ABS released the ABS Guide for Building and Classing Floating Offshore Wind Turbine Installations to provide the most comprehensive requirements to date.
Based on the results of case studies and existing technologies, the new guide provides criteria for the design, construction, installation and survey of permanently sited floating offshore wind turbines and includes specific guidelines for areas subject to cyclonic storms. The guide addresses the floating support structure, the stationkeeping system and onboard machinery, equipment and systems that are not part of the turbine rotor-nacelle assembly.
"What makes floating offshore wind turbines unique is the strong interaction among the wind turbine rotor, turbine control systems, floating hull structure and stationkeeping system," ABS Managing Principal Engineer, Offshore Technology Qing Yu explained. "We took this interaction into account, developing the criteria based on understanding the characteristic global responses of representative floating offshore wind turbine designs that included a tension leg platform, semisubmersible and spar."
The design environmental conditions and design load cases specified in the Guide were determined on the basis of International Electrotechnical Commission (IEC) 61400-3 standards in conjunction with a number of revisions and refinements to address the uniqueness of floating offshore wind turbines. The site-specific design is directly reflected in the definition of the design load cases, and the effects of tropical hurricane conditions were one of the main considerations in the calibration studies.
In addition to the design load cases, a set of survival load cases are defined for a further check of the robustness of the stationkeeping system. "It is important to bear in mind that drift-away of a single floating offshore wind turbine due to the failure of its stationkeeping system could cause severe damage to an offshore wind farm where dozens or even hundreds of floating turbines and subsea power cables can be installed in close proximity," Yu said.
The main content of the Guide includes:
• Design environmental conditions and design load analysis
• Criteria for designing floating support structures and stationkeeping systems
• Requirements and recommended practices for global performance analysis
• Design requirements for mooring systems and foundations
• Design requirements for steel structures
• Design requirements for concrete structures
• Stability criteria
• Requirements for machinery and systems
• Survey and inspection requirements for construction, installation and in-service.
ABS offers the +A1 Offshore Wind Turbine Installation (Floating) class notation for floating offshore wind turbine support structures, stationkeeping systems, and onboard machinery and systems that comply with the requirements and conditions in the Guide.
"Extensive case studies using the latest simulation techniques, coupled with ABS' experience in certifying the design, construction and installation of the world's first full-scale semisubmersible floating wind turbine were the basis for the design criteria specified in the Guide," said ABS Vice President of Offshore Technology Bret Montaruli. "ABS has a wealth of information and resources available globally that will be integral as the industry realizes the value of this renewable energy source."