Pseudo-Negative Stiffness Control And Real-Time Hybrid Testing Of Mr Dampers

Semi-active control with magnetorheological (MR) fluid damper can obtain a similar control effect with active control without huge power input. It has been a hotspot of structural control researches for a long period. The control force of pseudo-negative stiffness control can be represented by damping force and "negative stiffness" control force. The damping force can be achieved by the viscous damping element of MR damper force, while the "negative stiffness" control force can be achieved through changing the drive voltage of MR damper. Due to the velocity-dependent and strong nonlinear properties of MR damper, it is difficult for pseudo-dynamic test and shaking table test to verify the performances of control systems with MR dampers. As an important method to evaluate the performance of the control system with MR damper, the Real-time Hybrid Testing (RHT) has got a lot of attentions. However, it is difficult to calculate the response of the structure, drive physical substructure to reach the desired velocity, and measure and feedback the restoring force of physical substructure in a single time step for RHT. Usually, time delay exists in the RHT can introduce inaccurate result even instability to the system. Therefore, it is significant to investigate the time delay compensation for RHT.In this study, the dynamic characteristics and control effects of structures with pseudo-negative stiffness dampers, pseudo-negative stiffness control and its control effect for MDOF structure, influence of measured displacement on Equivalent Force Control (EFC) method and model-based EFC method were studied.1. It has been proved that structures with pseudo-negative stiffness dampers and pseudo-negative stiffness and viscous dampers are nonlinear homogeneity structures. The homogeneity ensures that dynamic characteristics and control effects can be analyzed through transmissibility, deformation response factor and response ratio spentrum. The analyses of transmissibility, deformation response factor and response ratio spectrum show that pseudo-negative stiffness control can extend the equivalent period of structure. For structures with longer periods, acceleration of structure with pseudo-negative stiffness dampers is smaller than that of structures with different damping ratios, while the displacement is larger. Both of displacement and acceleration of structure with pseudo-negative stiffness and viscous dampers are smaller than that of structures with different damping ratios.2. Pseudo-negative stiffness control with a five-story isolated structure incorporating MR damper was studied through analytical and RHT methods. It is proved that isolated structure with pseudo-negative stiffness and viscous dampers is also nonlinear homogeneity structure. Pseudo-negative stiffness and viscous damper control can reduce displacement without increasing the base shear. The analyses of stability and influence of time delay show that RHT technique is sufficient for the study of the performance of pseudo-negative stiffness and viscous damper control system. The test results show that control effects of displacement and acceleration with pseudo-negative stiffness and viscous damper controller are better than that of passive-off controller. The pseudo-negative stiffness and viscous damper controller can reduce the acceleration more than passive-on controller while control effect of displacement is worse than passive-on controller. The numerical analysis of Bohai JZ20-2NW offshore platform with pseudo-negative stiffness and viscous dampers also show that the pseudo-negative stiffness and viscous damper control system has good control effect.3. The EFC method has been developed for RHT to replace the numerical iteration for implicit integration with a force-feedback control loop. With this control loop, the EFC method can also compensate the time delay in RHT. However, some other factors may influence the delay compensation effect of EFC method, such as calculating restoring force of numerical substructure and pseudo-dynamic force using actuator displacement command or response, measured noise in the displacement of physical substructure. This study analyzes the influence of calculating restoring force of numerical substructure and pseudo-dynamic force using actuator displacement command and response, respectively, and the influence of measured noise on EFC method. To ensure the synchronization of restoring forces of numerical substructure and physical substructure and psudo-dynamic force, actuator displacement response have to be used to calculate restoring force of numerical substructure and pseudo-dynamic force. With a higher proportional gain of PID equivalent force (EF) controller, measured noise on actuator displacement response can introduce component with high frequency, which can not be disregarded, into the restoring force of physical substructure. To reduce the influence of the measured noise, a Kalman filter was employed to filter the noise in this study. A higher proportional gain of PID controller can be obtained with the Kalman filter, which improves the effect of time delay compensation of EFC method. The results of RHTs demonstrate that EFC method with Kalman filter can reduce the influence of measured noise on resoring force of physical substructure and effectively compensate the time delay, and its effect is similar with that of model-based compensation method.4. The model-based EFC method was proposed and studied. This method reduces the time delay between the EF command and EF response using the open-loop or closed-loop compensations based on the model of experimental system. Then, the EF response can track the EF command well which can improves time delay compensation effect of EFC method. Time delay compensation effects of SDOF and MDOF model-based EFC methods were studied with spring and MR damper specimens and compared with that of EFC method, respectively. The results show that the time delay compensation effect of model-based EFC method is better than that of EFC method. The test results of RHTs with a 200kN MR damper specimen also show that the model-based EFC method can effectively compensate the time delay.