Design optimisation of mooring systems with load reduction devices for floating offshore wind

Abstract

Floating offshore wind (FOW) has introduced new technical challenges to mooring system design including shallow waters and extreme wind loading relative to oil & gas installations, which contribute to high mooring stiffness and require expensive mooring and anchoring systems. Non-linear extensible mooring components known as load reduction devices (LRDs) enable significant cost reduction for FOW moorings, which introduce new design variables including a range of non-linear stiffness curves that must be optimised for each project. Current modelling and design methods are not adapted to rapidly screen these design variables, making it difficult for developers to understand the benefits of LRDs, leading to over-conservative design choices and reluctance to adopt innovative designs. For FOW, the financial risk associated with selecting an over-conservative design is higher than in hydrocarbon projects, as tens or hundreds of structures need to be moored for a single project. This thesis proposes a design optimisation framework for FOW mooring systems with LRDs, which can be applied to any project-specific location parameters, constraints and objectives. This was achieved by analytical modelling, numerical finite element modelling, surrogate modelling with neural networks, and optimisation using genetic algorithms. The output framework includes: 1) the development of a novel analytical model for catenary moorings with LRDs; 2) a parametric study of LRD design variables using dynamic analysis software; 3) the development of an optimisation methodology. The framework is applied to the design of taut moorings with 3-phase stiffness LRDs, and demonstrates reductions in peak loads by 58 %, fatigue damage by 74 %, nacelle accelerations by 59 % and seabed footprint by 78 % compared to traditional mooring designs. The analytical and optimisation models have been converted into free-to-use web applications, providing an efficient means for mooring designers to consider the benefits of innovative mooring systems.

More information

Identifiers

ORCID for Adam Sobey: orcid.org/0000-0001-6880-8338

ORCID for Susan Gourvenec: orcid.org/0000-0002-2628-7914

ORCID for Jared Charles: orcid.org/0000-0002-2256-3846

Catalogue record

Export record