The relationship between cross-flow at a waterjet inlet and delivered thrust is not fully understood. A direct thrust measurement system was designed for a waterjet propelled, free running USV. To induce sway velocity at the waterjet inlet, which was considered equivalent to the cross flow, circles of varying radii were performed at Reynolds Numbers between 3.48 x 106 and 8.7 x 106 and radii from 2.7 to 6.3 boat lengths. Sway velocities were less than twenty percent of mean forward speed with slip angles that were less than 20°. Thrust Loading Coefficients were compared to sway as a percent of forward speed. In small radius turns, no relationship was seen, while in larger radius turns, peaks of sway velocity corresponded with drops in thrust, but this was determined to be caused by reduced vehicle yaw in these intervals . Decoupling of thrust and yaw rate is recommended for future research. / Thesis (M.S.)--Florida Atlantic University, 2013.

In this thesis, the analysis of the dynamic response of a Linear Induction Motor as an electromechanical system is done, accounting for all the governing equations implied in the process which are used to develop the corresponding simulation models. Once this model is presented, a feedback control system is implemented in order to analyze the controlled response of the motor, considering the applications and conditions analogue to aircraft launcher systems. Also a comparison between the Linear and Rotary induction motors describing the differences, similarities and equivalences will be developed. / by Armando Josâe Sinisterra. / Thesis (M.S.C.S.)--Florida Atlantic University, 2011. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2011. Mode of access: World Wide Web.

Neste trabalho é pesquisada a aplicação de um controlador adaptativo auto-ajustável multivariável à instalação propulsora de um navio com motor Diesel e hélice de passo variável. Os sistemas convencionais de controle de propulsão marítima são projetados deterministicamente e, geralmente, baseados na condição nominal de operação da embarcação, definida pelo seu deslocamento de projeto, estado de mar e de casco. Entretanto, o navio raramente opera na sua condição nominal, já que o seu deslocamento não é sempre o mesmo e continuamente ocorrem variações no estado do casco e do mar. Adicionalmente deve-se mencionar o efeito de perturbações estocásticas como vento, ondas e corrente que atuam sobre o navio. Estas considerações sugerem que o controlador de uma instalação propulsora deva ser adaptativo, isto é , que os seus ganhos se ajustem às alterações que ocorrem no sistema ou no meio ambiente. A teoria do controlador adaptativo auto-ajustável empregada neste trabalho é desenvolvida para sistemas multivariáveis lineares estocásticos, descritos por uma equação vetorial de diferenças com coeficientes desconhecidos. A lei de controle é obtida a partir da minimização de um índice de desempenho onde são ponderados os vetores de saída, de referência e de controle. A aplicação do controlador auto-ajustável exige a estimação de parâmetros do modelo. Neste trabalho é utilizado o modo implícito, que estima diretamente os parâmetros do controlador, através do método dos mínimos quadrados recursivo. Para adequar a aplicação da teoria a um sistema não linear, que é o caso da instalação propulsora, é introduzido no algorítimo de estimação de parâmetros um fator de esquecimento variável para alterar a velocidade de convergência dos parâmetros.O desempenho do controlador auto-ajustável é verificado através de uma série de testes de simulação, envolvendo manobras de regulação e de traqueamento. Com estes testes é analisada também a influência da matriz do ruído, do tempo de processamento do controlador, da matriz de ponderação do vetor de controle, da condição inicial da matriz de parâmetros, do intervalo de amostragem e da condição de operação do sistema sobre o desempenho do controlador. Os resultados de cada manobra são comparados com os obtidos com um controlador convencional projetado especificamente para o navio considerado, constatando-se o bom desempenho do controlador auto-ajustável. / This work is concerned with the application of multivariable self-tuning controllers to diesel engine propulsion plant with variable pitch propeller. Conventional control systems for marine propulsion plants are designed employing deterministic criteria based on the ship\'s operating condition, which is defined by the design displacement, sea state and hull roughness. However, only seldom if ever will the ship find itself operating in such nominal condition since her displacement is not always the same and the sea state and hull roughness vary continuously with time. In addition one should take into consideration the effect on the ship of stochastic factors such as winds, waves and sea currents. The preceding considerations suggest that the controller for a marine propulsion plant should be capable of adjusting itself to varying operating conditions. In other words, it should be capable of tuning its gains according to alterations occurring within the system or imposed by the environment. The theory of self-tuning controller employed in this work has been developed for stochastic multivariable linear systems describe by a linear vector difference equation with unknown parameters. The control law is obtained by the minimization of one performance index in which are weighted the output, reference and control vectors. The application of the self-tuning controller requires the estimation of the model parameters. In this work the implicit way is used wich directly estimates the parameters of the controller by means of the recursive minimum least-square algorithm. In order to apply the theory to non-linear systems such as propulsion plants, a variable forgetting factor is introduced in the estimation algorithm to change the convergence speed of the parameters. The performance of the self-tuning controller is assessed by means of several simulations tests involving regulating and tracking maneuvers.The tests also assess the influence on the controller performance of such factors as the noise matrix, controller process time, initial condition of parameters matrix, sampling time and operating condition of the system. The results of each maneuver are compared with those obtained by a conventional controller specifically designed for the ship under consideration and it was verified that the self-tuning controller has a good performance.

