APPLICATION OF PARABOLIC EQUATION METHOD IN UNDER WATER ACOUSTIC PROPAGATION

• Main Author: NG RACHMAT POENGOET , JAMES
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/10715
• Institution: Institut Teknologi Bandung

In this thesis, the Parabolic Equation method was applied in underwater acoustic propagation. The Parabolic Equation method solves the basic acoustic equation, Helmholtz equation, which have been derived from mass conservation equation, momentum conservation, and state equation. Application of this method have been done at twelve data stations in the Indian Ocean. The measured temperature and salinity were approximated by using polynomial curve fitting method. The Mackenzie empirical sound velocity equation is used, because it shows the smallest error compared to the data provided at every station.<p>The application results at twelve data stations show that underwater acoustic propagation using high frequency have many shadow zones compared to underwater acoustic propagation using low frequency. This shadow zone has transmission loss greater than 95 dB. The ray formed in underwater acoustic propagation with high frequency have narrow width than the ray formed in underwater acoustic propagation with low frequency.<p>Analysis of sound intensity reduction were done at GeoB10044-1 and GeoB10061-2 Stations. Analysis have done with varying depth, frequency, and discrete interval. The analysis of the sound intensity reduction at GeoB10044-1 Station was done by varying the depth of the acoustic source at 500 meters and 2.500 meters with 250 Hertz. Meanwhile, the sound intensity reduction at GeoB10061-2 Station was done by varying the frequency of 500 Hertz and 1.500 Hertz at 750 meters acoustic source depth. Discrete interval variation have been done at GeoB10044-1 Station with 0,25 meters dan 1,0 meters interval. Meanwhile, the discrete variation at GeoB10061-2 Station have used 0,375 meters and 1,5 meters discrete interval.<p>The comparison of the sound intensity reduction was done using three methods, Parabolic Equation Method which compared with Normal Mode Method and Ray Tracing. At GeoB10044-1 Station, the result of sound intensity reduction using Parabolic Equation is higher than the Normal Mode, about 29,63 % and 25,13 % higher. Meanwhile at GeoB10061-2 Station, the result of sound intensity reduction using Parabolic Equation is 18,77 % and 14,75 % lower than the Normal Mode Method.<p>The average differences of sound intensity reduction using Parabolic Equation is between 2,66%-15,12% lower than Ray Tracing. Meanwhile the sound intensity reduction using Normal Mode is between 10,51%-43,51% than Ray Tracing. The model shows that underwater acoustic propagation using Parabolic Equation method will correspond with the result from the Ray Tracing method. The advantage of Parabolic Equation method compared with Normal Mode method is the Parabolic Equation method can be used in high frequency source for far field. Meanwhile, the weakness of underwater acoustic propagation with The Parabolic Equation method compared with Normal Mode method is the method can only be used to model single source frequency underwater acoustic propagation.