Showing papers in "Journal of Vibration and Acoustics in 2010"
TL;DR: In this paper, a nonlinear electromagnetic energy harvesting device with a broadly resonant response was presented, which is generated by a particular arrangement of magnets in conjunction with an iron-cored stator.
Abstract: In this paper, we present a nonlinear electromagnetic energy harvesting device that has a broadly resonant response. The nonlinearity is generated by a particular arrangement of magnets in conjunction with an iron-cored stator. We show the resonant response of the system to both pure-tone excitation and narrow-band random excitation. In addition to the primary resonance, the superharmonic resonances of the harvester are also investigated and we show that the corresponding mechanical upconversion of the excitation frequency may be useful for energy harvesting. The harvester is modeled using a Duffing-type equation and the results are compared with the experimental data.
324 citations
TL;DR: In this paper, the authors investigated dispersion curves and the band gap structure of a multiresonator mass-in-mass lattice system, which consists of three separate masses connected by linear springs.
Abstract: In this study, we investigated dispersion curves and the band gap structure of a multiresonator mass-in-mass lattice system. The unit cell of the lattice system consists of three separate masses connected by linear springs. It was demonstrated that the band gaps can be shifted by varying the spring constant and the magnitude of the internal masses. By using the conventional monatomic (single mass) lattice model as an equivalent system, the effective mass was found to become negative for frequencies in the band gaps. An attempt was made to represent the two-resonator mass-in-mass lattice with a microstructure continuum model. It was found that the microstructure continuum model can capture the dispersive behavior and band gap structure of the original two-resonator mass-inmass system. DOI: 10.1115/1.4000784
269 citations
TL;DR: In this article, the effect of nonlinearities on harmonic wave propagation in one-dimensional nonlinear periodic structures is investigated through a novel perturbation analysis and accompanying numerical simulations, where several chain unit cells are considered featuring a sequence of masses connected by linear and cubic springs.
Abstract: Wave propagation in one-dimensional nonlinear periodic structures is investigated through a novel perturbation analysis and accompanying numerical simulations. Several chain unit cells are considered featuring a sequence of masses connected by linear and cubic springs. Approximate closed-form, first-order dispersion relations capture the effect of nonlinearities on harmonic wave propagation. These relationships document amplitude-dependent behavior to include tunable dispersion curves and cutoff frequencies, which shift with wave amplitude. Numerical simulations verify the dispersion relations obtained from the perturbation analysis. The simulation of an infinite domain is accomplished by employing viscous-based perfectly matched layers appended to the chain ends. Numerically estimated wavenumbers show good agreement with the perturbation predictions. Several example chain unit cells demonstrate the manner in which nonlinearities in periodic systems may be exploited to achieve amplitude-dependent dispersion properties for the design of tunable acoustic devices.
202 citations
TL;DR: In this paper, the authors compared two adaptive decomposition methods: local mean decomposition and empirical mode decomposition (EMD) from four aspects, i.e., local mean, decomposed components, instantaneous frequency, and the wavelet-like filtering characteristic through numerical simulation.
Abstract: Health diagnosis of the rotating machinery can identify potential failure at its early stage and reduce severe machine damage and costly machine downtime. In recent years, the adaptive decomposition methods have attracted many researchers’ attention, due to less influences of human operators in the practical application. This paper compares two adaptive methods: local mean decomposition (LMD) and empirical mode decomposition (EMD) from four aspects, i.e., local mean, decomposed components, instantaneous frequency, and the waveletlike filtering characteristic through numerical simulation. The comparative results manifest that more accurate instantaneous frequency and more meaningful interpretation of the signals can be acquired by LMD than by EMD. Then LMD and EMD are both exploited in the health diagnosis of two actual industrial rotating machines with rub-impact and steam-excited vibration faults, respectively. The results reveal that LMD seems to be more suitable and have better performance than EMD for the incipient fault detection. LMD is thus proved to have potential to become a powerful tool for the surveillance and diagnosis of rotating machinery.
