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Recently, piezo-aeroelastic energy harvesting has received greater attention. In the present study, a piezo-aeroelastic energy harvester using a nonlinear trailing-edge flap is proposed, and its nonlinear aeroelastic behaviors are investigated. The energy harvester is modeled using a piezo-aeroelastic model of a two-dimensional typical section airfoil with a trailing-edge flap (TEF). A piezo-aeroelastic analysis is carried out using RL and time-integration methods, and the results are verified with the experimental data. The linearizing method using a describing function is used for the frequency domain analysis of the nonlinear piezo-aeroelastic system. From the linear and nonlinear piezo-aeroelastic analysis, the limit cycle oscillation (LCO) characteristics of the proposed energy harvester with the nonlinear TEF are investigated in both the frequency and time domains. Finally, the authors discuss the air speed range for effective piezo-aeroelastic energy harvesting.

Measuring high-intensity turbulence with fast response pressure probe sensors has proved to be an effective and accurate technique; unfortunately, according to the available literature, most pressure probe research focuses primarily on high-velocity (>100 m/s) applications. Commercially available pressure probe sensor systems are available; however, most designs are intended for not only high-velocity flow but also for high bandwidth ( $\sim 10$ kHz) and multidirectional applications, which drastically increase cost and complexity. Extremely limited options exist for those seeking a simple yet sensitive and accurate unidirectional turbulent flow measurement method; therefore, the intended purpose of this paper is to provide a means for future scientists and engineers to develop a pressure probe sensor tailored to their specific needs. Research presented in this paper focuses on the design and analysis of two high-sensitivity, low-cost pressure probes for invasive measurements in low-velocity (

This article presents a fatigue crack characterization technique using a nonlinear instantaneous baseline not only to identify but also to locate fatigue damage in an aluminum plate. In conventional ultrasonic structural health monitoring approaches, damage is identified by comparing the newly measured signal with the baseline signal prerecorded when the structure is in its pristine state. The need to compare the current signals with prerecorded signals makes these methods unattractive, since the measured signals are also affected by the changing environment and load conditions of the structure. To overcome this deficiency, the technique proposed here replaces the prerecorded baseline with an instantaneous baseline which can be obtained when the structure is inspected. The measurement of instantaneous baseline utilizes the nonlinear properties of fatigue cracks when subjected to different amplitudes of excitations. Then damage is characterized in terms of a damage index value which is defined as the spectral changes in each path. The short-time Fourier transform is adopted to obtain the spectrogram. The experimental tests are presented to validate the effectiveness of this damage detection technique. A fatigue crack on an aluminum plate was located accurately with a set of surface-bounded piezoceramic (lead zirconate titanate) transducers by adopting the instantaneous baseline.

This work addresses the influence of nonlinearities in energy harvesting from a piezomagnetoelastic structure subjected to random vibrations. Nonlinear equations of motion that describe the electromechanical system are given along with theoretical simulations. The numerical analysis presents a comparison between the voltage provided from a linear, nonlinear bistable and nonlinear monostable systems due to random vibration. Experimental performance of the generator exhibits qualitative agreement with the theory, showing an enhancement of piezoelectric power generation in a bistable system when it vibrates around both stable equilibrium points. A relationship between variations in the excitation and a bistable system response is established from numerical simulations, defining a region of enhanced power generation when compared to the linear and nonlinear monostable cases.

In an effort to model the vibration response of cabled structures, the distributed transfer function method is developed to model cables and a simple cabled structure. The model includes shear effects, tension, and hysteretic damping for modeling of helical stranded cables, and includes a method for modeling cable attachment points using both linear and rotational damping and stiffness. The damped cable model shows agreement with experimental data for four types of stranded cables, and the damped cabled beam model shows agreement with experimental data for the cables attached to a beam structure, as well as improvement over the distributed mass method for cabled structure modeling.

This study presents the development of a miniature wind turbine that can be used for powering wireless sensors deployed at remote locations. The wind turbine utilizes piezoelectric transducers in order to reduce the start-up speed. Six piezoelectric bimorphs with magnetic tip mass were actuated through attractive and repulsive force between permanent magnets. The design and characterization of the prototype is discussed along with a Finite Element Model (FEM) of the piezoelectric elements. The wind turbine was 23 cm high and 16.5 cm wide. It was able to achieve low cut-in speeds of 1m/s providing power outputs ranging between 0.5 mW and 3 mW for wind speeds in the range of 1 m/s to 4 m/s.

We propose in this paper a numerical modal appropriation method for use with in-operation modal analysis (INOPMA). The key idea is to realize that the correlation sequence of the system output is the sum of decaying sinusoids with a certain phase shift and therefore it may be considered as an impulse response. The method is based on performing a numerical convolution of a single sine wave force with the system output correlation sequence. The steps are then similar to the classical modal appropriation method, although the characteristic frequencies are different. This approach is validated and compared to a subspace method on simulated data as well as on experimental data and it is shown that INOPMA outperforms the subspace method.

