Vol. 7, No. 3 (2023): Regular Issue

Energy harvesting is the process of capturing and transforming ambient energy into a useable form. Solar energy, thermal gradients, acoustical and mechanical vibrations are all examples of energy harvesting sources. Vibration Energy Harversting Systems (VEHS) are systems that employ vibrations as a source. VEHS-based energy harvesters are known as a supplementary power source, which provide small amounts of energy for slow-load applications or to charge and operate remote devices and sensors whose require small amounts of energy to operate, such as hearing aids, pacemakers, spinal cord stimulators, and microelectromechanical systems. The objective of this work is to analyze the stability of a parametrically excited energy harvesting system that uses piezoelectric materials as a transducer. The objective is to optimize the energy produced by analyzing the system's behavior while the physical parameter values are changed. In this regard, it is essential to do a preliminary global sensitivity analysis of the physical parameters in order to determine which parameters, when altered, influence more to energy production. The Sobol' indices are used to do the sensitivity analysis. The stability analysis is then performed using the results of Floquet's Theory and the state transition matrix approximation techniques developed by Sinha and Butcher. Sinha and Butcher's technique, based on Picard iterations and Chebyshev polynomial expansions, aims to find approximate solutions for periodic systems in time. An essential characteristic that is well documented in the literature is that vibrational energy harvesting systems have efficient responses when the physical parameters of the system are set so that the system operates in resonance with the parametric excitation source. As a result, when the system is in resonance with the external excitation source, significant system stability outcomes are obtained.

The paper studies quasiperiodic vibration-based energy harvesting in a forced and delayed Rayleigh-Duffing oscillator coupled to a piezoelectric circuit. The study focuses on the effect of the time delay on the output power performance near the subharmonic resonance of order 3. Using the multiple scales method, quasiperiodic solutions and the corresponding output powers are obtained near the subharmonic resonance. The effect of the delay parameters on the energy extraction performance is analyzed in the case where the delay is introduced either in the position, in the velocity or in both. The analytical results supported by numerical simulations showed the potential of the time delay to achieve hight quasiperiodic output power over a large bandwidth around the 3-subharmonic resonance region.

This paper addresses energy transmission via an electro-dynamical transducer from the amplifier and energy harvesting from wave field. In the first case an amplifier is considered as a self-exciting system with a limited power. Electrical current produced by it is converted by the transducer into mechanical force, which leads to vibrations of the base. A mechanical oscillator is mounted on the transducer base. The influence of oscillator vibrations on the formation of the driving force leads to the Sommerfeld --Kononenko effect. Expressions for supplied and consumed powers are shown. The energy harvesting problem is also discussed. The classical results for wave power harvesting by wave energy extractor as a single degree of freedom system are presented in the second considered problem. The example includes an axisymmetric buoy which oscillates and is subjected to its natural hydrostatic restoring force. Main attention is focuses on the values and expressions for the mean powers. The expression for the maximum mean power is given for the considering system.

In this paper the direct scattering problem by an impenetrable obstacle embedded in a given homogeneous background chiral medium is studied. Incident electromagnetic waves are propagated in a homogeneous chiral environment. We assume that the chirality measures of the background and exterior medium are both distinct positive constants. Our scatterer has a smooth boundary that is divided into two open disjoint parts for which an impedance boundary condition on the one part of the boundary, and a perfectly conducting boundary condition on the other part, are satisfied. Uniqueness results for the above scattering problem, using the Bohren decomposition into Beltrami fields, are established. Consequently, we introduce a chiral Calderon operator, for which its basic properties are proved, and its connection with the existence of our problems solution is presented. The well-posedness of our problem is completed by proving the continuous dependence of the solution on the boundary data. Finally, some discussion and conclusions are given.

Active controls have been used to enhance the stability of high speed trains against hunting instability. The control system uses motion measurements of the train for decision making. These measurements can also be used to estimate wear of the wheel due to dynamic interactions with the rail. In this paper, we present an approach that makes use of the well-known extended state estimator to estimate interaction forces between the wheel and rail from motion measurements. Archard's wear model is adopted to compute the damage of the wheel. To take advantages of motion measurements further, we treat Archard's wear model as a surrogate to generate a large set of wear data from simulated motions. This is valuable because it is expensive and time consuming to collect real data of wheel wear. We develop a neural networks model to directly link train motions with the wheel wear. With the neural networks model, we can then predict the wheel wear from motion measurements of high speed train in service. It is expected that the neural networks wear model can help engineers to develop more effective maintenance schedule.

In this paper, nonlinear dynamics of dynamical systems possessing bivariate quadratic vector fields is presented. The bivariate quadratic vector field is a product of two different-variable univariate functions in two directions. The dynamical systems with two crossing-variable product bivariate vector fields are presented, and the corresponding global dynamics of such dynamical systems is presented. The hyperbolic and hyperbolic-secant flows with directrix flows are discussed. From the infinite-equilibriums, the inflection sink (or source) bifurcation is presented for the switching of hyperbolic flow and saddles with hyperbolic-secant flow and sink (or source). Parabola-saddle bifurcations are for the switching of saddle and hyperbolic-secant flow with center and hyperbolic flow, which is called the saddle-center switching bifurcation. Inflection diagonal-saddle bifurcations are presented for the switching of the network of saddle and sink (or saddle and source) with hyperbolic and hyperbolic-secant flows.