Session: 09-04-01 Wind Energy: Monopile structures

Submission Number: 157230

A Methodology for Site-Wide Structural Optimisation and Advanced Clustering of Monopile Foundations for Next-Generation Offshore Wind Turbines 

Despite ongoing industry trends of using ever-larger wind turbine generators and developing in deeper waters, monopile foundations for offshore wind turbines remain a favourable foundation type where feasible due to their relative simplicity and cost advantage over more complex foundation solutions. As such it is crucial that monopile designs are optimised for specific site conditions at an early stage to ensure feasibility can be adequately assessed, and optimised on a position-specific basis during later design stages to minimise capital expenditure and reduce overall levelised cost of energy. The structural design process for monopiles to support next-generation wind turbines (i.e. 15MW and above) is complex and involves consideration of many loadcases and a large parameter space, posing challenges for optimisation. This paper presents a rapid methodology to perform site-wide design parameter exploration and position-specific optimisation of monopile structures using OPTIF, Arup’s in-house tool for design and optimisation of offshore wind foundation structures. The methodology embeds heuristic approaches to efficiently explore diameter profiles and embedment lengths for all positions in a wind farm, considering site-specific geotechnical and metocean conditions as well as fabrication constraints, and balancing trade-offs between serviceability, ultimate, and fatigue limit states. Advanced frequency-based methods for evaluating fatigue loads are employed to assess the complex and often design-governing fatigue limit state, and thickness profiles are optimised using a state-of-the-art algorithm accounting for the highly nonlinear, non-continuously differentiable, and highly sensitive constraints imposed by the design code checks. The methodology allows for rapid development of highly optimised designs for many thousands of design configurations, providing designers with invaluable insight into the design space. At early design stages, this insight can be used to inform key decisions regarding layout, fabrication, and foundation types, and to give confidence in early-stage foundation mass and cost estimates. During later design stages, these insights and rapid exploration of the design space allow for site-wide optimisation considering position-specific loading, and an advanced approach to clustering is presented to achieve mass and cost savings not accessible through a typical approach.

Presenting Author: Christopher Hamilton Arup

Presenting Author Biography: Chris is a structural/mechanical engineer within the Specialist Technology, Analytics and Research group of Arup’s wider Technical Services Portfolio. Chris' focus is in the offshore wind industry, with a strong track record in structural design of offshore foundations, aeroelastic integrated loads analysis, fatigue analysis, probabilistic design methods, and advanced nonlinear computational structural analysis. Chris is also the Product Manager for OPTIF, Arup's in-house software for offshore wind foundation structural analysis, design, and optimisation. Chris has a strong academic background with a specialism in Structural, Mechanical and Geotechnical engineering, recently leading research into the seismic behaviour of large-diameter monopile-transition piece connections for offshore wind turbines in collaboration with the University of Cambridge.