Failure of oilwell drillstrings is very costly in terms of money and time. There are many reasons for drillstring failure, such as vibration, fatigue, and buckling. Stick-slip vibration has received considerable attention in recent years with increasing use of polycrystalline diamond compact (PDC) bits in harder formations, and has motivated extensive research on this type of drillstring vibration. This paper addresses the advantages of a linear quadratic regulator (LQR) controller, compared to a spring-damper isolator, for stick-slip and bit-bounce mitigation in an oilwell drillstring. A bond graph model of a drillstring has been used for simulation that predicts axial vibration, torsional vibration, and coupling between axial and torsional vibration due to bit-rock interaction.

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