Abstract Summary
In this work, modelling of non-smooth dynamics of an Anti Stick–Slip Tool (ASST) is carried out. ASST is used to protect a drill-string from a severe form of torsional vibrations known as stick-slip. A drill string is an essential component of any downhole drilling process and it exhibits a highly complex dynamic behaviour due to strong geometrical and material nonlinearities present in the system. To protect the drill-string and to maximize the rate of penetration, the stick-slip phenomenon should be suppressed. One of proposed solutions is to employ Anti Stick-Slip Tool, which is a mechanical device designed to control torsional vibrations by converting the excessive external torque into the axial movement of the bit allowing to avoid unwanted stick phase. In this paper the ASST is considered as a non-smooth dynamic system, where the presented modelling accounts for switching between Activated and Non-Activated states and proposes quantitative conditions for observing each state. The internal friction between coupled components contributes to the conversion of excessive loads to a relative motion of two coupled parts. The proposed models describe the effect of internal friction forces on the operation of the tool whilst the tool is subject to nonlinear cutting forces from bit–rock interactions. Prescribed kinematics imposed on the tool allows to simplify of the model of the entire system and provide insight into the complex behaviour of the tool. Nonlinear responses of the developed model for a range of system parameters were numerically simulated to explore the dynamic behaviour of the ASST. Various external loadings are considered including scenarios when the tool is activated and de-activated during the operation. This allows the tool to be tested and its performance to be optimised.
