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This paper presents a simulation method that is used to study subcritical vibrations of a tube roll in a paper machine. This study employs asymmetric 3D beam elements based on the Timoshenko beam theory. An asymmetric beam model accounts for varying stiffness and mass distributions. Additionally, a detailed rolling element bearing model defines the excitations arising from the set of spherical roller bearings at both ends of the rotor. The results obtained from the simulation model are compared against the results from the measurements. The results indicate that the waviness of the bearing rolling surfaces contributes significantly to the subcritical vibrations while the asymmetric properties of the tube roll have only a fractional effect on the studied vibrations. [ABSTRACT FROM AUTHOR]

Abstract A vibration absorber, also known as a tuned mass damper (TMD), is a passive vibration control device. This is achieved by attaching a secondary oscillator to a primary oscillator. In general, the aim is to reduce the vibration of the primary oscillator by suitably choosing the parameters of the secondary oscillator. The effectiveness of a TMD depends on (a) optimised the value of the tuned parameters, and (b) the nature of ambient damping of the absorber. They theory of TMD when the secondary and the primary oscillators are undamped or viscously damped is well developed. This paper presents an analytical approach to obtain optimal parameters of a TMD when the vibration absorber is viscoelastically damped. Classical results on viscously damped vibration absorbers can be obtained as a special case of the general results reduced in the paper. It is shown that by using a viscoelastically damped TMD, it is possible to obtain superior vibration absorption compared to an equivalent viscously damped TMD. [ABSTRACT FROM AUTHOR]

Abstract A new multi-impulse robust shaper (MIR) is put forward to control the residual vibration of the flexible system actively in this paper. This technique designs a sequence of impulses according to the undamped natural frequency and the damping ratio of the flexible system to shape the input command. The input command shaped by MIR shaper can suppress the transient vibration and residual vibration and is robust to modeling errors in natural frequency and damping ratio of the flexible system to some extent. The shaped input command by MIR shaper can also suppress the high mode residual vibration under a certain level in a wide range of normalized frequency. The characteristic of the proposed MIR shaper is investigated in this paper, which shows a good advantage and broad application with comparison to the traditional ZV shaper, ZVD shaper and EI shapers. [ABSTRACT FROM AUTHOR]

Although vortex-induced vibration (VIV) has been extensively studied, much of existing literature deals with uniform flow in the absence of a boundary. The VIV flow field of a structure close to a boundary generally remains unexplored, but it can have important engineering implications, such as pipeline scour if the boundary is an erodible seabed. In this paper, laboratory experiments are performed to investigate the flow characteristics of an elastically mounted circular cylinder undergoing VIV, and a rigid plane boundary is considered to simplify the problem. The initial gap-to-diameter ratio is fixed at 0.8, and six different reduced velocities are considered. The velocity field is measured using a high resolution particle image velocimetry (PIV) system, which has several advantages over traditional PIV systems, including high sampling rate and the ability to mitigate scatter of laser light near the boundary, allowing accurate measurements at the viscous sublayer. This paper presents the vibration amplitude and oscillation frequency for different V r ; in addition, the mean velocity field, turbulence characteristics, vortex behavior, gap flow velocity, and normal/shear stresses on the boundary were measured/calculated, leading to new insights on the flow field behavior. [ABSTRACT FROM AUTHOR]

Abstract This paper reports findings from an experimental study on vortex-induced vibration of a horizontal, flexibly-mounted cylinder positioned near the free surface of fluid flow. The cylinder is allowed to oscillate in the vertical direction only. Oscillation amplitude and frequency data are presented as a function of reduced velocity and dimensionless depth from the free surface. Data are presented for cases of decreasing depth from where the resting cylinder is fully-submerged until its centerline is even with the free surface of the water. For a fully-submerged cylinder, VIV behavior is consistent with published findings of similar systems, producing a well-documented lock-in region with initial, upper, and lower branches. Broadly, as the cylinder is raised from the fully-submerged case, the amplitudes diminish and the lock-in region decreases in range and shifts toward higher reduced velocities. When the cylinder is very near the surface, a second region of oscillations occurs at higher reduced velocities. This region emerges in cases where the cylinder's top edge is half a diameter below the free surface. For a short range of depths, the lock-in region and the non-zero amplitude region at higher reduced velocities coexist. But after a critical depth, the lock-in region disappears and oscillations are observed only at the higher reduced velocity region. Multi-frequency oscillations and regions of hysteresis are observed for some cases of low depth and high reduced velocity. [ABSTRACT FROM AUTHOR]

Abstract Nonlinear normal modes (NNMs) of a mechanical structure provide a mean to understand nonlinear vibrational phenomena measured experimentally. As they are an interesting extension of the linear normal modes (LNMs), numerical methods are needed to estimate these oscillatory motions, generally including continuation aspects with respect to the circular frequency. In this paper, a continuation method combined to a model reduction based on Proper Generalized Decomposition (PGD) technique is described. This formulation mixes PGD, harmonic balance method (HBM) and basic continuation techniques in order to reach a highly reduced description of the NNMs. This PGD/HBM-based continuation algorithm includes a modal enrichment as the NNM energy grows. The method is applied to two conservative problems including a cubic spring and a unilateral contact. Highlights • An algorithm to compute Nonlinear Normal Modes using few variables is exposed. • A PGD combined to HBM method describes the modes. • Continuation with on the fly enrichment keeps the number of variable very low. • Nonlinear Normal Modes of beams with localised non linearities are computed. [ABSTRACT FROM AUTHOR]

