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Aims at increasing the wing's lift and weakening the wing's shock wave, flow active control is studied by using the fluid mechanics. A new active control method based on piezoelectric elements is proposed, in which piezoelectric elements are buried on upper surface of winginduces periodic disturbance of boundary layer. The numerical simulation of the aerodynamic characteristics during the deformation process is done using the structural grid and the unsteady flow calculation method. The effect of piezoelectric elements on increasing the lift and weakening the shock of the aircraft wing is analyzed using computational fluid dynamics (CFD). Most previous studies were confined in a two-dimensional air-foil numerical simulation. In this article, its computing method is extended to a three-dimensional wing model to verify the validity of the new control method. Research shows that through appropriate parameter optimization, partial active deformation can improve the aerodynamic characteristics of airfoil. With the low roach number, the lift coefficient can be increased by 15% and the drag coefficient can be descended by 16%. The shock wave will move backward by control in the condition of high roach number and the lift coefficient of symmetrical airfoil can be improved by 17%. The self-adaptive wing can meet aerodynamic needs in variety of conditions. [ABSTRACT FROM AUTHOR]

Abstract: Considering the spillover and harmonic effect in real active vibration control, a novel composite controller based on disturbance observer (DOB) for the all-clamped panel is presented. The single-mode of the piezoelectric panel can be regarded as a second-order system. The unmodeled error of the current controlled mode, harmonic effects, uncontrolled mode effects, etc., are regarded as the lumped disturbances which can be estimated by the DOB, and the estimated value is used for the feed-forward compensation design. Then, an optimal linear quadratic regulator (LQR) strategy is employed for the feedback design. In order to solve the difficulty of determining the weight matrices of LQR, a chaos optimization method based on logistic map is proposed. So the weight matrices can be tuned automatically. Combining with a new transient performance function, the optimal weight matrices can be obtained. The composite controller can effectively suppress the lumped disturbances of the all-clamped panel. Experiment comparisons with conventional LQR are given to verify the effectiveness of the proposed method. [Copyright &y& Elsevier]

Abstract: This paper presents a new self-powered vibration damping technique, which is an application of the enhanced synchronized switching harvesting technique. Compared with other self-powered vibration damping techniques, it not only shows its robustness (particularly facing environmental drifts), but also can harvest the energy and supply power to other electronic circuits, while does not simply dissipate the electrical energy. Experimental results show that a vibration damping of about 5dB is achieved as a result of energy harvesting, in good agreement with the theory. In addition, the vibration damping system can be not only self-powered, but also supply power to other electronic circuits. In other words, there is a good trade-off between energy scavenging and vibration damping. Along with experimental results demonstrating the effectiveness of the ESSH implementation, we discuss the design of a device aimed at bridging the gap between research in this area and practical application. [Copyright &y& Elsevier]

Abstract: The synchronized switch damping (SSD) approaches based on piezoelectric actuators have been successfully used in multimode vibration control of structures. By suppressing voltage inversion at some displacement extrema, the control performance of SSD approaches can be significantly improved. In this study, conversion of energy from mechanical to electrical in two-mode control is analyzed for different amplitude ratios and frequency ratios. The results show that the converted energy in two-mode control with voltage inversion at every extremum is smaller than the sum of the energies of the two modes in single-mode control, but the converted energy of the second mode in two-mode control may exceed that in single-mode control when the amplitude ratio of the second mode to the first mode is small enough. The influence of voltage threshold used to suppress voltage inversion on energy conversion of the system and each individual mode is also investigated. The converted energy of the first mode in two-mode control may be much larger than that in single-mode control when voltage inversion is suppressed suitably. The analytical results can successfully explain the phenomenon in the previous control experiments and can also be extended to multimode control. [Copyright &y& Elsevier]

Abstract: In this paper, a new switch control strategy based on an energy threshold is proposed for the synchronized switch damping techniques in multimode control. This strategy is derived from the total converted energy of a synchronized switch damping (SSD) system in a given time window. Using the new strategy the voltage is inverted only at those extrema where the effective distance, which is proportional to the converted energy between two neighboring extrema, exceeds the threshold. The new switch control strategy is used in both the synchronized switch damping on inductor (SSDI) technique and the synchronized switch damping on voltage source (SSDV) technique, which are applied to the two-mode control of a composite beam. Their control performances are compared with those of the single-mode control and those of classical SSDI and SSDV techniques in two-mode control. The experimental results show that voltage inversion is prevented at some of the displacement extrema to increase the total converted energy, and exhibit better global damping effect than classical SSDI and classical SSDV, respectively. In single mode, the best control performance is achieved when the voltage is inverted at every extremum. But in multimodal control, the total converted energy in a given time window is increased and the control performance is improved when some extrema are skipped. [Copyright &y& Elsevier]

