Optimal structural modifications to enhance the optimal active vibration control of large flexible structures

Active vibration control of large flexible space structure is a challenging topic in the system dynamics and control of spacecraft. This paper proposes a novel approach for vibration control on a large hoop truss structure, typically used as mesh satellite antenna. First, to suppress the first-order bending modal response of the hoop truss structure with an initial disturbance, a piezoelectric bending actuator with excellent bending actuation performance was carefully designed as a key component of an active vibration control system. Then, the actuating characteristics of the actuator and the dynamic equations of the active structure were analyzed and formulated based on a finite element method. In order to improve the vibration-attenuating effect of the control system, a Mamdani-type fuzzy logic algorithm was employed in a closed-loop control system. Finally, simulations and experiments were implemented to validate the effectiveness of the proposed active control approach and structure. The experimental results showed that the decay time of first-order bending modal response (around 0.34 Hz) of control system reduces by 75% compared with that of the uncontrolled system. The results demonstrate that the proposed active vibration control system has good application potential in controlling the bending modes of a large flexible spacecraft.

Sliding mode control of a large flexible space structure

Active robust vibration control of flexible structures

The interest of this paper is to develop a general and systematic robust control methodology for active vibration control of flexible structures. For this purpose, first phase and gain control policies are proposed to impose qualitative frequency-dependent requirements on the controller to consider a complete set of control objectives. Then the proposed control methodology is developed by employing phase and gain control policies in the dynamic output feedback H∞ control: according to the set of control objectives, phase and gain control policies incorporate necessary weighting functions and determine them in a rational and systematic way; on the other hand, with the appropriate weighting functions efficient H∞ control algorithms can automatically realize phase and gain control policies and generate a satisfactory H∞ controller. The proposed control methodology can be used for both SISO and MIMO systems with collocated or non-collocated sensors and actuators. In this paper, it is validated on a non-collocated piezoelectric cantilever beam. Both numerical simulations and experimental results demonstrate the effectiveness of the proposed control methodology.

This paper advances a unified theory for the modalspace control method developed by these authors for the control of large flexible structures and places the theory on a more rigorous foundation. The unified approach permits the simultaneous treatment of a broad spectrum of interrelated problems. In particular, the theory is valid for both nongyroscopic and gyroscopic systems and for systems with ignorable coordinates resulting from rigid body motions. In addition, it permits a convenient way of studying the question of control spillover. The modal-space control method is different from any other modal control method in that it provides both internal (plant) and external (controller) decoupling.

A semi-active shunted piezoelectric tuned-mass-damper for multi-modal vibration control of large flexible structures

Different kinds of membrane structures have been proposed for future space exploration and earth observation. However, due to the low stiffness, high flexibility, and low damping properties, membrane structures are likely to generate large-amplitude (compared to the thickness) vibrations, which may lead to the degradation of their working performance. In this work, the governing equations are established at first, taking into account the modal control force induced by the polyvinylidene fluoride (PVDF) actuator. The optimal vibration control of the membrane structure is explored subsequently. A square PVDF actuator is attached on the membrane to achieve the vibration suppression. The influence of actuator position and control gains on the vibration control performance are studied. The optimal criteria for actuator placement and energy allocation are developed. Several case studies are numerically simulated to demonstrate the validity of the proposed optimization criteria. The analytical results in this study can serve as guidelines for optimal vibration control of membrane structures. Additionally, the proposed optimization criteria can be applied to active control of different flexible structures.

This paper presents investigations of modeling the flexible plate structures using particle swarm optimization (PSO) and active vibration control (AVC) of such structures. The optimization technique is utilized to obtain a dynamic model of a flexible plate structure based on auto-regressive with exogenous (ARX) input structure. The structure is subjected to two different disturbance signal types, namely random, and finite duration step. The fitness function for the PSO is the mean-squared error (MSE) between the measured and estimated outputs of the plate. The validation of the algorithm is presented in both time and frequency domains. The developed PSO modeling approach is used for AVC system design to suppress the vibration of the flexible plate. The performance of the controller is assessed in terms of level of attenuation achieved in the power spectral density (PSD) of the observed signal.

An area of current interest in the decentralized control of large flexible structures is the development of adaptive strategies that will allow for acceptable vibration suppression and tracking in the presence of uncertainties. One such strategy is the Gavel-Siljak approach, which is based upon direct control using adaptive gains. The approach treats the interconnections effects between subsystems as uncertain quantities. The current study is aimed at examining the appropriateness of such an algorithm for the control of multibody flexible structures. A two body simulation model is developed. The application of the adaptive control algorithm to this structure is discussed in the context of the simulation model. Results using this model are presented and discussed.

