Numerical harbour simulations with the model TRIWAQ - NH

Abstract

The focus is on the numerical flow model TRIWAQ. It is developed as a hydrostatic free-surface flow model, which is currently being used by the KNMI and Rijkswaterstaat for predictions of water levels in the North Sea and Dutch estuaries. TRIWAQ has successfully been extended to the realm of nonhydrostatic modeling, TRIWAQ-NH, this allows the use of full Navier-Stokes equations. It has been validated to perform well for multiple processes such as dispersion and propagation. The goal is to assess the ability of TRIWAQ-NH for harbour problems. This has not been attemptedbefore and poses a new challenge. Before an attempt is made to simulate a harbour, methods of imposing reflection are tested. For that matter, the thesis is split in two parts. The current use of the model TRIWAQ-NH holds practical restrictions to the implementation of open boundary conditions. When such a definition spawns a length of more than grid cell, it needs to comply with the edges of the grid. For instance, a boundary under the angle of 77 degrees is only possible by creation of a multitude of smaller open boundaries, leading to human error. The thesis results in two recommendations. The first part covered reflections, from that segment of the thesis, it is recommended to further explore the option of a stronger and smaller grid sized sponge layer with either an open or closed boundary condition for future development as method for partial reflections. The second recommendation is of a more practical nature and does not emerge in the work. However, the current tools available for non-hydrostatic modelling are insufficient. The smaller wave lengths require smaller time frames then the current tools provide, which is in the order of hours, days and months.