Lateral pile design for offshore wind turbines - Piling 2020 Keynote Lecture - Professor Byron Byrne

This lecture, on lateral pile design for offshore wind turbines, was delivered on 24 March 2020 by Professor Byron Byrne (Department of Engineering Science, University of Oxford) at the Piling 2020 Conference.


Conference Website: https://www.piling2020.org/
Keynote speakers: https://www.piling2020.org/keynote-sp...


Abstract:
Offshore wind energy is a major component of the UK’s energy mix, with nearly 2500 offshore turbines either operational or being constructed, and many more planned for the next few decades. Similarly ambitious plans exist across Europe and elsewhere in the world. Advanced engineering design plays a crucial role in reducing capital and operational costs, and is necessary for the wind energy industry to be cost competitive and sustainable.


Large diameter monopile foundations are the preferred foundation type for offshore wind turbines, and are likely to remain so for the medium term, even as water depths and turbine sizes increase. Design of the monopile foundation must address initial stiffness for input to turbine natural frequency calculations, as well as ultimate capacity to ensure the turbines do not fall over during the life of the wind farm.


The PISA project, completed from 2013 to 2018, addresses both of these design drivers through a combination of numerical modelling, theoretical developments and medium scale field experiments. The scope and outcomes of the PISA project will be addressed in this paper, moving from design in homogeneous soils through to application to realistic layered soil profiles found offshore UK and Europe. A further design driver relates to the impact of cyclic loading, derived from the wind and wave loading, as well as from the operation of the wind turbine as a machine. The designer must be satisfied that the turbine will not gradually lean over, to an unacceptable level, due to the aggregated effects of cyclic loading over time, nor more rapidly in an extreme storm.


New design procedures, based on the Hyperplastic Accelerated Ratcheting Model (HARM), will be described that address cyclic loading, along with the experimental evidence that supports its development and application. An overview will be given of the PICASO project, which aims to further develop cyclic loading design methods, building on the PISA design method, specifically addressing pseudo-random multi-directional loading relevant to offshore wind turbines. The paper finishes with a brief description of the ALPACA project that explores lateral pile design for driven piles in chalk.