Sharif Digital Repository

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...