Computational Methods in Engineering

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In this paper the problem of minimum cost communication network design is considered where the costs are piecewise linear concave. Several methods are compared: Simulated Annealing method, a heuristic based on the method proposed by Minoux, and a lagrangian method based on lower bounding procedure.

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Routing is one of the basic parts of a message passing multiprocessor system. The routing procedure has a great impact on the efficiency of a system. Neural algorithms that are currently in use for computer networks require a large number of neurons. If a specific topology of a multiprocessor network is considered, the number of neurons can be reduced. In this paper a new recurrent neural network and its energy function is introduced. This network requires a significantly smaller number of neurons compared to its counterparts. Also presented is the performance of this neural network. Keywords: Routing, Multicomputer systems, Recurrent neural networks, Mesh interconnection networks.

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Finding the collapse susceptible portion of a power system is one of the purposes of voltage stability analysis. This part which is a voltage control area is called the voltage weak area. Determining the weak area and adjecent voltage control areas has special importance in the improvement of voltage stability. Designing an on-line corrective control requires the voltage weak area to be determined by a sufficiently rapid and precise method. In this paper, a new algorithm based on assigning a vector to each power system bus is presented. These vectors indicate buses conditions from the viewpoint of voltage stability. In this new method, using the clustering methods such as kohonen neural network, fuzzy C-Means algorithm and fuzzy kohonen algorithm, voltage control areas are determined The proposed method has advantages such as determining PV and PQ buses which belong to the weak area simultanously, under all operating conditions and without a need to system model. Also by comparing the results of applying clustering methods, it has been observed that, due to simplicity of implementation and precision of the results, the two dimensional kohonen neural network is a more suitable tool for clustering power system to voltage control areas than the fuzzy C-Means and fuzzy kohonen methods. Keywords: Voltage stability, Voltage weak area, Voltage control area, Corrective control, Pattern recognition, Kohonen neural network, Fuzzy C-Means algorithm, Fuzzy Kohonen algorithm.

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In this research, behaviour of clayey soils under triaxial loading is studied using Neural Network. The models have been prepared to predict the stress-strain behaviour of remolded clays under undrained condition. The advantage of the model developed is that simple parameters such as physical characteristics of soils like water content, fine content, Atterberg limits and so on, are used to model the stress-strain behaviour of clays under triaxial loading, without performing exact and time-consuming tests on samples. Results from the network show that neural network is a good tool for prediction of stress-strain behaviour of clayey soils using simple physical characteristics of such soils

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Bus network design is an important problem in public transportation. A main step to this design is determining the number of required terminals and their locations. This is a special type of facility location problem, which is a time-consuming, large scale, combinatorial problem. In a previous attempt by the authors, this problem had been solved by GAMS, based on a branch and bound algorithm. In this research, different techniques for solving the problem are investigated to choose the best one. One of these methods is Simulated Annealing (SA), which is an efficient algorithm for solving complex optimization problems. SA’s parameters vary from one problem to another. Here, for the bus terminal location problem, SA’s parameters are determined, then the problem is solved. Another algorithm is the Implicit Enumeration method. In this paper, the results obtained from the above 3 techniques are compared. The criteria for this comparison are the CPU time and the accuracy of the solution. In all the cases studied, SA gave the most accurate results. Its CPU time is lower than the others, too. Solving the bus terminal location problem for the Mashhad network shows that SA is about 150 times faster than GAMS and 50 times faster than Implicit Enumeration. Moreover, bus terminal location problem for the network of the city of Tehran, which is a more difficult problem, has been solved by the SA algorithm successfully. Keywords: Bus network, Lacation problem, Heuristic, Simulated Annealing, Implicit Enumeration

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In recent years, active filters have been considered and developed for elimation of harmonics in power networks. Comparing with passive, they are smaller and have better compensating characteristics and resistance to line distortions. In this paper, a novel idea based on adaptive filter theory in presented to develop an active filter to eliminate the distortions of an arbitrary signal. Using this idea, new methods of active power filters, are introduced to remove harmonic distortions in single phase power networks. Stability of these methods are analyzed and the simulation results are shown. Design and implementation of this adaptive active filter are done and the performance and advantages of this technique are affirmed by the practical results. Exact estimation of amplitude, frequency and phase of input signal first harmonic is the most important advantage of this adaptive technique. Furthermore, this method is for canceling the harmonic of any arbitrary signal and can easily be modified for other systems, and three phase networks. Due to its adaptive nature, this technique can adopt itself with variation in environment and system parameters and be adjusted for optimal behaviour. Keywords: Adaptive active filter, ac network, amplitude, Phase and frequency Estimation, Floque theorem, Averaging theorem.

