Foundations for Offshore Wind Energy Converters – A Review of Some Current Scandinavian Development Projects-PDF

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The article reviews foundation design challenges for the transition from small offshore wind demonstrations to large commercial farms, drawing on Scandinavian projects. Foundations can account for 30–40% of total installation costs, making safe and economical design central to project viability.<br /><br />Offshore turbines experience complex, cyclic wind, wave and sometimes ice loads. Their horizontal forces and overturning moments can greatly exceed their weight, while fatigue and resonance risks require detailed dynamic analysis. Design must consider the interaction of the tower, foundation and soil, including nonlinear and cyclic soil behavior. Because full time-domain simulations are demanding, practical analyses often approximate soil response with load-specific springs.<br /><br />The main foundation options are gravity-based structures, monopiles and tripods. Gravity foundations can suit varied seabeds but require seabed preparation and scour protection. Monopiles are simple and need little seabed preparation, but require heavy installation equipment and are difficult to use where boulders occur. Tripods can be advantageous in deeper water but are less suitable for shallow sites and also face installation constraints.<br /><br />The projects discussed illustrate how site conditions shape foundation choices. At Lillgrund, shallow water, relatively uniform sediments and limestone make gravity foundations and monopiles possible. At Kriegers Flak, greater depths and coarse material may complicate pile installation, so monopiles, tripods or other approaches require detailed evaluation.<br /><br />The authors recommend systematic, staged geophysical and geotechnical investigations, dividing sites into areas with similar ground conditions and assessing installation feasibility. A common foundation method should be selected for each sub-area where practical, balancing cost, performance and safety without over- or under-designing.

Keywords

offshore wind foundations

foundation design

monopiles

gravity-based structures

tripods

cyclic loading

soil-structure interaction

geotechnical investigation

installation costs

Scandinavian offshore projects