Site Exploration for Anchoring of Wave Energy Converters

Abstract

Wave energy converters (WECs), a form of marine hydrokinetic (MHK) energy device, transform the mechanical energy of water waves into electricity. They are typically held on station using anchoring systems embedded into the seafloor sediments (as opposed to, e.g., concrete gravity anchors). The design of WEC anchors is particularly challenging for two primary reasons: (1) WECs are often deployed in previously undeveloped areas of the ocean, so the engineering properties of the seabed are largely unknown; and (2) the economic margins on wave energy are quite thin, so heavily overdesigned anchor systems in response to data sparsity are not feasible. This paper describes the planning, execution, and outcomes from a dedicated in-situ testing campaign informed only by limited geophysical data a priori. A series of 22 cone penetration tests (CPTs) were performed at a 7-km2 site approximately 11 km off the United States’ west coast. Water depth was up to approximately 75 m and the target depth for the cone soundings was 10.5 m below the seafloor. Measurements indicated that much of the site subsurface consisted of dense sand and gravel, though tests identified an overlying softer layer in some parts of the site. A summary of lessons learned and recommendations for future explorations at similarly unexplored sites are provided.

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