反转点附近声场的渐近理论

水下声道中一般有三类反转点,在它们附近形成不同类型的反转点会聚区。收、发深度不等的第Ⅲ类反转点会聚区的强度比前两类稍低,但其空间分布范围广泛,在低频远程声场中占有重要地位。
本文着重讨论第Ⅲ类反转点附近的声场,给出了计算反转点附近以及焦散线声强的简明表式,提出了形成焦散线会聚的物理条件。理论分析表明,低频情况下第Ⅲ类反转点会聚区的声强与距离的平方成反比、与频率的1/3次方成正比。

AN ASYMPTOTIC THEORY OF THE SOUND FIELDS NEAR THE TURNING POINTS

In underwater sound channel there are three types of turning points,near which different types of turning-point convergence-zones are formed.Though in the turning-point convergence-zones of the third type with unequal source and receiver depths there are slightly weaker intensities than in those of the first and second types,convergence-zones of the third type play an important part in the low-frequency,long-range sound fields owing to their wider distribution in space.
In this paper,the sound fields near the turning points of the third type are discussed emphatically,concise expressions of the intensities in the vicinity of the turning points and at the caustics are given,and the physical condition on which the caustic convergence can be formed is put forward.The theoretical analysis shows that in the case of low frequency the intensity ont the turning-point convergence-zone of the third type is proportional to the cube root of the frequency and inversely proportional to the square of the range.