Solve The Nonlinear Contacted Problem Between Drillstring And Hole Wall By The Optimization Method

This paper's research object is the whole drillstring and it builds nonlinear equations of the tangent drillstring by the finite element method on the base of the built drillstring mechnics model.Firstly,The optimization method is adopted to solve the nonlinear equations of the touched drillstem. Two optimization-models are built according to the character of the equations. The optimization-function for the single joint is finally adopted because of its higher computational efficiency by the comparison and analysis between the two models. On the choose of the optimization method for the optimization function MATLAB is utilized to work out the procedure of optimizing because MATLAB optimization toolbox selects the best method to solve problem , its input initial parameter is simply and it has high computational efficiency. The method that is to compute the problem from the first joint by the method of recursion is adopted. It proves the validity of the method for the single joint by computing a example. It is connected by a series of joints for the whole structure of drillstring so this not merely only requires a nodal calculation is correct, it is the calculation which involves the whole structure .A similar to the whole drillstring reference topic is set up to prove further the validity of the established computing method to the nonlinear optimization-computation of the whole drillstring ,namely simply supporting beam structure .Prove that It is valid for the computation established to the whole structure through computing and analyzing for horizontal and vertical simply supporting beam structure.