A Research On The Damping Characteristics Of Composite Propellers

The propeller will produce a non-uniform wake field at the stern during normal operation,which will cause the propeller to produce non-constant thrust and torque during operation.In the stern flow field,the thrust and torque will not only cause the vibration of the propeller,but also transfer to the hull through the bearing system with high stiffness,which will induce the vibration noise of the hull.Therefore the research of reducing propeller vibration is of great importance.In the marine field,copper alloy propellers are widely used because of their high strength and corrosion resistance,but they have violent vibration and high noise.Compared with metal propellers,the designability and high damping properties of composite propellers can effectively reduce their vibration during normal operation,so the structural design of composite propellers is studied in this paper.In this paper,we first explores the lay-up modeling method of composite propeller blades and validates the numerical calculation method applied to the arithmetic cases.In order to make the modal strain energy method applicable to the multi-interface hybrid fiber structure,this paper further explores the equation and numerical simulation method of the interface loss factor,and obtains the damping loss factor of the hybrid fiber structure with different number of interfaces through the vibration test experiment of the hybrid fiber cantilever beam,and compares it with the calculated results of the modal strain energy method if considering the interface damping to verify that for the hybrid it is found that for the hybrid fiber structure with more interfaces,the contribution of interface damping to the overall damping is significant and cannot be neglected.Then,in this paper,based on the common dimensions of propellers,the propeller blades of the series of propellers without side-tracking and longitudinal inclination are simplified into a plate model,and the modified modal strain energy method is applied to quantitatively study the effect of the variation of material damping parameters and structural damping parameters on the overall damping and inherent frequency of the structure,and two types of structural plates with mixed fiber structure and damping layer structure are designed according to the obtained laws,and the damping performance and mechanical properties are compared with those of copper plates and pure carbon fiber plates.The results show that the damping structure can improve the damping performance as much as possible at the expense of the mechanical performance compared with the hybrid fiber structure.Finally,considering the fact that reducing the propeller with large side-tracking and longitudinal inclination to a plate model will lead to large deviations in calculation,this paper further uses the propeller with side-tracking and longitudinal inclination as the model for structural damping design,and optimizes the thickness,relative position and number of damping layers to obtain a damped structural propeller with high damping.The damping and mechanical properties of the propeller were compared with those of the optimized hybrid fiber propeller and carbon fiber propeller,and it was found that the damped propeller had the strongest vibration suppression ability and the middle mechanical properties.The strength characteristics of the final damped propeller are analyzed by calculating the unevenly distributed pressure on the propeller blade surface under actual working conditions to ensure that it does not suffer from deformation damage and maximum stress damage during normal operation.The research content of this paper can provide some reference value for the design of composite propeller structure with high damping performance.