176 citations
TL;DR: In this paper, the authors describe a numerical and experimental investigation on the flexural wave propagation properties of a novel class of negative Poisson's ratio honeycombs with tetrachiral topology.
Abstract: This paper describes a numerical and experimental investigation on the flexural wave propagation properties of a novel class of negative Poisson's ratio honeycombs with tetrachiral topology. Tetrachiral honeycombs are structures defined by cylinders connected by four tangent ligaments, leading to a negative Poisson's ratio (auxetic) behavior in the plane due to combined cylinder rotation and bending of the ribs. A Bloch wave approach is applied to the representative unit cell of the honeycomb to calculate the dispersion characteristics and phase constant surfaces varying the geometric parameters of the unit cell. The modal density of the tetrachiral lattice and of a sandwich panel having the tetrachiral as core is extracted from the integration of the phase constant surfaces, and compared with the experimental ones obtained from measurements using scanning laser vibrometers.
140 citations
TL;DR: In this article, it was shown that the amplitude of the vibrations decays exponentially with the distance to the base of a cylinder made of a microstretch thermoelastic material for which one plane end is subjected to plane boundary data varying harmonically in time.
Abstract: Consider a cylinder made of a microstretch thermoelastic material for which one plane end is subjected to plane boundary data varying harmonically in time. On the lateral surface and other base, we have zero body force and heat supply. By using a Toupin type measure associated with the corresponding steady-state vibration, and by assuming that the angular frequency of oscillations is lower than a certain critical frequency, we show that the amplitude of the vibrations decays exponentially with the distance to the base. This decay estimate is similar to that of the Saint-Venant type.
79 citations
TL;DR: In this article, a damping strategy for integrally bladed disks (blisks) based on the use of friction rings is investigated, and the steady-state forced response of the blisk with friction rings was derived using the so-called dynamic Lagrangian frequency-time method adapted to cyclic structures with rotating excitations.
Abstract: This paper investigates a damping strategy for integrally bladed disks (blisks) based on the use of friction rings. The steady-state forced response of the blisk with friction rings is derived using the so-called dynamic Lagrangian frequency-time method adapted to cyclic structures with rotating excitations. In addition, an original approach for optimal determination of the number of Fourier harmonics is proposed. In numerical applications, a representative compressor blisk featuring several rings is considered. Each substructure is modeled using finite-elements and a reduced-order modeling technique is used for the blisk. The efficiency of this damping technology is investigated, and friction dissipation phenomena are interpreted with respect to frequency responses. It is shown that the friction damping effectiveness depends mainly on the level of dynamic coupling between blades and disk, and on whether the dynamics features significant alternating stick/slip phases. Through parameter studies, design guidelines are also proposed.
76 citations
TL;DR: In this article, a model of the coupled planar vibration of axially moving viscoelastic beams subjected external transverse loads is established by introducing a coordinate transform, and the model can reduce to two nonlinear models of transverse vibration.
Abstract: Steady-state periodical response is investigated for planar vibration of axially moving viscoelastic beams subjected external transverse loads. A model of the coupled planar vibration is established by introducing a coordinate transform. The model can reduce to two nonlinear models of transverse vibration. The finite difference scheme is developed to calculate steady-state response numerically. Numerical results demonstrate there are steady-state periodic responses in transverse vibration, and resonance occurs if the external load frequency approaches the linear natural frequencies. The effect of material parameters and excitation parameters on the amplitude of the steady-state responses are examined. Numerical results also indicate that the model of coupled vibration and two models of transverse vibration predict qualitatively the same tendencies with the changing parameters, and the two models of transverse vibration yield satisfactory results.
71 citations
TL;DR: In this article, the vibro-acoustic performance of a rectangular double-panel partition with enclosed air cavity and simply mounted on an infinite acoustic rigid baffle is investigated analytically.
