Tag Archives: Doctoral dissertation

Grid Connected Three-Level Converters


Remya Krishna – Uppsala University, Doctoral Dissertation, March 2014

Abstract

This thesis presents an electrical system analysis of a wave energy converter (WEC) for the objective of grid connection. To transfer the enormous amount of power from waves to the load centers, efficient power electronic systems are essential. This thesis includes the modeling of a buoy–translator dynamics and the modeling of a linear permanent magnet generator along with simulation and experimental validation. Continue reading

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Development of numerical wave power prediction tool offshore oscillating water column wave energy converter


Ahmed Seif-Eldine Mohamed Bayoumi, Doctoral Dissertation, University of Strathclyde, 2013
Abstract
Marine renewable energy sources are crucial alternatives for a sustainable development. The idea of generating electrical power from water waves has been realized for many years. In fact, waves are now considered as an ideal renewable energy source since a Wave Energy Converter (WEC) has no fuel cost and provides cleanly a high power density that is available most of the time. The third generation of WECs is intended to be installed offshore. This allows the device to harvest the great energy content of waves found in deep water and minimise the environmental impacts of the device. Continue reading

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Energy Extraction from Shallow Tidal Flows


Jack William Giles – University of Southampton, PhD Dissertation, December 2013

Abstract

Over the past decade within the renewable energy sector a strong research and development focus has resulted in the growth of an embryonic tidal stream energy industry. Previous assessments of the tidal stream resource appear to have neglected shallow tidal flows. This resource located in water depths of 10-30m is significant because it is generally more accessible for energy extraction than deeper offshore tidal sites and hence a good location for first generation tidal stream arrays or fences. The close proximity to shore may lead to improvements in construction feasibility and economic prospects. The objective of this project is to investigate several aspects concerning the exploitation of shallow tidal flows for energy extraction. Fundamental to this project is the importance of developing research alongside and in conjunction with industrial shallow water
prototype projects. Continue reading

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Wave-structure interaction of offshore wave energy converters


William Finnegan – Doctoral Dissertation, National University of Ireland, Galway – November 2013

Abstract

With the continuing rise in oil prices and greater concern for the damage to the atmosphere, the world is continually looking for a cleaner and more sustainable form of energy. Ocean wave energy as a renewable source of energy, which as of yet is relatively unexploited, offers a possible solution to this energy crisis. The concept of harnessing ocean wave energy is by no means a new idea. However, the topic only gained international interest in the 1970s with the publication of Stephen Salter’s ground-breaking paper on his Wave Energy Duck. The current research study aims to aid the exploitation of this resource by developing robust and reliable analytical and numerical models. Continue reading

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Synergy of multiple cylinders in flow induced motion for hydrokinetic energy harvesting


Eun Soo Kim – University of Michigan, Doctoral Dissertation, 2013

Abstract

Vortex Induced Vibrations for Aquatic Clean Energy (VIVACE) Converter is a converter of marine hydro-kinetic energy invented in the Marine Renewable Energy Lab (MRELab) and patented by the University of Michigan. It harnesses hydrokinetic energy from ocean/tidal/river currents. In its simplest form the VIVACE Converter is a single circular cylinder on springs with a power take-off system. Using passive turbulence control, VIVACE maximizes and utilizes flow induced motion in the form of vortex induced vibration or interference/proximity/wake/soft/hard galloping. MRELab has achieved back-to-back vortex induced vibration and galloping for a single cylinder with passive turbulence control thus more than doubling the range of synchronization of flow induced motion (FIM). Continue reading

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The automation of PDE-constrained optimisation and its applications


Simon Funke, Doctoral Dissertation, Imperial College, UK, 2013

Abstract

This thesis is concerned with the automation of solving optimisation problems constrained by partial differential equations (PDEs). Gradient-based optimisation algorithms are the key to solve optimisation problems of practical interest. The required derivatives can be efficiently computed with the adjoint approach. However, current methods for the development of adjoint models often require a significant amount of effort and expertise, in particular for non-linear time-dependent problems. This work presents a new high-level reinterpretation of algorithmic differentiation to develop adjoint models. This reinterpretation considers the discrete system as a sequence of equation solves. Applying this approach to a general finite-element framework results in an automatic and robust way of deriving and solving adjoint models. Continue reading

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On the Design, Modeling, and Testing of Ocean Wave Energy Converters


