High costs and very slow deployment rates of floating offshore wind turbines (FOWTs) are preventing the UK offshore wind sector from reaching its target of 5 GW of FOWT capacity by 2030 (currently at approximately 0.07 GW).

Standardisation and mass production are urgently needed; however, there are currently around 100 proposed designs, with no convergence towards a few proven concepts.

Classification societies (for example, DNV [1]) have suggested the definition of 'environmental classes', which would allow FOWT systems to be designed for a class of environmental conditions rather than for site-specific ones. This approach recognizes that overengineered, but mass-produced, standardized systems can achieve cost savings compared to bespoke, wind farm-specific designs.

The widely accepted “wind turbine class” system by the IEC [2] partially achieves this by defining a finite set of wind conditions, enabling wind turbine generator OEMs to focus on a limited set of designs. However, a similarly accepted approach that considers the other metocean parameters to which a FOWT is subjected (i.e., waves and currents) does not yet exist. Defining such an approach poses several challenges:

• What are the limiting environmental conditions, among all possible, that drive the design of FOWT support structures in the early design phases?
• For each environmental condition (such as wind and waves), what is a suitable set of representative variables that quantify the loading regime, yet avoid requiring an excessive number of parameters that would hinder the definition of a practical set of environmental classes?
• For each variable, how can “severity thresholds” be robustly defined based on the underlying physics, while remaining interpretable?

Proposed aims & objectives

The aim is to develop a methodology for defining simple, adaptable environmental classes that balance usability with accurate environmental representation. It will provide a framework for FOWT substructure designers to identify and characterise these classes based on their individual criteria. This aim is broken down in five objectives:

1. Definition of the design load cases (DLC) driving the design of floating offshore wind turbine support structures
2. Definition of the critical set of environmental conditions representing the design-driving DLCs
3. Collection of the values of the critical set of environmental conditions for a given geographical region (Scotland Exclusive Economic Zone)
4. Development of a robust methodology to derive unbiased, data-driven severity level thresholds, defining the "environmental classes", based on the clustering statistical data analysis approach
5. Application of the methodology developed to a specific geographical region,, as a case study, performing a sensitivity analysis between number of environmental classes and extension of the area covered by each environmental class