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The vibro-acoustic responses of coupled pump-jet-submarine systems excited by fluid excitations on the wall of the duct are numerically investigated. The unsteady excitations are calculated by computational fluid dynamics and the vibration responses for different excitations on the inner and outer walls are contrastively analyzed through establishing a finite element model of the coupled system. Meanwhile, the effect of fluid–structure interaction and the excitation loading methods for the inner flow of duct are considered. The sound radiation characteristics for different excitation sources are predicted through using a boundary element model. The results show that the excitation force spectra of the inner wall have a remarkable discrete peak at blade passing frequency and its multiple, while the excitation force spectra of the outer wall show a broadband characteristic and discrete components appear at blade passing frequency. The modes of hull both dominate the vibro-acoustic responses of the coupled system for different excitation sources of the duct. The transmitted energy for inner excitation forces is significantly greater than that of outer excitation forces, but the sound radiation efficiency is relatively close. The excitations of the duct can transfer to the thrust bearing through stators as well as the hull and cause a coupled vibration between the duct–stator–hull and the shafting system. Besides, the method for applying distributed forces on the inner wall is more reliable. [ABSTRACT FROM AUTHOR]

For a pre-swirl pump-jet propulsor (PJP), the stator inevitably induces the problem of rotor–stator interaction (RSI). In this paper, the mechanism of RSI in a PJP is analyzed through dynamic mode decomposition (DMD). The coherent flow structures and corresponding frequencies have been decomposed and analyzed. The results show that the dominant frequencies of pressure fluctuation in the stationary domain are BPF (rotor blade passing frequency) and its multiples. In contrast, the dominant frequencies in the rotational domain are SPF (stator passing frequency) and its multiples. The frequencies of k*SF (SF, shafting frequency; k = 4, 5, and 8) have also been found. The mode structure corresponding to the SPF is stable and has the highest mode energy. The reconstruction residual formula is introduced, and the axial velocity flow field is reconstructed well by the DMD modes compared with the raw flow field. This research can provide a reference for studying and suppressing RSI in a PJP. [ABSTRACT FROM AUTHOR]

[Objectives] To meet the demand of on-board machinery for components with high transmission loss and vibration and shock isolation,[Methods] a hybrid vibration isolation system using Dynamic Vibration Absorber(DVA)with Negative Stiffness(NS)is proposed. Then the non-dimensional dynamic model of the proposed isolation system with rigid base is established,and the fixed-point method is employed to obtain the optimal parameters of stiffness ratio and damping ratio under the influence of exciting force. Runge-Kutta method is adopted to study the shock response of the proposed isolation system with optimal parameters by using different shock pulse widths under base excitation,and then this shock response is compared with that of the traditional DVA.[Results] It shows that the proposed isolation system has a transmission characteristic without a resonance peak by using certain parameters. The shock acceleration response and the relative displacement of the proposed isolation system are smaller than those of the traditional DVA by using different pulse widths.[Conclusions] The proposed isolation system provides a new approach for the design of the vibration absorber with high load carrying capacity and high transmission loss.