KEYWORDS: Actuators, Microsoft Foundation Class Library, Feedback control, Composites, Sensors, Signal attenuation, Vibration control, Finite element methods, Modal analysis, Structural dynamics
In this study, the geometry of the handlebars of bicycle is simulated as a hollow cylindrical rod, subjected to flexural vibration transmitted from a head tube. Analytical prediction as well as experimental investigation are implemented to evaluate the effectiveness of active control of flexural vibration of the handlebars using Macro-Fiber Composite (MFC) actuators. The newly developed MFC actuators are typically directional or anisotropic, and more flexible and conformable as compared to traditional monolithic isotropic piezoceramic actuators. Predictions of the finite element model are validated experimentally using a cantilevered cylindrical rod surface bonded with three flexible MFC actuators, two placed at the clamped end and the third at the bend location. A primary disturbance is assumed to be transmitted from the clamped end, while a secondary force from the MFC actuators. The velocity feedback and the LQR controller are utilized to determine appropriate voltage inputs into the MFC actuators. Close agreement is found between theoretical assumptions and experiments. The results obtained suggest that using the MFC actuators in controlling the flexural wave transmission through hollow cylindrical rod has been effective.
A shear mode PZT actuator for the microdroplet ejecting system is proposed. The plate-shaped actuator poled with remnant polarization perpendicular to actuating field induces piezoelectric shear effect. Two poling designs for the shear mode piezoelectric actuator are compared by both the analysis and experiment. The two poling designs are single-surface poling design and dual-surface poling design. The single-surface poling design arranges poling electrodes only on one surface, while the dual-surface poling design arranges poling electrodes on the opposite surfaces. Although the single-surface poling design is convenient for poling process, its requirement of the higher poling voltage for achieving coercive field induces specimen failure of surface cracks. So, the dual-surface poling design is preferred because the higher yield and better electromechanical coupling characteristic can be obtained. In both poling designs, the relations of shear piezoelectric coefficient, d15, and actuating electric field are obtained with three kinds of sample thicknesses.
KEYWORDS: Actuators, Finite element methods, Ferroelectric materials, Metals, Aerodynamics, Chemical elements, Aerospace engineering, Matrices, Acoustics, Control systems
The primary objective of active flow control research is to develop a cost-effective technology that has the potential for revolutionary advances in aerodynamic performance and maneuvering compared to conventional approaches. The development of such systems have many implications for aerospace vehicles including: reducing mechanical complexity and hydraulic failure, reducing noise and weight, lowering energy and fuel consumption, lowering downtime and maintenance, enhancing maneuvering and agility with enhanced aerodynamic performance and safety. Interest in active flow control for aerospace applications has stimulated the recent development of innovative actuator designs that create localized disturbances in a flowfield.
A novel class of devices, known as synthetic jet actuator, has been demonstrated to exhibit promising flow control capabilities including separation control and thrust vectoring. The basic components of a synthetic jet actuator are made of cavity and oscillating materials. The synthetic jet actuator developed at NASA LaRC has a small housing in which a cylindrical cavity is enclosed by two metal diaphragms, 50 mm in diameter, placed opposite each other. A circular piezoelectric wafer is attached to the center of the outside face of each metal diaphragm. The pair of piezoelectric metal diaphragms is operated with a 180° phase differential at the same sinusoidal voltage and frequency. With actuation, a synthetic jet issues from a 35.5mm long by 0.5mm wide slot on the top of the device.
In this study, a finite element model of synthetic jet actuator developed at NASA LaRC is investigated. The developed finite element model can be utilized to design and determine the performance of synthetic jet actuator. The analysis includes the FE model of circular plate, FE model of piezoelectric actuator/circular plate, piezoelectric (electrical field)/circular plate (structural field)/cavity (flow field) coupled system and experimental validation. The phase-average jet center velocity and amplitude of input voltage of piezoelectric actuator are predicted by this finite element model. The theoretical prediction is validated experimentally in this study.
