Offshore wind structural design for Inch Cape Offshore

Background

Inch Cape Offshore Limited (ICOL) proposed to develop a wind farm on a site in the North Sea around 15 km off the Angus coastline which will cover an area of approximately 150 km2 and would consist of up to 1GW of generation capacity.

Project challenges

We were required to execute the foundations and substructures work package (FST) as part of the concept selection phase. This scope of work covered both wind turbine generator (WTG) structures and transmission works, including offshore substation platforms (OSPs).

Lloyd's Register approach

Key elements of the FST scope of work were:

  • Steel jacket design, including transition piece concepts
  • Design of a novel hybrid concrete GBS and jacket substructure
  • Review of 3rd party concrete GBS
  • Structural design of steel framed topsides and jacket substructures for OSPs
  • Production of robust CAPEX estimates
  • Screening of structural design concepts

Our primary objective was to develop and assess design concepts to a level that would allow the client to successfully pass its Appraise stage gate process.

Outcome

Notable highlights included:

  • Robust structural designs for both WTG and OSP substructures
  • Alternative bracing arrangements designed for the WTG jackets that yielded significant weight saving as well as reduced fabrication time
  • Development of a novel hybrid structure comprising a steel jacket installed on a concrete GBS that eliminated piling
  • Design recommendations for accommodating varying water depths using a standardised design: Parametric studies using non-linear analyses demonstrated that "stretching" the jacket or adding additional bays was more efficient than increasing "pile stick-up", resulting in lighter, more robust structures
  • Development of transition piece concepts to optimise WTG installation; alternative TP configurations were considered
  • Robust CAPEX estimates, commensurate with concept screening of the project, for input to client's economic model
  • Independent review of the design and assessment of the suitability for deployment at Inch Cape of a number of proprietary gravity based structures
  • Completed HIRA workshops covering structural design and offshore construction methods
  • Preparation of FEED documentation to be used at the next phase of the project
  • Concept screening to determine which concept(s) should be taken forward to the FEED stage of the project. This was achieved by creating a series of development strategies aligned to the client's key business drivers