Thesis (Ph. D.)--University of Wisconsin--Madison, 1981. / Typescript. Vita. Includes bibliographical references (leaves 192-196).

The objective of this research is to analyze and develop controller to minimize vibrations of the drill string in rotary drilling rigs. The rotary drilling process is affected by many vibrations which adversely affect the drilling efficiency. The vibrations are mainly classified into three: lateral, tosional and axial. Among the vibrations, lateral vibrations are the most destructive. The research conducted a detailed analysis on lateral vibrations. Bent drill string and unbalanced drill bit was found to be its major causes; and the resultant phenomenon was known as drill bit whirl. Practical demonstration and analysis of the bit whirl phenomenon was done by conducting experiments using an unbalanced drill bit model. Their controllability issues were also discussed and practical solutions suggested. Black box identification methods were applied to develop mathematical models for the system. Box Jenkins structure model was identified and validated by a twofold procedure. Accurate simulations results were obtained with a mere 0.05% residual. Studies revealed that the vibrations in rotary drilling were aggravated by two major causes: borehole friction and critical operation speeds. This research developed a self tuning adaptive controller which could effectively mitigate the vibration aggravating causes and improve overall drilling efficiency. On practical implementation, the controller automatically detected vibrations, mitigated the vibration aggravating causes, and resumed normal drilling operation in less than 10 seconds. The controller action was proven experimentally in two cases: (1) when affected by borehole friction and (2) in presence of an unbalanced drill bit. All the experiments and control techniques applied in this research are validated by experimental data. The prototype used in this research is also distinguished from the rest due to a universal joint, providing an additional two degrees of freedom. Thus, the laboratory set-up provided better dynamic analysis.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 104-106). Also available via the Internet.

Active control constitutes the state of the art in vibration management in rotating machines. However, existing designs are impractical and costly, and hence not yet widely applied. The goal of the research reported here was to develop a design which would allow the implementation of active technology in a wider range of rotating machine applications. Thus, this study focuses on a novel active rotor topology, consisting of a hollow rotor with internally mounted sensors and actuators. This layout provides greater freedom to select the sensor and actuator positions along the rotor, and naturally protects the devices from harsh working environments. The research was structured according to four themes. Firstly, the concept feasibility was explored by constructing a fully functioning prototype. MEMS accelerometers and mass balancer actuators were mounted in an assembled rotor, together with a microcontroller and radio unit to enable wireless transmission of data. Secondly, the behaviour of MEMS accelerometers in a rotating frame of reference was studied. An output model was derived and applied to the study of whirl orbits and transient vibration. Further, techniques were developed to extract mean displacement and angular velocity information from the sensor signals. An analysis of potential sources of measurement error was conducted, and methods for their mitigation devised. The third theme focused on developing active vibration control techniques suitable for use with active rotors. The core of this work is the development and successful implementation of a non a priori method, Algorithmic Direct Search Control. This technique enables vibration to be minimised without knowledge of the system characteristics, by applying a direct search optimisation technique as a control law. Finally, the combination of active rotors and Active Magnetic Bearings was considered to tackle the problem of sensor/actuator non-collocation. The challenge of levitating a rotor on AMBs using only internal accelerometers was approached via integration-based displacement information extraction, to exploit existing PID controllers. This method proved unfeasible in practice, but valuable lessons were derived from the study. The key finding of this work is that active rotor technology is versatile, cost-effective, powerful and feasible. As such, it offers great potential as a route to achieving a more practical and generalised implementation of active control technology in rotating machinery.

Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Kenneth A Cunefare; Committee Member: Christopher Lynch; Committee Member: Massimo Ruzzene; Committee Member: Nader Sadegh; Committee Member: Reginald DesRoches. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Orientador: Alberto Luiz Serpa / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-13T17:01:09Z (GMT). No. of bitstreams: 1 CanahuireCabello_RuthVanessa_M.pdf: 2405747 bytes, checksum: 148678565951eb1c7507a6c9c63048fd (MD5) Previous issue date: 2009 / Resumo: Neste trabalho estudou-se o problema de controle H8 de vibrações levando em conta os efeitos da saturação dos atuadores. Duas situações de interesse foram exploradas. A primeira é aquela em que a saturação deve ser evitada para não causar danos no sistema, mesmo que nesta situação ocorra uma perda de desempenho. A segunda alternativa procuramodificar o controlador no sentido de obter um melhor desempenho, mesmo que ocorra a saturação. O projeto dos controladores H8 foi feito usando as formulações baseadas em desigualdades matriciais lineares (Linear Matrix Inequalities - LMI). Entre as técnicas que evitam a saturação, foram empregadas as funções de ponderação, escolha do peso do esforço de controle como uma das saídas de desempenho do problema de otimização, o escalonamento da matriz de saída do controlador e a inclusão de uma restrição adicional na forma de LMI para limitar o esforço de controle. Para as técnicas que procuram melhorar o desempenho mesmo na presença da saturação, o controlador foi modificado através da metodologia conhecida como Anti-windup. As técnicas estudadas foram avaliadas em dois problemas de controle de vibrações: um sistema massa-mola-amortecedor de dois graus de liberdade e em uma viga flexível. Estas técnicas foram implementadas usando o aplicativo MATLAB e ferramentas específicas para a solução de problemas de otimização com restrições na forma de LMI tais como o Yalmip, SeDuMi e SDPT3. Os resultados para estes dois exemplos são discutidos no trabalho. / Abstract: In this work, the H8 control of vibrations problem taking into account the effects of saturation of actuators is studied. Two situations of interest were explored. The first one considers that saturation should be avoided and does not cause damage to the system, even if this situation leads to loss of performance. The second alternative seeks to modify the controller to achieve better performance, even when the saturation occurs. The design of H8 controllers was done using the formulation based on linear matrix inequalities (LMI). The techniques that avoid saturation are the weighting functions selection, selecting of the weight of the control signal as a performance output of the optimization problem, the scaling of the output matrix of the controller and the inclusion of an additional restriction in the form of LMI to limit the control effort. A technique that seeks to improve performance, even in the presence of saturation, is the controller modification using the methodology known as Anti-windup. These techniques were evaluated in two problems of control of vibrations: a mass-springdamper system of two degrees of freedom and a flexible beam. These techniques were implemented using MATLAB and with the application of specific tools to solve problems of optimization with restrictions in the form of LMI, such as Yalmip, SeDuMi and SDPT3. The results for these two examples are discussed in the work. / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

Thesis (M.A.)--University of South Florida, 2007. / Title from PDF of title page. Document formatted into pages; contains 55 pages. Includes bibliographical references.