Analytical study on vibration behaviors of pump-jet–shaft–submarine hull system in wavenumber–frequency​ domain

Abstract

The pump-jet excitation is transmitted to submarine hull along rotor–shaft system and duct–stator system, which is one of the main causes of structural vibration of the hull. This paper proposes an analytical method for the coupled shaft–submarine hull system. The submarine hull is modeled as a jointed conical-orthogonally stiffened cylindrical–spherical shell coupled with several circular plates. The shaft is modeled with a three-dimensional beam and connected to the hull by bearings. A unified variational modeling procedure is developed to assemble each substructure. The hydrodynamic pressure acting on the rotor and the duct–stator system are respectively considered as single point force and multiple uniformly or non-uniformly spaced point forces acting on the shaft and the conical shell. The vibration displacements are analytically expanded with Fourier series in the circumferential direction. Thus, the wavenumber components that contribute to vibration responses are naturally separated and quantified. The convergence and accuracy of the proposed method are verified by the finite element method. The analytical study on vibration characteristics of the pump-jet–shaft–submarine hull system along distinct vibration transferring paths in circumferential wavenumber–frequency domain is conducted. The results indicate that the rotor excitation can excite more resonance peaks compared to the duct–stator excitation when neglecting the elasticity of the pump-jet propulsor. It mainly owns to the strong circumferential modal coupling and abundant modal contributions when the system is under the rotor excitation. Besides, the non-uniform distribution of external load contributes to the augmentation of resonance peaks compared to the responses under uniform load, which attributes to the participation of extra wavenumber components.