Vibroacoustic Transfer Characteristics of Underwater Cylindrical Shells Containing Complex Internal Elastic Coupled Systems

Abstract

Cylindrical shells containing complex elastic coupling systems are the main structural form of underwater vehicles. Therefore, in this paper, the vibroacoustic radiation problem of underwater cylindrical shells containing complex internal elastic coupling systems is studied. Firstly, the dynamics model of the complex elastic coupled system is established through the method of integrated conductivity. The sound pressure distribution law and the general magnitude relationship between the performance index of hydroacoustic radiation and vibration isolation are investigated through numerical simulation. A strategy of global sensitivity analysis and related parameter optimization is carried out, by applying the Sobol’ method to the dynamics model. It could be concluded that the main flap of sound pressure at low and medium frequencies appears in the direction of the excitation force or the perpendicular to the excitation force, the magnitudes correspondence between the vibration level drop—power flow—hydroacoustic radiation at low frequencies can be expressed as a relatively simple function, and the vibroacoustic transmission of the system at lower order resonance frequencies is dominated by the parameter configuration of the vibration isolation device, while at higher frequencies is more influenced by the modalities of the base structure. The transfer power flow and the level drop are used as objective functions to optimise the acoustic radiation index of the coupled system, with the best results obtained when the transfer power flow and the level drop are used together as objective functions.

Effect of Support Stiffness Nonlinearity on the Low-Frequency Vibro-Acoustic Characteristics for a Mechanical Equipment—Floating Raft—Underwater Cylindrical Shell Coupled System

“…To obtain sufficient amplitude for the system to fully demonstrate its nonlinear vibration characteristics, the amplitude of the excitation force applied to the units A 1 and A 2 is set to 500 N. The values of the variable stiffness isolators and system structural parameters involved in the numerical simulations are set as shown in Tables 1 and 2, and other control parameters are shown in Appendix B. Stiffness control parameters outside the linear working interval Taking the displacement derivative functions H 11 , H 12 , and H 14 as examples, their fitting spectra obtained from the modal parameter identification method are compared with the numerical spectra obtained by the calculation method in the literature [33], as shown in Figure 3. It can be seen that the fitting results can match well with the original data, and the difference between the two is mainly related to the modal truncation (residual admittance) and the computational error of the original data.…”

“…However, the cylindrical shell coupled with the external underwater acoustic field becomes a dissipative system, so it is difficult to obtain an analytical expression of the modal parameters through theoretical deduction. In view of the above problem, a discrete numerical solution of displacement admittance functions is first calculated for the cylindrical shell-underwater acoustic field coupled subsystem by referring to Equations ( 11)- (18) in the literature [33]. Then, analytical expressions are fitted according to the admittance functions data, and then system modal parameters are identified from the expressions.…”

“…Taking the displacement derivative functions H 11 , H 12 , and H 1 4 as examples, their fitting spectra obtained from the modal parameter identification method are compared with the numerical spectra obtained by the calculation method in the literature [33], as shown in Figure 3. It can be seen that the fitting results can match well with the original data, and the difference between the two is mainly related to the modal truncation (residual admittance) and the computational error of the original data.…”

“…For the calculation of the admittance functions of the cylindrical shell-underwater acoustic field coupled subsystem, see also Equations ( 11)-( 18) in [33]. It can be seen from these equations that, due to the complexity of the calculation formulas, only discrete numerical solutions of the admittance functions can be given.…”