Journal of Advanced Materials in Engineering (Esteghlal)

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Cohesive-frictional soils are widely used in the construction of embankment structures and due to the method of construction, i.e. applying compactive efforts in the vertical direction in these cases, the occurrence of anisotropy in the soil strength and permeability seems to be inevitable. In this study, attempts have been made to evaluate the shear strength of c-f soils through modifying a large shear box apparatus. Conducting more than 108 direct shear tests, the effects of compaction method and moisture on the shear strength anisotropy of a selected c-f soil (a clayey sand) have then been investigated. According to the test results, firstly strength anisotropy was observed in all the soil specimens and the shear strength in the vertical direction was about 14% to 21% higher than that in the horizontal direction. Secondly, it was found that an increase in the compaction moisture led to an increase in the degree of anisotropy. Furthermore, the anisotropy in the cohesive strength was more pronounced in the specimens with a moisture content higher than the optimum one. The highest degree of anisotropy was observed in the specimens compacted by impacting effort and the lowest one belonged to those with the vibratory compaction.

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A numerical simulation has been carried out to study the detonability characteristics of two- phase unconfined clouds. The parameters equivalence ratio, turbulence, shape, volume and uniformity of the cloud and the delay time distribution are recognized and introduced as the most important factors determining the reactivity of the cloud and influencing the initiation of a successful detonation. With regard to the dynamic behavior of the cloud and the changes in the magnitude of these significant characteristic parameters, the best ranges of time and position for secondary detonator action are determined. Comparisons are also performed with experimental results along with theoretical analyses to validate the numerical results obtained in this study.

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The rapid growth of space utilization requires extensive construction, and maintenance of space structures and satellites in orbit. This will, in turn, substantiate application of robotic systems in space. In this paper, a near-minimum-time optimal control law is developed for a rigid space platform with flexible links during an orientating maneuver with large angle of rotation. The time optimal control solution for the rigid-body mode is obtained as a bang-bang function and applied to the flexible system after smoothening the control inputs to avoid stimulation of the flexible modes. This will also reflect practical limitations in exerting bang-bang actuator forces/torques, due to delays and non-zero time constants of existing actuation elements. The smoothness of the input command is obtained by reshaping its profile based on consideration of additional first-order and second-order derivative constraints. The platform is modeled as a linear undamped elastic system that yields an appropriate model for the analysis of planar rotational maneuvers. The developed control law is applied on a given satellite during a slewing maneuver. The simulation results show that the modified realistic optimal input compared to the bang-bang solution agrees well with the practical limitations and also alleviates the vibrating motion of the flexible appendage, which reveals the merits of the new control law developed here.

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In this paper, an analytical method based on Modified Slab Method of analysis is presented to study the asymmetrical rolling process due to difference in work rolls radii, rolls speeds and interface frictions. The shear force imposed on material along the contact region is considered to be a function of the frictional factor and the roll gap geometry. Elastic-plastic with linear work hardening constitutive law was assumed. Asymmetric factors considered are roll diameter ratio, roll speed mismatch and differential interface friction conditions. Neutral points’ location along the contact region in relation to the variations on thickness reduction, roll speed ratios, roll diameters ratio and front and back tensions are investigated. Predicted values for rolling force and torque from the present analytical model are compared with those of other workers, which are shown to be in good agreement

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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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A series of supersonic wind tunnel tests on an ogive-cylinder body were performed to investigate the pressure distribution, the boundary layer profiles, and the flow visualization at various angles of attack. All tests were conducted in the trisonic wind tunnel of the Imam Hossein University. The theoretical shock angle at different model positions compared well with those we obtained via Schilerian results. The static surface pressure results show that the circumferential pressure at different nose sections vary significantly with angle of attack. However, minor changes in the circumferential pressure signatures along the cylindrical part of the body were observed. The total pressure measurements in the radial direction, perpendicular to the incoming flow, vary significantly both radially and longitudinally (along body length). The boundary layer thickness increases along the body. At the beginnig and at the midle part of the cylinderical portion of the body, the boundary layer thickness increases uniformly with increasing angle of attack. However, this situation differs near the end of the body. Our measurements indicated a turbulent boundary layer along the model, which is probably due to the high turbulence level in the tunnel test section.

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Mobile robotic systems, which include a mobile platform with one or more manipulators, mounted at specific locations on the mobile base, are of great interest in a number of applications. In this paper, after thorough kinematic studies on the platform and manipulator motions, a systematic methodology will be presented to obtain the dynamic equations for such systems without violating the base nonholonomic constraints. Combining the kinematic model with the initial dynamic equations and eliminating Lagrange multiplier with natural orthogonal complement technique lead to the comprehensive dynamic model. The variables of this model include the path of a reference point of the base and the position and orientation of the end-effector. The proposed approach will be applied on a car-like platform and a manipulator with 5 degrees-of freedom. The calculations for deriving such a model will be implemented by a program in Maple which can be used for control design and simulation purposes. The validity of the methodology is demonstrated using a second model and comparing the elements of these two models with each other. With trajectory generation for platform and manipulator generalized coordinates separately, set points for control system design will be provided. Motion generation for the platform, which due to the nonholonomic constraint has more sensitivity, will be dealt with by two motion modes. Inverting the model in terms of joint space variables, strict control of the work space variables is accomplished. Introducing state space variables and inverting the system into first order equations, the necessary preliminaries for control system design will be provided. Based on two simulation programs in Matlab, two controllers are designed with model-based algorithm (MBA) and Transposed Jacobian (TJ) control. Simulating different external conditions such as parameter perturbation, disturbances and noise, the robotic system behavior in the vicinity of real conditions will be examined. The results obtained show the merits of the TJ algorithm in controlling highly nonlinear and complex systems with multiple degrees- of freedom (DOF), without requiring a priori knowledge of plant dynamics, and with reduced computational burden which motivates further work on this algorithm

