利用压电陶瓷作动器对柔性悬臂梁正位反馈控制试验

目的验证压电陶瓷智能传感器和驱动器以及正位反馈控制对柔性结构主动控制的有效性.方法将压电陶瓷片分别作为传感器和作动器使用,并粘贴于铝制悬臂梁的表面,对其振动反应实施实时控制.试验过程分为2个阶段,第1阶段5 s为启振阶段,通过激励压电陶瓷作动器使结构产生振动;第2阶段为控制阶段.利用压电陶瓷传感器得到的反馈信号,通过正位反馈算法计算出控制信号.驱动压电陶瓷作动器对结构的振动响应进行实时控制.结果试验得到了模态振动控制与瞬时脉冲振动控制的振动响应曲线,并分别对有控与无控情况进行对比.结论试验结果证明利用压电陶瓷以及正位反馈控制算法能够有效抑制外界激励下的一阶、二阶模态振动和瞬时脉冲扰动引起的结构振动.

Improved suboptimal Bang-Bang control of aseismic buildings with variable friction dampers

One of the challenges in civil engineering is to find an innovative means of suppressing the structural vibration due to earthquake and wind loadings. This paper presents an approach for effectively suppressing vibrations of a structure with variable friction damper using a new Bang-Bang control input. A continuous function of story velocities is used to represent the improved control to reduce chatter, high frequency switching and avoid instability. With a genetic algorithm, the amplitudes of control and preloading friction forces individually prescribed in the controller and damper are optimized for enhancing the seismic performance of buildings. The control strategy for the friction damper is proposed for a three story building with one variable friction damper installed at the first story for seismic reduction. The numerical results indicate that a better reduction of peak response accelerations of floors can be achieved than those of the unmodified controller, and the adaptability of the control system is also improved greatly by comparison with the reduction ratios of the structural response energy excited by different earthquake intensities.

Water presence detection in a concrete crack using smart aggregates

Liquid migrating into existing concrete cracks is a serious problem for the reliability of concrete structures and can sometimes induce full concrete structural failures.In this paper,the authors present recent research on water presence detection in concrete cracks using piezoceramic-based smart aggregate(SA)transducers.The active sensing approach,in which one piezoceramic transducer is used to generate stress waves and others are used to detect the stress wave responses,is adopted in this research.Cracks formed in concrete structures act as stress reliefs,which attenuate the energy of the signals received by the SAs.In case of a crack being filled with liquid,which changes the wave impedance,the piezoceramic transducers will report higher received energy levels.A wavelet packet-based approach is developed to provide calculated energy values of the received signal.These different values can help detect the liquid presence in a concrete crack.A concrete beam specimen with three embedded SAs was fabricated and tested.Experimental results verified that the SA-based active sensing approach can detect a concrete crack and further detect the liquid presence in the concrete crack.

Wind turbine blade health monitoring with piezoceramic-based wireless sensor network

In this paper,a piezoceramic-based wireless sensor network(WSN)was developed for health monitoring of wind turbine blades with active sensing approach.The WSN system has an access point that coordinates the network and connects to a PC to control the wireless nodes.One wireless node functions as an actuator to excite an embedded piezoceramic patch with desired guided waves.The remaining wireless nodes function as sensors to detect and transmit the wave responses at distributed locations.The damage status inside the blade was evaluated through the analysis of the sensor signals.Based on wavelet packet analysis results,a damage index and a damage matrix were developed to evaluate the damage status at different locations.To verify the effectiveness of the proposed approach,a static loading test and a wind tunnel test were performed in the Laboratory of Joint Wind Tunnel and Wave Flume at Harbin Institute of Technology(HIT),China.Experimental results show that damage in wind turbine blades can be detected and evaluated by the proposed approach.

WiSeREmulator: An Emulation Framework for Wireless Structural Health Monitoring

Many competing approaches exist in evaluating sensor network solutions differing by levels of ease of use, cost, control, and realism. Existing work concentrates on simulating network protocols or emulating processing units at the machine cycle level. However, little has been done to emulate the sensors and the physical environments that they monitor. The main contribution of this work is the design of WiserEmulator, an emulation framework for structural health monitoring, which gracefully balances the trade-offs between realism, controllability, and cost. WiserEmulator consists of two main components -- a testbed of wireless sensor nodes and a software emulation environment. To emulate the excitation and response of piezo-electric transducers, as well as the wave propagation inside concrete structures, the COMSOL Multi-Physics software was utilized. Digitized sensing output from COMSOL was played back via a multi-channel Digital-to-Analog Converter （DAC） connected to the wireless sensor testbed. In addition to the emulation of concrete structures, WiSeREmulator also allows users to choose pre- stored data collected from field experiments and synthesized data. A user-friendly Graphical User Interface （GUI） was developed that facilitates intuitive configurations of experimental settings, control of the on-set and progression of the experiments, and real-time visualization of experimental results. We have implemented WiSeREmulator in MATLAB. This work advances the state of the art in providing low cost solutions to evaluating Cyber Physical Systems such as wireless structural health monitoring networks.

Multifunctional nanocomposite coating for wind turbine blades

In this study,multifunctional carbon nanofiber(CNF)paper-based nanocomposite coating was developed for wind turbine blades.The importance of vibration damping in relation to structural stability,dynamic response,position control,and durability of wind turbine blades cannot be underestimated.The vibration damping properties of the nanocomposite blades were significantly improved and the damping ratio of the nanocomposite increased by 300%compared to the baseline composite.In addition,the CNF paper-based composite exhibited good impact-friction resistance,with a wear rate as low as 1.78×10^(−4)mm^(3)/Nm.The nanocomposite also shows the potential to improve the blockage of water from entering the nanocomposite,being a superhydrophobic material,with a contact angle higher than 160.0◦,which could improve the longevity of a wind turbine blade.Overall,multifunctional nanocomposite coating material shows great promise for usage with wind turbine blades,owing to its excellent damping properties,great friction resistance,and superhydrophobicity.