ABSTRACT

The oil film lubrication characteristics is one of the key dynamic factors affecting the marine shafting alignment. Considering the limitation that the oil film equivalent stiffness method is only applicable for small disturbances, this paper researches the influence of the lubrication characteristics on the dynamic alignment of the shafting system from the view of equivalent displacement of the oil film.

Firstly, based on the theory of hydrodynamic lubrication, the oil film characteristics of the bearing under different speeds, inclination angles and loads are analyzed; Secondly, a coupling model for shafting alignment and oil film characteristics calculation is established, which comprehensively considers the variation of journal inclination angle and effective support position at each bearing position in dynamic condition, also the regularity of bearing load distribution under different rotational speeds is analyzed; Finally, the bearing offset under dynamic condition is optimized based on the quadratic programming method. The results show that: the speed, inclination angle and bearing load have a great influence on the oil film stiffness and equivalent displacement; the variation of bearing load with rotational speed have strong nonlinearity, and the load changes most in low speed region but come to be stable in high speed region; the dynamic alignment optimization results are different from that in reasonable alignment, it is suggested that the alignment and optimization work should be carried out at the rated speed condition.

INTRODUCTION

Shafting alignment is to make the load of each bearing and the stress, inclination angle, moment of each section in the allowable range or optimal state by adjusting the bearing offsets. As the main component of the ship's power system, the propulsion shafting system is responsible for transmitting the power of the main engine to the propeller and driving the ship to sail. Keeping its alignment in good condition is an important factor to ensure the safe and stable operation of the ship (Lai, 2018).

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