Computational Methods in Engineering

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The use of roller compacted concrete (R.C.C) without conventional cover in important hydraulic structures is investigated through laboratory observation of abrasion phenomena sujected to high velocity flow and floating particles. The main parameters affecting abrasion and erosion resistance of R.C.C. studied in the present study include: Mixed Hydraulic Mean Radius (which collectively represents several different parameters such as shape, type of surface, fine and coarse aggregate ratio, mixture irregularity, and energy of compaction), water cement ratio, and age of R.C.C. samples. It should be noted that most references in this filed concentrate on conventional concrete abrasion with often soft surfaces. In the present study, however, research findings on abrasion-erosion resistance of R.C.C. and their applications in new investigations will be investigated using a new test device called Evaluation of Concrete Resistance designed by H. Bayat. The device works with several phase flows. Single and multivariate analyses of the results, graphs, and empirical relations are used to determine abrasion and erosion resistance in terms of the above parameters. It is expected that in future only one parameter, namely, the Mixture Hydraulic Mean Radius, will suffice for evaluating R.C.C. abrasion resistance.

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In this paper an analytical model for cold rolling of strip has been described. This model is developed based on the slab method of analysis and the hydrodynamic lubrication. The characteristics of rolling are obtained from the equations of equilibrium and the plate was allowed to strain harden assuming that the lubricant behaves as a Newtonian fluid. The shear stress to the plate is obtained by calculating the thickness of the lubricant film by employing a viscosity-pressure-temperature relation. The governing equations are obtained by composing these relations and the final differential equations have been solved. From the solution of the final equation, the rolling force، torque and shear stress to the plate are calculated. To verify the validity of the proposed model, these values are compared with experimental and analytical results of other investigators. It was also noted that by employing the proposed analytical model, a large amount of computation time and costs are saved

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The presence of defects in cold mercerizing of cotton goods led to the creation of a new method, called hot mercerizing in which caustic soda solution is used at a high temperature. Hot mercerizing is successfully used in cotton blended with some other fibers. In cotton/polyester blend fabrics, this treatment serves a dual purpose: subjectively, it imparts a silklike soft handle to the polyester and brings about mercerizing of the cotton. In this work, the mercerizing operation with caustic soda solution was performed on a 65/35 polyester/cotton fabric in sixteen different temperatures (from 15°C to 90°C), in two states: with tension and without tension. Finally, the effect of temperature of treatment on some properties of fabric such as tensile properties, weight loss, and shrinkage have been studied. Alkali treatment cause weight loss in cotton/polyester blend fabrics, the main part of the weight loss attributed to the polyester component of the blend. Increasing temperature leads to a corresponding increased in weight loss. The resulting weight loss leads to more yarn release and consequently, to the improvement of the drape and soft handle in the fabric. However, it decreases the tensile strength and causes weakness of the fabric, therefore, an optimum of temperature must be considered. In the alkali treatment, the internal stresses in the fabric can be released. Release of tension in the fabric causes shrinkage, particularly in the warp direction. The effect of tension on properties of cotton/polyester blend fabric is not considerable in alkali treatment.

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Regarding the importance of ring spinning method among spinning systems, great potentials exist for research about on the improvement of the quality and properties of ring spun yarn. This study aims to improve yarn quality by changing the shape and dimensions of spinning triangle through forming a groove in the middle zone of the front darfting roller with a curvature of 5 to 7 mm. For the top drafting roller, we used an elastic O-Ring with dimensions similar to those of the groove. With this change, the geometry of spinning triangle is expected to change as an Euclidean geometry to a half cone Riemannian shape. The results show improvement in yarn tenacity, elongation at break, yarn evenness and faults, shape of spinning baloon, decrease in yarn tension and yarn breakage, improvement in fiber packing in the yarn cross section, more evenness in the yarn count and twist, and, finally, better inter-structure compared to the normal ring spun yarn.

