Investigation into the validity of two-dimensional models for sound radiation from waves in rails

The sound radiation from a vibrating rail can be predicted using a two-dimensional model under certain conditions. This paper explores these conditions and shows that, if the decay rate of vibration along the rail becomes large or the wavelength in the rail becomes small, it becomes necessary to allow for three-dimensional radiation characteristics. In practice, however, noise from a rail can be predicted using a two-dimensional model for frequencies above about 250 Hz, and even where three-dimensional effects become important, these can be allowed for by simple correction terms. When the wavelength in the rail approaches that of acoustic waves in air, the angle between the direction of sound radiation from the rail and the normal to the rail increases, in some cases to more than 45 degrees. This must be accounted for if the performance of noise barriers is to be calculated using a two-dimensional approach.