Spatial coherence of ocean waves in multiline anchor systems for floating offshore wind turbines

Abstract

A shared multiline anchor system may reduce material and installation costs for floating offshore wind farms, but the concept also expands the physical space over which the analysis of the system must be considered. The multiline anchor force is a combination of forces that originate from different floating offshore wind turbine (FOWT) platforms, and this interconnectivity mandates investigation of spatial coherence of waves over the area of the connected turbines. The goal of this work is to determine if anchor force characteristics are sensitive to spatial coherence of the wave field, or if an assumption of independent wave fields at different FOWT locations provides sufficiently accurate anchor load characterizations. Spatially coherent irregular wave fields are generated and applied to FOWT systems in 3-line and 6-line anchor systems, revealing negligible sensitivity of multiline anchor force to wave spatial coherence. These results are continued with a parametric study showing how wave characteristics affect correlation lengths of spatially coherent waves. A review of installed offshore wind turbine spacings is presented as a context for these results. In each section, regular waves are first used to examine the dynamics in a simple context, then irregular waves are used to more realistically simulate ocean conditions.