1,721,328 research outputs found
An experimentally verified model of a membrane mirror strip actuated using piezoelectric bimorph
No full textThe behavior of a membrane mirror strip actuated using a piezoelectric bimorph is treated. An improved model for the transverse vibration is presented. The model accounts for the changes in physical properties of the membrane strip at the location of the piezoelectric bimorph. The membrane strip is modeled as a pinned-pinned beam under tension and the finite element method (FEM) is used to represent the system mathematically. The beam under tension assumption allows accounting for the traveling wave effect experienced by a membrane strip and the added flexural rigidity induced by the piezoelectric bimorph. Additionally, the structural and air damping effects are included in the model. An experimental setup is built to verify the proposed model. The frequency response obtained from the proposed model is shown to be in agreement with conducted experiments. Furthermore, the importance of including local mass and stiffness effects is demonstrate
An outlier analysis of MFC-based impedance sensing data for wireless structural health monitoring of railroad tracks
No full textThis paper presents an outlier analysis for damage detection of railroad tracks using a macro-fiber composite (MFC) impedance-based wireless structural health monitoring (SHM) system. The impedance-based SHM method has some limitations because the measured impedance data may have considerable deviations caused by environmental or operational condition changes, including temperature, humidity, external loadings, or MFC patch bonding conditions. Thus, the method sometimes gives false-positive indication even for healthy structures. In order to overcome this limitation, an outlier analysis based on Mahalanobis squared distance (MSD) was proposed by taking root mean square deviation (RMSD) values of impedance signatures as a damage-sensitive feature vector. Optimal threshold values for both RMSD and MSD were determined through the proposed outlier analysis. The results showed that the use of MSD improved the damage detection capability with a lower threshold level as compared to that of RMSD. In this study, the applicability of the proposed method was experimentally verified by detecting three types of the railroad track damage, including head damage, web damage, and flange damage, which were simulated under the laboratory setting. (C) 2008 Elsevier Ltd. All rights reserved
Modeling and control of membrane mirror strip using single piezoelectric bimorph
No full textThis paper presents an improved finite-element model of a membrane strip actuated by a single piezoelectric bimorph. The paper also treats the static shape control problem of the structure under study. The membrane strip is modeled as an Euler—Bernoulli beam under tension, with non-uniform physical properties. The finite-element method allows the development of a model that accounts for the actuator dynamics. The static shape control problem is formulated as a disturbance rejection problem and solved using a proportional-integral (PI) controller. The PI control gains are obtained using the linear quadratic regulator theory. The proposed model is verified experimentally, and the closed loop system is simulated to demonstrate the effectiveness of the control law
Energy harvesting from a piezoelectric bender through rigid body motion of a two-link manipulator
No full textHarvesting energy from persistent ambient vibrations for powering small electronic components has been an attractive subject for researchers in recent years. The direct piezo-electric effect of piezoceramic materials makes them very appealing for such applications. Typically, a piezoelectric harvester is a cantilevered bender with one or more piezoceramic layers. Usually, such harvester is located on a vibrating host structure for energy harvesting. The problem of extracting electrical outputs from structural vibrations by this approach has been examined in the literature. In this paper, we investigate a different approach for piezoelectric energy harvesting through a particular application. Rather than the structural vibrations of the host structure, we focus on its inertial fluctuations due to the rigid body motion. The host structure we consider is a typical two-link manipulator which executes a pick-place operation. The piezoelectric bender is located at a point on the elbow link of the manipulator and it vibrates due to the periodic rigid body motion of this link. The kinematics of a two-link manipulator is reviewed to obtain the acceleration at the base of the harvester for a given pick-place motion trajectory of the end effector. The analysis of the piezoelectric harvester is then presented based on a recently developed distributed parameter electromechanical model. The idea and the analysis presented here may be useful for powering sensors and other small electronic components attached to two-link manipulators and more sophisticated industrial robots
2-D differential quadrature solution for vibration analysis of functionally graded conical, cylindrical shell and anular plate structures