Abstract: The vibro-acoustic performance of a rectangular double-panel partition with enclosed air cavity and simply mounted on an infinite acoustic rigid baffle is investigated analytically. The sound velocity potential method rather than the commonly used cavity modal function method is employed, which possesses good expandability and has significant implications for further vibro-acoustic investigations. The simply supported boundary condition is accounted for by using the method of modal function and the double Fourier series solutions are obtained to characterize the vibro-acoustic behaviors of the structure. The results for sound transmission loss, panel vibration level, and sound pressure level are presented to explore the physical mechanisms of sound energy penetration across the finite double-panel partition. Specifically, focus is placed on the influence of several key system parameters on sound transmission including the thickness of air cavity, structural dimensions, and the elevation angle and azimuth angle of the incidence sound. Further extensions of the sound velocity potential method to typical framed double-panel structures are also proposed.
63 citations
TL;DR: In this paper, the authors proposed a class of one-dimensional acoustic metamaterials with tunable effective densities in an attempt to enable the adaptation to varying external environment, which can be tailored to have increasing or decreasing variation of the material properties along and across the material volume.
Abstract: Extensive efforts are being exerted to develop various types of acoustic metamaterials to effectively control the flow of acoustical energy through these materials. However, all these efforts are focused on passive metamaterials with fixed material properties. In this paper, the emphasis is placed on the development of a class of one-dimensional acoustic metamaterials with tunable effective densities in an attempt to enable the adaptation to varying external environment. More importantly, the active metamaterials can be tailored to have increasing or decreasing variation of the material properties along and across the material volume. With such unique capabilities, physically realizable acoustic cloaks can be achieved and objects treated with these active metamaterials can become acoustically invisible. The theoretical analysis of this class of active acoustic metamaterials is presented and the theoretical predictions are determined for an array of fluid cavities separated by piezoelectric boundaries. These boundaries control the stiffness of the individual cavity and in turn its dynamical density. Various control strategies are considered to achieve different spectral and spatial control of the density of this class of acoustic metamaterials. A natural extension of this work is to include active control capabilities to tailor the bulk modulus distribution of the metamaterial in order to build practical configurations of acoustic cloaks.
60 citations
TL;DR: In this article, the sensitivity of general compound planetary gear natural frequencies and vibration modes to inertia and stiffness parameters is analyzed. But the model admits planetary gears having any combination of stepped-planet, meshed-planet and multiple stage arrangements.
Abstract: This paper studies the sensitivity of general compound planetary gear natural frequencies and vibration modes to inertia and stiffness parameters. The model admits planetary gears having any combination of stepped-planet, meshed-planet, and multiple stage arrangements. Eigensensitivities in terms of eigenvalue and eigenvector derivatives are analytically derived for both tuned (i.e., cyclically symmetric) and mistuned systems. The results are expressed in compact closed-form formulas. The well-defined modal properties of general compound planetary gears simplify the expressions of eigenvalue sensitivities to ones that are proportional to modal strain/kinetic energies. Inspection of the modal strain/kinetic energy distribution plots provides an effective way to quantitatively and qualitatively determine the parameters that have the largest impact on a certain mode. For parameter perturbations that preserve the system symmetry, the structured modal properties imply that the modes of the same type are independent of the same group of system parameters. Parameter mistuning, with a few exceptions, splits a degenerate natural frequency of the unperturbed system into two frequencies; one frequency keeps its original value and retains its well-defined modal properties, while the other frequency changes and its associated mode lose its structured modal properties. DOI: 10.1115/1.4000461
TL;DR: In this article, a linear distributed parameter electromechanical model is proposed to predict the structural response to MFC actuated clamped-free thin cantilevered beams and the structural frequency response behavior between the tip velocity of the cantilever beam and the actuation voltage of the piezoelectric material is investigated experimentally for cantileve unimorph MFC-actuated benders with aluminum, brass, and steel substrate materials with different thicknesses.
