Showing papers in "Journal of Vibration and Acoustics in 2004"
TL;DR: In this article, a dynamic model of a multi-shaft helical gear reduction unit formed by N flexible shafts is proposed, which consists of a finite element model of shaft structures combined with a three-dimensional discrete model of helical gears pairs.
Abstract: A dynamic model of a multi-shaft helical gear reduction unit formed by N flexible shafts is proposed in this study. The model consists of a finite element model of shaft structures combined with a three-dimensional discrete model of helical gear pairs. Bearing and housing flexibilities are included in the model as well. Eigenvalue solution and the Modal Summation Technique are used to predict the free and forced vibrations of the system. Results of experimental study on a helical gear-shaft-bearing system are also presented for validation of the model. It is demonstrated that the predictions match well with the experimental data in terms of excited modes and the forced response given in the form of the dynamic transmission error. Forced vibrations of an example system formed by three shafts are also studied to demonstrate the influence of some of the key system parameters.
195 citations
TL;DR: In this article, a detailed study of the transient nonlinear dynamics of an electrically actuated micron scale beam is presented, and a model developed using the Galerkin procedure with normal modes as a basis accounts for the distributed nonlinear electrostatic forces, nonlinear squeezed film damping, and rotational inertia of a mass carried by the beam.
Abstract: A detailed study of the transient nonlinear dynamics of an electrically actuated micron scale beam is presented. A model developed using the Galerkin procedure with normal modes as a basis accounts for the distributed nonlinear electrostatic forces, nonlinear squeezed film damping, and rotational inertia of a mass carried by the beam. Special attention is paid to the dynamics of the beam near instability points. Results generated by the model and confirmed experimentally show that nonlinear damping leads to shrinkage of the spatial region where stable motion is realizable. The voltage that causes dynamic instability, in turn, approaches the static pull-in value.
165 citations
TL;DR: A new method for wavelet threshold de-noising that not only employs the Morlet wavelet as the basic wavelet for matching the impulse, but also uses the maximum likelihood estimation for thresholding by utilizing prior information on the probability density of the impulse.
Abstract: For gears and roller bearings, periodic impulses indicate that there are faults in the components. However, it is difficult to detect the impulses at the early stage of fault because they are rather weak and often immersed in heavy noise. Existing wavelet threshold de-noising methods do not work well because they use orthogonal wavelets, which do not match the impulse very well and do not utilize prior information on the impulse. A new method for wavelet threshold de-noising is proposed in this paper; it not only employs the Morlet wavelet as the basic wavelet for matching the impulse, but also uses the maximum likelihood estimation for thresholding by utilizing prior information on the probability density of the impulse. This method has performed excellently when used to de-noise mechanical vibration signals with a low signal-to-noise ratio.
146 citations
TL;DR: In this paper, a two-time-scale modeling strategy based on phase space reconstruction is used to estimate the damage evolution of an electromechanical system with a failing supply battery.
Abstract: In this paper, a previously published damage tracking method is extended to provide failure prognosis, and applied experimentally to an electromechanical system with a failing supply battery. The method is based on a dynamical systems approach to the problem of damage evolution. In this approach, damage processes are viewed as occurring in a hierarchical dynamical system consisting of a “fast”, directly observable subsystem coupled to a “slow”, hidden subsystem describing damage evolution. Damage tracking is achieved using a two-time-scale modeling strategy based on phase space reconstruction. Using the reconstructed phase space of the reference (undamaged) system, short-time predictive models are constructed. Fast-time data from later stages of damage evolution of a given system are collected and used to estimate
125 citations
TL;DR: In this paper, the authors used the 3D discrete element method (DEM) for computer simulation and characterization of particle damping, which is a technique of providing damping with granular particles embedded within small holes in a vibrating structure.
