Alessandro Mancinelli

An efficient solver for nearshore flows based on the WAF method

Abstract We describe an efficient and robust flow solver for the integration of the classic Nonlinear Shallow Water Equations (NSWE) on a beach of arbitrary topography. On the basis of the ‘shock capturing’ Weighted Average Flux (WAF) method, a numerical code is implemented which employs a space-splitting technique to integrate the NSWE over a horizontally two-dimensional domain (2DH). Special care is put in handling the moving shoreline and a new, efficient formulation of the shoreline boundary conditions is presented. This is based on the hydrodynamic equivalent of the cavitation condition used in gas dynamics. Model capabilities are illustrated by means of a number of tests (both 1DH and 2DH). These reveal that, though primarily conceived for modelling nearshore hydrodynamics, the solver can be successfully adopted even for studying the run-up of large tsunami waves.

Topographically controlled, breaking-wave-induced macrovortices. Part 1. Widely separated breakwaters

In this and the companion paper (Part 2) we examine experimentally, computationally, and analytically the behaviour of breaking-wave-induced macrovortices during startup conditions. Widely separated breakwaters and rip current topographies are chosen as opposite ends of the parameter space. Part 1 examines generation mechanisms using phase-resolving and phase-averaged approximations, and suggests several simple predictive relations for general behaviour. Vortex trajectories and shedding periods for wave breaking on widely spaced breakwaters are also considered in detail. Results show broad agreement with theoretical trajectories. Predictions of vortex shedding periods on breakwater heads show excellent agreement with computations. Part 2 examines startup macrovortices on rip current topographies using computations and laboratory experiments, and changes in behaviour as the system transitions from wide to narrow gap width.

Comparative analysis of sea wave dissipation induced by three flow mechanisms

A comparative analysis is performed on the wave energy dissipation efficiency on various coastal protection devices. In-house experimental data on the performance of two innovative coastal defence methods and of traditional submerged breakwaters have been used. The analysis provides a quantitative comparison of the efficiency of wave dissipators based on either wave-breaking turbulence, near-bed turbulence, or inside-seabed turbulence decay. The comparison is made on the basis of wave height decay patterns described as a function of suitable dimensionless parameters. The dimensionless volume of maximum turbulence decay is found to be a useful parameter for the analysis. Efficiencies in reducing the intensity of the incident waves are measured by the wave transmission coefficient, which is found to range between 0.4 and 1.0. Submerged breakwaters were found to be the most efficient wave dissipators, especially for large waves, while comparable efficiencies are provided by the three mechanisms under analysis if the flow is forced by moderate waves.

Working of Defense Coastal Structures Dissipating by Macroroughness

The working features of innovative coastal defense structures that can dissipate the energy of incoming waves by the action of large-scale bottom unevennesses (rigid blades covering the lower half of the water depth) were investigated by means of a laboratory experimental campaign. The goal of the study was to characterize the ability of the structures to efficiently reduce the wave height with a minimal change in the mean water superelevations. Similar wave height reductions were achieved for both vertical and inclined blades; their efficiency was slightly superior to that of traditional submerged rubble-mound breakwaters of the same cross-shore extension. For the incident waves examined, very low mean water elevations were observed inshore of the structures, with the inclined blades producing the smallest values. These results suggest that the structures analyzed here could represent an alternative to submerged rubble-mound breakwaters from a hydrodynamic point of view to protect coastlines prone to erosion with minimal risk of dangerous rip currents.

Simple Physical Models to Simulate the Behavior of Buckling-Type Marine Fenders

AbstractThis paper presents a simple physical model for the numerical simulation of the behavior of buckling-type marine fenders. The proposed model is characterized by four parameters and is derived starting from similarities between the unstable behavior of marine fenders and shallow arches. In this model, the large displacements solution expressing the relationship between the model displacements and reaction force is determined in a nondimensional form, and the model parameters are calibrated to minimize residuals between real and predicted normalized reaction force–deflection curves. By considering an in-series arrangement of two elementary physical models, the approach can be also used to simulate the behavior of parallel-motion fenders. The proposed model can be directly implemented in commercial computer programs for structural analysis to study interactions arising between buckling-type marine fenders and flexible berthing structures. In this paper, the model effectiveness in capturing the behavi...

Summertime conditions of a muddy estuarine environment: the EsCoSed project contribution.

As part of the Estuarine Cohesive Sediments (EsCoSed) project, a field experiment was performed in a highly engineered environment, acting as a natural laboratory, to study the physico-chemical properties of estuarine sediments and the associated hydro-morphodynamics during different seasons. The present contribution focuses on the results obtained from the summertime monitoring of the most downstream part of the Misa River (Senigallia, Italy). The measured hydrodynamics suggested a strong interaction between river current, wave forcing and tidal motion; flow velocities, affected by wind waves traveling upstream, changed significantly along the water column in both direction and magnitude. Surficial salinities in the estuary were low in the upper reaches of the estuary and exceeded 10 psu before the river mouth. Montmorillonite dominated the clay mineral assemblage, suggesting that large, low density flocs with high settling velocities (>1 mm s(-1)) may dominate the suspended aggregate materials.

Modelling the Effects of Structures on Nearshore Flows

The effects of defense structure on nearshore water flows are analyzed by means of an efficient and robust flow solver. This is both flexible enough to incorporate bathymetric data typically collected in field surveys and accurate enough to allow for a detailed description of important flow features. Such a tool is believed to be capable of providing useful information for design activities of coastal structures like submerged breakwaters.

Scouring Below Pipelines: The Role of Vorticity and Turbulence

A numerical study on the turbulence and vorticity of local scour underneath an offshore pipeline placed on a non-cohesive sandy seabed and forced by a steady flow current is presented. The numerical model solves the Navier-Stokes equations using an innovative Level Set technique. The model predicts the behavior of the movable sediments through both drift and lift force components. Mean and turbulent flow quantities were extracted by temporal averaging. Results on the distribution and evolution of turbulent kinetic energy and vorticity will be illustrated at the conference.Copyright

Parallel computing for nearshore hydrodynamics

We present the results of an ongoing research about the use of parallel computing for the numerical modelling of nearshore hydrodynamics. An overview is given on strategies for building a parallel, small supercomputer and performing parallel computing. We mainly focus our analysis on the parallelization of the code used to numerically solve the Nonlinear Shallow Water Equation (NSWE) and on the evalution of the performance gained by using a parallel code.