Abstract: A type of piezoceramic composite actuator known as Macro-Fiber Composite (MFC) is used commonly for actuation in smart-material structures. In this paper, a linear distributed parameter electromechanical model is proposed to predict the structural response to MFC actuated clamped-free thin cantilevered beams. The structural frequency response behavior between the tip velocity of the cantilever beam and the actuation voltage of the piezoelectric material is investigated experimentally for cantilevered unimorph MFC actuated benders with aluminum, brass, and steel substrate materials with different thicknesses. Good correlation is observed between the model and the experimental observations.
TL;DR: In this article, the authors consider the dynamic response and performance characteristics of a special class of centrifugal pendulum torsional vibration absorbers and present results that generalize these stability results to include absorbers whose dynamics differ slightly from tautochronic by varying the absorber path such that both linear and nonlinear perturbations of perfect tuning are included.
Abstract: This paper considers the dynamic response and performance characteristics of a special class of centrifugal pendulum torsional vibration absorbers. The absorbers of interest are designed by selection of the path that their center of mass follows, such that their dynamics are linear or nearly so, out to large amplitudes of motion, thereby avoiding the nonlinear-induced detuning that typically accompanies such responses. These order-tuned, tautochronic or isochronic, absorbers have been the subject of previous investigations, including analyses of the synchronous and certain nonsynchronous responses of systems comprised of a set of identical absorbers. The analysis and experiments have demonstrated that the synchronous response of such absorber systems can experience an instability that results in nonsynchronous responses in which a subset of absorbers have significantly larger amplitude than the corresponding synchronous response. In this study, we present results that generalize these stability results to include absorbers whose dynamics differ slightly from tautochronic by varying the absorber path such that both linear and nonlinear perturbations of perfect tuning are included. It is shown by analysis and verified by simulations that the perfect tuning case is quite special, specifically that the instability described above occurs for tunings very close to ideal and that the synchronous response can be made stable over the entire feasible operating range by employing small levels of linear and/or nonlinear detuning. Such detuning is known to have the additional benefit of resulting in smaller absorber responses and an attendant larger operating range albeit at the expense of absorber performance in terms of attenuating rotor torsional vibrations. The main conclusion of these results is that one can select a very small amount of detuning to avoid this undesirable instability and that such detuning does not have a significant effect on absorber effectiveness. The analytical results derived also provide a quantitative means of predicting synchronous absorber response amplitudes and the associated rotor torsional vibration levels, as well as the stability properties of these responses, results are very useful for the design of absorber systems.
TL;DR: In this paper, two new command generators for tower cranes are developed for a point-to-point slewing motion for reducing payload swing on industrial bridge and gantry cranes.
Abstract: Input shaping has been shown to be a practical and effective control scheme for reducing payload swing on industrial bridge and gantry cranes. However, when applied to tower cranes, standard input shapers will have degraded performance due to the nonlinear dynamics of rotational motion. To alleviate this problem, two new command generators for tower cranes are developed for a point-to-point slewing motion. It is shown that standard shaping techniques greatly reduce oscillation and the new tower crane command generators cause even less residual vibration. Simulations and experiments verify the results.
TL;DR: In this paper, a generalized Fourier method is presented for the in-plane vibration analysis of rectangular plates with any number of elastic point supports along the edges, where each of the inplane displacement components is expressed as a 2D Fourier series plus four auxiliary functions in the form of the product of a polynomial times a Fourier cosine series.
Abstract: In comparison with the transverse vibrations of rectangular plates, far less attention has been paid to the in-plane vibrations even though they may play an equally important role in affecting the vibrations and power flows in a built-up structure. In this paper, a generalized Fourier method is presented for the in-plane vibration analysis of rectangular plates with any number of elastic point supports along the edges. Displacement constraints or rigid point supports can be considered as the special case when the stiffnesses of the supporting springs tend to infinity. In the current solution, each of the in-plane displacement components is expressed as a 2D Fourier series plus four auxiliary functions in the form of the product of a polynomial times a Fourier cosine series. These auxiliary functions are introduced to ensure and improve the convergence of the Fourier series solution by eliminating all the discontinuities potentially associated with the original displacements and their partial derivatives along the edges when they are periodically extended onto the entire x-y plane as mathematically implied by the Fourier series representation. This analytical solution is exact in the sense that it explicitly satisfies, to any specified accuracy, both the governing equations and the boundary conditions. Numerical examples are given about the in-plane modes of rectangular plates with different edge supports. It appears that these modal data are presented for the first time in literature, and may be used as a benchmark to evaluate other solution methodologies. Some subtleties are discussed about corner support arrangements.
