Variable length representation in evolutionary electronics

This work investigates the application of variable length representation (VLR) evolutionary algorithms (EAs) in the field of Evolutionary Electronics. We propose a number of VLR methodologies that can cope with the main issues of variable length evolutionary systems. These issues include the search for efficient ways of sampling a genome space with varying dimensionalities, the task of balancing accuracy and parsimony of the solutions, and the manipulation of non-coding segments. We compare the performance of three proposed VLR approaches to sample the genome space: Increasing Length Genotypes, Oscillating Length Genotypes, and Uniformly Distributed Initial Population strategies. The advantages of reusing genetic material to replace non-coding segments are also emphasized in this work. It is shown, through examples in both analog and digital electronics, that the variable length genotype's representation is natural to this particular domain of application. A brief discussion on biological genome evolution is also provided.     

NONSTAGGERED BOUNDARY-FITTED COORDINATE METHOD FOR FREE SURFACE FLOWS

A new approach based on the finite-difference technique has been developed to study the steady incompressible Navier-Stokes equations in the laminar region, where the domain is partially bounded by a free surface. The nonstaggered fractional step method is used to solve the flow equations written in terms of primitive variables. The physical domain is transformed to a rectangle by means of a numerical mapping technique. The location of the phase boundary is accomplished by means of two methods depending on the surface tension effect: the normal-stress boundary condition or the kinematic boundary condition. We have tested the accuracy and efficiency of the numerical method by solving four different test problems: lid-driven flow in an inclined cavity, film in the absence of gravity, the "stick-slip" problem, and the Newtonian jet swell problem.     

Carter's factor calculation using domain transformations and the finite element method

The main purpose of this work is to present a methodology to calculate Carter's factor using the actual air‐gap geometry, that is, without simplifications of the slot geometry. The methodology is based on the finite element method, and its results are compared with some traditional procedures used for Carter's factor calculation and also with a domain transformation technique. It is shown that the finite element method and the domain transformation methodologies present similar results, which are different from the results obtained with traditional procedures. Copyright © 2011 John Wiley & Sons, Ltd.     

A new methodology to calculate Carter factor using genetic algorithms

This paper presents a methodology to calculate the value of Carter's factor for airgaps with polygonal slots. A numerical evaluation of the Schwarz–Christoffel transformation is performed using Genetic Algorithms. The methodology presented here extends Carter's method to airgaps with more complicated geometry. Some case studies compare the results of the developed methodology to Carter's results. Copyright © 2010 John Wiley & Sons, Ltd.     

Methodology for the reduction of parameters in the inverse transformation of Schwarz–Christoffel applied to electromagnetic devices with axial geometry

This paper presents a method for calculating the parameters of the Schwarz–Christoffel inverse transformation using the Genetic Algorithm. It is shown that for problems involving a polygonal geometry with axial symmetry, the number of estimated parameters is reduced by half. Simulations are performed with polygonal figures with several different geometries and with up to 27 sides. A four‐sided polygon is inversely mapped in order to verify the accuracy of the method. The method is also applied for calculating the induction lines and the flux lines in the region of a doubly slotted airgap of an electrical machine. Finally, based on the length of the midline of induction in the airgap, a new and very simple formula to calculate the Carter factor of an electrical machine is presented, which takes into account the actual geometry of the airgap. Copyright © 2011 John Wiley & Sons, Ltd.     

Methodology of Investment Risk Analysis for Wind Power Plants in the Brazilian Free Market

Despite the strong growth of wind power in the world, it is considered a high risk investment due to variability and unpredictability of wind speed. If the energy trade occurs in the free market, there is another risk factor that is the short-term price. This study proposes a methodology of investment risk analysis for wind power plants using innovative stochastic models to generate synthetic time series of wind speed and short-term price. The simulation is implemented using the Monte Carlo method associated with a Cholesky decomposition. The cashflow's gross revenue is obtained through an energy trading model for the Free Contracting Environment (FCE) in Brazil. The investment analysis is based on probability distribution of Net Present Value (NPV) of the power plant's cash flow, as well as the Value at Risk (VaR) and the Conditional Value at Risk (CVaR). A case study was performed for Natal city of Rio Grande do Norte (RN) state in Brazil, and the results indicated the economic viability of the power plant. A sensitivity analysis is developed considering important parameters of the modeling, and its results provide information to the decision-making process.     

A Note on the Aging Properties of the Run Length of Markov-Type Control Charts

Abstract

A change in a production process must be detected quickly so that a corrective action can be taken. Thus, it comes as no surprise that the run length (RL) is usually used to describe the performance of a quality control chart.

This popular performance measure has a phase-type distribution when dealing with Markov-type charts, namely, cumulative sum (CUSUM) and exponentially weighted moving average (EWMA) charts, as opposed to a geometric distribution, when standard Shewhart charts are in use.

In this article, we briefly discuss sufficient conditions on the associated probability transition matrix to deal with run lengths with aging properties such as new better than used in expectation, new better than used, and increasing hazard rate.

We also explore the implications of these aging properties of the run lengths, namely when we decide to confront the in control and out-of-control variances of the run lengths of matched in control Shewhart and Markov-type control charts.     

Hydrocracking: An improved Kinetic Model and Reactor Modeling

Stangeland's kinetic model for predicting hydrocracker yields was modified to explicitly account for the mass balance closure in each individual hydrocracking reaction and for the effect of hydrogen partial pressure on the hydrocracking reaction rate. This improved kinetic model has two additional parameters. The model was applied to the modeling of a fixed bed reactor for mild hydrocracking of vacuum gas oils in the framework of the Aspen Plus® process simulator. The kinetic parameters were regressed using the algorithm of Levenberg-Marquardt such that the mass balance in each individual hydrocracking reaction is satisfied. The reactor model assumed gas-liquid equilibrium and was used to quantify the effect upon conversion of the operating variables--liquid hourly spatial velocity, reactor pressure, and hydrogen-to-feed ratio--showing that both the kinetic and reactor models predict the appropriate trends compared to the reference data. The practical implications of explicitly introducing the mass balance closure for each hydrocracking reaction in the kinetic model are discussed.