Axial-torsional mode correlation analysis of a drill string system with non-smooth characteristics

Abstract

Axial-torsional coupling vibrations are dangerous and complex vibrations that can cause abnormal working conditions in the drilling system. Therefore, the vibration mode correlation is essential in the dynamic analysis of the response complexity of the system to reduce the vibration risk level. In this paper, an axial-torsional lumped parameter model with 5-DOF (degrees of freedom) is proposed to investigate the axial-torsional mode correlation of a drill string system with non-smooth characteristics. Numerical simulations are carried out by using the 4th-5th order Runge-Kutta method with adaptive time steps, and the simulation results are compared and verified by the 5-DOF torsional lumped parameters model and field measurement data. It also performs time domain, frequency domain, and correlation coefficient analysis. The results reveal the mode shape and correlations of an axial-torsional mode in coupled vibrations with and without a bit-bounce. Bit-bounce and stick-slip coupling vibration can be produced by increasing the rotary table speed. The torsional angular velocity of the proposed model is smaller than that of the comparative model, which is in good agreement with the field data.