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IDRODINAMICA COSTRIERA GENERATA DA STRUTTURE DISSIPATIVE
No full textversione integrale in formato elettronico: CD ROM L127, 9 pp
Topographically-controlled, breaking wave-induced macrovortices. Part 3. The mixing features.
No full textThe series of papers on the flow dynamics due to wave-induced macrovortices is
completed with a statistical analysis of the mixing of the shallow flows occurring
around submerged structures used for coastal protection. This is investigated with
specific focus on the role played by large-scale horizontal eddies shed in coastal areas
by waves breaking corresponding to topographic features like submerged breakwaters.
As in Part 2, conditions due to isolated or arrays of breakwaters are studied. Analysis
of particle statistics is used to determine both the features of the induced quasi-twodimensional
flow and to derive general properties. In particular three distinct regimes
are found to characterize the flow evolution. Asymptotic regimes for small and large
times share in any of the features of typical ‘ballistic’ and ‘Brownian’ regimes. Focus
is mainly placed on properties of the ‘intermediate time’ regime which are seen to
depend on the chosen topographic configuration. In agreement with the deterministic
results of Part 2, we find that, because of an intense longshore current, an isolated
breakwater induces a larger dispersion than that due to an array of breakwaters,
characterized by a rip current. Moreover, for the same topography, the diffusivity
grows with the local wavelength. Comparison with field data suggests that results
of scaled-down laboratory experiments reproduce well natural mixing conditions. A
simple formulation of absolute diffusivity, to be used in practical applications related
to environmental quality management, is, finally, proposed
Coherent flow structures, horizontal mixing and dispersion measured at the surface of compound channel flows
No full textMacrovortices-induced horizontal mixing in compound channels
No full textWe investigate, within the framework of the
nonlinear shallow water equations (NSWE), the generation
and evolution of large-scale eddies with vertical
axis (macrovortices hereinafter) which are responsible
for much of the horizontal mixing occurring at the
boundaries between the main channel and the flood
planes of a compound channel. We show that the
mechanism of generation of vorticity is essentially
inviscid and is analogous to that occurring at a curved
shock. Numerical experiments performed by means of a
recently developed shock-capturing model for the solution
of the NSWE, and described in Brocchini et al.
(2001), clarify some features of macrovortices generation
and allow us to quantify the momentum transfer across
the channel
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