Antonino Viviano

Influence of Regular Surface Waves on the Propagation of Gravity Currents: Experimental and Numerical Modeling

AbstractThe propagation of gravity currents is analyzed in the presence of regular surface waves, both experimentally and numerically, by using a full-depth lock-exchange configuration. Full-depth ...

Interaction between waves and gravity currents: description of turbulence in a simple numerical model

Effects of surface waves on gravity current propagation are studied by means of a numerical model. The adopted modeling approach couples a Boussinesq-type of model for surface waves and a gravity current model for stratified flows. In particular two different turbulence closure models are introduced which take into account subgrid turbulence and an additional depth-constant eddy-viscosity. The turbulence parameters are calibrated by means of experimental data on the time evolution of the heavy front, obtained both in the absence and in the presence of regular surface waves. Velocity fields, heavy and light front position, shear stresses, vorticity and entrainment calculated by the model are analyzed. The turbulence closure which includes both uniform and Smagorinsky type eddy viscosity allows a better description of the actual gravity current propagation. In particular, the results highlight the fact that the presence of the oscillatory motion causes, simultaneously, a reduction in turbulence and an increase in the mixing of heavy and light fluids. Such a result is in agreement with the experimental observations.

Experiments on Surface Waves Interacting with Flexible Aquatic Vegetation

Surface wave interaction with aquatic vegetation appears to play a key role in coastal hydro-morpho-dynamics. As an example, the presence of a dense meadow at intermediate water depth is usually associated with a stable and resilient shore. Wave-meadow interactions are investigated here by means of physical modelling, with a focus on wave height distribution and hydrodynamics. The central part of a wave flume is covered by flexible artificial seagrass, composed of polyethylene leaves. This vegetation is tested in both near emergent and submerged conditions. The wave height reduction is evaluated by means of a drag coefficient defined from linear wave theory, which contains all the unknowns of the adopted methodology. The behaviour of such a coefficient is investigated as a function of a wave related Reynolds number. The influence of the flexibility of the leaves is also considered, together with a wave frequency parameter. The results show a complex behaviour with three different trends for near rigid, intermediate or highly flexible leaves. Amplitudes of the orbital velocities are investigated and show a fairly good match with the linear wave theory. On the contrary, the mean velocity along the water column appears to be modified by the seagrass for submerged leaves.