Abstract: Particle damping is a technique of providing damping with granular particles embedded within small holes in a vibrating structure. The particles absorb kinetic energy through particle-to-wall and particle-to-particle frictional collisions. While the concept of particle damping seems to be simple and it has been used successfully in many fields for vibration reduction, it is difficult to predict the damping characteristics due to complex collisions in the dense particle flow. In this paper, we utilize the 3D discrete element method (DEM) for computer simulation and characterization of particle damping. With the DEM modeling tool validated with experimental results, it is shown that the particle damping can achieve a very high value of specific damping capacity. Furthermore, simulations provide information of particle motions within the container hole during three different regions and help explain their associated damping characteristics. The particle damping is a combination of the impact and the friction damping. The damping is found to be highly nonlinear as the rate of energy dissipation depends on amplitude. Particularly, the damping effect results in a linear decay in amplitude over a finite period of time. These characteristics are examined with respect to a simple single-mass impact damper and a dry-friction damper. It is concluded that the particle damping is a mix of these two damping mechanisms. It is further shown that the relative significance of these damping mechanisms depends on a particular arrangement of the damper. This study represents an effort towards a deeper understanding of particle damping to provide a comprehensive methodology for its analysis and design.
106 citations
TL;DR: In this article, the authors presented two alternative implementations of skyhook control, named skyhook function and no-jerk skyhook, for reducing the dynamic jerk that is often experienced with conventional sky hook control in semi-active suspension systems.
Abstract: This paper presents two alternative implementations of skyhook control, named skyhook function and no-jerk skyhook, for reducing the dynamic jerk that is often experienced with conventional skyhook control in semiactive suspension systems. An analysis of the relationship between the absolute velocity of the sprung mass and the relative velocity across the suspension are used to show the damping-force discontinuities that result from the conventional implementation of skyhook control. This analysis shows that at zero crossings of the relative velocity, conventional skyhook introduces a sharp increase (jump) in damping force, which, in turn, causes a jump in sprung-mass acceleration. This acceleration jump, or jerk, causes a significant reduction in isolation benefits that can be offered by skyhook suspensions. The alternative implementations of skyhook control included in this study offer modifications to the formulation of conventional skyhook control such that the damping force jumps are eliminated. The alternative policies are compared to the conventional skyhook control in the laboratory, using a base-excited semiactive system that includes a heavy-truck seat suspension. An evaluation of the damping force, seat acceleration, and the electrical currents supplied to a magnetorheological damper, which is used for this study, shows that the alternative implementations of skyhook control can entirely eliminate the damping-force discontinuities and the resulting dynamic jerks caused by conventional skyhook control.
103 citations
TL;DR: In this article, a new approach based on the fusion of the wavelet transform and envelope spectrum is proposed for detecting and localizing defects in rolling element bearings, which is capable of completely extracting the characteristic frequencies related to the defect from the resonant frequency band.
Abstract: In order to overcome the shortcomings in the traditional envelope analysis in which manually specifying a resonant frequency band is required, a new approach based on the fusion of the wavelet transform and envelope spectrum is proposed for detecting and localizing defects in rolling element bearings. This approach is capable of completely extracting the characteristic frequencies related to the defect from the resonant frequency band. Based on the Shannon entropy of wavelet-based envelope spectra, a criterion to select optimal scale to monitor the condition of bearings is also presented. Experiment results show that the proposed approach is sensitive and reliable in detecting defects on the outer race, inner race, and rollers of bearings.
101 citations
TL;DR: In this article, a theoretical model based on multiphase flow theory of gas-particle is developed to evaluate the granular particle damping characteristics, and the nonlinear free vibration of an exemplified cantilever particle-damping beam is analyzed by using the averaging method based on the first approximation.
Abstract: A theoretical model based on multiphase flow theory of gas-particle is developed to evaluate the granular particle damping characteristics. Expressions for the drag forces of the equivalent viscous damping and the Coulomb friction damping are formulated respectively. The nonlinear free vibration of an exemplified cantilever particle-damping beam is analyzed by using the averaging method based on the first approximation. Numerical results are also presented to illustrate general characteristics of the particle-damping beam. An experimental verification is performed, and a good correlation between the theoretical results and the experimental data shows that the theoretical work in this paper is valid.
