Effect of Wall-axial Wave Component on the Active Control of Water-borne Noise in Steel Pipes

Active control of low frequency pump noise in water-filled pipes is being developed at AMRL for acoustic signature control on maritime platforms. The present approach is based on separate fluid and wall-axial wave control with collocated control sources. One of the main problems encountered in the design of suitable control sources is their operating effectiveness over a large range of internal hydrostatic pressures. A prototype of a fluid-wave control source has been built which is able to provide some control at low frequencies in a steel pipe system. However, at higher frequencies, the control is considerably compromised through a mechanism believed to be linked to flanking via wall-axial wave components. This paper reports the results of experiments designed to study the effect of flanking with the ultimate aim of establishing requirements for the design of a complementary source for the control of wall-axial waves.