Research On Noise Reduction Performance Of Underwater Motor Composite Elastic Cavity Structure

The stealth technology of an underwater vehicle has been a significant research work,which is aiming to reduce the underwater motor self-noise,e.g.mechanical noise,electromagnetic noise.In this thesis,a composite elastic cavity structure and the performance of shielding self-noise coming from the vibration of the propeller motor is well studied numerically and experimentally.Eventually,the theoretical foundation and reasonable suggestion are supplied by evaluating the sound insulation performance.Using the simplified models of motor and acoustic enclosure,the method of transferring the rotational excitation into the point excitation force on the cap and wall of the propeller,the characteristics of sound field of the acoustic enclosure is simulated by a computational fluid dynamics(CFD)software Virtual Lab which is finite element method based.By changing the machine rationalities,e.g.the boundary condition of acoustic enclosure,structure,size and material,parametric studies of the influences of acoustic enclosure on the characteristic of sound field are explored quantitatively in terms of mass effect,coincidence effect,additional impedance,and modal analysis.It is founded that the sound insulation performance is improved by optimizing the structure and size.Specifically,according to the theoretical analysis and simulation on the elastic cavity,decreasing the thickness of acoustic enclosure will not only reduce the mass,but improve the overall performance of sound insulation.Additionally,taking the costs and practical operability into considerations,an optimal design scheme is determined finally.Based on the simulation result,an experimental acoustic enclosure is designed and its characteristic of sound field is tested in a reverberation pool.By employing a reverberation test method with correction,the acoustic radiation power is obtained based on the spatial average sound pressure level which is measured in the reverberation control area and calibrated by the correction value.The experimental test indicates a good consistence with the numerical conclusion,which proves that the composite elastic cavity structure designed in this thesis has a satisfactory effect on the sound insulation or noise reduction.Consequently,this cavity shielding the motor self-noise will provide the stealth technology of an underwater vehicle with reasonable proposals or suggestions.