Estimation of longitudinal excitation of propeller using a novel hybrid method

Kai Chai,Haiping Wu

doi:10.21595/jve.2021.21789

Abstract

Due to the limitation of working environment and structure conditions, it is difficult to directly measure the propeller excitation of ship propulsion shafting system. A method based on waveguide function and modal method combining with shafting vibration response measurement was proposed to estimate the propeller longitudinal excitation indirectly. Firstly, a waveguide transfer model for the general structure of the propulsion shafting is proposed that is suitable for estimating propeller excitation from shafting vibration response. Secondly, the longitudinal excitation of the propeller is calculated by measuring the waveguide coefficients of any shaft sections via the proposed hybrid method. Finally, the scheme is verified by a concrete example. The simulation results prove its feasibility and effectiveness for estimating propeller excitation by measuring the shafting vibration response, which provides a novel scheme for accurately grasping the propeller excitation and effectively controlling the vibration and noise of hull structure.

Highlights

The propeller excitation force is an essential exciting source for submarine underwater navigation
The spectrum of the unsteady force of the propeller is composed of the spectrum of the low-frequency discrete force with the blade-passing-frequency (BPF) and double-BPF generated by the uneven force on the blades, and the spectrum of the low-frequency broadband force generated by the interaction between the stern turbulence and the propeller, which can be obtained mainly through experimental tests, semi-empirical formulas [3], and numerical calculations [4]
The unsteady force generated by the propeller in the non-uniform wake field at the stern of the hull, the radial simple harmonic component force generated by the main engine device and the longitudinal component force generated by the torsional vibration of the propulsion shafting all make the propulsion shafting produce periodic longitudinal tension and compression deformation, which is the common longitudinal vibration of the propulsion shafting of large ships and submarines

Summary

Introduction

The propeller excitation force is an essential exciting source for submarine underwater navigation. Since the waveguide model and the vibration response observation data of the shaft section are used to estimate the waveguide coefficients, the boundary conditions of the shaft section are not involved, so the estimation of the longitudinal oil film stiffness of the thrust bearing and the admittance of the joint structure between the thrust bearing housing and the hull are avoided. After the waveguide model of the entire shafting is established, the method for estimating the waveguide coefficient of a shaft section using the vibration response can be used to calculate the longitudinal excitation from the shafting to the hull through the thrust bearing, which is the same as the principle of estimating the longitudinal excitation of the propeller. The admittance function test problem of thrust bearing housing can be discussed

Theoretical model construction

Examples

The relationship between wave solution and modal superposition solution

Conclusions