Energy storage systems for wave energy converters and microgrids

The thesis initially gives an overview of the wave industry and the current state of some of the leading technologies as well as the energy storage systems that are inherently part of the power take-off mechanism. The benefits of electrical energy storage systems for wave energy converters are then outlined as well as the key parameters required from them. The options for storage systems are investigated and the reasons for examining supercapacitors and lithium-ion batteries in more detail are shown. The thesis then focusses on a particular type of offshore wave energy converter in its analysis, the backward bent duct buoy employing a Wells turbine. Variable speed strategies from the research literature which make use of the energy stored in the turbine inertia are examined for this system, and based on this analysis an appropriate scheme is selected. A supercapacitor power smoothing approach is presented in conjunction with the variable speed strategy. As long component lifetime is a requirement for offshore wave energy converters, a computer-controlled test rig has been built to validate supercapacitor lifetimes to manufacturer’s specifications. The test rig is also utilised to determine the effect of temperature on supercapacitors, and determine application lifetime. Cycle testing is carried out on individual supercapacitors at room temperature, and also at rated temperature utilising a thermal chamber and equipment programmed through the general purpose interface bus by Matlab. Application testing is carried out using time-compressed scaled-power profiles from the model to allow a comparison of lifetime degradation. Further applications of supercapacitors in offshore wave energy converters are then explored. These include start-up of the non-self-starting Wells turbine, and low-voltage ride-through examined to the limits specified in the Irish grid code for wind turbines. These applications are investigated with a more complete model of the system that includes a detailed back-to-back converter coupling a permanent magnet synchronous generator to the grid. Supercapacitors have been utilised in combination with battery systems for many applications to aid with peak power requirements and have been shown to improve the performance of these energy storage systems. The design, implementation, and construction of coupling a 5 kW h lithium-ion battery to a microgrid are described. The high voltage battery employed a continuous power rating of 10 kW and was designed for the future EV market with a controller area network interface. This build gives a general insight to some of the engineering, planning, safety, and cost requirements of implementing a high power energy storage system near or on an offshore device for interface to a microgrid or grid.

The influence of thermal plasma profiles on low-frequency Alfvén eigenmode dynamics in a tokamak

The confinement of fast particles, present in a tokamak plasma as nuclear fusion products and through external heating, will be essential for any future fusion reactor. Fast particles can be expelled from the plasma through their interaction with Alfvén eigenmode (AE) instabilities. AEs can exist in gaps in the Alfvén continuum created by plasma equilibrium non-uniformities. In the ASDEX Upgrade tokamak, low-frequency modes in the frequency range from f ≈ 10 − 90kHz, including beta-induced Alfvén eigenmodes (BAEs) and lower frequency modes with mixed Alfvén and acoustic polarisations, have been observed. These exist in gaps in the Alfvén continuum opened up by geodesic curvature and finite plasma compressibility. In this thesis, a kinetic dispersion relation is solved numerically to investigate the influence of thermal plasma profiles on the evolution of these low-frequency modes during the sawtooth cycle. Using information gained from various experimental sources to constrain the equilibrium reconstructions, realistic safety factor profiles are obtained for the analysis using the CLISTE code. The results for the continuum accumulation point evolution are then compared with experimental results from ASDEX Upgrade during periods of ICRH only as well as for periods with both ICRH and ECRH applied simultaneously. It is found that the diamagnetic frequency plays an important role in influencing the dynamics of BAEs and low-frequency acoustic Alfvén eigenmodes, primarily through the presence of gradients in the thermal plasma profiles. Different types of modes that are observed during discharges heated almost exclusively by ECRH were also investigated. These include electron internal transport barrier (eITB) driven modes, which are observed to coincide with the occurrence of an eITB in the plasma during the low-density phase of the discharge. Also observed are BAE-like modes and edge-TAEs, both of which occur during the H-mode phase of the discharge.

“Something isn’t right here”: American exceptionalism and the creative nonfiction of the Vietnam War

In this thesis, I argue that few attempts were as effective in correcting the exceptionalist ethos of the United States than the creative nonfiction written by the veterans and journalists of the Vietnam War. Using critical works on creative nonfiction, I identify the characteristics of the genre that allowed Paul John Eakin to call it ‘a special kind of fiction.’ I summarise a brief history of creative nonfiction to demonstrate how it became a distinctly American form despite its Old World origins. I then claim that it was the genre most suited to the kind of ideological transformation that many hoped to instigate in U.S. society in the aftermath of Vietnam. Following this, the study explores how this “new” myth-making process occurred. I use Tim O’Brien’s If I Die in a Combat Zone and Philip Caputo’s A Rumor of War to illustrate how autobiography/memoir was able to demonstrate the detrimental effect that America’s exceptionalist ideology was having on its population. Utilising narrative and autobiographical theory, I contend that these accounts represented a collective voice which spoke for all Americans in the years after Vietnam. Using Neil Sheehan’s A Bright Shining Lie and C.D.B. Bryan’s Friendly Fire, I illustrate how literary journalism highlighted the hubris of the American government. I contend that while poiesis is an integral attribute of creative nonfiction, by the inclusion of extraneous bibliographic material, authors of the genre could also be seen as creating a literary context predisposing the reader towards an empirical interpretation of the events documented within. Finally, I claim that oral histories were in their essence a synthesis of “everyman” experiences very much in keeping with the American zeitgeist of the early Eighties. Focussing solely on Al Santoli’s Everything We Had, I demonstrate how such polyphonic narratives personalised the history of the Vietnam War.