对记录脉冲声场的光学方法及对沙中埋藏的类圆柱体的散射声场的研究

Study on the optical system for the record of the pulsed acoustic field andthe scattering of the cylinderical-like objects buried in underwater sand

本文对用于记录流体中脉冲声场的两种方法——Schlieren法和Shadowgraph法的响应进行了研究。研究表明对于Schlieren法,成像屏上的光强的响应对于声压是非线性关系;对于 Shadowgraph法来说,则是线性关系。由于 Shadowgrph法的工作不受频率限制,适用于在低超声频下研究海底模型和埋藏物的声场。本文利用Shaodowgraph法记录了埋在沙中圆柱体、类圆柱体的低超声频脉冲的散射声场,对半埋体记录到5种散射波,对全埋体则记录到3种散射波,对半埋体与全埋体都记录到两种爬波(纵波爬波、横波爬波)。

The response of the two working mode of the optical systems, the schlieren mode and shdowgraph mode, fortaking of optical photograph of the pulsed acoustic field in liquid are studied in this paper. It shows that, the response ofthe optical intensity on the screen to the acoustic pressure is linear for shadowgraph mode and nonlinear for the schlierenmode. Because the function of shadowgraph mode has no limit on working frequency it is suitable for the studies ofthe acoustic field of laboratory model of the seabed or the buried objects at low ultrasonic range. The ultrasonic pulsescattered by the cylindrical-like objects buried in underwater sand was studied experimentally by the shadowgraph modeat low ultrasonic frequency in this paper. There are five kinds of the scattered waves from the half-buried object andthree kinds of the waves from the full-buried objects were recorded. The two kinds of creeping waves (the longitudinalwave and the shear wave of the object) appear in both of the two cases.