Corrections and comments on the mathematical model presented in [Hosseinzadeh Ali and Bakhtiari-Nejad Firooz. A new dynamic model of coupled axial-torsional vibration of a drill string for investigation on the length increment effect on stick-slip instability. Journal of Vibration and Acoustics-Transactions of the ASME 2017; 139(6): 061016

Abstract

In this paper, analyses on the mathematical model presented in [Hosseinzadeh Ali and Bakhtiari-Nejad Firooz. A new dynamic model of coupled axial-torsional vibration of a drill string for investigation on the length increment effect on stick-slip instability. Journal of Vibration and Acoustics-Transactions of the ASME 2017; 139(6): 061016] are presented. The results indicate that the mathematical model described in the original paper is fallacious due to errors in the governing equations, continuity equations, and boundary conditions, as well as the absence of initial or periodicity conditions. The appropriate mathematical models for axial and torsional vibrations of drill string are proposed in this paper.