81 citations
TL;DR: In this article, the normal mode approach is used to reduce the differential equation of a fractionally damped continuous beam into a set of infinite equations, each of which describes the dynamics of the system.
Abstract: This paper presents a general analytical technique for stochastic analysis of a continuous beam whose damping characteristic is described using a fractional derivative model. In this formulation, the normal-mode approach is used to reduce the differential equation of a fractionally damped continuous beam into a set of infinite equations, each of which describes the dynamics of a fractionally damped spring-mass-damper system. A Laplace transform technique is used to obtain the fractional Green's function and a Duhamel integral-type expression for the system's response. The response expression contains two parts, namely, zero state and zero input. For a stochastic analysis, the input force is treated as a random process with specified mean and correlation functions. An expectation operator is applied on a set of expressions to obtain the stochastic characteristics of the system. Closed-form stochastic response expressions are obtained for white noise for two cases, and numerical results are presented for one of the cases. The approach can be extended to all those systems for which the existence of normal modes is guaranteed.
71 citations
TL;DR: In this paper, the authors examined passive energy pumping in a system of damped coupled oscillators and showed that the energy dependence of the nonlinear normal modes of the underlying undamped, unforced system determines, in essence, the resonance capture and energy pumping dynamics in the corresponding damped system.
Abstract: We examine passive energy pumping in a system of damped coupled oscillators. This is a one-way, passive and irreversible energy flow from a linear main system to a nonlinear attachment that acts, in essence, as a nonlinear energy sink (NES). Energy pumping is caused by 1:1 resonance captures on resonant manifolds of the damped systems. We show that the NES is capable of absorbing significant portions of the energies generated by transient, broadband external excitations. By performing a series of numerical simulations we confirm that the energy dependence of the nonlinear normal modes (NNMs) of the underlying undamped, unforced system determines, in essence, the resonance capture and energy pumping dynamics in the corresponding damped system. We present numerical simulations of single- and multi-mode energy pumping, that involve isolated resonance captures or resonance capture cascades, respectively. In addition, we discuss methodologies for enhancing the nonlinear energy pumping phenomenon by properly selecting the system parameters. The described technique of passively localizing and locally eliminating externally induced energy provides a new paradigm for vibration and shock isolation of mechanical oscillators.
70 citations
TL;DR: In this article, Tungsten carbide particles are embedded within longitudinal (and latitudinal) holes drilled in the structure, as a simple and passive means for vibration suppression, and the experimental results confirm a numerical prediction that shear friction in the longitudinal and the latitudinal directions is effective as the major contributing mechanism of damping in the case.
Abstract: This paper describes an experimental investigation of a particle damping method for a beam and a plate. Tungsten carbide particles are embedded within longitudinal (and latitudinal) holes drilled in the structure, as a simple and passive means for vibration suppression. Unlike in traditional damping materials, mechanisms of energy dissipation of particle damping are highly nonlinear and primarily related to friction and impact phenomena. Experiments are conducted with a number of arrangements of the packed particles including different particle sizes and volumetric packing ratios. The results show that the particle damping is remarkably effective and that strong attenuations are achieved within a broad frequency range. The effects of the system parameters including particle size, packing ratio and particle material are studied by broadband and narrowband random excitations. The experimental results confirm a numerical prediction that shear friction in the longitudinal (and the latitudinal) directions is effective as the major contributing mechanism of damping in the case. Another unique feature of linear decay in free vibrations is also observed in this case of particle damping.
TL;DR: In this article, a generic methodology for machinery fault diagnosis through pattern recog-nition techniques is presented, which has the advantage of dealing with complicated signatures, such as those present in the vibration signals of rolling element bearings with and without defects.
