Mode excitation of rotating rod bending oscillations under the axial vibro-impact load

The paper presents the investigation results of a vibro-drilling machine's drill-rod dynamic behavior when drilling wells in hard soil under the action of axial vibro-impact load, in order to identify the frequency ranges of higher-order vibration excitation. The drilling process of such wells is significantly facilitated in case of vibro-impact action. The destruction of rocks during vibro-rotary drilling occurs via the complex effect of vibration impulses and rotational motion. In this case, oscillations can occur with the growth of spatial harmonics, during which the mode of the natural oscillations increases. Thus, the task of studying the dynamic behavior of the system, in order to identify the frequencies of vibro-impact action at which the mode excitation of bending oscillations occurs with the growth of the half-wave number, becomes interesting. To find such frequency ranges of axial impact load action on an oscillating rod during rotation, a theoretical study was conducted using developed software, which implements a technique for computer simulation of the oscillatory motion of considerable length rotating rods under the action of axial periodic loads. Such software provides the possibility to model the oscillatory motion of rotating rods and determine the parameters by which the mode number of transverse oscillations of the studied system increases. Using this software, diagrams showing the ranges of impact frequencies in which mode excitation occurs with the growth of the half-wave number of the rod's elastic line were drawn for different parameters of the considered system. The presented results show that for rods with different lengths there are ranges of frequencies of vibro-impact load at which the mode excitation of transverse oscillations occurs with the growth of the half-wave number. It is noted that with increasing rotational speed, the range of impact frequencies expands. The process of oscillation is considered in space with account of inertia forces and geometric nonlinearity of the rod. The conclusion about the possibility of running the equipment in certain frequency ranges is made.