Modelling Controlled Arrays of Wave Energy Converters

Given the great potential resource, the utilization of wave energy for electricity production can make a signicant contribution to the renewable energy portfolio of coastal nations such as Ireland and the UK. There are, however, many challenges that must be overcome in order for wave energy to be commercially viable. One of the key objectives of the wave energy industry today is to produce commercially viable wave farms by placing multiple wave energy converters (WECs) together in an array. In this thesis, the WEC array problem is investigated from two dierent points of view: control and layout of individual WECs in an array. WEC arrays are modelled using hydrodynamic coecients from the Boundary Element Method code WAMIT R in the frequency domain, and a discretized time-domain controller is then applied to calculate motion and energy of the system. A new application of an energy equivalent linearization procedure is developed to model viscous forces for a heaving cylinder. Three control methods are subsequently applied to arrays of two and three WECs in various sea states and the resulting power output of the array is investigated. Results are presented which show the benet of using adaptive control for arrays of WECs over a simple xed damping schemes. Additionally, the layout of a controlled array of multiple WECs is investigated given the objective of power maximization. It is shown that as the number of devices in closely-spaced arrays increases, a control scheme that is able to utilize radiation properties of devices can oset the net loss of power eected by shadowing. Furthermore, the relationship between the inter-device spacing and wave angle of incidence is derived for a two-body array and shown to hold for multi-body arrays. A recommendation on the optimal spacing and number of devices given a specic WEC geometry is made for a controlled array