Author(s): Arico Costanza; Ciraolo Giuseppe; Nasello Carmelo; Tucciarelli Tullio
Linked Author(s): Tullio Tucciarelli
Keywords: Numerical methods; Shallow water equations; Unstructured meshes; Unsteady flow; Hydrodynamic measurements; Lagoon; Irregular topography 1
Abstract: A novel methodology, recently proposed for the solution of the 2D shallow water equations, is applied for the simulation of an experimental lagoon test. The algorithm is based on a fractional step decomposition of the original system in 1) a convective prediction, 2) a convective correction, and 3) a diffusive correction step. The convective components are solved using a Marching in Space and Time (MAST) procedure, that solves a sequence of small ODEs systems, one for each computational cell, ordered according to the cell value of a scalar approximated potential. The scalar potential is sought after computing first the minimum of a functional via the solution of a large linear system and then refining locally the optimum search. The diffusive correction step computes the diffusive corrective fluxes by means of the solution of a linear system, that has the order of the cell number, but is sparse, symmetric and well conditioned. The main advantage of the proposed numerical methodology is that, even if the computational effort is almost proportional to the number of computational cells, no evidence of stability restriction on the maximum CFL number has been found. Model results are compared with field measurements carried out in a shallow coastal lagoon, called Stagnone di Marsala, in the western part of Sicily (Italy). An unstructured triangular mesh is used for the numerical simulations. The measured physical variables are: 1) tide at the lagoon mouths; 2) velocities and elevations in selected stations within the lagoon; 3) wind speed. Under windy conditions, velocities collected near the surface show the typical orbital behaviour and it is possible to recognize the tidal influence on the flow superimposed to this signal. The mean horizontal flow field seems influenced mainly by the tide, while the wind affects mostly the vertical momentum exchange. For each mesh element, the bottom roughness have been set using a submerged vegetation map retrieved using remote sensing techniques. First results are encouraging for the next research steps.
Year: 2007