Sharif Digital Repository

This paper presents a new algorithm based on integrating the use of genetic algorithms and simulated annealing methods to optimal allocation of distributed generation resources in distribution networks. Through this algorithm a significant improvement in the optimization goal is achieved. With a numerical example the superiority of the proposed algorithm is demonstrated in comparison with the simple genetic algorithm. © 2005 IEEE  

A new analytical method for finding the general solution of the nth-order linear differential equation with variable coefficients is given based on generalizing the idea of differential transfer matrix method already proposed for solving the second order Helmholtz equation. Our generalization has two aspects. First, the given formulation copes with the nth-order linear differential equations, rather than the special case of second order wave equations. Second, the proposed approach is generalized in several different ways each yielding different types of differential transfer matrices with correspondingly different numerical accuracies. The presented methods can be applied to problems such... 

A new analytical method is introduced for the analysis of wave propagation in one-dimensional tapered transmission lines. Based on the analytical extension of ordinary transfer matrix into differential transfer matrix, this approach can be used for calculating reflection and transmission coefficients. Different numerical test cases are thoroughly studied and in each case an excellent agreement between the results of our differential transfer matrix method and exact solutions is observed. It is also shown that our approach is superior to the more common small reflection method  

In this paper, an effective sliding mode design is applied to chaos synchronization. The proposed controller can make the states of two identical modified Chua's circuits globally asymptotically synchronized. Numerical results are provided to show the effectiveness and robustness of the proposed method. COPYRIGHT © ENFORMATIKA  

The simultaneous planning of the production and the maintenance in a flexible manufacturing system is considered in this paper. The manufacturing system is composed of one machine that produces a single product. There is a preventive maintenance plan to reduce the failure rate of the machine. This paper is different from the previous researches in this area in two separate ways. First, the failure rate of the machine is supposed to be a function of its age. Second, we assume that the demand of the manufacturing product is time dependent and its rate depends on the level of advertisement on that product. The objective is to maximize the expected discounted total profit of the firm over an... 

We report an empirical study of Tehran price index (TEPIX). To analyze our data we use various methods like as, rescaled range analysis (R/S), modified rescaled range analysis (Lo's method), detrended fluctuation analysis (DFA) and generalized Hurst exponents analysis. Based on numerical results, the scaling range of TEPIX returns is specified, long-memory effect or long-range correlation property in this market is investigated, fractal dimension of probability space of TEPIX returns is derived and finally the stage of development in Tehran stock exchange is determined. © 2005 Elsevier B.V. All rights reserved  

In this paper, the parallel implementations of different iterative polynomial root finding methods on a processor with SIMD processing capability are reported. These methods are based on the construction of a sequence of approximations that converge to the set of roots. We have chosen four widely used methods namely Newton's, Durand-Kerner's, Aberth-Ehrlich's, and QD and implemented them using the SIMD instruction set of the Pentium processor with C++ and assembly language. Experiments show that a speedup of 3 or higher can be achieved, depending on the order of polynomial, required accuracy, and the method employed. © 2005 IEEE  

The numerical errors associated with explicit upstream finite difference solutions of two-dimensional advection - Dispersion equation with linear sorption are formulated from a Taylor analysis. The error expressions are based on a general form of the corresponding difference equation. The numerical truncation errors are defined using Peclet and Courant numbers in the X and Y direction, a sink/source dimensionless number and new Peclet and Courant numbers in the XY plane. The effects of these truncation errors on the explicit solution of a two-dimensional advection-dispersion equation with a first-order reaction or degradation are demonstrated by comparison with an analytical solution in... 

Most available numerical methods face problems, in the presence of variable topographies, due to the imbalance between the source and flux terms. Treatments for this problem generally work well for structured grids, but most of them are not directly applicable for unstructured grids. On the other hand, despite of their good performance for discontinuous flows, most available numerical schemes (such as HLL flux and ENO schemes) induce a high level of numerical diffusion in simulating recirculating flows. A numerical method for simulating shallow recirculating flows over a variable topography on unstructured grids is presented. This mass conservative approach can simulate different flow... 

