Contact Nonlinear Finite Element Analysis Of Rotary Sucker Rod String

In the practical operation process of screw pump production technology,the rotary rod string of screw pump makes a rotary eccentric movement under the complex load,which causes vibration of the rod string and it is easy to contact and collide with the tubing string,resulting in serious eccentric wear and failure.In order to improve the working efficiency of sucker rod string,extend the service life of rod pump and reduce the economic loss,the author of this dissertation conducts in-depth research to study the nonlinear contact problem of rod and pipe based on finite element theory and demonstrates relationship between the speed,diameter of the sucker rod string,the depth of the pump,and the contact force and rotational friction work.The main contents of this dissertation are as follows:Firstly,through simplification and assumption,the theory of finite element theory is adopted to analyze the coupled lateral and torsional vibration of rotating sucker rod string during normal work;then,the nonlinear coupling vibration dynamics finite element model of rod string is established and the overall stiffness matrix and mass matrix of rotary sucker rod string are derived and calculated;finally,the dynamic equilibrium equation of the overall lateral torsional vibration of the rod string is established.ANSYS software is used to simulate the analysis for coupled lateral and torsional vibration of sucker rod string,then the basic law of coupled lateral and torsional vibration is obtained,and the vibration theory and method of rod string are further improved.Secondly,the contact nonlinear static analysis is carried out on the sucker rod string,and a new contact model between the rotary sucker rod string and the tubing string is put forward.The model can ensure that the rotating sucker rod string and the tubing string in the contact section are close together and meet the conditions: The displacements of the nodes in the contact section are all equal to the limit value;The rotation angle of the cross section of the rod string around its deformation curve is 0.In the analysis of contact nonlinear dynamics,based on the previous study of the boundary method,a new idea is proposed,which combines the finite element method to establish shape function and applies the shape function of time history to construct the dynamic boundary of rotating sucker rod string and the tubing wall,the dynamic boundary model is integrated with the sucker rod string dynamics model to study thedynamic characteristics of sucker rod string and the calculation of the frictional drag moment.Finally,this dissertation initially calculates the parameter values such as the amount of wear and the maximum wear depth of the sucker rod string and the tubing string during the partial wear of the rod tube.The position of the contact point and the contact force are determined by simulation,and the rotational friction work of the rod string is calculated.The impacts of contact force and rotational friction work of the sucker rod string are analyzed from three aspects: rotary speed,diameter of sucker rod string,and pump depth.It is finally concluded that the rotary speed,diameter of sucker rod string,and depth of the sucker rod string are directly proportional to the contact force and rotational friction work:The greater rotary speed,the greater contact force and rotational friction work,and the more serious near-pump rod tube wear is;the more diameter increases,the greater contact force and rotational friction work.