Hongjun Xiang

Periodic materials-based vibration attenuation in layered foundations: experimental validation

Guided by the recent advances in solid-state research in periodic materials, a new type of layered periodic foundation consisting of concrete and rubber layers is experimentally investigated in this paper. The distinct feature of this new foundation is its frequency band gaps. When the frequency contents of a wave fall within the range of the frequency band gaps, the wave, and hence its energy, will be weakened or cannot propagate through the foundation, so the foundation itself can serve as a vibration isolator. Using the theory of elastodynamics and the Bloch–Floquet theorem, the mechanism of band gaps in periodic composites is presented, and a finite element model is built to show the isolation characteristic of a finite dimensional periodic foundation. Based on these analytical results, moreover, a scaled model frame and a periodic foundation were fabricated and shake table tests of the frame on the periodic foundation were performed. Ambient, strong and harmonic vibration attenuations are found when the exciting frequencies fall into the band gaps.

Theoretical analysis of piezoelectric energy harvesting from traffic induced deformation of pavements

The problem of energy harvesting using piezoelectric transducers for pavement system applications is formulated with a focus on moving vehicle excitations. The pavement behavior is described by an infinite Bernoulli–Euler beam subjected to a moving line load and resting on a Winkler foundation. A closed-form dynamic response of the pavement is determined by a Fourier transform and the residue theorem. The voltage and power outputs of the piezoelectric harvester embedded in the pavements are then obtained by the direct piezoelectric effect. A comprehensive parametric study is conducted to show the effect of damping, the Winkler modulus, and the velocity of moving vehicles on the voltage and power output of the piezoelectric harvester. It is found that the output increases sharply when the velocity of the vehicle is close to the so-called critical velocity.

Exact analysis of multi-layer piezoelectric/composite cantilevers

Both multi-layer piezoelectric cantilevers and multi-layer piezoelectric composite cantilevers are studied based on 2D linear theory of elasticity and piezoelectricity. Both the piezoelectric coefficient and the thickness for different layers are taken as variables. As opposed to traditional investigations based on the elementary theory of elasticity, the present investigation gives exact solutions for the variation of these parameters by introducing several recurrence formulae. The solutions obtained in the present paper are compared with numerical results and the results obtained by other investigators; good agreement is found.

Modeling on energy harvesting from a railway system using piezoelectric transducers

Theoretical models of piezoelectric energy harvesting from railway systems using patch-type and stack-type piezoelectric transducers are studied. An infinite Euler–Bernoulli beam on a Winkler foundation subjected to moving multi-loads is adopted to describe the dynamic behavior of railway track. The voltage and electric power of piezoelectric transducers installed at the bottom of a steel rail are derived analytically. Comparisons with earlier works and experimental results are given, indicating that the present solutions are reliable. Additionally, a parametric study is conducted to discuss the effects of axle loads, running velocity and load resistors on the solutions. The numerical results show that patch-type and stack-type piezoelectric transducers can harvest the available energy from track vibration to supply power for a wireless sensor network node and can also serve as sensors to monitor basic train information, such as the running velocity, the location and the axle load. The present investigations provide a theoretical guide in the design of piezoelectric patch and stack energy harvesters used in railway systems, which can serve as power sources for distributed wireless sensor networks in remote areas. The research results also demonstrate the potential of piezoelectric patches and stack harvesters in designing self-powered wireless sensor networks used in railway systems to ensure train operation safety.

Locally resonant periodic structures with low-frequency band gaps

Presented in this paper are study results of dispersion relationships of periodic structures composited of concrete and rubber, from which the frequency band gap can be found. Two models with fixed or free boundary conditions are proposed to approximate the bound frequencies of the first band gap. Studies are conducted to investigate the low-frequency and directional frequency band gaps for their application to engineering. The study finds that civil engineering structures can be designed to block harmful waves, such as earthquake disturbance.

