Bibliography : leaves 124-127 / iii, 127 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Applied Mathematics, 1991

Thesis (M.S.)--Ohio University, June, 1994. / Title from PDF t.p.

Thesis (M.S.)--State University of New York at Binghamton, Department of Computer Science, 2005. / Includes bibliographical references.

Bed connected support structures such as monopiles are expected to be impractical for water depths greater than 30 m and so there is increasing interest in alternative structure concepts to enable cost-effective deployment of wind and tidal stream turbines. Floating, moored platforms supporting multiple rotors are being considered for this purpose. This thesis investigates the dynamic response of such floating structures, taking into account the coupling between loading due to both turbulent flow and waves and the dynamic response of the system. The performance and loading of a single rotor in steady and quasi-steady flows are quantified with a Blade Element Momentum Theory (BEMT) code. This model is validated for steady flow against published data for two 0.8 m diameter rotors (Bahaj, Batten, et al., 2007; Galloway et al., 2011) and a 0.27 m diameter rotor (Whelan and Stallard, 2011). Time-averaged coefficients of thrust and power measured by experiment in steady turbulent flow were in agreement with BEMT predictions over a range of angular speeds. The standard deviation of force on the rotor is comparable to that on a porous grid for comparable turbulence characteristics. Drag and added mass coefficients are determined for a porous disc forced to oscillate normal to the rotor plane in quiescent flow and in the streamwise axis in turbulent flow. Added mass is negligible for the Keulegan Carpenter number range considered ( less than 1). The drag coefficient in turbulent flow was found to decay exponentially with number, to 2±10% for values greater than 0.5. These coefficients were found to be in good agreement with those for a rotor in the same turbulent flow with disc drag coefficient within 12.5% for less than 0.65. An extreme-value analysis is applied to the measured time-varying thrust due to turbulent flow and turbulent flow with waves to obtain forces with 1%, 0.1% and 0.01% probability of exceedance during operating conditions. The 1% exceedance force in turbulent flow with turbulence intensity of 12% is around 40% greater than the mean thrust. The peak force in turbulent flow with opposing waves was predicted to within 6% by superposition of the extreme force due to turbulence only with a drag force based on the relative wave-induced velocity at hub-height estimated by linear wave theory and with drag coefficient of 2.0. Response of a floating structure in surge and pitch is studied due to both wave- forcing on the platform defined by the linear diffraction code WAMIT and due to loading of the operating turbine defined by a thrust coefficient and drag coefficient. Platform response can either increase or decrease the loading on the rotor and this was dependant on the hydrodynamic characteristics of the support platform. A reduction of the force on the rotor is attained when the phase difference between the wave force on the support and the surface elevation is close to ± and when the damping of the support is increased. For a typical support and for a wave condition with phase difference close to , the 1% rotor forces were reduced by 8% when compared to the force obtained with a rotor supported on a stiff tower.