Electric propulsion for spacecraft has become increasingly commonplace in recent decades as designers take advantage of the significant propellant savings it can provide over traditional chemical propulsion. As electric propulsion systems are designed for very low thrust, the operational time required over the course of an entire mission is often quite long. The two most common types of electric thrusters both use hollow cathodes as electron emitters in the process of ionizing the propellant gas. These cathodes are one of the main life-limiting components of both ion and Hall thrusters designed to operate for tens of thousands of hours. Failure often occurs as a result of erosion by sputtering from high-energy ions generated in the plasma. The mechanism that is responsible for creating these high-energy ions is not well understood, and significant efforts have gone into characterizing the plasma produced by hollow cathodes. This work uses both a Langmuir probe and an emissive probe to characterize the variation of the plasma potential and density, the electron temperature, and the electron energy distribution function in the near plume region of a hollow cathode. The cathode used in this experiment is typical of one used in a 200-W class Hall thruster. Measurements were made to determine the variation of these parameters with radial position from the cathode orifice. Changes associated with varying the propellant and flow rate were also investigated. Results obtained from the cathode while running on both argon and xenon are shown. Two different methods for calculating the plasma density and electron temperature were used and are compared. The density and temperature were not strongly affected by reductions in the propellant flow rate. The electron energy distribution functions showed distinct shifts toward higher energies when the cathode was operated at lower flow rates. The plasma potential also displayed an abrupt change in magnitude near the cathode centerline. Significant increases in the magnitude of plasma potential oscillations at lower propellant flow rates were observed. Ions formed at the highest instantaneous plasma potentials may be responsible for the life-limiting erosion that is observed during long-duration operation of hollow cathodes.

L’effet Biefeld-Brown, du nom de ses découvreurs dans les années 1920, désigne la force électrohydrodynamique (EHD) s’appliquant sur deux électrodes sous haute tension dans l’air. Si l’origine de cette force a pu faire l’objet de certaines spéculations, il est aujourd'hui admis qu’elle repose sur l’accélération par un fort champ électrique d’un volume d’air partiellement ionisé. Cet effet aussi appelé vent ionique intéresse diverses applications : contrôle actif d’écoulement, augmentation du transfert de chaleur par convection forcée, séchage de denrées alimentaires ou encore la propulsion. Cette thèse, présente une étude expérimentale, théorique et numérique du vent ionique dans une configuration modèle à deux électrodes parallèles. Le faible rendement du vent ionique l’a écarté des applications à la propulsion mais des expériences récentes menées en 2013 montrent qu’il permet d’atteindre un rapport poussée/puissance étonnement élevé. Nous montrons dans une première partie, à partir de mesures et de considérations aérodynamique générales que la poussée générée pourrait suffire à contrebalancer la force de traînée pour certains aéronefs ultra-légers. Ces mesures ont permis de quantifier la force EHD et sa dépendance avec la géométrie des électrodes. En outre, la meilleure configuration à deux collecteurs peut produire une poussée presque deux fois plus importante qu’une configuration avec un seul collecteur, à tension fixée. Ces premiers résultats ont été affinés dans un second temps par les mesures PIV qui ont permis la reconstruction de l’écoulement et du champ de force entre les électrodes. Les vitesses mesurées dépassent rarement 3 m/s, et la force volumique est de l’ordre de 10 N/m 3. L’origine physique de la configuration optimale à deux collecteurs a été éclaircie par la mise en évidence des structures de sillages et de leurs effets instationnaires. Par ailleurs, une analyse théorique générale de la force propulsive nous a permis de confirmer sa dépendance explicite avec le rapport courant sur mobilité ionique. Le courant étant directement lié à la physique de la décharge couronne, la seconde partie de la thèse s’est concentrée sur son analyse théorique et numérique. Une analyse asymptotique a ainsi permis de trouver une expression analytique du champ électrique critique et de la caractéristique courant-tension permettant de connaître l’influence de la densité du gaz et de sa composition sur le courant produit dans des électrodes concentriques. Cette approche asymptotique a été associée à une formulation de décomposition de domaine dans le cadre d’une discrétisation par éléments finis pour analyser des configurations plus générales. Une résolution itérative du système d’équations stationnaires non-linéaire couplées par méthode de Newton est proposée, testée et validée. Cette méthode peut être étendue à des géométries plus complexes, permettant ainsi d’obtenir une condition d’injection des charges prenant en compte la physique complexe de la décharge.

Thesis. 1978. Ocean E.--Massachusetts Institute of Technology. Dept. of Ocean Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / Ocean E.

Thesis (Ocean.E)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / Ocean.E

Thesis. 1978. Ocean E.--Massachusetts Institute of Technology. Dept. of Ocean Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references and index. / Ocean E.

The Multiple Use Plug Hybrid for Nanosats (MUPHyN) prototype thruster incorporates solutions to several major challenges that have traditionally limited the deployment of chemical propulsion systems on small spacecraft. The MUPHyN thruster offers several features that are uniquely suited for small satellite applications. These features include 1) a non-explosive ignition system, 2) non-mechanical thrust vectoring using secondary fluid injection on an aerospike nozzle cooled with the oxidizer flow, 3) a non-toxic, chemically-stable combination of liquid and inert solid propellants, 4) a compact form factor enabled by the direct digital manufacture of the inert solid fuel grain. Hybrid rocket motors provide significant safety and reliability advantages over both solid composite and liquid propulsion systems; however, hybrid motors have found only limited use on operational vehicles due to 1) difficulty in modeling the fuel flow rate 2) poor volumetric efficiency and/or form factor 3) significantly lower fuel flow rates than solid rocket motors 4) difficulty in obtaining high combustion efficiencies. The features of the MUPHyN thruster are designed to offset and/or overcome these shortcomings. The MUPHyN motor design represents a convergence of technologies, including hybrid rocket regression rate modeling, aerospike secondary injection thrust vectoring, multiphase injector modeling, non-pyrotechnic ignition, and nitrous oxide regenerative cooling that address the traditional challenges that limit the use of hybrid rocket motors and aerospike nozzles. This synthesis of technologies is unique to the MUPHyN thruster design and no comparable work has been published in the open literature.

Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains ix, 86 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 82-86).