Dynamic Responses of a Structure with Periodic Foundations

AbstractThe dynamic responses of a structure with different foundations, including the so-called periodic foundation, are studied. Based on the calculation and optimization regarding the band of frequency gap of a periodic structure, a new kind of periodic isolated foundation is designed. To test the validity of this periodic isolated foundation, the dynamic responses of a seven-storey frame structure with three different foundations are conducted and compared. The analysis assumes that seismic wave input is from the arbitrary direction. This investigation shows that the seismic waves cannot propagate in the periodic foundation without being attenuated when the frequencies of the seismic wave fall within the band of frequency gap of the foundation. Thus, the dynamic responses of the supported structure will be greatly reduced. The investigation supports this new and effective method to block seismic waves for structures in civil engineering.

Modeling on piezoelectric energy harvesting from pavements under traffic loads

Piezoelectric energy harvesting from deformation in pavements caused by moving vehicles is investigated in this work. The behavior of pavement is described by a plate resting on a Winkler foundation. Two types of moving distributed loads are considered: single-wheel load and four-wheel load. The loads and the displacement of the pavement are expanded with trigonometric series. Two explicit solutions for the dynamic response of the pavement are then obtained using the Fourier transform and Cauchy’s residue theorem. The voltage and power outputs of a piezoceramic transducer embedded in the pavement are then obtained by the direct piezoelectric effect. Finally, a comprehensive numerical study is conducted to show the effect of the Winkler modulus, the velocity of moving load, the position of moving load, and the position of transducer on the voltage and power outputs. Numerical results show that, compared with a previously studied beam model, the plate model is more suitable for predicting the harvested energy from pavements over soft subgrade.

The primary resonance of laminated piezoelectric rectangular plates

Based on Hamiltons principle and the Rayleigh- Ritz method, a model of a nonlinear dynamic laminated piezoelectric rectangular plate was established, and the governing equations were derived and solved for both the thin-plate and thick-plate models. In the present investigation, the nonlinear constitutive relations of piezoelectric materials were considered and the effects of the nonlinearity on the response of the plate were discovered. The primary resonance of rectangular plate is investigated with the use of the method of multiple scales. The results obtained in the present paper agree very well with the experiment results.

A stack-based flex-compressive piezoelectric energy harvesting cell for large quasi-static loads

In this paper, a flex-compressive piezoelectric energy harvesting cell (F-C PEHC) is proposed. This cell has a large load capacity and adjustable force transmission coefficient assembled from replaceable individual components. A statically indeterminate mechanical model for the cell is established and the theoretical force transmission coefficient is derived based on structural mechanics. An inverse correlation between the force transmission coefficient and the relative stiffness of Element 1s limbs is found. An experimental study is also conducted to verify the theoretical results. Both weakened and enhanced modes are achieved for this experiment. The maximum power output approaches 4.5 mW at 120 kΩ resistive load under a 4 Hz harmonic excitation with 600 N amplitude for the weakened mode, whereas the maximum power output approaches 17.8 mW at 120 kΩ under corresponding load for the enhanced mode. The experimental measurements of output voltages are compared with the theoretical ones in both weakened and enhanced modes. The experimental measurements of open-circuit voltages are slightly smaller for harmonic excitations with amplitudes that vary from 400 N to 800 N and the errors are within 14%. During the experiment, the maximum load approaches 2.8 kN which is quite large but not the ultimate bearing capacity of the present device. The mechanical model and theoretical transmission coefficient can be used in other flex-compressive mode energy transducers.

Attenuation of Building Vibration Using Periodic Foundations

Periodic structures exhibit a unique dynamic characteristic called band of frequency gap, which lends a new insight into the isolation of engineering vibration. Based on the theory of elasto-dynamics, the band of frequency gaps of one-dimensional (1D) layered periodic structure and two-dimensional (2D) periodic structure is studied by using the differential quadrature method and finite element method. The periodicity is taken into account by introducing Bloch-Floquet theorem. To investigate the vibration isolation effects of periodic structures, three different periodic foundations are then designed. Simulations demonstrate that periodic foundations can greatly reduce the dynamic response of upper structures under both vertical and longitudinal ground motion. Therefore, this work offers a new view in application of periodic foundations in civil engineering.