A new active control performance index for vibration control of three-dimensional structures

This study provides a method of vibration control of large space structures by simultaneously integrating the structure and control design to reduce the structural response from a disturbance. The formulation of the design scheme is obtained by the structural modification of some nominal finite element model, which is controlled in an optimal fashion by a linear regulator, to increase the active modal damping factor beyond that of the nominal structure. The structural modifications are achieved by using a nonlinear mathematical optimization technique. The objective function is the weight of the structure with a constraint on the damping parameter of the closedloop system. The application of the algorithm is illustrated by designing an ACOSS-FOUR model with different constraint values.

In this paper we propose an active vibration control method for multiple high-rise buildings arranged in parallel. According to the proposed method, some flexible buildings connected by control devices called "active control bridges", are controlled through active interactions among them. This method has the merit of achieving sufficient control force under low frequency. Using this method, it is possible to control vibrations of super-tall buildings against strong winds and large earthquakes. In this study, three model buildings are connected with two actuators. The objective of this research is to control the first bending and torsional modes of each building using this method. The control effect is evaluated by exciting the base of the structures by time response and measuring the frequency response of the structures. Both simulation and experimental results show that fairly good control performance has been achieved by this method.

A new method is devised for the active control of flexible structures using output rate weighted linear optimal control. The method has an advantage over the traditional linear optimal control method in that it assigns weightage to the time rate-of-output, which may not be available for direct measurement in several important applications, such as gust and maneuver load alleviation in airplanes and ridequality augmentation in a variety of passenger vehicles. In applications to a single degree-offreedom system and a cantilevered beam, the rate-weighted optimal controller demonstrates a much better performance in terms of the smoothness of transient response, peak rate of transient response and settling time when compared to the traditional linear quadratic regulator. Introduction Generally, there are three different approaches applied to controlling flexible structures: (a) passive addition of structural damping and stiffness (b) generating specificaNy shaped input&* ,and (c) designing an optimal feedback controlle?S4. The first option is usually cumbersome and adds mass to the structure, while the second option, requiring generation of inputs that are insensitive to modeling errors and which do not excite unwanted dynamics, is di&tilt to achieve in practice. This leaves the third option of an active feedback controller as the most practical choice for controlling structural dynamics. The optimal linear *Assistant Professor, Department of Aerospace Engineering. Senior Member, AIAA. Copyright

This paper studies the feasibility of self-powered active vibration control of structures with Tuned Mass Dampers (TMDs). Without consuming external energy, the proposed self-powered vibration control strategy can provide better performance than the passive TMD in mitigating the vibration of buildings induced by wind load. the vibration-dissipative element of TMD is replaced with an electromagnetic machine, which serves as actuator and harvester at the same time. First, the desired force is obtained by adopting Linear Quadratic Regulator (LQG) optimal control. Then, the self-powered active control strategy is designed based on the essence of the desired force, which can be passive or active types. The energy of the vibration can be harvested as electricity in energy harvesting mode, and pumped back into the mechanical system when instant active force is required. Switch based circuits with capability of bi-directional power flow are presented for the implementation of self-powered active TMDs. With taking the efficiency of the harvesting and driving circuits into account, numerical simulations are carried out based on a tall building with a TMD under random and harmonic excitations. The results indicate the feasibility and effectiveness of self-powered active TMDs.

The synthesis of structural health monitoring and vibration control is important in order to provide facilities for constructing smart structures. In recent years, some techniques have been developed to integrate structural identification and optimal vibration control. However, it is still challenging to integrate the identification and vibration control of time-varying structures subject to unknown earthquake excitation. The main difficulties are that structural dynamic responses collected by a simple harmonic motion system are absolute responses under unknown earthquake ground motion while previous identification approaches for unknown external excitation are not applicable for this situation and the need of an efficient algorithm to accurately track the various scenarios of time-varying structures with inexpensive computation to ensure the real-time performance requested by structural vibration control. In this paper, a novel algorithm is presented, in which structural time-varying parameters are treated as ‘virtual unknown inputs’ to the underlying time-invariant structure, a generalized Kalman filter with unknown inputs is proposed for joint identification of joint structural state, unknown earthquake excitation and ‘virtual unknown inputs’ with only partially measured structural absolute responses, and the identification results are integrated in real-time with the instantaneous optimal control scheme to reach the goal of optimal semi-active control provided by magneto-rheological dampers. Some numerical examples of integrated identification and vibration control of various time-varying structures subject to unknown earthquake excitation are used to demonstrate the performances of the proposed algorithm.