Sara Corvaro

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.

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.

A Novel Two-fluid Model for the Identification of Possible Multiple Solutions in Slightly Inclined Pipelines

Abstract A novel mechanistic two-fluid model (CB model) similar, in spirit, to the Taitel and Dukler [1, 2] (TD model), for the identification of possible multiple solutions of a multi-phase (gas-liquid) stratified flow in slightly inclined pipelines, is proposed. While Blasius-type closures are used in the TD model to represent the wall friction coefficients, the newly-implemented CB model makes use of Colebrook-White-type closures. Moreover, different closures for the interfacial shear are also employed in the CB models. The predictive capabilities of the CB model have been tested by using several experimental data, finding a better agreement between measured and calculated data than that existing when the TD model is used. The region of multiple solutions is influenced by the closures in use, such a dependence is more evident when different interfacial friction factors are used. Moreover, for the CB model also the fluid mixture in use influences the boundaries of the non-uniqueness region, while by using the TD model the multiple-solution region is unchanged. The choice of closures for the interfacial friction strongly influences the holdups, the Andritsos and Hanratty [10] correlation significantly shifting the non-uniqueness region to small values of the inclination parameter. Such a behaviour is more and more significant with the increase of the superficial gas velocity, even if for values of the inclination parameter within the range of inclinations for stratified flows (i.e. less than about 30° from the horizontal [11]), multiple solutions were not found. Finally, for the fluid mixture and flow conditions analyzed, multivalued solutions are obtained only for upward flows. Moreover, the portion of multiple-solution region interested by co-current flow (that occurs for slightly upward and downward pipes) is rather small, so that the operational point unlikely falls within such a region in the case of the studied hydrocarbon gas-liquid mixture.