Abstract
The vibrational behavior of an underwater structure in the free field is different from that in bounded noisy environments because the fluid–structure interaction is strong in the water and the vibration of the structure caused by disturbing fields (the reflections by boundaries and the fields radiated by sources of disturbances) cannot be ignored. The conventional free field recovery (FFR) technique can only be used to eliminate disturbing fields without considering the difference in the vibrational behavior of the structure in the free field and the complex environment. To recover the free-field acoustic characteristics of a structure from bounded noisy underwater environments, a method combining the boundary element method (BEM) with the vibro-acoustic coupling method is presented. First, the pressures on the measurement surface are obtained. Second, the outgoing sound field and the rigid body scattered sound field are calculated by BEM. Then, the vibro-acoustic coupling method is employed to calculate the elastically radiated scattered sound field. Finally, the sound field radiated by the structure in the free field is recovered by subtracting the rigid body scattered sound field and the elastically radiated scattered sound field from the outgoing sound field. The effectiveness of the proposed method is validated by simulation results.
Highlights
It is important to characterize a target in an intrinsic way for target identification and control [1]
The sound field radiated by a target in a large lake or anechoic tank can be approximated as a free sound field, the measurement is susceptible to bio-acoustic background noise and climate change in the large lake [2], and it is difficult to satisfy the free-field condition in the anechoic tank at low frequencies
To recover the free-field acoustic characteristics radiated by the structure in the bounded noisy underwater environment, the vibration of the structure caused by disturbing fields must be considered, especially when the structure is a kind of thin-shell structure
Summary
It is important to characterize a target in an intrinsic way for target identification and control [1]. The statistically optimized nearfield acoustic holography (SONAH) was developed to predict the pressure and velocity in complex environments [9,10] This technique cannot accurately reconstruct the local sound field. Langrenne et al [16] presented a method based on BEM to recover the free sound field of a structure in a complex environment by considering the scattering effects on the machine. Wu et al [22] presented a BEM-based NAH in conjunction with the FFR technique to reconstruct the free sound field in a non-anechoic environment. A method combining the BEM with the vibro-acoustic coupling method is proposed to recover the free-field acoustic characteristics in a bounded noisy underwater environment by considering the fluid–structure interaction.
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