Vibration analysis of the fully coupled nonlinear finite element model of composite drill strings

In recent years to overcome many limitations of drilling operations, composite drill strings as high-tech rotors with complex dynamic behavior are under development. In this research, the fully coupled nonlinear vibration of composite drill strings, which consist of orthotropic layers, is investigated using the Lagrangian approach and the finite element method. In addition to the main nonlinear terms and particularly the geometric stiffening effect, which resulted from the interaction of the drill string weight and the axial bit force, the gyroscopic effect has also been taken into account. The analysis ability of the dynamic model, which is intended to furnish a basic model for the further development of a more comprehensive model, is examined. The fully coupled nonlinear vibrations and modal analysis of the composite drill strings due to various fiber orientations and stacking sequences in the different drilling conditions are studied, and are compared with the steel drill string.