Semi-active Isolation Of Helicopter Vibration With Variable Stiffness Fluid Elastomer Isolator

It is important to effectively utilize the vibration control method to reduce the vibration level of helicopter in the course of helicopter design and research.The hub vibration force of rotor is the main vibration source of the helicopter airframe,and transmits to the fuselage through main gear box resulting in the vibration of the fuselage.Fluid elastomer isolator is a highly efficient helicopter isolator installed between the main gear box and fuselage and can significantly reduce the transmissibility of vibration forces to the fuselage.Hence,the vibration level of the fuselage can be reduced notably.In this thesis,a semi-active isolation method of helicopter vibration with variable stiffness fluid elastomer isolator has been presented.The dynamic model of fluid elastomer isolator was established,the dynamic equation was derived,and the vibration isolation performance of isolator was analyzed.According to the basic working principle of the Voice Coil Motor(VCM)actuator,the relationship between the input current of the VCM and the stiffness of the variable stiffness spring was studied,and the structure and working principle of the variable stiffness liquid elastomer vibration isolator was designed,which provides the basis for the design of the semi-active vibration isolation system.The state space model of vibration isolation system was established.The simulation results by applying single frequency excitation to the vibration isolation system utilizing Simulink simulation software indicate that the isolator can achieve good isolation effect on vibration isolation frequency.According to the output characteristics of the VCM and the vibration isolation principle of the fluid elastomer isolator,a semi-active vibration isolation system using the fluid elastomer isolator was designed.The simulation analysis program of the vibration isolation system is compiled by MATLAB software.The force response of the vibration isolation system under varying excitation was calculated by applying the varying excitation to the system.The simulation results indicate that when the external excitation changes,the stiffness of the variable stiffness spring in the fluid elastomer isolator can be controlled by changing the input current of the VCM so as to change the vibration isolation frequency of the vibration isolation system to be the same as the frequency of the external excitation.The designed vibration isolation system can obtain good vibration isolation effect and achieve semi-active vibration isolation.