Bandgap adjustment of a sandwich-like acoustic metamaterial plate with a frequency-displacement feedback control method

Several types of acoustic metamaterials composed of resonant units have been developed to achieve low-frequency bandgaps.In most of these structures,bandgaps are determined by their geometric configurations and material properties.This paper presents a frequency-displacement feedback control method for vibration suppression in a sandwich-like acoustic metamaterial plate.The band structure is theoretically derived using the Hamilton principle and validated by comparing the theoretical calculation results with the finite element simulation results.In this method,the feedback voltage is related to the displacement of a resonator and the excitation frequency.By applying a feedback voltage on the piezoelectric fiber-reinforced composite(PFRC)layers attached to a cantilever-mass resonator,the natural frequency of the resonator can be adjusted.It ensures that the bandgap moves in a frequency-dependent manner to keep the excitation frequency within the bandgap.Based on this frequency-displacement feedback control strategy,the bandgap of the metamaterial plate can be effectively adjusted,and the vibration of the metamaterial plate can be significantly suppressed.

Bandgaps and vibration isolation of local resonance sandwich-like plate with simply supported overhanging beam

The concept of local resonance phononic crystals proposed in recent years provides a new chance for theoretical and technical breakthroughs in the structural vibration reduction.In this paper,a novel sandwich-like plate model with local resonator to acquire specific low-frequency bandgaps is proposed.The core layer of the present local resonator is composed by the simply supported overhanging beam,linear spring and mass block,and well connected with the upper and lower surface panels.The simply supported overhanging beam is free at right end,and an additional linear spring is added at the left end.The wave equation is established based on the Hamilton principle,and the bending wave bandgap is further obtained.The theoretical results are verified by the COMSOL finite element software.The bandgaps and vibration characteristics of the local resonance sandwich-like plate are studied in detail.The factors which could have effects on the bandgap characteristics,such as the structural damping,mass of vibrator,position of vibrator,bending stiffness of the beam,and the boundary conditions of the sandwich-like plates,are analyzed.The result shows that the stopband is determined by the natural frequency of the resonator,the mass ratio of the resonator,and the surface panel.It shows that the width of bandgap is greatly affected by the damping ratio of the resonator.Finally,it can also be found that the boundary conditions can affect the isolation efficiency.

Actively tunable sandwich acoustic metamaterials with magnetorheological elastomers

Sandwich structures are widespread in engineering applications because of their advantageous mechanical properties.Recently,their acoustic performance has also been improved to enable attenuation of low-frequency vibrations induced by noisy environments.Here,we propose a new design of sandwich plates(SPs)featuring a metamaterial core with an actively tunable low-frequency bandgap.The core contains magnetorheological elastomer(MRE)resonators which are arranged periodically and enable controlling wave attenuation by an external magnetic field.We analytically estimate the sound transmission loss(STL)of the plate using the space harmonic expansion method.The low frequency sound insulation performance is also analyzed by the equivalent dynamic density method,and the accuracy of the obtained results is verified by finite-element simulations.Our results demonstrate that the STL of the proposed plate is enhanced compared with a typical SP analog,and the induced bandgap can be effectively tuned to desired frequencies.This study further advances the field of actively controlled acoustic metamaterials,and paves the way to their practical applications.

WAVE PROPAGATION IN TWO-DIMENSIONAL DISORDERED PIEZOELECTRIC PHONONIC CRYSTALS

The wave propagation is studied in two-dimensional disordered piezoelectric phononic crystals using the finite-difference time-domain （FDTD） method. For different cases of disorder, the transmission coefficients are calculated. The influences of disorders on band gaps are investigated. The results show that the disorder in the piezoelectric phononic crystals has more significant influences on the band gap in the low frequency regions than in the high frequency ones. The relation between the width of band gap and the direction of position disorder is also discussed. When the position disorder is along the direction perpendicular to the wave transmission, the piezoelectric phononic crystals have wider band gaps at low frequency regions than the case of position disorder being along the wave transmission direction. It can also be found that the effect of. size disorder on band gaps is analogous to that of location disorder. When the perturbation coefficient is big, it has more pronounced effects on the pass bands in the piezoelectric phononic crystals with both size and location disorders than in the piezoelectric phononic crystals with single disorder. In higher frequency regions the piezoelectric effect reduces the transmission coefficients. But for larger disorder degree, the effects of the piezoelectricity will be reduced.