Abstract: We present a generic methodology for machinery fault diagnosis through pattern recog-nition techniques. The proposed method has the advantage of dealing with complicatedsignatures, such as those present in the vibration signals of rolling element bearings withand without defects. The signature varies with the location and severity of bearing defects,load and speed of the shaft, and different bearing housing structures. More specifically,the proposed technique contains effective feature extraction, good learning ability, reli-able feature fusion, and a simple classification algorithm. Examples with experimentaltesting data were used to illustrate the idea and effectiveness of the proposedmethod. @DOI: 10.1115/1.1687391#
TL;DR: In this paper, a new eigenstructure assignment algorithm is developed to more directly suppress vibration in regions of interest, and the active control input is applied through an active-passive hybrid piezoelectric network.
Abstract: The underlying principle for vibration confinement is to alter the structural vibration modes so that the corresponding modal components have much smaller amplitude in concerned area than in the remaining part of the structure. In this research, the state-of-the-art in vibration confinement technique is advanced in two correlated ways. First, a new eigenstructure assignment algorithm is developed to more directly suppress vibration in regions of interest. This algorithm is featured by the optimal selection of achievable eigenvectors that minimizes the eigenvector components at concerned region by using the Rayleigh Principle. Second, the active control input is applied through an active-passive hybrid piezoelectric network. With the introduction of circuitry elements, which are much easier to implement than changing or adding mechanical components, the state matrices can be reformed and the design space for eigenstructure assignment can be greatly enlarged. To maximize the system performance, a simultaneous optimization/optimal eigenvector assignment approach to decide the passive and active parameters concurrently is outlined. The merits of the proposed system and scheme are demonstrated and analyzed using numerical examples.
TL;DR: In this paper, the effect of hysteretic damping in rotordynamics has been clarified in terms of the practical applications of the theory in an unequivocal way.
Abstract: Even though the role of damping in rotordynamics has been known for more than half a century, some incorrect statements on the effect of hysteretic damping, particularly in the subcritical range, can be found still in even the most authoritative journals. Although clarified in the 1970s, this issue recently resurfaced with the incorrect statement that hysteretic damping of rotating elements is destabilizing at any speed (even subcritical). The aim of the present paper is to clarify this issue in terms of the practical applications of the theory in an unequivocal way
TL;DR: In this paper, a new regularization of Coulomb's law of friction is presented, which permits a straightforward incorporation of frictional forces within existing numerical simulations, and provides a computationally efficient scheme to obtain time-accurate simulations.
Abstract: We present a new regularization of Coulomb's law of friction that permits a straightforward incorporation of frictional forces within existing numerical simulations. Similar to existing regularizations, the proposed modification to Coulomb friction leads to a continuous representation of friction and does not require the identification of transitions between slip and stick. However, unlike more common regularizations, the current reformulation maintains a structure at zero contact velocity that is identical to the classical, discontinuous form of Coulomb friction. The implementation of this regularization is presented through two examples in which slip-stick motion induced by sliding friction is of primary importance. The first is a simple one degree-of-freedom system and illustrates the existence of nontrivial equilibrium states. The second example is a multi-degree-of-freedom system in which the present model provides a computationally efficient scheme for simulating the dissipation arising from sliding friction. For systems in which slip-stick transitions are important the proposed regularization provides a computationally efficient scheme to obtain time-accurate simulations.
TL;DR: In this article, the influence of internal resonance on nonlinear rotational properties of the Jeffcott rotor and rotor systems with a small gyroscopic moment was investigated. And the results showed that the shape of resonance curves becomes far more complex than that of a single resonance, almost periodic motions occur, and the internal resonance phenomena are strongly influenced by the degree of the discrepancies among critical speeds.
