Summary

ACTIVE VIBRATION CONTROL AND SUPPRESSION FOR INTELLIGENT STRUCTURES

Recently, the necessity of lighting and high-speed for the machines is increasing. This paper concerns the vibration and motion control by the the control system which combined a servo controller with a hybrid dynamic absorber. In our method, the vibration control and the servo control are designed independently. Firstly, the dynamics of the tower structure and the servo motor are modeled. It is shown experimentally that although vibration control by the servo controller alone causes the instability due to nonlinear elements such as the friction or the rattle, the hybrid dynamic absorber is hard to cause this sort of the instability. On the comparison of the vibration control effect and the control force, the hybrid dynamic absorber needs the less force. Finally, to know its effect we evaluated the motion (triangle wave, sine wave) of the flexible structure. Effectiveness of this vibration and motion control method to the flexible structure is demonstrated by simulation and experiment.

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.

The synthesis of structural identification with vibration control is cost-effective and beneficial for developing smart building structures. In the past several decades, techniques have been put forward for the combination of structural identification and vibration control. However, it is still a challenging task to synthesize identification and vibration control of time-varying structures under unknown earthquake excitation. First, structural dynamic responses collected by a structural health monitoring (SHM) system are absolute responses under unknown earthquake excitation, so existing identification approaches for unknown external excitations are not applicable for this situation. Moreover, it is essential to have an efficient algorithm for accurately tracking the various scenarios of time-varying structural physical parameters with inexpensive computation to ensure the real-time performance requested by structural vibration control. In this paper, an algorithm is put forward to tackle this challenging problem. It is proposed to treat structural time-varying effect as “virtual unknown inputs” to the corresponding time-invariant structure. A generalized extended Kalman filtering with unknown input (GEKF-UI) is proposed to circumvent the limitations of the existing EKF-UI approaches. The proposed GEKF-UI can simultaneously identify structural system, unknown earthquake excitation, and the “virtual unknown inputs” using only partially measured structural absolute responses. Then, the identified structural state is synthesized in real time with the instantaneous optimal control strategy for optimal semiactive control provided by magnetorheological dampers. Therefore, the proposed algorithm can track various structural time-varying with much less computation, which is more suitable for synthesis with structural control compared with other existing approaches. Some numerical cases of synthesizing identification and vibration control of various type time-varying structures under unknown earthquake motion are adopted to investigate the feasibilities of the proposed algorithm.

With the development of economy, many tall buildings, slender towers, offshore platforms and long bridges have been built, which are subjected to huge dynamic loadings from winds, earthquakes, water waves and human motions. The large vibration amplitude can spoil the structures or the secondary components or cause discomfort to its human occupants (Kareem et al., 1999). Therefore, many control theories and methods were developed. Yao (Yao, 1972) put forward the control method for the first time based on control theory of civil structure vibration, followed by rapid development of the theory and method of structural vibration control (Spencer Jr and Nagarajaiah, 2003, Den Hartog, 1985). Structural vibration control based on external energy input can be divided into active, passive, semi-active, and mixed control.

For the harshness of launch load, in-orbit disturbance and thermal load, vibration and shape control are crucial to the success of large deployable antennas. This article addresses the implementation of electromagnetic damping in vibration and shape control of a large deployable antenna. Mechanical-electromagnetic coupling of the damping is analyzed theoretically. Simulations of SDOF systems with the electromagnetic damping are conducted and control efficiencies of the damping for vibration isolation, vibration absorption and shape control are verified. Vibration isolation of the antenna under launch load, vibration absorption of the antenna under in-orbit disturbance and shape control of the antenna under thermal load are studied, and the control results show that the proposed electromagnetic damping provides a promising control method for vibration and shape control of large space structures.

