Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

The Influence of Oil Film Lubrication Characteristics on Marine Shafting Dynamic Alignment
Ziqi Chen, Ji Wang, Yujun Liu, Rui Li and Xiao Liu

School of Naval Architecture & Ocean Engineering, Dalian University of Technology
Dalian, Liaoning, China

ABSTRACT

lifted due to the thickness of the oil film during operation. For large ship
propulsion shafting, with the existence of bearing clearance, theinfluence of oil film on alignment can’t be ignored (Lei, 2020). Therefore,
it is especially important to research the oil film characteristics underdynamic condition and its influence on shafting alignment.

The oil film lubrication characteristics is one of the key dynamic factors
affecting the marine shafting alignment. Considering the limitation thatthe 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 theview of equivalent displacement of the oil film.

In recent years, with the development of high-power and large-scale inship manufacturing, the bearing abnormal wear and shafting damage
accidents caused by poor alignment have occurred frequently. However,up to now, the traditional reasonable alignment method is still adopted
by most countries in the world, which has ignored dynamic factors suchas propeller hydrodynamic force (Shin, 2015), wave load (Zhang, 2020),
hull deformation (Seo, 2020), shafting vibration (Zhang, 2019) andlubricating oil film in alignment calculation. With the influence of thesecomplex dynamic factors, the load distribution of the shafting is quite
different from that of the reasonable alignment, which results in overload
on some bearings, and leads to poor alignment problems. Therefore, thetraditional reasonable alignment method is hard to satisfy therequirements for safe and stable operation of the shafting system, so thatthe dynamic alignment method considering the influence of complex
dynamic factors has become a urgent problem in the field of shaftingalignment (Shi, 2010).

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 shaftingalignment and oil film characteristics calculation is established, which
comprehensively considers the variation of journal inclination angle andeffective 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 conditionis 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; thevariation of bearing load with rotational speed have strong nonlinearity,and the load changes most in low speed region but come to be stable inhigh speed region; the dynamic alignment optimization results aredifferent from that in reasonable alignment, it is suggested that thealignment and optimization work should be carried out at the rated speed
condition.

Massive research work has been carried on to bearing lubrication
characteristics and shafting alignment, Murawski (2005) calculated thecoupling stiffness among bearing structure, hull and oil film, andanalyzed the influence of support characteristics on shafting alignment.
Sun (2004) pointed out that the shaft misalignment has a great influenceon the thickness and pressure distribution of the oil film, themisalignment caused by shaft deformation should be considered inalignment calculation. Zhou (2005) discussed the method to determine
the effective support position of the oil film, and calculated the effect of
the oil film on alignment, but ignored the bearing clearance. Lu (2009)
researched the influence of oil film on variation of bearing load andeccentricity under different rotational speed, but didn’t consider theinclination angle of journal. Lee (2019) pointed out that the inclination
angle at the after stern bearing will adversely affect the steady state of
the shafting, it should be considered when estimating the effective
support position of the oil film. Geng (2004) took the oil film stiffness
as the support stiffness, by comparing the results with the rigid support
method, the load distribution of each bearing was quite different. Jiang

KEY WORDS: Oil film characteristics; shafting system; equivalentdisplacement; dynamic alignment; optimization.

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 importantfactor to ensure the safe and stable operation of the ship (Lai, 2018).
The equivalent displacement of the oil film is the height of the journal3925