A key risk driver in offshore wind projects is the potentially detrimental interaction between offshore wind substructures/cables and the seafloor. In previous years, Sandia developed methods for evaluating 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 shoreline—can help optimize array layouts and cable routes by identifying seabed locations that are highly volatile.

Sediment deposition and erosion around a single pile with 3-D representation (flow is left to right).

Figure 1.  Sediment deposition and erosion around a single pile with 3-D representation (flow is left to right).

The present work was 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 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 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.

Sediment deposition and erosion around a tandem pile with 3-D representation (flow is left to right).

Figure 2.  Sediment deposition and erosion around a tandem pile with 3-D representation (flow is left to right).

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 used 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 1, 2, and 3 show the scour and deposition patterns around the one-, two-, and three-pile scenarios, respectively. For the single and tandem piling scenarios, an additional 3D 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.

Sediment erosion and deposition around a three pilings configuration (flow is left to right).

Figure 3.  Sediment erosion and deposition around a three pilings configuration (flow is left to right).

Ultimately, development of tools to accurately assess sediment dynamics will guide more rigorous and robust standards to support the offshore wind industry.