This paper investigates the spin resonance of a rattleback subjected to base oscillations which is able to transduce vibrations into continuous rotary motion and, therefore, is ideal for applications in Energy harvesting and Vibration sensing. The rattleback is a toy with some curious properties. When placed on a surface with reasonable friction, the rattleback has a preferred direction of spin. If rotated anti to it, longitudinal vibrations are set up and spin direction is reversed. In this paper, the dynamics of a rattleback placed on a sinusoidally vibrating platform are simulated. We can expect base vibrations to excite the pitch motion of the rattleback, which, because of the coupling between pitch and spin motion, should cause the rattleback to spin. Results are presented which show that this indeed is the case—the rattleback has a mono-peak spin resonance with respect to base vibrations. The dynamic response of the rattleback was found to be composed of two principal frequencies that appeared in the pitch and rolling motions. One of the frequencies was found to have a large coupling with the spin of the rattleback. Spin resonance was found to occur when the base oscillatory frequency was twice the value of the coupled frequency. A linearized model is developed which can predict the values of the two frequencies accurately and analytical expressions for the same in terms of the parameters of the rattleback have been derived. The analysis, thus, forms an effective and easy method for obtaining the spin resonant frequency of a given rattleback. Novel ideas for applications utilizing the phenomenon of spin resonance, for example, an energy harvester composed of a magnetized rattleback surrounded by ferromagnetic walls and a small scale vibration sensor comprising an array of several magnetized rattlebacks, are included. [ABSTRACT FROM AUTHOR]

As the number of degrees of freedom (DOFs) in structural dynamic problems becomes larger, the analyzing complexity and CPU usage of computers increase drastically. Condensation (or reduction) method is an efficient technique to reduce the size of the full model or the dimension of the structural matrices by eliminating the unimportant DOFs. After the first presentation of condensation method by Guyan in 1965 for undamped structures, which ignores the dynamic effects of the mass term, various forms of dynamic condensation methods were presented to overcome this issue. Moreover, researchers have tried to expand the dynamic condensation method to non-classically damped structures. Dynamic reduction of such systems is far more complicated than undamped systems. The proposed non-iterative method in this paper is introduced as 'Maclaurin Expansion of the frequency response function in Laplace Domain' (MELD) applied for dynamic reduction of non-classically damped structures. The present approach is implemented in four numerical examples of 2D bending-shear-axial frames with various numbers of stories and spans and also a floating raft isolation system. The results of natural frequencies and dynamic responses of models are compared with each other before and after the dynamic reduction. It is shown that the result accuracy has acceptable convergence in both cases. In addition, it is indicated that the result of the proposed method is more accurate than the results of some other existing condensation methods. [ABSTRACT FROM AUTHOR]

This paper deals with active sound attenuation in lined ducts with flow and its application to duct modes damping in aircraft engine nacelles. It presents an active lining concept based on an arrangement of electroacoustic absorbers flush mounted in the duct wall. Such feedback-controlled loudspeaker membranes are used to achieve locally reacting impedances with adjustable resistance and reactance. A broadband impedance model is formulated from the loudspeaker parameters and a design procedure is proposed to achieve specified acoustic resistances and reactances. The performance is studied for multimodal excitation by simulation using the finite element method and the results are compared to measurements made in a flow duct facility. This electroacoustic liner has an attenuation potential comparable to that of a conventional passive liner, but also offers greater flexibility to achieve the target acoustic impedance in the low frequencies. In addition, it is adaptive in real time to track variable engine speeds. It is shown with the liner prototype that the duct modes can be attenuated over a bandwidth of two octaves around the resonance frequency of the loudspeakers. [ABSTRACT FROM AUTHOR]

Car judder is a kind of back-forth vibration during vehicle starting which caused by the torsional oscillation of the driveline. This paper presents a systematic study on the dynamic response characteristics of the clutch driven disc for suppression of the judder during vehicle starting. Self-excited vibration behavior of the clutch driven disc is analyzed based on the developed 4DOF non-linear multi-body dynamic model of the clutch driving process considering stick-slip characteristics and using Karnopp friction models. Physical parameters of a clutch determining the generations of the judder behaviors are discussed and the revised designs of the driven disc of a clutch for suppression of the judder are consequently investigated and validated with experiments for two real cars. [ABSTRACT FROM AUTHOR]

Structural flexibility can impact negatively on machine motion control systems by causing unmeasured positioning errors and vibration at locations where accurate motion is important for task execution. To compensate for these effects, command signal prefiltering may be applied. In this paper, a new FIR prefilter design method is described that combines finite-time vibration cancellation with dynamic compensation properties. The time-domain formulation exploits the relation between tracking error and the moment values of the prefilter impulse response function. Optimal design solutions for filters having minimum H2 norm are derived and evaluated. The control approach does not require additional actuation or sensing and can be effective even without complete and accurate models of the machine dynamics. Results from implementation and testing on an experimental high-speed manipulator having a Delta robot architecture with directionally compliant end-effector are presented. The results show the importance of prefilter moment values for tracking performance and confirm that the proposed method can achieve significant reductions in both peak and RMS tracking error, as well as settling time, for complex motion patterns. [ABSTRACT FROM AUTHOR]

As an extremely dangerous phenomenon in autonomous aerial refueling (AAR), the flexible refueling hose vibration caused by the receiver aircraft’s excessive closure speed should be suppressed once it appears. This paper proposed a permanent magnet synchronous motor (PMSM) based refueling hose servo take-up system for the vibration suppression of the flexible refueling hose. A rapid back-stepping based anti-disturbance nonsingular fast terminal sliding mode (NFTSM) control scheme with a specially established finite-time convergence NFTSM observer is proposed for the PMSM based hose servo take-up system under uncertainties and disturbances. The unmeasured load torque and other disturbances in the PMSM system are reconstituted by the NFTSM observer and to be compensated during the controller design. Then, with the back-stepping technique, a rapid anti-disturbance NFTSM controller is proposed for the PMSM angular tracking to improve the tracking error convergence speed and tracking precision. The proposed vibration suppression scheme is then applied to PMSM based hose servo take-up system for the refueling hose vibration suppression in AAR. Simulation results show the proposed scheme can suppress the hose vibration rapidly and accurately even the system is exposed to strong uncertainties and probe position disturbances, it is more competitive in tracking accuracy, tracking error convergence speed and robustness. [ABSTRACT FROM AUTHOR]

