Small scale wind turbines operating in an urban environment produce dismal amounts of power when compared to their expected output [1-4]. This is largely due to the gusty wind conditions found in an urban environment, coupled with the fact that the wind turbines are not designed for these conditions. A new concept of a Segmented Variable Pitch (SVP) wind turbine has been proposed, which has a strong possibility to perform well in gusty and variable wind conditions. This dissertation explains the concept of a SVP wind turbine in more detail and shows analytical and experimental results relating to this concept. Also, the potential benefits of the proposed concept are mentioned. The results from this dissertation show that this concept has potential with promising results on possible turbine blade aerofoil configurations. Scaled model tests were completed and although further design optimisation is required, the tests showed good potential for the SVP concept. Lastly a proof-of-concept full scale model was manufactured and tested to prove scalability to full size from concept models. Along with the proof-of-concept full scale model, a wireless control system (to control the blade segments) was developed and tested.

The typical methodology for analytically designing a wind turbine blade is by means of blade element momentum (BEM) theory, whereby the aerofoil angle of attack is optimized to achieve a maximum lift-to-drag ratio. This research aims to show that an alternative optimisation methodology could yield better results, especially in gusty and turbulent wind conditions. This alternative method looks at increasing the aerofoil Reynolds number by increasing the aerofoil chord length. The increased Reynolds number generally increases the e_ectiveness of the aerofoil which would result in a higher or similar lift-to-drag ratio (even at the decreased angle of attacked require to maintain the turbine thrust coe_cient). The bene_t of this design is a atter power curve which causes the turbine to be less sensitive to uctuating winds. Also, the turbine has more torque at startup, allowing for operatation in lower wind speeds. This research is assumed to only be applicable to small wind turbines which operated in a low Reynolds number regime (<500 000), where Reynolds number manipulation is most advantageous.

This thesis describes four novel superconducting machine concepts, in the pursuit of finding a suitable design for large offshore wind turbines. The designs should be reliable, modular and light-weight. The main novelty of the topologies reside in using a single loop shaped stationary superconducting field winding, which eliminates the rotating transfer couplers and electric brushes or brushless exciters. Furthermore, the electromagnetic forces in the superconducting wire are also eliminated, which simplifies the design and manufacturing of the cryostat and the support structure. Among the four topologies presented, the claw pole type machine is the most promising one. The rotor of the machine composes of claw-poles made from laminated electrical sheets, the superconducting field winding and the armature winding are stationary. The machine is analysed using 3D FEA simulations and a small linear machine prototype is manufactured to verify the simulations. For large scale applications, a double-sided claw pole machine is proposed, which has balanced magnetic attraction forces in the rotor. The machine has a modular cryostat structure, which increases the availability of the machine. Thus, even if a fault occurs in the cryocoolers or in the armature coils, the rest of the machine can operate at partial load until the maintenance is performed. Moreover, it is much easier to replace the faulty parts, as full disassemble of the machine is not required, and a small on-site crane can be used. As a result, it offers operational advantages over the existing superconducting topologies. A 10 MW, 10 rpm generator design is presented, which has a diameter of 6.6 m and an axial length of 1.4 m. The total active mass of the generator is 58 tonnes, and the structural mass is 126 tonnes, which gives a total mass of 184 tonnes. There are four independent cryostats and two independent armature windings in the machine to improve modularity. The biggest advantage of the design is the significantly less superconducting wire usage compared to any other designs; 10 MW machine just needs 15 km of MgB2 wire at 30 K. Thus, it is believed that the proposed topology is a very cost effective and suitable candidate for a successful entry to the wind turbine market.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

