فهرست مطالب

  • Volume:33 Issue: 3, 2020
  • تاریخ انتشار: 1399/01/06
  • تعداد عناوین: 15
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  • S. M. M Salehi *, A. A. Pouyan Pages 366-376
    In network analysis, a community is typically considered of as a group of nodes with a great density of edges among themselves and a low density of edges relative to other network parts. Detecting a community structure is important in any network analysis task, especially for revealing patterns between specified nodes. There is a variety of approaches presented in the literature for overlapping and disjoint detection of community in networks. In recent years, many researchers have concentrated on feature learning and network embedding methods for node clustering. These methods map the network into a lower-dimensional representation space. We propose a model in this research for learning graph representation using deep neural networks. In this method, a nonlinear embedding of the original graph is fed to stacked auto-encoders for learning the model. Then an overlapping clustering algorithm is performed to obtain overlapping communities. The effectiveness of the proposed model is investigated by conducting experiments on standard benchmarks and real-world datasets of varying sizes. Empirical results exhibit that the presented method outperforms some popular community detection methods.
    Keywords: community detection, Overlapping Communities, Deep Learning, Social Networks, Graph embedding
  • R. Barzegar Nozari, H. Koohi *, E. Mahmodi Pages 377-386
    Today, the trust has turned into one of the most beneficial solutions to improve recommender systems, especially in the collaborative filtering method. However, trust statements suffer from a number of shortcomings, including the trust statements sparsity, users' inability to express explicit trust for other users in most of the existing applications, etc. Thus to overcome these problems, this work presents a method for computing implicit trust based on user ratings, in which four influential factors including Similarity, Confidence, Analogous Opinion, and Distance are utilized to achieve trust. For computing users’ similarity, the Pearson Correlation Coefficient measure was applied. Confidence was computed through users’ common in items rated. To compute users’ analogous opinions, what rating they have given to items was analyzed in three aspects of their satisfaction, dissatisfaction, and indifference about the items. Euclidean distance was employed on users’ ratings for computing the distance. Finally, the factors were combined to reach implicit trust. Moreover, fuzzy c-means clustering was applied to initially partition similar users for enhancing the performance positively. Finally, two MovieLens datasets of 100K and 1M have used to evaluate this approach, and results have shown that the approach significantly increases Accuracy, Precision, and Recall, compared to some other methods.
    Keywords: Recommender systems, collaborative filtering, Implicite Trust, Fuzzy C-Means
  • S. R. Sabbagh Yazdi, H. Najar Nobari * Pages 387-400

    This paper introduces a computational strategy to collaboratively develop the Galerkin Finite Volume Method (GFVM) as one of the most straightforward and efficient explicit numerical methods to solve structural problems encountering material nonlinearity in a small limited area, while the remainder of the domain represents a linear elastic behavior. In this regard, the Element Free Galerkin method (EFG), which is remarkably robust and accurate, but presumably more expensive, has locally been employed as a nonlinear sub-model to cover the shortcomings of the GFVM in the elastoplastic analysis. Since the formulations of these two methods are fundamentally different, the iterative zonal coupling has been accomplished using overlapping Multi-Grid (MG) patches with a non-matching interface and Iterative Global/Local (IGL) approach. The main property of such an algorithm is its non-intrusiveness, which means the complex nonlinear EFG solver is locally utilized over an elastic global GFVM without any geometric modification. This method is verified and investigated with available analytical and numerical solutions which gave quiet promising results showing the robustness and accuracy of the method. The Moving Least-Square approximation (MLS) has widely been applied on transfer level due to the non-conforming interface at the patch edges, and easily allows us to attach complex geometries with different mesh patterns. The new type of Quasi-Newtonian accelerator is adopted on the global material constitutive matrices and its convergence property and accuracy is compared with dynamic Aitken accelerators for two-dimensional problems in MATLAB. Finally, various accelerator types and mapping strategies are also concerned in the examination.