Acoustic emission testing has proven useful for real-time damage detection in a variety of situations, however the need for externally bonded sensors limits the feasible applications. This work investigates an alternative approach to traditional acoustic emission testing by using piezoelectric zinc oxide (ZnO) nanowires fully integrated into fiber-reinforced polymer composites. The ZnO nanowires are conformally grown on the surface of woven aramid fabrics via a hydrothermal growth process after which the fabric with ZnO nanowires is placed between layers of woven carbon fiber using vacuum assisted resin transfer molding forming multilayer composites. While the nanowires serve as embedded sensors in the samples, the carbon fiber layer serve as electrodes across which the voltage of the composite can be measured. The composite samples are subjected to a standard tensile test during which the sample voltage output is measured using wire leads attached to the carbon fiber electrodes. Damage to the composite sample during testing results in elastic waves which are converted to measurable electric field by the piezoelectric nanowires. The recorded sample voltage is used to detect instances of internal damage by evaluating the amplitude and number of acoustic emission hits during mechanical testing up to the point of failure. The measured voltage is used to detect internal damage to the composite at less than 50% of the maximum strain thus demonstrating the use of ZnO nanowires in real-time damage detection.

3D printing technologies have made creating prototypes with complex geometries relatively simple thus it has become an increasingly popular method for creating prototypes in a research setting. Therefore, it is crucial to understand the properties of the materials being used. This paper examines the effects of printing direction and testing method type on the complex modulus of viscoelastic materials printed using the Objet Connex 3D Printer from Stratasys. Because of its ability to print multiple materials in a single print job, this printer is a popular choice to create models. Throughout these tests the sample material will be kept constant to isolate the effects of print direction and test performed. DM 8430 is produced by mixing VeroWhitePlus™ and TangoPlus™ in a specific ratio. Since the 3D printer threads and smooths the sample uniaxially, the print direction of the sample can be manipulated by changing the orientation at which the sample is placed on the printer. Two different print directions, that are perpendicular with respect to each other, will be examined. The two test methods that will be used to determine the complex modulus are the Dynamic Mechanical Analysis (DMA) test, which examines the tensile behavior of the material, and the vibrating beam test, which examines the bending behavior. The goal is to gain greater insight into the uncertainty in the complex modulus that results from changing the test and printing direction used to determine this value. This will be done by performing a total of four tests. For each testing method, DMA and vibrating beam, the complex modulus will be found for two samples of different print direction, vertical and horizontal. These results will permit a greater understanding of the amount of variability produced by print direction.

Recently, considerable research works have been conducted towards finding fast and accurate pattern classifiers for identifying structural damage when applied to Structural Health Monitoring (SHM) systems. In this way, this paper presents a novel approach for damage identification in SHM systems by proposing the use of the Kappa coefficient as a metric for damage detection in SHM systems. Here, Kappa is also proposed along with PSO-Fuzzy ARTMAP neural network aiming to reduce the amount of attributes, leaving only the most representative features. It is important to highlight that Kappa coefficient analyses the whole confusion matrix instead of using only the principal diagonal as used, for instance, when we compute success rates. Additionally, the Particle Swarm Optimization (PSO) algorithm is used in searching for a set of criteria employees in training damage classifier, in order to maximize the accuracy rate of the classifier. Hence, the Fuzzy ARTMAP Network (FAN) algorithm is used to identify structural damage. The performance of this new strategy is evaluated considering an experimental setup based on the Electromechanical Impedance (EMI) technique, in the time domain, which uses four piezoelectric patches glued onto a unidirectional composite plate. Damage scenarios were simulated by loosening bolts at different positions. The paper discusses the effectiveness of the proposed methodology in light of the experimental results.

Along with recent advancements in novel materials and manufacturing processes, the interest in morphing wings has increased in order to further improve the aerodynamic performance of flying bodies. The morphing wing can be tailored to deliver superior performance, compared to its non-morphing counterparts, for multiple operating conditions and in varying flows. In particular, the morphing wing is implemented for drag reduction and lift enhancement, and hence, the maneuverability, adaptability, and capability of the morphing wing can encompass an even wider spectrum by changing the wing shape. In this research, an existing morphing UAV wing design, Spanwise Morphing Trailing Edge (SMTE), actuated by bending Macro Fiber Composites (MFCs), is considered to generate the spanwise sinusoidal variations on the trailing edge of the morphing wing. A comparative aerodynamic study of the morphing wing by varying the spatial frequency (i.e., number of waves along the span) and the phase shift (i.e., wave shape along the span) at different angles of attack is conducted through analytical approaches and numerical Computational Fluid Dynamic (CFD) simulations, which are validated with previous experimental measurements. The analytical approach uses the three-dimensional (3D) Prandtl lifting line theory, and the CFD modeling in turbulence flow solves the 3D Reynolds-Averaged Navier-Stokes (RANS) equations with the k-ω Shear Stress Transport (SST) turbulence model. Note that the numerical simulations of a morphing wing focus on the pre-stall condition to estimate the aerodynamic performance. This work extends a prior study about a nominal flight condition testing a morphing wing at multiple flight conditions to evaluate multi-point 1 performance. The results show that there are governing aerodynamic efficiency zones of the lift-to-drag ratio, endurance, and aircraft range within a zone of angles of attack. Therefore, the morphing wing is shown to have a good aerodynamic performance as compared to the non-morphing wing.

