Differential-Difference Equations. By Richard Bellman and Kenneth L. Cooke. Pp. xvi, 465. 1963. (Academic Press)

This chapter introduces the finite element method (FEM) as a tool for solution of classical electromagnetic problems. Although we discuss the main points in the application of the finite element method to electromagnetic design, including formulation and implementation, those who seek deeper understanding of the finite element method should consult some of the works listed in the bibliography section.

Introduction to the Finite Element Method

: This thesis applies neural network feature selection techniques to multivariate time series data to improve prediction of a target time series. Two approaches to feature selection are used. First, a subset enumeration method is used to determine which financial indicators are most useful for aiding in prediction of the S&P 500 futures daily price. The candidate indicators evaluated include RSI, Stochastics and several moving averages. Results indicate that the Stochastics and RSI indicators result in better prediction results than the moving averages. The second approach to feature selection is calculation of individual saliency metrics. A new decision boundary-based individual saliency metric, and a classifier independent saliency metric are developed and tested. Ruck's saliency metric, the decision boundary based saliency metric, and the classifier independent saliency metric are compared for a data set consisting of the RSI and Stochastics indicators as well as delayed closing price values. The decision based metric and the Ruck metric results are similar, but the classifier independent metric agrees with neither of the other metrics. The nine most salient features, determined by the decision boundary based metric, are used to train a neural network and the results are presented and compared to other published results. (AN)

/pdf/nonlinear-time-series-analysis-1j3a35n4y3.pdf

Nonlinear Time Series Analysis.

The investigation of the conversion of vibrational energy into electrical power has become a major field of research. In recent years, bistable energy harvesting devices have attracted significant attention due to some of their unique features. Through a snap-through action, bistable systems transition from one stable state to the other, which could cause large amplitude motion and dramatically increase power generation. Due to their nonlinear characteristics, such devices may be effective across a broad-frequency bandwidth. Consequently, a rapid engagement of research has been undertaken to understand bistable electromechanical dynamics and to utilize the insight for the development of improved designs. This paper reviews, consolidates, and reports on the major efforts and findings documented in the literature. A common analytical framework for bistable electromechanical dynamics is presented, the principal results are provided, the wide variety of bistable energy harvesters are described, and some remaining challenges and proposed solutions are summarized.

https://iopscience.iop.org/article/10.1088/0964-1726/22/2/023001/pdf

A review of the recent research on vibration energy harvesting via bistable systems

Ambient energy harvesting has been in recent years the recurring object of a number of research efforts aimed at providing an autonomous solution to the powering of small-scale electronic mobile devices. Among the different solutions, vibration energy harvesting has played a major role due to the almost universal presence of mechanical vibrations. Here we propose a new method based on the exploitation of the dynamical features of stochastic nonlinear oscillators. Such a method is shown to outperform standard linear oscillators and to overcome some of the most severe limitations of present approaches. We demonstrate the superior performances of this method by applying it to piezoelectric energy harvesting from ambient vibration.

/pdf/nonlinear-energy-harvesting-1c9nlmso3f.pdf

Nonlinear energy harvesting.

https://eprints.whiterose.ac.uk/8882/2/EnergHarv_MagSuspFinal.pdf

Energy harvesting from the nonlinear oscillations of magnetic levitation

Nonlinear dynamics for broadband energy harvesting: Investigation of a bistable piezoelectric inertial generator

We model and experimentally validate a nonlinear energy harvester capable of bidirectional hysteresis. In particular, both hardening and softening response within the quadratic potential field of a power generating piezoelectric beam (with a permanent magnet end mass) is invoked by tuning nonlinear magnetic interactions. Not only is this technique shown to increase the bandwidth of the device but experimental results additionally verify the capability to outperform linear resonance. Engaging this nonlinear phenomenon is ideally suited to efficiently harvest energy from ambient excitations with slowly varying frequencies.

Reversible hysteresis for broadband magnetopiezoelastic energy harvesting

Chatter in milling and other interrupted cutting operations occurs at different combinations of speed and depth of cut from chatter in continuous cutting. Prediction of stability in interrupted cutting is complicated by two facts: (1) the equation of motion when cutting is not the same as the equation when the tool is free; (2) no exact analytical solution is known when the tool is in the cut. These problems are overcome by matching the free response with an approximate solution that is valid white the tool is cutting. An approximate solution, not restricted to small times in the cut, is obtained by the application of finite elements in time. The complete, combined solution is cast in the form of a discrete map that relates position and velocity at the beginning and end of each element to the corresponding values one period earlier. The eigenvalues of the linearized map are used to determine stability. This method can be used to predict stability for arbitrary times in the cut; the current method is applicable only to a single degree of freedom. Predictions of stability for a 1-degree of freedom case are confirmed by experiment.

Brian P. Mann

Papers

Energy harvesting from the nonlinear oscillations of magnetic levitation

Nonlinear dynamics for broadband energy harvesting: Investigation of a bistable piezoelectric inertial generator

Reversible hysteresis for broadband magnetopiezoelastic energy harvesting

Stability of Interrupted Cutting by Temporal Finite Element Analysis

Investigations of a nonlinear energy harvester with a bistable potential well