Reza Kazemi - Department of Mechanical Engineering, K.N. Toosi University of Technology, Tehran, Tehran, Iran
Ali Asghar Jafari - Department of Mechanical Engineering, K.N. Toosi University of Technology, Tehran, Tehran, Iran
Mohammad FarajiMahyari - Department of Mechanical Engineering, Islamic Azad University,Shahr Rey Branch, Tehran, Iran

The main goal of this research is to analyze the effects of drilling mud flow rate and weight on bit on stability and vibration of drill string. To this end, kinetic and potential energies are writtenwhile axial and lateral vibrations are considered. The effects drill string's Weight, weight on bit and geometrical shortening, whichleads to nonlinear terms, are considered in the model. Drilling mud's effects are modeled by the Paidoussis formulations. Finite elementmethod is employed to discretize the formulations. The stabilizers are modeled by dropping the coincided nodes. Linear (Fluttermethod) and nonlinear methods are employed to analyze drill string’s stability for different weight on bit, drilling mud flow rate andnumbers and arrangements of stabilizers. These results representthe significant effects of nonlinear terms. Also, the effects of drilling mud flow rate and weight on bit on the natural frequencies and time responses are illustrated. Increasing drilling mud flow rate causes decreasing of natural frequencies and vibrational amplitude. Also increasing weight on bit causes reduction of natural frequencies and increasing of vibrational amplitude. These formulations can be used to choose the safe working conditions in drilling process

drill string, stability, vibration, drilling mud flow rate,weight on bit