Vibration response and acoustic radiation of a thin floating plate

Abstract

Remote sensing may be used to detect and locate acoustic sources on a thin floating plate as well as predict the geometry and material of the structure based on recordings of vibratory and acoustic waves. Remote detection and localization of impacts on a thin floating structure is desirable. For a transient excited thin floating structure, the coupling of the vibration waves in the structure and the acoustic waves radiating from it into the air above and water below can introduce complexity not encountered with traditional source identification techniques. To study this problem, repeatable axisymmetric transient impact experiments are conducted in a 1.2-m diameter cylindrical water tank by dropping a stainless-steel ball bearing onto a 6.4-mm-thick aluminum plate suspended at the air-water interface. Accelerometers and laser Doppler vibrometry are used to record the vibration of the plate. Acoustic radiation is recorded in the air above the plate and in the water below it using linear arrays of 6 microphones and hydrophones, respectively. Wave speeds in the plate ranging between 430 m/s and 1550 m/s are considered. Results are compared to a combined acoustic-structure finite element model. [Sponsored by NAVSEA through the NEEC.]