Whilst energy can be efficiently extracted from waves by a device exhibiting sloped motion, sustaining that performance in a deep water environment would conventionally rely on a costly support structure. Introduced herein, the Wave-Train device provides an alternative approach to retain the benefits of sloped motion, using a series of joints and struts to mechanically interconnect a series of sloped modules, each of which houses an internal water column to allow reaction against the surrounding water inertia. With a view to maximal power extraction in a real wave climate, this paper presents an optimisation of key parameters associated with the geometry and mass distribution. This relies upon an efficient hydrodynamic model, whose development is presented, particularly with respect to the use of 'generalised' modes to model hinges, for which a somewhat didactic treatment is given. A genetic algorithm, tailored specifically to handle the discontinuous parameter space and the numerical hydrodynamic model, is then used to identify design criteria that are essential for optimal power extraction. Five necessary but not sufficient criteria are presented, in addition to guidance regarding the remaining parameters, which is used to briefly highlight the potential benefits for the practical engineering design.
An efficient numerical model of a spine of ten Edinburgh duck modules is developed. The spine joints and duck modules are modelled using a linear approach based on the theory of generalized modes, which mitigates the need for a more computationally expensive time- domain solver. This approach also allows for computation of the shear forces acting on the spine joints, and has the added benefit of enabling the use of complex conjugate control. The resulting hydrodynamic model is verified for a three duck spine against an alternative implementation that uses a nonlinear multibody solver to enforce the joint motions. A conservative weighted motion constraint is imposed on the controlled degrees of freedom of the ten duck spine, in order to ensure results stay within the bounds of the linear theory. Pertinent sections of the theory underpinning the constrained complex conjugate control method are elaborated upon for the case in which not all degrees of freedom are controlled. An implementation of this control method for a solo duck is compared against a result from the literature, in order to confirm the suitability of the choice of duck design in this study. The control force coefficients that maximise the absorbed power, subject to the motion constraint, are computed for the ten duck spine over a range of wave periods and wave heading angles. The resulting dynamics of the spine of ducks are explored, with particular emphasis on aspects related to the power extraction and forces acting within the system.
A semi-analytical method is derived, which enables optimisation of the power absorption of a collection of wave-interacting bodies, subject to a weighted global motion constraint associated with both the controlled and uncontrolled modes of motion. As an illustrative example, the method is then applied to a six degree of freedom solo duck with various modes of motion under direct control. This is in order to highlight the benefits of employing the extended constraint and to explore the dependence of the existence of a solution on the physical properties of the system. The method is also used to investigate the effects of conceding control of certain degrees of freedom on the capture width ratio of the solo duck.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.