Showing papers by "Amirkabir University of Technology published in 2000"

Carbon Black-Reinforced Dynamically Cured EPDM/PP Thermoplastic Elastomers. I. Morphology, Rheology, and Dynamic Mechanical Properties

Abstract: The structure development, rheological behavior, and viscoelastic proper- ties of carbon black-filled dynamically vulcanized thermoplastic elastomers based on the ethylene-propylene- diene terpolymer (EPDM) and polypropylene (PP) with the ratio range of 50/50 to 80/20 were studied and compared with similar but unfilled samples. Two-phase morphology was observed at all ratios for the dynamically cured samples in which rubber particles are dispersed in the thermoplastic matrix. Carbon black distribution in each phase and damping behavior was found to be dependent upon the mixing condition and route of carbon black feeding. However, carbon black tends to stay mainly in the rubber phase, which leads to increase in the viscosity difference and, therefore, increase in the rubber particle size. Tensile strength and rupture energy increased with carbon black loading. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1127-1137, 2000

A new fuzzy logic filter for image enhancement

Abstract: This paper presents a new fuzzy-logic-control based filter with the ability to remove impulsive noise and smooth Gaussian noise, while, simultaneously, preserving edges and image details efficiently. To achieve these three image enhancement goals, we first develop filters that have excellent edge-preserving capability but do not perform well in smoothing Gaussian noise. Next, we modify the filters so that they perform all three image enhancement tasks. These filters are based on the idea that individual pixels should not be uniformly fired by each of the fuzzy rules. To demonstrate the capability of our filtering approach, it was tested on several different image enhancement problems. These experimental results demonstrate the speed, filtering quality, and image sharpening ability of the new filter.

Elasto‐plastic modelling of stress‐path‐dependent behaviour of interfaces

Abstract: A single-surface elasto-plastic model developed by Desai and his coworkers is used to predict the behaviour of an interface between sand and a steel plate. The loading in the experiments and in their predictions followed various stress and displacement paths. The results of predictions of the two- and three-dimensional behaviour of the interface under both constant normal stress and constant normal stiffness conditions are presented. The predictions are compared with their corresponding experimental results. The model parameters were determined on the basis of 2-D conventional experiments under the condition of constant normal stress and they were used in the prediction of the interface behaviour in various stress paths. There is, in general, a good agreement between the predicted and experimental results. Copyright © 2000 John Wiley & Sons, Ltd.

Maximization of Manufacturing Yield of Systems with Arbitrary Distributions of Component Values

Abstract: This paper presents a general method for maximizing manufacturing yield when the realizations of system components are independent random variables with arbitrary distributions. Design specifications define a feasible region which, in the nonlinear case, is linearized using a first-order approximation. The method attempts to place the given tolerance hypercube of the uncertain parameters such that the area with higher yield lies in the feasible region. The yield is estimated by using the joint cumulative density function over the portion of the tolerance hypercube that is contained in the feasible region. A double-bounded density function is used to approximate various bounded distributions for which optimal designs are demonstrated on a tutorial example. Monte Carlo simulation is used to evaluate the actual yields of optimal designs.

A Fuzzy Logic Control Based Approach for Image Filtering

Abstract: This chapter is devoted to introduce a new filtering approach based on fuzzy-logic control concepts with the properties of removing impulsive noise and smoothing out Gaussian noise while, simultaneously, preserving edges and image details efficiently The main idea behind the proposed filtering approach is that each pixel is not allowed to be uniformly fired by each of the fuzzy rules In this chapter, different modifications of this filtering approach (Iterative Fuzzy Control based Filter — IFCF) named by MIFCF, EIFCF, SFCF, SSFCF, FFCF, AFCF and ACFCF are presented along with some test experiments highlighting the merit of each filter From the experimental results we may list the concluding remarks of the proposed filtering approach: high quality of edge preserving ability, high filtering quality especially for complex images, multiplicative noise removing property for IFCF based filters, floating point free calculations and very fast performance for FFCF based filters

Boundary element analysis of coupled thermoelasticity with relaxation times in finite domain