TL;DR: In this paper, a statistical energy analysis (SEA) approach is used to predict the sound transmission loss (STL) of sandwich panels numerically, which accounts for both antisymmetric and symmetric (dilatational) motions.
Abstract: A statistical energy analysis (SEA) approach is used to predict the sound transmission loss (STL) of sandwich panels numerically. Unlike conventional SEA studies of the STL of sandwich panels, which consider only the antisymmetric (bending) motion of the sandwich panel, the present approach accounts for both antisymmetric and symmetric (dilatational) motions. Using the consistent higher-order sandwich plate theory, the wave numbers of the waves propagating in the sandwich panel were calculated. Using these wave numbers, the wave speed of the propagating waves, the modal density, and the radiation efficiency of the sandwich panels were determined. Finally, the sound transmission losses of two sandwich panels were calculated and compared with the experimentally measured values, as well as with conventional SEA predictions. The comparisons with the experimental data showed good agreement, and the superiority of the present approach relative to other approaches is discussed and analyzed.
TL;DR: In this paper, a finite element-based formal asymptotic expansioh method was used for vibration analysis of composite beams, where cross-sectional coordinates are scaled by the characteristic length of the beam.
Abstract: Vibration analysis of composite beams is carried out by using a finite element-based formal asymptotic expansioh method The formulation begins with three-dimensional (3D) equilibrium equations in which cross-sectional coordinates are scaled by the characteristic length of the beam Microscopic two-dimensional and macroscopic one-dimensional (ID) equations obtained via the asymptotic expansion method are discretized by applying a conventional finite element method Boundary conditions associated with macroscopic ID equations are considered to investigate the end effect It is then described how one could form and solve the eigenvalue problems derived from the asymptotic method beyond the classical approximation The results obtained are compared with those of 3D finite element method and those available in the literature for composite beams with solid cross section and thin-walled cross section
TL;DR: In this article, a simple approach is employed to determine an equivalent continuum representation of a lattice type structure with flexible joints, which takes the assumptions of a micropolar continuum into account rather than an ordinary continuum.
Abstract: A simple approach is employed here to determine an equivalent continuum representation of a lattice type structure with flexible joints. Kinetic and strain energy expressions are written in terms of the nodal velocities and strain components of the beam members, as well as the joints stiffness values. Necessary assumptions are made to reduce the order of the strain variables while retaining the effects of the microrotations that are coupled to the primary strain terms. As a result, an equivalent one-dimensional model has been found, which takes the assumptions of a micropolar continuum into account rather than an ordinary continuum. The frequency response function of the presented model has been validated experimentally and is shown to be in good agreement with the experimental results for a planar truss with Pratt girder configuration.
TL;DR: In this article, a new segmentation approach is developed based on two port analysis techniques in order to model perforated pipes using general two port codes which are widely available Examples are given for simple muffler configurations and the convergence of the technique is investigated based on the number of segments used.
Abstract: One of the main sources of noise of a vehicle is the engine where its noise is usually damped by means of acoustic mufflers A very common problem in the modeling of automotive mufflers is that of two flow ducts coupled through a perforate A new segmentation approach is developed here based on two port analysis techniques in order to model perforated pipes using general two port codes which are widely available Examples are given for simple muffler configurations and the convergence of the technique is investigated based on the number of segments used The results are compared with closed form solutions form the literature Finally an analysts of a complicated multi chamber perforated muffler system is presented The two port simulation results show good agreement with both the measurements and the simulations using the classical four port elements [DOI 10 1115/1 4001510]
TL;DR: In this paper, a finite element formulation for vibration reduction in structural-acoustic systems using passive or semipassive shunt techniques is presented, and numerical results for an elastic plate coupled to a parallelipedic air-filled interior acoustic cavity are presented.
