厚みのある障壁及び角柱による回折音場

抄録

The diffracted sound field arround a many-sided barrier or pillar for the incidence of a spherical wave is presented by an application of the general spirit of Keller's geometrical theory of diffraction,which is given by the sum of the singly and multiply diffracted waves produced by the straight edges,as shown in Eqs.(3)〜(6). For the single-edge diffraction by each wedge, Pierce's approximate expression-Eqs.(7)〜(9) based on Macdonal's rigorous solution are used and Pierce's equation for the double-edge diffraction, which is derived by an appication of Keller's theory and his first approximate expressions-Eqs. (7) and (8) for the single edge diffraction, is applied for the multiple edge diffraction as shown in Eqs. (16) and (17).It is shown in Figs. (7)〜(9) that if the distances from each edge to the neighbouring edges, a source and an observating point are larger than a half wave-length, the experimental results are in excellent agreement with the numerical results by the above method where Pierce's second approximate expression Eq. (9) for wedges is used.Consequently, by applying this method, we can predict and control very accurately the propagation of noise arround a thick barrier or a building or a slit or a group of those obstacles etc..