Vibration analysis and active control of nearly periodic two-span beams with piezoelectric actuator/sensor pairs

The piezoelectric materials are used to investigate the active vibration control of ordered/disordered periodic two-span beams. The equation of motion of each sub-beam with piezoelectric patches is established based on Hamilton＇s principle with an assumed mode method. The velocity feedback control algorithm is used to design the controller. The free and forced vibration behaviors of the two-span beams with the piezoelectric actuators and sensors are analyzed. The vibration properties of the disordered two-span beams caused by misplacing the middle support are also researched. In addition, the effects of the length disorder degree on the vibration performances of the disordered beams are investigated. From the numerical results, it can be concluded that the disorder in the length of the periodic two-span beams will cause vibration localizations of the free and forced vibrations of the structure, and the vibration localization phenomenon will be more and more obvious when the length difference between the two sub-beams increases. Moreover, when the velocity feedback control is used, both the forced and the free vibrations will be suppressed. Meanwhile, the vibration behaviors of the two-span beam are tuned.

Relationship between the Local Vibration Mode Characteristics and the Charge State of Carbon Acceptor in GaAs

The local vibration mode(LVM)of carbon acceptor in GaAs is studied by measuring directly the change in LVM absorption with a NIC-170 SX FT-IR spectrometer.The change in the charge state of carbon acceptor and the temperature dependence of the LVM absorption were investigated also.The contents of the impurities other than carbon were estimated by secondary ion mass spectrometry.It is observed that the frequency,the spectral form and the integrated absorption of the LVM are not affected by the change in charge state of car- bon acceptor.

Sideband Absorption and its Effects on Temperature Dependence of Local Vibrational Mode Main Absorption Band for Carbon Acceptor in Gallium Arsenide

The local vibrational mode (LVM) optical absorption band of carbon acceptor was investigated carefully. Because of the appearance of a sideband on the low energy side of the LVM main absorption band, it is found that the measured value of the integrated area for the main absorption band is sensitive to the choice of integration baseline wavenumber range (BWR). This is the main cause that the experimental results from different investigators show a wide spread for the temperature dependence of the integrated area. The origin of the sideband is also discussed.

OPTIMAL CONTROL OF THE FLEXI-BLE LINK MANIPULATOR WITH CONTROLLABLE LOCAL DEGREES OF FREEDOM

Although flexible manipulators own many potential advantages, one of their major disadvantages is the deterioration of the end-effector accuracy due to the flexibility. Therefore, how to reduce vibration is a significant problem. Inspired by the observation on the motion behaviors of animals, a new idea of decreasing motion deflection of the flexible manipulator is suggested. The concept of controllable local degrees of freedom is proposed and analyzed. By way of optimizing local motion provided by the controllable local degrees of freedom, the end-effector deflection of the flexible manipulator can be effectively decreased through dynamic coupling. The corresponding optimal method for vibration control of the flexible manipulator is put forward. The kinematic simulation is carried ant on a three-link flexible manipulator The corresponding results verify the feasibility of this method.

FLEXURAL WAVE PROPAGATION IN NARROW MINDLIN'S PLATE

Appling Mindlin＇s theory of thick plates and Hamilton system to propagation of elastic waves under free boundary condition, a solution of the problem was given. Dispersion equations of propagation mode of strip plates were deduced from eigenfunction expansion method. It was compared with the dispersion relation that was gained through solution of thick plate theory proposed by Mindlin. Based on the two kinds of theories, the dispersion curves show great difference in the region of short waves, and the cutoff frequencies are higher in Hamiltonian systems. However, the dispersion curves are almost the same in the region of long waves.

C-H complex defects and their influence in ZnO single crystal

Infrared absorption local vibration mode（LVM） spectroscopy is used to study hydrogen related defects in n-type ZnO single crystal grown by a closed chemical vapor transport（CVT） method under Zn-rich growth conditions, in which carbon is used as a transport agent. Two C-H complex related absorption peaks at 2850 cm-1and 2919 cm-1 are detected in the sample. The formation of the C-H complex implies an effect of carbon donor passivation and formation suppression of H donor in ZnO. The influence of the complex defects on the electrical property of the CVT-ZnO is discussed based on Hall measurement results and residual impurity analysis.