Abstract: In this paper, we present a finite element formulation for vibration reduction in structural-acoustic systems using passive or semipassive shunt techniques. The coupled system consists of an elastic structure (with surface-mounted piezoelectric patches) filled with an inviscid linear acoustic fluid. An appropriate finite element formulation is derived. Numerical results for an elastic plate coupled to a parallelipedic air-filled interior acoustic cavity are presented, showing the performances of both the inductive shunt and the synchronized switch shunt techniques.
TL;DR: In this article, the authors present procedures and results of a more realistic 3DOF active control of a pneumatic vibration isolation table, consisting of heaving, rolling, and pitching.
Abstract: Based on previous feasibility study on one degree of freedom (1DOF) pneumatic active control of pneumatic springs, this paper presents procedures and results of a more realistic 3DOF active control of a pneumatic vibration isolation table. The 3DOF motion of the pneumatic table, consisting of heaving, rolling, and pitching, is controlled directly by adjusting air pressure in four pneumatic cylinders in a dynamic manner with pneumatic valves, without any external actuator such as an electromagnet or voice coil. The time delay control, which is a software chosen in this study, together with the hardware, i.e., the pneumatic actuator, is shown to be very powerful in enhancing the performance of vibration isolation for ground excitation as well as in settling time reduction for payload excitation through simulations and measurements on the 3DOF motion control system. New key results found in the experimental approach are that the pneumatic actuator shows a dynamic behavior of a second-order system, instead of a first-order system, which has been used in existing literatures so far, and that just feed-forward control of the pneumatic actuator by the second-order model can compensate for the inherently slow response characteristics of the pneumatic actuator very successfully. Effectiveness of the proposed active pneumatic control technique in the multi-input and multi-output system is shown via singular value decomposition analysis on the transmissibility matrix. Promising future of the proposed control and performance analysis technique is further discussed based on the results in the case of payload excitations as well.
TL;DR: In this paper, a nonlinear anti-symmetric damping characteristic has almost no effect on the transmissibility of SDOF vibration isolators over both low and high frequency ranges where the frequencies are much lower or higher than the isolator's resonant frequency.
Abstract: In the present study, the concept of the Output Frequency Response Function (OFRF), recently proposed by the authors, is applied to theoretically investigate the transmissibility of SDOF passive vibration isolators with a nonlinear anti-symmetric damping curve. The results reveal that a nonlinear anti-symmetric damping characteristic has almost no effect on the transmissibility of SDOF vibration isolators over both low and high frequency ranges where the frequencies are much lower or higher than the isolator’s resonant frequency. On the other hand, the introduction of a nonlinear anti-symmetric damping can significantly reduce the transmissibility of the vibration isolator over the resonant frequency region. The results indicate that nonlinear vibration isolators with an anti-symmetric damping characteristic have great potential to overcome the dilemma encountered in the design of passive linear vibration isolators, that is, increasing the level of damping to reduce the transmissibility at the resonance could increase the transmissibility over the range of higher frequencies. These important theoretical conclusions are then verified by simulation studies.
TL;DR: In this article, the authors investigated the feasibility of utilizing the Hilbert-Huang transform method for diagnosing the looseness faults of rotating machinery by measuring the similarities among the information-contained marginal Hilbert spectra of vibration signals.
