Le calcul numérique de l'état de la mer

Ingénieurs à la Météologie nationale.

Résumé

This type of calculation is still basically empirical and none of the attempts to bring it within the scope of hydrodynamics theory had so far been successful. Forms of spectral representation of the state of sea in terms of wind proposed by various specialists had been showing discrepancies for a long time, mainly on the following points a) Total spectrum energy. b) The tendency of the spectrum to develop into a more or less hypothetical limited spectrum. These discrepancies have now been cleared up, as follows : a) Wind conditions should be referred to a standard height, as with the currently applied meteorological relationships between "surface wind" and pressure gradient. b) Recent theory has confirmed the more or less simultaneous growth of the various spectrum components. These theories, which are mainly based on linearisation of the hydrodynamics equations, involve average wind conditions, the turbulence spectrum above the waves and the average wind profile in the lower layers, all of which are unfortunately still difficult to establish. With the equations, however, five simultaneous change processes can be considered, which are combined into a spectral energy balance equation. They are the following : 1. Propagation (or advection). 2. The Phillips growth term. 3. The Miles growth term. 4. The third-order interaction term. 5. Passive resistance damping. Hence, a digital model is characterised by its spectral energy equation. Five digital models are described and a certain number of their responses are classified into groups in terms of schematic special situations (Figs. 1 to 3 and 10 to 32 inclusive.) The results of a computation with model DSA representing the North Atlantic are compared with various observed and estimated data (Figs. 4 to 9 inclusive).