State-Of-The-Art Floating Offshore Wind Turbine Design Practice

Introduction

With floating offshore wind turbine (FOWT) technology approaching commercial status, it becomes important to develop recommended (industry-) design practices for general reference and guidance through the design process. This will support existing, adjacent and new industries. The goal of this paper is to gather, evaluate and discuss existing design procedures for FOWT substructure related components (tower, hull, moorings, dynamic cable and the controller) which have been applied in research and industry, taking into account requirements by recognized class societies outlined in standards, guidelines and recommended practices.

Approach

Based on the evaluation of existing design procedures, a high level definition of the design process of the early FOWT substructure design is provided, constituting a general overview of necessary actions, procedures and methods applied in the design of a FOWT system. Additionally, state-of-the-art approaches of the design-related disciplines experimental analysis, numerical design methods, industrialization considerations as well as cost and risk analysis are addressed. The content is aligned with work performed in the University of Stuttgart-led work package “Design Practice” of the European H2020 LIFES50+ project, with the participating floating substructure designers Iberdrola, IDEOL, Nautilus and Olav Olsen.

Main body of abstract

Based on previous research and communication with partners from the consortium of LIFES50+, a general design process was established. This process is based on three key design stages (conceptual, basic and detailed design) and includes categories and topics addressing relevant disciplines to be applied in the design phase of FOWT substructures.

Adding to this overview, specific topics are addressed:
• Certification procedures: The scope of this paper is in line with the first steps of the certification process (concept, design base and design). Key steps are addressed to provide indication of main tasks that need to be performed and the information that need to be provided to the certification body.
• Design of main components: Major design and evaluation procedures are described for the main components of the FOWT substructure. Particular focus is put on the assessment of the controller design, for which a questionnaire was submitted to contacts in industry and research, addressing relevant topics of feedback control, supervisory control and the safety system. The main findings of this questionnaire are described.
• Experimental design practices: The different options for FOWT model tests are described and common workflows for model validation and certification are provided.
• Numerical simulation design practices: The application of numerical models for the description of hydrodynamics, aerodynamics, structural dynamics and mooring dynamics of floating offshore wind turbines in simulation tools at different design steps is described.
• Industrialization consideration in design practice: Follow-up processes such as standardization, manufacturing, transportation, installation and operation and maintenance that follow the design of the main components are addressed.
• LCOE and Risk: Different approaches for LCOE calculation are evaluated and the necessary components are described. Methods for risk assessment of FOWTs are summarized and the influence of risk on LCOE is addressed.


Conclusion

The described design process represents a general high level overview of the current state-of-the-art of the design procedures applied in industry and research, and offers a basic reference when designing substructures for floating wind turbines.


Learning objectives
The established process serves as reference and baseline of future development in any of the addressed key disciplines of early FOWT design. The presented work is funded partially by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 640741.