A Transmission Line Matrix model for sound propagation in arrays of cylinders normal to an impedance plane

The present paper focuses on two of the acoustic phenomena involved in sound propagation through forested areas, namely multiple scattering caused by tree trunks at mid-frequencies and ground effect at low frequencies. The use of time domain methods can be of interest for the simulation of transient phenomena such as scattering. The study aims at evaluating the ability of an alternative time-domain approach, the Transmission Line Matrix (TLM) method, to model sound scattering by cylindrical scatterers. The TLM method is applied to the study of both single and multiple scattering coupled to ground effects, in two- and three-dimensional domains. Keeping in mind the initial purpose of this study, the size and the location of the scatterers (tree trunks), as well as the noise frequency range, are related to outdoor noise propagation in realistic forests. In order to validate the TLM method, numerical simulations are compared to analytical solutions as well as measurements on 1:10 scale-models. The most complete cases of cylinders arrays placed normal to impedance floors are in agreement with the measurement results.