Cavitation estimates by orbit prediction of a journal bearing – Finite element modelling and experimental studies

The paper presents a two-sided approach to establish understanding of the cavitation phenomenon in dynamically loaded journal bearings, more specifically the engine bearings of large two-stroke marine diesel engines. One disadvantage of the journal bearing is the converging-diverging geometry making it prone to cavitation which again affects the load carrying capacity of the bearing. In combustion engines the journal bearing plays a vital role especially as main and crosshead bearings transmitting the combustion forces. Those forces vary highly during one combustion cycle which is further influencing the load carrying capacity and ultimately the chances of fatal shaft-sleeve contact. By solving Reynolds equation numerically using finite elements and incorporating a cavitation algorithm, the dynamic coefficients can be used to establish the journal orbit for a given bearing and load pattern. Validation of the results is done against the Ruston and Hornsby 6VEB-X Mk III engine. Besides the numerical investigations a cavitation test rig has been developed. With this rig it is possible to generate cavitation under controlled conditions in terms of load/eccentricity and rotational speed. The development of cavitation in time in terms of position and distribution can be visually recorded

Comparison and Implementation of a Rigid and a Flexible Multibody Planetary Gearbox Model

We propose algorithms for developing (1) a rigid (constrained) and (2) a flexible planetary gearbox model. The two methods are compared against each other and advantages/disadvantages of each method are discussed. The rigid model (1) has gear tooth reaction forces expressed by Lagrange multipliers. The flexible approach (2) is being compared with the gear tooth forces from the rigid approach, first without damping and second the influence of damping is examined. Variable stiffness as a function of base circle arc length is implemented in the flexible approach such that it handles the realistic switch between one and two gear teeth in mesh. The final results are from modelling the planetary gearbox in a 500 kW wind turbine which we also described in Jørgensen et.al (2013)

Lubricant transport across the piston ring with flat and triangular lubrication injection profiles on the liner in large two-stroke marine diesel engines

A theoretical investigation of the lubricant transport across the top compression piston ring in a large two-stroke marine diesel engine is presented. A numerical model for solving Reynolds equation between the piston ring and cylinder liner based on the finite difference method in one dimension has been made. The model includes force equilibrium of the piston ring, perturbation of Reynolds equation, and transient mass conservation. The model represents a new method of achieving mass conservation across the piston ring and between different time-dependent positions. For analyzing the lubricant transport across the piston ring, two different kinds of initial lubricant profile on the liner and two different kinds of load are investigated i.e. a flat profile and an approximated triangular profile as well as no load and a combustion load based on a combustion pressure profile. The impact from the different load conditions and different lubricant profiles on the liner are presented for film thicknesses, development in the lubricant profiles on the liner as well as the lubricant consumption at each stroke

Investigation of different piston ring curvatures on lubricant transport along cylinder liner in large two-stroke marine diesel engines

A theoretical investigation of the hydrodynamic lubrication of the top compression piston ring in a large two-stroke marine diesel engine is presented. The groove mounted piston ring is driven by the reciprocal motion of the piston. The ring shape follows a circular geometry and the effect of changes in radii is analysed. A numerical model based on the finite difference method in 1D has been developed for solving Reynolds equation in combination with the load equilibrium equation together with flow continuity between the piston ring surface and liner for analysis of the lubricant transport. The cyclic variation throughout one stroke is presented for the minimum film thicknesses at different interesting locations of the piston ring surface together with the friction and the pressure distribution history. The aforementioned parameters have been investigated numerically. The numerical results are presented and discussed. </jats:p