Riccardo Briganti

Wave Transmission behind Low-Crested Structures

This paper describes how, with the European Union funded project DELOS, a wide database containing more than 2000 2D laboratory tests on wave transmission behind low created structures has been collected. The data has been reanalyzed in order to test and improve the reliability of the existing design formulae by improving the description of the dependency of wave transmission on structural and hydraulic parameters. Also the change of wave energy spectra has been analyzed and related to governing parameters.

Analysis of Wave Transmission Behind Low-Crested Structures Using Neural Networks

This paper aims to improve the prediction of wave transmission behind low-crested rubble mound breakwaters by employing artificial neural networks. Data from physical experiments on rubble mound low-crested structures have been gathered within the European research program DELOS and this dataset has been used. The results compared to classical formulations in the prediction of the wave transmission coefficient as a function of both hydraulic and structural parameters.

WAVE TRANSMISSION AT LOW-CRESTED STRUCTURES, INCLUDING OBLIQUE WAVE ATTACK

A part of the DELOS research focused on wave transformation at low-crested structure and is summarised in this paper. Several flume tests have been carried out within the project to analyse wave transmission on rubble mound structures and simultaneously an existing database has been extensively increased by receiving data from other researchers in the world. This new database consists of more than 2300 tests and has been used to come up with the best 2D wave transmission formula for rubble mound LCS. Oblique wave attack on LCS was a second objective within DELOS. Small scale model results were produced and analysed leading to new transmission formulae for smooth LCS and to conclusions on 3D effects for both rubble mound and smooth LCS.

Topographically-induced enstrophy production/dissipation in coastal models

Vorticity and enstrophy production and dissipation are studied for both wave-averaged and wave-resolving (Boussinesq-type) models of wave-induced near shore circulation. Quadratic flow properties of fundamental importance for shallow-water turbulence, i.e., energy and enstrophy, whose sources/sinks are clearly identifiable by positive/negative-definite contributions in the appropriate transport equations, are taken as the most suitable indicators for assessing model performance in describing flows characterized by large-scale vortices. Two state-of-the-art models, SHORECIRC and FUNWAVE2D, have been evaluated in detail. Suitable transport equations for enstrophy are derived and analyzed to get a clear insight into the mechanisms of generation/dissipation of this quantity in both models. Analytical results show that steep gradients of the total flow depth act as sinks as well as sources for vorticity and entrophy, similar to the results of Brocchini and Colombini [M. Brocchini and M. Colombini, Phys. Fluids...

Gravitational mode calculation of basins discretized by orthogonal curvilinear grids

Abstract This paper presents a simple and straightforward method for carrying out the direct numerical solution of the eigenvalue problem associated to the homogeneous linear shallow-water equations expressed using orthogonal curvilinear coordinates, when ‘adiabatic’ boundary conditions apply. These equations, together with the boundary conditions, define a self-adjoint problem in the continuum. The method presented here, which is thought for calculating the 2-D theoretical gravity modes of both natural and artificial basins, relies on a change of basis of the dependent variable vector. This preliminary transformation makes it, in fact, possible to formulate two different numerical approaches which guarantee the self-adjoint property of the discrete form of the system consisting of the governing equations and the boundary conditions. The method is tested using a square and a fully circular domain, both of which allow comparisons with well-known analytical and numerical solutions. Discretizing the physical domain of a fully circular basin by a cylindrical coordinate grid makes it possible to show the actual efficiency of the method in calculating the theoretical gravity modes of basins discretized by a boundary-following coordinate grid which allows laterally variable resolution.

Wave-averaged and Wave-resolving Numerical Modeling of Vorticity Transport in the Nearshore Region: the SANDYDUCK Case Study

INTRODUCTION Numerical modeling of unstable nearshore flows has become quite popular in the last decade. A class of models, usually adopted for this purpose, relies on averaging the equations over the time scales of the short waves (hence wave averaged models). The wave characteristics, and in turn the forcing terms are provided by another model (wave driver). Examples of longshore current studies using these models are Ozkan Haller and Kirby (1999), Zhao et al. (2003), among others. On the other hand in wave resolving models, all the time scales of the hydrodynamics are explicitly solved. Boussinesq-type models (BTMs hereinafter) belong to this class of models and have been used, for instance, in Chen et al. (2003), Gobbi et al. (2000) and Johnson and Pattiaratchi (2006) among others. When applied in similar conditions, the two approaches may produce different results in terms of flow description due to different forcing mechanisms. Differences may arise within the same class of models that share a similar set of equations. In particular it has been shown in Gobbi et al. (2000) that different transport equations for vertical vorticity may be written starting from different BTMs, depending on the order of magnitude of the retained vertical vorticity. The modeled flows in wave averaged models are characterized by less energetic fluctuations with respect to those predicted by BTMs. In turn the vorticity transport is radically different,

The Uncertainty in the Prediction of the Distribution of Individual Wave Overtopping Volumes Using a Nonlinear Shallow Water Equation Solver

ABSTRACT Williams, H.E.; Briganti, R.; Pullen, T., and Dodd, N., 2016. The uncertainty in the prediction of the distribution of individual wave overtopping volumes using a nonlinear shallow water equation solver. This work analyses the uncertainty of the prediction of individual overtopping volumes using the nonlinear shallow water equations. A numerical model is used to analyse the variability from seeding. The effect of the incident wave height distribution on the distribution of individual overtopping volume is also considered. The numerical results are then compared with both the laboratory tests and available empirical methods. A large variability was found across the distributions, which produced some results showing significant diversion from the empirical prediction methods. The magnitude of that departure was directly related to the accuracy of the numerical model in reproducing the incident wave height distribution at the toe of the structure in the physical model.

Full-Scale Measurement of Wave Overtopping at Ostia-Rome Yacht Harbour Breakwater

This paper describes new wave overtopping field measurements at Ostia yacht harbor breakwater (Rome, Italy). The structure, the measurement strategy and the equipment are described in some details. Preliminary results of a recently measured overtopping storm, which are occurred in October of 2003, are presented in the paper. The activities are carried out within the framework of the European Union research project CLASH, aimed at studying model scale effects in overtopping studies and at providing scientific and professional communities with reliable crest level design criteria for coastal structures.