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Stator flux oriented vector control of induction motor (IM) drives for speed sensorless control has several advantages. But the application of a pure integrator for the flux estimation is difficult due to the presence of measurement noise and dc offset. To overcome these problems, some have used a programmable cascaded low pass filter (PCLPF). In this paper, it is shown that some problems still exist and some new problems arise from this approach. In order to solve these problems, a novel compensation method is proposed. In this scheme, the dc offset is detected and subtracted from the estimated flux along d and q axes. The simulation results show that it works well in the low speed region as well as in the transient state. The oscillation of the torque and the estimated flux are also reduced notably when the torque reference changes rapidly.

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The new techniques in seismic design of structures are usually attributed to high damping ratios. In such systems, the assumption of classical (i.e. proportional) damping is not valid and in most cases they should be considered as Non-classical systems. Since the analytical tools for studying the behavior of such structures are not easily available, the present work attempts to find the limits, in which, a non-classical system can be approximated as a classical one. This is accomplished, first, by introducing the mass participation factor for non-classical systems. Subsequently, a relevant spectrum analysis technique such systems is developed. Using the spectrum analysis technique, the limitation of damping ratios in which two different types of Mass Isolated structures can be approximated as classical ones are determined. The results indicate that in the usual range of damping capacity for such structures, a well distribution of dashpots along the height of the system considerably reduces the non-classical characteristics of the structure.

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The study of two-phase fluid flow behavior in hydraulic structures such as pressurized flow tunnels, culverts, sewer pipes, junctions and other similar conduits is of great importance. A two-phase mixture flowing in a pipe can exhibit several interfacial geometries such as bubbles, slugs or films, depending on the fluid and hydrodynamic properties of flow. The main variables, giving rise to a variety of flow patterns, include relative discharge rate of fluids and the pipe slope. The flow patterns mostly attainable with air and water include stratified include and slug patterns. In this paper, the experimental results of pressurized water tunnel model are presented. The results include pressure transient and its variations for different hydraulic and geometric properties. It is shown that trapped and released air can cause tremendous pressure surges in the system and, eventually, may cause failure in systems (e.g. the maximum pressure inside the pipe would reach up to 10 times of upstream hydrostatic pressure). Finally, relations for forecasting maximum and minimum pressure in these situations are presented as a function of mean pressure, flow characteristics and pipe geometry.

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Flame bending process is one of the forming processes of steel plates. During this process, plate is formed with heating by gas torch flame followed by controlled cooling along specified paths. Considering simple tools used in the process, it is a popular and economical forming method. At present, this process is manually done on the basis of skilled technician’s experience. Experimental and non-automated procedures decrease productivity of the process. In this paper, a method is proposed for simulation of material deformation. Regarding the physics of the process, large deformation thermoelastic-plastic analysis has been applied. In the simulations, a new analytical solution is used for thermal analysis of plate. The analytical solution along with finite element analysis of the deformation in ANSYS program is able to interpret experimental observations. The simulations show reasonable results, compared with the analytical results by other researchers and with experimental data. The method and simulation results can be used to study the process automation

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Nanowire is a cylindrical nano-structure with nanometer dimensions. In this research, the studied nanowire was made from the magnetic triple Ni-Fe-Co alloy. We utilized ordered porous anodic aluminum oxide as a template for the nanowire deposition. The nanowire arrays were electrodeposited in the cylindrical pores of the oxide layer by AC potential in a simple sulfate bath. Then the relation of shape and composition of the nanowires with their fabrication parameters was investigated. The results showed that the barrier layer modification had an essential role in the deposition process and a composition gradient was detected in a single nanowire.

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: The CIECAM97s and its revision, as a colour appearance model, were applied for a series of fabrics with different colours and depths to explain their colour appearance coordinates in similar viewing conditions. The results show that due to some modifications which expand the scale, the modified model has improved capadilities in calculating chroma. Besides, the calculations were simpler for the revised version of CIECAM97s model while the results from the two models were the same.

