Abstract
Investigation of the underwater noise produced by ships by means of intensity method This paper presents results of research on spectral structure of underwater noise acoustic field radiated into water by selected ships moving in shallow waters. Underwater acoustic field of ships in motion is associated with acoustic activity of ship mechanisms and equipment under work. Vibration energy radiated by the mechanisms and devices is transmitted by ship structural elements to surrounding water where it is propagated in the form of acoustic waves of a wide frequency band. In this paper are presented results of the research on propagation of energy of acoustic waves in the near fiel, obtained from acoustic pressure measurements by means of two sensors located close to each other.
Highlights
Research on spectral structures of underwater noise generated to water by vessels of different classes have been used for many years in the detection, location and identification systems, and in the homing guidance and initiation units of sea weapons systems
Underwater sound field of the vessels is connected with the activity of acoustic wave sources installed on ships, i.e. ship mechanisms and equipment and hydrodynamic sources such as screw propeller and water flow around the hull
Theoretical estimation of the level of acoustic energy near the wave source and attempts to present the vertical and horizontal distribution of energy in the plane of trajectory are difficult and currently not very effective. This follows from the fact that the theoretical model of extended source, which is a superposition of several different types of sources of acoustic waves, namely those due to water flow, ship hull vibration and cavitation, makes that their full description is extremely complicated and difficult to apply in practice
Summary
Research on spectral structures of underwater noise generated to water by vessels of different classes have been used for many years in the detection, location and identification systems, and in the homing guidance and initiation units of sea weapons systems. For the assumed depth of the coastal water region, amounting from 10 to 70 m at which underwater noise measurements are made, the condition of the far field would be satisfied for the frequency f 31000 [Hz] in the trial area situated at the depth of 10 m This limitation is dependent on radiating surface dimension and sound propagation velocity in water. Sound intensity measurement of underwater noise enables to carry out more accurate research in this water region Such measurement based on a suitable spacing of acoustic sensors and precise phase matching of hydrophones and measuring setups, will make it possible to process of recorded data in the frequency band of interest. Where: 0 < k < N Im[Gxy(k)] - complex part of cross spectrum
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