Abstract: The Jeffcott rotor is a two-degree-of-freedom linear model with a disk at the midspan of a massless elastic shaft. This model, executing lateral whirling motions, has been widely used in the linear analyses of rotor vibrations. In the Jeffcott rotor, the natural frequency of a forward-whirling mode p f (>0) and that of a backward-whirling mode p b (<0) have the relation of internal resonance p f :p b = 1: (-1). Recently, many researchers analyzed nonlinear phenomena by using the Jeffcott rotor with nonlinear elements. However, they did not take this internal resonance relationship into account. Furthermore in many practical rotating machines, the effect of gyroscopic moments are relatively small. Therefore, the one-to-one internal resonance relationship holds approximately between forward and backward natural frequencies in such machinery. In this paper, nonlinear phenomena in the vicinity of the major critical speed and the rotational speeds of twice and three times the major critical speed are investigated in the Jeffcott rotor and rotor systems with a small gyroscopic moment. The influences of internal resonance on the nonlinear resonances are studied in detail. The following were clarified theoretically and experimentally: (a) the shape of resonance curves becomes far more complex than that of a single resonance; (b) almost periodic motions occur; (c) these phenomena are influenced remarkably by the asymmetrical nonlinearity and gyroscopic moment; and (d) the internal resonance phenomena are strongly influenced by the degree of the discrepancies among critical speeds. The results teach us that the usage of the Jeffcott rotor in nonlinear analyses of rotor systems may induce incorrect results.
TL;DR: In this paper, a wavelet filter is combined with cyclostationary analysis for detection of gear tooth faults in a gearbox, and the parameters of the filter are optimized by using the proposed entropy minimization rule.
Abstract: Wavelet filtering is combined with cyclostationary analysis for detection of gear tooth faults in a gearbox. The parameters of the wavelet filter are optimized by using the proposed entropy minimization rule. This method is shown to be effective in detecting gear faults when cyclostationary analysis by itself fails. @DOI: 10.1115/1.1760565#
TL;DR: In this article, the frequency and responses of a microelectro-mechanical system with time-varying capacitors are determined under an equivalent direct current (DC) voltage.
Abstract: The natural frequency and responses of a micro-electro-mechanical system (MEMS) with time-varying capacitors are determined under an equivalent direct current (DC) voltage. Under alternating current (AC) voltages, the resonant condition and the corresponding resonant motion possessing a wide energy band for such a system are investigated because the motion with the wide energy band is very easily sensed. For a given voltage strength, the AC frequency band is obtained for chaotic resonant motions in the specific resonant layer. The numerical and analytical predictions of such a motion are in a acceptable agreement, and the dynamic model provides the range prediction of the alternating current and voltage on the capacitor agreeing with experimental measurements. The lower-order resonant motion has a higher energy than the higher-order resonant motions, which indicates that the lower-order resonant motion can be easily sensed. Although this model is developed from a specified MEMS, the analysis and results can be applied to other dynamic systems.
TL;DR: In this paper, the Smaller Alignment Index (SALI) method was applied to evaluate the stability properties of discrete breathers in phase space, and the results showed that the regions of existence and stability of the breathers of the hard spring lattice are considerably larger than those of the soft spring system, mainly due to the fact that the conditions for resonances between breathers and linear modes are much less restrictive in the former than the latter case.
Abstract: ‘‘hard spring’’ and (2) to ‘‘soft spring’’ interactions. These localized oscillations—when they are stable under small perturbations—are very important for physical systems because they seriously affect the energy transport properties of the lattice. Discrete breathers have recently been created and observed in many experiments, as, e.g., in the Josephson junction arrays, optical waveguides, and low-dimensional surfaces. After showing how to construct them, we use Floquet theory to analyze their linear (local) stability, along certain curves in parameter space ( a,v), where a is the coupling constant andv the frequency of the breather. We then apply the Smaller Alignment Index method (SALI) to investigate more globally their stability properties in phase space. Comparing our results for the 6 cases of V~u!, we find that the regions of existence and stability of breathers of the ‘‘hard spring’’ lattice are considerably larger than those of the ‘‘soft spring’’ system. This is mainly due to the fact that the conditions for resonances between breathers and linear modes are much less restrictive in the former than the latter case. Furthermore, the bifurcation properties are quite different in the two cases: For example, the phenomenon of complex instability, observed only for the ‘‘soft spring’’ system, destabilizes breathers without giving rise to new ones, while the system with ‘‘hard springs’’ exhibits curves in parameter space along which the number of monodromy matrix eigenvalues on the unit circle is constant and hence breather solutions preserve their stability character. @DOI: 10.1115/1.1804997#
TL;DR: In this paper, a method for estimating Coulomb and viscous friction coefficients from responses of a harmonically excited dual-damped oscillator with linear stiffness is presented. But the method is applicable only if the damping ratio of viscous component can be considered small.
