Case Study: Cost Savings via Advanced Geotechnical Design, Seastar Offshore Wind Farm, Belgium

Starts: Thu, Oct 10, 2019 9:00 AM CST
Ends: Thu, Oct 10, 2019 10:00 AM CST
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Offshore wind is a booming global industry, with tumbling costs resulting in zero-subsidy offshore windfarms becoming a reality. Optimisation of the foundations over recent years has played a significant part in reducing the CAPEX costs of offshore windfarms. Monopiles have proved to be the most popular foundation concept to date, being utilised for 87% of the installed offshore wind turbines in Europe (Wind Europe, 2018). Monopiles are single large diameter steel tubes, typically driven into the soil, with diameters generally between 8 m to 10 m for recent offshore wind farms (Byrne et al., 2017). 

New geotechnical design methodologies (i.e. the PISA design method) are now being utilised to develop site-specific monotonic and cyclic soil reaction curves for the structural design analysis of large diameter monopile foundations. Although there has been a number of recent publications outlining new geotechnical design approaches for monopiles (e.g. Peralta et al., 2017; Byrne et al., 2017), which allow for optimisation of foundation sizes, there are few examples in the literature of real case studies outlining the practical application of such approaches in design. 

This case study presents detailed structural design using a combination of time domain and spectral dynamic analysis techniques considering recommendations from the Pile Soil Analysis (PISA) joint industry project (Byrne et al., 2017) to develop site-specific soil reaction curves. The application of such new geotechnical methodologies presents a number of challenges when applied in design projects with respect to the site characterisation for calibration of the numerical model, suitable rigorous approaches to consider cyclic loading and a suitable workflow for application of site-specific reaction curves (e.g. PISA type approach) within detailed structural analysis. Therefore, this work presents a detailed description of the geotechnical and structural design analysis performed for the Seastar and Mermaid offshore substation platform, Belgium Sector North Sea. Three-dimensional (3D) finite element analysis is performed using a multi-surface plasticity constitutive model to develop site-specific soil reaction curves, according to the PISA approach, for use in detailed structural analysis. A developed dynamic structural analysis tool capable of capturing ringing effects, due to high order wave loading, and modelling diffraction effects including directionality for appurtenances as well as p-δ effects and linear buckling is used for the structural design analysis and is described in the paper. Using such bespoke models is shown to reduce costs and schedules when compared with more standard codified approaches, significantly reducing the foundation-related project risks.

About the Presenters

Scott Whyte, Geotechnical Consultant, Fugro UK

Scott Whyte is a Geotechnical Consultant within Fugro’s UK office. His focus is on offshore wind and the numerical analyses of foundations. He is at the final stages of his Doctorate of Engineering (DEng) at the University of Oxford as part of the Renewable Energy Marine Structures (REMS) center for doctoral training (CDT) and is continuing his seven years of experience with Fugro as a Geotechnical Consultant.  His Doctorate focused on the development, implementation and calibration of constitutive soil models for use in finite element analysis. 





Joe Hilton, General Manager, Sea and Land Project Engineering (SLPE)

Joe Hilton is a highly experienced Chartered Civil Engineer with 11 years’ experience, possessing expert knowledge in offshore substructure design. Joe is the General Manager of Sea and Land Project Engineering (SLPE), responsible for the day-to-day running of the London business and Technical Authority for SLPE’s offshore projects. Joe specialises in advanced structural analysis and dynamic analysis of offshore substructures and leads a team of experienced engineers delivering class leading designs for the offshore Oil and Gas and Renewables industry.

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