Research On Axial Vibration Reduction Of Submarine Propelling Shafts Based On Phononic Crystal Theory

The periodic composite materials and/or structure, known as phononic crystals (PCs), may exhibit elastic band gaps. The elastic wave in the frequency range of the band gaps will not propagate in the phononic crystal. The locally resonant band gap can restrain the propagation of the low frequency vibration, where the wave length is much longer than the periodic structures. The band gaps of locally resonant phononic crystal provide a new idea for vibration and noise reduction.Propagation of axial vibration in submarine propelling shafts is investigated in this paper. According to the theory of locally resonant phononic crystal, the locally resonators are installed on the shafts to enhance axial vibration attenuation. The main contents and results are as follows:Based on the theory of four-pole parameters method, we build a model of axial vibration of submarine propelling shafts, which includes the shafts, thrust bearing, foundation, and elastic hull. The axial vibration can be accurately simulated by the model, which is verified by finite element method (FEM) analyzing in Msc/Nastran software.Axial force transmissibility and power flow are selected to evaluate the propagation of the axial vibration in the shafts. It is found that the resonance peak is determined by the mass of shafts and the stiffness of thrust bearing. More importantly, many resonances are arisen while taking the elasticity of the hull into account.Four-pole parameters transfer matrix of propelling shafts with locally resonators is proposed. It is found that by attaching locally resonators on shafts we can attenuate the axial force transmission and power flow significantly. However, it also should be noted that new resonance peak are also arisen. In order to enhance the attenuation and avoid inducing large resonance peak, parameters optimization of the locally resonators is necessary. Genetic algorithm is used for optimizing the locally resonators to minimize the power flow of the shaft system.The structure scheme of the locally resonators is provided in this paper. The optimization results are validated with the popular FEM software Msc/Nastran, which are in good agreement with the results of the four-pole parameters method. Both results confirm us that the axial transmissibility of submarine shafts could be substantially attenuated by periodically attaching locally resonators on the shaft.It is also presented that the axial vibration of propelling shafts with locally resonators meets the requirement of criterions.In summary, PC theory is introduced in the axial vibration reduction in the propelling shafts of submarine. The results of this thesis indicate that periodically installing locally resonators on the shaft is a feasible cure of the axial vibration transmission of submarine.