Chaotic Technique Research For Noise-Reduction And Vibration-Isolation Systems On Warships

In order to improve the combat performance and survivability of warships, the acoustic stealth must be advanced. Only the amplitude of line spectra not the spectrum configuration can be altered with the traditional vibration-isolation method. The problem of acoustic stealth, hence, cannot be resolved fundamentally. Combining with the "Tenth Five" national defense advanced research item "Research on the Active Vibration Isolation Technique in Submarine" and the naval weaponry and equipment research item "Study on the Application of Chaos Technique to Control the Line-spectra in the Structure-borne Noise", this paper studied the vibration-isolation system actually used in naval vessels, applied the chaotic dynamics to the nonlinear vibration analysis, and finally settled on a solution to the problem how the line spectra can be changed into the continuous spectrum. The effectiveness of the chaotic vibration-isolation method was verified through simulations and experiments. A new method for vibration-isolation was hence established and the acoustic stealth of marine vessels would be improved. The static and dynamic performances of isolators with different stiffness characteristics as well as the application of these isolators to the vibration-isolation system were studied. The chaotic vibration isolation was realized in vibration-isolation system and the line spectra were controlled or removed.The prime innovations of this paper are as follows:(1) A method using the chaotic motion state in the nonlinear vibration-isolation system to weaken or eliminate the line spectra in marine vessels was advanced.(2) The linearization of nonlinear stiffness was theoretically investigated, and the effect of static load to the performance of vibration-isolation system was analyzed.(3) The nonlinear dynamics of a two-degree-of-freedom vibration-isolation system with nonlinear damping and nonlinear spring was studied. Numerical simulations showed that the system exhibits periodic motions, quasiperiodic motions, and chaotic motions. It was also shown that the purposes of reducing the response amplitude of the system can be realized by adjusting properly the system parameters according to the exciting frequency. (4) A new method was proposed to eliminate the noise in chaotic signals on the basis of wavelet analysis.(5) A new performance index for evaluating the vibration-isolation effectiveness of the chaotic vibration-isolation system was presented, namely, the vibration-level difference was used to evaluate the whole vibration isolation performance and the energy attenuation at frequencies of the line spectra was used to evaluate the local isolation performance at the special dominant frequency.(6) The presented method was experimentally verified. Experiment results show that the reduction of the line spectra when the system is chaotic is much greater than that when the system is non-chaotic, and that the overall effectiveness of vibration-isolation in chaotic state is better than that in non-chaotic state.