  A wave energy converter (WEC) similar to the CETO system developed by
Carnegie Clean Energy is considered for design optimisation. This WEC is able
to absorb power from heave, surge and pitch motion modes, making the
optimisation problem nontrivial. The WEC dynamics is simulated using the
spectral-domain model taking into account hydrodynamic forces, viscous drag,
and power take-off forces. The design parameters for optimisation include the
buoy radius, buoy height, tether inclination angles, and control variables
(damping and stiffness). The WEC design is optimised for the wave climate at
Albany test site in Western Australia considering unidirectional irregular
waves. Two objective functions are considered: (i) maximisation of the annual
average power output, and (ii) minimisation of the levelised cost of energy
(LCoE) for a given sea site. The LCoE calculation is approximated as a ratio of
the produced energy to the significant mass of the system that includes the
mass of the buoy and anchor system. Six different heuristic optimisation
methods are applied in order to evaluate and compare the performance of the
best known evolutionary algorithms, a swarm intelligence technique and a
numerical optimisation approach. The results demonstrate that if we are
interested in maximising energy production without taking into account the cost
of manufacturing such a system, the buoy should be built as large as possible
(20 m radius and 30 m height). However, if we want the system that produces
cheap energy, then the radius of the buoy should be approximately 11-14~m while
the height should be as low as possible. These results coincide with the
overall design that Carnegie Clean Energy has selected for its CETO 6
multi-moored unit. However, it should be noted that this study is not informed
by them, so this can be seen as an independent validation of the design
choices.
