Enhance limit cycle oscillation in a wind flow energy harvester system with fractional order derivatives

Advances in material science and mathematics in conjunction with technological needs have triggered the use of material and electric components with fractional order physical properties. This paper considers the mathematical model of a piezoelectric wind flow energy harvester system for which the capacitance of the piezoelectric material has fractional order current-voltage characteristics. Additionally the mechanical element is assumed to have fractional order damping. The analysis is focused on the effects of order of derivatives on the appearance and characteristics of limit circle oscillations (LCO). It is obtained that, the order of derivatives to enhance the amplitude of LCO and lower the threshold condition leading to LCO. The domains of efficiency of the system are illustrated in various parameters spaces.     

Constructing a multidimensional free energy surface like a spider weaving a web

Complete free energy surface in the collective variable space provides important information of the reaction mechanisms of the molecules. But, sufficient sampling in the collective variable space is not easy. The space expands quickly with the number of the collective variables. To solve the problem, many methods utilize artificial biasing potentials to flatten out the original free energy surface of the molecule in the simulation. Their performances are sensitive to the definitions of the biasing potentials. Fast‐growing biasing potential accelerates the sampling speed but decreases the accuracy of the free energy result. Slow‐growing biasing potential gives an optimized result but needs more simulation time. In this article, we propose an alternative method. It adds the biasing potential to a representative point of the molecule in the collective variable space to improve the conformational sampling. And the free energy surface is calculated from the free energy gradient in the constrained simulation, not given by the negative of the biasing potential as previous methods. So the presented method does not require the biasing potential to remove all the barriers and basins on the free energy surface exactly. Practical applications show that the method in this work is able to produce the accurate free energy surfaces for different molecules in a short time period. The free energy errors are small in the cases of various biasing potentials. © 2017 Wiley Periodicals, Inc.     

Vibrations and Dissipative Heating of a Cylindrical Panel under a Periodic Moving Load

An analytic solution is obtained to describe the vibrations and dissipative heating of a simply supported infinite cylindrical panel under periodic normal loads moving over its surface with a constant velocity. Special attention is focused on resonant vibrations, which result in the most intensive dissipative heating. It is additionally assumed that the material of the panel is viscoelastic, its properties are independent of temperature, and Poisson’s ratio is real. The influence of thickness, radius of curvature, load velocity, and viscoelastic properties on the thermal state of the panel is analysed against the thermal state of the plate__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 4, pp. 100–109, April 2005.     

Contribution to 3D impact problems: collisions between two slender steel barsUne contribution aux problèmes d'impact en trois dimensions : collisions entre deux barres élancées

This Note deals with the three-dimensional phenomenon of collision between two slender steel bars. The problem posed is whether the restitution concept developed in rigid-body theory is relevant in the case of such slender contactors. Some elements of an answer are provided through the use of two complementary approaches of collision, a theoretical one based on coefficients of restitution and series of experiments. Our main conclusion is that the alleged Newton coefficient of restitution varies according to the impact location on the rods. To cite this article: C. Le Saux et al., C. R. Mecanique 332 (2004).     

The Complexity of Collective Decision

This paper is about the dynamics of collective decision when an individual adapts his rational decision to the others'. We consider an organization of heterogeneous agents, in which each agent faces the binary decision problem. The standard way of modeling a collective decision is to assume everyone has the same value or payoff structure. This paper considers collective decision of agents with heterogeneous payoffs. We obtain and classify rational decision rules of heterogeneous agents into a few categories depending on their idiosyncratic payoff structure. We also obtain the micro–macro dynamics that relate the aggregate collective decision with the underlying individual decisions. We investigate the roles of particular types of agents such as hardcore, conformists, and nonconformists. We show that agents' rational behavior combined with the others produce stable orders, and sometimes complex cyclic behavior.     

Factors affecting temperature measurement using phase measurement interferometry in small scale devices

This paper presents full-field temperature measurements of buoyancy opposing mixed convection flow within a miniscale fluidic geometry. The technique used is phase measurement interferometry and a Mach–Zehnder layout is employed. The popular two-dimensional microfluidic geometry of three streams merging at a junction is chosen for this analysis. The apparatus set-up is described and measures taken to limit experimental errors discussed. Also presented, are corresponding flow visualization images for comparison with the interferometric results. The results are compared for similar boundary conditions over the range of Richardson numbers of 0.5–1.7. The results of the interferometric study are presented in the form of full-field temperature maps depicting the type of thermal plume structure present through isotherms and are seen to compare well with the results of the flow visualization study. Some factors affecting the measurement technique at this scale are then discussed. These include the effect of using different transparent materials for sealing the fluidic device and temporal vibrations caused by either varying boundary conditions or by slight pulsations in the flow supplied. Also, due to discrepancies that exist in the literature for the temperature coefficient of the refractive index of the working fluid, thermocouples are embedded in the flow field and used to convert the measured phase change to a corresponding temperature change. The corresponding values of refractive index change with temperature are discussed and compared to published values. Overall, PMI is demonstrated to provide excellent full-field temperature plots that can be used to measure local heat transfer rates from this non-intrusive measurement technique.     

Stress Concentration Near an Elliptic Crack in the Interface Between Elastic Bodies under Steady-State Vibrations

The paper addresses the three-dimensional problem on steady-state vibrations of an elastic body consisting of two perfectly joined dissimilar half-spaces with an elliptic mode I crack located in one of the half-spaces normally to the interface. The problem is reduced to a boundary integral equation for the crack opening function. The integration domain of the equation is bounded by the crack domain, and the interaction between the crack and the interface is described by a regular kernel. The equation is solved using the mapping method. Numerical results are obtained for the case where the surfaces of the elliptic crack are subjected to harmonic loading with constant amplitude. The dependences of the stress intensity factors on the wave number are presented for various relationships among the mechanical constants that ensure the absence of near-surface waves     

Forced Oscillations of a System,Containing a Snap-Through Truss,Close to Its Equilibrium Position

The nonlinear dynamics of a two-degree-of-freedom mechanical system is considered. This system consists of a linear oscillator under the action of a time-periodic force and a snap-through truss, which acts as an absorber of the forced oscillations of the linear main system. The forced oscillations of the snap-through truss close to its equilibrium position are analyzed by the multiple scales method.     

Nonaxisymmetric Vibrations of Discretely Reinforced Inhomogeneous Multilayer Cylindrical Shells under Nonstationary Loads

The equations of nonaxisymmetric vibrations of discretely reinforced multilayer cylindrical shells are analyzed. A refined Timoshenko model of shells and beams is used to analyze elements of an elastic structure. The vibration equations for an inhomogeneous elastic system are derived using the Reissner variational principle. The numerical solver of the dynamic equations is based on the integro-interpolation method used to construct finite-difference schemes for equations with discontinuous coefficients. The dynamic behavior of a five-layer cylindrical shell under distributed nonstationary loading is analyzed