Water- en zandbeweging in golven en stroom

Abstract

The purpose of the investigation which is described in this report, is to contribute to the study of the motion of water and sand in waves and currents. A one-dimensional (vertical) numerical model of oscillatory turbulent flow is used to determine velo city distributions. The so called k-€ model is applied to oscillatory flow over a flat bed, with and without a steady current. Velo city, turbulent energy, dissipation of turbulent energy, eddy viscosity and shear stress distributions are presented. For determining the watermotion a coefficient is used to describe the mixing processes caused by turbulent motions. In the k-€ model this coefficient, the eddy viscosity, is obtained out of equations concerning the energy which is present in eddies. The eddy viscosity describes the vertical exchange of horizontal momentum. The model is also used to investigate the possibility to determine concentration distributions out of the watermotion. The coefficient which describes the exchange of sediment by the turbulent motion is taken equal to the coefficient which describes the exchange of momentum. As far as the prediction of concentration distributions is concerned, the model fails; considerable differences appear when the results are compared with measurements. An explanation for the differences is given: Exchange of momentum in the vertical direction is assumed to be less than the exchange of mass in the vertical direction. The approximation which is used to describe the transport in the vertical direction can also cause deviations (transport is related to the local velo city gradient). The model pro duces reliable velo city distributions but the concentration distributions deviate from measured distributions. These deviations are explicable. To gain better understanding of the processes, more research concerning the transport of mass must be carried out.