-empirical model provides good estimations for single- and double-chamber JTBs under regular as well as random waves.