Presentations - WindEurope Annual Event 2024

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An integrated design workflow for offshore jacket joint andmember structural analysis

Hassan Moharram, Product Owner, DNV


This paper explores the design workflows for jacket support structures for fixed offshore wind turbines, with an aim to optimise the design to reduce the substantial capital expenditure associated with these structures. Two established design workflows, the "superelement" and "integrated" approaches, are discussed. The integrated approach, though less commonly used, offers potential cost savings of up to 10% due to its ability to consider coupled non-linear effects. One key challenge in the integrated approach is that aero-elastic tools, used for wind turbine dynamics, often lack substructure modelling features. This can lead to inaccuracies in load transfer and design conservatism. The paper introduces enhancements to the aero-elastic tool Bladed, enabling the modelling of local joint flexibility (LJF) and member end offsets (MEO). Further enhancements allow for the calculation of sectional loads along each structural beam. The paper presents a case study of an offshore jacket supporting a wind turbine, considering fatigue and ultimate loading. It evaluates the impact of LJF and MEO on structural eigenfrequencies and member end loads. It demonstrates the capability to calculate loads along each beam and evaluates fatigue life for select beams. Key findings show significant changes in local stiffness with the addition of LJF, particularly affecting higher modes of vibration. The paper highlights that fatigue life varies along a beam, emphasizing the importance of calculating member loads rather than only joint forces.

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