Paparella, Francesco
(2017)
Modeling and Control of a
Multibody HingeBargeWave Energy
Converter.
PhD thesis, National University of Ireland Maynooth.
Abstract
Wave Energy Converters (WECs) are devices used to extract energy from the waves. The particular
WEC considered in this thesis is a threebody hingebarge WEC, which is an articulated
floating structure composed of 3 rectangular bodies interconnected by hinges, and it operates longitudinally
to the direction to the incoming wave. The relative motion between each pair of bodies
drives a Power TakeOff (PTO) system, which extracts the energy from the waves. The objective
of this thesis is to increase the energy that can be extracted by a threebody hingebarge WEC
using an optimal control strategy, which computes the optimal loads applied by the PTOs driven
by the relative motion between the bodies. The optimal control is formulated in the time domain,
and computes the PTO loads in a coordinated way, so that the total energy extracted by the device
is maximized. The optimal control strategy is formulated for a threebody hingebarge WEC that
is equipped with either passive or active PTOs.
In this thesis, an optimal control strategy, for the maximization of the energy extracted by a
threebody hingebarge WEC, is derived with PseudoSpectral (PS) methods, which are a subset
of the class of techniques used for the discretisation of integral and partial differential equations
known as mean weighted residuals. In particular, PS methods based on Fourier basis functions,
are used to derive an optimal control strategy, for a finite time horizon. Therefore, an optimal
control strategy, with PS methods based on Fourier basis functions, cannot be applied for realtime
control of the WEC, as Fourier basis functions can only represent the steadystate response
of the WEC. However, PS methods based on Fourier basis functions provide a useful framework
for the evaluation of the achievable power absorption performance of the WEC, with both active
and passive PTOs. The Receding Horizon (RH) realtime optimal control of a threebody hingebarge
WEC is derived with PS methods based on HalfRange ChebyshevFourier (HRCF) basis
functions. The RH optimal realtime controller, with PS methods based on HRCF basis functions,
maximizes the energy extracted by the WEC at each time step over a moving control horizon. In
contrast to Fourier basis functions, HRCF basis functions are well suited for the approximation of
nonperiodic signals, allowing the representation of both the transient and steadystate response of
the WEC.
The optimal control strategy, with PS methods based on either Fourier or HRCF basis functions,
is based on a dynamic model of the device, which is derived with two different modeling
methodologies, that can be also applied to other types of multiple body WECs. The modeling
methodologies are validated against wavetank tests carried out on a 1/7th scale twobody hingebarge
device, and a 1/25th and 1/20th scale threebody hingebarge device.
Repository Staff Only(login required)

Item control page 
Downloads per month over past year