Ruud van Damme

The cross-sectional shape of tidal sandbanks: modeling and observations

To improve our understanding of tidal sandbank dynamics, we have developed a nonlinear morphodynamic model. A crucial property of the model is that it fully resolves the dynamics on the fast (tidal) timescale, allowing for asymmetric tidal flow with an M0, M2, and M4 component. This approach, extending earlier research on the formation of tidal sandbanks, leads to equilibrium profiles. Their heights (60-90% of the water depth) and shapes are controlled by the mode of sediment transport and the hydrodynamic conditions. Bed load transport under symmetrical tidal conditions leads to high spiky banks. Several mechanisms tend to lower and smooth these profiles, such as the relaxation of suspended sediment, wind wave stirring, and tidal asymmetry. This last causes the profiles to be asymmetric, as well. The morphodynamic equilibrium expresses a tidally averaged balance between a destabilizing flux due to fluid drag and the downslope transport induced by both tidal flow and wind wave stirring. The modeled profiles are in fair agreement with observations from the North Sea.

Numerical simualation of sand wave evolution in shallow shelf seas

Sand waves form a prominent regular pattern in the offshore seabed of sandy shallow seas. A 2DV morphological numerical model describing the behaviour of these sand waves is under development. The first goal is to make the new numerical model reproduce the results obtained with a linear stability analysis. We start with a constant current after which the behaviour of sand waves is investigated in a tidal environment. Furthermore, calculations using Delft3D have been made to test the general setup of the new numerical model.

Degenerate polynomial patches of degree 11 for almostGC2 interpolation over triangles

We consider the problem of interpolating scattered data in ℝ3 by analmost geometrically smoothGC2 surface, where almostGC2 meansGC2 except in a finite number of points (the vertices), where the surface isGC1. A local method is proposed, based on employing so-called degenerate triangular Bernstein-Bézier patches. We give an analysis of quintic patches forGC1 and patches of degree eleven for almostGC2 interpolation.

Fixed point iteration on pointsymmetric interference graphs

Interference graphs are used for performance analysis of multiprocessor interconnection networks. In order to model blocked transmissions, nodes can have three states: idle, active or blocked. The resulting steady state probability distribution has a non-product form. Macro states are introduced to calculate performance measures, and the corresponding macro state probability distribution is approximated by a special type of fixed point iteration: the macro approximation, which is very efficient for pointsymmetric interference graphs.