Abstract: The objective of this research in this paper is to investigate the feasibility of utilizing the Hilbert–Huang transform method for diagnosing the looseness faults of rotating machinery. The complicated vibration signals of rotating machinery are decomposed into finite number of intrinsic mode functions (IMFs) by integrated ensemble empirical mode decomposition technique. Through the significance test, the information-contained IMFs are selected to form the neat time-frequency Hilbert spectra and the corresponding marginal Hilbert spectra. The looseness faults at different components of the rotating machinery can be diagnosed by measuring the similarities among the information-contained marginal Hilbert spectra. The fault indicator index is defined to measure the similarities among the information-contained marginal Hilbert spectra of vibration signals. By combining the statistical concept of Mahalanobis distance and cosine index, the fault indicator indices can render the similarities among the marginal Hilbert spectra to enhanced and distinguishable quantities. A test bed of rotor-bearing system is performed to illustrate the looseness faults at different mechanical components. The effectiveness of the proposed approach is evaluated by measuring the fault indicator indices among the marginal Hilbert spectra of different looseness types. The results show that the proposed diagnosis method is capable of classifying the distinction among the marginal Hilbert spectra distributions and thus identify the type of looseness fault at machinery.
TL;DR: In this paper, a simplified analytical approach for modeling the synchronous instability phenomenon known as the Morton effect is presented, which is straightforward and easily applied to any rotor supported on fluid film bearings.
Abstract: A simplified analytical approach for modeling the synchronous instability phenomenon known as the Morton effect is presented. The analysis is straightforward and easily applied to any rotor supported on fluid film bearings. The analysis clarifies the interaction of three distinct machine characteristics, which combine to create a case of the Morton effect. Some example calculations are shown illustrating the possible types of spiral vibration. In addition, an analytical approach is described for estimating the magnitude of the shaft temperature difference in a journal bearing as a direct function of the shaft orbit. It is significant that this method can readily be applied to any type of journal bearing, from plain sleeve bearings to tilting pad bearings. Example calculations using the method are shown.
TL;DR: In this paper, a trust region approach is employed to make the optimization process more robust and reliable, and the relative weighting scheme between different parts in the objective function is also investigated.
Abstract: This paper proposed a practical damage detection method for frame structures based on finite element model-updating techniques. An objective function is defined as minimizing the discrepancies between the experimental and analytical modal parameters (namely, natural frequencies and mode shapes), which is set as a nonlinear least-squares problem with bound constraints. Unlike the commonly used line-search methods, the trust-region approach, a simple yet very powerful concept for minimization, is employed in order to make the optimization process more robust and reliable. Noting the objective function may sometimes be underdetermined for complex structures due to a relatively larger number of potential damaged elements, this paper attempts to propose a simple and convenient solution by expanding the original objective function. Moreover, the relative weighting scheme between different parts in the objective function is also investigated. One numerical two-story portal frame structure and two laboratory-tested frame structures, including a simple three-story steel frame structure and a more complex frame structure with bolted joints, are all adopted to evaluate the efficiency of the proposed technique. Some important issues about the application of the proposed method are also discussed in this paper.
TL;DR: In this paper, the authors present the design and measured performance of a compact hybrid actuation system driven by the single-crystal electrostrictive material PMN-32%PT.
Abstract: The basic operation of smart material-based hybrid electrohydraulic actuators involves high frequency bidirectional length change in an active material stack (or rod) that is converted to unidirectional motion of a hydraulic fluid by a set of valves. In this study, we present the design and measured performance of a compact hybrid actuation system driven by the single-crystal electrostrictive material PMN-32%PT. The active material was actuated at different frequencies with variations in the applied voltage, fluid bias pressure, and external load to study the effects on output velocity. The maximum actuator velocity was 330 mm/s and the corresponding flow rate was 42.5 cc/s; the blocked force of the actuator was 63 N. The results of the experiments are presented and compared with simulation data to validate a nonlinear time-domain model. Linearized equations were used to represent the active material while the inertia, viscous losses, and compressibility of the fluid were included using differential equations. Factors affecting system performance are identified and the inclusion of fluid inertia in the model is also justified.
