Panagiotis D. Sparis

The Fourier series operational matrix of integration

A general expression of the Fourier operational matrix of integration P is derived which is analogous to that previously derived for other types of orthogonal functions such as Walsh, block-pulse, Laguerre, Legendre and Chebyshev. This matrix P may be used to solve problems like identification, analysis and optimal control.

Taylor series approach to system identification, analysis and optimal control

Abstract The problems of system identification, analysis and optimal control have been recently studied using orthogonal functions. The specific orthogonal functions used up to now are the Walsh, the block-pulse, the Laguerre, the Legendre, the Chebyshev, the Hermite and the Fourier functions. In the present paper solutions to these problems are derived using the Taylor series expansion. The algorithms proposed here are similar to those already developed for the orthogonal functions; however, due to the simplicity of the operational matrix of integration, the Taylor series presents considerable computational advantages compared with the other polynomial series, provided that the input and the output signals may be assumed to be analytic functions of t .

Correlation of wind speed between neighboring measuring stations

A method for establishing wind speed correlation between neighboring measuring stations is presented in this paper. The aim of this study is to develop a model, in which given the wind speed at a particular site to simulate the wind speed at another, nearby site, in order to estimate the wind power of an area. This method takes into account the evolution of the sample cross correlation function (SCCF) of wind speed in time domain and uses an artificial neural network to perform the wind speed simulation. Four separate pairs of wind data measuring stations at two different regions were examined. Tests showed that the higher the SCCF value between two sites, the better simulation achieved. Also, in a pair of stations under investigation the reference station must be the one that contains more information in its wind speed signal, in order to obtain the optimum simulation performance.

An estimation of three-way catalyst performance using artificial neural networks during cold start

Abstract In this paper, an estimation of a three-way catalyst performance with artificial neural networks is presented. It may be an alternative approach far an on-board diagnostic system (OBD) to predict the catalyst performance. This method was tested using data sets from two specific kind of ceramic catalysts, a brand new and an old one on a laboratory bench at idle speed. Further experiments are needed for different catalyst types before the method is proposed generally. The catalyst operation during the “ cold start ” phase (the phase that the catalyst has not reached its operating conditions yet) is examined. It consists of 200 elements of catalyst inlet–outlet temperature difference (DT), hydrocarbons (HC), and carbonmonoxide (CO) and carbon dioxide (CO 2 ) emissions. The simulation: detects the values of HC, CO, CO 2 using the DT as an input to our network forms a neural network. Results showed serious indications that artificial neural networks could estimate the catalyst performance adequately depending their training process. In this paper the “ cold start ” period experimental results are presented.

A method for generating boundary-orthogonal curvilinear coordinate systems using the biharmonic equation

Abstract The biharmonic equation transformed in the computational domain is solved for the generation of boundary-orthogonal curvilinear coordinate systems. The method permits direct and complete control of the mesh point location on the boundary as well as the angle of intersection of the coordinate lines with the boundary. The method may also be used for the generation of meshes in segmented fields. Finally, the method can be easily extended in three dimensions.

Emission reduction during cold start via catalyst surface control

Abstract The present paper is a preliminary investigation of a new approach to the reduction of pollutant emissions during a cold start. During a cold start the volume of the exhaust gases is considerably smaller than those under full load. Therefore, only a small portion of the catalyst active surface is required to process the gases. As the exhaust gases flow from the upstream surface to the downstream surface, they meet with the cold surface of the catalyst, which they should warm up first, before light-off. The larger that surface, the more time will be needed for its warm-up, which will increase the time required for a light-off. The experimental results presented here indicate that there can be a significant reduction of the pollutant emissions during the cold start of an engine, if a system can be devised that could adjust the catalyst active surface during start-up proportionally to the exhaust gas volume. There are strong indications that a quicker warm-up of the catalyst and a faster initiation of catalysis can be achieved by focusing the gas flow towards the centre core of the monolith. In this way the remaining ceramic body of the catalytic converter operates as a heat insulator. This idea may be utilized in the design of catalyst system with variable active surface.

Shift and product Fourier matrices and linear delay-differential equations

Abstract The paper introduces a new approximate method for the analysis of delay time-invariant and lime-varying systems via Fourier series. The present approach utilizes the shift and product operational matrices of the Fourier series for the analysis of linear systems via the Fourier operational matrix of integration. The method developed is applied to the analysis of a number of illustrative model systems.

The operational matrix of polynomial series transformation

This paper introduces the operational matrix of polynomial series transformation T that may be applied to transform any polynomial series basis vector to the Taylor polynomials. The matrix is determined for most commonly used polynomial series expansions, such as the Chebyshev, the Laguerre, the Legendre and the Hermite. Using the polynomial series transformation matrix, the corresponding operational matrix of integration of a polynomial series, may easily be determined. Finally, it is shown that all the approximate methods using polynomial-based operational matrices of integration may be connected to the Taylor-series method.

A comparative study of the operational matrices of integration and differentiation for orthogonal polynomial series

In the paper a comparison is made between two approximate methods of system analysis based on the use of the operational matrices of integration and differentiation. Both methods applied to model problems involving linear time-invariant differential equations yielded results of equal order of accuracy for the same number of orthogonal polynomial terms. However, the operational matrix of differentiation method is not limited to initial-value problems, but may easily be applied to boundary-value problems. In addition, due to the exact definition of this matrix, transformations from an orthogonal polynomial base to another may easily be performed with the use of the operational matrix of polynomial series transformation. The operational matrix of differentiation approach may be easily applied to the analysis of other types of systems such as time-varying and distributed parameter systems, and can be easily extended for other types of orthogonal differentiable base functions such as the Fourier trigonometric ...

Environmental pollution from the use of alternative fuels in a four-stroke engine

This paper discusses the use of the fuels propane and butane–propane (80:20) in a four-stroke engine made to function with gasoline (petrol). The experiment covered gas emissions, emissions temperature and fuel consumption. It was observed that gas emissions were reduced compared with gasoline. The reduction for carbon monoxide emissions was greater when butane–propane was used. The same was true for hydrocarbon emissions when the electrical load was below 1500 W, but above 1500 W propane performed better. Higher emissions temperatures were observed with both alternative fuels. Under unloaded conditions the emissions from propane combustion have higher temperature, whereas under full load conditions the emissions from the combustion of the butane–propane mixture have higher temperature. The consumption of propane is lower than that of the mixture.