The main aim of this study is to predict the elastic and damping properties of composite laminated plates. This problem has an exact elasticity solution for simple uniform bending and transverse loading conditions. This paper presents a new stress analysis method for the accurate determination of the detailed stress distributions in laminated plates subjected to cylindrical bending. Some approximate methods for the stress state predictions for laminated plates are presented here. The present method is adaptive and does not rely on strong assumptions about the model of the plate. The theoretical model described here incorporates deformations of each sheet of the lamina, which account for the effects of transverse shear deformation, transverse normal strain-stress and nonlinear variation of displacements with respect to the thickness coordinate. Predictions of the dynamic and damping values of laminated plates for various geometrical, mechanical and fastening properties are presented. Comparison with the Timoshenko beam theory is systematically made for analytical and approximation variants. [ABSTRACT FROM AUTHOR]

In this paper, nonviscous, nonproportional, vibrating structures are considered. Nonviscously damped systems are characterized by dissipative mechanisms which depend on the history of the response velocities via hereditary kernel functions. Solutions of the free motion equation lead to a nonlinear eigenvalue problem involving mass, stiffness and damping matrices. Viscoelasticity leads to a frequency dependence of this latter. In this work, a novel closed-form expression to estimate complex eigenvalues is derived. The key point is to consider the damping model as perturbed by a continuous fictitious parameter. Assuming then the eigensolutions as function of this parameter, the computation of the eigenvalues sensitivity leads to an ordinary differential equation, from whose solution arises the proposed analytical formula. The resulting expression explicitly depends on the viscoelasticity (frequency derivatives of the damping function), the nonproportionality (influence of the modal damping matrix off-diagonal terms). Eigenvectors are obtained using existing methods requiring only the corresponding eigenvalue. The method is validated using a numerical example which compares proposed with exact ones and with those determined from the linear first order approximation in terms of the damping matrix. Frequency response functions are also plotted showing that the proposed approach is valid even for moderately or highly damped systems. [ABSTRACT FROM AUTHOR]

Abstract: Complex mode shapes are quite often encountered in structural dynamics. However, there is no universally accepted parameter for the quantification of mode shape complexity. After reviewing the existing methods, a novel approach is proposed in this paper in order to quantify mode shape complexity for general structures. The new parameter proposed in this paper is based on conservation of energy principle when a structure is vibrating at a specific mode during a period of vibration. The levels of complexity of the individual mode shapes of a sample structure are then quantified using the proposed new parameter and the other parameters available in the literature. The corresponding results are compared, the validity and the generality of the new parameter are demonstrated for various damping scenarios. [Copyright &y& Elsevier]

Abstract: In this paper the dynamic response of a double-string system traversed by a constant or a harmonically oscillating moving force is considered. The force is moving with a constant velocity on the top string. The strings are identical, parallel, one upon the other and continuously coupled by a linear Winkler elastic element. The classical solution of the response of a double-string system subjected to a force moving with a constant velocity has a form of an infinite series. The main goal of this paper is to show that in the considered case a part of the solution can be presented in a closed, analytical form instead of an infinite series. The presented method of finding the solution in a closed, analytical form is based on the observation that the solution of the system of partial differential equations in the form of an infinite series is also a solution of an appropriate system of ordinary differential equations. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this paper is to improve the phenomenological modeling of vortex-induced vibration of an elastically mounted cylinder in fluid flow. To this end an attempt is made to introduce a wake oscillator model that conforms to both the free and forced vibration experiments. This approach is new as in the past wake oscillator models have been tuned to the free vibration experiments only. First, an existing wake oscillator model is improved by properly including the effect of stall and that of the relatively large attack angles in the course of vortex-induced vibration. Then, to comply with the forced vibration experiments, the model is enhanced by introducing frequency dependent coupling. Such a coupling allows reproduction of the measured frequency dependence of the fluid force on the cylinder. The time domain representation of this coupling is a convolution integral. It is found in this paper that if the wake oscillator is modeled with a Van der Pol equation, it is impossible to find one set of frequency dependent coefficients that conforms to the forced vibration experiments at all amplitudes of cylinder motion. Moreover, the frequency dependencies identified for each frequency separately do not seem to satisfy the Kramers–Kronig relations. Based on the above findings, it is concluded that the nonlinearities in the wake oscillator model used in this paper cannot accurately model the results of vortex-induced vibration measurements. The idea proposed in this paper, that a consistent wake oscillator model must conform to the forced vibration experiments as well, is expected to be a powerful tool in the search for the correct nonlinearity. [Copyright &y& Elsevier]

Abstract: This paper discusses the results of an experimental study of the effect of pipe oscillations on the wall pressure field and flow rate through a metallic pipe with air flowing through it. The data presented in this paper show that the frequencies of pressure oscillations in a non-oscillating pipe are identical to the natural structural modes of the pipe suggesting the influence of structural properties on the fluid dynamics of the flow. The results presented in this paper also show that the wall pressure undergoes both a temporal as well as a spatial oscillation if the pipe is forced to oscillate periodically. The pressure oscillations are found to be harmonics of the pipe oscillations. There is a drop in the mean pressure when the pipe is subjected to periodic oscillations. The flow rate through the pipe is seen to undergo a periodic change over a range of almost 7 percent variation when the pipe is oscillated. The study presented in this paper elucidates the dominant effect of system dynamics on determining the flow behavior through a rigid pipe. The adverse effect of flow oscillations, induced by pipe motion, can lead to departure of the flow from the intended design conditions and can render the fluid supply system inadequate. [Copyright &y& Elsevier]

In this paper a new analytical method for solving the differential equations which describe the motion of the oscillator with fraction order elastic force is introduced. Using the first integral of motion the exact period of vibration in the form of the Euler beta function is obtained. Based on that value the approximate solution of the strong nonlinear fraction order differential equation is formed. The suggested procedure is applied for various fraction values, but also for the pure quadratic, cubic and quintic oscillators. The advantage of the suggested method is that is valid for all fraction values , the accuracy of the approximate solution is very high as the period of vibration is exactly analytically determined and is independent on the time. In the paper the fraction order differential equation with small linear and nonlinear terms is also considered. The Krylov–Bogolubov method is extended due to the fact that frequency of vibration depends on the amplitude of vibration. The approximate solution is with time variable amplitude, phase and frequency. The linear damped fraction order oscillator is widely discussed. The approximate solution of the differential equation which describes the vibrations of such oscillator is compared with exact numerical one and shows a good agreement. [Copyright &y& Elsevier]

