Radiated Noise Prediction And Acoustic-Structure Sensitivity Analysis Of Marine Gearbox

The marine gearbox is an important transmission part of ships, which hankeringhigh power, high speed and low noise with the development of science and technology.Presently, a big gap between China and foreign advanced level in designing gear devicestill exists. Especially in the field of high speed and heavy load gear transmission,vibration and noise reduction has become a bottleneck which restricts the developmentof high-performance marine gearbox in China. Therefore, the research on vibration andnoise reduction of the marine gearbox can bring important theory significance and greatengineering values.The topic of this paper is supported by National Natural Science Foundation ofChina. Using the theories of multi-body dynamics, nonlinear vibration andacoustic-structure coupling method comprehensively, the prediction of radiated noiseand analysis of acoustic-structure sensitivity of the marine gearbox are carried out. Themain research work in this paper can be summarized as follows:(1) The multi-body dynamics analysis model of the marine gearbox is establishedin the software of LMS Virtual.Lab/Motion. Taking the time-varying mesh stiffness,mesh damping, tooth backlash, bearing stiffness and damping into consideration, therigid body dynamics is analyzed by using variable step backward difference method.Hence the mesh forces of gears and reaction forces of bearings are obtained.(2) After flexible processing of the gearbox, the model of dynamic responseanalysis is established. Through the finite element based modal analysis of the gearbox,the natural frequency and normal mode of the gearbox are obtained. Dynamic responseof the gear system is analyzed by mode superposition method, and then the vibrationdisplacement, velocity and acceleration of the gearbox are obtained.(3) Acoustic-structure coupling analysis model which contains structured mesh,acoustic mesh and field point mesh of the marine gearbox is established. Based on theresult of multi-body dynamics analysis, the forces of bearings are applied as theboundary conditions of acoustic-structure coupling analysis model. Using the finiteelement method, the surface acoustic pressure contour on the housing and the radiatednoise at determined field points are obtained.(4) The acoustic-structure sensitivity model of the marine gearbox is establishedwhich considers the structure wall thickness parameters and the elastic modulus of the marine gearbox housing as design parameters, acoustic pressure at determined fieldpoints as the acoustics parameters, and the design parameters which have larger impactfor the acoustic pressure at determined field points are obtained by using the software ofNastran and LMS Virtual.Lab. The analysis of acoustic-structure sensitivity can providethe basis for choosing the design variable of acoustical optimization of gearbox.