Research Information System
Thesis Type: Doctorate
Institution Of The Thesis: Gazi University, Turkey
Approval Date: 2018
Thesis Language: Turkish
Student: Hikmet Bal
Supervisor: NİZAMİ AKTÜRK
Abstract:The dynamic behavior of the elasto-hydrodynamic lubricated (EHL) rolling bearings which is one of the main causes of the early failure of wind turbines and affects the life and the energy efficiency, is the subject of this thesis. The characteristics of EHL rolling bearings used in the high speed and low speed shafts in wind turbines vary due to change in combined load, speed, hydro-dynamic effect and load-deformation relationship depending on the nonlinear contact characteristics. This behavior complicates the examination of the dynamic of system despite the simple design of the rolling bearing. Hence, in order to analyse the dynamic behavior of the rolling bearing, it is necessary to formulate the EHL contact forces between the ball - raceway contact and to establish a model of the shaft bearing system with appropriate assumption. In this thesis, firstly, Hertz contact theory and EHL theory were used to obtain contact characteristics and EHL contact forces of bearings. The stiffness and damping in the EHL contact are modeled as equivalent spring and damper. Thus overall bearing model established. Simplified rolling contact theory was used for kinematic analyse and pure rolling motion was assumed. The contact angle and the squeeze effect of the rings are obtained analytically. Because of the unstabilities and slowness in the numerical method used in the solution of the EHL contact problem, the contact forces were calculated iteratively by the quasi-static method. Thereafter, a rigid shaft supported by a pair of angular contact ball bearing is modeled in 5 DoF and nonlinear equations of motion are obtained. Finally, the nonlinear equations of motion shaft-bearing system is solved by the numerical method for different operating conditions and lubricants. The results are presented in time and frequency domains. Simulation results indicates that; stiffness in the EHL contact increase with the viscosity increase and the preload increase, damping in the EHL contact decrease with increase of shaft speed and the decrease of viscosity, the vibration behavior of the shaft - EHL contact rolling bearing system is more complex than the vibration behavior of the shaft-dry contact rolling bearing, the natural frequency of the shaft - EHL contact rolling bearing system depends on shaft speed also, finally for low speed especially large load starvation or mixed lubrication regimes should be considered