Modeling And Analysis Of Helicopter Noise Under Water

Owing to great improvement in anti-submarine technology, especially widely application of airborne anti-submarine equipment, the survivability of underwater submarine faced great threat. Therefore, development of a technology for the submarine to detect the anti-submarine helicopter by monitoring the helicopter radiated noise in underwater is urgently required. This thesis presents the study in the following aspects:1. Investigation of the phenomena of sound transmittion into the water from the source in the air. Firstly, the ray method and normal mode method are used to calculate the acoustic field in underwater with the source in the air. The shortcomings of the two methods are analyzed. And then a Fast Field Program (FFP) is developed and used to calculate and analyze the underwater acoustic field with the source in the air. Some important results have been obtained.2. Analysis of the helicopter noise signature. A sorting method of the helicopter noise sources is given. The temporal waveform and spectrum of the noise signature is analyzed. At last, the sound pressure spectrum density level is estimated with the experimental data taken from a specific navy helicopter.3. Helicopter detection method from underwater received noise signature. Since the spectrum of the helicopter noise contains wide band continuous component and narrow band line component, we can use the wide band signal detection method or narrow band signal detection method .Both detection methods are discussed.