Highlights • A GVM is used to characterize an unknown and complex structural component. • Damage detection based on GVMI approach is developed. • The key parameters on detection resolution are investigated. • Results in honeycomb sandwich structure show the validity of damage detection without any blind area. Abstract This paper presents a novel vibration-based damage detection method using a general vibration model identification (GVMI) approach. A damage index based on the identified general vibration model is constructed for damage detection and localization, with the damage being regarded as a virtual excitation on the structure. The proposed GVMI approach utilizes a general form of high order derivative equation that to be identified and further used to detect changes in the vibration characteristics of the structure. Therefore, the proposed damage detection method requires neither baseline signals nor prior knowledge on the structural parameters, thus offering great application potentials for complex structures with unknown parameters. As a proof-of-concept example, a honeycomb sandwich cantilever beam is investigated for validating the proposed approach. The influences of the key parameters on the detection resolution, such as the measurement interval, the order of the displacement derivative and the selection of the excitation frequency, are investigated. Furthermore, an enhanced version of the GVMI method with an excitation frequency extension is developed by using a data fusion scheme. Taking advantages of the broadband excitations, the blind inspection area can be completely eliminated, whilst improving the effectiveness and the accuracy of the detection. Experimental results with both single and multiple structural damage show the validity and the accuracy of the proposed approach. [ABSTRACT FROM AUTHOR]

Noise and vibration induced by turbulent boundary layer (TBL) wall pressure is a widespread issue for aircrafts and vehicles. One way to alleviate this problem is to enhance the structure’s sound isolation performance using active structural acoustic control. It is often difficult and costly to generate TBL excitation in laboratories for academic research, especially when the convection velocity is high. Thus, a numerical investigation in the early stages of research is appropriate. This paper proposes a prototyping method. The updated TBL semi-empirical model is chosen through a detailed survey of relevant literature. A tensioned panel used as a control target is intended to simulate realistic aircraft flight conditions. Decentralized control law is considered for active control. A finite element model is built which takes into account the property of TBL excitation. A model reduction technique is also adopted to decrease the order of the analysis model. Numerical simulation results show that the pre-stress effect and the hydrodynamic coincidence have a significant influence on plate vibro-acoustic performance and control channel number selection. Decentralized control of the tensioned plate structure under the pressure of TBL excitation is revealed in this work. A virtual prototyping loop justifies the control law’s effectiveness for analyzing TBL excitation. Finally, the procedure proposed may be extended to use in other models or real-life applications. [ABSTRACT FROM AUTHOR]

This paper proposes a new energy harvesting architecture that optimizes the energy conversion under broadband vibrations, which is called adaptive synchronized switch harvesting (ASSH) technique. This technique is derived from the enhanced synchronized switch harvesting (ESSH) technique and based on a new and effective switch control law, which can prevent the switch in energy transferring circuit from over-frequent on-and-off and accordingly enhance the extracted power under multimode vibration. Compared with the ESSH technique, theoretical and experimental results demonstrate the new technique can improve electromechanical conversion efficiency when the piezoelectric energy harvester is excited under two-mode vibration, especially in the case of higher vibration amplitude of the second mode. The extracted power with the new technique is more than three times the ESSH technique in the case of the exciting signal of amplitude ratio (3:6). Furthermore, a self-powered circuit which implements the technique (ASSH) is proposed, which validates that the new technique can be truly self-powered, thus addressing the issue of harvesting environmental energy by autonomous devices. [ABSTRACT FROM AUTHOR]

Most research about using piezoelectric stacks to suppress vibration of mechanical structures didn't involve the similarity problem for the piezoelectric stacks. The goal of this paper is to investigate the dynamic similarity between a prototype piezo stack and a scaled up or down piezo stack, whilst discussing the feasibility of predicting the vibration of prototype structure which use the piezoelectric stacks for vibration control. To illustrate this problem concisely, a single-DOF system consists of a proof mass and a piezo stack shunted with a series RL circuit is considered. Firstly, the governing equation of such piezo-electromechanical system in frequency domain is derived. Next the dynamic similarity of prototype and model stack is analyzed by similitude theory. After that the scaling laws are derived. Finally, a numerical simulation and relative error analysis are given to demonstrate the scaling laws. [ABSTRACT FROM AUTHOR]

• The bandgap of a periodic ABH strip is dominated by two flexural wave modes. • There are two types of bandgaps with one satisfying Bragg condition. • The mechanism of the attenuation band splitting is clarified. • The method of tuning attenuation band splitting is investigated. Acoustic black holes (ABH) lattice is an effective way to realize the bandgaps (BGs) through lightweight design. The predicted BGs using infinitely large periodic structures are commonly believed to enable corresponding attenuation bands (ABs) even the structure only contains a limited number of unit cells. This paper reports an unusual splitting phenomenon in the ABs of a finite plate strip with two-dimensional (2D) ABHs. A wide AB predicted by BG is split into two ABs in the finite strip separated by a high resonance peak, which challenges the aforementioned common belief. Results show that the increasing number of periodic unit cells has a negligible effect on the frequency and amplitude of the resonance peak. Its underlying mechanism is clarified by investigating the relationship between the BGs and ABs, obtained from infinite and finite periodic plate strips with the same 2D ABHs respectively. Complex wavenumber analysis results show the existence of two flexural wave modes in the considered frequency range due to the finite width of the strip. Two types of BGs, in which one satisfies the Bragg condition, are found when both wave modes fail to propagate. Analysis of structural modes further uncover the physical reason for the emerging AB splitting: a certain natural frequency of the boundary portion of the 2D ABHs strip falling into the theoretical BG. Due to the boundary reflection and energy concentration, this structural portion can loosely be regarded as a clamped-free plate strip. It is demonstrated that the resonance peak splitting the AB becomes tunable via disrupting the structural details of finite ABH strips. In particular, extending the terminal end of a finite ABH strip allows the change in boundary portion, which is conducive to eliminating the splitting peak. The reported study is helpful for the design of finite periodic structures with broadband attenuation bandgap. [ABSTRACT FROM AUTHOR]