Investigations on the vibrational and acoustic characteristics of a submarine

An experimental study aiming at investigating the vibrational and acoustic characteristics of a submarine-like system is implemented in this article. For comparison purpose, a finite element model is used to calculate the dynamic behaviors and sound radiation of the system. With consideration of the interaction between the shaft and hull structure, the dynamic response and the radiated sound pressure of the system are presented. Associated with the finite element model, the modes that correspond to the main peaks in the radiated sound pressure are identified. The results indicate that the forces transmitted to the hull could be amplified at the natural frequencies of the shaft, and a relative high radiated sound pressure level can be observed if the hull is also resonating simultaneously. Due to the non-uniformity of the structure and external excitation, the bending modes (n？=？1) and the longitudinal modes (n？=？0) are coupled with each other and result in a more complex dynamic response of the system. Moreover, considering the foundation is critical to supporting the axial force transmitted from the propeller, and a lower foundation model is constructed to investigate its influence on the acoustic response of the system. The comparison results show that lower foundation would lead to a rise of the natural frequency of the mode that relates to the axial impedance of the foundation. And, a slight decrease in the radiated sound pressure can be achieved in the frequency range below these natural frequencies