Study for Practical use of Magnetic Fluid SemiActive Damper Characterized by Strong Nonlinearity

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Previous study proposed a novel semi active damper that is composed of a cylinder injected with magnetic fluid (M. F.) and a nonlinearly controlled electromagnet Generally M. F. has the very interesting property that the viscosity can be easily changed by the outside magnetic field. Additionally, the damping coefficient of the system is absolutely positive even if the control signals for changing the viscosity fail. This advantage of M. F. is just fit for safe semi active damper systems.In this study, at first, a modified model considering nonlinear characteristics of M. F. such as a Non-Newtonian-Fluid was proposed. Next, in order to enhance the control effects, two kinds of improvements were made in the semi active damper. One was to change the voltage control input to an electromagnet into the current control input. The other was to expand the control range for the M. F. damper by means of feeding a bias current to the electromagnetFinally, the advantages such as better damping performance, smaller control current and flexibility for disturbance with mixed frequencies were confirmed by various digital simulations and vibration experiments and the possibility to practical uses was shown clear.