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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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Control of a class of uncertain nonlinear systems, which estimates unavailable state variables, is considered. A new approach for robust tracking control problem of satellite for large rotational maneuvers is presented in this paper. The features of this approach include a strong algorithm to estimate attitude, based on discrete extended Kalman filter combined with a continuous extended Kalman filter and attitude nonlinear model, and a robust controller based on sliding-mode with perturbation estimation. Estimation accuracy in this method is five times higher than other recent approaches based on Kalman filter. We have used sliding-mode controller in this paper. Not only the controller and the corresponding observer but also their composition must be robust. To make this controller robust against the uncertainty of parameters, the robust Kalman filter is used. Based on interval algebra, an upper bound and a lower bound are estimated for state variables of the system and considering these bounds in indicating the sliding conditions, stability of the controller in combination with the observer will be satisfied simultaneously. The simulation results show the capability of this method in spite of different uncertainty levels (up to %50).

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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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A novel version of Ant Colony Optimization (ACO) algorithms for solving continuous space problems is presented in this paper. The basic structure and concepts of the originally reported ACO are preserved and adaptation of the algorithm to the case of continuous space is implemented within the general framework. The stigmergic communication is simulated through considering certain direction vectors which are memorized. These vectors are normalized gradient vectors that are calculated using the values of the evaluation function and the corresponding values of object variables. The proposed Gradient-based Continuous Ant Colony Optimization (GCACO) method is applied to several benchmark problems and the results are compared and contrasted with other population-based algorithms such as Evolutionary Strategies (ES), Evolutionary Programming (EP), and Genetic Algorithms (GA). The results obtained from GCACO compare satisfactorily with those of other algorithms and in some cases are superior in terms of accuracy and computational demand.

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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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To assess the performance criteria of the reinforced-concrete, five-storey residential buildings common in Iran, an experimental study in the structural laboratory of the University of Tehran has been conducted. The test program includes cyclic and monotonic load tests of six beams that represent three-to-five storey buildings with rigid frame structures. Using definitions given in FEMA-356 and ATC-40, stages of immediate occupancy, life safety, and collapse prevention have been identified on the drift- force curves of all specimens. Based on the test results, values of the plastic rotation, ductility, strain in concrete cover and in longitudinal bar, crack width, damage index, and length of plastic region at different levels have been determined. It was found that the recommended values of plastic rotation and ductility for reinforced concrete beams by FEMA-356 are conservative. The length of plastic hinge region in the stage of immediate occupancy is about half the plastic hinge length in the stage of life safety and it increases by 20% from life safety to collapse prevention

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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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In this paper, an analytical model based on Modified Slab Method is presented for rolling of clad sheet or double-layers in which the two layers are bounded prior to rolling. This model considers the general case of asymmetrical rolling due to unequal surface speed, different contact friction, roll diameters, flow stress, and thickness ratios of the two layers. Using this model, rolling parameters such as pressure distribution along the arc of contact of the rolls and the clad sheet, rolling force, and torque with respect to reduction in thickness can be easily calculated. The analytical rolling force and torque computed by the proposed model were compared with the analytical results of other researchers and were shown to be in good agreement. The proposed model is very suitable for online control application due to its completeness and its capability of predicting the rolling parameters

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There is a demand for reduced power consumption in the vapor compression refrigeration cycle. Coefficient of performance of window-air conditioners considerably decreases and power consumption increases under very hot conditions. These problems have encouragecl studies aimed at improving the performance of window-air-conditioners by enhancing the heat transfer rate in the condenser. In this article, a new design for application of evaporative cooling in the condenser of window-air conditioners is introduced and experimentally investigated. In this design, two pads equipped with a water injection system are located on both sides of the air-conditioner to cool down the air flow passing over the condenser. The experimental results showed that thermodynamic characteristics of the system considerably improved while power consumption decreased by about 15% and the coefficient of performance increased by about 55%.

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In this study, two CCCT diagrams are drawn to be compared with a CCT diagram. The CCCT diagrams represent continuous cooling transformations in stress assisted state. The increased Md and Bd temperatures of CCCT diagrams were also compared with those of the CCT diagrams and the cause was investigated from both thermodynamic and metallurgical viewpoints. Thermodynamic examinations revealed that stress causes the mechanical driving force to increase but the total free energy of transformation to decrease hence, Md and Bd will rise. Metallurgical investigations showed that if deformation temperatures are selected in a manner to increase the structural strength of the original austenite grains prior to deformation, the shear force required for martensite and bainite transformations will arduously obtain hence, Md and Bd will fall. However, if recrystallization or full recovery occurs during or after deformation, interior grain structure softens and the shear force required for martensite and bainite transformations will readily obtain hence, Md and Bd will rise. It was also found that the nose in CCCT curves are shifted to the left as compared to that of CCT curves. This indicates that deformation of steel enhances bainite formation more readily than that of the martensite phase.