Dynamic characteristics of magneto-rheological fluid damper

Two kinds of Magneto-rheological fluid damper (MRF damper) have been designed and manufactured. One has a nominal capacity of 2 kN and the other 20 kN. A bypass flow system is adopted for both dampers and each has the same capacity of electromagnet attached to the bypass portion. The effective fluid orifice is the rectangular space and the magnetic field is applied from the outside. A test was performed by applying different magnetic fields to the orifice portion of the rectangular space. The damping force and the force-displacement loop were evaluated. The test results yielded the following: 1) Two type's of dampers functioned by using one unit of the electromagnet under an appropriate electrical current control. 2) The magnitude of the damping force depends on the input magnetic field, but it has an upper limit. 3) Without an applied magnetic field, the MRF damper exhibits viscous-like behavior, while with a magnetic field it shows friction-like behavior. A mechanical model of the damper is estimated by taking account of the force-displacement loop. It is clarified that MRF dampers provide a technology that enables effective semi-active control in real building structures.