Abstract: This paper presents a method for estimating Coulomb and viscous friction coefficients from responses of a harmonically excited dual-damped oscillator with linear stiffness. The identification method is based on existing analytical solutions of non-sticking responses excited near resonance. The method is applicable if the damping ratio of viscous component can be considered small. The Coulomb and viscous friction parameters can be extracted from two or more input-output amplitude pairs at resonance. The method is tested numerically and experimentally. Experimental results are cross checked with estimations from free-vibration decrements and also from friction measurements.
TL;DR: In this article, the dynamic response of a parametrically excited cantilever beam with a pendulum is theoretically and experimentally presented, and the equation of motion and associated boundary conditions are derived considering the static friction of the rotating motion at the supporting point (pivot) of the pendulum.
Abstract: The dynamic response of a parametrically excited cantilever beam with a pendulum is theoretically and experimentally presented. The equation of motion and the associated boundary conditions are derived considering the static friction of the rotating motion at the supporting point (pivot) of the pendulum. It is theoretically shown that the static friction at the pivot of the pendulum plays a dominant role in the suppression of parametric resonance. The boundary conditions are different between two states in which the motion of the pendulum is either trapped by the static friction or it is not. Because of this variation of the boundary conditions depending on the pendulum motion, the natural frequencies of the system are automatically and passively changed and the bifurcation set for the parametric resonance is also shifted, so that parametric resonance does not occur. Experimental results also verify the effect of the pendulum on the suppression of parametric resonance in the cantilever beam.
TL;DR: In this paper, a passivity-based robust control of a piezo-actuated flexible beam is presented, which is a cantilever aluminum beam with a piezoelectric transducer used as the actuator and tip-accelerometer as the sensor.
Abstract: This paper presents modelling, system identification, simulation, and experimental results for passivity-based robust control of piezo-actuated flexible beam. The flexible beam configuration considered is a cantilever aluminum beam with a piezoelectric transducer used as the actuator and tip-accelerometer as the sensor. The actuator and sensor are non-collocated. The Lagrangian formulation is used to obtain mathematical model of the flexible link dynamics with piezo actuator. For control design purposes, a finite dimensional approximate model is derived using assumed modes approach. It is shown that the approximate model compares very well with the experimentally identified model. Since the system is inherently not passive, passification techniques are used to render the system robustly passive which enables the use of passivity-based feedback control design. The controller design is validated both in simulation as well as in experiments. The simulation and experimental results demonstrate the effectiveness of controller in suppressing the tip vibrations of the link. The controller design is shown to be robust to both parametric uncertainties and unmodeled dynamics.
TL;DR: In this paper, an extension of the force appropriation approach was proposed to identify the modal mass, damping and stiffness matrices of nonproportionally damped systems using multiple exciters.
Abstract: This paper describes an extension of the force appropriation approach which permits the identification of the modal mass, damping and stiffness matrices of nonproportionally damped systems using multiple exciters. Appropriated excitation bursts are applied to the system at each natural frequency, followed by a regression analysis in modal space. The approach is illustrated on a simulated model of a plate with discrete dampers positioned to introduce significant damping nonproportionality. The influence of out-of-band flexible and rigid body modes, imperfect appropriation, measurement noise and impure mode shapes is considered. The method is shown to provide adequate estimates of the modal damping matrix.
TL;DR: In this paper, a single lap joint is modeled as Euler-Bernouli beams joined in the lap area by a viscoelastic adhesive layer and the effects of adhesive layer thickness, mechanical properties and its loss factor on the dynamic response of the joint are investigated.