    Keywords: Iterative Global, Local Method, Matrix-Free Galerkin Finite Volume Method, Non-Intrusive Coupling, Nonlinear Element-Free Galerkin, Overlapping Multi-Grid Patch
  • A. Ghannadiasl *, H. Rezaei Dolaghb Pages 401-409
    Railway structures are one of the most important structures in transportation. So the lack of precise study of their dynamic behavior leads to irreparable damages. The significant factors contributing to the accurate analysis of the dynamic behavior of railways are the type of load and foundation used in it. In this study, an Euler-Bernoulli beam subjected to a moving load on a finite depth foundation is presumed. According to the feature of finite beams, just the dynamic equilibrium in the vertical direction is regarded. In this paper, by using equilibrium equations and considering the influence of soil and structure interaction, the physical problem is simulated and by using Fourier transform method the governing differential equations are obtained. Then, the mathematical model based on suggested models is expanded and verified. By assessing the efficiency of the recommended method, dynamic behavior of beam is specified and the deflection ratios for various foundations are illustrated. The sensitivity analysis is provided to study the influence of various parameters such as velocity of moving load, elastic foundation depth and damping. Eventually, by considering the sequences of shear waves, critical velocity, which is dependent on the mass ratio, and various kinds of damping, deflection shapes of the beam are attained for the different velocities of the moving load, and the effect of soil depth on the dynamic behavior of the beam is discussed. It is indicated that, foundation inertia leads to a considerable reduction in critical velocity and can also intensify the response of the beam.
    Keywords: Euler-Bernoulli beam, Moving load, Railway structure, Soil depth
  • H. Jahangir, M. Bagheri * Pages 410-418
    Shape memory alloys (SMAs) are unique smart materials that have many advantages, such as ability to resist large strains without leaving residual strains and ability to recover original form. However, the high costs of SMAs have limited their usage. This paper evaluates the behavior of concrete structures equipped with SMAs in an optimal manner as they are being used along the plastic hinge of the beams. For this purpose, a reinforced concrete (RC) beam, a 2D RC frame and a 3D RC building are considered, which were tested in previous studies under cyclic loading and on a shaking table. After verifying RC beam in the Seismostruct software, the steel rebars are replaced by SMAs in all connections of models and time history analysis is performed. The seismic response of concrete structures equipped with SMAs is compared with the conventional RC structures. The maximum base shear and roof displacement, amount of residual displacement and distribution of interstory drift at the structure height are among the factors to be evaluated. The results show that, due to the use of SMAs in concrete structures, the maximum base shear does not significantly change compared with the conventional RC structures, and the residual displacements in the structure roof have been reduced. On the other hand, the maximum displacement of the roof was increased in the structures with SMAs. The concrete structures equipped with SMAs experience a slight residual deformation, and the distribution of interstory drift is even more uniform at the height of such structures.
    Keywords: Maintenance costs, plastic hinge length, Reinforced Concrete Structures, Shape memory alloys, time history analysis
  • B. Rezayibana * Pages 419-426
    Random vibration analysis of tall structures faces multiple problems due to the large number of elements and high degrees of freedom; that is why this type of analysis is mostly used in simple structures and low degrees of freedom. In the past two decades, changes have been occurred in this type of analysis to be used in complex structures and the large number of elements. Pseudo-Excitation Method (PEM) presents a simple formulation for reducing the volume of operations. In this paper, a tall telecommunication tower is fully modeled as an example of such towers; it is analyzed by random vibration analysis with the help of the above method. Different conditions of the soil under the tower and different damping are used in modeling and analysis. The results show that structure response is strongly influenced by the soil conditions. In addition, higher modes have significant effects on the telecommunication tower response
    Keywords: Telecommunication Tower, damping, Random vibration, Pseudo-excitation Method, Soil
  • M. Farzinfar*, M. Shafiee, M. Amirahmadi, A. Kia Pages 427-438

    The integration of Distributed Energy Resources (DER) in the distribution network has plenty of advantages if their allocation and Penetration Level (PL) are done appropriately. Hence, the challenge of finding the best allocation and PL of DERs in large distribution networks is an important but intricate problem. This paper proposes a novel methodology to simultaneously determine the optimal location/capacity and PL of DERs based on both power losses and voltage deviation minimization, while constraints of voltage profile of feeders under light loading and short circuit capability of the CBs are met. Moreover, a Multi-Objective Mutation based PSO (MOMPSO) is presented that by introducing two modifications of dynamic inertia weight and utilizing a mutation operator improves exploration and exploitation searchability as well as convergence capability of the PSO algorithm. The proposed methodology is tested on a practical distribution network to evaluate its effectiveness in finding optimal location and capacity of DERs along with the feeders.