KEYWORDS: Actuators, Ferroelectric materials, Composites, Chemical elements, Finite element methods, Microsoft Foundation Class Library, Transducers, Matrices, Electrodes, Acoustics
The anisoparametric three-node MIN6 shallow shell element is extended for modeling Macro-fiber Composite/Active Fiber Composites (MFC/AFC) actuators for active vibration and acoustic control of curved and flat panels. The recently developed MFC/AFC actuators exhibit enhanced performance, they are anisotropic and highly conformable as compared to traditional monolithic isotropic piezoceramic actuators. The extended MIN6 shell element formulation includes embedded or surface bonded MFC/AFC laminae. The fully coupled electrical-structural formulation is general and is able to handle arbitrary doubly curved laminated composite and isotropic shell structures. A square and a triangular cantilever isotropic plates are modeled using the MIN6 elements to demonstrate the anisotropic actuation of a surface bonded MFC actuator for coupled bending and twisting plate motions. Steady state bending and twisting modal amplitudes of the cantilever square and triangular plates with MFC actuator are compared with the plate's modal amplitudes with traditional PZT 5A actuator. Frequency Response Function (FRF) for the square plate with MFC and PZT 5A are also compared.
A finite element method for predicting critical temperature and postbuckling deflection is presented for composite plates embedded with prestrained shape memory alloy (SMA) wires and subjected to high temperatures. The temperature- dependent material properties of SMA and matrix, and the geometrical non linearities of large deflection are considered in the formulation. An incremental method consisting of small temperature increments and including the effect of initial deflection and initial stresses for materials non linearities is presented. Within each temperature increment, the Newton-Raphson iteration method is used for calculating large thermal deflection. Results show that the critical buckling temperature can be raised high enough and the postbuckling deflection can be reduced and controlled for a given operating temperature range by the proper selection of SMA volume fraction, prestrain and alloy composition.
A finite element formulation and solution procedure for the free vibration behavior of composite plates with embedded shape memory alloy (SMA) at elevated temperatures is presented. The temperature-dependent material properties of MA and composite matrix, and the geometrical nonlinearity due to large thermal deflection are considered in the formulation. The solution procedure consists of two steps: large thermal deflection is determined first, then followed by the free vibration analysis about the thermally buckled equilibrium position. Examples of hybrid composite plates are given to show the variation of lowest few frequencies versus temperature and the influence of SMA on the natural frequencies at elevated temperatures. Potential applications to frequency turning and sonic fatigue using SMA are discussed.
A novel concept proposed is the use of SMA to reduce the panel thermal deflection and linear flutter responses. SMA has the unique ability of recovering large prestrain completely when the alloy is heated. During the recovery process, a large tensile recovery stress occurs if the SMA is restrained. In this paper, a panel subject to the combined aerodynamic and thermal loading is investigated. A nonlinear finite element model based on von Karman strain displacement relation is utilized to study the effectiveness of an SMA embedded panel on the flutter boundary, critical buckling temperature and post-buckling deflection. The study is performed on an isotropic panel, with embedded SMA. The aerodynamic model is based on the first order quasi-steady piston theory. The aerodynamic pressure effect on the buckling and post-buckling behavior of the panel is investigated by introducing the aerodynamic stiffness term, which changes both the critical buckling temperature and the post-buckling shape. Panels with SMA embedded in either x or y-direction and either partially or fully embedded are investigated for post-buckling behavior. Similarly, the influence of the temperature elevation on the flutter boundary is investigated by including the thermal terms.
Considerable attention has been devoted to actively and passively control of the sound radiating from vibrating plates into closed cavities. With the advent of smart materials, extensive efforts have been exerted to control the vibration and sound radiation from flexible plates using smart sensors/actuators. Active Constrained Layer Damping (ACLD) treatment has been used successfully for controlling the vibration of various flexible structures. The treatment provides an effective means for augmenting the simplicity and reliability of passive damping with the low weight and high efficiency of active controls to attain high damping characteristics over broad frequency bands. The proposed study is investigated using a numerically simulated example consisting of an ACLD treated plate/acoustic cavity system excited by a point harmonic force. In this study, an ACLD treated plate/acoustic cavity coupled finite element model is utilized to calculate the structural intensity and sound pressure radiated by vibrating plates. In the passive control, the optimum placements of ACLD patches are determined by structural intensity of ACLD treated plates and compared to the results obtained by modal strain energy approach. The influence on structural intensity of plate due to damping treatment is investigated.
