海面ダクト仮想モード伝搬のトンネル効果

抄録

This paper presents a theoretical study of tunnel effect of virtual modes propagating in a surface duct. The ocean model used to describe a stratified duct assumes the smooth surface and the bilinear sound velocity profile. Using Labianca's virtual mode treatment (J. Acoust. Soc. Am. , 53, 1137 (1973)), an exact representation of virtual field excited by a point source are derived. Introducing the tunnel effect of sound field from the surface duct to the lower duct, relation between the tunnel effect and the leakage coefficient is derived. The leakage attenuation is negligible for usual ocean parameters in comparison with the surface reflection loss, but the tunnel effect of virtual modes in the vicinity of maximum mode number is important and the effect of tunnel field below the duct can not be neglected. Some design formulas are derived and calculated for actual ocean parameters.