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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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Introducing distributed generation into a power system can lead to numerous benefits including technical, economic, environmental, etc. To attain these benefits, distributed generators with proper rating should be installed at suitable locations. Given the similar effects of distributed generators and capacitor banks on operation indices of a distribution system, simultaneous assignment of best locations and sizes to both will not only lead to greatest benefits from distributed generators but also to lower reactive power capacity requirements. In this paper, a new combined planning problem involving distributed generation and Volt/VAr control means planning is formulated and solved in which the quantity of distributed generators and reactive power sources are simultaneously assigned to buses in a distribution system. Also tap positions of voltage regulators are computed such that with a given distributed generation under peak load conditions, power losses and the reactive power capacity required are minimized. Like many other problems in power network planning, the problem formulated here is a nonlinear combinatorial one. Hence, we employ the tabu search algorithm to solve the optimization problem. The results from applying the algorithm to distribution networks with 6, 19, and 33 buses are presented and compared with those obtained from employing the second order method.

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Bridges are potentially one of the most seismically vulnerable structures in the highway system during earthquake events. It is known that the seismic performance of transportation systems plays a key role in the post-earthquake emergency management. Hence, it is necessary to evaluate both physical and functional aspects of bridge structures. The physical aspects of the seismic performance of bridges are evaluated by seismic fragility functions or damage probability matrices of transportation facilities. The fragility curves represent the probability of structural damage due to various levels of ground shaking. The fragility curve describes a relationship between a ground motion and a level of damage. In this paper, the fragility curves (F.C) are developed. The vulnerability of a railway prestreed concrete bridge is assessed using fragility curves derived from dynamic nonlinear finite element analysis. A software package is developed in MATLAB to study the results obtained. Modeling of the bridge using 3D nonlinear models and modeling of abutments, bearings, effect of falling of girder on its bearings, and nonlinear interaction of soil-structure are some of the advantages of this research compared to previous ones. Reliability curves developed in this study are unique in their own kind. The proposed method as well as the results are presented in the form of vulnerability and structural reliability relations based on two damage functions.

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Energy absorber systems like metallic dampers for controlling the structural vibrations due to earthquake have witnessed considerable development in the past few decades. Also there are some studies on the energy absorption of thin-walled tubes due to impact load. Thin-walled tubes have a large deformation capacity and are suitable energy absorbers in the structure during an earthquake provided that a suitable inelastic buckling mode obtains. This paper deals with the study of energy dissipation in accordion thin-walled tubes and their behavior due to axial cyclic loads. For this purpose, experimental and analytical studies have been performed. Experimental studies were conducted on specimens available in the market by dynamic tension and compression actuator. Analytical studies are based on finite element methods and nonlinear inelastic dynamic analysis. These studies are focused on the effects of mechanical and geometrical parameters of these tubes like shape, thickness, diameter, length and material type of tube on the amount of energy dissipation and axial stiffness. The results show that accordion thin-walled tubes exhibit satisfactory energy absorption behavior and that proper selection of the parameters yields the optimum design of this metallic damper.

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Aluminum matrix composites reinforced with Al2O3 and SiC particles (5 Vol%) were produced using the hot powder extrusion method. Extrusion temperature and extrusion reduction in area were chosen in the range of 500 to 600°C and 90 to 95%, respectively. The physical and mechanical properties of the extruded composites such as density, tensile strength, elongation and microhardness were evaluated and discussed as a function of extrusion parameters. The microstructure and fracture surface of the products were examined using SEM. The results showed that the composites were fully densified and reinforcement particles were distributed uniformly in the matrix. Presence of Al2O3 and SiC particles increased both strength and microhardness, but decreased the ductility of the composites. Experimental results for hot extrusion of the compacted powder billets also showed that the extrusion pressure was dependent on the ram speed or deformation strain rate.

