THE EXPERIMENTAL EXAMINATION, BY MEANS OF PULSES, OF CIRCUMFERENTIAL WAVES ON ALUMINUM CYLINDERS IN WATER.
NAVAL RESEARCH LAB WASHINGTON D C
Pagination or Media Count:
Three types of waves which contribute to the total acoustic diffracted field of an aluminum cylinder in water are isolated by generating each wave to the exclusion of the other two. Observations of circumferential propagation speed and attenuation are made. The Franz type or creeping wave is generated separately on the outside of aluminum cylinders with ka ranging from 54 to 1008. The circumferential-wave speed is found to be 1 less than that of the free water-borne wave in agreement with the theory for a rigid cylinder. The attenuation of these waves on aluminum cylinders is significantly less than the theory for the rigid cylinder predicts. Another circumferential wave with approximately a 30 deg incidence and emergence angle is found to propagate on the inside of the curved boundary. This wave has an attenuation ranging between 0.10 and 0.18 Nprad and has a speed of 2.5 times that of the free water-borne wave. This is classified as a Rayleigh type wave. A third wave is observed which is similar to the wave generated at 30 deg incidence but has a 15 deg incidence and emergence angle. The attenuation is between 0.08 and 0.14 Nprad and has a speed of 6.5 times that of the free water-borne wave. Experimental measurements of differential-scattering cross section are compared to those calculated by means of the creeping wave formulation. Author