Research On Torsional Vibration Of DTH Drill String Without Buckling Based On Domain Decomposition Method

With the rapid development of drilling engineering,more and more scholars began to study the vibration characteristics in the process of percussive rotary drilling.DTH hammer,with its unique advantages,is more and more widely used and the study of its system has become more urgent.With the DTH hammer drill string as the research object,based on the domain decomposition method,the discrete dynamics equations of the drill string are established in this paper and the rules of drill string vibration contain stick-slip motion are studied,specific contents are as follows:Firstly,DTH hammer drill string with variable cross-section model is established,and the potential energy functional of DTH hammer drilling string is proposed based on the generalized variational principle.The discrete dynamics equations of drill string are obtained through the functional variational extremum method and we can use matlab to programme and solve the drill string coupling vibration response.Later Newton-Raphson method is applied to solve the nonlinear load problem of drill string,and the drill string load is able to adjust according to the drill string vibration state.Finally we could solve the nonlinear problem of drill string coupling vibration.Secondly,using the coupled vibration solving system of the drill string in front,we studied the influence on the coupling vibration response of damping effect and variable cross-section of drill string.Further more,using the DTH hammer impact as example,we studied the characteristics of the torsion stick-slip vibration of the drill string and the influence of impact duration,the drill string length and driving speed at the top of the drill string.The results showed that drill string is more likely to have stick-slip motion as the impact duration is longer.Compared with the short drill string,the space among each modal frequency of long drill string decreases and the resonance occur.With the driving speed increase,the kinetic energy of the drill bit increase,and the stick-slip motion may disappear.Finally,based on one-dimensional wave theory,the mathematics model of the torsional vibration of the elastomer drill string was established.The steady-state forced response of the drill string torsional vibration is solved using modal superposition method under periodic force,and we can get the theoretical solutions of the drill string torsional vibration under linear condition.Comparing its results with the domain decomposition method,we can verify the reliability of both methods.It is showed that the response solved by domain decomposition method is superposed by the transient response and the steady state response of the drill string,and the theoretical method only contains the steady state response.We can see that the domain decomposition method and theoretical method can get approximate response of torsional vibration in the short drill string.As for the the long drill string,the drill string response is given priority to high order modes,and the domain decomposition method has more advantages for the steady-state response of the long drill string.Through the research on the laws of the coupling vibration of the DTH hammer drill string and the discussion of solving nonlinear dynamics,we have a more comprehensive understanding about the DTH hammer drill string vibration characteristics,and it has an important guiding significance to the actual drilling process.This paper provides an important method and theoretical basis to the research of the drill string vibration response.