This study is at attempt to explore the nonlinear behavior of bistable composite laminates for vibration energy harvesting. Asymmetric four-ply [0/90/0/90] carbon-fiber plate with two cylindrical stable equilibria supported at its center and free at all boundaries is used for the experimental testing. Macro-fiber composite (MFC) patches are attached to the plate to transform the mechanical vibration energy into electrical energy. The mechanical bistable property of the plate makes it possible to snap from one stable equilibrium state to the other. This snapthrough motion is highly nonlinear and associated with large-amplitude vibrations. The experimental tests aim at exploiting the nonlinearity due to the snapthrough motion to enhance the energy extraction. First, the resonant frequencies and damping of the plate are identified. A primary-resonance excitations of the first mode are carried out using two schemes: amplitude sweep and frequency sweep. In the first case, amplitude sweep, the excitation frequency is kept fixed at the resonant frequency and the amplitude of excitation is increased. The time history and FFT of the response as well as the output voltage are measured and reported. In the second case, frequency sweep, the excitation frequency is varied around the resonant frequency while the excitation amplitude is kept fixed. In both cases, the response shows a small-amplitude single-well vibrations at low excitation amplitudes and chaotic and periodic snapthrough motion as the amplitude and frequency of excitation are varied. The snapthrough motion has been found to greatly enhance the energy extraction capability. This study can serve as a motive for more testing and modeling efforts in order to understand the complex nonlinear behavior of bistable composite laminates and exploit it for vibration energy harvesting.

The article examines the effectiveness of metastructures for vibration suppression from a weight standpoint. Metastructures, a metamaterial inspired concept, are structures with distributed vibration absorbers. In automotive and aerospace industries, it is critical to have low levels of vibrations while also using lightweight materials. Previous work has shown that metastructures are effective at mitigating vibrations, but do not consider the effects of mass. This work takes mass into consideration by comparing a structure with vibration absorbers to a structure of equal mass with no absorbers. These structures are modeled as one-dimensional lumped mass models, chosen for simplicity. Results compare both the steady-state and the transient responses. As a quantitative performance measure, the H 2 norm, which is related to the area under the frequency response function, is calculated and compared for both the metastructure and the baseline structure. These results show that it is possible to obtain a favorable vibration response without adding additional mass to the structure. Additionally, the performance measure is utilized to optimize the geometry of the structure, determine the optimal ratio of mass in the absorber to mass of the host structure, and determine the frequencies of the absorbers. The dynamic response of this model is verified using a finite element analysis.

Presented in this paper is a method for force analysis of a single-input multiple-output (SIMO) linkage array that is designed for curve morphing applications, such as morphing airfoils. Different from the existing force methods, this method is developed to determine the force of a single actuator at the front that is needed to resist the forces on each loop for the entire multiloop linkage system. The proposed method is based on a full force model of a single loop four-bar linkage. When this model is applied to a multiloop system, two force sources are considered for each loop, namely the external point force on the coupler and the internal transition torque from the proceeding loop. As a result, a recursive method is proposed to compute the force from the last loop through intermediate loops to the first loop. The force vector of the first loop represents the required force of the single actuator needed to counteract the forces experienced by all the coupler forces. A number of simulations are performed and compared with FEM results to prove its effectiveness.

This paper presents an overview of impedance-based structural health monitoring, which has been pioneered by Inman and his research group. The basic principle behind this technique is to apply high frequency structural excitations (typically greater than 30 kHz) through the surface-bonded piezoelectric transducers, and measure the impedance of structures by monitoring the current and voltage applied to the piezoelectric transducers. Changes in impedance indicate changes in the structure, which in turn can indicate that damage has occurred. For the last two decades, extensive research works have been performed to various applications, including mechanical, aerospace and civil structural components. The technique has been also extended to piezoelectric sensor diagnostics, concrete cure monitoring, and biomedical applications. This paper presents the summary of how this technique has been evolved with the significant contribution by Inman.

This work addresses two issues in lightweight structural composites suitable for aerospace systems. The first is to add additional functionality to multifunctional composites and the second is to provide damping in structures that cover a wide range of frequencies and temperatures. Passive damping in all materials suffer from failing at certain temperature and in certain frequency ranges. The extreme environments often seen by aerospace structures provide high temperature, which is exactly where damping levels in structures reduce causing unacceptable vibrations. In addition, as loading frequencies decrease damping levels fall off, and many loads experienced by aerospace structures are low frequency. This work looks at the implementation of a control system to a longitudinal metastructure bar. A metastructure is a structure which has distributed vibration absorbers which provide passive damping to the system. The active control system will be implemented by adding piezoelectric materials to one of the absorbers to make the absorber active. The structure with the active vibration absorber will be compared to a structure of equal weight with no active components. Since the two comparison structures are of equal weight, the performance improvements are strictly due to the control system and not at the cost of additional weight.