Abstract: Dynamic response of single lap joints, subjected to a harmonic peeling load is studied theoretically and experimentally. In the theoretical part, dynamic response of a single lap joint clamped at one end and subjected to a harmonic peeling load at the other end is investigated. Adherents are modeled as Euler-Bernouli beams joined in the lap area by a viscoelastic adhesive layer Both axial and transverse deformations of adherents are considered in deriving the equations of motion. The effects of adhesive layer thickness, mechanical properties and its loss factor on the dynamic response of the joint are investigated. Furthermore, effects of defects such as a void in the lap area on the dynamic response of the joints are studied. The results showed that frequencies where peak amplitudes occurred were little dependent on the adhesive loss factor However, peak amplitudes reduced for joints with a higher adhesive loss factor. Furthermore, the results indicated that for the joint geometries and properties investigated the system resonant frequencies were not affected by the presence of a central void covering up to 80% of the overlap length. In the experimental part, single lap joints were fabricated using 6061-T6 Aluminum. Adherents were joined together using Hysol EA 9689 adhesive film. Joints with various central voids were manufactured by removing adhesive film from the desired area of lap joints prior to bonding adherents. Dynamic responses of the joints were investigated using the hammer test technique. The system response was measured using both an accelerometer and a noncontact laser vibrometer. The natural frequencies of the joints obtained by using the laser vibrometer were very close to those obtained theoretically. However, natural frequencies obtained by using an accelerometer depended on the accelerometer location in the system, which was attributed to its mass contribution to the overall system mass. A central void covering less than 80% of the overlap length had little effect on the system resonance frequencies. This was in agreement with the theoretical results. In contrast total system-damping ratios were a function of the void size. Joints without a void exhibited higher damping.
TL;DR: In this article, a POD approach is developed for generalized second-order differential equations; however, the application of POD to the governing equations in state space form is also discussed.
Abstract: The nonlinear panel flutter problem solved by Dowell in 1966 is used to investigate the new application of the proper orthogonal decomposition model reduction technique to aeroelastic analysis. Emphasis is placed on the nonlinear structural dynamic equations with nonconservative forcing modeled assuming a supersonic, inviscid flow. Here the aeroelastic coupled equation is presented in discrete form using a finite difference approach, and subsequently in state space form, to be integrated as a set of first order differential equations. In this paper, a POD approach is developed for generalized second-order differential equations; however, the application of POD to the governing equations in state space form is also discussed. This study compares the results and effectiveness of the model reduction technique for integration of the full set of degrees of freedom. The solution is compared to Dowell's classic results which forms the base reference for the model reduction study. The reduced order model is then created from the full simulation model. Accuracy of the solution, reduced computational time, limits of stability, and the strengths and weaknesses of the model reduction are investigated.
TL;DR: In this article, the axisymmetric dynamic stability of rotating sandwich circular plates with a constrained damping layer subjected to a periodic uniform radial loading along the outer edge of the host plate is studied.
Abstract: The axisymmetric dynamic stability of rotating sandwich circular plates with a constrained damping layer subjected to a periodic uniform radial loading along the outer edge of the host plate is studied in the present paper The viscoelastic material in middle layer is assumed to be frequency dependent and incompressible, and complex representations of moduli are used. Equations of motion of the system are derived by the finite element method where the geometry stiffness matrices induced by rotation and external load are evaluated from solutions of static problems. Bolotin's method is employed to determine the regions of dynamic instability while the eigenvalue problems with frequency dependent parameters are solved by the modified complex eigensolution method. Numerical results show that the effects of constrained damping layer tend to stabilize the circular plate system and the widths of unstable regions decrease with increasing of rotational speeds.
TL;DR: In this paper, a semi-active electro-rheological (ER) fluid was developed to attenuate the disturbances generated by a momentum wheel and to improve pointing performance, and two control laws for a semiactive approach were proposed.
Abstract: A semiactive isolator filled with liquid-crystal type electro-rheological (ER) fluid was developed to attenuate the disturbances generated by a momentum-wheel and to improve pointing performance. The principal characteristics of an ER isolator were measured in dynamic tests, and a mathematical model of the isolator was proposed. Two control laws for a semiactive approach were proposed. Numerical simulation results indicated that the proposed semiactive control system produced much better isolation performance than a passive system.
