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Abstract
The stability of oilwell drillstring rotation is analyzed. The drillpipe is represented by a one-dimensional continuum in torsion, while the bottom-hole-assembly is considered to be a rigid body. Conditions of asymptotical stability of the drillstring rotation are obtained in closed form. The obtained conditions introduce the critical length and the critical rotational speed. The uniform rotation is unstable if the drill- string is longer than the critical length or if it rotates below the critical rotational speed. Recommendations for nimiAance of self-excited torsional oscillations are offered and discussed
