Type
PhD research
Duration
July 2021 – March 2026
Persons involved
Ir. Pauline Overes (PhD Candidate)
Dr. Ir. B.W. Borsje (Daily supervisor)
Dr. Ir. A.P. Luijendijk (External advisor)
Prof. Dr. Ir. S.J.M.H. Hulscher (Promotor)
Funding of the project
Combined funding from University of Twente and Deltares
Summary of the research
Large parts of the sandy seabed of shallow seas are covered with rhythmic bed patterns. These bed patterns result from the complex interaction among hydrodynamics, seabed topography and sediment transport. The most dynamic bed patterns are tidal sand waves which generate in several years time, may grow up to 25% of the water depth, have wavelengths of hundreds of meters and migrate at a speed of several meters per year. With their dynamic behavior, sand waves may pose a hazard to offshore activities by for example reducing the water depth of navigation channels or exposing power cables of wind farms. Moreover, sand waves may also serve as source of sand for building and nourishment purposes.
Various offshore infrastructural projects, like offshore wind farms, thus require long term (30-50 years) predictions of the seabed dynamics. Currently data-driven methods are used to determine the range of expected bed levels. However, the uncertainty in these predictions is significant, with sand wave dynamics being the largest source of uncertainty. Moreover, no real understanding of the systems at hand forms the base of these predictions. On the other hand, predicting sand wave dynamics using process-based models has proven to be difficult. Due to the need for small grid sizes (caused by steep sand wave slopes), large areas, long timescales and vertical refinement computational efforts may become unacceptable, especially in case of 3D models.
The aim of this project is to develop efficient ways to model local sand wave dynamics. To achieve this the newly developed Delft3D Flexible Mesh (FM) is used. The Delft3D FM model offers various opportunities to increase numerical efficiency, such as unstructured grids. These flexible grids allow you to refine the model locally to reach the right level of detail. Combined with the possibility to run simulations in parallel, on multiple cores, computation times can be reduced significantly. These improvements open the door to 3D modelling of sand wave areas.
This project contains the first application of Delft3D FM to sand wave cases. Using this model, the importance of various 3D influences on sand wave dynamics will be studied (e.g. along-crest variations in sand wave bathymetry, non-aligned current, wave and storm influences and tidal ellipticity). In addition, methods to increase model efficiency will be explored. Furthermore, the recovery of sand waves after human intervention, such as sand mining or cable installation, will be studied. As a final part of the research the model experience will be used to derive design strategies for offshore activities in sand wave areas.
Keywords
Sand Waves, Marine Dunes, Modelling, Offshore Engineering, Delft3D, Flexible Mesh, Morphodynamics
More information
Pauline Overes
Room Horst Z236
E-mail p.h.p.overes@utwente.nl