Abstract: This paper presents the extended Lindstedt–Poincare (EL–P) method, which applies multiple time variables to treat non-stationary oscillations arising in dynamical systems with cubic nonlinearities due to the slowly varied excitation parameters. The method is applied extensively in research of non-stationary vibrations of clamped-hinged beams. Recognizing the aperiodic nature of non-stationary oscillations, the new formulation is presented by adding an additional, slow time scale beside time scales of the nonlinear system, which generally correspond to the incommensurate nonlinear frequencies of the response. Using this concept, a generalized approach of the study to the passage through fundamental, superharmonic and subharmonic resonances is presented in the paper. Effects of slowly varying excitation frequency and slowly varying excitation amplitude on the non-stationary oscillations are studied with the computation of deviations from the stationary response. Although the method is formulated for N-dof dynamical systems having weak cubic nonlinearities, it is applied for non-stationary vibrations, where two-mode shape approximation of damped and undamped clamped-hinged beam, respectively, is used and the simultaneous appearance of internal resonance is taken into account. Stability analysis of stationary solutions is performed and comparisons of stationary resonance curves by results obtained with the incremental harmonic balance (IHB) method show good agreement. The passage through the fundamental resonance of damped and undamped clamped-hinged beam, respectively, is investigated in detail. [Copyright &y& Elsevier]

Abstract: In this paper the wind-induced, horizontal vibrations of a weakly damped vertical Euler–Bernoulli beam with and without a tip-mass will be studied. The damping is assumed to be boundary damping and global Kelvin–Voigt damping. The boundary damping is assumed to be proportional to the velocity of the beam at the top. The horizontal vibrations of the beam can be described by an initial-boundary value problem. In this paper, the multiple-timescales perturbation method will be applied to construct approximations of the solutions of the problem. Also it will be shown that a combination of boundary damping and Kelvin–Voigt damping can be used to damp the wind-induced vibrations of a vertical beam with tip-mass uniformly. [Copyright &y& Elsevier]

Abstract: A new formulation able to predict the behaviour of structures in the mid-frequency range is presented in this paper. The mid-frequency field is a hybrid domain for which assembled structures exhibit simultaneously low- and high-frequency behaviours, depending on the material and geometrical properties of different subsystems. Thus, dealing with the mid-frequency field requires simulation methods which are able to account the differences in behaviour of different subsystems. The hybrid formulation is based on the coupling of two different formulations, the finite elements for the low-frequency behaving subparts and a probabilistic formulation, the smooth integral formulation, applied to the high-frequency subsystems. The hybrid method enables to correctly predict the deterministic response of the low-frequency parts which is not affected by randomness, and the smooth trend of the contributions of the high-frequency parts. The paper is concluded with several numerical examples computed for coupled one- and two-dimensional structures. [Copyright &y& Elsevier]

A new approach to identification of modal damping ratios from free vibration response of a linear structure with viscous damping is proposed in this paper. For a single degree of freedom (dof) system, the formulated relations among areas forming from time history of response are used to determine the damping ratio for the free decay vibration. Comparing with traditional logarithmic-decrement method, the approach in this paper has advantages such as stronger anti-noise ability, higher precision, better stability and convenience. For a multi-dof system, the free vibration response measured at one point on the structure is expressed in an analytical form at first, and then multiplied by e at . Giving the initial value, a can be obtained by Newton's dichotomy or golden section method while the product of the response and e at has equal vibration amplitudes after a period of time. Accordingly, the damping ratio for this mode can be determined. Repeating the above-mentioned process, all damping ratios for different modes can be obtained in the same way. Results of digital simulations and field tests for the Dongting Lake Cable-stayed Bridge in Yueyang show that the approach presented in this paper is effective and practical. [Copyright &y& Elsevier]

Abstract: This paper investigates the complex dynamics induced by antibody-dependent enhancement (ADE) in multiserotype disease models. ADE is the increase in viral growth rate in the presence of immunity due to a previous infection of a different serotype. The increased viral growth rate is thought to increase the infectivity of the secondary infectious class. In our models, ADE induces the onset of oscillations without external forcing. The oscillations in the infectious classes represent outbreaks of the disease. In this paper, we derive approximations of the ADE parameter needed to induce oscillations and analyze the associated bifurcations that separate the types of oscillations. We then investigate the stability of these dynamics by adding stochastic perturbations to the model. We also present a preliminary analysis of the effect of a single serotype vaccination in the model. [Copyright &y& Elsevier]

Abstract: This paper discusses modelling of floating-slab tracks on rigid foundations. The model consists of an upper Euler–Bernoulli beam to account for both the rails and a lower Euler–Bernoulli beam to account for the slab. There are two continuous resilient layers in the model: one to account for railpads between the rails and the slab and one to account for slab-bearings underneath the slab. The Fourier transformation method is used to calculate displacements of such a track under an oscillating moving load. These results are used to calculate the cut-on frequencies and critical velocity of the track. The work in this paper also demonstrates some basic concepts in the context of vibration of infinite systems including dispersion curves, critical velocities, load-velocity lines and coupling of systems in the wavenumber-frequency domain. The paper offers a complete treatment of the issues important to the analysis of a double-beam system not elsewhere available in the published literature. [Copyright &y& Elsevier]

