A key risk driver in Offshore Wind (OW) projects is the potentially detrimental interaction between OW sub-structures and cables, and the seafloor. In previous years Sandia National Laboratories (SNL) developed methods for the evaluation of regional sediment stability with the use of combined wave, circulation, and sediment dynamics modeling. Knowledge of sediment stability not only in the vicinity of an offshore wind deployment, but all the way to the shore line can help optimize array layouts and cable routes by identifying seabed locations that are highly volatile.
The present work is focused on evaluating the use of these same tools to assess scour around offshore wind foundations. Combining the knowledge of regional sediment stability with local scour potential can ultimately help lower project risk and costs because foundations may be over or under designed to compensate for lack of accurate characterization of local sediment dynamics.
Sandia National Laboratories (SNL) is testing, validating, and calibrating the SNL-EFDC model for use in seafloor scour studies. The scour cases are being validated with laboratory and field measurements to provide a robust modeling tool for scour assessment. At present, unidirectional scour cases around multiple pile configurations have been developed and are being compared with the results from analytic and laboratory scour test cases. Additional cases that include wave action will be the focus of future efforts.
Thus far, scour patterns and erosion rates have been analyzed around three distinct pile configurations consisting of a single pile, two pilings oriented parallel to the flow direction, and three pilings in a triangle pattern. Curvilinear grids were utilized to allow for greater resolution around the piling than at the model edges to improve computation time. This also allowed for the grid to follow the curvature of the piling, reducing grid stair-stepping and associated potential numerical instabilities.
Figures 3, 4 above, and 5 below, show the scour and deposition patterns around the one, two, and three pile scenarios, respectively. For greater clarity, pick on each image. For the single and tandem piling scenarios, an additional three-dimensional representation of scour around the piles is also presented. Work is ongoing to compare the scour predictions with analytical and test data, including determining the sensitivity of the predictions to grid parameters. Ultimately, development of tools to accurately assess sediment dynamics will guide more rigorous and robust standards to support the offshore wind industry.
Jesse Roberts, (505) 844-5730
Filed Under: News, Offshore wind