PILOT APPLICATION OF DELFT3D FLEXIBLE MESH: ASSISTING A FIELD CAMPAIGN AT THE SAND ENGINE

摘要

For the execution of field measurements around the Sand Engine during MegaPEX2014 there was a need for operational model predictions. Local river outflow causes non-uniform velocities and spatially complex current patterns near the Sand Engine. For assessing the optimal timing and location of the instruments and GPS drifters, information on the predicted hydrodynamics was desired. A pilot application with the new Flexible Mesh version of Delft3D was therefore set up focusing on 3D hydrodynamic operational forecasts for the area covering the Rhine river mouth and Sand Engine. One single mesh was developed with flexible resolution in cell sizes in the areas of interest while covering all relevant (tide-influenced) areas, such as part of the river network, all port basins, Maasvlakte2 and large parts of the open sea. The number of grid cells did not exceed 100,000 while a resolution of tenths of meters was obtained around the Sand Engine and the river mouth area, which was virtually impossible to achieve using curvilinear grid methods. Comparisons of the model results with observed water levels, velocities and salinities showed very satisfying results. First comparisons with X-Band radar images show a remarkable good reproduction of the fresh water plume passing the Sand Engine. Besides the limited amount of grid cells, the flexible time step saved computational time as well. The present pilot application has clearly shown the benefits of the Flexible Mesh approach in saving grid cells and enclosing complex geometries with desired resolution in one single mesh, but more important it provides the ability to easily incorporate relevant large-scale phenomena in your simulation that at some moments can dominate the local hydrodynamics.