Yoon, Jong Rak

The theoretical solution for acoustic propagation in a wedge-shaped ocean with ideal pressure-release boundaries predicts a well-defined beam which diverges as the energy propagates out towards deep water. Outside of the beam, shadow zones are formed, and the beam's spatial extent is determined by the lowest mode of propagation. The purpose of the experimental results presented here is to check the theoretical analyses, as part of an ongoing investigation into three dimensional propagation in the ocean environment, and to investigate further the propagation characteristics of this type. It has been found that for downslope propagation, the spatial characteristics of the field in a direction parallel to the shore line are in good agreement with the theoretical solution and the azimuthal extent of the beam depends on the wedge angle and frequency.

A measurement method for the equivalent noise source height of an arbitrary distribution of moving noise sources is developed to investigate the highway vehicle equivalent source heights which are currently used by the FHWA for noise barrier design. The study is intended to provide information required to improve this noise barrier design code. The equivalent point source position is defined for an arbitrary distribution of acoustic sources above a reflecting plane and a method for its measurement using a microphone array is developed. The normalized errors of the measured equivalent source heights are defined including the effects of background noise, the geometric near field, source size, and source directionality. Normalized errors of the measured source heights obtained by a numerical simulation for each parameter lead to optimization of the microphone spacing and to the design of an array of microphones which give the equivalent source height as a function of frequency. The method is then applied to the measurement of the equivalent source height of stationary loudspeakers and is shown to give results which are consistent with theoretical predictions. The effect of the Doppler frequency shift of moving vehicles is investigated using a loudspeaker mounted on the roof of a moving car. If the speed of a moving noise source is less than 97 kph, the error due to the Doppler frequency shift was found to be negligible. Results of measurement on highway vehicles show that the noise source heights for heavy trucks and for automobiles are different from those used currently by the FHWA.