M Mossa

How vegetation in flows modifies the turbulent mixing and spreading of jets

While studies on vegetated channel flows have been developed in many research centers, studies on jets interacting with vegetation are still rare. This study presents and analyzes turbulent jets issued into an obstructed cross-flow, with emergent vegetation simulated with a regular array of cylinders. The paper presents estimates of the turbulence diffusion coefficients and the main turbulence variables of jets issued into a vegetated channel flow. The experimental results are compared with jets issued into unobstructed cross-flow. In the presence of the cylinder array, the turbulence length-scales in the streamwise and transverse directions were reduced, relative to the unobstructed crossflow. This contributed to a reduction in streamwise turbulent diffusion, relative to the unobstructed conditions. In contrast, the transverse turbulent diffusion was enhanced, despite the reduction in length-scale, due to enhanced turbulent intensity and the transverse deflection of flow around individual cylinders. Importantly, in the obstructed condition, the streamwise and transverse turbulent diffusion coefficients are of the same order of magnitude.

SPH numerical investigation of characteristics of hydraulic jumps

In the present work, oscillating characteristics and cyclic mechanisms in hydraulic jumps are investigated and reproduced using a weakly-compressible XSPH scheme which includes both an algebraic mixing-length model and a two-equation turbulence model to represent turbulent stresses. The numerical model is applied to analyze oscillations of different hydraulic jump types based on the laboratory experiments. The comparison between SPH and experimental results shows an influence of different turbulence models on the amplitude spectrum and peak amplitude of the time-dependent surface elevation upstream and downstream of the hydraulic jump. By analyzing a single cycle of the oscillating phenomena of a hydraulic jump it is possible to indicate their correlation with the vortex structures of the roller. Furthermore, analysis of the oscillating phenomena indicates a correlation among the surface profile elevations, velocity components and pressure fluctuations. This observation leads to conclude that oscillations phenomena are particularly important for analysis of the turbulence characteristics.

Coastline evolution based on statistical analysis and modelling

Wind, waves, tides, sediment supply, changes in relative sea level and human activities strongly affect shorelines, which constantly move in response to these processes, over a variety of time scales. Thus, the implementation of sound coastal zone management strategies needs reliable information on erosion and/or deposition processes. To suggest a feasible way to provide this information is the main reason for this work. A chain approach is proposed here, tested on a vulnerable coastal site located along southern Italy, and based on the joint analysis of field data, statistical tools and numerical modelling. Firstly, 10 the coastline morphology has been examined through interannual field data, such as aerial photographs, plane-bathymetric surveys, seabed characterization. After this, rates of shoreline changes have been quantified with a specific GIS tool. The correlations among the historical positions of the shoreline have been detected by statistical analysis and have been satisfactorily confirmed by numerical modelling, in terms of recurrent erosion/accretion area and beach rotation trends. Finally, based on field topographic, sediment, wave and wind data, the response of the beach through numerical simulation has been 15 investigated in a forecasting perspective. The purpose of this study is to provide a feasible, general and replicable chain approach, which could help to thoroughly understand the dynamics of a coastal system, identify typical and recurrent erosion/accretion processes, and predict possible future trends, useful for planning of coastal activities.