An experimental study of acoustically induced rocking motion of simple asymmetric geometries

Abstract

A series of experiments were done to test theoretical predictions that an acoustically small, rigid (aluminum) hemisphere and semicircular cylinder excited by a plane acoustic wave in water would each produce a rocking motion perpendicular to the incident wave direction about the axis parallel to the incident wave. A plane standing wave was generated in a short open-ended thick-walled cylindrical waveguide with the waveguide's axis perpendicular to the symmetry axis of the hemisphere. Measurements were taken along the hemisphere from top to bottom to determine if any rocking motion occurred. The expected vibrational motion in the incident direction and symmetry-forbidden perpendicular vibrational motion were also measured. The transverse displacement of the hemisphere at each point was determined by using an ultrasonic vibrometer. The incident wave direction motion was measured using a hydrophone, an accelerometer, and a Laser Doppler Vibrometer (LDV). The motion in the incident wave direction was found t...