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Harnessing ambient vibration energy using piezoelectric materials is a promising alternative solution to batteries to inexhaustibly power small-scale mobile devices. This paper presents an innovative energy harvester, named high-efficiency compressive-mode piezoelectric energy harvester (HC-PEH). It consists of a pair of elastic beams and a flex-compressive center where the piezoelectric element bears a dynamic compressive load. The compressive mode is preferred than the commonly-used bending mode and tensile mode due to the superior compressive strength of piezoceramics. To cater to the characteristic of piezoceramics: large ultimate stress, but extremely small ultimate strain, a multi-stage force amplification mechanism is developed in the design. The HC-PEH shows superior capability of high power output and favorable nonlinear phenomena at low frequency range. Under an acceleration of 0.5 g (g = 9.8 m/s 2 ), a maximum power of 19 mW is produced at 21 Hz, which is about one order of magnitude higher than the power output of energy harvesters previously reported. The capability of high power output of the HC-PEH demonstrates the practicability of using energy harvesters to power most of wireless sensors. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the nonlinear dynamics of a thin-plate workpiece during milling process with cutting force nonlinearities. By modeling the thin-plate workpiece as a cantilevered thin plate and applying the Hamilton's principle, the equations of motion of the thin-plate workpiece are derived based on the Kirchhoff-plate theory and the von Karman strain-displacement relations. Using the Galerkin's approach, the equations of motion are reduced to a two-degree-freedom nonlinear system. The method of Asymptotic Perturbation is utilized to obtain the averaged equations in the case of 1:1 internal resonance and foundational resonance. Numerical methods are used to find the periodic and chaotic oscillations of the cantilevered thin-plate workpiece. The results show that the cantilevered thin-plate workpiece demonstrate complex dynamic behaviors under time-delay effects, the external and parametric excitations. [ABSTRACT FROM AUTHOR]

This work explores the steady-state periodic transverse responses with their stabilities of axially accelerating viscoelastic strings. Longitudinally varying tension due to the axial acceleration is recognized in the modeling, while the tension was approximatively assumed to be longitudinally uniform in previous investigations. Exact internal resonances are highlighted in the analysis, while the resonances have been neglected in all available works. A governing equation of transverse nonlinear vibration is derived from the generalized Hamilton principle and the Kelvin viscoelastic model on the assumption that the string deformation is not infinitesimal, but still small. The axial speed is supposed to be a small simple harmonic fluctuation about the constant mean axial speed. The method of multiple scales is applied to solve the governing equation in the parametric resonances when the axial speed fluctuation frequency approaches the first three natural frequencies of the linear generating system based on 1-3 term truncations. The amplitude, the existence conditions, and the stability are determined, and the effects of the viscosity, the mean axial speed, the axial speed fluctuation amplitude, and the axial support rigidity on the amplitude and the existence are examined via the numerical examples. It is found that the 1-term, the 2-term, and the 3-term truncations yield the qualitatively same and the quantitatively close results in the case that there exist the exact internal resonances among the first three frequencies. [ABSTRACT FROM AUTHOR]

In this article, a broadband magnet-induced dual-cantilever piezoelectric energy harvester is designed and developed. The dual-cantilever structure consists of an outer and an inner beams with magnets attached to the tips. The magnets generate nonlinear repulsive force between the two beams and make the structure bistable. In the theoretical model, each beam is considered as a single-degree-of-freedom system with magnetic force applied at the free end. From the simulation results, chaotic motion is observed in a wide frequency range. A prototype of the harvester is built and verified with the simulation results. The simulation and experimental results show good agreement with respect to the power bandwidth and amplitude. The distance between magnets is adjusted to observe its effect on the power response of the harvester. The inner and outer beams are simulated and tested independently first to observe the performance of each beam. Finally, an interface circuit is designed to combine all piezoelectric plates to acquire the overall performance. By comparing with the traditional piezoelectric energy harvester, the new design is shown to provide a significant improvement in bandwidth. [ABSTRACT FROM PUBLISHER]

