FINITE ELEMENT ANALYSIS OF ELASTOHYDRODYNAMIC STERN TUBE BEARINGS (LUBRICATION, JOURNAL, OPTIMIZATION)

A finite element analysis is performed for a marine shafting/bearing system utilizing a hydrodynamic oil-lubricated stern tube bearing. The stern tube bearing analysis consists of a three-dimensional finite element analysis of the shafting system, a two-dimensional finite element analysis of the oil film hydrodynamics, a three-dimensional finite element analysis of the bearing liner, and iterative techniques to establish the equilibrium position among the shaft, the oil film, and the bearing material.;A non-derivative optimization (minimization) technique is utilized to search systematically for the equilibrium position of the shaft in the bearing clearance. This is necessary because the shaft and the bearing boundaries are difficult to control because of their extreme softness compared with the effective spring constant of the oil film. Both the Nelder and Mead and the Powell methods are found to be effective. The shaft is assumed to remain circular but flexible along the stern bearing. A convergent predictor-corrector process which takes full advantage of the physics of this particular problem is introduced within each objective function evaluation.;The results of this analysis are in very good agreement with a wide range of experimental data from a stern tube bearing simulation apparatus.;The shafting system analysis is formulated as a coupled, three-dimensional problem using beam elements which include bending, shear, thrust, and possible continuous elastic foundation effects. The forward shaft bearings can be taken either as (1) point supports with or without lateral and rotational flexibility or (2) regions of continuous elastic foundation. The two-dimensional finite element analysis of the oil film hydrodynamics is based on the Reynolds equation. The oil film domain is discretized into linear or quadratic triangular elements. The three-dimensional finite element analysis of the bearing material is modeled by linear isoparametric rectangular prism elements. This bearing material analysis includes capability to treat either (1) an inelastic metalic stern bearing or (2) a highly elastic, low-modulus, anistropic plastic bearing.