Reseach On MR Damper And Its Application

Most Passive dampers possess some disadvantages, such as uncontrollable parameters, limited application field. This paper studies semi-active MR damper, and applies it to isolating vibration for devices on board and suppressing the Ground Resonance in helicopters.MR dampers on squeeze mode are usually used for the purpose of small displacement and great force. This paper proposes a design plan based on squeeze mode and verifies its magnetic circuit through qualitative analysis and finite element numerical simulation. Also, it obtains the relationship between the magnetic flux density in the working gap and the current or the gap length. The output force of the MR damper is also obtained in theory, based on the double viscous model of MR fluid. These researches provides theory basis for the design of MR damper.The amount of magnetic flux leakage, static output force and dynamometer card are important basis for the application of MR damper. The results of determination test on magnetic flux leakage and static output force show that the design of magnetic circuit is reasonable, the static output force has a sudden increase when the current increases to nearly 0.5A and is markedly influenced by the sedimentation of MR fluid when the current is high. Through gathering time-domain signal of force and displacement, dynamometer cards, average stiffness coefficient and equivalent damping coefficient can be obtained. It shows that, if other conditions do not change, the greater current is, the bigger area of the dynamometer card has, while the effect of excitation frequency is very small. When the current is zero, the MR damper has a negative stiffness, and the higher excitation frequency is, the bigger negative stiffness coefficient is, while the effect law isn’t obvious when the current is higher.When the current is zero and the frequency is in 2-26 Hz, the frequency has little influence upon equivalent damping coefficient. When the current is 0.5A or 1A, the frequency has great influence upon equivalent damping coefficient in 2-8Hz, and has little influence in 10-16 Hz.A new-style isolation system is presented for devices on board from vibration, which is composed of steel wire spring and a MR damper connected in parallel. Through simulating the MR isolation system with variable stiffness and damping, a kind of control strategy based on “switch stances” is put forward. Also, its performance is tested in different condition which are “no damper”, “with damper in zero current”, “with damper in 1A current”, “damper with the controller”. It shows that the transmissibility of vibration of the MR semi-active system can be less than 103% in transient condition, while having good vibration isolation effects, in the range of 5-60 Hz. At last, a style of vibration isolator is brought up, through connecting cylindrical helical spring and MR damper in parallel, which is a new ideal for vibration isolation.MR Damper is used as shimmy damper with the layouts of propeller-hub to solve the problem of “ground resonance” in helicopters. Through modeling the coupled rotor/fuselage system and the Routh-Hurwitz criterion, the stability area of the “ground resonance” system is obtained in different damping of shimmy and landing gear. Numerical results indicate that MR damper can suppress the “ground resonance”, as well as adjusting the MR damper and damping of landing gear by some control algorithm, can provide security for helicopters under different operating state.