Abstract: Even though the nonlinear damping characteristics inherently pertain to most structural systems, many useful dynamic models are still linear. As a consequence, a method that is able to equivalently linearize (EQL) the nonlinear damping so that it can be directly applied in these existing linear models is essential. In the present paper, a novel EQL method for nonlinearly damped and single-degree-of-freedom systems is developed. The method is theoretically derived by modulating the steady-state responses of the original nonlinear system. During the linearization, the new EQL method requires the dissipated energy of the target linear system to equal that of the original nonlinear one. In effect, this criterion is equivalent to forcing both the phase angles and amplitudes of the two systems to be equal, or at least to within a small allowable error. Furthermore, the present paper proves that it is possible for the dissipative energy to be expressed in terms of the Fourier coefficients of the modulated signal. Thus, the equivalent viscous damping ratio can be computed from these Fourier coefficients. This new EQL method is numerically tested using examples of bi-linear damping models, and subjected to experimental measurements. Both the simulation results and the experimental data verify the validity of the method. They also prove that the current method gives the equivalent viscous damping with good accuracy. In addition, a quality index that signifies how well the EQL system reaches is appropriately added. [Copyright &y& Elsevier]

Abstract: The paper considers a problem of random vibrations of swings—a pendulum with variable length. The goal of the paper is to estimate mean response energy of the system, subjected to external Gaussian white noise. The Energy Balance method is used to derive analytical results. [Copyright &y& Elsevier]

Nonlinear energy harvesters are very sensitive to ambient vibrations. If the excitation level is too low, their large-amplitude oscillations for high-energy voltage output cannot be obtained. A nonlinear tristable energy harvester has been previously proposed to achieve more effective broadband energy harvesting for low-level excitations. However, the sensitivity of its dynamic characteristics to the system parameters remains uninvestigated. Therefore, this paper theoretically analyzes the influence of the external load, the external excitation, the internal system parameters and the equilibrium positions on the dynamic responses of nonlinear tristable energy harvesters by using the harmonic balance method. In addition, numerical acceleration excitation thresholds and basins of attraction are provided to investigate the potential for energy harvesting performance enhancement using the suitable equilibrium positions, appropriate initial conditions or external disturbances, due to high-energy interwell oscillations in the multi-solution ranges. More importantly, experimental voltage responses of a given tristable energy harvester versus the external excitation frequency and amplitude verify the existence of experimental multi-solution ranges and the effectiveness of the theoretical analysis. It is also revealed that achieving high-energy interwell oscillations in the multi-solution ranges of tristable energy harvesters will be feasible for improving energy harvesting from low-level ambient excitations. [ABSTRACT FROM AUTHOR]

Operating cranes is challenging because payloads experience large and dangerous oscillations, especially when the system is suffering from wind disturbances and the large-size payload is modeled as a distributed-mass model. The payload oscillations induced by both intentional motions commanded by the human operator and by the external wind disturbances make the dynamics more complicated. This paper presents a novel combined control architecture to limit oscillations of the distributed-mass payload caused by both human-operator commands and wind disturbances. While a smoothed command suppressed operator-induced oscillations, a wind-rejection command eliminated the payload swing resulting from the wind gusts. Through simulations, a large range of system parameters and motions are analyzed to investigate the dynamic behavior of bridge cranes with distributed-mass beams and wind disturbances by using the new control scheme. Experimental results obtained from a small-scale bridge crane validate the simulated dynamic behavior and the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper focuses on the further development of a previously published semi-empirical method for time domain simulation of vortex-induced vibrations (VIV). A new hydrodynamic damping formulation is given, and the necessary coefficients are found from experimental data. It is shown that the new model predicts the observed hydrodynamic damping in still water and for cross-flow oscillations in stationary incoming flow with high accuracy. Next, the excitation force model, which is one component of the total hydrodynamic force model, is optimized by simulating the VIV response of an elastic cylinder in a series of experiments with stationary flow. The optimization is performed by repeating the simulations until the best possible agreement with the experiments is found. The optimized model is then applied to simulate the cross-flow VIV of an elastic cylinder in oscillating flow, without introducing any changes to the hydrodynamic force modeling. By comparison with experiment, it is shown that the model predicts the frequency content, mode and amplitude of vibration with a high level of realism, and the amplitude modulations occurring at high Keulegan–Carpenter numbers are well captured. The model is also utilized to investigate the effect of increasing the maximum reduced velocity and the mass ratio of the elastic cylinder in oscillating flow. Simulations show that complex response patterns with multiple modes and frequencies appear when the maximum reduced velocity is increased. If, however, the mass ratio is increased by a factor of 5, a single mode dominates. This illustrates that, in oscillating flows, the mass ratio is important in determining the mode participation at high maximum reduced velocities. [ABSTRACT FROM AUTHOR]

Inerter is a recently proposed mechanical element with two terminals. The novelty of this paper is to present the improved design which aims to add traditional dynamic vibration absorber to the vehicle body by using the inerter. Based on this background, a new vehicle suspension structure called ISD suspension, including the inerter, spring and damper has been created. A dual-mass vibration model including the ISD suspension is considered in this study. Parameters are obtained by using the genetic optimizing algorithm. The frequency-domain simulation confirms that the ISD suspension can effectively improve the damping performance of the suspension system, especially at the offset frequency of the vehicle body, which is consistent with the feature of the dynamic vibration absorber added to the vehicle body mass. At last, a prototype ball screw inerter has been designed and the bench test of a quarter-car model has been undertaken. Under the conditions of the random road input, the vehicle ride comfort evaluation of body acceleration RMS value decreases by 4% at most, the suspension deflection RMS value decreases by 16% at most, the tire dynamic load RMS value decreases by 6% at most. Power spectral density results also indicate that the ISD suspension has superior damping performance than passive suspension which proves that the proposed ISD suspension is deemed effective. [ABSTRACT FROM AUTHOR]