Active Constrained Layer Damping (ACLD) treatment has been used successfully for controlling the vibration of various flexible structures. The treatment provides an effective means for augmenting the simplicity and reliability of passive damping with the low weight and high efficiency of active controls to attain high damping characteristics over broad frequency bands. In this study, a self-sensing configuration of the ACLD treatment is utilized to simultaneously suppress the bending and torsional vibrations of plates. The treatment considered ensures collocation of the sensors/actuators pairs in order to guarantee stable operation. A three-layer network of the Self-sensing Active Constrained Layer Damping (SACLD) treatment is used to control multi-modes of vibration of a flexible aluminum plate (0.264 m X 0.127 m X 4.826E-4 m) which is mounted in a cantilevered arrangement. Two ACLD patches (0.264 m X 0.0635 m) with self-sensing polyvinylidine fluoride (PVDF) actuators oriented by (14 degrees/-14 degrees) configuration are treated on one side of plate. The theoretical characteristics of the multi-layer treatment are presented in this paper and compared with the experimental performance.
Active Constrained Layer Damping (ACLD) treatment has been used successfully for controlling the vibration of various flexible structures. It provides an effective means for augmenting the simplicity and reliability of passive damping with the low weight and high efficiency of active controls to attain high damping characteristics over broad frequency bands. In this paper, optimal placement strategies of ACLD patches are devised using the modal strain energy (MSE) method. These strategies aim at minimizing the total weight of the damping treatments while satisfying constraints imposed on the modal damping ratios. A finite element model is developed to determine the modal strain energies of plates treated with ACLD treatment. The treatment is then applied to the elements that have highest MSE in order to target specific modes of vibrations. Numerical examples are presented to demonstrate the utility of the devised optimization technique as an effective tool for selecting the optimal locations of the ACLD treatment to achieve desired damping characteristics over a broad frequency band.
Sound radiation from a plate into an acoustic cavity is controlled using patches of active piezoelectric-damping composites (APDC). The APDC, under consideration, consists of piezoelectric fibers embedded across the thickness of a visco-elastic matrix in order to control the compressional damping characteristics of the composite. The effectiveness of the APDC treatments in attenuating the sound radiation from thin plates into cavities is demonstrated theoretically and experimentally. A finite element model (FEM) is developed to describe the dynamic interaction between the plate, the APDC patches and the acoustic cavity. The FEM is used to predict the dynamics of the plate/acoustic cavity and the sound pressure distribution for different control strategies. The predictions of the FEM are validated experimentally using a square aluminum plate whose sides are 29.8 cm and thickness of 0.04 cm. The plate is mounted on a 29.8 cm $ MUL 29.8 cm X 75 cm cavity. The test plate is treated with a single APDC patch placed at the plate center. The patch is 5 cm X 5 cm X 0.03125 cm which is made of 15-25 percent lead zirconate titanate fibers embedded in soft and hard polymeric resin matrices and provided with silver-epoxy electrodes. Vibration and sound pressure level attenuations of about 70 percent are obtained a the plate/cavity first mode of vibration, with a maximum control voltage of 330 volts using a derivative feedback controller. Such attenuations are attributed to the effectiveness of the APDC treatment in increasing the modal damping ratios by about a factor of four over those of conventional passive constrained layer damping treatments. Comparisons between the theoretical predictions of the FEM with the experimental results indicate close agreement between theory and experiments. The obtained results suggest the potential of the APDC treatments in controlling the sound radiation from plates into acoustic cavities. Such potential can be exploited in many critical applications such as cabins of aircrafts and automobiles to ensure quiet environment for the occupants.
The sound radiation from vibrating NITINOL-reinforced plates coupled with acoustic cavities are controlled by heating sets of shape memory alloy (NITINOL) fibers embedded along the neutral planes of these plates. Thermal, dynamic and acoustic finite element models are developed to study the fundamental phenomena governing the coupling between the dynamics of the NITINOL plates and the acoustic cavities. The models are used to compute the frequencies, mode shapes and sound radiation for different initial tensions and activation strategies of the NITINOL fibers. The predictions of the models are validated experimentally using a square glassfiber/polyester resin plate, whose sides are 19 cm and thickness is 0.254 cm, mounted on a 19 cm X 19 cm X 38 cm cavity. The plate is reinforced with 58 NITINOL fibers that are 0.55 mm in diameter which are embedded inside vulcanized rubber sleeves placed at the plate mid-plane. The results obtained indicate close agreement between the theory and experiments. Also, it is shown that activating all the NITINOL fibers results in increasing the first mode of vibration from 240 Hz to 277.5 Hz and increasing the corresponding loss factor from 0.014 to 0.039. Such significant shift of the modal characteristics of the plates results in suppressing the amplitude of vibration of the plate by 76% and attenuating the sound pressure level radiated inside the cavity by 62%. Therefore, the experimentally validated theoretical models presented in this paper provide invaluable means for predicting sound radiation from NITINOL-reinforced plates in coupled acoustic cavity.
