Abstract:

Applying nonlinear energy sinks (NESs) to suppress acoustic radiation from underwater targets represents a cutting-edge research frontier. Accurately predicting the acoustic radiation of underwater targets coupled with NESs is a key challenge. To address this problem, this study investigates an elastic spherical shell to analytically derive the acoustic radiation solutions for underwater targets equipped with NESs in two installation configurations. The system is decomposed into three subsystems: the NESs, the spring-mass oscillator, and the spherical shell. An explicit and highly accurate vibro-acoustic coupling solution is developed by the finite difference method, the Taylor series expansion, and the Newmark method. This approach enables the real-time computation of the system vibration response and underwater radiated sound power. The accuracy and validity of the proposed computational method and program are verified through two numerical case studies. Finally, regarding the NES installed on the spring-mass oscillator, the suppression effect of the NES on the acoustic radiation of the spherical shell is thoroughly analyzed. The calculations reveal two noteworthy phenomena that are closely related to the nonlinear effects of the NES: (i) the NES can effectively suppress the acoustic radiation at the resonant frequency of the mechanical isolation system, but it also induces a superharmonic component at a frequency which is three times the resonant frequency; (ii) the superharmonic frequency is strongly correlated with the resonant frequency, and the dominant superharmonic component no longer exhibits a strict tripling relationship when the excitation frequency deviates from the resonance.

Key words: underwater acoustic radiation, vibro-acoustic coupling, spherical shell, vibration suppression, nonlinear energy sink (NES), superharmonic