Investigation on the influence of bearing certainty and random elevation on the friction self-excited vibration of ship propeller shaft system

Abstract

Considering the random error of bearing installation and random deformation of the hull caused by waves, this paper establishes the probability distribution model of bearing random elevation and the bearing load distribution model, deduces the friction force expression of the stern bearing, puts forward the transverse-torsional coupling friction self-excited vibration model of the propeller shaft system considering the bearing random elevation. Using the proposed model, the influence of bearing determinism and random elevation on the stability and response of friction self-excited vibration of the propeller shaft system is analyzed. Immediately after that, the vibration response of the system under different bearing elevations was tested by using the propeller-shaft experiment bench with adjustable stern bearing position, which verified the accuracy of the model as well as the validity of the analysis results. The analysis results show that, the stability and response of the system self-excited vibration show randomness after considering the bearing random elevation, which is consistent with the characteristics of significant intermittent and uncertain occurrence of friction vibration in the actual ship propulsion system. In addition, the instability critical speed increases by 64 % and the maximum amplitude of self-excited vibration response increases by 120 % after considering the random elevation, which indicates that the random elevation caused by waves is a factor that needs to be emphasized urgently.