Multilayer substructure integration calculation method for acoustic radiation of an underwater structure strictly coupled with a floating raft isolator system

Abstract

This paper presents an efficient method to predict the acoustic radiation of arbitrary underwater structures with a multilayer floating raft isolator system. It breaks through in realizing the strict coupling between the floating raft isolator system, the main hull, and the water. The main structure is separate from the floating raft isolator system and the lower vibration isolator. The fluid-structure coupling effect is considered in the sono-elasticity analysis between the main structure and the water. Modal superposition and simple source boundary integral methods are employed for analyzing fluid-solid coupling vibration and underwater acoustic radiation of the main structure. The floating raft isolator system is modeled as a finite element model and solved by the modal superposition method. By introducing the modal strain energy method, the calculation of the variable damping ratio of different structures can be realized. The multi-degree of freedom mass-stiffness spring system models the upper vibration isolator, whereas the four-terminal parameter method establishes a vibration transmission model of the lower vibration isolator. The coupling between the main structure, floating raft isolator system, and lower vibration isolator is achieved by introducing the virtual mode at the connection boundary. Then, the coupled dynamic equation for the entire underwater structure is obtained. The influence of different excitation directions and isolator parameters on vibration isolation effect is analyzed, which has certain guiding significance for the design of floating raft isolation system. When any component within the floating raft isolator system is modified, only the mass and stiffness matrices of the component need to be re-imported to re-calculate the overall vibration and acoustic response without remodeling the entire structure. This paper discusses the basic principles, computation formulas, and the findings of several numerical examples of the proposed method.