OPTIMIZATION METHODS FOR BATHYMETRY AND OPEN BOUNDARY-CONDITIONS IN AFINITE-ELEMENT MODEL OF OCEAN TIDES

A bidimensional, spectral in time, quasi-linearised hydrodynamic ocean tide model has been developed at the Institut de Mecanique de Grenobl e. This model is derived from the classical shallow water equations by removing velocity unknowns in the continuity equation, that leads to an elliptic, second-order differential equation where tide denivellati on remains the only unknown quantity. The problem is solved in its var iational formulation and the finite elements method is used to discret ise the equations in the spatial domain with a Lagrange-P2 approximati on. Bottom topography has to be known at the integration points of the elements. In the case of the large oceanic basins, a specific method, called the bathymetry optimisation method, is needed to correctly tak e into account the bottom topography inside the model. The accuracy of the model's solutions is also strongly dependent on the quality of th e open boundary conditions because of the elliptic characteristics of the problem. The optimisation method for open boundary conditions reli es on the use of the in situ data available in the modelled domain. Th e aim of this paper is to present the basis of these optimisations of bathymetry and open boundary conditions. An illustration of the relate d improvements is presented on the North Atlantic Basin. (C) 1994 Acad emic Press, Inc.