Made available in DSpace on 2018-12-11T17:11:57Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-05-01 This article presents a novel approach for damage detection applied to structural health monitoring systems exploring the residues obtained from singular spectrum analysis. In this technique, a lead zirconate titanate patch acting as actuator excites the structure, and three other patches are used as sensors to receive the structural responses. This method is based on a high-frequency excitation range in order to overcome the problem caused when the low-vibration modes are excited. In this method, a wideband chirp signal, with low amplitude and variable frequency, is used to excite the structure. The response signals are acquired in the time domain, and the singular spectrum analysis procedure is performed. The residues obtained between the reconstructed and original time series are used to compute statistical metrics. The residues calculated from singular spectrum analysis are used to compute the root mean square deviation and correlation coefficient deviation metric indices, rendering the damage detection approach more reliable. Tests were carried out on an aluminum plate, and the results have demonstrated the effectiveness of the proposed method making it an excellent approach for structural health monitoring applications. The results exploring different numbers of components used during the reconstruction process of time series are obtained, and the highlights are presented. Department of Electrical and Electronic Federal Institute of Education Science and Technology of Mato Grosso (IFMT), Campus de Cuiaba Department of Telecommunication Engineering Universidade Estadual Paulista (UNESP), Campus de Sao Joao da Boa Vista Department of Mechanical Engineering Universidade Estadual Paulista (UNESP), Campus de Ilha Solteira Department of Aerospace Engineering University of Michigan Department of Telecommunication Engineering Universidade Estadual Paulista (UNESP), Campus de Sao Joao da Boa Vista Department of Mechanical Engineering Universidade Estadual Paulista (UNESP), Campus de Ilha Solteira

Inspired by the wave-like camber variation in the trailing edge feathers of large birds, the aerodynamic impact of similar variations in the geometry of morphing wings is investigated. The scope of this problem is reduced by exploring parametrically generated geometries derived from an existing morphing wing design, namely the Spanwise Morphing Trailing Edge (SMTE), which is actuated via conformally integrated Macro Fiber Composites (MFCs). Utilizing this design, the deformation of the trailing edge of the SMTE is parameterized as a function of the spanwise location using a sinusoidal relationship. The aerodynamic responses are then obtained using Computational Fluid Dynamics (CFD) simulations, while the efficacy of the proposed approach is explored using a Pareto-like frontier approach.

Macro-Fiber Composites (MFCs) are a piezoelectric material typically employed in applications ranging from vibration damping to actuation to structural health monitoring. These composites have flown in space but only with thermal protection and for a short duration. They have not been significantly tested under thermally cyclic conditions similar to those they would experience in Low-Earth Orbit (LEO) without shielding. Research has shown that the performance of MFCs varies when the MFC undergoes a thermal cycle. This paper outlines an autonomous experiment that will be able to run impedance measurements and actuate MFCs, further testing their performance in a space environment where thermal cycles are common. This will be installed on a CubeSat and flown to LEO where it will collect data and downlink it back for study. Details of the layout of the experiments and electronic systems being used on the CubeSat for the payload are presented alongside future steps that need to be taken to ensure a successful flight.

The bistability and snap through capability of an unsymmetric laminate consisting of only Macro Fiber Composites (MFC) are investigated. The non-linear analysis predicts two cylindrically stable configurations when strain anisotropy is piezoelectrically induced within a [0MFC/90MFC]T laminate. This is achieved by bonding two MFCs in their actuated states and releasing the voltage post cure to create in-plane residual stresses. The minimization of total potential energy with the Rayleigh-Ritz method are used to analytically model the resulting laminate. A finite element analysis is conducted in MSC Nastran using the piezoelectric-thermal analogy approach to verify the analytical results. The effects of adhesive properties, bonding cure cycles, MFC layup, and its geometry on the curvatures, displacements, and bifurcation voltages are characterized. Finally, the snap through and reverse snap through capabilities with piezoelectric actuation are demonstrated. This adaptive laminate functions as both the actuator and the primary structure and allows large deformations under a non-continuous energy input. Its snap through capability allows full configuration control necessary in morphing applications.

The research presented in this paper focuses on a unique multifunctional structural design that not only absorbs vibration at desired frequency bands, but also extracts significant amounts of electrical energy. This is accomplished by first designing an array of low-frequency resonators to be integrated into a larger host structure. This array of resonators can contribute not only to static requirements, e.g., stiffness, strength, mass, etc., of the host structure but the array also functions as a distributed system of passive vibration absorbers. Structures having these distributed vibration absorber systems are known as metastructures. Here, the authors present a unique absorber design referred to as a zigzag beam, which can have a natural frequency an order of magnitude lower than that of a basic cantilever beam of the same scale. It will be shown that the zigzag beams can be designed with an added layer of piezoelectric material, which allows them to harvest significant amounts of electrical power as they suppress vibration of the host structure. This paper includes details of the fully-coupled electromechanical analytical and numerical models for energy harvesting metastructures. Experimental results used to validate the proposed modeling methods will be discussed. Lastly, results of a multi-objective design optimization will be presented and discussed. Results of the optimization study were able to show that allowing only an 82 % increase in the host structure vibration could yield more than a 1500 % increase in total power output. Other results show that the power output (or absorber motion) could be increased 241% without increasing host structure vibrations due to multiple design solutions existing at fixed host structure vibration levels.

