Mustafa Arafa

Dynamics of active piezoelectric damping composites

Abstract A finite element model is developed to investigate the dynamic characteristics of beams treated with discrete patches of Active Piezoelectric Damping Composites (APDC). The APDC patches, under consideration, consist of piezoelectric rods that are obliquely embedded in a viscoelastic matrix to actively control its shear and compression damping characteristics. With such active and passive control capabilities, the energy dissipation mechanism of the viscoelastic layer can be enhanced and the dynamic behavior of the system can be improved. The effectiveness of the APDC in damping the vibration of beams is compared with the performance of the conventional Passive Constrained Layer Damping (PCLD). The effect of the inclination angle of the piezoelectric rods on the performance of the APDC is presented. The results obtained demonstrate that the APDC, with their inherent active and passive capabilities, are an effective means for controlling structural vibrations over a broad frequency band.

Evaluation of spur gear mesh compliance using the finite element method

Abstract This paper presents a finite element (FE) modelling technique to evaluate the mesh compliance of spur gears. Contact between the engaging teeth is simulated through the use of gap elements. Analysis is performed on several gear combinations and the variation in tooth compliance along the contact location is presented in a non-dimensional form. Results are compared with earlier predictions based on analytical, numerical and experimental methods. Load sharing among the mating gear teeth is discussed, and the overall gear mesh stiffness together with its cyclic variation along the path of contact is evaluated.

Experimental implementation of a cantilevered piezoelectric energy harvester with a dynamic magnifier

Conventional energy harvester consists of a cantilevered composite piezoelectric beam which has a proof mass at its free end while its fixed end is mounted on a vibrating base structure. The resulting relative motion between the proof mass and the base structure produces a mechanical strain in the piezoelectric elements which is converted into electrical power by virtue of the direct piezoelectric effect. In this paper, the harvester is provided with a dynamic magnifier consisting of a spring-mass system which is placed between the fixed end of the piezoelectric beam and the vibrating base structure. The main function of the dynamic magnifier, as the name implies, is to magnify the strain experienced by the piezoelectric elements in order to amplify the electrical power output of the harvester. With proper selection of the design parameters of the magnifier, the harvested power can be significantly enhanced and the effective bandwidth of the harvester can be improved. The theoretical performance of this class of Cantilevered Piezoelectric Energy Harvesters with Dynamic Magnifier (CPEHDM) is developed using ANSYS finite element analysis. The predictions of the model are validated experimentally and comparisons are presented to illustrate the merits of the CPEHDM in comparison with the conventional piezoelectric energy harvesters (CPEH). The obtained results demonstrate the feasibility of the CPEHDM as a simple and effective means for enhancing the magnitude and spectral characteristics of CPEH.

On the Nonlinear Behavior of Piezoelectric Actuators

In this paper we present a theoretical and experimental study of the nonlinear behavior of piezoelectric actuators. The nonlinearities are introduced as quadratic terms in the piezoelectric constitutive relations. These relations are employed, together with supporting experimental results, to establish an engineering description of the nonlinearities present in piezoelectric materials. We present a lumped-parameter representation of a system consisting of a piezoactuator driving a mass. The representation is valid in the vicinity of the primary resonance. The resulting nonlinear differential equation of motion is analyzed by the method of harmonic balance to study the effects of nonlinearities on the dynamics of forced vibrations. Experimental measurements of the steady-state mechanical response to harmonic electrical excitation over a range of excitation frequencies and amplitudes quantify the nature and level of nonlinear behavior. The nonlinear behavior, which is mainly evident around the resonant frequency, is shown to be of the softening type and becomes more pronounced at higher drive voltage levels. Numerical simulations based on the developed nonlinear model have shown significant improvement over previous linear models in predicting the experimental behavior of piezoelectric materials at the vicinity of primary resonance.

Finite Element Analysis of Sloshing in Rectangular Liquid-filled Tanks

The focus of the present paper is on the development of a finite element formulation to investigate the sloshing of liquids in partially filled rigid rectangular tanks undergoing base excitation. The liquid domain is discretized into two-dimensional four-node rectangular elements with the liquid velocity potential representing the nodal degrees of freedom. Liquid sloshing effects induced by both steady-state harmonic and arbitrary horizontal base excitation are investigated in terms of the slosh frequencies, liquid velocity field, free surface displacement and hydrodynamic forces acting on the tank walls. The model is employed to study the effects of inserting a bottom-mounted vertical rigid baffle, as well as side-mounted horizontal baffles that are wholly immersed in the liquid region, in an attempt to investigate their viability in acting as slosh suppression devices.

