With the increasing interest in offshore wind power, the related technologies, including HVDC networks, are gaining similar levels of attention. For large scale wind farms far from shore, high voltage DC transmission can provide several advantages over traditional high voltage AC transmission. This thesis focuses on DC/DC converters, a core part of the HVDC network, especially for use in the high voltage, high power and offshore wind environment. The thesis examines a wide range of possible DC/DC converter topologies for the application. Different topologies are compared and evaluated in detail for use in a high power situation. Based on these results, three DC/DC converter topologies are selected for more detailed modelling. The simulation processes and results are presented in the thesis, which reveals the limitations and behaviour of the topologies when they are used at the MW level. In addition, the high power semiconductor switching devices are discussed and evaluated for each topology. To assess the suitability of the DC/DC converter topologies in the offshore wind application, the selected converter topologies are also analysed and modelled combined with a PMSG wind turbine. Finally, a down-scaled DC/DC converter prototype is built to verify the analysis and simulation results.

This thesis examines the joint venture relationship in the context of the exploration phase of the development of an oil and gas field in Great Britain and Australia. It considers a number of issues relating to the relationship between the Participants of a typical Joint Operating Agreement within the legal regimes of Great Britain and Australia. Against this background the main issues addressed in this thesis are- 1. the nature of the joint venture?; 2. the relationship between the Participants inter se; and 3. the relationship between the Operator and the Participants. In addressing these issues the following questions are addressed: - (i) what is a joint venture?; (ii) is a joint venture a separate legal relationship?; (iii) how is a joint venture distinguished from a partnership?; (iv) what is the relationship between the participants inter se?; (v) what rights does a participant of a joint venture have in relation to the joint venture and the other participants of a joint venture?; (vi) what interest, contractural or proprietary, does a participant of a joint venture have in the joint venture and the property thereof?; vii) what duties does a participant of a joint venture have to the joint venture and the other participants of the joint venture?; and (viii) what is the legal position when a participant of a joint venture defaults in complying with its duties?

Tese de mestrado. Engenharia Electrotécnica e de Computadores. Faculdade de Engenharia. Universidade do Porto. 2007

Tese de mestrado integrado. Engenharia Electrotécnica e de Computadores (Energia). Faculdade de Engenharia. Universidade do Porto. 2012

In my dissertation, I investigate the effects of budget-constraints in multi-unit auctions. This is done in three parts. First, I analyze a case where all bidders have a common budget constraint. Precisely, I analyze an auction where two units of an object are sold at two simultaneous, sealed bid, first-price auctions, to bidders who have demand for both units. Bidders differ with respect to their valuations for the units. All bidders have an identical budget constraint which binds their ability to spend in the auction. I show that if valuation distribution is atom-less, then their does not exist any symmetric equilibrium in this auction game. In the second and third parts of my thesis, I analyze the sale of licenses for the right to drill for oil and natural gas in the Outer Continental Shelf (OCS) of the United States. These sales are conducted using simultaneous sealed-bid first-price auctions for multiple licenses, each representing a specific area (called a tract). Using aspects of observed bidding-behavior, I first make a prima facie case that bidders are budget-constrained in these auctions. In order to formalize this argument, I develop a simple extension of the standard model (where bidders differ in their valuations for the objects) by incorporating (random) budgets for the bidders. The auction-game then has a two-dimensional set of types for each player. I study the theoretical properties of this auction, assuming for simplicity that two units are being sold. I show that this game has an equilibrium in pure strategies that is symmetric with respect to the players and with respect to the units. The strategies are essentially pure in the sense that each bidder-type has a unique split (up to a permutation) of his budget between the two auctions. I then characterize the equilibrium in terms of the bid-distribution and iso-bid curves in the value-budget space. I derive various qualitative features of this equilibrium, among which are: (1) under mild assumptions, there always exist bidder-types who submit unequal bids in equilibrium, (2) the equilibrium is monotonic in the sense that bidders with higher valuations prefer more unequal splits of their budgets than bidders with lower valuations and the same budget-level. With a formal theory in place, I carry out a quantitative exercise, using data from the 1970 OCS auction. I show that the model is able to match many aspects of the data. (1) In the data, the number of tracts bidders submit bids on is positively correlated with budgets (an R² of 0.84), even though this relationship is non-monotonic; my model is able to capture this non-monotonicity, while producing an R² of 0.89 (2) In the data, the average number of bids per tract is 8.21; for the model, this number is 10.09. (3) Auction revenue in the data was $1.927 billion; the model produced a mean revenue of $1.944 billion

