Proxy model for the design of extensible floating offshore wind turbine mooring systems

Abstract

Mooring systems for floating offshore wind turbines (FOWTs) are
designed to resist extreme loads, employing heavy mooring lines and
large anchors which contribute to high capital expenditure. Incorporating
extensible sections to mooring lines reduces peak dynamic
loading, enabling the use of smaller, easier to install and therefore
cheaper anchors. Finite element (F.E.) modelling of extensible mooring
lines is time consuming and is not well suited to optimization since
all the mooring line variables must be defined a priori. This paper
presents a quick and versatile approach to exploring the effect of linear
and non-linear stiffness extensible moorings on the FOWT system,
which can be used for automated optimization of one variable for
given constraints in the others. The proxy model was based on data
from fully-coupled F.E. analyses of the DeepCwind semi-submersible
FOWT. The proxy model is formed of numerical relationships between
environmental loads, fairlead tension, platform surge, and extensible
section design parameters (length L, axial stiffness EA). From these
relationships, the model can determine optimal extensible section
parameters which minimise fairlead tension for a given surge criterion,
or minimise surge for a given maximum tension criterion. When applied
to an example design scenario, results from the proxy model show good
agreement with F.E. results, with a maximum error of 1.2% for linear
stiffness results and 4.3% for non-linear stiffness section properties.

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Identifiers

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

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

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