基于钻头-岩石碰撞的激振冲击系统的非线性动力学研究

为了提升旋转冲击钻井过程中轴向冲击的辅助破岩效果,设计了一套用于测试钻头与岩石之间激振碰撞的试验装置,通过对钻头的激振频率、激振振幅和施加的静态压力3项可控参数的调节,研究了该激振冲击系统的动力学行为演化规律,且试验测试结果与数值模拟结果具有很好的一致性。通过进一步的分岔分析和相平面分析发现,由于激振冲击系统具有典型的接触非线性结构,其动态响应也呈现出复杂的非线性特征,钻头在与岩石发生激振碰撞后,主要保持单周期的振动状态,但随着控制参数的变化,钻头与岩石之间在一个激励周期内的碰撞次数会不断改变;此外,钻头的振动状态还会经由倍周期分岔转变为双周期振动,但最终又会经由逆倍周期分岔或者折叠分岔重新回到单周期振动状态。由于钻头的振动状态直接决定了其轴向冲击力的大小,因而会影响其破岩效率;因此,为了获得破岩效率最高的一周期一次碰撞的钻头振动状态,应该采用较高的激振频率和振幅,但应该避免较高的静态压力,因为它将触发钻头的颤振,反而降低其破岩效率。

Nonlinear Dynamics of a Vibro-impact System for Indenter-rock Interaction

In order to promote the auxiliary effect of axial impact in rotary-percussive drilling, an experimental set-up for testing the indenter-rock interaction is developed, the nonlinear dynamics of this vibro-impact system is studied numerically and experimentally by varying three control parameters, including frequency and amplitude of excitation, and static force applied on the indenter, and the obtained experimental measurements and the numerical simulations show good agreements. Bifurcation analysis and phase-plane analysis indicate that the dynamic responses are mainly period-one motions with varied impact numbers, which can further develop into period-two motions via period-doubling bifurcations, but will go back to period-one motion via inverse period-doubling bifurcation or fold bifurcation. Since the vibration condition of the indenter determines the impact force, and thus the drilling efficiency, to obtain the most powerful percussion, the ideal vibration of the indenter is the period-one one-impact motion. Therefore, the high excitation frequency and amplitude are suggested, but the high static force should be avoided since it triggers harmful chattering for percussive drilling.