Multisource statistically optimized near-field acoustical holography

Abstract

This paper presents a reduced-order approach to near-field acoustical holography (NAH) that allows the user to account for sound fields generated by multiple spatially separated sources. In this method, an equivalent wave model (EWM) of a given field is formulated to include combinations of planar, cylindrical, spherical, or other elementary wave functions in contrast to an EWM restricted to a single separable coordinate system. This can alleviate the need for higher-order functions, reduce the number of measurements, and decrease error. The statistically optimized near-field acoustical holography (SONAH) algorithm is utilized to perform the NAH projection after the formulation of the multisource EWM. The combined process is called multisource statistically optimized near-field acoustical holography (M-SONAH). This method is used to reconstruct simulated sound fields generated by combinations of a vibrating piston in a sphere and linear arrays of monopole sources. It is shown that M-SONAH can reconstruct near-field pressures in multisource environments with lower errors and fewer measurements than a strictly plane or cylindrical-wave formulation using the same simulated measurement.

Dependence of High-performance Military Aircraft Noise on Frequency and Engine Power

“…II to reconstruct the pressure field in the area surrounding the aircraft. Part A discusses the step-by-step procedure which applies the work of Ref [24] to this measurement. Part B is a discussion on the limits on reconstruction accuracy, building on the work of Ref [8].…”

“…The adaptation of NAH used in this study to predict the noise field of a tied-down high-performance military aircraft was developed by Wall et al [24]. It is called multisource statistically-optimized near-field acoustical holography (M-SONAH) because it modifies the traditional SONAH algorithm [25] to use a two-source model: one along the jet centerline and an image source equidistant from but below the ground to account for the ground reflection.…”

“…The EWM methodology used in the M-SONAH algorithm is described in detail in Refs. [7,24]. For this case, the EWM uses one set of cylindrical wave functions centered on the jet centerline and a second set centered on the image source below the ground to model the reflection.…”

Partial-field decomposition analysis of full-scale supersonic jet noise using optimized-location virtual references

“…The next step is to perform an NAH reconstruction of the sound field in the proximity of the source. Multisource statistically optimized near-field acoustical holography (M-SONAH) 29 is used as it incorporates multiple, spatially distinct sources into the wave-function expansion of the field. Since the jet noise was measured over a concrete run-up pad, a rigid reflection created an interference pattern in the hologram.…”

Summary of “Supersonic Jet and Rocket Noise”

“…Numerical validation of using multisource statistically optimized near-field acoustical holography in the vicinity of a high performance military aircraft. 29 30 that has been used to reconstruct the acoustic field from measurements taken in the vicinity of a high-performance military aircraft 31 . The implementation of MSONAH for tactical jet noise relies on creating an equivalent wave model using two cylindrical sources, one along the jet centerline and one below the ground as an image source, to represent the field surrounding an aircraft tethered to a reflecting ground run up pad.…”