To determine the horizontal directivity of a train pass-by

Based on the assumption that railway noise can be modeled as a group/line of incoherent point sources a calculation scheme has been proposed for determining the horizontal directivity of train pass-by noise: with a certain directivity function(s) assigned to the individual point sources, the model will determine the effective horizontal directivity of the train pass-by noise. The sample calculations show that: (1) if all point sources are assigned monopole directivity the effective horizontal directivity of the train pass-by noise shall have the monopole pattern, for any measurement distance; (2) if all point sources are assigned the same directivity other than a monopole, the effective horizontal directivity of the train pass-by noise shall have the same directivity pattern when a measurement distance is not less than 3 times the train length, otherwise the effective directivity pattern of the train pass-by noise will vary with the distance; (3) the horizontal-directivity function used in some existing national models can be derived when some reasonable assumptions are applied.