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In this study, colorimetric calibration of scanner has been done via perceptron neural network with three or four layers by back propagation algorithm for colored polyester fabrics. The results obtained for random training samples are not satisfactory but application of selective training samples for L*a*b* or RGB leads to good results, with better results obtained for the L*a*b* method. On the other hand, the color differences between calculation XYZ and real XYZ for unknown samples, are not only in agreement with the results of polynomials and regression methods, but are also better than the results obtained in previous studies where neural networkhad been used for colorimetric calibration of scanner.

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In this paper, a new method for developing a lower bound on exact completion time distribution function of stochastic PERT networks is provided that is based on simplifying the structure of this type of network. The designed mechanism simplifies network structure by arc duplication so that network distribution function can be calculated only with convolution and multiplication. The selection of duplicable arcs in this method differs from that of Dodin’s so that it must be considered a different method. In this method, best duplicable arcs are adopted using a new mechanism. It is proved that duplicating numbers is minimized by this method. The distribution function of this method is a lower bound on exact network distribution function and an upper bound on distribution function of Dodin’s and Kleindorfer’s methods. After the algorithm for the method is presented, its efficiency is discussed and illustration examples will be used to Compare numerical results from this method with those from exact network distribution and Dodin’s method.

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Generation Expansion Planning (GEP) is one of major modules of power system planning studies, normally performed for the nex 10-30 years horizon. The current industrial practices are to find the generation requirements based on a nodal analysis. In this way, the allocations are not determined and subequent studies are required to find the exact locations which as decomposed from the earlier stage, may result in non-optimum solution. A new approach is proposed in this paper in which, based on dynamic programming and sensitivity factors, GEP is performed with due to consideration of transmission system effects. In this way, the allocations of justified generation plants are also determined. The results for Iranian Power Grid for the years 2011 to 2021 are demonstracted.

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Flow separation at water intake is the main cause of head loss and flow discharge reduction. As a result, study of shape and size of separation is very essential when designing an optimum water intake. Water intake is normally built with a 90 degree angle to the main channel flow direction. However, the flow structure in this type of water intake consists of large separation size along with vortex generation. In this study, the effect of the ratio of discharge at water intake to the main channel discharge (Qr) on the location and size of separation is investigated numerically and experimentally. The velocity of the flow at each point is measured in two dimensions using electromagnetic velocity meter. The results from the experimental data indicate that the location and shape of separations are a function of flow discharge ratio (Qr). These results also indicate that at higher ratios of flow discharge, the separation occurs downstream the water intake, whereas at lower flow discharges, the flow separation occurs upstream the water intake. Additionally, the capabilites of numerical turbulence computation models including standard k-e and RNG k-e models are investigated in this study. The computed flow velocity from the turbulence models showed that the result of standard k-e model is approximately close to the experimental data when compared with RNG k-e model

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Artificial Neural Networks are information processing systems. Over the past several years, these algorithms have received much attention for their applications in pattern completing, pattern matching and classification and also for their use as a tool in various areas of problem solving. In this work, an Artificial Neural Network model is presented for predicting the tensile properties of cotton-covered nylon core yarns. Multilayer Feedforward network with Back Propagation learning algorithm was used to study the relationship and mapping among the process parameters, i.e. count of sheath part, count of core part, applying pretension to the core part, inserted twist to the core spun-yarn as well as tensile properties, i.e. breaking strength and breaking elongation. The results show that ANN is an effective method for the prediction of the tensile properties of these yarns. This is due to the fact that in each case, standard deviation of prediction error for test and train data was less than that obtained from the expreiments.

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This paper presents a method based on neural networks to detect broken rotor bars and end rings in squirrel cage induction motors. In the first part, detection methods are reviewed and traditional methods of fault detection as well as dynamic model of induction motors are introduced using the winding function method. In this method, all stator and rotor bars are considered independently in order to check the performance of the motor for any faults in the parts. Then the frequency spectrum of current signals is derived using the Fourier transform and analyzed under various conditions. In the second part of the paper, an analytical discussion of the theoretical principles is presented to arrive at a simple algorithm for fault detection based on neural networks. The neural network has been trained using the information from a 1.1 KW induction motor. Finally, the system is tested with different values of load torque and is found capable of working on-line to detect all normal and ill-performing conditions.