Bret Bosma – PhD Dissertation, Oregon State University, July 2013

Abstract

Ocean wave energy converter technology continues to advance and new developers continue to emerge, leading to the need for a general design, modeling, and testing methodology. This work presents a development of the process of taking a wave energy converter from a concept to the prototype stage. A two body heaving point absorber representing a generic popular design was chosen and a general procedure is presented showing the process to model a wave energy converter in the frequency and time domains. A scaled prototype of an autonomous small scale wave energy converter was designed, built, and tested and provided data for model validation. The result is a guide that new developers can adapt to their particular design and wave conditions, which will provide a path toward a cost of energy estimate. This will serve the industry by providing sound methodology to accelerate the continued development of wave energy converters.

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Modelling and geometry optimisation of wave energy converters


Adi Kurniawan – NTNU, Doctoral Dissertation, April 2013

Abstract

The ultimate goal of wave energy undertaking is to find a solution that minimises the cost of delivered energy. Not only should a device maximise its energy absorption, but also the costs associated with absorbing and converting that energy into useful forms should be minimised. Towards realising this goal, this thesis contributes in three main areas, namely, numerical modelling, geometry optimisation, and geometry control.

The highlights of numerical modelling include the use of bond graph—a domain-independent, graphical representation of dynamical systems—in developing numerical models of wave energy converters (WECs), and the use of state-space models to represent the wave radiation terms. It is shown that bond graph is well-suited for modelling WECs, which involve interactions between multiple energy domains, and that state-space models of the wave radiation terms are efficient and sufficiently accurate for use in time-domain simulations of WECs. Both bond graph and state-space models are used in the modelling of a floating oscillating water column device, which, from the point of view of hydrodynamics, is a complex device involving various hydrodynamic radiation terms. Continue reading

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Hydro-Kinetic Energy Conversion: Resource and Technology


M. Grabbe – PhD Dissertation, Uppsala University, April, 2013

Abstract

The kinetic energy present in tidal currents and other water courses has long been appreciated as a vast resource of renewable energy. The work presented in this doctoral thesis is devoted to both the characteristics of the hydro-kinetic resource and the technology for energy conversion. An assessment of the tidal energy resource in Norwegian waters has been carried out based on available data in pilot books. More than 100 sites have been identified as interesting with a total estimated theoretical resource—i.e. the kinetic energy in the undisturbed flow—in the range of 17 TWh. A second study was performed to analyse the velocity distributions presented by tidal currents, regulated rivers and unregulated rivers. The focus is on the possible degree of utilization (or capacity factor), the fraction of converted energy and the ratio of maximum to rated velocity, all of which are believed to be important characteristics of the resource affecting the economic viability of a hydro-kinetic energy converter.

The concept for hydro-kinetic energy conversion studied in this thesis comprises a vertical axis turbine coupled to a directly driven permanent magnet generator. One such cable wound laboratory generator has been constructed and an experimental setup for deployment in the river Dalälven has been finalized as part of this thesis work. It has been shown, through simulations and experiments, that the generator design at hand can meet the system requirements in the expected range of operation. Experience from winding the prototype generators suggests that improvements of the stator slot geometry can be implemented and, according to simulations, decrease the stator weight by 11% and decrease the load angle by 17%. The decrease in load angle opens the possibility to reduce the amount of permanent magnetic material in the design.

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Development of a point absorber wave energy converter: realisation of power take-off, optimisation of geometry and installation techniques


A. Van de Sijpe – PhD Thesis, Ghent University, 2012

Abstract

The development of renewable energy resources is strongly required due to the increasing energy demand, the shrinking reserves of fossil fuels and the effect of greenhouse gas emissions on the change of the wave climate. At Ghent University, study around the extraction of energy from ocean waves is being performed, more specifically with the aid of point absorber wave energy converters (WECs). To deliver a considerable amount of energy output at one location, large numbers of such devices need to be arranged in arrays or farms at sea. Several performed numerical and experimental studies around point absorbers and WEC-arrays are mentioned, indicating the knowledge gap of large scale physical model tests on WEC-farms, which are necessary to study the near- and far-field effects and to verify and improve numerical models. Within the HYDRALAB IV European programme in the frame of the project WEC wakes, large farms of point absorbers will be tested in the Shallow Water Wave Basin of DHI (Denmark). Continue reading

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