The developed pre-stressed cable reinforced concrete truss (PCT) floor system is a relatively new floor structure, which can be applied to various long-span structures such as buildings, stadiums, and bridges. Due to the lighter mass and longer span, floor vibration would be a serviceability concern problem for such systems. In this paper, field testing and theoretical analysis for the PCT floor system were conducted. Specifically, heel-drop impact and walking tests were performed on the PCT floor system to capture the dynamic properties including natural frequencies, mode shapes, damping ratios, and acceleration response. The PCT floor system was found to be a low frequency (<10 Hz) and low damping (damping ratio<2 percent) structural system. The comparison of the experimental results with the AISC׳s limiting values indicates that the investigated PCT system exhibits satisfactory vibration perceptibility, however. The analytical solution obtained from the weighted residual method agrees well with the experimental results and thus validates the proposed analytical expression. Sensitivity studies using the analytical solution were also conducted to investigate the vibration performance of the PCT floor system. [ABSTRACT FROM AUTHOR]

In this paper, we propose an impact damper which consists of multiple vibrators installed on a main structure and dissipates the vibrational energy by collisions between the vibrators. Transient vibration of the main system subject to an impact rapidly converges to zero by the impact damper. DE (Differential Evolution) method which is one of the optimization methods is employed to determine mass and spring constant of the every vibrators to maximize damping effect. We discuss the effect of a coefficient of restitution of vibrators, a ratio of total mass of the vibrators to the main structure mass and the number of the vibrators on the damping performance. The damping effect of the impact damper with three vibrators is demonstrated experimentally. [ABSTRACT FROM AUTHOR]

The vibration signal of faulty gearbox commonly involves complex coupling modulation components. The method of sparse representation has been successfully used for gearbox fault diagnosis, but most of the literatures only focus on the extraction of impact modulation and always neglect the steady modulation representing the distributed faults. This paper presents a new method for separating coupling modulation from vibration signal of gearbox based on match pursuit and correlation filtering. To separate the steady modulation caused by distributed fault and the impact modulation caused by impact fault, two sub-dictionaries are specially designed according to the gearbox operating and structural parameters and the characteristics of vibration signal. The new dictionaries have clear physical meaning and good adaptability. In addition, an amplitude recovery step is conducted to improve the matching accuracy in the match pursuit. Simulation and experimental results show that the proposed method can separate the coupling components of gearbox vibration signal effectively under intensive background noise. [ABSTRACT FROM AUTHOR]

Analyzing the propagation of vibrational excitations from a source substructure to receiving components is an important issue in many high-tech engineering applications. Two equivalent and mutually dual methods to characterize a vibration source consist in determining either the force on its blocked interface or the vibration of its interface left free. Those source properties, together with information on the impedance (or admittance) of the system, allow predicting the coupled dynamic response of an assembly even though the detailed excitation origin in the source is not known. Despite the fact that the methods were already described more than fifty years ago, applying them in practical engineering problems remains challenging. The purpose of the present paper is to outline the blocked force and free velocity methods in a unified way, starting from the general notions of primal and dual assembly of impedances and admittances. An application example is shortly discussed. [ABSTRACT FROM AUTHOR]

Natural frequencies, mode shapes and modal damping values are the most important parameters to describe the noise and vibration behavior of a mechanical system. For rotating machinery, however, the directivity of the propagation wave of each mode should also be taken into account. For rotating systems, this directivity can be determined by complex modal testing. In this paper, a rolling tire is represented as a flexible ring model. The limitation of application of the complex modal testing which requires two directional measurements at a certain point, which is difficult to measure in practice, has been overcome through a modified complex modal testing which requires only one directional measurements at any two points. The technique is described in detail and applied to both a numerical example and to an experimental data set of a real rotating tire. [ABSTRACT FROM AUTHOR]

In this paper, the application of weak signal detection based on chaotic oscillator is studied in a MEMS resonant beam sensor. Chaotic oscillator can detect weak signal which is submerged in the background of large noise. According to the frequency and phase characteristic of the output vibrating signal, reference current signal with fixed frequency difference and same phase to the output signal is set. Frequency and phase of the signal are fixed by detection resistor which works as a multiplier. By calculating the maximum Lyapunov exponent, detection threshold is obtained, and motion change of detection system is monitored. The results of numerical simulation and experiment show that this method can effectively detect the weak resonant signal and find the resonant frequency accurately by setting the threshold of the chaotic oscillator, and it is immune to the noise. [ABSTRACT FROM AUTHOR]

Abstract: The cables in cable-stayed bridges can vibrate at large amplitudes during rain and windy conditions, a phenomenon known as rain-wind induced vibration (RWIV). Previous studies have demonstrated that the formation and oscillation of rivulets on stay cable surfaces play an important role in RWIV.This paper presents a new numerical method for simulating the evolution of rivulets on stay cable surfaces based on a combination of the gas–liquid two-phase theory and the volume of fluid method (VOF method), which allows for the straightforward determination of the cables’ aerodynamic lift when RWIV occurs. To verify the accuracy of this method and analyze the effects of wind velocity on the water film and the aerodynamic lift around the cable, three cases with different loadings were investigated using the computational fluid dynamics (CFD) software CFX. To verify the method’s accuracy, the aerodynamic lifts calculated from these cases were applied to the cable to obtain its vibrational response. In accordance with the experimental results, the numerical results demonstrated that an upper rivulet with a periodic oscillation was formed at a specific wind speed, causing the aerodynamic lift to change with a similar periodicity. The aerodynamic lift’s frequency was approximately the cable’s natural frequency, and induced large vibrations in the cable. No obvious upper rivulets were formed at sufficiently low wind speeds. The frequency of an aerodynamic lift that was significantly larger than the cable’s natural frequency induced small vibrations in the cable. When the wind speed was sufficiently high, despite the eventual formation of a continuous upper rivulet, the frequencies of the upper rivulet’s oscillation and the aerodynamic lift remained distinct from the natural frequency, and the cable continued to exhibit small-amplitude vibrations. These observations confirmed the conclusion that periodic variations in the water film morphology could lead to periodic changes in the aerodynamic lift that would induce RWIV. [Copyright &y& Elsevier]

