Dynamic stability analysis of a novel hydro-mechanical sensor for drill string vibration control system

Drill string (DS) is equipped with drill string vibration measurement and control systems (DSVMCS) in order to protect DS from axial vibrations. The reliability of DSVMCS electronic sensor components, as well as metrological reliability, is highly dependent on extreme loads and external conditions. A novel DSVMCS is introduced, featuring the use of alternative resources for recording vibration information using a hydro-mechanical sensor (HMS). Apart from HMS, DSVMCS does not require new borehole equipment. HMS operation principle is based on redistributing part of the flow into HMS which affects the flow rate and/or RPM. These indicators can be recorded, transmitted and analyzed by DSVMCS, which is used to take DS out of vibration mode. The aim of this study is to research HMS dynamic stability and performance. HMS mathematical and simulation movement models were developed. HMS dynamic stability is investigated using the Lyapunov and Nyquist stability criterion. Dynamic system transient characteristics were constructed; frequency analysis with the construction of Bode diagrams was carried out. Dynamic characteristics are improved by investigating the influence of a correction device and PID controller. When using the correction device, the transient process is completed in 0.8 s with continuous vibrations not exceeding ±5% of the steady-state amplitude value of 2×10-7 m. When using PID controller, the transient process is completed in 0.25 s with no residual vibrations. Keywords: drill string; drilling; vibrations; sensor; dynamic stability; measurement system.