SINGULAR CHARACTERISTICS OF NONLINEAR NORMAL MODES IN A TWO DEGREES OF FREEDOM ASYMMETRIC SYSTEMS WITH CUBIC NONLINEARITIES

Nonlinear normal modes in a two degrees of freedom asymmetric system with cubic nonlinearities as singularity occurs in the system are studied, based on the invariant space in nonlinear normal modes and perturbation technique. Emphasis is placed on singular characteristics as the linear coupling between subsystems degenerated. For nonresonances, it is analytically presented that a single-mode motion and localization of vibrations occur in the system, and the degree of localization relates not only to the coupling stiffness between oscillators, but also to the asymmetric parameter. The parametric threshold value of localization is analytically given. For 1 : 1 resonance, there exist bifurcations of normal modes with nonlinearly coupling stiffness and asymmetric parameter varying. The bifurcating set on the parameter and bifurcating curves of normal modes are obtained.

Numerical investigation on dynamic response of the screen mesh in vibrating screening through DEM-FEM co-simulation

Dynamic response of the screen mesh is of great significance in the optimum vibrating screen design.In this paper,based on the DEM-FEM co-simulation method,the effect of screening parameters on the dynamic response of the screen mesh is explored and the mechanism is revealed on the particle level.Firstly,a virtual experiment on a linear vibrating screen was carried out to analyze the screening pa-rameters'effect with both impact load and sustained stress inflicted on the screen mesh.Then,the time-domain evolution regularity of the screen mesh LVA(Local Vibration Amplitude)under different particle plugging conditions was investigated based on the co-simulation.Finally,the influence of screening parameters on LVA and its distribution was discussed.The results show that the screening parameters can greatly affect the screen mesh LVA and its distribution by changing the movement of the granular material and the particle penetration probability,which provides an important basis for the optimal design of the screen mesh and its supporting structure.

Nonlinear Vibrations of Two-Span Composite Laminated Plates with Equal and Unequal Subspan Lengths

The nonlinear transverse vibrations of ordered and disordered twodimensional(2D)two-span composite laminated plates are studied.Based on the von Karman’s large deformation theory,the equations of motion of each-span composite laminated plate are formulated using Hamilton’s principle,and the partial differential equations are discretized into nonlinear ordinary ones through the Galerkin’s method.The primary resonance and 1/3 sub-harmonic resonance are investigated by using the method of multiple scales.The amplitude-frequency relations of the steady-state responses and their stability analyses in each kind of resonance are carried out.The effects of the disorder ratio and ply angle on the two different resonances are analyzed.From the numerical results,it can be concluded that disorder in the length of the two-span 2D composite laminated plate will cause the nonlinear vibration localization phenomenon,and with the increase of the disorder ratio,the vibration localization phenomenon will become more obvious.Moreover,the amplitude-frequency curves for both primary resonance and 1/3 sub-harmonic resonance obtained by the present analytical method are compared with those by the numerical integration,and satisfactory precision can be obtained for engineering applications and the results certify the correctness of the present approximately analytical solutions.

Dynamic responses of cable-stayed bridges to vehicular loading including the effects of the local vibration of cables

Stay cables, the primary load carrying components of cable-stayed bridges (CSBs), are characterised by high flexi-bility which increases with the span of the bridge. This makes stay cables vulnerable to local vibrations which may have significant effects on the dynamic responses of long-span CSBs. Hence, it is essential to account for these effects in the assessment of the dynamics CSBs. In this paper, the dynamic responses of CSBs under vehicular loads are studied using the finite element method (FEM), while the local vibration of stay cables is analyzed using the substructure method. A case study of a cable-stayed steel bridge with a center span of 448 m demonstrates that stay cables undergo large displacements in the primary mode of the whole bridge although, in general, a cable’s local vibrations are not obvious. The road surface roughness has significant effects on the interaction force between the deck and vehicle but little effect on the global response of the bridge. Load impact factors of the main girder and tower are small, and the impact factors of the tension of cables are larger than those of the displacements of girders and towers.

Local vibration therapy promotes the recovery of nerve function in rats with sciatic nerve injury

