Journal of Advanced Materials in Engineering (Esteghlal)

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Deterioration of concrete, which is mainly due to ignorance of environmental and service conditions, causes considerable costs for the construction industry. With this in mind, in this paper, results of investigation into the major causes of concrete deterioration in the Urumie Lake are presented. For the purposes of this investigation, samples were obtained by mixing two types of cement (OPC types 1&2), micro silica, anti oxide, water proof and air entraining agent, with different w/c ratios and tested at the ages of 7,14, and 28 days. In addition to compression strength, tensile strength of the samples was measured. Regarding the durability studies, abrasion resistance, electrical resistivity, chloride penetration, water absorption and freeze-thaw tests were carried out under both laboratory and real conditions in the Urumieh lake. Based on our findings recommendations are made about optimum w/c ratio, most suitable types of cement, optimum percentage of micro silica content, and additive .

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Considering the vulnerability of double-layer grid space structures to progressive collapse phenomenon, it is necessary to pay special attention to this phenomenon in the design process. Alternate path method is one of the most appropriate and accepted methods for progressive collapse resistant design of structures. Alternate Path Method permits local failure to occur but provides alternate paths around the damaged area so that the structure is able to absorb the applied loads without overall collapse. Following the sudden initial local failure event, severe dynamic effects may arise which should be taken into account in determining the realistic collapse behavior of the structure. In this paper, a new methodology based on alternate path method is presented to apply dynamic effects of initial local failure. The method is called nonlinear dynamic alternate path method. Due to its capability to take account of dynamic nature of the failure, this method can be used to evaluate realistic collapse behavior of the structure and to investigate the vulnerability of the structure to progressive collapse phenomenon.

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An approximate numerical mthod is presented for analysis and determination of modal characteristics in straight, pretwisted non-unifom helicopter blades. The analysis considers the coupled flapwise bending (out of plane), chordwise bending (in plane), and torsion vibration of both rotating and non-rotating blades. The proposed method is based on the integral expansion of Green functions (structural influence functions) to develop the equations of motion for a clamped-free blade. Several examples are presented in various states such as flapwise bending, coupled bending-bending, coupled bending-torsion, and coupled bending-bending-torsion vibration analysis. The results obtained were compared with available numerical results in the literature. A modal testing and modal analysis were also carried out on a typical helicopter blade in static condition and the results were compared with the numerical ones. The results indicate that the proposed method is fast and robust and can be used for modeling of turbomachine blades, aircraft propellers and helicopter rotor blades.

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Design of a natural dry cooling tower has been accomplished in two sections: the design of heat exchangers and the numerical solution of flow through the tower. Heat exchanger (Heller type) has been simulated thermodynamically and then coupled with a computer program, which calculated the turbulent natural convection flow through the tower. The computer program developed for this purpose can be used to obtain thermodynamic propertied of the cooling tower such as mass flow rate of air, temperature of outlet water, distribution of temperature, distribution of velocity, and distribution of pressure through the tower. Numerical results have been compared with experimental data of Shahid Montazery Thermal Power Plant under different environmental conditions. Comparison between numerical results and experimental data showed good agreement.

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In this article, turbulent flow heat transfer in the air gap between rotor and stator of a generator under nonhomogeneous heat flux is studied experimentally. The rotor consists of four symmetrical triangular grooves. The stator surface is smooth and does not include any grooves. The relative heat flux between the rotor and the stator is 1 to 3. Temperature and heat flux are measured locally at three axial and two angular positions of inner and outer surface. The pressure drop of air flow through the air gap is also measured. In this work, the axial Reynolds number and rotational velocity of the rotor ranges are 4000

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The optimal path planning of cooperative manipulators is studied in the present research. Optimal Control Theory is employed to calculate the optimal path of each joint choosing an appropriate index of the system to be minimized and taking the kinematics equations as the constraints. The formulation has been derived using Pontryagin Minimum Principle and results in a Two Point Boundary Value Problem, (TPBVP). The problem is solved for a cooperative manipulator system consisting of two 3-DOF serial robots.

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An intensive experimental investigation was conducted to study the effect of vertical tail, single and twin (with different cant angles) on the flow field and the corresponding aerodynamic forces and moments of a model of a fighter A/C. Aerodynamic forces under different flight conditions and different vertical tail settings were measured in a supersonic wind tunnel. Furthermore, effects of vertical tail on the model wake at subsonic speed were investigated. In addition to the force and pressure measurements, schlieren system was used to visualize the shock formation and movement oat various locations on the model. The results show existence of a pair of symmetric vortices for the model equipped with a 22 degree vertical tail cant angle. The vortices burst symmetrically at moderate angle of attack. The drag coefficient increases with increasing cant angle at low to moderate alpha and decreases when alpha is further increased.

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In this paper, properties of slab deformation in sizing press mill as one of the slab reduction processes in hot rolling mills have been evaluated using the elastoviscoplastic finite element method with explicit formulation. Effect of prarameters such as initial slab width and thickness, reduction, feed pitch, and anvil speed on factors such as dogbone formation, head and tail fishtail profile, width necking at the leading end of slab, and slab edge quality have been studied. Furthermore, a comparison has been made between the two common width reduction methods, i.e. Vertical Rolling (Edging) and sizing Press, in order to determine their differences and the efficiency of each process. The amount of width return (back spread), one of the most important factors related to width reduction efficiency and also slab formation after the first horizontal rolling pass, has been evaluated. Also, in order to validate the applied finite element method, the results obtained have been compared with experimental ones found in the literature. The results show that deformation in sizing press is more favourable and that its efficiency is better than that of the vertical rolling mill.

