In response to the abnormal metallic sound in the stern area of a certain ship during its sea trials,this paper measures the vibration signals of the hull in the area of the noise and analyzes the frequency spectrum struc-ture changes of the vibration velocity at the measurement point when the abnormal sound occurred and disappeared.It determines that the propeller singing creates the sound.The study finds that when marine organisms attached to pro-pellers develop to a certain extent,they change the trailing edge shape of the blades,causing the fluid to form a Kar-man vortex street behind the propeller,which acts on the blades to produce a metallic sound.
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