Objective:It has been reported that local vibration therapy can benefit recovery after peripheral nerve injury,but the optimized parameters and effective mechanism were unclear.In the present study,we investigated the effect of local vibration therapy of different amplitudes on the recovery of nerve function in rats with sciatic nerve injury(SNI).Methods:Adult male Sprague-Dawley rats were subjected to SNI and then randomly divided into 5 groups:sham group,SNI group,SNI+A-1 mm group,SNI+A-2 mm group,and SNI+A-4 mm group(A refers to the amplitude;n=10 per group).Starting on the 7th day after model initiation,local vibration therapy was given for 21 consecutive days with a frequency of 10 Hz and an amplitude of 1,2 or 4 mm for 5 min.The sciatic function index(SFI)was assessed before surgery and on the 7th,14th,21st and 28th days after surgery.Tissues were harvested on the 28th day after surgery for morphological,immunofluorescence and Western blot analysis.Results:Compared with the SNI group,on the 28th day after surgery,the SFIs of the treatment groups were increased;the difference in the SNI+A-2 mm group was the most obvious(95%confidence interval[CI]:[5.86,27.09],P<0.001),and the cross-sectional areas of myocytes in all of the treatment groups were improved.The G-ratios in the SNI+A-1 mm group and SNI+A-2 mm group were reduced significantly(95%CI:[-0.12,-0.02],P=0.007;95%CI:[-0.15,-0.06],P<0.001).In addition,the expressions of S100 and nerve growth factor proteins in the treatment groups were increased;the phosphorylation expressions of ERK1/2 protein in the SNI+A-2 mm group and SNI+A-4 mm group were upregulated(95%CI:[0.03,0.96],P=0.038;95%CI:[0.01,0.94],P=0.047,respectively),and the phosphorylation expression of Akt in the SNI+A-1 mm group was upregulated(95%CI:[0.11,2.07],P=0.031).Conclusion:Local vibration therapy,especially with medium amplitude,was able to promote the recovery of nerve function in rats with SNI;this result was linked to the proliferation of Schwann cells and the activation of the ERK1/2 and Akt signaling pathways.

Stability and vibrational properties of the hydrogen atom for p-type AlN doped with group-Ⅱ:a first-principles study

The stability and local vibrational mode（LVM） of hydrogen related p-type AlN have been studied by firstprinciples calculations based on density functional theory.The stable and metastable microscopic geometries of group-Ⅱ（Be,Mg,Ca,Sr,Ba）-H complexes have been investigated.The calculated results indicate that BC_（‖） is the most stable configuration for isolated interstitial H~＋ and Be-H complexes,while it is AB_（n,⊥） for Mg-H,Ca-H,Sr-H and Ba-H complexes.Moreover,the vibrational frequencies and the values of k and ｜α｜ for the H atom with LVM are calculated. Here,the values of k and ｜α｜ are used to describe the parameters of the harmonic and anharmonic contributions,respectively. The calculated results indicate that the larger the size of the doped ion is,the shorter the N-H bond length is,and the larger the potential energy,the vibrational frequencies,the values of k and ｜α｜ are.This implies that the size of the doped ion has an important influence on the vibrational properties of H.

Flow-pipe-soil coupling mechanisms and predictions for submarine pipeline instability

The stability of a submarine pipeline on the seabed concerns the flow-pipe-soil coupling, with influential factors related to the ocean waves and/or currents, the pipeline and the surrounding soils. A flow-pipe-soil coupling system generally has various instability modes, including the vertical and lateral on-bottom instabilities, the tunnel-erosion of the underlying soil and the subsequent vortex-induced vibrations（VIVs） of free-spanning pipelines. This paper reviews the recent advances of the slip-line field solutions to the bearing capacity, the flow-pipe-soil coupling mechanism and the prediction for the lateral instability, the multi-physical coupling analysis of the tunnel-erosion, and the coupling mechanics between the VIVs and the local scour. It is revealed that the mechanism competition always exists among various instability modes, e.g., the competition between the lateral-instability and the tunnel-erosion. Finally, the prospects and scientific challenges for predicting the instability of a long-distance submarine pipeline are discussed in the context of the deep-water oil and gas exploitations.

Local characteristics and acoustical energy of radiation on vibrating surface: Ⅰ. Theory

From a point of view of the auto-spectrum, the local characteristics and the acous-tical energy of radiating on a vibrating surface are theoretically studied in this paper. The point radiation impedance at any point on a vibrating surface is defined a-s the ratio of the sound pressure to the vibrating velocity, which establishes the relation between the vibration of the surface and the sound field. Applying the Cauchy iategral theorem, the chromatic disper-sion relation between the real and imaginary components of the point radiation impedance is given, and some characteristics are discussed. The discussion about two typical sound sotirces,pulsating and oscillating spheres, supports the arguments of this paper.

Local characteristics and acoustical energy of radiation on vibrating surface: Ⅱ. application

Applying the theory put forward in Ref. [3], the radiation mechanism of sound energy on a vibrating steel plate was studied. Between the point radiation resistance efficiency and the point radiation reactance efficiency exists the chromatic dispersion relation that is one to one. The chromatic dispersion relation fits not only smooth curves, but also the dispersed curves with sharp-pointed peaks. While the vibrating surface radiates the sound energy into field, it absorbs some energy from the field.