By E.M. Salomons
Noise from automobiles, trains, and aeroplanes will be heard at huge distances from the resource. actual predictions of the loudness of the noise require exact computations of sound propagation within the surroundings. This e-book describes types that may be used for those computations. The types consider advanced results of the ambience and the floor floor on sound waves, together with the consequences of wind and temperature distributions, atmospheric turbulence, abnormal terrain, and noise boundaries.
the most textual content of the ebook specializes in actual results in atmospheric acoustics. the consequences are illustrated by way of many numerical examples. the most textual content calls for a really restricted mathematical historical past from the reader; exact mathematical descriptions of the types, built from the fundamental rules of acoustics, are offered in appendices. versions for relocating media are in comparison with versions which are according to the powerful sound velocity process. either two-dimensional types and three-d versions are awarded. As meteorological results play a massive position in atmospheric acoustics, chosen themes from boundary layer meteorology and the speculation of turbulence also are presented.
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Noise from autos, trains, and aeroplanes might be heard at huge distances from the resource. exact predictions of the loudness of the noise require actual computations of sound propagation within the surroundings. This e-book describes versions that may be used for those computations. The versions keep in mind advanced results of the ambience and the floor floor on sound waves, together with the consequences of wind and temperature distributions, atmospheric turbulence, abnormal terrain, and noise limitations.
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Extra info for Computational Atmospheric Acoustics
As a consequence of the Fourier transformation to the horizontal wave number domain, the FFP method is restricted to systems with a layered atmosphere and a homogeneous ground surface. Systems with a range-dependent sound speed profile or a range-dependent ground impedance cannot be modeled with the FFP method. In contrast to the FFP method, the Parabolic Equation (PE) method is not restricted to systems with a layered atmosphere and a homogeneous ground surface. The PE method is based on a parabolic equation, which is an approximate form of the wave equation.
Thus, destructive interference occurs if the path length difference R2 - Rl between the direct sound ray and the reflected sound ray is equal to (n + ~)A, so that direct waves and reflected waves have a phase difference of 1800 • With increasing height in Fig. 5, one successively passes the regions corresponding to n = 0,1,2, .... 6 demonstrates the effect of 1/3-octave band averaging, both for a rigid ground surface and for an absorbing ground surface. L(f) , while the minima in the 1/3-octave band spectrum are considerably less deep (cf.
Consequently, the interference minima for an absorbing ground surface occur at lower frequencies than for a rigid ground surface. The interference minima in Fig. 6 are deeper for the rigid ground surface than for the absorbing ground surface. This can be explained as follows. For the rigid ground surface, direct waves and reflected waves have approximately equal amplitudes, so the waves cancel each other almost completely in regions where the phases are opposite. For the absorbing ground surface, the amplitude of reflected waves is smaller than the amplitude of direct waves, due to the absorption of acoustic energy by the ground, so only a partial cancellation occurs.