Abstract: This study focuses on the nonlinear steady-state response of a belt-drive system with a one-way clutch. A dynamic model is established to describe the rotations of the driving pulley, the driven pulley, and the accessory shaft. Moreover, the model considers the transverse vibration of the translating belt spans for the first time in belt-drive systems coupled with a one-way clutch. The excitation of the belt-drive system is derived from periodic fluctuation of the driving pulley. In automotive systems, this kind of fluctuation is induced by the engine firing harmonic pulsations. The derived coupled discrete–continuous nonlinear equations consist of integro-partial-differential equations and piece-wise ordinary differential equations. Using the Galerkin truncation, a set of nonlinear ordinary differential equations is obtained from the integro-partial-differential equations. Applying the Runge–Kutta time discretization, the time histories of the dynamic response are numerically solved for the driven pulley and the accessory shaft and the translating belt spans. The resonance areas of the coupled belt-drive system are determined using the frequency sweep. The effects of the one-way clutch on the belt-drive system are studied by comparing the frequency–response curves of the translating belt with and without one-way clutch device. Furthermore, the results of 2-term and 4-term Galerkin truncation are compared to determine the numerical convergence. Moreover, parametric studies are conducted to understand the effects of the system parameters on the nonlinear steady-state response. It is concluded that one-way clutch not only decreases the resonance amplitude of the driven pulley and shaft's rotational vibration, but also reduces the resonance region of the belt's transverse vibration. [Copyright &y& Elsevier]

This paper is focused on nonlinear dynamics of a shell-shaped workpiece during high speed milling. The shell-shaped workpiece is modeled as a double-curved cantilevered shell subjected to a cutting force with time delay effects. Equations of motion are derived by using the Hamilton principle based on the classical shell theory and von Karman strain-displacement relation. The resulting nonlinear partial differential equations are reduced to a two-degree-of-freedom nonlinear system by applying the Galerkin approach. The averaging method is used to obtain four-dimensional averaged equations for the case of foundational parametric resonance and 1:2 internal resonance. Using a numerical method, the dynamics of the cantilevered shell-shaped workpiece is studied under time-delay effects, parametric excitation, and forcing excitation. It is found that time-delay parameters have great impact on chaotic motion. With increasing amplitude of forcing and parametric excitations, the shell-shaped workpiece exhibits different dynamic behavior. [ABSTRACT FROM AUTHOR]

There are many studies on vibrations of moving belts originated from automotive belt drives. These studies, however, mainly consider the nonlinear effect of the transversal vibration of the belt under transversal excitation without considering the coupling effect between the transversal and longitudinal vibrations under longitudinal excitation. In this paper, a nonlinear model is built for a standing tensioned belt periodically excited longitudinally at one end with a known amplitude and frequency and with the other end clamped, which allows for coupling between the periodic longitudinal excitation and transversal vibration. The nonlinear system is solved using the Analog Equation Method. The two coupled nonlinear hyperbolic differential equations of the system are reduced to two uncoupled linear equations pertaining to the longitudinal and transverse deformation of a substitute beam with unit longitudinal and bending stiffness, respectively. The reduced equations are under a fictitious time-dependent load distribution with the same boundary and initial conditions. The fictitious forces are established numerically from the integral expression of the oscillation solution with the requirement that the equations of motion be satisfied at discreet time intervals. It is found that the transversal vibration appears as a stable and predictable beating phenomenon due to an internal resonance from the periodic energy transfer between the longitudinal excitation and the transversal vibration, which manifests itself as a standing wave. [ABSTRACT FROM PUBLISHER]

