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 country’s 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

The essence and content of illegal obstruction of the organization or holding meetings, rallies, marches and demonstrations and forensic aspects of its analysis

The aim of the article lies in improving the institution of pre-trial investigation in particular and criminal liability for committing illegal obstruction of the organization or holding of meetings, rallies, marches and demonstrations in general. The object of the analysis is the social relations that arise in the process of organizing or holding meetings, rallies, marches and demonstrations by citizens of Ukraine. Methodology. Taking into account the outlined research object, it is considered appropriate to use the following methods: analysis, logical, interpretation, system analyzes, hermeneutic, generalization. Research results. The article, based on the examination of the scientific views and the relevant legal basis, outlines the essence and content of illegal obstruction of the organization or holding of meetings, rallies, marches and demonstrations and the forensic aspects of its analysis. Practical implementation. The content of obstruction is aimed at impossibility of the realization of the relevant rights, which is characterized by the intention, understanding by the person, who does this, all the features of the activity, its focus and anticipation of a positive result. Value/originality. These characteristics are treated as elements of a criminal offence through the prism of provisions and rules of criminal law and play a main or auxiliary role both in the qualification of such an act and during the conduct of a pre-trial investigation depending on objective circumstances and certainty in the legislation of Ukraine

Comparison of wave-body interaction modelling methods for the study of reactively controlled point absorber wave energy converter

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The Prospect of Combining a Point Absorber Wave Energy Converter with a Floating Offshore Wind Turbine

With recent advances in offshore floating wind and wave energy technology, questions have emerged as to whether the two technologies can be combined to reduce their overall levelised cost of energy. In this paper, the potential for combining a floating offshore wind turbine to a point absorbing wave energy converter is investigated. The focus of the investigation is how much power might be produced by a combined floating wind and wave energy converter system, and the resultant changes in motion of the floating wind platform. A model for the combined wave and wind system is developed which uses the standardised NREL OC3 5 MW spar type wind turbine and a cylindrical buoyant actuator (BA), which is attached to the spar via a generic wave power take-off system (modelled as a spring-damper system). Modelling is conducted in the frequency domain and the tests span a wide range of parameters, such as wave conditions, BA sizes, and power take-off coupling arrangements. It is found that the optimal (with respect to power production) BA size is a draft and radius of approximately 14 m. It is found that this BA can theoretically produce power in the range of 0.3 to 0.5 MW for waves with a significant wave height of 2 m, and has the potential to produce power greater or near to 1 MW for waves with a significant wave height of at least 3 m. However, it is also found that, in terms of the relative capture width, significantly smaller BAs are optimal, and that these smaller BA sizes less significantly alter the motion of the floating wind platform

MODERN SYSTEMS OF ORGANIZATION OF DECISIONS ENFORCEMENT AND LEGAL STATUS OF EXECUTORS

The relevance of the study is as follows: if the substantive decision of a court or other jurisdiction (offi-cial) is subject to enforcement, the state must provide an effective mechanism for such kind of enforce-ment (otherwise, in case of non-compliance with the decision by the obligated person, protection of rights, freedoms, interests of the person will remain only on paper). An important component of such a mechanism is the system of enforcement of decisions. Therefore, each state faces the question of which system of enforcement of decisions to choose, and here we need the experience of other states that have already passed this path and can already clearly understand the results. The purpose of the article is to consider the experience of foreign states in reforming the system of enforcement of decisions and the legal status of executors in order to implement it in Ukraine. Methodological basis of the scientific arti-cle is general and special methods of scientific research (deductive, analytical, synthesis method, hermeneutic method, comparative, statistical, historical, dialectical and other methods), which were used to cover the topic of the scientific article. The results of the study contain a generalization of the experience of foreign countries in reforming the system of enforcement of decisions and the legal status of executors. The practical significance of the study is that the scientific article analyzes the application of different systems of organization of enforcement of court decisions, other bodies (officials), different approaches to the legal regulation of the legal status of executors. This can be useful for both legal scholars and legal practitioners, as well as anyone interested in reforming executive legislation

Multi-Mode Wave Energy Converter Design Optimisation Using an Improved Moth Flame Optimisation Algorithm

Ocean renewable wave power is one of the more encouraging inexhaustible energy sources, with the potential to be exploited for nearly 337 GW worldwide. However, compared with other sources of renewables, wave energy technologies have not been fully developed, and the produced energy price is not as competitive as that of wind or solar renewable technologies. In order to commercialise ocean wave technologies, a wide range of optimisation methodologies have been proposed in the last decade. However, evaluations and comparisons of the performance of state-of-the-art bio-inspired optimisation algorithms have not been contemplated for wave energy converters’ optimisation. In this work, we conduct a comprehensive investigation, evaluation and comparison of the optimisation of the geometry, tether angles and power take-off (PTO) settings of a wave energy converter (WEC) using bio-inspired swarm-evolutionary optimisation algorithms based on a sample wave regime at a site in the Mediterranean Sea, in the west of Sicily, Italy. An improved version of a recent optimisation algorithm, called the Moth–Flame Optimiser (MFO), is also proposed for this application area. The results demonstrated that the proposed MFO can outperform other optimisation methods in maximising the total power harnessed from a WEC

A New Bi-Level Optimisation Framework for Optimising a Multi-Mode Wave Energy Converter Design: A Case Study for the Marettimo Island, Mediterranean Sea

To advance commercialisation of ocean wave energy and for the technology to become competitive with other sources of renewable energy, the cost of wave energy harvesting should be significantly reduced. The Mediterranean Sea is a region with a relatively low wave energy potential, but due to the absence of extreme waves, can be considered at the initial stage of the prototype development as a proof of concept. In this study, we focus on the optimisation of a multi-mode wave energy converter inspired by the CETO system to be tested in the west of Sicily, Italy. We develop a computationally efficient spectral-domain model that fully captures the nonlinear dynamics of a wave energy converter (WEC). We consider two different objective functions for the purpose of optimising a WEC: (1) maximise the annual average power output (with no concern for WEC cost), and (2) minimise the levelised cost of energy (LCoE). We develop a new bi-level optimisation framework to simultaneously optimise the WEC geometry, tether angles and power take-off (PTO) parameters. In the upper-level of this bi-level process, all WEC parameters are optimised using a state-of-the-art self-adaptive differential evolution method as a global optimisation technique. At the lower-level, we apply a local downhill search method to optimise the geometry and tether angles settings in two independent steps. We evaluate and compare the performance of the new bi-level optimisation framework with seven well-known evolutionary and swarm optimisation methods using the same computational budget. The simulation results demonstrate that the bi-level method converges faster than other methods to a better configuration in terms of both absorbed power and the levelised cost of energy. The optimisation results confirm that if we focus on minimising the produced energy cost at the given location, the best-found WEC dimension is that of a small WEC with a radius of 5 m and height of 2 m