One main challenge in numerical treatment of incompressible fluid flow problems is to suppress the decoupling of pressure and velocity fields. The challenge has prompted research toward suggesting and implementing various coupling strategies. In this work, a novel strategy which suitably couples pressure and velocity in a collocated grid arrangement is presented. The current strategy develops a unique cell-face velocity expression which provides infinite cell-face velocity magnitudes in the algorithm. A smoothing factor is incorporated in the cell-face velocity expression in order to produce a wide range of velocity magnitudes. The smoothing factor provides a smooth transition from an unreal... 

In this paper, we first propose a new continuous action-set learning automaton and theoretically study its convergence properties and show that it converges to the optimal action. Then we give an adaptive and autonomous call admission algorithm for cellular mobile networks, which uses the proposed learning automaton to minimize the blocking probability of the new calls subject to the constraint on the dropping probability of the handoff calls. The simulation results show that the performance of the proposed algorithm is close to the performance of the limited fractional guard channel algorithm for which we need to know all the traffic parameters in advance. © 2005 Elsevier Ltd. All rights... 

In this article, behavior of cantilever retaining walls with various flexibilities, which retain saturated cohesive soil behind, is studied using numerical modeling. Generally, pattern of lateral earth pressure behind retaining walls is complex and this complexity becomes greater for clayey soils. In this investigation, effects of different wall bending stiffnesses, and backfill drainage conditions on the failure height and on the lateral earth pressure are investigated using finite elements. Comparison between the obtained results from numerical simulation and those based on empirical or conventional design methods indicate that soil-structure interaction and c drainage conditions play... 

In this work, a multigrid acceleration technique is suitably developed for solving the two-dimensional incompressible Navier-Stokes equations using an implicit finite element volume method. In this regard, the solution domain is broken into a huge number of quadrilateral finite elements. The accurate numerical solution of a flow field can be achieved if very fine grid resolutions are utilized. Unfortunately, the standard implicit solvers need more computational time to solve larger size of algebraic set of equations which normally arise if fine grid distributions are used. Past experience has shown that the convergence of classical relaxation schemes perform an initial rapid decrease of... 

Steady-state laminar and incompressible fluid flow and forced-convection heat transfer from a circular cylinder and an array of circular cylinders in the presence and no-presence of porous media are investigated. Various mathematical and numerical models are compared and the effects of porous media on heat transfer enhancement are studied. Navier-Stokes equations are used for the analysis of laminar fluid flow and heat transfer. However, the Darcy and extended Darcy-Brinkman models are used for the analysis of fluid flow and heat transfer in porous media. The cylinders are at constant temperature and the analysis is restricted to the low- and intermediate-Peclet-number regimes (Pr = 1, Re ≤... 

The objective of this paper is to introduce a new numerical method for neutronic calculation in a reactor core. This method can produce the final finite form of the neutron diffusion equation by classifying the neutronic variables and using two kinds of cell complexes without starting from the conventional differential form of the neutron diffusion equation. The method with linear interpolation produces the same convergence as the linear continuous finite element method. The quadratic interpolation is proven; the convergence order depends on the shape of the dual cell. The maximum convergence order is achieved by choosing the dual cell based on two Gauss' points. The accuracy of the method... 

For elastic scattering of 133Cs atoms by 85Rb and 87Rb atoms, interacting via the X 1Σ+ and a 3Σ+ molecular states of RbCs, calculations are presented of the scattering length and the effective range and also of two volume parameters, one for low energy p-wave scattering and one for the energy of an ensemble of fermions. The calculations are performed by various methods, with several representations of the interatomic potentials, including new ab initio potentials presented here. It is shown how the calculated data may be corrected to include the influence of the long range interactions, thus removing the need for numerical solutions of the radial Schrödinger equation at very large... 

The laminar natural convection from an isothermal horizontal cylinder confined between vertical walls is investigated by experimental and numerical methods. The experimental and numerical data are well correlated, independently, to equations which give the average Nusselt number in terms of the wall spacing to cylinder diameter ratio, t/D, and the Rayleigh number, Ra, for two different values of the wall height to cylinder diameter ratios, H/D=7 and 15.2. For the low Rayleigh numbers considered (Ra<1000), there are certain conditions for the confining walls under which heat transfer from the cylinder is maximum. Results are compared with the reported numerical and/or experimental results...