Abstract: A boundary element method based on the Laplace technique is developed for transient coupled thermoelasticity problems with relaxation times in a two-dimensional finite domain. The dynamic thermoelastic model of Green and Lindsay (Green, A. E., and Lindsay, K. E., Thermoelasticity, Journal of Elasticity, Vol. 2, No. 1, 1972, pp. 1-7) and Lord and Shulman (Lord, H. W., and Shulman, Y., A Generalized Dynamic Theory of Thermoelasticity, Journal of the Mechanics and Physics of Solids, Vol. 15, 1967, pp. 299-309) are selected. The Laplace transform method is applied in the time domain, and the resulting equations in the transformed field are discretized using a boundary element method. The nodal dimensionless temperature and displacements in the transformed domain are inverted to obtain the actual physical quantities, using the numerical inversion of the Laplace transform method. The concern is with thermoelastic waves detection, propagation, and reflection in a finite domain that have not been reported on in the past. Comparison is made with other solutions, and coupling and relaxation time effects in stress, displacement, and temperature distribution are investigated. Details of the formulation and numerical implementation are presented.

BEM analysis of thermal and mechanical shock in a two-dimensional finite domain considering coupled thermoelasticity

Abstract: A boundary element method based on the Laplace-transform technique is developed for transient coupled thermoelasticity problems of two-dimensional finite domain The Laplace-transform method is applied to the time domain and the resulting equations in the transformed field are discretized using the boundary element method The nodal dimensionless temperature and displacements in the transformed domain are inverted to obtain the actual physical quantities, using the numerical inversion of the Laplace-transform method The work is concerned with the thermal and mechanical shocks in a finite domain considering classical coupled theory of thermoelasticity Elastic and thermoelastic wave creation and propagation in a finite domain and their effects on each other are investigated Numerical implementations are presented and compared with the known data

The Wicking of Water in Yarn as Measured by an Electrical Resistance Technique

Abstract: An apparatus was developed to study water-transport behaviour along yarns. The rise of the liquid water in the yarn triggered an electrical circuit which was coupled with a personal computer, and so the distance of water rise as a function of time was determined. To smooth the data, the method of least squares was applied and the theoretical equation of the flow through the vertical cylindrical capillary was used. Polypropylene filaments and polyester yarns in various forms were examined. The rate constants and the relations between vertical water transport and time in different yarns are reported.

A hybrid analysis direct method in the calculus of variations

Abstract: This paper presents a direct method for finding the solution of variational problems using a hybrid function. The properties of hybrid functions which consists of block-pulse functions plus Legendre polynomials are presented. An operational matrix of integration and the cross product of two hybrid function vectors are used to reduce a variational problem to the solution of algebraic equation. Illustrative examples are included to demonstrate the validity and applicability of the technique.

TASOM: the time adaptive self-organizing map

Abstract: The time-decreasing learning rate and neighborhood function of the basic SOM (self-organizing map) algorithm reduce its capability to adapt weights for a varied environment. In dealing with non-stationary input distributions and changing environments, we propose a modified SOM algorithm called "time adaptive SOM", or TASOM, that automatically adjusts the learning rate and neighborhood size of each neuron independently. The proposed TASOM is tested with stationary environments and its performance is compared with that of the basic SOM. It is also tested with non-stationary environments for representing the letter 'L', which may be translated, rotated, or scaled. Moreover, the TASOM is used for adaptive segmentation of images which may have undergone gray-level transformation.

Application of a Continuous Two Impinging Streams Reactor in Solid−Liquid Enzyme Reactions

Abstract: The isomerization of d-glucose to d-fructose, using the immobilized glucose isomerase, as a typical example of solid−liquid-catalyzed reactions has been carried out in a tangential flow two impinging streams reactor (TFTISR). The results obtained for the conversion of glucose in TFTISR were much higher than those expected in conventional reactors. This indicates the greater performance capability of TFTISR relative to those of classical reaction systems. A compartment model was devised to describe the pattern of flow within the reactor. Considering such a flow pattern, a stochastic model for the residence time distribution (RTD) of solid particles was developed, using Markov chains discrete formulation. The latter was correlated with the experimental RTD data, obtained by applying a tracer analysis method.