Abstract: The vibration isolator using a novel magnetic spring with negative stiffness (MS-NS) is proposed in this paper. The proposed isolator which combines a positive stiffness spring with the MS-NS in parallel possesses the characteristic of high-static–low-dynamic stiffness. The MS-NS is composed of three cuboidal magnets configured in repulsive interaction. An analytical expression of the stiffness of the MS-NS is derived by using the magnetic charge model, and the approximation to the exact analytical expression is sought. Then, the nonlinearity of the stiffness is analyzed, and it is shown that the MS-NS is approximately linear for small oscillations. In order to validate the correctness and effectiveness of the MS-NS, the vibration transmissibility of the proposed isolator with and without the MS-NS is measured. The experimental results demonstrate that combining a vibration isolator with the MS-NS in parallel can lower the natural frequency of the isolator; and the analytical calculations and experimental results show a good consistency. [Copyright &y& Elsevier]

Abstract: A classical problem in vortex-induced vibration is to know the flow field past an oscillating cylinder. In this paper we use system theory to identify the oscillatory behaviour of a circular cylinder from flow variables in the wake. We use numerical simulations (CFD) of the flow past a cylinder oscillating in the cross-flow direction at different oscillation frequencies and amplitudes to construct a transfer function that relates the displacement of the cylinder and the resulting flow field. This transfer function can then be inverted to ‘predict’ the displacement of the cylinder given the flow field (as determined by simulations or measurements). We investigate this technique in the so-called lock-in region, where the vortex shedding frequency is synchronised with the oscillation frequency of the cylinder. [Copyright &y& Elsevier]

Abstract: One of the critical parameters that can deteriorate the effectiveness of active vibration control (AVC) is the delay in sensors. Especially, in remote sensing where delays are large, and in high-speed applications with even small delays, instability can be inevitable. This paper presents algebraic approaches to design controllers in order to achieve stability regardless of the amount of delays for AVC applications modeled by linear time-invariant systems with “multiple” constant delays. The approaches are based on a nonconservative framework, and can identify the regions in the controller gain space where delay-independent stability (DIS) is achievable. With these controllers, we demonstrate via simulations that vibration suppression, within certain excitation frequency bands, can be improved or be as effective as those in AVC applications without delays. [Copyright &y& Elsevier]

Abstract: Vibrational energy harvesting devices are often designed in a manner analogous to classical dynamic vibration absorbers (DVAs). An electromechanical mass–spring system is devised so as to resonate at the frequency most dominant in the environmental vibration spectrum; the consequent device oscillation is converted to a electrical signal which is harnessed for immediate usage or as a charging mechanism for a battery. The DVA is likewise designed but with the intention of inducing substantial inertial influence upon a host structure for vibration control purposes, either to globally dampen the vibration of the main body or, in an undamped configuration to “absorb” the primary system vibration at a single frequency. This paper describes the development of an electromechanical mass–spring–damper which seeks to serve both goals of passive vibration control and energy harvesting. The device utilizes a piezoelectric film spring and a distributed mass layer so as to be suitable for the attenuation of surface vibrations and to convert a portion of the absorbed energy into electric power. The development and design of the device are presented and the results of realistic tests are provided to show both the potentials and the challenges encountered when attempting to superpose the goals of vibration control and energy harvesting. [Copyright &y& Elsevier]

Abstract: A new excitation principle for the piezoelectric actuator of traveling wave type is proposed and analyzed in the paper. The symmetric and asymmetric traveling waves of longitudinal vibrations are generated on the upside area of the cylindrical actuator. Two electrode patterns are proposed for excitation of the actuator. Harmonic voltage with phase shifts of 2π/3 and π/2 are used for achieving a traveling wave. Numerical modeling based on the finite element method was performed to analyze the oscillations of contact points of the actuator under different excitation schemes. Experimental measurements of the oscillation distribution on the surface of the cylinder have been done while different electrode patterns were used for excitation. Results of the numerical and experimental studies are discussed. [Copyright &y& Elsevier]

Abstract: This paper deals with the damping caused by friction in joints. A new test bench is presented and justified by comparisons made with devices described in the literature. The purpose of this academic bench is to measure the damping induced by partial slip and friction in a planar joint. Moreover, allows uncoupling normal static and dynamic tangential forces. A new method for so-called stopped-sine excitation was developed. It allows more precise monitoring of the evolution of the vibration frequency and damping of non-linear modes. This method is associated with piezoelectric exciters for greater efficiency when stopping excitation. A large number of experimental results are presented and discussed. They are used to characterize the damping induced by micro-sliding in the bonds. [Copyright &y& Elsevier]

Abstract: This paper is concerned with the radiation of sound waves from a submerged cylindrical body which is coated by an imperfect elastic layer; that is, the coating only covers part of the cylinder. The focus of the study is to quantify the effect of the gap in the elastic layer on the radiated acoustic power. A finite element method is employed to determine the acoustic pressure field in the fluid and the displacement field in the coupled layer. This reveals that the effect of a modest sized gap in the coating does not markedly alter the radiated field except at distinct frequencies, at which values the coating exhibits strong fluid-coupled oscillations. We develop a simple analytical model to explain the resonance phenomenon and show that quasi-resonances arise when the wavelength of the deformation pattern ‘matches’ the azimuthal length of the surface of the coating. This resonant behaviour is conveniently captured by a single parameter Q, which is the ratio of the typical inertial fluid pressure induced by the wall oscillation to the stiffness of the elastic coating. For each choice of material parameters, there is shown to be an infinite set of values of Q corresponding to distinct quasi-resonance mode numbers. The effects on the radiated field due to variations in various physical parameters, such as acoustic wavenumber and elastic layer inertia, are also discussed. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental study of the motions, forces and flow patterns of a positively buoyant tethered cylinder (m ⁎<1) in uniform flow undergoing vortex-induced vibration (VIV). The flow fields have been measured using digital Particle Image Velocimetry (PIV) technique, in conjunction with a piezoelectric load cell for direct measurement of drag and lift forces acting on the tethered cylinder. The effects of varying mass ratio and Reynolds number over the range 0.61≤m ⁎≤0.92 and 4000≤Re≤12 000 are examined. Results of a fixed (or stationary) cylinder at the same Reynolds numbers are provided to serve as the benchmark reference. The peak amplitude of oscillation, , generally increases with Re and deceases with m ⁎. Similar to previous studies, the results reveal the existence of a critical mass ratio , below which large-amplitude oscillations would take place when Re is high enough, with the largest peak amplitude of observed for the case of m ⁎=0.61 and Re=12 000. Thus two distinct states of oscillation are categorized, namely, the small- and large-amplitude oscillation states. The distinction between the two states is also vivid in the mean and root-mean-square (r.m.s.) force coefficients (including , and ). The frequency of vortex shedding (f V) from the tethered cylinder is always synchronized with the cylinder''s oscillation frequency (f osc), regardless of the oscillation state. A time series of instantaneous vorticity fields illustrate that vortex shedding from the tethered cylinder undergoing VIV maintains the 2S mode, but at an inclined angle to the free stream, which is most obvious in the large-amplitude oscillation state. This leads to an asymmetry in the shear layers separated from opposite sides of the cylinder, as shown by the distribution of ensemble-averaged Reynolds stress. [Copyright &y& Elsevier]