This thesis assessed the use of radar as a remote technique for monitoring seabirds in offshore locations.  The study site was in the Moray Firth, Scotland, at the Beatrice oil field, where two 5 MW wind turbines were installed in the summers of 2006 and 2007.  An S-band marine surveillance radar, equipped with commercially available automatic detection and tracking software was installed on the Beatrice Alpha platform to collect ornithological data.  Significant amounts of radar clutter were also recorded in this offshore environment, so bespoke filters were developed, to remove non-avian tracks from the dataset.  Filtered data showed temporal patterns in avian activity at the site, which could be linked to existing knowledge of the use of the site by seabirds.  Flight directions during the breeding season indicated that birds using the site were also attending colonies at the East Caithness cliffs SPA to the north west.  The flight speed parameter included in models of collision between birds and wind turbines was evaluated empirically using radar data.  Ground speed, which is influenced by wind was  highly variable, and was on average 0.707 ms^-1 slower than airspeed, increasing the collisions risk relative to the model’s predictions for many birds. Boat-based visual surveys were used to investigate the impact of turbine installation on the abundance and distribution of birds at the site during the breeding season.  No effect of turbine installation was detected, but environmental variation was shown to have a significant impact on bird abundance.  This demonstrates the difficulty of designing impact studies that can detect the faint signal of an impact, against background variability inherent in marine environments.

No description available.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING / Includes bibliographical references. / by David Roland Mustelier. / B.S.

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Large eddy simulations are considered for wind plants with varied spanwise and streamwise spacing. Data from five different configurations of staggered and aligned LES wind turbine arrays with a neutrally stratified atmospheric boundary layer are employed for analysis. Fields are analyzed by evaluating the anisotropy stress invariants based on the Reynolds shear stresses and dispersive stress tensor. The relationship between quantities are drawn as a function of the wind plant packing. Reynolds stresses and dispersive stresses are investigated alongside a domain altered version of the second and third scalar invariants, ξ, η, as well as the combination of the two invariants described by the function F = 1−27η 2 + 54ξ 3. F is a measure of the approach to either a two-component turbulence (F=1) or an isotropic turbulence (F=0). The invariant η describes the degree of anisotropy while ξ describes the characteristic shape. For the purposes of this study, the LES data is analyzed to understand the effects of canopy density on anisotropy and dispersive stresses, adding further insight and detail for future modeling techniques.

This thesis covers the analysis, dynamic modelling and control of an isolated selfexcited induction generator (SEIG) driven by a variable speed wind turbine. The voltage build up process of an isolated induction generator excited by AC capacitors starts from charge in the capacitors or from a remnant magnetic field in the core. A similar voltage build up is obtained when the isolated induction generator is excited using an inverter/rectifier system with a single DC capacitor on the DC link of the converter. In this type of excitation the voltage build up starts from a small DC voltage in the DC link and is implemented using vector control. The dynamic voltage, current, power and frequency developed by the induction generator have been analysed, simulated and verified experimentally for the loaded and unloaded conditions while the speed was varied or kept constant. Results which are inaccessible in the experimental setup have been predicted using the simulation algorithm. To model the self excited induction generator accurate values of the parameters of the induction machine are required. A detailed analysis for the parameter determination of induction machines using a fast data acquisition technique and a DSP system has been investigated. A novel analysis and model of a self-excited induction generator that takes iron loss into account is presented in a simplified and understandable way. The use of the variation in magnetising inductance with voltage leads to an accurate prediction of whether or not self-excitation will occur in a SEIG for various capacitance values and speeds in both the loaded and unloaded cases. The characteristics of magnetising inductance, Lm, with respect to the rms induced stator voltage or magnetising current determines the regions of stable operation as well as the minimum generated voltage without loss of self-excitation. In the SEIG, the frequency of the generated voltage depends on the speed of the prime mover as well as the condition of the load. With the speed of the prime mover of an isolated SEIG constant, an increased load causes the magnitude of the generated voltage and frequency to decrease. This is due to a drop in the speed of the rotating magnetic field. When the speed of the prime mover drops with load then the decrease in voltage and frequency will be greater than for the case where the speed is held constant. Dynamic simulation studies shows that increasing the capacitance value can compensate for the voltage drop due to loading, but the drop in frequency can be compensated only by increasing the speed of the rotor. In vector control of the SEIG, the reference flux linkage varies according to the variation in rotor speed. The problems associated with the estimation of stator flux linkage using integration are investigated and an improved estimation of flux linkage is developed that compensates for the integration error. Analysis of the three-axes to two-axes transformation and its application in the measurement of rms current, rms voltage, active power and power factor from data obtained in only one set of measurements taken at a single instant of time is discussed. It is also shown that from measurements taken at two consecutive instants in time the frequency of the three-phase AC power supply can be evaluated. The three-axes to twoaxes transformation tool simplifies the calculation of the electrical quantities.