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The theory of distributed detection is receiving a lot of attention. A common assumption used in previous studies is the conditional independence of the observations. In this paper, the optimization of local decision rules for distributed detection networks with correlated observations is considered. We focus on presenting the detection theory for parallel distributed detection networks with fixed fusion rules to develop a numeric algorithm based on Neyman-Pearson criterion. Simulation results are presented to demonstrate the efficiency and convergence properties of the algorithm.

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In welded tubular joints, when the fatigue crack depth is less than 20% of chord wall thickness, the crack growing process is highly affected by weld geometry. Hence, T-butt solution and weld magnification factor (Mk) are applicable tools for evaluating the crack growth rate in this domain. In this research, the capability of Artificial Neural Network (ANN) for estimating the Mk of weld toe cracks in T-butt joints is investigated. Four Multi-Layer Perceptron (MLP) networks are designed and trained to predict the Mk in deepest point and ends of weld toe cracks under membrane and bending stresses. Training and testing data of networks are extracted from a reputable resource on finite element modeling. Comparison of the results obtained and those from the most recently published equations shows that using ANN seems to be very beneficial in this field

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This paper tries to estimate the capital investment required for the fixed-telephony network switching equipment as demanded by the fourth national development plan. As a first step, the Cobb-Douglas model is used as a successful demand forecasting model to estimate the demand over the target years. Then, an architectural plan is developed for the fixed-telephony switching network that takes into account the expansion of the existing exchanges as well as the addition of new ones. The number of the required ports in local exchanges, the intercity traffic (including cell phone subscribers), and the required trunks in transit exchanges are then estimated. Two scenarios are used to estimate the investment needed: expanding legacy network (circuit-based), and NGN adoption (a combination of circuit and packet-based networks). Finally, conventional pricelists from different local and foreign suppliers are used to arrive at two total investment estimates: 6,013 billion Rials and 6330 billion Rials for the two mentioned scenarios, respectively.

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Prediction of SCC risk of austenitic stainless steels in aqueous chloride solution and estimation of the time to failure as a result of SCC form important and complicated topics for study. Despite the many studies reported in the literature, a formulation or a reliable method for the prediction of time to failure as a result of SCC is yet to be developed. This paper is an effort to investigate the capability of artificial neural network in estimatiing the time to failure for SCC of 304 stainless steel in aqueous chloride solution and to provide a sensitivity analysis thereof. The input parameters considered are temperature, chloride ion concentration, and applied stress. The time to failure is defined as the output parameter and the key criterion to evaluate the effective parameters. The statistical performance of the neural network is expressed as the average of three learning and testing results. The SCC database is divided into two sections designated as the learning set and the testing set. The output results show that artificial neural network can predict the time to failure for about 74% of the variance of SCC experimental data. Furthermore, the sensitivity analysis also exhibits the effects of input parameters on SCC of 304 stainless steel in aqueous chloride solutions.

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Many efforts have been done in recent years to decrease the required time for analysis of FKP (Forward Kinematics
Problem) of parallel robots.This paper starts with developing kinematics of a parallel robot and finishes with a suggested
algorithm to solve forward kinematics of robots. In this paper, by combining the artificial neural networks and a 3rd-order
numerical algorithm, an improved hybrid strategy is proposed in order to increase the accuracy and speed of forward kinematics
analysis of parallel manipulators. First, an approximate solution of the forward kinematics problem is produced by the neural
network. This approximate solution is then considered as the initial guess for the 3rd-order Newton-Raphson numerical
technique. By applying Stewart-Gough parallel manipulator, the efficiency of the proposed method is evaluated. It is shown that
replacing the Newton-Raphson algorithm by the 3rd-order one leads to a reduction of the iterations required to reach the desired
accuracy level and thus a reduction of the FKP analysis time. Finally, Stewart robot is used to simulate the movement of jaw.
This novel algorithm can be applied to any forward kinematics of serial or parallel robots.

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Financial crises in banking systems are due to inability to manage credit risks. Credit scoring is one of the risk management techniques that analyze the borrower's risk. In this paper, using the advantages of computational intelligence as well as soft computing methods, a new hybrid approach is proposed in order to improve credit risk management. In the proposed method, for modeling in uncertainty conditions, parameters of the neural network, including weights and errors, are considered in the form of fuzzy numbers. In this method, the underlying system is firstly modeled using neural networks and then, using fuzzy inferences, the optimal decision will be determined with the highest degree of superiority. Empirical results of using the proposed method indicate the efficiency and high accuracy of this method in analyzing credit rating problems.