Abstract: A bi-stable vibration-based energy harvester excited by low frequency base motions exhibits vibrations characterised by a combination of slow and non-stationary fast components. The conversion of slow into fast oscillations by a nonlinear potential barrier can increase the amount of harvested power as has been shown before. In this paper the dynamical behaviour leading to the conversion of low-frequency oscillations into high frequency ones is discussed and explained. A non-parametric response decomposition approach able to separate the slow and fast parts is employed. This decomposition provides deeper insight into the effect of the nonlinear potential barrier by identifying the local evolution of instantaneous amplitude and frequency near the potential barrier and far from it. The slow and fast components are utilised to identify the backbone-curves of the two asymmetric potential wells and the nonlinear stiffness of the system. The proposed decomposition and analysis allow one to examine the repetitive transient dynamics near the potential barrier without resorting to averaging or perturbation based methods. The proposed approach and the subsequent analysis are demonstrated and explained via numerical and experiment results. [Copyright &y& Elsevier]

Abstract: In this paper the forced vibrations of an undamped single degree of freedom oscillator with a time varying mass will be studied. An initial value problem for an oscillator equation with a Rayleigh type of nonlinearity will be formulated, and by applying a straight-forward perturbation method the problem will be solved approximately. The approximations of the solutions will be used to construct a map. By using this map the stability properties of the solutions can be determined. The stability properties of the nonlinear problem will be compared to those for the linear problem, which have been studied earlier in the literature. The instability regions in the parameter space and some phase-space figures for the nonlinear problem will be computed numerically. It will also be shown how the behaviour of the solutions changes when the instability regions in the parameter space are crossed. [Copyright &y& Elsevier]

Abstract: In this paper, we study flexural vibrations of a cantilever beam with thin rectangular cross section submerged in a quiescent viscous fluid and undergoing oscillations whose amplitude is comparable with its width. The structure is modeled using Euler–Bernoulli beam theory and the distributed hydrodynamic loading is described by a single complex-valued hydrodynamic function which accounts for added mass and fluid damping experienced by the structure. We perform a parametric 2D computational fluid dynamics analysis of an oscillating rigid lamina, representative of a generic beam cross section, to understand the dependence of the hydrodynamic function on the governing flow parameters. We find that increasing the frequency and amplitude of the vibration elicits vortex shedding and convection phenomena which are, in turn, responsible for nonlinear hydrodynamic damping. We establish a manageable nonlinear correction to the classical hydrodynamic function developed for small amplitude vibration and we derive a computationally efficient reduced order modal model for the beam nonlinear oscillations. Numerical and theoretical results are validated by comparison with ad hoc designed experiments on tapered beams and multimodal vibrations and with data available in the literature. Findings from this work are expected to find applications in the design of slender structures of interest in marine applications, such as biomimetic propulsion systems and energy harvesting devices. [Copyright &y& Elsevier]

Abstract: Edgewise vibrations with low aerodynamic damping are of particular concern in modern multi-megawatt wind turbines, as large amplitude cyclic oscillations may significantly shorten the life-time of wind turbine components, and even lead to structural damages or failures. In this paper, a new blade design with active controllers is proposed for controlling edgewise vibrations. The control is based on a pair of actuators/active tendons mounted inside each blade, allowing a variable control force to be applied in the edgewise direction. The control forces are appropriately manipulated according to a prescribed control law. A mathematical model of the wind turbine equipped with active controllers has been formulated using an Euler–Lagrangian approach. The model describes the dynamics of edgewise vibrations considering the aerodynamic properties of the blade, variable mass and stiffness per unit length and taking into account the effect of centrifugal stiffening, gravity and the interaction between the blades and the tower. Aerodynamic loads corresponding to a combination of steady wind including the wind shear and the effect of turbulence are computed by applying the modified Blade Element Momentum (BEM) theory. Multi-Blade Coordinate (MBC) transformation is applied to an edgewise reduced order model, leading to a linear time-invariant (LTI) representation of the dynamic model. The LTI description obtained is used for the design of the active control algorithm. Linear Quadratic (LQ) regulator designed for the MBC transformed system is compared with the control synthesis performed directly on an assumed nominal representation of the time-varying system. The LQ regulator is also compared against vibration control performance using Direct Velocity Feedback (DVF). Numerical simulations have been carried out using data from a 5-MW three-bladed Horizontal-Axis Wind Turbine (HAWT) model in order to study the effectiveness of the proposed active controlled blade design in reducing edgewise vibrations. Results show that the use of the proposed control scheme significantly improves the response of the blade and promising performances can be achieved. Furthermore, under the conditions considered in this study quantitative comparisons of the LQ-based control strategies reveal that there is a marginal improvement in the performances obtained by applying the MBC transformation on the time-varying edgewise vibration model of the wind turbine. [Copyright &y& Elsevier]