Ball bearing performance is predicated on the ball-race interface. Simple analytical models can predict the required torque and power lost if the interface is absent of lubricant. Lubricant is added to the interface to decrease bearing frictional power loss and bearing wear. Depending on the operating conditions of speed and load, hydrodynamic forces can fully separate the ball from the bearing interface. This is called full film lubrication. Although this is just one possible lubrication regime, it has the best performance in terms of friction and power lost. Engineers strive to operate bearings in this regime. In this work, the details of the lubricated interface are studied numerically with the finite element analysis (FEA) software COMSOL. A simplified version of the Navier-Stokes equations, the Reynolds equation, is used to model the fluid to reduce the problem size and avoid a highly nonlinear fluid structure interaction (FSI) problem. This is coupled with a full 3D elastic representation of the race and an equation that satisfies load continuity. The pressure in these interfaces can easily exceed 1GPa which has dramatic effects on the fluid’s properties. Therefore, we model the fluid as Newtonian with temperature and pressure dependent viscosity and density. Multiple rheological models are compared. This method is then extended to include non-isothermal effects, surface roughness, and solid-solid contact in cases where the surface roughness is larger than the fluid film to study bearing performance under a variety of conditions. Elastic and plastic asperity contact models are considered. The result is an engineering tool that can aid in the design of bearing systems. Many results are specific to the system being studied, but where possible, results are represented as a function of nondimensional parameters.
Propeller shaft bearings in marine and Naval applications operate on a similar set of principles as oil lubricated ball bearings. The geometry and lubricant differ significantly. However, the underlying physics are similar. Hydrodynamic forces can separate the shaft from the bearing depending on the operating conditions of speed and load, solid contact occurs if these requirements aren’t met. The model developed for oil lubricated ball bearings is applied to water lubricated polymer lined journal bearings. The results of this model are presented non-dimensionally with analytic functions so that engineers can use them. A parameter study is presented consisting of over 500 unique solutions. Multiple second order effects are considered. Comparison to experimental data is presented.
|Advisor:||Welch, Sam, Rorrer, Ron|
|Commitee:||Ingber, Marc, Graham, Alan, Schreyer, Lynn|
|School:||University of Colorado at Denver|
|School Location:||United States -- Colorado|
|Source:||DAI-B 81/2(E), Dissertation Abstracts International|
|Keywords:||Ball bearing, FEA Modeling, Journal Bearing, Mixed-thermal-elastohydrodynamic lubrication, Oil lubricated, Water lubricated|
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