No full textThis paper focuses on the dynamic behavior of functionally graded conical, cylindrical shells and annular plates. The last two structures are obtained as special cases of the conical shell formulation. The first-order shear deformation theory (FSDT) is used to analyze the above moderately thick structural elements. The treatment is developed within the theory of linear elasticity, when materials are assumed to be isotropic and inhomogeneous through the thickness direction. The two-constituent functionally graded shell consists of ceramic and metal that are graded through the thickness, from one surface of the shell to the other. Two different power-law distributions are considered for the ceramic volume fraction. The homogeneous isotropic material is inferred as a special case of functionally graded materials (FGM). The governing equations of motion, expressed as functions of five kinematic parameters, are discretized by means of the generalized differential quadrature (GDQ) method. The discretization of the system leads to a standard linear eigenvalue problem, where two independent variables are involved without using the Fourier modal expansion methodology. For the homogeneous isotropic special case, numerical solutions are compared with the ones obtained using commercial programs such as Abaqus, Ansys, Nastran, Straus, Pro/Mechanica. Very good agreement is observed. Furthermore, the convergence rate of natural frequencies is shown to be very fast and the stability of the numerical methodology is very good. Different typologies of non-uniform grid point distributions are considered. Finally, for the functionally graded material case numerical results illustrate the influence of the power-law exponent and of the power-law distribution choice on the mechanical behavior of shell structures
Nonlinear control of a membrane mirror strip actuated axially and in bending
Full text linkThe sliding mode technique is used to control the deformation of a membrane mirror strip augmented with two
macrofiber composite bimorphs located near the ends of the strip. The first bimorph is actuated in bending and the
second is actuated axially. The structure is modeled as an Euler–Bernoulli beam under tensile load and the
macrofiber composite patches are modeled as monolithic piezoceramic wafers. To cast the system into a finitedimensional
state-space form, the finite element method is used, and the model presented accounts for the dynamics
of the augmented bimorphs. The membrane strip is placed under uniform tension. Because one of the bimorphs acts
axially, the resulting tension in the membrane strip is discontinuous at the location of this bimorph and, consequently,
the obtained model is nonlinear. First, we validate the model experimentally by considering the system in its quasilinear
state, then we consider the control problem. We formulate the regulation problem by using the sliding mode
technique. Additionally, to allow coupling this system with an adaptive optics scheme, the shape-control problem is
considered as well. The control law uses both actuators: the bending and axial bimorphs. However, a system
singularity dictates using a switching command to avoid this singularity. Various examples are presented for the
regulation and shape-control problems. The simulation results demonstrate the efficacy of the proposed control law
On the optimal energy harvesting from a vibration source
No full textThe optimization of power acquired from a piezoelectric vibration-based energy harvester which utilizes a harvesting circuit employing an inductor and a resistive load is described. The optimization problem is formulated as a nonlinear program wherein the Karush–Kuhn–Tucker (KKT) conditions are stated and the resulting cases are treated. In the first part of the manuscript, the case of a purely resistive circuit is analyzed. While this configuration has received considerable attention in the literature, previous efforts have neglected the effect of damping on the optimal parameters. Here, we explore the impact of damping on power optimality and illustrate its quantitative and qualitative effects. Further, we analyze the effect of electromechanical coupling demonstrating that the harvested power decreases beyond an optimal coupling coefficient. This result challenges previous literature suggesting that higher coupling coefficients always culminate in more efficient energy harvesters. In the second part of this work, the effect of adding an inductor to the circuit is examined. It is demonstrated that the addition of the inductor provides substantial improvement to the performance of the energy harvesting device. It is also shown that within realistic values of the coupling coefficient, the optimal harvested power is independent of the coupling coefficient; a result that supports previous findings for the purely resistive circuit
Modeling of piezoelectric energy harvesting from an L-shaped beam-mass structure with an application to UAV's [in special issue on Energy Harvesting]
No full textCantilevered piezoelectric energy harvesters have been extensively investigated in the literature of energy harvesting. As an alternative to conventional cantilevered beams, this article presents the L-shaped beam-mass structure as a new piezoelectric energy harvester configuration. This structure can be tuned to have the first two natural frequencies relatively close to each other, resulting in the possibility of a broader band energy harvesting system. This article describes the important features of the L-shaped piezoelectric energy harvester configuration and develops a linear distributed parameter model for predicting the electromechanically coupled voltage response and displacement response of the harvester structure. After deriving the coupled distributed parameter model, a case study is presented to investigate the electrical power generation performance of the L-shaped energy harvester. A direct application of the L-shaped piezoelectric energy harvester configuration is proposed for use as landing gears in unmanned air vehicle applications and a case study is presented where the results of the L-shaped — energy harvester — landing gear are favorably compared against the published experimental results of a curved beam configuration used for the same purpose
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