1987 年 56 巻 1 号 p. 106-113
Wave propagation phenomena in a semicylindrical concave boundary excited by a line source located on the boundary surface are investigated in this paper. The field observed at an arbitrary position in the boundary can be represented in terms of contributions from the direct ray, “legitimate rays” with a maximum finite number of reflections, and an integral type interference wave accounting for “illegitimate rays” with too many reflections. The validity of the field representation is confirmed numerically by comparison with the reference solution obtained rigorously from the whispering gallery mode series and continuous spectrum representation. The integral type interference wave plays an important role for the observation point located in the interference region. When the observation point is outside the interference region, the field can asymptotically be expressed by geometrical ray(s) only. The width of the interference region and the number of geometrical rays for an arbitrary observation point are also discussed.