TL;DR: In this paper, the authors proposed a simple method by utilizing discontinuous spring characteristics, which can suppress steady-state resonances, and showed that this method is also effective to suppress unstable vibrations.
Abstract: Unstable vibration occurs in the vicinities of the major critical speeds of asymmetrical shaft and rotor systems. It occurs also in a wide rotational speed range higher than the major critical speed of a shaft with a hollow disk partially filled with liquid. The occurrence of the unstable vibrations is a serious problem because the amplitude increases exponentially, and finally, the system is destroyed. The active vibration control can suppress unstable vibrations but the method is generally complicated and costly. No simple effective method to suppress unstable vibrations has been developed yet. In the previous paper, the authors proposed a simple method by utilizing discontinuous spring characteristics, which can suppress steady-state resonances. This paper shows that this method is also effective to suppress unstable vibrations. By using this method, the unstable vibrations can be changed into almost periodic motions, and the amplitudes are suppressed to the desired small level even in an unstable range. The validity of the proposed method is also verified by experiments.
TL;DR: In this article, the authors developed a closed-form solution for the optimal parameter of a resistive shunt damping system, which is validated through experimental testing and provided a simple yet accurate method to predict the induced damping in a smart structure.
Abstract: This paper studies the piezoelectric damping of resistively shunted beams induced by the conversion of the vibration energy into electrical energy that is dissipated in the resistor through Joule heating. Significant contributions have been made in the modeling and development of the resistive shunt damping technique; however, many approaches involve complex models that require the use of numerical methods to determine system parameters and predict damping. This paper develops a closed-form solution for the optimal parameter of a resistive shunt damping system. The model is validated through experimental testing and provides a simple yet accurate method to predict the induced damping in a smart structure.
TL;DR: In this paper, a tool holder employs a high bandwidth piezoelectric actuator with an adaptive positive position feedback control algorithm for vibration and chatter suppression, and the performance of this method is evaluated by comparing the surface finish obtained with active vibration control versus baseline uncontrolled cuts.
Abstract: The machining process is very important in many engineering applications. In high precision machining, surface finish is strongly correlated with vibrations and the dynamic interactions between the part and the cutting tool. Parameters affecting these vibrations and dynamic interactions, such as spindle speed, cut depth, feed rate, and the part's material properties can vary in real-time, resulting in unexpected or undesirable effects on the surface finish of the machining product. The focus of this research is the development of an improved machining process through the use of active vibration damping. The tool holder employs a high bandwidth piezoelectric actuator with an adaptive positive position feedback control algorithm for vibration and chatter suppression. In addition, instead of using external sensors, the proposed approach investigates the use of a collocated piezoelectric sensor for measuring the dynamic responses from machining processes. The performance of this method is evaluated by comparing the surface finishes obtained with active vibration control versus baseline uncontrolled cuts. Considerable improvement in surface finish (up to 50%) was observed for applications in modern day machining.
TL;DR: In this paper, the authors investigated the use of cable tension for active vibration control in frame structures and developed a general control scheme that uses cable actuation to take advantage of these effects, both separately and together.
Abstract: We investigate the use of cable tension for active vibration control in frame structures. A general formulation for this class of systems is developed using finite elements, which includes the dynamics of the structure and the effects of cable-structure interactions. It is found that the cable tension has two distinct effects on the structure. The first is a parametric effect in which the cable tension changes the stiffness of the structure, and the second is a direct effect that provides an external force on the structure. Based on this model, a general control scheme is developed that uses cable actuation to take advantage of these effects, both separately and together. The control scheme for all cases is based on modal amplitudes, and it applies and releases tension in such a manner that vibration energy is removed from the modes of the structure over a prescribed frequency range that depends on the bandwidth(s) of the actuator(s). The stability of the controlled systems is proven using nonlinear control theory. In addition, a method is developed for determining the optimal placement of cables for parametric stiffness control, which is verified via simulations. Finally, an experimental realization of the direct force control is tested on a frame structure and compared with simulations, demonstrating its effectiveness.