Research Of The Propagation Of The Structure-Borne Noise In High-Speed Ship And The Inactive Noise Controlling By Damping Treatments

The problem of the ship noise and it's controlling had received an increasing attention. To the high-speed ships the structure-borne noise became a serious matter for their flexible rigidity and the high- frequency excitation. And because the high-speed ship is sensitive and strict to the bulk weight, the optimum effect should be gotten by using a small quantity of damping material during the noise controlling. The controlling of the vibration and noise had become one of the key technologies in the design of the high-speed ships.In this thesis, on the basis of the study of the elastic wave propagation in the ship bulk structures, the vibration power flow in the periodical beams and the L-shape plate had been investigated. We focused on the effect of the damping material to the input and the output power flow. This can give a theoretical explanation to the damp measurements in the noise controlling.In the beams, there are several types of complex elastic waves. In plates there exits a cylindrical bending wave, this wave runs with the same chance in all directions. In stiffened plate, when the exterior forces add on the stiffeners, the main vibration powers propagate in the beam at near field but in the plate at far field.Beam and plate are the basic object of the damping treatments. In ship structures, beam is main carrier of the propagation of solid-elastic waves. And plate is the radiating body of the noise. From the vibration power flow we can see an interesting phenomenon that the same point and same resource have different input power in different vibration modes. We can select a right location of the vibration resource from the vibration modes so as to reduce the input power flow to the structures. In the passing band, the power flow will attenuate exponentially if adding the damping material to the basic structures, but an incensement of power flow in the stopping band. In the plate with a discontinuous material there are optimum parameters of the damp, such as the thickness, width, etc.The damping materials are ease to be effected by the environment, construction, etc. and their mechanical characters are nonlinear. All this can bring fallibility of the results in the computing and analysis of the structures. The noise controlling trial by using the damping material in the practical ship showed that the damping treatmentscould get a good effect. And it can prove the logicality of the damping scheme.