engleski

Advanced shafting alignment: behaviour of shafting in operation

Main propulsion shafting plays a significant role in merchant marine ships of nowadays. The shafting transmits the torque produced by the prime mover to the ship propeller, as well as the propeller thrust backward to the thrust bearing. Although extensive shafting alignment calculations and checking procedures are implemented nowadays almost in every newbuilding, many problems especially with sterntube bearings still appear in practice. One of the reasons may lie in the fact that all of these calculation and verification procedures refer to the alignment of motionless shafting, instead to the shafting in operation. This paper presents an advanced shafting model and a numerical calculation procedure for a shaftline in operating conditions. Shaftline is modelled as a multiple supported girder, taking into account the static properties of the oil-film, formed in the radial journal bearings in operating conditions. Important steps in development of the calculation procedure, based on simple girder finite elements, as well as an advanced static elastic non-linear model of oil-film in bearings have been outlined in the paper. Results of the incremental-iterative calculation of bearing reactions comprise the shafting deflection curve, together with the internal forces and stationary stresses in operation at a selected rpm. Example of calculated results for a particular ship are shown. Comparison of these results with the ones based upon a conventional calculation procedure for a shafting at rest, where the oil-film properties are neglected, confirms the stated hypothesis as significant differences are obtained among them.

shafting alignment; bearings; oil-film; calculations; merchant ships

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