TL;DR: In this paper, the authors explored the possibility of using Harmonic balance based nonlinear system identification methods to extract from the nonlinear vibration spectrum of resonant atomic force silicon microcantilevers, the Hamaker constants between a few atoms at the tip of the micro cantilever and graphite, gold and silicon carbide samples.
Abstract: Hamaker constants are characteristic material properties that determine the magnitude of the nonlinear van der Waals force between atoms, molecules and nanoscale aggregates of atoms This paper explores the novel possibility of using Harmonic Balance based nonlinear system identification methods to extract from the nonlinear vibration spectrum of resonant atomic force silicon microcantilevers, the Hamaker constants between a few atoms at the tip of the microcantilever and graphite, gold and silicon carbide samples First, the nonlinear dynamics of a diving board microcantilever coupled to the samples through van der Waals force potentials are investigated through a discretized model of the system Next, the feasibility of using Harmonic Balance based nonlinear system identification techniques are demonstrated using simulations of the discretized model Finally the method is implemented on an AFM system The results indicate that the proposed method provides a novel alternative way to measure Hamaker constants and the measured results are within the range of known experimental data
TL;DR: In this paper, the authors studied the dynamic behavior of a shallow arch under a point load Q traveling at a constant speed and found that when Q is greater than Q d cr, there exists a finite speed zone within which the arch runs the risk of dynamic snap-through either while the point load is still on the arch or after the point loads leaving the arch.
Abstract: In this paper we study the dynamic behavior of a shallow arch under a point load Q traveling at a constant speed. Emphasis is placed on finding whether snap-through buckling will occur. In the quasi-static case when the moving speed is almost zero, there exists a critical load Q cr in the sense that no static snap-through will occur as long as Q is smaller than Q cr . In the dynamic case when the point load travels with a nonzero speed, the critical load Q d cr is, in general, smaller than the static one. When Q is greater than Q d cr , there exists a finite speed zone within which the arch runs the risk of dynamic snap-through either while the point load is still on the arch or after the point load leaves the arch. The boundary of this dangerous speed zone can be determined by a more conservative criterion, which employs the concept of total energy and critical energy barrier, to guarantee the safe passage of the point load. This criterion requires the numerical integration of the equations of motion only up to the instant when the point load reaches the other end of the arch.
TL;DR: In this article, a switch-shunted damper (SSD) is used to increase the damping of the structure to which the damper is applied, and experimental measurements with this prototype SSD indicate that quarter-cycle switching algorithms which include switching states at a condition of maximum strain yield enhanced damping effectiveness but also leads to the generation of potentially undesirable mechanical transients.
Abstract: Significant interest has been generated by the possibilities of active vibration control through the implementation of state switching, with a specific implementation embodied through piezoceramic shunting. A state-switched absorber (SSA) is a vibration absorber that has the unique ability to change its resonant state amongst multiple distinct resonant states while in motion, thereby increasing the effective bandwidth over that of a single frequency device and thereby allowing control of multi-frequency, transient, and time-varying disturbances. In contrast, a switch-shunted damper (SSD) is a variant of an SSA that is used to increase the damping of the structure to which the damper is applied. Active vibration control applications discussed in the literature indicate the potential advantages of SSDs which employ piezoelectric ceramics as switchable springs with control algorithms that require switching states at points of non-zero strain. However, consideration of the constitutive equations for piezoelectric materials indicates a discontinuity in the electrical and mechanical conditions imposed by switching the stiffness at non-zero strains. A prototype SSD has been built and tested to experimentally investigate switching control logic and electrical and mechanical discontinuities at switching points; experimental measurements with this prototype SSD indicate that quarter-cycle switching algorithms which include switching states at a condition of maximum strain yield enhanced damping effectiveness but also leads to the generation of potentially undesirable mechanical transients.