Abstract: This paper presents finite amplitude transient vibration analysis of nearly incompressible hyperelastic axisymmetric solids by a mixed p-type method. In this method, displacement and pressure fields are separately defined using high degree polynomials and the solution is obtained with one or a few elements depending upon the nature of the problem. Geometry of the element is defined by polynomials of degrees much lower than that of displacement fields. The degrees of polynomials for pressure fields are lower than those used for displacement fields. Hyperelastic material is modelled by the Mooney–Rivlin material description. The total Lagrangian formulation is utilized to describe the deformations of axisymmetric solids subjected to pressure loads. Equations of motion are derived using the principle of virtual work and solved by the Newmark''s method along with the Newton–Raphson iterative technique. The present formulation also includes the asymmetric tangent load matrix, resulting in linearization of deformation dependent load, which greatly reduces the number of equilibrium iterations to get the convergence of results at large strains. A convergence study of the results is presented with respect to the degrees of polynomials for displacement and pressure fields. The present method is verified by successfully comparing the results with those from finite element method using the commercial software ANSYS. The numerical simulations are conducted on circular plate, solid cylinder and spherical shells subjected to time dependent pressure loads and the highly non-linear behaviour of hyperelastic solids undergoing finite amplitude vibrations is studied. The method, presented herein, is very efficient, locking free, and accurate, which does not require a large number of elements or the total degrees of freedom as it is required in conventional finite element method for the convergence of results. [Copyright &y& Elsevier]

Knowledge of tissue mechanical properties is widely required by medical applications, such as disease diagnostics, surgery operation, simulation, planning, and training. A new portable device, called Tissue Resonator Indenter Device (TRID), has been developed for measurement of regional viscoelastic properties of soft tissues at the Bio-instrument and Biomechanics Lab of the University of Toronto. As a device for soft tissue properties in-vivo measurements, the reliability of TRID is crucial. This paper presents TRID's working principle and the experimental study of TRID's reliability with respect to inter-reliability, intra-reliability, and the indenter misalignment effect as well. [ABSTRACT FROM AUTHOR]

Integrated vehicle dynamics control has been an important research topic in the area of vehicle dynamics and control over the past two decades. The aim of integrated vehicle control is to improve the overall vehicle performance including handling, stability, and comfort through creating synergies in the use of sensor information, hardware, and control strategies. This paper proposes a two-layer hierarchical control architecture for integrated control of the active suspension system (ASS) and the electronic stability programme (ESP). The upper-layer controller is designed to coordinate the interactions between the ASS and the ESP. While in the lower layer, the two controllers including the ASS and the ESP are developed independently to achieve their local control objectives. Both a simulation investigation and a hardware-in-the-loop experimental study are performed. Simulation results demonstrate that the proposed hierarchical control system is able to improve the multiple vehicle performance indices including both the ride comfort and the lateral stability, compared with the non-integrated control system. Moreover, the experimental results verify the effectiveness of the design of the hierarchical control system. [ABSTRACT FROM AUTHOR]

Abstract: Scratch drive actuators (SDAs) are one of the important microelectromechanical devices that have been recently used for many applications. This paper presents a new analytical model for the scratch drive actuators to facilitate the design of this device. In order to model the working states of SDA, three different static modes are considered: non-contact mode, transitional mode, and full-contact mode. The SDA is simplified as an L-shape plate with different boundary conditions in each mode. Using Euler–Bernoulli theory, governing equations are derived and solved in every mode. The non-contact mode allows identifying the deflection and driving voltage at which the actuator plate reaches to the substrate. From the transitional mode, primary contact length is calculated and used for the analysis of full-contact mode. In the full-contact mode, where SDA is completely snapped down in its working cycle, the relationships between input voltage and design parameters, such as SDA geometry, contact length and step size, are obtained. In addition, output force, as another important design parameter, is characterized based on the physics and geometry of SDA. To validate our model, the results are also compared with accessible experimental data. This analytical model provides an efficient framework to estimate the design parameters of SDA before any expensive empirical process. [Copyright &y& Elsevier]