In this paper, a new design is presented for shape morphing using parameterized curves. Inspired by minimal actuation effort, a multiloop linkage is designed with a single input, allowing a morphing curve to take on three distinct shapes. The underlying design is based on a network of four-bar linkages connected together to form a multiloop linkage, referred to as the curve adaptive linkage array (CALA). A three-step method is developed and presented here to find the geometric dimensions of the CALA. The proposed solution is based on the simultaneous recursive solving of the traditional single-loop dyad equations for multiple loops. The key in obtaining a feasible solution is through parameterization of the curves that the linkage is required to morph. To show the effectiveness of the method, an airfoil morphing application is presented, solved using the proposed method, and validated by a prototype. The presented synthesis method provides an effective means for designing a multiloop linkage with a single input.

This work looks at the effectiveness of constant weight metastructures for vibration suppression. A metastructure is a structure with distributed vibration absorbers. The metastructures are compared to a baseline structure of equal mass. The equal mass constraint shows that any increase in performance is due to the addition of the vibration absorbers and not due to adding additional mass to the structure. In this paper, two different metastructure designs are compared. These structures are designed to suppress longitudinal vibrations traveling along the length of the bar. The metastructures have ten vibration absorbers distributed on the length of the bar and the ratio of mass of the absorbers to mass of the host structure is 0.26. One metastructure has all the absorbers tuned to the natural frequency of the host structure and the other metastructure uses absorbers that are tuned to frequencies that have linearly varying natural frequencies. These structures were modeled using two different methods, a one-dimensional (1D) finite element method with lumped mass vibration absorbers and a fully three-dimensional (3D) finite element model. The results show that the metastructure with linearly varying natural frequencies outperforms that metastructure with vibration absorbers tuned to a single natural frequency.

Structural health monitoring (SHM) and vibration-based structural damage detection have been a continuous interest for civil, mechanical and aerospace engineers over the decades. Early and meticulous damage detection has always been one of the principal objectives of SHM applications. The performance of a classical damage detection system predominantly depends on the choice of the features and the classifier. While the fixed and hand-crafted features may either be a sub-optimal choice for a particular structure or fail to achieve the same level of performance on another structure, they usually require a large computation power which may hinder their usage for real-time structural damage detection. This paper presents a novel, fast and accurate structural damage detection system using 1D Convolutional Neural Networks (CNNs) that has an inherent adaptive design to fuse both feature extraction and classification blocks into a single and compact learning body. The proposed method performs vibration-based damage detection and localization of the damage in real-time. The advantage of this approach is its ability to extract optimal damage-sensitive features automatically from the raw acceleration signals. Large-scale experiments conducted on a grandstand simulator revealed an outstanding performance and verified the computational efficiency of the proposed real-time damage detection method.

Vibration suppression remains a crucial issue in the design of structures and machines. Recent studies have shown that with the use of metamaterial inspired structures (or metastructures), considerable vibration attenuation can be achieved. Optimization of the internal geometry of metastructures maximizes the suppression performance. Zigzag inserts have been reported to be efficient for vibration attenuation. It has also been reported that the geometric parameters of the inserts affect the vibration suppression performance in a complex manner. In an attempt to find out the most efficient parameters, an optimization study has been conducted on the linear zigzag inserts and is presented here. The research reported in this paper aims at developing an automated method for determining the geometry of zigzag inserts through optimization. This genetic algorithm based optimization process searches for optimal zigzag designs which are properly tuned to suppress vibrations when inserted in a specific host structure (cantilever beam). The inserts adopted in this study consist of a cantilever zigzag structure with a mass attached to its unsupported tip. Numerical simulations are carried out to demonstrate the efficiency of the proposed zigzag optimization approach. The financial support for this research was provided by Qatar National Research Fund, QNRF (a member of Qatar Foundation) via the National Priorities Research Program (NPRP), Project Number: NPRP 6-526-2-218 . Daniel J. Inman's work is supported in part by the U.S. Air Force Office of Scientific Research under the grant number FA9550-14-1-0246 Electronic Damping in Multifunctional Material Systems monitored by Dr. B.L. Lee. The statements made herein are solely the responsibility of the authors. Scopus

Research involving energy harvesters to power systems are often carried out in a laboratory setting where vibration excitations are created using shakers. These excitations can be tuned to the natural frequency of the harvester to achieve the highest power output possible for the harvester design. Adapting these designs for use in real world applications introduces many additional layers of complexity. These added complications come in various forms including different input vibration and acceleration profiles, sensor energy requirements, and space constraints. Existing optimization for application-based research is limited to one set of constraints and cannot be applied to different cases.