This thesis focuses on the factors which lead to off-shore manufacture of Australian inventions. It establishes this phenomenon as a problem, both in terms of its incidence in the post-war period, and in the strategic importance of innovative activity to economic growth. The thesis utilises a case study approach and concentrates on the experiences of one company, the Orbital Engine Corporation (Orbital). In 1989 Ralph Sarich, inventor of the Orbital Combustion Process (OCP) engine and founder of Orbital, signed an agreement with the Michigan state government to manufacture the engine in the United States of America (USA), in preference to several alternative sites in Australia and overseas. This occurred in the context of Orbital actively pursuing assistance from the Australian government to secure local production. The research question is: Why did Orbital decide to manufacture its engine invention ofshore? A multi-disciplinary approach to this question is adopted. Three different conceptual frameworks are employed: industrial organisation theory, market failure theory and policy network theory. The analysis is not structured around a pre-existing hypothesis; instead, the aim is to generate potential explanations for more rigorous testing by subsequent researchers. The thesis concludes that, in terms of industrial organisation theory, the decision to manufacture OCP engines off-shore was a function of the poor quality of the Australian industrial context and the failure by those seeking assistance from the Commonwealth government to stress Orbital's status as an exemplary enterprise in Australian industry. Market failure theory indicated that offshore production of the OCP engine was made more likely by the suboptimal operation of the price mechanism, the neglect of market failure arguments by those supporting local production of the engine and 'government failure'. Policy network theory explained Orbital's decision as the result of: ineffective employment of negotiation tactics by proponents of the engine's domestic manufacture; and the chaotic nature of negotiations which allowed certain personal and ideological prejudices to dominate the issue resolution process. It is shown that some or all of these explanations underlie a number of other examples where Australian inventions have been manufactured offshore. In commenting on policy implications, the thesis points to the economic potential of the Orbital invention and the value of interventionist industry policy. The thesis identifies a number of actions which might be taken to lower the incidence of foreign manufacture of Australian inventions. Further research is necessary to determine the relative importance of the various factors which are identified as leading to offshore production. In addition, there remains a particularly crucial need to improve the social efficiency of existing cost-benefit techniques employed by government policy-makers and commercial analysts.

Doctor of Philosophy / Suction caissons have been used in the offshore industry in the last two decades as both temporary mooring anchorages and permanent foundation systems. Although there have been more than 500 suction caissons installed in various locations around the world,understanding of this concept is still limited. This thesis investigates the installation aspect of suction caissons, focusing on the installation in dense sand and layered soils, where sand is inter-bedded by silt and weakly cemented layers. The research was mainly experimental, at both normal gravity and elevated acceleration levels in a geotechnical centrifuge, with some numerical simulations to complement the experimental observations. This study firstly explored the suction caisson installation response in the laboratory at 1g. The influence and effect of different design parameters, which include caisson size and wall thickness, and operational parameters including pumping rate and the use of surcharge were investigated in dense silica sand. The sand heave inside the caisson formed during these installations was also recorded and compared between tests. The 1g study also investigated the possibility of installing suction caissons in layered sand-silt soil, where caissons were installed by both slow and rapid pumping. The heave formation in this case is also discussed. The mechanism of heave formation in dense sand and deformation of the silt layer was further investigated using a half-caisson model and the particle image velocimetry (PIV) technique. The installation response at prototype soil stress conditions was then investigated in a geotechnical centrifuge. The effects of caisson size, wall thickness, as well as surcharge were investigated in various types of sand, including silica sand, calcareous sand dredged from the North Rankin site in the North West Shelf (Australia), and mixed soil where silica sand was mixed with different contents of silica flour. Comparison with the 1g results was also made. The general trend for the suction pressure during installation in homogenous sand was identified. The installation in layered soil was also investigated in the centrifuge. The installation tests were performed in various sand-silt profiles, where the silt layers were on the surface and embedded within the sand. Comparison with the results in homogenous sand was made to explore the influence of the silt layer. Installations in calcareous sand with cemented layers were also conducted. The penetration mechanism through the cemented layer is discussed, and also compared with the penetration mechanism through the silt layer. Finite element modelling was performed to simulate key installation behaviour. In particular, it was applied to simulate the sand deformation observed in the PIV tests. The likely loosening range of the internal sand plug during suction installation in silica sand was estimated. By investigating the development of hydraulic gradient along the inner wall, the principle underlying the suction response for different combinations of selfweight and wall thickness was identified. FE modelling was also performed to explore the influence of the hydraulic blockage by the silt layer. This study found that the caissons could penetrate into all soils by suction installation. Among the key findings are the observations that the suction pressure increases with depth following a distinct pressure slope, corresponding to a critical hydraulic condition along the inner wall; and the installation was possible in both layered sand-silt and uncemented-cemented soils if sufficient pumping was available. While the caisson could penetrate the weakly cemented layers well with no notable adverse effects, problems were observed in the installation in layered sand-silt soil. These include piping failure in slow pumping rate installation at 1g, and the formation of extremely unstable soil heave during installation.

