Hongmei Sun

An effective algorithm for simulating acoustical wave propagation

Abstract In this paper, the acoustical wave propagator scheme is implemented in Fortran for predicting sound propagation in a one-dimensional duct. Example calculations are performed for a semi-infinite duct and a duct with a solid blockage. Numerical accuracy of our results is examined and compared with the finite-difference time-domain method. This scheme is found to be highly accurate and computationally effective for describing the time-domain evolution of acoustic waves. Multiple reflections within the solid blockage and phase changes of the transmitting wave from solid back into air are illustrated through the implementation of this scheme.

Near-field error sensing for active directivity control of radiated sound

Near-field error sensing is beneficial to the compactness and stability of an active noise control system. This paper proposes an error sensing strategy based on the spatial Fourier transform to achieve active directivity control of radiated sound. The error microphone array is located on a plane close to the primary source and the cost function is the weighted sum of the error signals from the microphones. The weighting factor is related to the phase shift from the error microphones to the plane perpendicular to the direction where noise reduction is required. The geometric configurations of the error microphone array for effective directivity control are investigated. It is found that the distance between neighboring error microphones must be less than approximately half the wavelength of the frequency of interest and the equivalent size of the microphone array should be larger than twice the size of the primary source. Numerical simulations and experiments demonstrate the feasibility of the proposed strategy.

On the retrofitted design of a truck muffler with cascaded sub-chambers

Mufflers are widely used in engine exhaust systems for providing sound attenuation in a specific frequency range. In this case study, an engineering problem on reducing the noise radiation from a truck is investigated. The original muffler used by the truck consists of four reactive sub-chambers with similar geometries. Both experiments and numerical simulations revealed the narrow band transmission loss (TL) characteristics of the muffler which limit its attenuation performance, resulting in noise leakage at some particular frequencies. With an aim to broadening the attenuation bandwidth, a recently proposed sub-chamber design method is implemented to retrofit the muffler. The inner structure of the muffler is modified under the guidance of numerical simulations, in order to create extra acoustic stop-bands for an overall broadband performance. The retrofitted muffler is experimentally verified with a better TL response in the design frequency of interest. Analyses demonstrate the effectiveness of using the proposed simulation based design method, which also show potentials to a wide range of muffler design applications.

Effect of Water Pressure on the Frequency Response of a Thin Rigidly Clamped Plate

A detailed understanding of the vibrational properties of submerged objects such as submarines is essential in order to minimize sound emission and optimise sonar performance. In this work we present some results on the effect of water loading on a simple rigidly clamped plate. Complications arise when hollow structures are submerged in water producing loading on one side. Not only does the water dampen the resonances of the structure but the increase in depth also produces mechanical strain within the structure that also changes the modal frequencies. In this paper some results are presented on the effect of water loading on a simple rigidly clamped plate. The aim of this work is to accurately measure these effects and identify any interesting features that need to be taken into account when modelling.