Effect of parameters on modeling low-frequency propagation of petrochemical plant noise over water

Abstract

Modeling noise is vital to designing petrochemical plants to meet community noise limits. Models are used to specify equipment noise, choose add-on controls, and confirm limits will be met. For propagation over land, there are substantial variations of actual levels from the long-term average computed using ISO 9613-2. Commercial modeling software based on ISO 9613-2 excludes propagation over water, where levels are often higher and more variable than at the same distance over land. Over water, higher levels and variability arise primarily from wind, thermal inversions, and lack of attenuations from ground clutter. Often a petrochemical plant and receivers are separated by a large body of water, which reduces modeling accuracy. To better understand propagation over water, full-wave Green’s Function-Parabolic Equation (gf−pe) software was used to predict levels between 50 m and 10 km for various lapse rates (temperature increase with elevation) as well as inversion, source, and receiver heights. Plots of attenuation with distance and contours in a vertical plane are presented for 63 Hz. Rates of attenuation considerably less than −6 dB per distance doubling for spherical spreading were found; these and implications for design are discussed. The potential application of gf−pe to verify algorithms for outdoor propagation is indicated.