This thesis presents numerical techniques which have been developed to analyse three dimensional problems in offshore engineering. In particular, the three dimensional liquefaction analysis of offshore foundations on granular soils is the main subject of the thesis. The subject matter is broadly divided into four sections: 1)Development of an efficient method for the three dimensional elasto?plastic finite element analysis of consolidating soil through the use of a discrete Fourier representation of field quantities. 2)Validation of the three dimensional method through analyses of shallow offshore foundations subjected to three dimensional loading and investigation of the yield locus for foundations on purely cohesive soils. 3)Formulation of governing equations suitable for three dimensional liquefaction analyses of offshore foundations founded on granular soil, presentation of a method for liquefaction analyses, and application of the method in modified elastic liquefaction analyses of offshore foundations. 4)Application of a conventional elasto?plastic soil model in the liquefaction analyses of offshore foundations using the three dimensional finite element method. The finite element method developed in this thesis provides a rigorous and efficient numerical tool for the analysis of geotechnical problems subjected to three dimensional loading. The efficiency of the numerical tool makes it possible to tackle some of the problems in geotechnical engineering which would otherwise need enormous computing time and thus would be impractical. The accuracy of the numerical scheme is demonstrated by solving the bearing capacity problem of shallow foundations subjected to three dimensional loading. The generalized governing equations and the numerical method for liquefaction analyses presented in this thesis provide a solid base for the analysis of offshore foundations subjected to cyclic wave loading where they are founded on potentially liquefiable soil. The practicability of the numerical scheme is also demonstrated by a modified elastic liquefaction analysis of offshore foundations. The liquefaction phenomenon is redefined in the context of the conventional Mohr?Coulomb model, so that a relatively simple and practical model for elasto?plastic liquefaction analysis is presented. The three dimensional finite element method together with the numerical scheme for liquefaction analysis and the elasto?plastic soil model provide a suitable practical engineering tool for exploring the responses of offshore foundations subjected to cyclic wave loading.

This thesis is concerned with robust control of an offshore steel jacket platform subject to nonlinear wave-induced forces. Since time delay and uncertainty are inevitably encountered for an offshore structure and their existence may induce instability, oscillation and poor performance, it is very significant to study on how the delay and uncertainty affect the offshore structure. In this thesis, a memory robust control strategy is, for the first time, proposed to reduce the internal oscillations of the offshore structure under wave-induced forces, so as to ensure the safety and comfort of the offshore structure. Firstly, when the system's states are adopted as feedback, memory state feedback controllers are introduced for the offshore structure. By using Lyapunov-Krasovskii stability theory, some delay-dependent stability criteria have been established, based on which, and by combining with some linearization techniques, memory state feedback controllers are designed to control the offshore structure. The simulation results show that such controllers can effectively reduce the internal oscillations of the offshore structure subject to nonlinear wave-induced forces and uncertainties. On the other hand, a new Lyapunov-Krasovskii functional is introduced to derive a less conservative delay-dependent stability criterion. When this criterion is applied to the offshore structure, an improved memory state feedback controller with a small gain is obtained to control the system more effectively, which is sufficiently shown by the simulation. Secondly, when the system's outputs are adopted as feedback, memory dynamic output feedback controllers are considered for the offshore structure. By employing a projection theorem and a cone complementary linearization approach, memory dynamic output feedback controllers are derived by solving some nonlinear minimization problem subject to some linear matrix inequalities. The simulation results show that the internal oscillations of the offshore structure subject to nonlinear wave-induced forces are well attenuated. Finally, robust H control is fully investigated for the offshore structure. By employing Lyapunov-Krasovskii stability theory, some delay-dependent bounded real lemmas have been obtained, under which, via a memory state feedback controller or a dynamic output feedback controller, the resulting closed-loop system is not only asymptotically stable but also with a prescribed disturbance attenuation level. The simulation results illustrate the validity of the proposed method.

<p>Problem: Leveranser av IT tjänster från lågkostnadsländer till Sverige.</p><p>Syfte: Att ta reda på hur svenska företag ser på leveranser av IT tjänster från lågkostnadsländer och ta reda på vilka drivkrafter och hinder som existerar. Eftersom Indien är det land som står för de största volymerna vad gäller produktion av IT tjänster så blir det naturligt att fokusera mest på det landet.</p><p>Teori och modell: Idag produceras hälften av världens IT tjänster i Indien. Svenska företag ligger ungefär tre år efter sina brittiska och amerikanska kollegor vad gäller att köpa IT tjänster från Indien.</p><p>Metod: Vi valde en kvalitativ metod för att få fördjupad information kring ämnet och genomförde nio intervjuer med olika svenska företag. Förutom dessa intervjuer hämtade vi data från publicerade artiklar.</p><p>Resultat: Vår undersökning visar på att Indien är ett land att satsa på vad det gäller leveranser av IT tjänster. Att hitta tillräckligt stora IT projekt för att Indien ska ses som lönsamt, verkar vara det främsta hindret. Kompetensen i Indien och kostnadsreduktion är de starkaste drivkrafterna.</p>