    Keywords: Distributed energy resources, Optimal allocation, Power Loss, Voltage Deviation, Short Circuit Current, Modified PSO
  • N. Rasouli, M. R. Amin Naseri *, I. Nakhai Kamalabadi, A. Hosseinzadeh Kashan Pages 439-447

    This paper deals with the coordination of pricing and order quantity decisions for two seasonal and substitutable goods in one firm. We assume that the customers are price sensitive and they are willing to buy the cheaper products, which is known as one way and customers-based price driven substitution. First, a mathematical model is developed for one firm, which contains two replaceable products considering seasonality. The model aims to maximize the profit by determining optimal dynamic prices, order quantities and the number of periods for both of the products. Then, we show that the objective function is strictly concave of price and has a unique maximum solution. Next, an exact algorithm based on the Karush Kuhn Tucker (KKT) conditions is presented to determine the optimal decisions. Finally, a numerical example accompanied by sensitivity analysis on key parameters  is developed  to illustrate the efficiency of solution procedure and the algorithm.

    Keywords: pricing, Order Quantity, Seasonal Products, substitution, Karush Kuhn Tucker Conditions
  • M. Yazdi *, M. Zandieh, H. Haleh Pages 448-458
    The ever-increasing demands for surgeries and the limited resources force hospitals to have efficient management of resources, especially the expensive ones like operating rooms (ORs). Scheduling surgeries including sequencing them, assigning resources to them and determining their start times is a complicated task for hospital managers. Surgery referrals usually include elective surgeries that are admitted before the planning horizon of the schedule and emergency surgeries that arrive during this horizon and require fast services. In this paper, we presented a mathematical model for scheduling electives and emergencies. In our model, we considered surgeries as projects with multi-activities. We implemented the Break-in-Moments (BIMs) technique in this structure, which to our best knowledge has not been implemented in the literature before. We examined this method with real data from a medium-sized Norwegian hospital and observed that this method reduces the waiting time of emergencies to be inserted into the schedule without dedicating any OR merely to emergencies. In such a way, this method counterbalances between efficient OR usage and responsiveness for emergency surgeries.
    Keywords: Break-in-Moments, Mixed-Integer Programming, Operating Room Management, Project scheduling, Surgery Scheduling Problem
  • M. Ghayoomi, M. H. Abooei *, M. A. Vahdatzad, A. Ebrahimi Pages 459-467
    Today, small and medium enterprises are considered as one of the main components of economic development for various reasons. To name a few, job creation, resource efficiency, the ability to enhance local technology, the ability to meet new needs, quick decision-making, and training successful managers will all lead to the growth and economic development of countries. Despite these benefits, small and medium enterprises face restrictions in areas such as human resources, specialist forces, and market access. To address these challenges, strategies need to be adopted to support and reinforce the enterprises. Creating a network of export consortium is one of the strategies that help providing a better access to the target market. In this study, first, we identified various dimensions in creating export consortiums and ranked them for small and medium enterprises. Second, based on the grounded theory research methodology, we proposed a model by examining the dimensions, components and categories affecting the establishment of successful export consortia. Accordingly, 26 subcategories are categorized into 6 main categories. Then, their relative importance in the success of the export consortia is determined by identifying the weights of each category and using the Hierarchical Analysis Method (AHP).
    Keywords: Export Consortia, Industrial cluster, Small, Medium Enterprises, Analytic Hierarchy Process, Grounded theory
  • M. Delkhosh, M. Saadat Foumani *, N. Lashgarian Azad Pages 468-476
    Power management strategies play a key role in the design process of hybrid electric vehicles. Electric Assist Control Strategy (EACS) is one of the popular power management strategies for hybrid electric vehicles (HEVs). The present investigation proposes a new framework to advance the EACS. Dynamic Programming method is applied to an HEV model in several drive cycles, and as a result, some optimal operating regions are found. The obtained regions are almost distinct, and consequently, some threshold lines can be defined to separate them. The obtained threshold lines are used to eliminate some parameters of the EACS to reduce its sensitivity to the driving behavior. It is shown that by applying the mentioned modification, the sensitivity of the EACS decreases without a significant increase in the HEV’s FC. All in all, our findings indicate the effectiveness of the proposed methodology to improve the EACS strategy for HEV supervisory control applications.
    Keywords: Hybrid Electric Vehicle, Control Strategy, Dynamic programming, Electric Assist Control Strategy, Sensitivity, Driving Cycle, Fuel consumption
  • Soheila Saleh Mirhasani, S. Jafarmadar *, S. Khalilarya, A. Chitsaz Pages 477-485
    In the present study, thermo-economic analysis of a combined solid oxide fuel cell (SOFC) with a gas turbine, a generator-absorber heat exchanger (GAX) and heating process heat exchanger for heating, cooling and power production as a tri-generation system is conducted. Also, an external steam reformer is applied to convert methanol as oxygenated fuel to hydrogen for the electrochemical process of the SOFC. The influence of the primary design parameters (anode inlet temperature and current density) on several variables (energy and exergy efficiencies, exergy destruction, SUCP and unit costs of the products) are examined. Results showed that energy efficiency of proposed system was 55% higher than standalone SOFC. It was found that the maximum exergy destructions occurred in fuel and water mixer, after burner and SOFC. Unit cost of cooling was higher than the other products in the proposed system. It was equal to $220.3/GJ  at a specific condition, while unit cost of power and heating were $34.22/GJ and $1.24/GJ, respectively. That was because cooling system needed more components than other systems.
    Keywords: solid oxide fuel cell, Methanol Fuel, Tri-Generation, External Reforming, Exergoeconomic Analysis, Efficiency
  • F. Jafarian *, E. Mohseni, O. Kalantari Pages 486-493
    Surface integrity of workpieces after machining processes is one of the most essential requirements of engineers in advanced industries, since it has significant effect on performance and service life of the components. Based on this, thermal and mechanical loads generated by machining are responsible for change in mechanical properties of the machined workpiece and consequently, they should be controlled. Among them, Ti-6Al-4V is utilized extensively by engineers because of its excellent properties. Therefore, at the present study, extensive experiments were conducted to characterize the performance of machining operation regarding the surface integrity of Ti-6Al-4V super alloy. Hence, the effect of experimental conditions on microhardness profile, surface roughness, grain size, and maximum machining temperature was studied. The results indicated that, cutting speed is a predominant parameter for enhancement of surface microhardness and increase in feed rate has the striking influence on thermal loads enhancement. The results also demonstrated that, increasing depth of cut has the lower influence on grain size variation.
    Keywords: Titanium, surface integrity, machining, microhardness, Grain Size, Roughness
  • H. Yazdi, R. Shafaghat *, R. Alamian Pages 494-504