A uniaxial cyclic stretch apparatus is designed and developed for tissue engineering research. The biostretch apparatus employs noncontact electromagnetic force to uniaxially stretch a rectangular Gelfoam® or RTV silicon scaffold. A reliable controller is implemented to control four stretch parameters independently: extent, frequency, pattern, and duration of the stretch. The noncontact driving force together with the specially designed mount allow researchers to use standard Petri dishes and commercially available CO2 incubators to culture an engineered tissue patch under well-defined mechanical conditions. The culture process is greatly simplified over existing processes. Further beyond traditional uniaxial stretch apparatuses, which provide stretch by fixing one side of the scaffolds and stretching the other side, the new apparatus can also apply uniaxial stretch from both ends simultaneously. Using the biostretch apparatus, the distributions of the strain on the Gelfoam® and GE RTV 6166 silicon scaffolds are quantitatively analyzed. [ABSTRACT FROM AUTHOR]

A complex cam shape optimization problem is studied to optimize a unique cam mechanism for a new cam drive engine. First, the optimization problem is defined through analyzing the unique cam mechanism. Multiple design specifications are included in the optimization problem by defining the output torque of the engine as the objective function and the contact stress, radius of curvature, and pressure angle as the constraints. Second, an analytical scenario is designed to find the best ever cam profiles through manipulating the different combinations of cam profile representations and optimization methods. Two types of curve representations, including general polynomial spline and B-spline, are employed in cam profile synthesis. In addition, both a classical optimization technique and a genetic algorithm (GA) based method are applied to solve the complex optimization problem. Finally, comparative studies are performed among the initial profile and the optimal profiles to demonstrate the effectiveness of these proposed design approaches on solving the cam profile optimization problem. Results show that the best profiles are obtained from a combination of the B-spline representation and the GA-based method. In addition, compared to the initial design, the engine performance is improved greatly by the proposed optimization approaches. [ABSTRACT FROM AUTHOR]

Stiction, which is a term commonly used in micro-electromechanical systems (MEMS) to refer to adhesion, is a major failure mode in MEMS. Undesirable stiction, which results from the contact between surfaces, can severely compromise the reliability of MEMS. In this paper, a model is developed for predicting stiction between uncharged micro parts interacting in a humid environment. In this condition, for hydrophilic surfaces, the capillary and asperity deformation forces are dominant. Here, using a newly developed multiple asperity contact model, a model is developed for the capillary force between rough micro sur- faces, and the new model is combined with a newly developed elastic/plastic deformation model for rough surfaces to solve for the equilibrium of the forces. This in turn yields the equilibrium distance between micro surfaces using which the apparent work of adhesion can be found. The theoretical results are compared with the available experimental data from literature. The developed model can be easily used for design purposes. If the topographic data and material constants are known, the desirable adhesion parameters can be quickly found from the model. [ABSTRACT FROM AUTHOR]

Abstract: The mechanical properties of tissues are essential in diagnosing medical pathologies, with the tissue''s viscoelastic properties being of particular interest. However, current technology is inadequate in its capability to measure accurately the viscoelastic properties of living tissues, thus limiting progress in the medical field. To overcome the limitations of the current technology, this paper develops the design of a new mechanical resonator device to measure the viscoelastic properties of tissues. The device will be minimally invasive and measure quantitatively the localized properties of tissues in a living state. To achieve the design of the resonator, extensive modeling and analysis of biological tissues are performed. The resonator system is modeled using both analytical lumped-mass models and finite element models. Simulations validate the resonator as an effective measurement technique for viscoelastic tissue properties. [Copyright &y& Elsevier]