Metastructures are known to provide considerable vibration attenuation for mechanical systems. With the optimization of the internal geometry of metastructures, the suppression performance of the host structure increases. While the zigzag inserts have been shown to be efficient for vibration attenuation, the geometric properties of the inserts affect the suppression performance in a complex manner when attached to the host structure. This paper presents a genetic algorithm based optimization study conducted to come up with the most efficient geometric properties of the zigzag inserts. The inserts studied in this paper are simply cantilever zigzag structures with a mass attached to the unsupported tips. Numerical simulations are run to show the efficiency of the optimization process. Scopus

Most of the classical structural damage detection systems involve two processes, feature extraction and feature classification. Usually, the feature extraction process requires large computational effort which prevent the application of the classical methods in real-time structural health monitoring applications. Furthermore, in many cases, the hand-crafted features extracted by the classical methods fail to accurately characterize the acquired signal, resulting in poor classification performance. In an attempt to overcome these issues, this paper presents a novel, fast and accurate structural damage detection and localization system utilizing one dimensional convolutional neural networks (CNNs) arguably for the first time in SHM applications. The proposed method is capable of extracting optimal damage-sensitive features automatically from the raw acceleration signals, allowing it to be used for real-time damage detection. This paper presents the preliminary experiments conducted to verify the proposed CNN-based approach. Scopus

This paper proposes the theoretical model and experimental investigations of a broadband piezoelectric based vibration energy harvester with a triple-well potential induced by a magnetic field. The mathematical model is derived from the energy method to describe the response characteristics of nonlinear tristable energy generators. The parameters of the linear energy harvesting system without magnetic force actuation are obtained through intelligent optimization of the minimum error between numerical simulations and experimental responses. The equivalent nonlinear restoring force of the tristable oscillator is experimentally identified as a high order polynomial. Numerical simulations and experiments are performed at different harmonic excitation levels ranging from 1 to 20 Hz. The results verify that the identified electromechanical model can describe the dynamic characteristics of broadband tristable energy harvesters. Furthermore, in comparison to bistable nonlinear energy oscillators with deeper potential well, the tristable arrangement passes easily through potential wells for generating higher energy output over a wider range of frequency.

Spaceflight cables are investigated to determine the effect of bakeout on their dynamic response, including resonant frequencies and damping ratios. The addition of cable harnesses to spacecraft structures can affect the dynamic response of the entire structure, especially for lightweight structures with high cable mass ratios. Bakeout, a heat and vacuum treatment that spaceflight components must undergo, may change the dynamic stiffness of flight cables and thus the dynamics of the cabled host structure. Bakeout effects are examined by experimentally identifying natural frequencies and damping values for spaceflight cables before and after the bakeout process. After bakeout, the first natural frequency decreases by an average of 14% for all single-strand cables and by 24% for multistrand cables. The second natural frequency decreases by 8 to 17% for all cables. Bakeout also increases the damping percentage for single and multistrand cables. These results show that bakeout affects the dynamic response of ...

To obtain predictive modeling of the spacecraft, we investigate the effects of adding cables to a simple structure with the goal of developing an understanding of the effects of cables interacting with a structure. In this paper, we present modeling of a cable-harnessed structure by means of the Spectral Element Method (SEM). A double beam model is used to emulate a cable-harnessed structure. SEM modeling can define the location and the number of connections between the two beams in a convenient fashion. The presented modeling is applied and compared with the conventional FEM. The modeling approach was compared and validated with experimental measurements. The validated modeling was implemented to investigate the effect of the number of connections and of the spring stiffness of interconnections. The results show that the proposed modeling can be used as an accurate and efficient solution methodology for a cable-harnessed structure.

This article describes the development and characterization of the synergistic smart morphing aileron concept, which leverages the properties of two different smart material actuators to achieve performance that exceeds that of the constituent materials. Utilizing the relatively higher work density and phase transformation of shape memory alloys combined with the larger bandwidth and conformal bending of bonded piezoelectric macro-fiber composites, the resultant synergistic morphing design improves the range of static tip deflections, enabling the capability to hold more trim positions over long timescales while still quickly compensating for dynamic loading. By commanding an input of full-range square waves of 0.01–10 Hz to the actuators, first-order time responses were measured and characterized using a common methodology by tracking a relative time constant. Using this method, aeroelastic effects for each actuator and the combined system were characterized in a wind tunnel at 0° angle of attack with flow speeds ranging from 0 to 15 m/s. This novel approach characterized a large-deflection morphing actuation system with multiple smart materials operating over different timescales. The combined system achieved additive amplitude while tracking the faster actuation response of the macro-fiber composite between 0.1 and 1 Hz.

When a mechanical and/or structural component is immersed in a fluid and it vibrates, the reasonable assumption is that part of the energy is transmitted to the adjacent media. For some engineering applications the energy transport between these two domains, i.e., structure and fluid, plays a central role. The work presented in this paper is focused on discussing the energy transport in beam-like structures as they can be used to represent flexible swimmers (fish-like pulsating mechanisms) in their simplest form. In order to expose the role of each of the fluid and beam properties effecting the energy transfer process, a simplified analytical fluid–structure interaction (FSI) model is derived. After analysis of the resulting coupled-systems' damping coefficient, a new energy transport component is added to the initial Euler–Bernoulli beam equation; a term associated with diffusion (fluid viscosity). In addition our modeling results in an added mass term, a characteristic consistent with previous literature. While deriving the model, an important assumption is made: beam mode shapes are not significantly affected by the domains' interaction. This hypothesis is experimentally tested in two different fluid media and confirmed to be reasonable for the first three vibration mode shapes.