    Ocean wave is one of the renewable energy resources that these days various devices are used to extract its energy. Oscillating Water Column (OWC) installed on the shore is one of the wave energy absorption systems which has received attention due to its simple structure. Investigation of the pneumatic power is of great importance in such systems as the conversion of wave energy to pneumatic energy is the first step in OWCs’ energy conversion cycle. This study aims to assess the power available in a fixed onshore OWC plant according to the wave characteristics of the Oman Sea on the shores of Chabahar. For this purpose, a small-scale model of OWC was tested in the wave tank, and its pneumatic power was evaluated. In these experiments, the effects of various parameters including incident wave height and frequency, the front wall draft and the orifice diameter on the pneumatic power were investigated. The results show that increasing the wave height generally increases the pneumatic power; however, variations of power with the draft depends on the incident wave frequencies. The maximum achieved capture performance and maximum generated pneumatic power of the model are 18% and 0.7 watts, respectively.

    Keywords: Oscillating Water Column, wave energy, Pneumatic Power, Experimental Optimization, Draft Height
  • J. Zamani, M. A. Samimi, F. Sardarzadeh *, M. H. Ghezelayagh Pages 505-512
    This paper introduces an optical measurement system for shock wave characteristics. The system works by mountinga metal plate attached to spring mounts against the shock wavefront. This set is sealed and can plot the shock wave pressure diagram by measuring plate's displacement, radiation and changing the reflection of light during shock wave conflict, and converting these optical data to voltage. In the experiments with the optical system, there was no delay time in the wave impact response. Using the optical system and the fixture designed and built, it is also possible to measure the velocity of moving objects and monitor the planar shock wave formation in addition to the shock wave velocity. Then the calibration was performed with the help of a standard piezoresistive sensor in a cold diaphragm shock tube, with a pressure of 5.5 to 12.5 bar by performing 12 tests. Relations and figures for output voltage and shock pressure are also explained.
    Keywords: Optic Sensor, Shock Wave, Piezoresistive Sensor, Shock Tube Calibration