Fluctuation Characteristics And Impending Method Application Of Hull Structure-borne Sound

In recent years, the naval vessels’ exposure and offence rates are substantially increased.With the modern detection equipments and the development of high-precision, long-rangeweapons, the survivability and tactical efficiency of naval vessels are under serious threat.The characteristics of vessel sound field and target properties can be controlled by systematicapplication of a variety of acoustic stealth techniques, and the ship-to-target discovery,tracking and hitting power are also improved. Therefore, the sound stealth technology is aneffective method to improve naval vessels’ survivability and tactical efficiency.The structure-borne sound is generated by the valves and plunger connecting rods ofmain and auxiliary machineries’ friction，impacting and alternating stress. The structure-bornesound is transferred through the main pathway of base--hull--field in the form of elastic wavepropagation. However, the structure vibrations generated by dynamic loading are notimmediately affected the hull structure, the vibration transmission requires some time and acertain pathway. Therefore, the structural dynamic analysis essentially reflects wavefluctuation.The characteristics of vessel structure-borne sound transmission and inhibition is across-field research about structure vibration, sound radiation and elastic wave control.Beginning with the typical hull plate girder structures, the stiffened double hull with acousticcovering layers is considered to be the main investigated subject in order to explore thefluctuation characteristics in hull structures. Based on dispersion characteristics, cumulativeeffect, power flow and sound radiation analysis, the wave propagation control technology oftypical power cabin is researched.Firstly, the characteristics of wave propagation from a variety of limited-scale typicalhull structure are analyzed according to wave conversion and impedance mismatch principle.The influence of liquid load on the fluctuation characteristics is discussed, and the waveimpending performance of different hull link structures are compared. The high transmission loss hull link structures are summed up.The currently vessel noise control only focuses on the analysis of flexural wave.Breaking through the limitations of thin plate theory, the movements of hull plate and beamare described as traveling waves, and the structure vibration is described as propagatingwaves in different directions. The multi-mode dispersion characteristics of hull plate girderwith shear deformation are analyzed, and the cumulative effect of hull structure under broadband motivation is explored.Stiffened double hull structure is generally composed of beam, plate, cylindrical shell,and it is of great importance to analyze its structure dispersion and power flow characteristicsin order to control the structure-borne main pathway of equipment--base--hull--fluid. Thestiffened double hull with acoustic covering layers is considered to be the main investigatedsubject in order to explore its structure dispersion and power flow characteristics. Theinfluences of hydrostatic pressure, acoustic covering layer and boundary condition on itsdispersion characteristics are discussed. Furthermore, the hull structure’s cumulative effectunder the combined motivation of propeller and impelling electric machine is explored.With development and application of quiet type equipments and vibration isolationtechnology, the mechanical noise has been effectively controlled. Therefore, the shellvibration and sound radiation motivated by air source is becoming more important. Based onmulti-source excitation characteristics of power cabin, sound radiation of double cylindricalshell under driving force and internal sound source is researched. The composite effect ofsound radiation and sound transmission is analyzed as well as the dominant noise component.On this basis, the engineering estimating method of hull structure’s under water soundradiation is preliminarily summed up, which is resulted by the airborne noise of fan systemand pumping machinery. Furthermore, the engineering control measures of airborne noise aresuggested.The mutations of hull structure have little effect on impeding wave propagation, so theeffective assembly process is developed in order to enhance the vibration isolation performance. Based on wave theory, the influence of blocking mass eccentric arrangementand fixation properties on its vibration isolation performance is discussed. The characteristicsof elastic interlayer impeding vibration wave propagation from typical hull structure areanalyzed, and the preliminary empirical equation of base isolation performance and blockingmass properties is developed. Combination elastic interlayer with rigid vibration isolation, acomposite wave impending techniqu is summed up.The high transmission loss link structures and composite wave impending technology areintroduced into the power cabin’s structure-borne sound three-dimensional design accordingto the analysis of stiffened double cylindrical shell dispersion characteristics, cumulativeeffect，power flow and sound radiation analysis. The high transmission loss structure styles ofbulkhead, base and brace are summed up,Based on theory analysis and numerical experiment, the effectiveness of structure-bornesound design is verified through large scale cabin model underwater vibration and soundradiation experiment. The preliminary methods of structure-borne sound three-dimensionaldesign of power cabin are developed.