Energy flow investigations on nonlinear 1 sea–marine structure–water lubricated bearing–shaft dynamic interaction systems

Abstract

Nonlinear interaction in a coupled sea–marine structure–water lubricated bearing–shaft system is investigated by the energy-flow method to reveal its dynamic behaviour affected by nonlinear friction damping of water-lubricated bearings. A substructure formulation is established for a shaft–hull with two bearings. For the linearised system, a critical damping condition is identified as a bifurcation point: negative bearing damping cancels positive system damping, yielding a zero-damping state with four pairs of energy flow characteristic factors and zero energy flow. When the bearing damping magnitude is below the critical level, the equilibrium is stable and free responses decay; exceeding it yields divergent motions. Under forced excitations, the responses for zero bearing damping and the critical condition are identical at low frequency, whereas at high frequency the responses are respectively damped and periodic/chaotic. For the nonlinear system, free vibration remains stable under moderately negative damping, but allowable initial disturbances differ among degrees of freedom. For forced vibrations, the critical damping shifts with excitation frequency. The response comprises multiple natural components modulated by wave frequency, producing chaotic-like phase portraits. Time-averaged energies converge, and energy flows tend to zero as averaging time increases. The proposed model supports dynamic assessment and design of coupled marine shafting systems.

More information

Identifiers

ORCID for Jing Tang Xing: orcid.org/0000-0003-3992-5265

Catalogue record

Export record

Altmetrics