To provide a practical design method for Magnetorheological fluid damper (MRFD), mechanical model is established for
two-exserted-pole gap type (TEP-GT) MRFD and the relationship between damping force and internal sizes is given.
The magnetic circuit is studied and the materials and structures of main components are discussed. A practical design
method for TEP-GT MRFD is obtained and several key expressions are provided. A kind of TEP-GT MRFD for the
cable-stayed vibration control system is designed and manufactured.
An experimental study on vibration control of one stay cable using a magnetorheological fluid (MR) damper is described in the paper. A 14m-long stay cable model, which is a 1:16 scale model of a 220m-long prototype stay cable in the actual structure, is established for the experimental investigation.The planar sinusoidal excitations with the resonant frequencies are generated by the exciter installed perpendicular to the stay cable model at a point near the low anchorage. The modal testing on the unimpeded stay cable is first performed to identify the actual modal properties and the dynamic performances. Then a series of vibration control tests are conducted on the stay cable incorporated with a small-size MR damper near the low anchorage under the sinusoidal excitations with the first two modal resonant frequencies. The control efficacies and the dynamic performances of the combined cable/MR damper system corresponding to the different current inputs to the MR damper and the semi-active MR damper are investigated comparatively. The experimental results of the vibration control of the stay cable model indicate that the semi-active MR damper can achieve much better control efficacy than the passive MR dampers supplied with constant currents, and the reason can be attributed to the pseudo-negative stiffness generated by the semi-active MR damper.
The possibility of reducing offshore structural response under strong external excitations such as wind storm, sea ice and
earthquake via control systems is attracting the interest of a large number of researchers. Up to now, lots of dampers
have been installed on different offshore platforms. As one new kind of effective semi-active device, magnetorheological
fluid (MRF) damper has been used in the field of mechanical equipment, automobile and civil buildings, however, the
practical application for vibration control of offshore platform has not seen before. In this paper, 8 MRF dampers with
maximum damping force of 100kN for vibration control of one offshore platform with total weight of 650t have been
manufactured and tested. The general situation of MRF damper system and the offshore platform include manufacturing
issues, powering, range of variability of the mechanical parameters and response time are introduced.
As having ability of changing its apparent viscosity in presence of magnetic field in millisecond, magnetorheological fluids (MRF) exhibit widely potential application in devices or systems for controlling vibration and noise. In addition to shear stress strength, another import performance index of MRF is its stability under long time static state. For most applied conditions, without hard agglomeration is more important than higher shear stress strength. However, up to now, only a few reports pay attention to evaluate method of MRF's settling. This make it is difficult to optimize manufacturing technique of MRF and study its principle. A novel testing instrument, which made based on theory of that varying magnetic particle's volume content of MRF would induce its correspondingly changing of magnetic conductivity, designed and fabricated. And settling state of several MRF were tested by that instrument, factors which influence accuracy of that instrument is also discussed. Research shows that, the novel settled and laminated testing instrument (NSLTI) is potential to be used to evaluate settling stator and monitor settling process of magnetic particles. Moreover, study also shows that strength of magnetic field, position of magnetic field sensor, sensitivity of Tesla meter, type of MRF and testing time may influence accuracy of NSLTI.
Due to their character of low power requirement, rapid-response and large force, the dampers that made based on the special rheologic performance of magnetorheological fluid (MRF) have shown to be one kind of ideal semi-active vibration control devices for civil engineering structures and vehicles. In this paper, the character of magnetic circuit of MRF damper was firstly studied; based on above results, a large-scale MRF damper whose adjustable multiple is about 16 and maximum damping force is about 170kN was then designed and tested. Experimental results show that, under lower electrical current, same or opposite of electric current direction of multi-coils winding on the piston do not influence damping performance of MRF damper; however, under higher electrical current, inverse connecting of adjacent coils is apt to improve damping force of MRF damper.
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