605 research outputs found
Modelling and Optimization of Wave Energy Converters
Wave energy offers a promising renewable energy source. This guide presents numerical modelling and optimisation methods for the development of wave energy converter technologies, from principles to applications. It covers oscillating water column technologies, theoretical wave power absorption, heaving point absorbers in single and multi-mode degrees of freedom, and the relatively hitherto unexplored topic of wave energy harvesting farms. It can be used as a specialist student textbook as well as a reference book for the design of wave energy harvesting systems, across a broad range of disciplines, including renewable energy, marine engineering, infrastructure engineering, hydrodynamics, ocean science, and mechatronics engineering. The Open Access version of this book, available at https://www.routledge.com/ has been made available under a Creative Commons Attribution-Non Commercial-No Derivatives 4.0 license
Exact and heuristic approaches for multi-component optimisation problems
Modern real world applications are commonly complex, consisting of multiple subsystems
that may interact with or depend on each other. Our case-study about wave
energy converters (WEC) for the renewable energy industry shows that in such a
multi-component system, optimising each individual component cannot yield global
optimality for the entire system, owing to the influence of their interactions or the
dependence on one another. Moreover, modelling a multi-component problem is
rarely easy due to the complexity of the issues, which leads to a desire for existent
models on which to base, and against which to test, calculations. Recently,
the travelling thief problem (TTP) has attracted significant attention in the Evolutionary
Computation community. It is intended to offer a better model for multicomponent
systems, where researchers can push forward their understanding of
the optimisation of such systems, especially for understanding of the interconnections
between the components. The TTP interconnects with two classic NP-hard
problems, namely the travelling salesman problem and the 0-1 knapsack problem,
via the transportation cost that non-linearly depends on the accumulated weight
of items. This non-linear setting introduces additional complexity. We study this
nonlinearity through a simplified version of the TTP - the packing while travelling
(PWT) problem, which aims to maximise the total reward for a given travelling tour.
Our theoretical and experimental investigations demonstrate that the difficulty of a
given problem instance is significantly influenced by adjusting a single parameter,
the renting rate, which prompted our method of creating relatively hard instances
using simple evolutionary algorithms. Our further investigations into the PWT
problem yield a dynamic programming (DP) approach that can solve the problem in
pseudo polynomial time and a corresponding approximation scheme. The experimental
investigations show that the new approaches outperform the state-of-the-art
ones. We furthermore propose three exact algorithms for the TTP, based on the DP
of the PWT problem. By employing the exact DP for the underlying PWT problem
as a subroutine, we create a novel indicator-based hybrid evolutionary approach for
a new bi-criteria formulation of the TTP. This hybrid design takes advantage of the
DP approach, along with a number of novel indicators and selection mechanisms
to achieve better solutions. The results of computational experiments show that the
approach is capable to outperform the state-of-the-art results.Thesis (Ph.D.) -- University of Adelaide, School of Computer Science, 201
[Report of] Specialist Committee V.4: ocean, wind and wave energy utilization
The committee's mandate was :Concern for structural design of ocean energy utilization devices, such as offshore wind turbines, support structures and fixed or floating wave and tidal energy converters. Attention shall be given to the interaction between the load and the structural response and shall include due consideration of the stochastic nature of the waves, current and wind
Committee V.4 - Offshore Renewable Energy
This is the author accepted manuscript. The final version is available from CRC Press via the DOI in this recordProceedings of the 19th International Ship and Offshore Structures Congress, Cascais, Portugal, 7 - 10 September 201
Empowering wave energy with control technology: Possibilities and pitfalls
With an increasing focus on climate action and energy security, an appropriate mix of renewable energy technologies is imperative. Despite having considerable global potential, wave energy has still not reached a state of maturity or economic competitiveness to have made an impact. Challenges include the high capital and operational costs associated with deployment in the harsh ocean environment, so it is imperative that the full energy harnessing capacity of wave energy devices, and arrays of devices in farms, is realised. To this end, control technology has an important role to play in maximising power capture, while ensuring that physical system constraints are respected, and control actions do not adversely affect device lifetime. Within the gamut of control technology, a variety of tools can be brought to bear on the wave energy control problem, including various control strategies (optimal, robust, nonlinear, etc.), data-based model identification, estimation, and forecasting. However, the wave energy problem displays a number of unique features which challenge the traditional application of these techniques, while also presenting a number of control âparadoxesâ. This review articulates the important control-related characteristics of the wave energy control problem, provides a survey of currently applied control and control-related techniques, and gives some perspectives on the outstanding challenges and future possibilities. The emerging area of control co-design, which is especially relevant to the relatively immature area of wave energy system design, is also covered
Three-Tether Wave Energy Converter: Hydrodynamic Modelling, Performance Assessment and Control
Hydro, wind and solar power have become major contributors to the global renewable energy market. However, ocean wave power is emerging as a strong contender in the renewable energy mix due to its high power density and minimal environmental impact. Wave energy has the potential to provide an off-grid electricity solution to remote island communities, and fulfil offshore power needs of small industrial projects. One of the best wave energy resources in the world is concentrated along the southern margin of Australia, and if harnessed, wave power could contribute up to 27 per cent of the countryâs electricity demand by 2050. Over the past few decades, a large number of concepts and designs have been suggested to convert wave energy into electricity. Despite a huge effort made by industry and the scientific community, the technology for extracting power from ocean waves still remains at a pre-commercial stage of development. The main challenge is to design an economically viable wave energy converter (WEC) where its life-cycle costs (investments, operation and maintenance) can be justified by the amount of generated electricity. This thesis focuses on the performance improvement of a particular class of wave energy converters, namely, a bottom-referenced fully submerged point absorber, by means of the three-tether mooring configuration. The main contribution is made towards the design, optimisation and control of the converter in order to answer three research questions: (i) what distinctive features of the fully submerged WECs can be utilised to increase their power absorption efficiency; (ii) how geometric parameters of the converter, such as the tether arrangement, shape, and aspect ratio affect the system performance; and (iii) what factors influence the practical implementation of the optimal control strategies on the three-tether WEC. To explore these questions, numerical frequency- and time-domain models have been developed using state-of-the-art techniques based on linear hydrodynamic theory. In order to gain background knowledge and build a core understanding of the submerged systems, the difference between floating and fully submerged point absorbers is investigated. Attention is given to the distinctive features observed in the hydrodynamic properties, power production limits, and control performance. Recommendations are provided on the choice of the buoy size and shape, depending on the wave climate of the deployment site. The advantages of employing multiple degrees of freedom in energy harvesting, especially for submerged converters, are demonstrated. The design considerations of the three-tether WEC are investigated from a number of perspectives including the tether arrangement, mass, shape, and aspect ratio of the buoy. A clear correlation between an optimal tether inclination angle and the buoy aspect ratio is identified. The comparison of three-tether WECs with different buoy geometries is performed not only based on their power output, but also taking into account a range of cost-related performance metrics. Moreover, the benefits of the three-tether converter over its single-tether counterpart are demonstrated through the detailed techno-economic analysis of both prototypes. The final aspect of this dissertation is devoted to the development of the advanced control system for the three-tether WEC. The causal velocity tracking controller is taken as a basis and extended to the multivariable control problem. It is demonstrated that the designed controller is able to improve the power absorption of the three-tether WEC as compared to a quasi-standard control approach while imposing a series of technical requirements on the power take-off machinery.Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 201
- âŠ