In the odyssey of achieving further lightweight space structures and systems, optical-quality membrane mirrors are expected to replace the conventional, metal-based and glass-based, rigid mirrors. These thin film membranes offer an order of magnitude size increase in apertures and in weight reduction. Some of these membrane mirrors are coupled to a pressurized cavity with the end goal of using the pressure in the chamber for shape control. The replacement of rigid mirrors for optical quality membrane mirrors is still a large area of research with many questions thus far requiring further investigation. These areas include modeling, material properties, fabrication due to high tolerances required for imaging, storage, and deployability. The ability to accurately model and predict the dynamics of these space-based membrane mirrors is of great importance. This will lead to more adequate design and manufacturing processes and optimized performance of such systems. The work presented here focuses on the validation of an impedance-based model of a membrane in air and of a coupled membrane–cavity system using experimental results. The impedance based model takes into account sound radiation and energy loss to the far field. This is crucial in earth-based telescopes and also very important when testing and validating these systems on earth before being launched into space.

Piezoelectric materials play a significant role in harvesting ambient vibration energy. Due to their inherent characteristics and electromechanical interaction, the system damping for piezoelectric energy harvesting can be adequately characterized by fractional calculus. This paper introduces the fractional model for magnetically coupling broadband energy harvesters under low-frequency excitation and investigates their nonlinear dynamic characteristics. The effects of fractional-order damping, excitation amplitude, and frequency on dynamic behaviors are proposed using the phase trajectory, power spectrum, Poincare map, and bifurcation diagram. The numerical analysis shows that the fractionally damped energy harvesting system exhibits chaos, periodic motion, chaos and periodic motion in turn when the fractional order changes from 0.2 to 1.5. The period doubling route to chaos and the inverse period doubling route from chaos to periodic motion can be clearly observed. It is also demonstrated numerically and experimentally that the magnetically coupling piezoelectric energy harvester possesses the usable frequency bandwidth over a wide range of low-frequency excitation. Both high-energy chaotic attractors and large-amplitude periodic response with inter-well oscillators dominate these broadband energy harvesting.

The exploitation of nonlinear behavior in vibration-based energy harvesters has received much attention over the last decade. One key motivation is that the presence of nonlinearities can potentially increase the bandwidth over which the excitation is amplified and therefore the efficiency of the device. In the literature, references to resonating energy harvesters featuring nonlinear oscillators are common. In the majority of the reported studies, the harvester powers purely resistive loads. Given the complex behavior of nonlinear energy harvesters, it is difficult to identify the optimum load for this kind of device. In this paper the aim is to find the optimal load for a nonlinear energy harvester in the case of purely resistive loads. This work considers the analysis of a nonlinear energy harvester with hardening compliance and electromagnetic transduction under the assumption of negligible inductance. It also introduces a methodology based on numerical continuation which can be used to find the optimum load for a fixed sinusoidal excitation.

Materials like the Macro-fiber Composite (MFC) are employed in energy harvesting applications utilizing the piezoelectric effect. However, energy harvesting using the pyroelectric effect in MFCs is an unexplored topic. This paper takes strides in understanding the thermal micromechanical interactions that MFCs experience due to this effect and leads to a better understanding of how MFCs behave in thermal environments. In this work, the pyroelectric coefficient (primary and secondary) are estimated for P1 and P2 Macro-fiber Composites (MFCs) using micromechanical modeling and experimental techniques. The coefficient of thermal expansion (CTE) is estimated using micromechanical theory for both MFC types which is consequently used in the modeling of the pyroelectric coefficient. Secant based moduli are used to better approximate the properties of components of MFCs in the regime of linear elasticity. Two experiments are conducted to measure the pyroelectric coefficient under different boundary conditions. In the first experiment, the thermal expansion of the MFC is constrained in a Kevlar envelope, while in the second experiment, the MFC is epoxied onto a metal shim allowing restricted deformations. Thermal experiments were conducted in an altitude chamber where the resulting average pyroelectric coefficient is calculated for both experiments.

In this paper, free vibration analysis of cracked composite beam subjected to coupled bending–torsion loading is presented. The composite beam is assumed to have an open edge crack of length a. A first order shear deformation theory is applied to count for the effect of shear deformations on natural frequencies as well as the effect of coupling in torsion and bending modes of vibration. Governing equations and boundary conditions are derived using Hamilton principle. Local flexibility matrix is used to obtain the additional boundary conditions of the beam in cracked area. After obtaining the governing equations and boundary conditions, generalized differential quadrature (GDQ) method is applied to solve the obtained eigenvalue problem. Finally, some numerical results of beams with various boundary conditions and different fiber orientations are given to show the efficiency of the method. In addition, to study the effect of shear deformations, numerical results of the current model are compared with previously given results in which shear deformations were neglected.

