Line spectra in the radiated noise of marine vessels are the most visible signs, which can be detected, tracked and identified by enemy's passive sonar, and hence it is of great significance to reduce the line spectra for improving the acoustic stealth of marine vessels. Insertion of resilient isolators between the machinery and the base is one of the most common methods for controlling unwanted vibration of the hull of submarine. Isolators in service are usually assumed to be linear and almost all the vibration isolation-n systems (VIS) are designed with linear theory, which satisfies engineering requirements in most situations. However, the nonlinear dynamical characteristics of VIS have attracted increasing attention in recent years due to the facts that onboard machinery trends towards more powerful and lighter, and that the demands in engineering for reducing vibration become more rigorous. Furthermore, some distinguishing features of nonlinear systems can be applied to achieve some special functions, among which the most important one is using chaos to reduce line spectra in the radiated noise of submarines based on the fact that response spectrum of a nonlinear system under harmonic excitation is a continuous one when chaos occurs. In this paper, a chaos synthesis method based on tracking control is prososed for a vibration isolation system (VIS) of on board machinery to make the chaotic motion in nonlinear VIS persistent. In this way, the line spectra in the radiated noise can be reduced effectively because the response spectrum of a chaotic system under harmonic excitations is a continuous and reduced one. Numerical simulations were carried out and the results showed that utilizing this method the nonlinear VIS not only possesses an excellent isolation performance of vibration and line spectra, but also reduces the amplitude of the isolated equipment notably.
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