Bending vibration of flat plates is controlled using patches of active constrained layer damping (ACLD) treatments. Each ACLD patch consists of a visco-elastic damping layer which is sandwiched between two piezo-electric layers. The first layer is directly bonded to the plate to sense its vibration and the second layer acts as an actuator to actively control the shear deformation of the visco-elastic damping layer according to the plate response. With such active/passive control capabilities the energy dissipation mechanism of the visco-elastic layer is enhanced and its damping characteristics of the plate vibration is improved. A finite element model is developed to analyze the dynamics and control of flat plates which are partially treated with multi-patches of ACLD treatments. The model is validated experimentally using an aluminum plate which is 0.05 cm thick, 25.0 cm long, and 12.5 cm wide. The plate is treated with two ACLD patches. Each of which is made of SOUNDCOAT (Dyad 606) visco- elastic layer sandwiched between two layers of AMP/polyvinylidene fluoride (PVDF) piezo- electric films. The piezo-electric axes of the patches are set at zero degrees relative to the plate longitudinal axis to control the bending mode. The effect of the gain of a proportional control action on the system performance is presented. Comparisons between the theoretical predictions and the experimental results suggest the validity of the developed finite element model. Also, comparisons with the performance of conventional passive constrained layer damping clearly demonstrate the merits of the ACLD as an effective means for suppressing the vibration of flat plates.
The shape of composite beams is controlled by sets of flat strips of a shape memory nickel-titanium alloy (NITINOL). A mathematical model is developed to describe the behavior of this class of SMART composites. The model describes the interaction between the elastic characteristics of the composite beams and the thermally- induced shape memory effect of the NITINOL strips. The effect of various activation strategies of the NITINOL strips on the shape of the composite beams is determined. The theoretical predictions of the model are validated experimentally using a fiberglass composite beam made of 8 plies of unidirectional BASF 5216 prepregs which are 9.75-cm wide and 21.20 cm long. The beams are provided with four NITINOL-55 strips which are 1.2 mm thick and 1.25 cm wide. The time response characteristics of the beam are monitored and compared with the corresponding theoretical characteristics. Close agreement is obtained between the theoretical predictions and the experimental results. The obtained results suggest the potential of the NITINOL strips in controlling the shape of composite beams without compromising their structural stiffness.
Theoretical and experimental performance characteristics of the new class of actively controlled constrained layer damping (ACLD) treatment are presented. The ACLD under consideration consists of a visco-elastic damping layer which is sandwiched between two piezo-electric layers. The three-layer composite ACLD when bonded to a vibrating structure acts as a SMART constraining layer damping treatment with built-in sensing and actuation capabilities. Particular emphasis is placed on studying the performance of ACLD treatments that are provided with sensing layers of different spatial distributions. The effect of the modal weighting characteristics of these sensing layers on the broad band attenuation of the vibration of beams that are fully treated with the ACLD is presented theoretically and experimentally. The equations governing the operation of ACLD treatments with modally shaped sensors are presented. The theoretical predictions of the model are compared with the experimental performance of a computer-controlled beam treated with Dyad 606 visco-elastic layer sandwiched between two layers of polyvinylidene fluoride (PVDF) piezo-electric films. Comparisons with the performance of conventional passive constrained layer damping are also presented.
Multisegment SMART traversing beams with built-in sensing and actuation capabilities have been considered in various critical applications where weight and deflection are of utmost importance, such as in long support bridges. With such capabilities, light weight SMART segments can be added one at a time to extend the traversing beam over long gaps with minimal deflections and stresses. Each segment of the SMART beam has a set of distributed wire sensors, embedded in its bottom fibers, to sense the beam deflection and another set of wire actuators, embedded in the top fibers, to compensate for the encountered deflections. The theory governing the operation of this class of SMART beams is developed and validated experimentally on a two-segment prototype of the traversing beam whose sides are made of a photoelastic material.
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