Investigation of a simplified open boundary condition for coastal and shelf sea hydrodynamic models

[摘要] ENGLISH ABSTRACT : In general, coastal and shelf hydrodynamic modelling is undertaken with limitedarea numerical models such as Delft3D or Mike 21. To conduct successfulnumerical simulations these programmes require appropriate boundary conditions.Various options exist to obtain boundary conditions such as Neumannconditions, specifying water levels, specifying velocities and combination ofthese, amongst others. In this study one specific method is investigated,namely the specification of water levels on all the open boundaries using areduced physics approach. This method may be more appropriate thanNeumann conditions when the domain is fairly large and is also of particularinterest as it allows measured data to be incorporated in the boundary conditions,although the latter was not considered in this study.The boundary conditions of interest are determined by separating the crossshoreand alongshore components of the momentum equations. To justify theseparation, the equations of motion are firstly non-dimensionalised to determinethe relative importance of various terms and then scaled to determineunder which conditions the cross-shore and alongshore components can besolved independently.The efficacy of a computer program, Tilt, to calculate the open boundaryconditions have been investigated for a number of idealised cases. Based on anunderstanding of the underlying physics and scaling assumptions, situationswhere these open boundary conditions underperformed have been analysedand reasons given for their underperformance. When applied to real-lifesituations it is likely that one or more of the scaling assumptions will be violated.Comment is provided on the likely errors in model simulations shouldthis occur.The main conclusions are that the reduced physics approach used in Tiltrestricts fairly significantly the range of flow that can be simulated. Shouldthe scaling assumptions underlying Tilt be satisfied, Tilt performs adequatelyfor limited area model simulations of coastal and shelf regions, however thereremain some concerns:• The no flux condition at the coast and clamped water level offshore

[发布机构] Stellenbosch University