Abstract: Previous nonlinear spinning disk models neglected the in-plane inertia of the disk since this permits the use of a stress function. This paper aims to consider the effect of including the in-plane inertia of the disk on the resulting nonlinear dynamics and to construct approximate solutions that capture the new dynamics. The inclusion of the in-plane inertia results in a nonlinear coupling between the in-plane and transverse vibrations of the spinning disk. The full nonlinear partial differential equations are simplified to a simpler nonlinear two degrees of freedom model via the method of Galerkin. A canonical perturbation approach is used to derive an approximate solution to this simpler nonlinear problem. Numerical simulations are used to evaluate the effectiveness of the approximate solution. Through the use of these analytical and numerical tools, it becomes apparent that the inclusion of in-plane inertia gives rise to new phenomena such as internal resonance and the possibility of instability in the system that are not predicted if the in-plane inertia is ignored. It is also demonstrated that the canonical perturbation approach can be used to produce an effective approximate solution. [Copyright &y& Elsevier]

Abstract: This paper considers the dynamics of a spinning disk with the inclusion of in-plane inertia. The inclusion of the in-plane inertia couples the in-plane and transverse vibrations of the spinning disk. By considering one mode of each vibration, the problem can be reduced to a non-linear 2 DOF model. An analytical solution of this 2 DOF model is then developed using a time-averaged canonical perturbation approach and is compared with that of a numerical procedure. Through the use of these analytical and numerical tools, it becomes apparent that the inclusion of the in-plane inertia leads to the possibility of internal resonance between the oscillators, depending on the relationship between the natural frequencies of the two oscillators. [Copyright &y& Elsevier]

Abstract: In this paper, the dynamic behavior of a block-on-belt system subjected to simultaneous parametric and external excitations is studied, in which the parametric excitation arises from the variable stiffness of a spring in the system while the external excitation consists of a harmonic force. In addition, the system is damped by dry friction that follows the classical Coulomb''s law. The focus of the paper is on analyzing the influence of the parametric excitation on the qualitative features of system dynamics, under various frequency ratios between the external and parametric excitations. Numerical simulations are carried out, whose results are visualized by means of bifurcation diagrams, Poincaré sections and Lyapunov exponents. The results show that the system possesses rich dynamics characterized by periodic, quasi-periodic and chaotic attractors. Furthermore, it is found that the parametric excitation amplitude and the frequency ratio between the excitations have a significant impact on the dynamical behavior of the system. [Copyright &y& Elsevier]

This paper studies the vibration of an optical fiber coupler which is used in telecommunications subjected to a half sine shock. The emphasis is focused on analyzing the vibration response of the optical fibers inside the coupler and examining the influence of various coupler parameters on the vibration of the optical fibers, since their dynamic behavior is a critical factor in optical fiber communications. A simplified model of the optical fiber coupler is proposed, which consists of a beam and a string representing the substrate and the bundle of the optical fibers of the coupler, respectively. The beam and the string are bonded at four points using adhesive material, and therefore the boundary conditions for their equations of motion are coupled, which increases the complexity of the problem. For the string, two models are developed— the linear model assumes that the tension in the string is constant, while the non-linear one takes into account large transverse deflection and tension variation. With each model, both analytical study and numerical simulations for the vibration of the system under a half shock are carried out. Furthermore, numerical results are compared between the two models. Finally, parametric study leads to conclusions which are of practical importance to the design of optical fiber couplers. [Copyright &y& Elsevier]

The two-to-one resonance in a parametrically excited axially moving viscoelastic string is investigated. The material of the viscoelastic string obeys an integral constitutive law. The method of multiple scales is applied directly the nonlinear partial-differential-integral equation that governs the transverse vibration of the string. Solvability conditions, which lead to the differential equations satisfied by the amplitude and the phase angle of the nontrivial response, are derived. Closed form solutions for the amplitude and the existence conditions of nontrivial steady-state response of the two-to-one resonance are presented. The effects of the viscoelastic parameter, the amplitude of excitation, the frequency of excitation, and the transport speed on the nontrivial solutions are demonstrated in several numerical examples. [ABSTRACT FROM AUTHOR]

Presents a study which looks at a method for reducing peak torques for kinematical redundant manipulators. Comparison with conventional methods; Detailed information on the methodology used to conduct the study; Discussion based on the results of the study.