Numerical modelling of tide-induced circulation

A finite difference computational model has been enhanced and refined to simulate tide-induced circulatory flows, with special reference to eddies shed in the lee of headlands and tidal circulation and flushing in narrow entranced coastal basins. The model is of the two-dimensional depth-integrated type and includes a relatively simple "zero-equation" turbulence model. In the turbulence model particular emphasis has been placed on the representation of the free shear layer turbulence, occurring in the mixing zone of eddying flows. This component of turbulent structure has been expressed in terms of a constant eddy viscosity across the shear layer and a semi-empirical velocity distribution. The finite difference representation of the hydrodynamic and mass transport equations was based on the Alternating Direction Implicit scheme, with the hydrodynamic equations involving a double iteration to represent the advective acceleration terms in a time-centred form. The solution of the governing equations yielded the depth-mean velocity, water elevation and concentration fields throughout the computational domain.The model's ability to simulate tide-induced circulatory flows was tested against field measurements from around Rattray Island, and laboratory model studies of idealised rectangular harbours. The agreement between numerical predictions and measurements proved to be encouraging in both cases. The one-way interaction nesting technique has been adopted and applied with success to the harbour simulations. A final application of the numerical model to prototype harbours, enabled comparisons to be made between prototype and laboratory model predictions, an exercise which highlighted the problems associated with scaling effects in distorted physical models