Experimental study on out-of-plane seismic performance of precast composite sidewalls of utility tunnel with grouting-sleeve joints

The precast composite reinforced concrete wall with the advantages of fewer joints,superior impermeability and rapid construction provides an efficient and environmental friendly alternative in the construction of underground utility tunnels in the last few years.To investigate the seismic performance of precast concrete composite walls of utility tunnels with grouting-sleeve connection under out-ofplane loads,a series of quasi-static cyclic tests were performed on the full-scale sidewall specimens with different axial compression ratios in this study.The experimental results including the failure modes,crack distributions,and the influence of different connections on the out-of-plane seismic performance of precast concrete composite wall were carefully examined and compared with those from the cyclic tests of the cast-in-place sidewalls of the utility tunnel.The test results show that the seismic performance of the precast concrete composite sidewall specimen,such as the hysteresis curves,the ultimate bearing capacity,stiffness degradation pattern and the ductility ratio,is basically the same as that of the cast-in-place specimen,indicating that the seismic performance of the prefabricated structure is equivalent to that of the cast-in-place structure.Moreover,the grouting-sleeves of the joints can effectively transfer the reinforcement stress until the failure of the precast concrete composite sidewall specimens,which exhibits excellent out-of-plane ductility and serviceability.

Flutter and Thermal Buckling Properties and Active Control of Functionally Graded Piezoelectric Material Plate in Supersonic Airflow

This paper is devoted to investigate the flutter and thermal buckling properties of the functionally graded piezoelectric material(FGPM)plate in supersonic airflow,and the active flutter control is carried out under different temperature fields.The piezoelectric material component of the FGPM plate has gradient changes along the thickness,such as piezoelectricity and dielectric coefficients.The supersonic piston theory is used to evaluate the aerodynamic pressure.Based on the first-order shear deformation theory and Hamilton’s principle with the assumed mode method,the equation of motion of the structural system is deduced.The effect of aerodynamic pressure on the frequency and damping ratio of the FGPM plate is analyzed.Moreover,the flutter and thermal buckling properties of the FGPM and pure metal plates are compared to show the superior aerothermoelastic properties of the FGPM plates.The influences of volume fraction exponent and temperature on the flutter and thermal buckling properties of the FGPM plate are also examined in detail.The LQR controller is adopted to achieve active flutter control.The simulation results show that the present control method can largely improve dynamic stability of the FGPM plate in supersonic airflow and high-temperature environment.

Active Control of Thermo-mechanical Buckling of Composite Laminated Plates Using Piezoelectric Actuators

This paper is concerned with the active control of thermomechanical buckling of composite laminated plates using piezoelectric facesheets as actuators.The four-variable trigonometric shear deformation theory and Hamilto's principle are applied to formulate the governing equation of structural system.The temperature feedback control strategy is proposed to conduct the active control of thermal-mechanical buckling.The simulation results show that the thermo-mechanical buckling of composite laminated plates can be effectively controlled by the presented control method.With a specific control gain,the critical mechanical buckling load can remain constant at different temperatures.The effects of geometric parameters,fiber angle,stacking sequence,position of piezoelectric layer and boundary conditions on the active control of thermo-mechanical buckling are also investigated.

A BCH error correction scheme applied to FPGA with embedded memory

Given the potential for bit flipping of data on a memory medium,a high-speed parallel Bose-Chaudhuri-Hocquenghem(BCH)error correction scheme with modular characteristics,combining logic implementation and a look-up table,is proposed.It is suitable for data error correction on a modern field programmable gate array full with on-chip embedded memories.We elaborate on the optimization method for each part of the system and analyze the realization process of this scheme in the case of the BCH code with an information bit length of 1024 bits and a code length of 1068 bits that corrects the 4-bit error.

Random Vibration Control of Laminated Composite Plates with Piezoelectric Fiber Reinforced Composites

This paper presents an analysis of the active control of random vibration for lami- nated composite plates using piezoelectric fiber reinforced composites （PFRC）. With Hamilton＇s principle and the Rayleigh-Ritz method, the equation of motion for the resulting electromechani- cal coupling system is derived. A velocity feedback control rule is employed to obtain an effective active damping in the suppression of random vibration. The power spectral density and mean- square displacements of the random vibration for laminated plates under different control gains are simulated and the validity of the present control strategy is confirmed. The effect of piezoelec- tric fiber orientation in the PFRC layer on the random vibration suppression is also investigated. The analytical methodology can be expanded to other kinds of random vibration.