Offshore floating wind turbine technology is growing rapidly and has the potential to become one of the main sources of affordable renewable energy. However, this technology is still immature owing in part to complications from the integrated design of wind turbines and floating platforms, aero-hydro-servo-elastic responses, grid integrations, and offshore wind resource assessments. This research focuses on developing methodologies to investigate the technical and economic feasibility of a wide range of floating offshore wind turbine support structures. To achieve this goal, interdisciplinary interactions among hydrodynamics, aerodynamics, structure and control subject to constraints on stresses/loads, displacements/rotations, and costs need to be considered. Therefore, a multidisciplinary design optimization approach for minimum levelized cost of energy executed using parameterization schemes for floating support structures as well as a frequency domain dynamic model for the entire coupled system. This approach was based on a tractable framework and models (i.e. not too computationally expensive) to explore the design space, but retaining required fidelity/accuracy. In this dissertation, a new frequency domain approach for a coupled wind turbine, floating platform, and mooring system was developed using a unique combination of the validated numerical tools FAST and WAMIT. Irregular wave and turbulent wind loads were incorporated using wave and wind power spectral densities, JONSWAP and Kaimal. The system submodels are coupled to yield a simple frequency domain model of the system with a flexible moored support structure. Although the model framework has the capability of incorporating tower and blade structural DOF, these components were considered as rigid bodies for further simplicity here. A collective blade pitch controller was also defined for the frequency domain dynamic model to increase the platform restoring moments. To validate the proposed framework, predicted wind turbine, floating platform and mooring system responses to the turbulent wind and irregular wave loads were compared with the FAST time domain model. By incorporating the design parameterization scheme and the frequency domain modeling the overall system responses of tension leg platforms, spar buoy platforms, and semisubmersibles to combined turbulent wind and irregular wave loads were determined. To calculate the system costs, a set of cost scaling tools for an offshore wind turbine was used to estimate the levelized cost of energy. Evaluation and comparison of different classes of floating platforms was performed using a Kriging-Bat optimization method to find the minimum levelized cost of energy of a 5 MW NREL offshore wind turbine across standard operational environmental conditions. To show the potential of the method, three baseline platforms including the OC3-Hywind spar buoy, the MIT/NREL TLP, and the OC4-DeepCwind semisubmersible were compared with the results of design optimization. Results for the tension leg and spar buoy case studies showed 5.2% and 3.1% decrease in the levelized cost of energy of the optimal design candidates in comparison to the MIT/NREL TLP and the OC3-Hywind respectively. Optimization results for the semisubmersible case study indicated that the levelized cost of energy decreased by 1.5% for the optimal design in comparison to the OC4-DeepCwind. / Graduate

This work describes the modeling, control design, and experimental verification of an electromagnetic suspension system with position feedback using infrared sensors. A nonlinear model is obtained by fitting a first principle analytical model of the system to experimental data. A sliding control strategy is designed using a sliding surface derived from the model to achieve robust stabilization for the closed-loop system. The control is then implemented on an embedded commercial DSP system for experimental verification of the designed control on a laboratory scale electromagnetic suspension system. To compensate for the steady-state tracking error, two modifications are considered. In the first method, a small magnitude integral term is added to the error feedback, equivalently adjusting the reference signal and eliminating the constant bias. In the second method, an integral sliding control is considered, using a higher-order sliding surface, which also eliminates the constant bias. The experimental results show the efficacy of all designed control techniques. The modified techniques, unlike the original design, effectively eliminate the constant position error.

Orientador: Claudio Angelo Agostinho / Resumo: O estudo teve como objetivo avaliar novos sistemas de criação de rãs-touro em tanques de grande volume com o fornecimento automático de ração em diferentes períodos ao longo do ano. Foram realizados dois trabalhos, o primeiro objetivou-se avaliar o desempenho produtivo de rãs-touro (Lithobates catesbeianus), em três classes de peso inicial (14,06g ± 1,14; 19,10g ± 1,33; 24,60g ± 2,45) mantidas em baias flutuantes com automação do fornecimento de ração e ajuste diario da oferta de ração. O experimento teve duração de 180 dias e as rãs foram alimentadas por meio de alimentadores automáticos controlados por um Controlador Lógico Programável (CLP) a cada meia hora durante o dia (06:00 as 18:00) e taxa de alimentação de 1% do peso vivo durante o outono, inverno (120 dias) e 3% do peso vivo durante a primavera (60 dias). Os animais com maior peso inicial (24,60g) apresentaram melhor ganho de peso (59,67Kg) e ganho de peso individual (251,12g), a sobrevivência não teve diferença entre o maior peso e o intermediário (80.93 e 76,61%), já a conversão alimentar não variou entre os tratamentos. Recomenda-se que o peso de entrada dos animais na baia flutuante seja de 24,60 g para iniciar a recria durante os períodos frios. O segundo trabalho teve como objetivo avaliar três tipos distintos de piso na criação de rãs touro em tanques-rede, sendo uma plataforma fixa feita de fibra de vidro, mantendo durante todo o período experimental uma parte fora da água, uma plataforma móvel, feita de cha... (Resumo completo, clicar acesso eletrônico abaixo) / Doutor

The effects of using limited precision floating point for intermediate storage in an embedded MP3 decoder are investigated in this thesis. The advantages of using limited precision is that the values need shorter word lengths and thus a smaller memory for storage. The official reference decoder was modified so that the effects of different word lengths and algorithms could be examined. Finally, a software and hardware prototype was implemented that uses 16-bit wide memory for intermediate storage. The prototype is classified as a limited accuracy MP3 decoder. Only layer III is supported. The decoder could easily be extended to a full precision MP3 decoder if a corresponding increase in memory usage was accepted.

