Study On Active Vibration Control Of Floating Raft System

Acoustic hiding ability is a key factor related with submarines' vitality and fighting strength,hence it is important to decrease their vibrations and noises. Floating raft is currently widely equipped in lots of nation's navy for vibration and noise attenuation in submarine.The high-frequency band vibration produced by equipments mounted on the raft can be reduced a lot by it,while low-frequency band vibration can't be depressed much.Research in this paper is focused on improving floating raft's ability in decreasing low-frequency band vibration via active vibration control.It includes following contents:modeling of floating raft with active absorbers,optimization of mounting positions of active absorbers,adaptive feed-forward control on mono-frequency vibration,adaptive feed-forward control with actuator saturation,and experiment study on active vibration control of simulative floating raft system.In order to have theoretical analysis on floating raft system,it often needs to do some simplification on its structures.In this paper,the raft is approximated by a thin plate with regular shape at first.Then the floating raft system is divided into several subsystems,such as plate raft,elastic foundation,etc,which are respectively modeled by four-parameter net method.After that,dynamic absorber and active absorber are put into a uniform frame to obtain the model of plate raft subsystem coupling with them.At last,according to the force and velocity relationship among each subsystem's interfaces,the entire plate floating raft system is modeled by subsystem structural admittance synthesis method.As the main structure of floating raft system is elastic,it is inevitably to study the optimization of actuators' mounting positions before designing control law.In this paper,two new criterions are proposed for it.They are close-loop allocation criterion based on states feedback and allocation criterion on the basis of piecewise weighing area performance index.The former one is appropriate for actuators' allocation in structure active vibration control,and the latter is applicable for allocation in wind-band vibration control.Finally,the best mounting positions of absorbers on floating raft are determined by using the criterion above.Accurate and steady reference signal is a key point that decides control's success in adaptive feed-forward control on simple harmonic vibration.A new frequency estimation method,which is based on an adaptive band-pass filter,is proposed.The estimated frequency is then used to generate reference signal.The band-pass frequency of filter is equal to that of estimated signal when filter's parameter is tuned to right value,and square of filter's output reaches its maximum.Because the band-pass can be set very narrow,signals except one with the band-pass frequency are attenuated much when pass the filter.Therefore,the proposed frequency estimation method is an anti-noise method.In this paper,the active vibration control on floating raft system is achieved by adaptive feed-forward control law with the core of Filtered x-Least Mean Square (LMS)algorithm.Influence imposed by system characteristics on Filtered x-LMS algorithm performance is studied,and a fact is realized that the performance of algorithm can be improved by increasing control path's damping ratio.Two realizations are given:damping compensation by forming close-loop subsystem and adaptive feed-forward damping compensation.Corresponding improved Filter x-LMS algorithms are derived,and the effectiveness and effect of them are confirmed by simulations.Active vibration control performs worse if the actuator saturation happens.An ideal anti-saturation strategy for adaptive feed-forward control is proposed in this paper.Its main idea is that the controller will stop updating when its output reaches the maximum amplitude allowed.Two different realizations in the form of LMS algorithm are put forward,which are anti-saturation LMS algorithm via continuous constraints on control quantity and predictive variable step anti-saturation LMS algorithm.Both the theoretical analysis and simulation results show their strict obedience to the saturation constraints along with the desirable control performance. In the end,algorithms mentioned above are widened to anti-saturation Filter x-LMS algorithms,which can be directly used in active vibration control.At the End of this paper,the experiment study on active vibration control of floating raft system is executed.A simulative floating raft system with 4 active absorbers is established firstly.Then,the optimal mounting positions of 4 active absorbers are determined by utilizing the wide-band criterion based on piecewise weighing area performance index.Finite Impulse Response(FIR)models of 16 control paths of system in 10～30Hz are identified offline by LMS algorithm.The experiment of active vibration control on simulative floating raft system is then carried out.In the experiment,the floating raft is excited by mono-frequency simple harmonic signal,and is controlled by multiple variables adaptive feed-forward control law based upon predictive variable step anti-saturation Filtered x-LMS algorithm.The reference signal is man-made,of which the frequency is estimated by adaptive band-pass filter.Experiments results demonstrate that the damping ability of simulative floating raft system in experimental frequency band is significantly improved by active vibration control methods proposed in this paper.