Calculation Method of Intermediate Bearing Displacement Value for Multisupported Shafting Based on Neural Network

Abstract

The mutual influence between the bearings of a ship’s multisupport shafting makes its installation and alignment very difficult. This article addresses the problem of the calculation of the precise displacement value of each intermediate bearing and proposes a method for fitting the shafting characteristic function by using the GA-BP (genetic algorithm-back propagation) neural network. The neural network uses the intermediate bearing reaction as input to calculate the theoretical height of the bearing, thereby accurately calculating the displacement value. Taking the installation and alignment of a ro-ro ship’s propulsion shafting as an application example, a neural network of the ship’s shafting is established with training samples based on finite element simulation, and the effect of network training is discussed. The accuracy of the method is verified by a comparative analysis with the measured data of the ship’s shafting. The calculation results of this method are used as a guide for the installation and alignment of the ship’s shafting and have passed the delivery inspection of the classification society. Introduction The main function of propulsion shafting is transferring power from the main engine and driving propeller rotation for ships and, at same time, transmitting the thrust and tension produced by the propeller to the hull through the thrust bearing (Korczewski 2017; Lai et al. 2018a). A large number of studies have shown that good shaft alignment can reasonably distribute the bearing reaction on each bearing (Kim et al. 2017; Ko et al. 2017; Dong et al. 2018; Lee et al. 2019), which is an important guarantee for the stable navigation of the ship. Improper alignment will result in excessive load on the individual bearing and abnormal wear, which will affect the safe, reliable and stable operation of a ship seriously and increase abnormal vibration (Zou et al. 2016; Guo et al. 2018) and noise (Huang et al. 2014) as well. Therefore, the classification societies have formulated relevant regulations for the magnitude of the bearing reaction during shafting installation. However, shafting of large ships is relatively long and usually adopts multiple intermediate bearing supports. Because of the lack of a certain height reference in the ship and the mutual coupling of intermediate bearings during shafting installation, shafting alignment is very difficult.