Research On Dynamic Characteristics Of Helicopter Rotor Fluid-Elastomeric Damper

Fluid-elastomeric damper(FED) is a new type of lead-lag damper for helicopter rotor, which is added by the hydraulic damping system on the basis of elastomeric damper. It overcomes the disadvantage of traditional elastomeric dampers with relatively small damping and large loads of blade root caused by hydraulic dampers, preventing dynamic instability induced by the coupling of lag regressing mode for blades and fuselage. Lead-lag damper is the key components of the helicopter rotor system. The dynamic characteristics of its stiffness and damping can directly affect the vibration movement of blades and have a significant impact on the stability of rotor and rotor/fuselage coupling system as well as aeroelastic vibration loads. This paper analyzed the nonlinear dynamic characteristics and performed experimental study on the FED. With adding the FED to the stability analysis of coupling system for helicopter rotor/fuselage and the calculation of aeroelastic vibration loads, the influence of the nonlinear dynamic characteristics for the FED on the helicopter dynamic system is studied.Firstly, the nonlinear dynamic analysis model including parameters of the FED was established based on the working principle of the FED, the vibration energy dissipation mechanism of filled materials, the comparison among different dynamic modeling methods for the FED, the nonlinear ADF model for the elastomeric materials and the fluid dynamic function. In this model, parameters have to be identified by the dynamic testing of the FED. This model is suitable for integrating with dynamics equations of rotor system, since that it can not only accurately reflects the vibration energy dissipation characteristics but also correctly describes the nonlinear stress-strain relationship for the FED.Test of dynamic characteristics for the FED was performed, providing necessary data support. With designing the test FED, their model structures were determined according to the design requirement of rotor lag damper and geometry structural parameters were selected according to results of influence analysis on the parameters. When the test FED was processed, the filled materials and processing methods were selected through the comparative analysis of physicochemical properties of different materials. After the metal pieces and cohere pieces bonding metal and rubber parts are processed, the FED is completely assembled. Dynamic characteristic tests were performed to analog the procedure that rotor lead-lag dampers subject to the incentive external loads using the fabricated principle samples of the FED. The tests measured the variation of the dynamic properties for the FED relatively to many parameters such as materials, structures and movement. Then the nonlinear relationships among stiffness or damping export and displacement import can be obtained by the analysis of testing data. Moreover, results from dynamic properties tests of the FED were compared with those from design calculations, verifying the feasibility of structure design methods for the FED.Genetic algorithm has been applied in the model parameters identification of the rotor FED, which is aimed at the unknown parameters in the nonlinear dynamic model of the FED and combined with the primitive principle of genetic algorithm and the data from dynamic tests for the FED. The advantages of genetic algorithm in optimizing the function and identifying the model parameters were explained and verified by calculated examples. Furthermore, the model parameters of the FED identified by the genetic algorithm are substituted into the model structures. The dynamic characteristics for different motion states were analogous according to this parameter model. Through the results comparison between the calculation and test, the validity and feasibility of identifying parameters method and dynamic model of FED are verified.At last, the dynamic model of FED, the dynamic model of rotor and rotor/fuselage coupling system of helicopter were integrated, using which the stability of the rotor/fuselage coupling system with FED was analyzed and the aeroelastic vibration loads of rotor was calculated. The impact of the nonlinear characteristics for the FED on the system stability and aeroelastic vibration loads was also studied, respectively. The results from the stability analysis for the coupling system indicates that the mode damping of lead-lag regressing increases and the stability of system is enhanced due to the introduction of FED. Different damper models are applied in calculating the aeroelastic vibration loads and the results suggest that the application of accurate lead-lag damper model can improve the precision in calculating vibration loads of rotor and prove the accuracy of the dynamic model for the FED. Moreover, the influence of parameters in the structure designing for the FED on the change trend of stability and dynamic loads was obtained.