Transmission of Low-Frequency Acoustic Waves in Seawater Piping Systems with Periodical and Adjustable Helmholtz Resonator

Boyun Liu,Liang Yang

doi:10.3390/jmse5040056

Abstract

The characteristics of acoustic wave transmitting in a metamaterial-type seawater piping system are studied. The metamaterial pipe, which consists of a uniform pipe with air-water chamber Helmholtz resonators (HRs) mounted periodically along its axial direction, could generate a wide band gap in the low-frequency range, rendering the propagation of low-frequency acoustic waves in the piping system dampened spatially. Increasing the air volume in the Helmholtz chamber would result in a sharply decrease in the central frequency of the resonant gap and an extension in the bandwidth in the beginning, yet very slowly as the air volume is further augmented. Acoustic waves will experience a small amount of energy loss if the acoustic–structure interaction effect is considered. Also, the structure-borne sound will be induced because of the interaction effects. High pressure loadings on the system may bring in a shrink in the band gap; nevertheless, the features of broad band gaps of the system is still be maintained.

Highlights

The topic of low-frequency acoustic waves transmitting in seawater piping systems in ocean surface ships and under-water vehicles, of which their outlets are underneath the water surface, etc., is of special interest [1,2]
It can be seen from the open public literature that there has been a considerable number of noise reduction methods available for the piping systems, e.g., (i) arrangement of elastic joints, corrugated pipe/bellows, or other components to the piping systems [5,6,7,8]; (ii) installation of a muffler elbow and micro-perforated plates [9,10]; (iii) avoidance of short-radius elbow, sharp bends, and branch pipes in pipeline [11]; (iv) laying damping materials [9]; (v) active control technologies [12,13,14,15]; and installation of pipe mufflers [16,17,18,19], etc
When the Helmholtz resonators (HRs) cavity is composed of a liquid chamber and a gas chamber, e.g., a water and air hybrid chamber, the acoustic impedance LH and capacitance CH should be changed to LH = ρwln/Sn and CH = (Vcw/κw2 + Vca/κa2), respectively

Summary

Introduction

The topic of low-frequency acoustic waves transmitting in seawater piping systems in ocean surface ships and under-water vehicles, of which their outlets are underneath the water surface, etc., is of special interest [1,2]. More recent studies have been on the nonlinear acoustic behavior of dispersion relation for the air-filled waveguide tube with an array of axially distributed resonators installed [28,29,30] These works showed that the usually observed band gaps for the wave transmission coefficient through the system are found to be amplitude-dependent. When the HR cavity is composed of a liquid chamber and a gas chamber, e.g., a water and air hybrid chamber, the acoustic impedance LH and capacitance CH should be changed to LH = ρwln/Sn and CH = (Vcw/κw2 + Vca/κa2), respectively Mounting this HR periodically into the seawater piping system with a fixed lattice space la that is much smaller than the acoustic wavelength λ (la ~λ/5), the periodic system will behave as a homogenized effective medium where the acoustic band gaps may be expected [32].

Sp O x

Imaginary part of μ