Hydroelastic Vibration And Noise Of A Marine Propeller

The marine propeller works in water, decoupling calculation is not accurate due to the properties of water. The sound velocity and density of water is quite different from air, it is the heavier fluid. The present work is aimed to hydrodynamic characteristics, static characteristics, dynamic characteristics and acoustical characteristic of marine propeller in water based on hydroelasticity theory. The fully coupled three dimensional structure finite element method (FEM), computational fluid dynamics (CFD) and acoustic FEM are applied. The concrete research content is as follows:3-D model of a propeller is build. Based on the model, a CFD is coupled with a FEM for hrdroelastic numerical analysis of the propeller under various operating conditions. The open water characteristic of the propeller is determined under the action of coupled and uncoupled. The values of numerical simulation agree well with the experimental results. The results obtained through two methods have few discrepancies, and each of them can satisfy the demands of engineering.The structure FEM is applied in static characteristics analysis by using the output result from CFD simulation. The contour map of blade surface pressure distribution and the curves of the radius of blade dependence of equivalent stress and total deformation are given. The results reveal that the distribution of equivalent stress and total deformation by using coupled method is in good agreement with that by using uncoupled method. The maximum equivalent stress is located in propeller trailing edge closer to hub and the maximum total deformation appears in blade tip. The peak values of equivalent stress and total deformation increases by considering fluid-structure interaction (FSI) effect. Along with the increase of advance coefficient, the difference through two methods would increase.Analyze the influence of water inertial effect to free vibration characteristics of marine propeller and the influence of pre-stressed effect on the structural modal. Analyze a marine propeller in air and in water with FEM analysis, the natural frequencies curves and shape modes are presented. Results show that the pre-stressed effect has an influence mainly on the natural frequency of the propeller, and less on its shape modes. The natural frequencies of propeller in water are significantly lower than those in air, the water inertia effect also has some influence on pre-stressed modes. The increase of natural frequencies in water are smaller than it in air.The dynamic response of the propeller induced by pulsating flow is studied. The unsteady hydrodynamics of the excitations from propeller and the behavior of the propeller’s structure transient and acoustic responses under the propeller excitations is simulated. The hydrodynamic coefficients, total deformation, equivalent stress and surface sound pressure response curves are given in time and frequency domain. Results show that the propeller excitations are 4 cycles periodic fluctuation per revolution in time domain, it corresponds with the number of blade. The maximum peak in amplitude appears at Blade passing frequency (BPF) in frequency domain. The maximum peak in amplitude of total deformation and equivalent stress appears at the first natural frequency. The amplitude in water is larger than it in air. The maximum peak in amplitude of sound pressure appears at the second natural frequency located in the middle of the suction surface.