Study On Far Field Criteria Of Underwater Cylindrical Shell Structure Acoustic Radiation Test

Acoustic waves have a pivotal position in the underwater communication and detection because it is the main channel for underwater information dissemination.Especially for the detection of submerged structures which relies on acoustic waves.The assessment of ship radiated noise level is becoming more and more important with continuous improvement of surface and underwater ship vibration and noise reduction.The measurement of large submerged and surface structures is must be satisfying the far filed condition.An empirical formula for far field decision is give in this article to assess submerged cylindrical shells acoustic radiation power and sound pressure.This paper uses finite element modeling,analyzing and other pre-and post-processing software to establish free-field and half-space acoustic finite models,then do the research on the far-field decision influence with changing submerged cylindrical shell height and depth in the water,this is important for measuring the sound field of underwater structures.The empirical formula of the submerged cylindrical shell far field decision is summarized after a series of cylindrical shell numerical calculation and experiment verification.This article studies the error caused by the cylindrical shell acoustic radiation power measurement by vertical array in the free-field and half-space environment from the far-field decision obtained from the vibration velocity and pressure phase difference.Simulation results show that there are still errors even if the acoustic radiation power measurement of cylindrical shell by vertical array,mainly because of that the measurement method doesn't avoid the error caused by energy leakage from taking structure closed envelope surface.The spatial averages of the measurements will greatly reduce this error,but it can not be completely eliminated.The reference value of the error correction is given for the results of vertical array at different distances from the cylindrical shell for this error.