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The aim of this research is to design a controlling loop that eliminates the irregularities in yarn tension during the winding process. In order to achieve this, we employed a relative feedback industrial control system. The yarn tension sensor measures the tension. Its output is analyzed in the automatic controlling unit. This unit adjusts the tension level according to feedback signals, thus adjusting the yarn tension to the desired value. The yarn package wound using this system will additionally experience the least yarn tension variations.

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In this paper, two suboptimum detectors are proposed for coherent radar signal detection in K-distributed clutter. Assuming certain values for several initial moments of clutter amplitude, the characteristic function of the clutter amplitude is approximated by a limited series. Using the Pade approximation, it is then converted to a rational fraction. Thus, the pdf of the clutter amplitude is obtained as a sum of simple exponential functions. Using such a pdf, we develop the suboptimum detectors PGLR and PAALR, which are simplified forms of the GLR and AALR. Computer simulations show that the suggested detectors have appropriate performance compared to OLD, GLR and AALR detectors.

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Forecasting models have wide applications in decision making. In the real world, rapid changes normally take place in different areas, specifically in financial markets. Collecting the required data is a main problem for forecasters in such unstable environments. Forecasting methods such as Auto Regressive Integrated Moving Average (ARIMA) models and also Artificial Neural Networks (ANNs) need large amounts of historical data. Although fuzzy forecasting models such as fuzzy regression are suitable metods when the data available is scant, their performance is not satisfactory at times. In this paper, a new Fuzzy Auto Regressive Integrated Moving Average (FARIMA) is presented. The proposed model can be run with less data, so it is more suitable than other models for cases where there are limited data available. The results obtained on exchange rate forecasting reveal the efficiency of the proposed model.

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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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This paper presents a nonlinear mixed-integer programming model to minimize the stoppage cost of mixed-model assembly lines. Nowadays, most manufacturing firms employ this type of line due to the increasing varieties of products in their attempts to quickly respond to diversified customer demands. Advancement of new technologies, competitiveness, diversification of products, and large customer demand have encouraged practitioners to use different methods of improving production lines. Minimizing line stoppage is regarded as a main factor in determining the sequence of processing products. Line stoppage results in idleness of operators and machines, reduced throughput, increased overhead costs, and decreased overall productivity. Due to the complexity of the model proposed, which belongs to a class of NP-hard problems, a meta-heuristic method based on a genetic algorithm (GA) is proposed to obtain near-optimal solutions in reasonable time, especially for large-scale problems. To show the efficiency of the proposed GA, the computational results are compared with those obtained by the Lingo software.

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In this paper, an elastoplastic constitutive model is presented for predicting sandy soil behavior under monotonic and cyclic loadings. The model is based on the CJS3 model that takes into account deviatoric and isotropic mechanisms of plasticity. The flow rule in deviatoric mechanism is non-associated and a kinematic hardening law controls the evolution of the yield surface. In the present study, the critical state surface and history surface separating the virgin and cyclic states in the stress space are defined. Hardening modulus and stress-dilatancy law for monotonic and cyclic loadings are effectively modified. Taking the hardening modulus as a function of deviatoric and volumetric plastic strain, the model will be capable of predicting sand behavior once the history surface and stress reversal are defined. All model parameters have clear physical meanings and can be determined simply from laboratory tests. The results of homogeneous tests on Hostun sand are used to validate the model. The results of validation indicate the capability of the proposed model.

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In this paper, the boundary-based estimation of pressure distribution in the cardiovascular system is investigated using two dimensional flow images. The conventional methods of non-invasive estimation of pressure distribution in the cardiovascular flow domain use the differential form of governing equations. This study evaluates the advantages of using the integral form of the equations in these calculations. The concepts provided with the Boundary Element Method (BEM) together with the boundary-based image segmentation tools are used to develop a fast calculation method. Boundary-based segmentation provides BEM with domain pixel extraction, boundary meshing, wall normal vector calculation, and accurate calculation of boundary element length. The integral form of the governing equations are reviewed in detail and the analytic value of integral constants at singular points are provided. The pressure data on boundary nodes are calculated to obtain the pressure data at every point in the domain. Therefore, the calculation of domain pressure could be considered as a post-processing procedure, which is an advantage of this approach. Both the differential and integral-based formulations are evaluated using mathematical Couette test flow image whose pressure domain is available. The resulting pressure distributions from both methods will be compared. According to the results obtained from this study, the use of BEM for estimating pressure values from a non-invasive flow image has the following advantages: reduced computational domain from two to one dimension, flexible calculation of pressure data at arbitrary points or at finer spatial resolutions, robustness against noise, less concern for its stability and compatibility, accuracy, and lower meshing attempts.

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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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Supply chain coordination has become a critical success factor for supply chain management (SCM). In the past few years, the researchers have widely emphasized that cooperation among supply chain (SC) firms is a key source of competitive advantage. This paper is focused on supply chain coordination from the perspective of inventory management. Li and Liu [1] developed a model for illustrating how to use quantity discount policy by price adjustment mechanism to achieve supply chain coordination. We extend this mechanism to three echelon supply chain and consider variable lead time which has more representation of the real world situation. For this purpose, we will develop a model with benefit objective function for the problem. We will then analyze the model with and without coordination. By solving the proposed model, proper order quantities will be obtained. Finally, the advantages of the proposed mechanism will be explored and a surplus benefit dividing method will be designed.