Presentations

Abstract

This work presents an innovative automated methodology for assessing self-buoyant Gravity-Based Structure (GBS) viability in challenging offshore wind environments, demonstrated through the pre-FEED assessment of Ireland's first west coast project. The study addresses a critical industry challenge: determining foundation feasibility in extreme conditions before investing in costly detailed design. The wind farm site highlights the limits of GBS application, with 50-year return period wave heights exceeding 23 m, highly variable bathymetry that complicates clustering, and poor seabed conditions dominated by very soft clays. These factors demanded a systematic evaluation of over 1,000 geometric configurations to identify the boundaries of technical and economic feasibility. The automated framework enables rapid, computationally efficient screening of GBS concepts against multiple criteria. It applies checks in a staged manner—such as geometric and consenting constraints, draft and weight compliance, transport and installation stability, or global service life stability—so that only the most promising configurations progress to the more resource-intensive analyses. These processes are fully automated through custom-developed programming codes, integrated with DNV Sesam software modules, producing a shortlist of the most suitable configurations prior to detailed structural and geotechnical verification.  The methodology systematically quantifies and optimizes design trade-offs. For example, larger caisson dimensions improve stability but increase hydrodynamic exposure and stone works requirements; increased compartmentalization reduces free surface effects but adds weight and complexity. Despite comprehensive geometrical optimization, exploring different shaft configurations, compartment arrangements, and ballasting strategies, the study concluded that GBS technology remained economically challenging for these extreme Atlantic conditions. Stone works requirements (gravel beds, scour protection, dredging) consistently approached or exceeded consenting limits, while the combination of poor soil conditions and extreme wave loading compounded technical risks. This study delivers a valuable decision-support tool, enabling the offshore wind industry to identify unfeasible concepts in an early stage and avoid costly missteps.