  The jacket substructure is a critical component of the offshore wind turbine
(OWT) that is the interface between the transition piece at the top and the
grouted connection. This paper presents a comprehensive study on the
optimization of a jacket substructure to achieve greater cost efficiency while
maintain acceptable structural performance. A fast parametric finite element
modelling (FEM) approach for jacket substructures was firstly proposed. The
generated models took into account realistic loading conditions, including
self-weight, wind load and section-dependent wave load, and soil-pile
interaction. Parametric studies were conducted afterwards to investigate the
trends of the mass and response of the jacket substructure with respect to the
variation of geometric and sectional parameters. Optimizations of the jacket
substructure were carried out using parametric optimization and numerical
genetic algorithm (GA) optimization under three different optimization
strategies corresponding to three groups of objective and constraint functions.
The trends obtained by parametric analysis were used to guide the parameter
selection in parametric optimization, while a rank-based mutation GA was
established with the proposed efficient FEM embedded in as the solver to the
optimization objective and constraint functions. Parametric optimization gained
its advantage in computational efficiency, and the mass reduction were 6.2%,10%
and 14.8% for the three strategies respectively. GA optimization was more
aggressive as the mass reductions were 16.8%,22.3% and 34.3% for the three
strategies, but was relatively more computational intense. The two proposed
optimization methods and the three optimization strategies are both expected to
be applied in practical engineering design of OWT jacket substructure with good
optimization output and high computational efficiency.
