A Method for Determination of Elastohydrodynamic Behavior of Line Shafting Bearings in Their Environment

Safe operation of a rotating line shafting needs to use proper tools and methodology for an accurate determination of its static and steady state behavior in running conditions. Taking into account properly the characteristics of shaft environment is of primary importance. These characteristics are mainly bearing material behavior, oil film dynamic coefficients (stiffness and damping), flexibility and deformations of structure supporting line shafting bearings. Global non linear behavior of the entire system needs to be analyzed to get an accurate solution, as oil film dynamic coefficients depend on steady state location of shaft inside the considered bearing, which depends itself on oil film stiffness, and also on flexibility and deformations of supporting structure. Calculations of structure flexibility and deformations, as well as line shafting stiffness characteristics are performed straightforwardly using finite element method. Solving global matrix equilibrium equation needs to solve elastohydrodynamic (EHD) problem on each bearing. A specific finite element method is developed for this purpose. This method is attractive for taking into account thick and flexible bearing materials such as multi layer synthetic materials. It can also support further developments (effects of geometry defects on bearings, solving thermoelastohydrodynamic problem). The application of the method to the propulsion line shafting of a large LNGC ship (Liquid Natural Gas Carrier) is presented, the final target being the determination of the most optimum bearing offsets for operating safely the vessel in all relevant conditions.