Wenhu Huang

Effects of inclusion shapes on the band gaps in two-dimensional piezoelectric phononic crystals

In this paper, the elastic wave propagation in piezoelectric phononic crystals with several inclusion shapes is investigated by taking the electromechanical coupling into account. The band structures for five different shapes of scatterers (regular triangle, square, hexagon, circle, and oval) with square lattice are calculated using the plane-wave expansion method. The effects of the inclusion shapes on the normalized band width are discussed. The largest complete band gap is obtained by selecting the scatterers with the same symmetry of lattice for the first band gap, but this rule is not valid for the second band gap.

Localization of elastic waves in randomly disordered multi-coupled multi-span beams

Abstract The wave localization in randomly disordered periodic multi-span continuous beams is studied. The transfer matrix method is used to deduce transfer matrices of two kinds of multi-span beams. To calculate the Lyapunov exponents in discrete dynamical systems, the algorithm for determining all the Lyapunov exponents in continuous dynamical systems presented by Wolf et al is employed. The smallest positive Lyapunov exponent of the corresponding discrete dynamical system is called the localization factor, which characterizes the average exponential rates of growth or decay of wave amplitudes along the randomly mistuned multi-span beams. For two kinds of disordered periodic multi-span beams, numerical results of localization factors are given. The effects of the disorder of span-length, the non-dimensional torsional spring stiffness and the non-dimensional linear spring stiffness on the wave localization are analysed and discussed. It can be observed that the localization factors increase with the increase of the coefficient of variation of random span-length and the degree of localization for wave amplitudes increases as the torsional spring stiffness and the linear spring stiffness increase.

Application of Bandwidth EMD and Adaptive Multiscale Morphology Analysis for Incipient Fault Diagnosis of Rolling Bearings

This paper presents a novel signal processing scheme, bandwidth empirical mode decomposition, and adaptive multiscale morphological analysis (BEMD-AMMA) for early fault diagnosis of rolling bearings. In this scheme, we propose a bandwidth based method to select the best envelope interpolation method. First, multiple envelope algorithms are defined and separately subtracted from the original data to obtain the preintrinsic mode functions (PIMFs). Second, an IMF with the smallest frequency bandwidth is selected to be the optimal IMF (OIMF). Third, this OIMF is subtracted from the original signal, and then repeat the sifting process until the residual is a constant or monotonic. Since the OIMF has the smallest frequency bandwidth, the mode mixing phenomenon can be significantly weakened. After that the OIMFs with clear fault information are used to construct the main component of the original signal. Then, the AMMA is introduced to demodulate the constructed main component. Simulation and experimental vibration signals are employed to evaluate the effectiveness of the proposed method. Results show that the proposed method outperforms EMD-AMMA, ensemble empirical mode decomposition-AMMA, and generalized empirical mode decomposition-empirical envelope demodulation in detecting early inner race fault.

ACTIVE VIBRATION CONTROL OF FINITE L-SHAPED BEAM WITH TRAVELLING WAVE APPROACH

In this paper, the disturbance propagation and active vibration control of a finite L-shaped beam are studied. The dynamic response of the structure is obtained by the travelling wave approach. The active vibration suppression of the finite L-shaped beam is performed based on the structural vibration power flow. In the numerical calculation, the influences of the near field effect of the error sensor and the small error of the control forces on the control results are all considered. The simulation results indicate that the structural vibration response in the medium and high frequency regions can be effectively computed by the travelling wave method. The effect of the active control by controlling the power flow is much better than that by controlling the acceleration in some cases. And the control results by the power flow method are slightly affected by the locations of the error sensor and the small error of the control forces.

Early Fault Diagnosis of Rotating Machinery by Combining Differential Rational Spline-Based LMD and K–L Divergence

First, an improved local mean decomposition (LMD) method called differential rational spline-based LMD (DRS) is developed for signal decomposition. Differential and integral operations are introduced in LMD, which can weaken the mode mixing problem. Meanwhile, an optimized rational spline interpolation is proposed to calculate the envelope functions aiming to reduce the large errors caused by moving average in the traditional LMD. A series of product functions (PFs) is obtained after the application of the proposed DRS-LMD. Then, Kullback–Leibler (K–L) divergence is adopted to select main PF components that contain most fault information. The machine fault can be easily identified from the amplitude spectrum of the selected PF component. The effectiveness of the proposed DRS-LMD and K–L strategy is tested on simulated vibration signals and experimental vibration signals. Results show that the proposed method can increase the decomposition accuracy of the signals and can be used to detect early faults on the gears and rolling bearings.

Transient impact responses of laminated composite cylindrical shells

The generalized ray method (GRM) has been successfully used to study the transient elastic wave transmitting in the beams, planar trusses, space frames and infinite layered media. In this letter, the GRM is extended to investigate the early short time transient responses of laminated composite cylindrical shells under impact load. By using the Laplace transformation and referring to the boundary conditions, the ray groups transmitting in the finite laminated cylindrical shells under the shock load are obtained and the transient response related to each ray group can be derived via FFT algorithm. From the numerical results, it is shown that the early short time transient accelerations of the laminated composite cylindrical shell under impact loads are very large. But the short time transient shear strain and displacement are very small.

Energy harvesting from water flow in open channel with macro fiber composite

Fluid-induced vibrational energy harvesting usually concerns small-scale wind energy extraction. A few efforts have been made into energy harnessing from low-velocity water flows. In this study, low-speed galloping and vortex induced vibration (VIV) are investigated for energy harvesting in an open channel via the macro fiber composite glued on the surface of a cantilever beam. A cylindrical or triangular-prism bluff body is attached at the free tip of the beam and fully immersed in the water. Beam’s deflection is perpendicular to the fluid flow. The flowrate of the water channel is measured by a built-in rectangular sharp-crested weir, and the average flow velocity is controlled by the inlet valve and weir plate. The fluid-structure interaction and electromechanical coupling at different flow velocities and load resistances are analyzed. At small flow velocities, the cylindrical bluff body exhibits better performance than the triangular-prism bluff body since it has been shown in previous work [So et al., J. Fluid Struct. 24, 481–495 (2008) and Daniels et al., J. Wind Eng. Ind. Aerod. 153, 13–25 (2016)] that for the same turbulence intensity the cylinder under VIV performs better than the triangular prism. As the flow velocity increases, the power of the triangular-prism case harvested from the interaction of low-speed galloping and VIV overtakes the power of the cylindrical case converted from the VIV motion that is usually smaller than the cylinder diameter. One dominant vibration frequency is noticed and associated with lock-in or wake capture, which increases with the flow velocity owing to the decreasing added mass. High efficient energy harvesting from the low-velocity water flow is realized via the integration of galloping and VIV.Fluid-induced vibrational energy harvesting usually concerns small-scale wind energy extraction. A few efforts have been made into energy harnessing from low-velocity water flows. In this study, low-speed galloping and vortex induced vibration (VIV) are investigated for energy harvesting in an open channel via the macro fiber composite glued on the surface of a cantilever beam. A cylindrical or triangular-prism bluff body is attached at the free tip of the beam and fully immersed in the water. Beam’s deflection is perpendicular to the fluid flow. The flowrate of the water channel is measured by a built-in rectangular sharp-crested weir, and the average flow velocity is controlled by the inlet valve and weir plate. The fluid-structure interaction and electromechanical coupling at different flow velocities and load resistances are analyzed. At small flow velocities, the cylindrical bluff body exhibits better performance than the triangular-prism bluff body since it has been shown in previous work [So et al....