| Since the happening of an 8-magnitude earthquake in Wenchuan, earthquake disasters have successively spread to Yushu, Ya’an and Nudian for the last 5 years in China, and our country is marching into the age with high frequent occurrence of earthquake. Apart from the huge collapse of buildings and other structures during the earthquake, the direct and indirect losses due to soil structure failure have been closely concerned by a lot of scholars. In order to study the failure mechanism of soil structure under earthquake circumstance, Institute of Engineering Mechanics, China Earthquake Administration, associating with Harbin Institute of technology, are developing the second largest uniaxial centrifuge shaker for earthquake simulation, which will provide a convenient experiment condition for domestic anti-earthquake research and have great realistic significance for the same. With consideration of the particularity of centrifuge shaker and centrifuge shaking test, the objective of this dissertation is to establish corresponding servo and vibration control strategy to guarantee the waveform replication accuracy of centrifuge shaker.Comparing with normal shaker, centrifuge shaker is mounted onto the dynamic basket, which is attached at the tail end of centrifuge arm, and the main test object of centrifuge shaker is the soil model with high scale ratio. On account of the excessive scale ratio, the excitation frequency of centrifuge shaker is much higher than normal shaker, which always ranges from 200 Hz to 300 Hz. In this situation, the dynamic characteristic of basket and soil model cannot be ignored. Firstly, the coupling characteristic between basket base and table is divided into kinematic coupling and dynamic coupling in this dissertation, which only considers the main model of basket base in the horizontal excitation direction. Then, the linear coupling model of centrifuge shaker’s hydraulic power element is established after the simplification of soil model’s dynamic characteristic into a one dimension mass-spring-damper system. After those, we derive the linear coupling transfer function of hydraulic power element on the basis of four kind fundamental equations, and the validity of this transfer function is testified in three special working conditions. At last, we put forward four nonlinear models to clarify the characteristic of accumulator, soil model, rubber bearing and hydraulic power element. And, the nonlinear coupling model of whole hydraulic power element is finally synthesized by analyzing the influence of these nonlinear factors to prior linear coupling model.Centrifuge shaker is a sort of complicated system, which is featured with strong coupling characteristic and simultaneous affected by four nonlinear factors. For the servo control strategy of centrifuge shaker, user is supposed to set forth an absolute acceleration reference for table, but the control objective of position close-loop is the relative displacement between the table and basket base. Hence, the major responsibility of decoupling controller is to transform the absolute motion into relative motion. In addition, four nonlinear factors are included in this centrifuge shaker. Another indispensable task of servo control strategy is to ensure the stability and control accuracy of position close-loop system, which is always disturbed by prior four nonlinear factors. Aiming to fulfill these tasks, the standard transfer function expression from relative motion to absolute motion is primarily derived according to the linear coupling model. Next, the coupling relationship between relative motion to absolute motion is also identified using recursive extended least squares algorithm. Then, the decoupling controller can be synthesized by comprehensively considering the deduced standard transfer function expression and the approximate inverse of identification result. On the other hand, the norminal transfer function and the relative error of block diagram’s each part is deduced with the consideration of four nonlinear factors. After the deduction, proper perturbation weight function is selected to tolerate all relative error for each part of block diagram. Furthermore, we employ m synthesis method to design robust controller to ensure the stability and certain control accuracy of position close-loop system. Finally, feed-forward compensator is presented on the basis of 2 DOF control strategy to further expand the position control system’s bandwidth. Through the simulation verification, the system bandwidth has been promoted to 220 Hz.The research object of centrifuge shaking test is soil model, irreversible destruction always happens inside the soil model for each earthquake waveform excitation. For the traditional off-line iteration algorithm, multiple earthquake excitations are necessary for generating the final drive signal for formal test. Theoretically, the soil model needs to be substituted by a new one with same characteristic for each drive signal update. Therefore, the main objective of vibration control strategy study is to reduce the times of iteration. In this dissertation, we firstly deduce the relationship between the convergence speed of off-line iteration algorithm and the identification accuracy of frequency response function(FRF). The conclusion manifests that higher FRF identification accuracy can boost the convergence speed of off-line iteration by choosing a larger error modification coefficient. Then, the integration method of optimal FRF is presented on the basis of Welch PSD estimate and Maximum Entropy PSD estimate. After the simulation verification, the result infers that the identification accuracy of optimal FRF and corresponding iteration process are better than traditional FRF. Lastly, an error compensator is outlined to further boost the convergence speed of off-line iteration process. And, H￥method based on sensitivity function and complementary sensitivity function is applied to design this error compensator. The simulation result indicates that error compensator can sharply reduce the times of off-line iteration.In the experiment part of this dissertation, overall arrangement of the ground tests, the mechanical and hydraulic system and the electronic system have been firstly introduced. Besides that, in view of x Pc Target rapid control prototyping technology, the real-time control software and the graphical user interface have been programmed. Subsequently, some specific tests are designed and conducted to verify the servo control strategy and vibration control strategy. The experiment al results further testify the conclusions drawn in simulation analysis, and verify the feasibility and advancement of various control methods in this paper. |
PDF Full Text Request