Finite element model updating approach to damage identification in beams using particle swarm optimization

The use of vibration-based techniques in damage identification has recently received considerable attention in many engineering disciplines. While various damage indicators have been proposed in the literature, those relying only on changes in the natural frequencies are quite appealing since these quantities can conveniently be acquired. Nevertheless, the use of natural frequencies in damage identification is faced with many obstacles, including insensitivity and non-uniqueness issues. The aim of this article is to develop a viable damage identification scheme based only on changes in the natural frequencies and to attempt to overcome the challenges typically encountered. The proposed methodology relies on building a finite element model (FEM) of the structure under investigation. An improved particle swarm optimization algorithm is proposed to facilitate updating the FEM in accordance with experimentally determined natural frequencies in order to predict the damage location and extent. The method is tested on beam structures and was shown to be an effective tool for damage identification.

Wind-driven pyroelectric energy harvesting device

Pyroelectric materials have recently received attention for harvesting waste heat owing to their potential to convert temperature fluctuations into useful electrical energy. One of the main challenges in designing pyroelectric energy harvesters is to provide a means to induce a temporal heat variation in a pyroelectric material autonomously from a steady heat source. To address this issue, we propose a new form of wind-driven pyroelectric energy harvester, in which a propeller is set in rotational motion by an incoming wind stream. The speed of the propellers shaft is reduced by a gearbox to drive a slider-crank mechanism, in which a pyroelectric material is placed on the slider. Thermal cycling is obtained as the reciprocating slider moves the pyroelectric material across alternative hot and cold zones created by a stationary heat lamp and ambient temperature, respectively. The open-circuit voltage and closed-circuit current are investigated in the time domain at various wind speeds. The device was experimentally tested under wind speeds ranging from 1.1 to 1.6 m s−1 and charged an external 100 nF capacitor through a signal conditioning circuit to demonstrate its effectiveness for energy harvesting. Unlike conventional wind turbines, the energy harvested by the pyroelectric material is decoupled from the wind flow and no mechanical power is drawn from the transmission; hence the system can operate at low wind speeds (<2 m s−1).

Modeling and Characterization of a Linear Piezomotor

This article presents the modeling and characterization of a new class of piezoelectric linear motor. The motor relies in its operation on a set of piezoelectric bimorphs which are sequentially activated to linearly move a drive rod along spring loaded rollers. Emphasis in this article is placed on studying the dynamic behavior of this class of piezoelectric motors, both theoretically and experimentally, in an effort to predict the piezomotor response to various loads and excitation schemes. To this end, a numerical model has been developed to simulate the dynamics of the piezoelectric bimorphs comprising the piezomotor. Friction between the bimorph elements and the drive rod are handled using an appropriate friction model. Experimental testing of the motor is carried out to validate the predictions of the theoretical model.

Energy-dissipation characteristics of active piezoelectric damping composites

A finite-element model is developed to investigate the energy dissipation characteristics of active piezoelectric damping composites (APDC). The APDC under consideration consists of piezoelectric rods that are obliquely embedded in a viscoelastic matrix to provide active control of its shear and compression damping characteristics. Discrete APDC patches may be bonded to or embedded within structural systems to control their vibrations. The APDC, with their inherent active and passive control capabilities, provide effective means of enhancing the energy dissipation mechanism of the viscoelastic layer and hence the overall dynamic behavior of the system can be improved. The effect of the inclination angle of the piezoelectric rods and the control gains on the energy-dissipation characteristics of APDC is presented. The results obtained indicate that effectively high loss factors may be attained by proper selection of the design parameters of the APDC patches, which makes the APDC suitable for controlling structural vibrations and noise.

Modeling and characterization of a linear piezomotor

This paper presents the modeling and characterization of a novel class of piezoelectric linear motors. The motor relies in its operation on a set of piezoelectric bimorphs which are sequentially activated to linearly move a drive rod along spring loaded rollers. Emphasis in this paper is placed on studying the dynamic behavior of this class of piezoelectric motors, both theoretically and experimentally, in an effort to predict the piezomotor response to various loads and excitation schemes. To this end, a numerical model has been developed to simulate the dynamics of the piezoelectric bimorphs comprising the piezomotor. Friction between the bimorph elements and the drive rod are handled using an appropriate friction model. Experimental testing of the motor is carried out to validate the predictions of the theoretical model. This effort aims ultimately at demonstrating the feasibility of employing this class of piezoelectric actuators in driving smart snake robots in order to use them as a simple and reliable mobility platform.