Study On Theory And Control Technology Of Magnetic Suspension Active Vibration Isolation For Flexible Floating Raft System

It has the extremely vital significance to the national defense security to improve the performance of the naval vessels acoustic stealthy. Vibration isolation technology widely used to reduce vibration transmission in many different engineering applications has become a key technique of vibration and noise reduction. It is traditionally classified into two types:passive, active. Although the passive systems offer simple and reliable means to protect mechanical systems from their respective environments, they have inherent performance limitations including their limited controllable frequency range and their unchangeable shapes of transmissibility. Active vibration isolation systems, on the other hand, can provide'enhanced vibration isolation performance through a feedback system. However, active vibration isolation systems are not cost-effective. Therefore, passive and active combined technology is regarded as a hotspot in current researches, due to performance improvement and simplicity of implementation. Magnetic Suspension Vibration Isolation(MSVI) technology is an excellent active isolation technology, which has some useful characteristics, such as non-contact, high response frequency, high reliability and long life-span, especially, the damping and stiffness adjusted by changing controller's parameters on-line. Therefore, it is significance that the technology is applied in the passive vibration isolation system in this research to improve the isolation performance.A two degree of freedom system and an multiple degree of freedom system models are established to analyze effect of system parameters on vibration isolation performance using power flow as evaluation criterion. Results show that with all other parameters definition, the stiffness and damping are the key parameters of influencing the performance of vibration isolation. And the MSVI technology has obvious advantages to be applied to change stiffness and damping parameter.The principle of magnetic suspension isolation technology is introduced. The math modeling of the Magnetic Suspension Isolator(MSI) is established. The MSI is designed according to practical parameters. For the work status of the MSI, static electromagnetic field distribution is calculated through 3D FEM with consideration of nonlinearities of armature and E-shape magnet magnetic, including material's nonlinear, magnetic saturation and leakage, magnetic coupling, and etc. On the basis of the theoretical analysis, the electromagnetic field distribution is measure using a three channel Guass meter to ascertain the accuracy of the FEM model at some specific spots. Then, the static and dynamic electromagnetic force of the MSI are measured by experiment. Through the experimental measurements and fitting a mathematical expression by least square method, the actual relation expression of static electromagnetic force-current-gap is obtained for accuracy control. In view of highly non-linear and hysteresis behavior of dynamic electromagnetic force, Artificial Neural Networks(ANN) is applied to identify the relationship of dynamic electromagnetic force. To achieve higher accuracy for ANN, an modified genetic algorithm is applied to train the neural networks. Results clearly show the MGA based neural networks is found better performance and higher accurate for MSI model comparing with conventional BP algorithm.The designed MSI is applied to the passive vibration isolation system. The dynamical equations and state equations of the single-layer, double-layer and (flexible) floating raft system are built, using the methods of rigid body dynamics, dynamic sub-structure, Finite Element methods.A control mechanism and a cost function of active vibration isolation based on the minimization of the weighted sum of squared output forces are proposed. Considering the practical capacity of the MSI, the value function is revised. The revised function and the optimal feedback matrix are deduced. A control model based on the control mechanism is established. The results of simulation show validity of the strategy. For the nonlinear of the MSI, according to the control strategy of the former, an output feedback fuzzy control algorithm is proposed to the active isolation system. The fuzzy control model are simulated using Matlab fuzzy logical toolbox. The results of simulation show that the fuzzy controller possesses better isolation performance than passive system and PID control system.In order to test the performance of the active system and control algorithm, an experimental platform is carried out. The experiment results show that the active isolation performance improve highly at around the resonant frequencies compared to the passive system. The experimental results are found to be in good agreement with the simulated results.At last, to solve the strain multi-position measurement of raft frame, the Fiber Bragg Grating(FBG) is introduced. According to the simplicity principles of raft, a platform is built to measure the stress and modal of simple raft using FBG sensors. The experimental results are found to be in good agreement with the FEA results.