PREFACE

Vibrations in mechanical systems are oscillations occurring without being intentionally provoked. They often have detrimental effects on the system performance and may cause premature wear of the system components, underperforming processes, and could even involve security problems, such is the case in aircraft wings; which in the worst case scenario, excessive vibration causes the aircraft to crash. In oilwell drillstring systems, vibrations constitute an important source of economic losses; drill bit wear, pipes disconnection, borehole disruption and prolonged drilling time, are only some examples of consequences associated with drilling vibrations. Extensive research effort on the modeling and control of drilling systems has been conducted in the last century. Before the sixties, investigations were focused on material strength of the drillstring components, but the trends have since changed to emphasize on its dynamic behavior [136]. In 1960, Bailey and Finnie of Shell Development Company conducted the first analytical and experimental study on torsional and axial drilling vibrations [20]. Since then, numerous approaches for modeling and control have been proposed. The most popular control techniques are listed below: