The Investigation Of Transmission Characteristics Of Sound Waves In Layer And Ship Hull Structures

Ship vibration and noise control is key point to its design. Noise and vibration index is one of the main tactical and technical indicators to combat vessels, especially of the submarine. The processing that covered layers on the hull structure to reduce noise and vibration has been common. The transmission characteristics of sound waves in layer and the hull structure will directly affect the damping and sound absorption effect. Therefore, transmission of acoustic waves in layer and the hull structure has a fundamental significance. It provided a direct basis to the optimize design of hull structure, and the design of acoustic layer structure and its laying way.Take the sound absorption wedge for instance, transfer characters of acoustic wave in cover layer were discovered. The sound absorption wedge is a series of circular structure with the cavity inside which made from viscoelastic material and closely aligned, on account of its structural symmetry and repetition, thus one unit of the wedge was studied as a viscoelastic finite cylindrical tube instead. Start from the viscoelastic cylindrical tube, firstly the way of axisymmetric wave transform in infinitely long viscoelastic cylindrical tube and decay characteristics was studied. Based on this, the impedance and sound absorption coefficient was introduced to study the sound absorption and reflection of the finite cylindrical tube. Further refine the model into variable cross-section section viscoelastic cylindrical tube, to equivalent the corresponding wedge structure to calculate its sound absorption coefficient. In addition, the absorption coefficient of the wedge could be increase by scattering particles in the material, thus the influence of it should be taking into account as the role of incident waveform conversion. The sound pulse tube test was proceed to obtained absorption coefficient, and compared with calculate result to verified reflection and absorption coefficient when sound normal incidence.Damping effect was played on the structural vibration by sound absorbing wedge laid on surface of ship structure, and absorbing self-noise caused by the vibration. Thus, cover the inside surface of sonar platform can not only absorb the reverberation noise and vibration can be suppressed either. However, the actual sound absorption capability of wedge was different from the result that obtained from sound pulse tube test. The sound reflected by the wall could bring the multiple absorption of the wedge, which enhance the capability of the actual absorption. The numerical simulation method was carried to research the acoustic transmission characters of structure of a sonar platform on submarine. In the simulation the acoustic reverberant field of the compartment was explored, under real condition, the effect of wedge for ship structural vibration and acoustic reverberant field was studied. The model experiment of the sonar platform was carried out to investigate the vibration and cabin noise of it under water in the marine environment. The sound absorption wedge has an obvious inhibitory effect to the vibration of the structure, and can effectively absorb the self-noise field that caused by vibration of structural.