Neural network based dynamic modeling of flexible-link manipulators with application to the SSRMS

Abstract: This paper presents an approach for dynamic modeling of flexible-link manipulators using artificial neural networks. A state-space representation is considered for a neural identifier. A recurrent network configuration is obtained by a combination of feedforward network architectures with dynamical elements in the form of stable filters. To guarantee the boundedness of the states, a joint PD control is introduced in the system. The method can be considered both as an online identifier that can be used as a basis for designing neural network controllers as well as an offline learning scheme to compute deflections due to link flexibility for evaluating forward dynamics. Unlike many other methods, the proposed approach does not assume knowledge of the nonlinearities of the system nor that the nonlinear system is linear in parameters. The performance of the proposed neural identifier is evaluated by identifying the dynamics of different flexible-link manipulators. To demonstrate the effectiveness of the algorithm, simulation results for a single-link manipulator, a two-link planar manipulator, and the Space Station Remote Manipulator System (SSRMS) are presented. ©2000 John Wiley & Sons, Inc.

Effect of pre-straining and grain size on the limit strains in sheet metal forming

Abstract: Forming processes of metal sheets are generally limited by plastic instability phenomena and flow localization. The occurrence of these phenomena is dependent on the material properties such as strain-hardening exponent, strain rate sensitivity, anisotropy parameters and grain size and is also dependent on the strain path. The formability of the sheet metals can be assessed by the forming limit diagram (FLD). In this study, a theoretical model using the ‘many slices’ approach is introduced to simulate the neck growth. The effects of changing strain path and grain sizes on the limit strains are then investigated both theoretically and experimentally. The low carbon steel ST12 and austenitic stainless steel 321 are used in the experimental approach. The theoretical and experimental FLDs of these sheets are obtained for different grain sizes and after pre-straining in uniaxial and biaxial tension parallel to the prior rolling direction. It is shown that the limit strains are quite sensitive to the gr...

On Thermal Dynamic Buckling Analysis of Imperfect Laminated Cylindrical Shells

Abstract: Based on the general form of Green's strain tensor in curvilinear coordinates, the exact strain-displacement expressions of an imperfect laminated composite circular cylindrical shell undergoing large deflections are developed. The resulted relations may also be used for postbuckling analysis. Employing Hamilton's variational principle, the most general three dimensional and exact integral equations of motion are introduced in a hybrid form. No assumption or simplification is made in deriving the formulations. The resulting equations are solved using a Kantorovich type power series. Dynamic buckling loads treated in this paper, include mechanical loads (axial compression, external pressure, external fluid pressure, and torsion), thermal loads, or a combination of them. The resulted equations are then solved by means of an efficient solution procedure. In contrast to the well-known higher-order and layer-wise theories which are displacement-based, due to the hybrid form of the final equations, various edge conditions (displacement, stress, force, and moment boundary conditions) can be accurately incorporated. Furthermore, in contrast to the existing 3–D elasticity approaches, the solution procedure of the present method is self-started. Finally, few examples of the well-known references done in the mechanical and thermal buckling of the composite circular cylindrical shells, which are based on other theories, are reexamined for comparison purposes. The results are extended to check the capability of the present theory and to enable a sensitivity analysis.

Measurement and correlation of the individual ionic activity coefficients of aqueous electrolyte solutions of KF, NaF and KBr

Abstract: Ion selective electrodes were used to measure the activity coefficients of individual ions at 298.2 K in aqueous solutions of KF, KBr and NaF up to 3, 2 and 1 molal, respectively. The mean ionic activity coefficients of the electrolytes obtained from the values of individual ions show good agreement with values reported in the literature. The experimental results confirm that the activity coefficients are different for the anion and the cation in an aqueous solution of a single electrolyte. It is also confirmed that the deviation from ideality for each ion depends on its counterion. The Khoshkbarchi—Vera equation was used to correlate the experimental data. On a utilise des electrodes selectives aux ions afin de mesurer les coefficients d'activite d'ions individuels a 298,2 K dans des solutions aqueuses de KF, KBr et NaF jusqu'a 3, 2 et 1 molals, respectivement. Les coefficients d'activite ionique moyens des electrolytes obtenus a partir des valeurs des ions individuels montrent un bon accord avec les valeurs indiquees dans la litterature scientifique. Les resultats experimentaux confirment que les coefficients d'activite sont differents pour l'anion et le cation dans une solution aqueuse d'une simple electrolyte. Les resultats confirment egalement que l'ecart avec l'idealite de chaque ion depend de son contre-ion. On s'est servi de l'equation de Khoshkbarchi et Vera pour correler les donnees experimentales.

