Evaluation of Truss Tower for Large Capacity Turbine Tension Leg Platforms

Abstract Wind turbine capacities for floating offshore wind turbines (FOWTs) are reaching levels of 15-Mega Watt (MW) and beyond. Large capacity turbines come with heavier rotor-nacelle assemblies (RNA) and higher hub-heights. Balancing the frequency restrictions, i.e., soft-stiff, stiff-stiff, etc., strength and fatigue requirements for conventional tubular towers supporting such turbines is a challenge. For FOWTs, it is important to limit the weight and base diameter of the tower to a minimum required to meet the strength, fatigue and frequency requirements. The use of tubular towers can lead to steel sections and wall thicknesses impractical for fabrication, transportation and installation. This paper demonstrates the challenges for tubular towers to meet fatigue requirements and introduces novel truss tower configurations tailored towards tension leg platforms (TLPs), designed to mitigate these issues. These innovative designs are compared to traditional tubular towers in terms of dynamic performance, structural efficiency, and load distribution, as well as fabrication, assembly, and installation. Modal analyses are conducted to assess the dynamic behavior of the platform, ensuring its conformance with the turbine frequency requirements and good structural performance under design environmental conditions. Through these analyses, insights into the platform's response to external environmental loads such as wind, waves, and currents are gained. Strength analyses, taking extreme loading scenarios into account, is undertaken to preliminarily validate the platform's structural integrity and resistance to buckling. The findings underscore the engineering and supply chain advantages of the proposed towers, demonstrating their potential to be used in high-capacity turbines.