Stability Analysis Of The Coupled Rotor/fuselage System With Fluid Elastic Dampers

Dynamic stability of coupled helicopter rotor/fuselage system is one of the basic issues for helicopter dynamic design. In order to improve the coupled rotor/fuselage dynamic stability, the damper is necessary to rotor system. In this thesis, the main work concentrated on the dynamic stability analysis for the system of coupled rotor/fuselage with fluid-elastic damper. In this thesis the mathematic model for the damper consisted of two parts: elastomeric and hydraulic model. The comprehensive elastomeric model which based on ADF model and the non-linearity of elastomeric material is applied in this model. The hydraulic damping force was calculated with the hydraulic mode which is established by the engineering method.The coupled rotor/fuselage dynamic model consists of two procedures: first the generalized Hamilton theory is applied to derive the dynamic equation, second based on the FEM method to model the fluid-elastic damper, finally assemble the fluid-elastic damper to the coupled rotor/fuselage system dynamic equation to form dynamic stability analysis model. The Fourth Order Runge-Kutta method is used to solve the dynamic mathematic model, and the steady system time history response is also achieved with this method. Base on the steady response, the Jacobian Matrix is applied to linearize the non-linear equation, by hand of the multi-blades frames transfer matrix the dynamic equation is transferred into the fixed frame, then the stability analysis is proceeded with eigenvalue analysis (ground, hovering) or the Floquet theory (forward flight). In this thesis, two cases which are non-linear fluid-elastic and equivalent linear stiffness and damping model are considered in the analysis of dynamic stability of the coupled rotor/fuselage with fluid-elastic damper, and meanwhile the comparison of dynamic response and load between two different cases are also presented.