Off-line unconstrained Farsi handwritten word recognition using fuzzy vector quantization and hidden Markov word models

Abstract: An unconstrained Farsi handwritten word recognition system based on fuzzy vector quantization (FVQ) and a hidden Markov model (HMM) for reading city names in postal addresses is presented. Preprocessing techniques including binarization, noise removal, slope correction and baseline estimation are described. Each word image is represented by its contour information. The histogram of chain code slopes of the image strips (frames), scanned from right to left by a sliding window, is used as feature vectors. Fuzzy c-means (FCM) clustering is used for generating a fuzzy code book. A separate HMM is trained by a modified Baum-Welch algorithm for each city name. A test image is recognized by finding the best match (likelihood) between the image and all of the HMM work models using a forward algorithm. Experimental results show the advantages of using an FVQ/HMM recognizer engine instead of conventional discrete HMMs.

Inlet induced flow in squirrel-cage fans

Abstract: Energy conversion in squirrel-cage fans is sensitive to the inlet geometry. It occurs at the inlet where a separation zone which occupies a major volume in the rotor and the volute starts. In this research, different inlets of inward and outward types were tested on two fans. First, the inlet diamenter and position were matched with the rotor, which improved the fan characteristic curves. The results of the experiments were sensitive to the width of the blade retaining ring (shroud). Later the tangential and radial components of the velocity out of the rotor were measured. The resulting velocity profiles across the scroll width showed that outward inlets produce a more uniform velocity angle inside the volute than inward inlets did. This was not because of a more aerodynamic flow through the rotor blades by was due to a better match between the inlet and the volute. The axial energy transfer resulted in tangential velocities larger than the rotor velocity, at axial positions across the volute wher...

Document skew detection using minimum-area bounding rectangle

Abstract: Detection of document skew is an important step in document image analysis. The paper presents a new method for calculation of document skew. The method forms large connected components by a smoothing algorithm and calculates the document skew by finding the orientation of the minimum-area bounding rectangle of one of several connected components. Connection of text to non-text in the smoothing step does not degrade the performance of the method. The smoothing parameters are determined automatically and no manual adjustment is necessary. The method is not limited in the range of detectable skew angles and the achievable accuracy. Experimental results show the high performance of the algorithm in detecting document skew for a variety of documents with different levels of complexity.

Adaptation of parameters of BP algorithm using learning automata

Abstract: The backpropagation (BP) algorithm is a systematic method for training multilayer neural networks. Despite the many successful applications of backpropagation, it has many drawbacks. For complex problems it may require a long time to train the networks, and it may not train at all. Long training time can be the result of the non-optimal parameters. It is not easy to choose appropriate value of the parameters for a particular problem. In the paper, by interconnection of fixed structure learning automata (FSLA) to the feedforward neural networks, we apply learning automata scheme for adjusting these parameters based on the observation of random response of neural networks. The main motivation in using learning automata as an adaptation algorithm is to use its capability of global optimization when dealing with multi-model surface. The feasibility of proposed method is shown through simulations on three learning problems: exclusive-or, encoding problems, and digit recognition. The simulation results show that the adaptation of these parameters using this method not only increases the convergence rate of learning but it increases the likelihood of escaping from the local minima.

Correlation of activity coefficients in electrolyte solutions using a kelvin hard sphere-mean spherical approximation (k-msa) model

Abstract: A hard sphere system, using Kelvin tetrakaidekahedron cells, coupled with the mean spherical approximation (MSA), accurately correlates the mean ionic activity, and the individual activities of ions, in aqueous solutions of single 1:1 electrolytes. For the mean ionic activity coefficients, the diameter of the anion is fixed at the Pauling value and the cation diameter is a function of composition. Hydrated diameters of cations are realistic in comparison with Pauling values, and the like and unlike ionic pair correlation functions at contact value are positive in the whole concentration range. The use of a simpler version of the MSA has little effect on the results and dramatically reduces the computation time. The results obtained from the Kelvin mean spherical approximation, K-MSA model, compare favorably with those of other models. The correlation of individual ionic activity coefficients requires composition-dependent diameters for the cation and anion.