In many dynamic systems such as robot and aerospace areas, flexible structures have been extremely employed to satisfy various requirements for large scale, light weight and high speed in dynamic motion. However, these flexible structures are readily susceptible to the internal/external disturbances (or excitations). Therefore, vibration control schemes should be exerted to achieve high performance and stability of flexible structure systems. Recently, in order to successfully achieve vibration control for flexible structures smart materials such as piezoelectric materials [1-2], shape memory alloys [3-4], electrorheological (ER) fluids [5-6] and magnetorheological (MR) fluids [7] are being widely utilized. Among these smart materials, ER or MR fluid exhibits reversible changes in material characteristics when sub‐ jected to electric or magnetic field. The vibration control of flexible structures using the smart ER or MR fluid can be achieved from two different methods. The first approach is to replace conventional viscoelastic materials by the ER or MR fluid. This method is very effec‐ tive for shape control of flexible structures such as plate [5]. The second approach is to de‐ vise dampers or mounts and apply to vibration control of the flexible structures. This method is very useful to isolate vibration of large structural systems subjected to external excitations [6-7]. In this work, a new type of MR mount is proposed and applied to vibration control of the 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 proposes the vibration control method of flexible structures arranged in parallel. In recent years, vibration control of a flexible structures using an active dynamic absorber has increasingly been utilized in practical applications. In the future, as the structure becomes more advanced and more flexible, its natural frequency gradually becomes lower. Thus, it will be difficult to assume enough force for vibration control using an active dynamic absorber. The authors proposed the method wherein two structures arranged in parallel are controlled actively using two actuators set between them. In general, a reduced-order-model is necessary to design a controller using the LQ control theory. Using the modeling method proposed here, reduced-order model of the 2-2 degree-of-freedom parallel structures can be easily fabricated. Using a root locus plot, the relationship between weighting parameters and control effect in the LQ control theory is clarified. It is demonstrated that this control method is able to control vibrations of 2-2 DOF system without the spillover instability, by simulation and experiment.

Inerter-based structural vibration control: A state-of-the-art review

Sheeted or fibrous piezoelectric devices have been recently developed as actuators or sensors. These light and flexible devices are expected to create many innovative methods for the vibration control of structures. In this paper, we discuss the active control of vertical and horizontal micro-vibration of an architectural frame structure using Macro Fiber Composites (MFCs). MFCs are sheeted piezoelectric devices constructed with fibrous piezoceramics that can produce relatively higher forces than other sheeted piezoelectric devices. We arranged MFCs at the lower flange of both ends of a beam as actuators. By the expansion and contraction of the MFC actuators, bending moments act at both ends of the beam. The synchronized movements of the MFC actuators control the vertical vibration of the beam or slab. The opposite phase movements control the horizontal vibration of the frame structure. MFCs used as sensors are arranged at arbitrary positions on the lower flange surface. An experiment of vertical and horizontal vibration control on a scaled frame model is conducted and the results show that the control method effectively minimizes the resonant vibration. A vertical vibration control test on a real architectural structure is also conducted. The MFCs are arranged at the ends of two beam-spanning girders. Consequently, the vertical floor vibration of 0.04 m/s 2 at 8.5 Hz at the center of the grid was reduced to 0.01 m/s 2 or about −12 dB.

Active control of structural vibrations requires sensors for control feedback. Strain rate sensing for vibration control is important for implementing effective control schemes. Here, an advanced strain rate sensor for active control of structural vibrations is presented. This rate sensor is based on electromagnetic principles. Technology development for this strain rate sensing method is complete; desirable resolution, noise rejection, fidelity, frequency response, and mass for control of structures applications are demonstrated. A structurally integral application of this technology to the NASA CSI Evolutionary Model is presented.

Attaching a piezoelectric transducer to a vibrating structure, and shunting it with an electric circuit, gives rise to different passive, semi-passive, and semi-active control techniques. This paper attempts to review the research related to structural vibration control, via passive, semi-passive, and semi-active control methods. First, the existing electromechanical modeling is reviewed, along with the modeling methods. These range from lumped parameters, to distributed parameters modeling of piezostructural systems shunted by electrical networks. Vibration control laws are then discussed, covering passive, semi-passive, and semi-active control techniques, which are classified according to whether external power is supplied to the piezoelectric transducers, or not. Emphasis is placed on recent articles covering semi-passive and semi-active control techniques, based upon switched shunt circuits. This review provides the necessary background material for researchers interested in the growing field of vibration damping and control, via shunted piezostructural systems.

Active robust vibration control of flexible structures

This review presents an up-to-date account of research in multi-hazard assessment and vibration control of engineering structures. A general discussion of the importance of multi-hazard consideration in structural engineering, as well as recent advances in this area, is presented as a background. In terms of performance assessment and vibration control, various hazards are considered with an emphasis on seismic and wind loads. Although multi-hazard problems in civil engineering structures are generally discussed to some extent, the emphasis is placed on buildings, bridges, and wind turbine towers. The scientific literature in this area is vast with rapidly growing innovations. The literature is, therefore, classified by the structure type, and then, subsequently, by the hazard. Main contributions and conclusions from the reported studies are presented in summarized tables intended to provide readers with a quick reference and convenient navigation to related publications for further research. Finally, a summary of the literature review is provided with some insights on knowledge gaps and research needs.