This paper investigates the frequency dependent viscoelastic dynamics of a multifunctional composite structure from finite element analysis and experimental validation. The frequency-dependent behavior of the stiffness and damping of a viscoelastic material directly affects the system's modal frequencies and damping, and results in complex vibration modes and differences in the relative phase of vibration. A second order three parameter Golla–Hughes–McTavish (GHM) method and a second order three fields Anelastic Displacement Fields (ADF) approach are used to implement the viscoelastic material model, enabling the straightforward development of time domain and frequency domain finite elements, and describing the frequency dependent viscoelastic behavior. Considering the parameter identification a strategy to estimate the fractional order of the time derivative and the relaxation time is outlined. Agreement between the curve fits using both the GHM and ADF and experiment is within 0.001 percent error. Continuing efforts are addressing the material modulus comparison of the GHM and the ADF model. There may be a theoretical difference between viscoelastic degrees of freedom at nodes and elements, but their numerical results are very close to each other in the specific frequency range of interest. With identified model parameters, numerical simulation is carried out to predict the damping behavior in its first two vibration modes. The experimental testing on the layered composite beam validates the numerical predication. Experimental results also show that elastic modulus measured from dynamic response yields more accurate results than static measurement, such as tensile testing, especially for elastomers.

The continuing need for reduced power requirements for small electronic components, such as wireless sensor networks, has prompted renewed interest in recent years for energy harvesting technologies capable of capturing energy from ambient vibrations. A particular focus has been placed on piezoelectric materials and devices due to the simplicity of the mechanical to electrical energy conversion and their high strain energy densities compared to electrostatic and electromagnetic equivalents. In this paper an arrangement of piezoelectric layers attached to a bistable asymmetric laminate is investigated experimentally to understand the dynamic response of the structure and power generation characteristics. The inherent bistability of the underlying structure is exploited for energy harvesting since a transition from one stable configuration to another, or "snap-through", is used to repeatedly strain the surface bonded piezoelectric and generate electrical energy. This approach has been shown to exhibit high levels of power extraction over a wide range of vibrational frequencies. Using high speed digital image correlation, a variety of dynamic modes of oscillation are identified in the harvester. The sensitivity of such modes to changes in vibration frequency and amplitude are investigated. Power outputs are measured for repeatable snap-through events of the device and are correlated with the measured modes of oscillation. The typical power generated is approximately 3.2 mW, comparing well with the needs of typical wireless senor node applications.

In the present study, a piezo-aeroelastic energy harvester using nonlinear aeroelastic behaviors is proposed, and their characteristics and performance are investigated. The energy harvester is modeled by a two-dimensional typical section airfoil. The nondimensional parameters of the harvester are introduced, and the nondimensional piezo-aeroelastic equations are formulated. For the piezo-aeroelastic analysis, the root-locus method and time-integration method are used, and the present method is verified with experimental and analytical results. The iterative method is introduced to calculate the frequency response functions of a nonlinear piezo-aeroelastic energy harvester. The aeroelastic characteristics of a linear piezo-aeroelastic energy harvester and the effects of parameters are investigated. The results show that the linear piezo-aeroelastic energy harvester can be used to generate electricity only at the vicinity of flutter speed. It is assumed that the nonlinear piezo-aeroelastic energy harvester has free play and cubic hardening in pitch. For free play, nonlinear aeroelastic results show that stable limit cycle oscillations are observed in the wide range of air speed below flutter speed when the frequency ratio is 1.3, and unstable limit cycle oscillations are observed at air speeds over flutter speed when the frequency ratio is 0.3. For cubic hardening, unstable limit cycle oscillations are observed at air speeds below flutter speed when the frequency ratio is 0.3, and stable limit cycle oscillations are observed at air speeds over flutter speed when the frequency ratio is 1.3. Finally, the authors discussed how to use these aeroelastic responses for piezo-aeroelastic energy harvesting.

This paper experimentally examines a multifunctional gust alleviation system and holds promise for improving small unmanned aerial vehicles performance in wind gusts. The designed multifunctional wing spar is able to harvest energy itself from the normal vibrations during flight. If the wing experiences any strong wind gust, it will provide vibration control to maintain its stability. The proposed wing spar carries on the functions of energy harvesting, strain sensing, and gust alleviation via piezoelectric materials. A closed form electromechanical cantilever multifunctional beam model is developed, which captures the basics of piezoelectric constitute equations using Euler-Lagrange equations. An enhanced two mode reduced energy control (REC) law is developed to saturate a positive strain feedback (PSF) control law, and therefore decrease energy consumption but maintains the same gust alleviation performance. An equivalent circuit model is also developed based on the distributed parameter method to represent a multifunctional gust alleviation system using harvested energy. Experimental results show that compared to conventional PSF control law, the REC decreases voltage supply from ±20 to ±4 V, uses 76% less energy whereas maintaining the same performance. Experimental results also show that it is feasible to alleviate wind gust disturbance using harvested power from ambient vibrations, but requires the harvesting time to be 0.42 times longer than the wind gust duration.

This paper presents a theoretical investigation of free vibration analysis of a functionally graded beam (FGM) under the bending-torsion loading using a classical elasticity theory. The FG beam is assumed to have an open edge crack. It is assumed that the material properties of the simply-supported cracked beam, vary along the beam thickness following a polynomial distribution in the thickness direction. This analysis is based on the linear fracture mechanics. First of all, governing equations and boundary conditions of the FG beam are derived using Hamilton's principle. The governing equations are solved using generalized differential quadrature (GDQ) method. By applying GDQ method, the governing differential equations convert to a linear system of algebraic equations. Then solving the eigenvalue problem, natural frequencies of the FG beam can be found. The results indicate that natural frequencies in the presence of a crack are affected by the crack ratio and location.