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Prediction-based Control for Mitigation of Axial-torsional Vibrations In a Distributed Drill-String System in the Presence of Parametric Uncertainties

Tashakori, Shabnam | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53114 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Vossoughi, Gholamreza; Zohoor, Hassan
  7. Abstract:
  8. Drill strings are subjected to complex coupled dynamics. Therefore, accurate dynamic modeling, which can represent the physical behavior of real drill strings, is of great importance for system analysis and control. The most widely used dynamic models for such systems are the lumped element models which neglect the system distributed feature. In this thesis, an infinite-dimensional model for the vibrational dynamics of the drill-string, called neutral-type time delay model, is modified to investigate the coupled axial-torsional vibrations in drill strings. This model is derived directly from the distributed parameter model by employing the d’Alembert method. Coupling of axial and torsional vibration modes occurs in the bit–rock interface. For the first time, the neutral-type time delay model is combined with a bit-rock interaction model that regards cutting process in addition to frictional contact. Moreover, mistakes made in some of the related previous studies are corrected. The resulting model is formulated in terms of neutral-type delay differential equations which involve constant state delays, state-dependent state delays, and constant input delays arising from the distributed nature of the drill-string dynamics and the cutting process at the bit. Using a spectral approach, the stability and stabilizability of the associated linearized dynamics are analyzed to support controller design. Then, a control strategy is proposed to stabilize the axial-torsional dynamics of the distributed drill-string system. An optimization-based continuous pole-placement technique has been employed to design the stabilizing controller. Since the designed state-feedback control law needs state prediction, a predictor with observer-structure is proposed. Both the controller and the predictor only employ top-side measurements. The effectiveness of the control strategy is shown in a representative case study. It is also shown that the controller is robust to parametric uncertainty in the bit-rock interaction
  9. Keywords:
  10. Stability Analysis ; Parameters Uncertainty ; Predictive Control ; Drill String ; Coupled Axial Torsional Vibrations ; Neutral-Type Time Delay Model

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