Nonlinear Finite Element Analysis Of Rod String In Rod Pumping System

At present,rod pumping is still the main oil production method at home and abroad.Analysis of the mechanical behavior of the rod pumping system can achieve the purpose of optimizing system parameters and rationally designing the combination of rod and column.Under the known working conditions,the displacement and corresponding load of each section of the sucker rod string need to be obtained through predictive calculation.Therefore,it is of great significance to accurately predict the dynamic behavior of various combined rod strings in the downhole.Since the finite element method is not limited by the calculation method,the concentrated mass can be considered,and the change of the rod column displacement and load can be visually displayed.Therefore,this paper uses the finite element method to analyze the mechanical behavior of the sucker rod string.The main research contents are as follows:1)Analyzing the force of the sucker rod string,establishing a nonlinear finite element analysis model of the rod string dynamics of the rod pumping system,and listing the finite element dynamic equations.2)Analyzing the kinematics model of the pumping unit mechanism,and obtaining the relationship between the displacement,velocity and acceleration of the pumping unit suspension point and time,which is the upper boundary condition of the wave equation.Performing a dynamic analysis on the oil pump to obtain the lower boundary conditions of the wave equation.The initial conditions are different in different time periods and need to be obtained gradually.3)Carrying out finite element analysis of the prediction of the mechanical behavior of the rod string in the rod pumping system,comparing and analyzing the calculation results of the Newmark method,Wilson method and the central difference method,and finally choosing the Wilson calculation method for solution calculation.Three non-linear problems in the model are proposed and analyzed and calculated.4)Due to the widespread use of FRP-steel hybrid rods,and the physical properties of FRP and steel are different,especially under the influence of steel couplings,the mechanical behavior will change greatly.The mixed rods with different combination ratios are studied,and the drawing some important conclusions through the analysis results.In addition,the dynamic behavior of the carbon fiber-steel hybrid rod string is also analyzed to effectively prevent the joint from breaking off.The calculation results in this paper are programmed using Matlab software.According to the precise upper and lower boundary conditions and initial conditions,a finite element analysis model suitable for steel rods,FRP-steel hybrid rods and carbon fiber-steel hybrid rod columns is established.The prediction result is not much different from the actual measurement result,which provides a theoretical basis for optimizing machines,rods,pumps,etc.and has developed related software,which has certain practical value.