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Thesis (M.S.)--California Polytechnic State University, 2010. / Title from PDF title page; viewed on June 10, 2010. Major professor: Xi Wu, Ph.D. "Presented to the faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Mechanical Engineering." "May 14, 2010." Includes bibliographical references (p. 46-47).

Tidal stream energy presents challenges that will require the development of new engineering tools if designs are to harness this energy source effectively. At first glance one might imagine that tidal stream energy can be treated as wind with appropriate adjustment for fluid properties of water over air, and account taken of the harsher offshore environment; both waves and turbulence. However, it is now well accepted that the flow past turbines that are constrained by the local sea bed, sea surface, and possibly also neighbouring turbines and channel sides, will differ markedly from that of an ostensibly unblocked wind turbine. Garrett & Cummins (2007) were the first to demonstrate that operating a turbine in a non- negligibly blocked flow passage presents a different flow solution and importantly a significant opportunity to enhance the power that can be delivered by blocked turbines with the limit of power extraction exceeding the Lanchester-Betz limit for operation of unblocked wind turbines. Although it is impractical to array real turbines across the entire width of a channel it has been proposed to use short arrays of turbines making use of local constructive interference (blockage) effects; Nishino & Willden (2012) showed that although the phenomenal power limits of Garrett & Cummins are unobtainable in a real flow, a significant uplift in the limit of power extraction can be achieved for short fences of turbines arrayed normally to the flow in wide cross-section channels. However, it does not follow that rotors designed using unblocked wind turbine tools are capable of extracting any more power than they are designed for and hence the power uplift made available through blockage effects may be squandered. This thesis sets out to develop design tools to assist in the design of rotors in blocked environments that are designed to make use of the flow confinement effects and yield rotors capable of extracting some of the additional power on offer in blocked flow conditions. It is the pressure recovery condition used in wind turbine design that requires relaxation in blocked flow conditions and hence it is necessary to resort to a computational framework in which the free stream pressure drop can be properly accounted for. The tool of choice is a computational fluid dynamics embedded blade element method. As with all models with semi-empirical content it is necessary to select and test correction models that account for various simplifications inherent to the use of the blade element method over a fully blade resolved simulation. The thesis presents a rigorous comparison of the computational model with experimental data with the various correction methods employed. The tool is then used to design rotors, first for unblocked operation, with favourable comparison drawn to lifting line derived optimal Betz rotor solutions. The final objective of the study is to design rotors for operation in short fence configurations of four turbines arrayed normally to the flow. This is accomplished and it is shown that by using bespoke in situ rotor design it is possible to extract more power than possible with non-blockage designs. For the defined array layout and operating conditions, the bespoke rotor array design yields a power coefficient 26% greater than the implied Betz limit for an unblocked rotor and 4% greater than operating a rotor designed in isolation in the same array.

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[pt] Este trabalho possibilita o desenvolvimento de um protótipo para uma bancada de rotação em escada reduzida pela modelagem, simulação e variação dos parâmetros usando o método analítico e o método dos elementos finitos. A estrutura da bancada é composta por duas seções, cada uma delas com três discos (rotores), unidas por um acoplamento. A bancada está ancorada numa base (estrutura), e foi montada sobre uma mesa isolada. As seções são acionadas por um motor elétrico (CA)monitorado por um inversor de frequência. A avaliação da sensibilidade dos parâmetros do sistema tais como características de eixo, dos rotores (massas e inércias) e mancais, forneceram um melhor entendimento do comportamento dinâmico. Os parâmetros do sistema foram escolhidos de tal forma a poder medir o desbalanceamento, empenamento do eixo, anisotropia dos mancais. Com este protótipo de bancada, será possível estudar as influências do acoplamento e desalinhamento nos mancais em sua operação, procurando-se obter dados experimentais que permitam conhecer o desenvolvimento dinâmico deste tipo de máquinas rotativas (sistemas multirotor-mancais). / [en] This work reports the modeling, simulation of the dynamics and assemblage of a reduced scale prototype of a Multi-span Rotor. Modeling and simulation were performed using both analytical and finite element approaches. The Multi-span Rotor is a two stage rotor, each stage with three disks (rotors). The two stages are joined by a coupler. An electric motor (CA), wich is controlled by frequency inversor supplies the power to the system. Results from simulation oriented the prototype design, guiding the choices of parameters that control the system response. These parameters were chosen in order to measure umbalancing, shaft bow, and anisotropy of bearing. This prototype allows the experimental study of the influences on the system response of couplings and bearing misalignment in operation, and may be helpful fordwards a better understanting of the dynamic behavior of this type of rotative machines (multirotorbearing system).

<p> Prototypes of the recently developed periscopter, a flying platform tethered to a ground station, are presently extremely difficult to fly. Tests conducted by the Defence Research Board of Canada in Valcartier, Quebec, and by Westinghouse of Canada near Hamilton, have led to several crashes. Possible causes for the lack of flying qualities are: unbalanced aerodynamic forces and moments; inadequate controls; and poor inherent stability characteristics. </p> <p> In this investigation, the system of counter-rotating lifting rotors used in the present periscopters is examined with a view to improvement of the flying qualities. The aerodynamic theory of helicopter rotors is considered as a background. </p> <p> The blades of the present periscopter rotors neither flap nor feather. The feasibility of using either articulated (flapping) blades or rigid feathering blades is examined. It is found that flapping blades are not feasible mainly because of associated stability and control problems. Also the two counter-rotating rotors would tend to strike against each other. A rigid rotor system featuring feathering blades is found to be feasible. Such a system is therefore examined in detail by computing all relevant aerodynamic parameters. It is shown that the feathering system can provide all required control moments. Its introduction would therefore eliminate the present bail mechanism. </p> <p> An analysis of the stability characteristics of a periscopter featuring a rigid feathering rotor system is developed. However, when hovering in still air, such a periscopter is shown to be unstable. The possibility of rendering it stable by the use of rotor controls is demonstrated. No attempt is made to suggest a specific design for the control system to be used. </p> <p> The effect of various operational parameters on the flying qualities of the periscopter is investigated. </p> / Thesis / Master of Engineering (ME)

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