Development of energy-based calculation methods of noise radiationfrom semi-underground road using a numerical analysis

摘要

As a calculation method of road traffic noise at the roadside area of a semi-undergroundroad, the "hypothetical point source method" was proposed in the road traffic noise prediction model"ASJ RTN-Model" proposed by the Acoustical Society of Japan. In this method, noise radiation froma straight semi-underground road is simply modeled as sound propagation from a hypothetical pointsource that has a directivity specific to the dimensions of the structure and is assumed to be at thecenter of the mouth. In the ASJ RTN-Model 2003, the directivity characteristics were determined onthe basis of the results of a scale model experiment, and the variation of the applicable dimensions ofthe road structures was limited. In this paper, the directivity characteristics of the hypothetical pointsource are examined by wave-based numerical analysis to extend the variation. In the numericalanalysis, a Fourier-type transformation technique from a two-dimensional field to a three-dimensionalfield is applied to the calculation results obtained by the two-dimensional finite-difference time-domain method. In addition, the practical expression of the sound power of the hypothetical soundsource is investigated.