Fabio Freschi

Multiobjective optimization by a modified artificial immune system algorithm

The aim of this work is to propose and validate a new multiobjective optimization algorithm based on the emulation of the immune system behavior. The rationale of this work is that the artificial immune system has, in its elementary structure, the main features required by other multiobjective evolutionary algorithms described in literature. The proposed approach is compared with the NSGA2 algorithm, that is representative of the state-of-the-art in multiobjective optimization. Algorithms are tested versus three standard problems (unconstrained and constrained), and comparisons are carried out using three different metrics. Results show that the proposed approach have performances similar or better than those produced by NSGA2, and it can become a valid alternative to standard algorithms.

Optimal energy management

This paper presents the operational planning of an integrated trigenerative system.The installation of a CHCP plant depends on the financial investments. This work shows an optimization procedure to foresee a management of the system aimed to increase yield of investment. The optimization procedure seems to work well as foreseen PBP is short if compared with other similar installed plants. Nothing can be said about IRR, whose quality depends on the kind of investment wished by the manager.

SMES Optimization Benchmark Extended: Introducing Pareto Optimal Solutions Into TEAM22

In 1996, a superconducting magnetic energy storage arrangement was selected to become a benchmark problem for testing different optimization algorithms, both deterministic and stochastic ones. Since the forward problem can be solved semianalytically by Biot-Savarts law, this benchmark became quite popular. Nevertheless, the demands on optimization software have increased dramatically since then. To give an example, methods looking for Pareto-optimal points rather than for a single solution only have been introduced by several groups. In this paper, a proposal for an extended version of the benchmark problem will be made and some results will be presented.

Dynamic Simulation of an Electromechanical Energy Scavenging Device

This paper presents a multi-physic modeling of an electromechanical energy scavenging device. A permanent magnet, connected to the inner liner of a tyre, is accelerated along a guide by the tyre deformation during car motion; by interacting with coils it generates a power which is conditioned by a proper electronic interfaced to an external load. The energy conversion process takes into account the simulation of different phenomena like: dynamic behavior of the seismic mass, electromagnetic coupling between moving mass and coils, transfer of the generated power to an external load by means of a nonlinear circuit interface. An integrated model of the cascaded energy steps is developed inside the Simulink environment. A good agreement is found in the comparison between theoretical model and experiments. The accurate modeling of the energy conversion device is a breakthrough in the modeling of these kinds of devices and allows to reach interesting power/volume ratios: small dimensions (about one cubic centimeter) and relatively high power output (more than one milliwatt).

Multiphysics Problems via the Cell Method: The Role of Tonti Diagrams

A common structure of several physical laws emerges naturally from the Tonti diagrams of different physical theories so that topological operators can be built only once and used to assemble the stiffness matrices and the coupling terms of the various problems. This process is known in algebraic topology as coboundary process and is presented as the theoretical background for solving multiphysics problems. The main contribution of this paper is to show that the discrete setting provided by Tonti diagrams not only allows to define discrete counterparts of the differential operators and constituive matrices, but that the same matrices can be used to set up the coupling terms in multiphysics problem formulations. The proposed method is compared with a commercial code on an electro-thermo-mechanical benchmark.

Educational value of the algebraic numerical methods in electromagnetism

Purpose – The aim of this paper is to highlight the educational value of algebraic numerical methods with respect to traditional numerical techniques based on differential formulation.Design/methodology/approach – Algebraic formulations of electromagnetic fields are gaining a new interest in the research community. One common characteristic of these methods is that they impose field equations, for instance charge or mass conservation, directly in algebraic form as a sum of partial contributes, without using differential operators like the divergence one. This feature leads directly to a system of linear equations without requiring any intermediate differential formulation as in finite element method. In addition, these systems of linear equations can be efficiently expressed as a product of matrices related to problem topology and material characteristics.Findings – Owing to these features, a MATLAB implementation of these theoretical frameworks is particularly efficient and simple and can be used by elec...

Exposure of Working Population to Pulsed Magnetic Fields

Reference values of exposure for working population at extremely low frequency electromagnetic fields have been stated in ICNIRP Guidelines of 1998, and accepted by European Parliament in 2004. Nevertheless, quantification of coupling mechanism under pulsed field conditions is still an open question. The effect of complex non-sinusoidal or non-periodic waveforms is not univocally defined and several ways of estimating it have been proposed. This paper compares different ways of assessing effects of pulsed electromagnetic fields with frequency spectrum below 100 kHz and compare them to the eddy currents induced in one realistic model of human body by a resistance spot welding system supplied by in pulsed medium frequency direct current mode.

Simplified Approach for 3-D Nonlinear Induction Heating Problems

The paper presents a two-stage approach to solve a class of nonlinear 3-D eddy current problems with high saturation, typical of induction heating processes. The proposed method separates the problem of heavy nonlinearity from the complexity of the geometry, by resorting to a 1-D fast nonlinear solver which is coupled with a linear 3-D solver. Under certain hypotheses on the geometry, the approach is shown to be effective and accurate. Comparison with a commercial 3-D nonlinear code are provided.

Comparison of artificial immune systems and genetic algorithms in electrical engineering optimization

Purpose – The purpose of this study is to investigate and compare the ability of a new optimization technique based on the emulation of the immune system to detect the global maximum with multimodal functions and to test the capability of exploring the parameter space with respect to clustering enhanced Genetic Algorithms (GA).Design/methodology/approach – Both algorithms have been tested on analytical test functions and on numerical functions of applicative interest. A set of performance criteria has been defined in order to numerically compare the performances of both optimization strategies.Findings – Results show the great ability of Artificial Immune Systems (AIS) in thoroughly exploring the space of variables. On the other side, GA are faster to converge to the global optimum, but selection pressure can reduce the number of detected local optima.Originality/value – This work is an attempt to assess the performances of a relatively new optimization algorithm based on AIS and to find its behavior on m...

An effective semi-analytical method for simulating grounding grids

The analytical study of grounding systems is only possible for basic electrodes, i.e. hemispherical and spherical electrodes, rods and horizontal wires. However, it is normal practice to employ more complex earthing systems, such as grounding grids integrated with rods, in order to obtain lower resistances-to-ground and improve the electrical safety of substations. This paper introduces a semi-analytical (or semi-numerical) method, consisting of an analytical approach integrated with a numerical solution, to study grounding grids of complex geometry and their effects on non-stratified soils. The algorithm that was created, and realized with MATLAB, allows the determination of all the quantities of interest for the design and the analysis of such grounding systems: ground-resistance, ground potentials and the distribution of the ground-fault current along the grids components (i.e. horizontal wires and rods). The model is based on the assumption that conductors forming grids have radii very small if compared to their lengths and that the wires can be considered equipotential cylindrical elements. A verification of the proposed algorithm through a finite element method (FEM) has also been carried out to confirm the validity of the results. Exemplary calculations of the ground resistance of grids are included in the paper.