This master thesis consists of implementation and evaluation of an AEC, Acoustic Echo Canceller, algorithm in a floating-point architecture. The most important question this thesis will try to answer is to determine benefits or drawbacks of using a floating-point architecture, relative a fixed-point architecture, to do AEC. In a telephony system there is two common forms of echo, line echo and acoustic echo. Acoustic echo is introduced by sound emanating from a loudspeaker, e.g. in a handsfree or speakerphone, being picked up by a microphone and then sent back to the source. The problem with this feedback is that the far-end speaker will hear one, or multiple, time-delayed version(s) of her own speech. This time-delayed version of speech is usually perceived as both confusing and annoying unless removed by the use of AEC. In this master thesis the performance of a floating-point version of a normalized least-mean-square AEC algorithm was evaluated in an environment designed and implemented to approximate live telephony calls. An instruction-set simulator and assembler available at the initiation of this master thesis were extended to enable; zero-overhead loops, modular addressing, post-increment of registers and register-write forwarding. With these improvements a bit-true assembly version was implemented capable of real-time AEC requiring 15 million instructions per second. A solution using as few as eight mantissa bits, in an external format used when storing data in memory, was found to have an insignificant effect on the selected AEC implementation’s performance. Due to the relatively low memory requirement of the selected AEC algorithm, the use of a small external format has a minor effect on the required memory size. In total this indicates that the possible reduction of the memory requirement and related energy consumption, does not justify the added complexity and energy consumption of using a floating-point architecture for the selected algorithm. Use of a floating-point format can still be advantageous in speech-related signal processing when the introduced time delay by a subband, or a similar frequency domain, solution is unacceptable. Speech algorithms that have high memory use and small introduced delay requirements are a good candidate for a floating-point digital signal processor architecture.

Floating wind technology has the potential to produce low-carbon electricity on a large scale: it allows the expansion of o shore wind harvesting to deep water, indicatively from 50-60 to a few hundred metres depth, where most of the worldwide technical resource is found. New design specifi cations are being developed for floating wind in order to meet diverse criteria such as conversion effi ciency, maintainability, buoyancy stability, and structural reliability. The last is the focus of this work. The mechanics of floating wind turbines in wind and waves are investigated with an array of numerical means. They demand the simulation of multiple processes such as aerodynamics, hydrodynamics, rotor and structural dynamics; understanding their interaction is essential for engineering design, verifi cation, and concept evaluation. The project is organised in three main parts, presented below. Aero-hydro-mechanical simulation, characterising the rigid-body motions of a floating wind turbine. An investigation of multi-physical couplings is carried out, mainly through EDF R&D's time-domain simulator CALHYPSO. Wave forces are represented with the potential- ow panel method and the Morison equation. Aerodynamic forces are represented by a thrust model or with the blade element momentum theory. Main fi ndings: Exposure of fi nite-angle coupling for semi-submersible turbines with focus on heave plate excursion; characterisation of the aerodynamic damping of pitch motion provided by an operating vertical-axis turbine. Dynamic mooring simulation, focussed on highly compliant mooring systems, where the fluid-structure interaction and mechanical inertial forces can govern line tension. EDF R&D's general-purpose, finite-element solver Code Aster is confi gured for this use exploiting its nonlinear large-displacement and contact mechanics functionalities. Main findings: Demonstration of a Code Aster-based work ow for the analysis of catenary mooring systems; explanation of the dynamic mooring eff ects previously observed in the DeepCwind basin test campaign. Aeroelastic analysis of vertical-axis rotors, aimed at verifying novel large-scale floating wind turbine concepts in operation, when aeroelastic-rotordynamic instabilities may occur. The finite-element modal approach is used to qualify rotor vibrations and to estimate the associated damping, based on the spinning beam formulation and a linearised aerodynamic operator. Main fi ndings: Characterisation of the vibration modes of two novel vertical-axis rotor concepts using the Campbell diagram; estimation of the related aerodynamic damping, providing information on the aeroelastic stability of these designs.