Identification of cylindrical shells with sets of reinforcing ribs by their acoustic Bragg diffraction (grating) patterns

摘要

Abstract: We present a basic study of the acoustic Bragg diffraction patterns produced by gratings with various types of slits, which are insonified by (monochromatic) acoustic waves of various frequencies. Given the spacing in-between the slits, the (Bragg) angular diffraction pattern generated by the grating can be predicted by the method of physical optics (acoustics), and can be numerically evaluated for gratings with either uniformly or irregularly spaced slits. It has been already established that the diffraction patterns of planar gratings can be used to model the far-field scattering patterns produced by thin, cylindrical, elastic shells in water that have many reinforcing ribs. Varying the size and slit spacing (i.e., the ribs), the diffraction pattern becomes distorted, and for very irregularly spaced cases, the distortion is substantially asymmetric and noticeable. A number of graphs are shown to illustrate these points. !6