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It is empirically established that, due to a number of factors involved, a classical (linear) analysis of buckling pressure is impossible. Nonlinear theories of buckling are, therefore, required that involve effective factors such as imperfections and welding effects. In this study, models are developed which are as close to allowable standard deviations as possible. In the next stage, their buckling behavior is investigated both experimentally and numerically using finite element packages ADINA, ANSYS, COSMOS, and MARC based on specific capabilities of each. Results show that reasonable estimates of real buckling pressure will become possible when material and geometrical nonlinearities and initial imperfections are introduced into the analytical system. Finally, in the light of the results obtained, a submarine pressure hull is analyzed.

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This paper deals with resource unconstrained project scheduling problems with the objective of maximizing the net present value (NPV) of project cash flows. Here we present a heuristic algorithm named as differential procedure (Dif_AOA). In order to evaluate the efficiency of this algorithm, networks with node numbers between 10-1000 and network complexity coefficients between 1.3-6.6 have been generated. We have compared both the total time for solving the problem and NPV of the Dif_AOA with those of the recursive search procedure. Computational results show that the Dif_AOA performs very effectively. Extensive analysis have been performed to evaluate the node number, complexity network coefficients(CNC), and deadline.

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This paper introduces an accurate, fast, and applicable method for optimization of slip surfaces in earth slopes. Using Genetic Algorithm (GA), which is one of the modern and non-classic optimization methods, in conjunction with the well -known Bishop applied method, the optimum slip surface in an earth slope is investigated and its corresponding lowest safety factor is determined. Investigations have shown that selection of appropriate variables to define and to solve the problem and determination of a good range for these variables have a profound effect on the speed of convergence in the problem. In the present study, appropriate variables have been defined for solving the problem in a way that the number of repetitions required to reach convergence are considerably reduced by up to 50% compared with other approaches. This has led to a drastic reduction in time and the memory required. The accuracy of the method is shown first by solving examples related to search for optimum failure surfaces of some homogenous, non-homogenous, and earth dam slopes and then by comparison of the results with those of other optimization techniques. In order to show the application of the present method in modern geotechnical engineering, a reinforced earth slope is studied and its failure surface is finally optimized

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Using Electrostatic Spray Coating Technique, Polypropylene Powder (EPD 60R) was applied on carbon steel substrates at room temperature. In order to obtain a uniform coating, steel substrates with powder coatings were heated in a vacuum oven at various temperatures up to 250° C for various periods of time up to 45 min and a pressure of 200 mb. The coatings produced had thicknesses of around 470 microns. In order to modify the chemical structure of this polymer, the powder coatings containing various weight percentages of maleic (anhydride (MA) and a peroxide (TBHP or DCP) were also applied onto the steel substrates under the above conditions. Adhesion strength, wear resistance, and ductility of polymer coatings produced were assessed using ASTM standard methods. Results obtained revealed that the polymer coating containing 5 wt%. MA and 0.1 wt% TBHP had the best mechanical properties. Adhesive strength and wear resistance of this coating were 14.3 kgf and 250.3 cm, at 6 kgf, respectively, under the applied load of 6kg. Results obtained from DSC thermographs and IR Spectroscopy also proved the chemical bond formation (grafting) between the polymer and MA. The mechanical properties of coatings on steel substrate stem from such graftings.

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An effective approach for strengthening masonry buildings is to apply shotcrete reinforced with mesh on the surface of the wall. It is not possible to assess the behaviour of coated walls solely using analytical approaches based on simple equations of theory of elasticity without the use of numerical methods. Unreinforcced masonry wall is modelled in this study using the finite element software “ANSYS” to assess the behavior of walls strengthened with reinforced jacket. The accuracy of the model is ensured by calibrating the model against results obtained from laboratory tests. Then the calibrated model is generilized to model the strengthed wall and, finally, the analytical results obtained from masonry walls and strengthed walls are compared and evaluated.