| Popis: |
Flow modelling in terms of the horizontal distribution of the depth-averaged velocity assumes vertical similarity of the horizontal velocity components. For some types of weakly three-dimensional flows (e.g. up- and downwelling), this is too restrictive an assumption. The concept of a method to include weak three-dimensional effects is given in the present paper. Assuming that the flow is locally uniform in the horizontal plane, the vertical distribution of the horizontal velocity is described. Subsequently, a relation between the depth-averaged velocity and the bottom shear stress is derived from that description. It is suggested that this relation is used in depth-integrated numerical models instead of, for example, a Chezy-type formulation. A modified version of Davies' shapefunction approach is used to describe the vertical flow structure. The modification is necessary in order to obtain a proper reflection of the surface and bottom boundary conditions. Since the method has not yet been implemented, only the concept is outlined. Furthermore, a limited error analysis is presented and an indication of the required computational effort is given. |
