Developments And Applications Of The Self-powered Magnetorheological Damper And TMDs Using Eddy Current Damping

To make magnetorheological (MR) dampers be free from dependence on the external power supply and improve the durability of tuned mass damper (TMD), self-powered MR dampers and novel TMDs using eddy current damping (ECD) were developed through electromagnetic induction principle and applied to vibration control of two kinds of structures, respectively. One is that they prefer to be equipped with direct energy dissipation devices, such as stay cables and base-isolated highway bridges. The other is that they are more suitable to be installed with shock absorbers, such as high-rise transmission towers, long-span pedestrian bridges and hangers with high slenderness ratio in arch bridges. The main contents and conclusions are summarized as follows:(1) A self-powered MR damper control system combining with an energy- harvesting generator and an MR damper with low power requirement was integrated. Its feasibility, advantages as well as control mechanisms have been illustrated through both experimental investigations and numerical simulations.(2) A test platform consisting of a self-powered MR damper and a model cable were established in the laboratory to evaluate the control performance of the cable. The test shows that the self-powered MR damper can greatly improve modal damping ratios in each of first five modes of the cable. In addition, damping ratios of the cable controlled by a self-powered MR damper are independent of the vibration amplitude, while a passively operated MR damper can only achieve good control performance at the stage of relative big amplitude. The excellent control performance of the self-powered MR damper is mainly due to two aspects: one is that it can work as a linear viscous damper, and the other is it can realize negative stiffness control.(3) The design strategy of applying self-powered MR dampers to real cables on bridges was given from the standpoint of practical application. The control performance of the self-powered MR damper was theoretically investigated for two typical cables, whose lengths are 114 meters and 577 meters, respectively. It is found that the self-powered MR damper perform quite well for both the short cable and the super long one with the designed self-powered MR dampers, implying that the self-powered MR dampers have broad feasibility. Moreover, it is demonstrated that only when the MR damper and the generator are attached at different locations can the control system show negative stiffness control characteristics, which can greatly enhance the control performance.(4) The self-powered MR dampers were then extended to control seismically excited base-isolated highway bridges. The simulation results show that the optimal control force of active control devices for a base-isolated bridge is almost dominated by damping components, and self-powered MR dampers can nearly achieve the same control performance as active control, making the self-powered MR dampers be potential to take the place of the active control devices.(5) A tiny TMD with the mass of 0.2kg using ECD was developed. The laboratory test on a foot bridge model with the developed TMD has demonstrated the realization of ECD and control mechanics of TMD. On this basis, several middle-size TMDs with ECD, of which damping and stiffness components are thoroughly separated, and damping ratios can be easily varied by adjusting the gap between permanent magnets and conductor plates, were developed to control the wind-induced vibration of hangers with high slenderness ratio in arch bridges. The design flow of a large-scale TMD using ECD was established and summarized based on analytic solutions, magnetic field finite element analysis as well as experimental investigations. Then, a protype vertical TMD is fabricated to be applied to vibration control of a foot bridge. Finally, the feasibility of TMDs using ECD was well demonstrated in view of both economic and durability analysis.(6) A large-scale horizontal TMD, adopting two cantilever beams as stiffness components and ECD as damping components, respectively, was developed with the proposed design strategy of ECD, which can well meet the need of transimission towers with simpliness, reliability, high durability as well as maintenance-free. Field tests were carried out to validate the control performance of a 124.1-meter-high transmission tower equipped with such two TMDs, whose parameters were optimized to control the first-order longitudinal bending mode of the tower. It is shown that the supplemental modal damping ratio in the first-order longitudinal bending mode of the tower with the attached TMDs is 0.03~0.04 in the case of both ambient vibration and impact tests.