فصلنامه مدل سازی در مهندسی
پیاپی 55 (زمستان 1397)

The project planning and control process is a complex task, including initial planning based on estimates and available resources, measuring progress and evaluating current programs, and undertaking corrective actions after the disruption. Disruptions in projects often occur due to the occurrence of random changes during the execution of activities. In this research, a model is developed to monitor the performance status of the critical and non-critical chains of the project in terms of buffer consumption index and also the calculation of the schedule performance index. Corrective action is required if warning signals predict possible future delays. The superiority of the method for determining the proposed precautionary reserve compared to the current and most commonly used critical chain methods for managing the project is illustrated by numerical examples and a case study. One of these advantages can be improved scheduling reliability through better allocation of buffer times and a decrease in the mean and variance of completion time delays for the output of the proposed method compared to other commonly used critical chain approaches. A robust project control model is based on integrating time management (critical chain) management and indicators of value management approach. The amount of precautionary consumption in critical and non-hazardous chains was investigated and analyzed. The results of the project management based on time-saving management showed that non-hazardous project chains also exacerbate the likelihood of delays if their precautionary consumption levels are at critical points.

Study of vapor - liquid and liquid – liquid Equilibrium plays an important role in the design, optimization and control of separation processes. In this research phase equilibrium of binary systems (1-propanol, water and 1-propanol, ethyl acetate) also ternary systems (water, ethylene glycol, 2-ethyl 1- hexanol and water, ethylene glycol, 1- heptanol) using thermodynamic models of NRTL and UNIQUAC were studied. Also Adaptive Nero-Fuzzy Inference System (ANFIS) and group method of Data handling (GMDH-type neural network) were used for modeling of systems. The VLE graphs (temperature based on mole fraction of vapor-liquid phases) for binary systems and LLE graphs for ternary systems at various temperatures by thermodynamics models were drawn. Accuracy of thermodynamic models, ANFIS model and GMDH type-Neural Network for the binary and ternary systems studied and compared with experimental data. Comparison of results shows that NRTL models have good fitness with the experimental data and the minimum error is related to the ANFIS Statistical model.

The capacity loss of lithium ion batteries during charge/discharge cycles is one of the important parameters in the evaluation of these kind of batteries, so that battery lifetime is defined as the number of charge/discharge cycles until the battery capacity reaches to 70% of its initial capacity. Therefore, it is important to have a simple mathematical model which can easily predict capacity loss of lithium ion batteries with acceptable accuracy. In this study, capacity loss were measured experimentally for first 10 cycles of Samsung commercial lithium ion battery at three temperatures of 25, 35 and 45oC. Further, a semi empirical model has been introduced including power law concept for temperature and the square root of cycle number to predict the lithium-ion battery lifetime or capacity loss. The parameters of the model have been obtained based on square of error of the prediction of experimental capacity using Levenberg -Marquardt algorithm. Using this model, maximum charge/discharge cycle of the battry is calculated acceptably with less than 15% of error.

The Persian Gulf and its coastal areas are considered to be the largest source of crude oil in the world. On the other hand, the waste heat from the refining and petrochemical industries located around the Persian Gulf region can be used based on simple feed conditions for membrane distillation. Therefore, in order to improve the performance of this system in the desalination of Persian Gulf water and increase the flux of output, the mass and heat transfer model is simultaneously introduced into a membrane distillation system and validated with experimental data. The effect of different operating conditions such as feed temperature, vacuum pressure on the permeate side, feed concentration and heat transfer coefficient on the flux permeated have been investigated. Also, the effect of feed temperature on the temperature polarization phenomenon has been studied. The results showed that permeate flux increased with increasing feed temperature and heat transfer coefficient and decreased with increasing vacuum pressure and feed concentration. It was also found that the temperature increase would have an adverse effect on the phenomenon of temperature polarization.

In the present study, a numerical model has been utilized to investigate the effects of operating parameters on the performance of a proton exchange membrane fuel cell in co-current and countercurrent patterns. The model considers the three-dimensional governing equations involve continuity, momentum, mass, electrode kinetics and potential fields across the channel of fuel cell. The coupled equations of the proposed model are then solved using the finite element method. The simulation results were validated with previous reported experimental data. In the results obtained from the model, the effect of variables such as temperature, pressure and length of channel on the current density of electrodes and the amount of waste hydrogen have been studied. It was found that at constant voltage, increasing the temperature from 60 to 90°C, raises the current density by 19.4%. At similar conditions, an increase in pressure from 1 to 5 atm, improves the fuel cell current density by 26.9%. In addition, with voltage drop across the channel, hydrogen consumption increases.

Data Envelopment Analysis (DEA) is a powerful tool to evaluate the performance of decision-making units. Some of decision- making units consist of several parts or stages that make a network of sub-processes. Data Envelopment Analysis (DEA) is used to evaluate such type of units. Two different types of inputs (variable and quasi-constant inputs) are considered based on the framework of Network Data Envelopment Analysis. One of the characteristics of the quasi-consist input is that it is considered as the output of current stage, while it will be used as the input of the next stage. The network DEA can measure the independence between the two stages. The present study investigates its cost efficiency and returns to scale (RTS) as a two-stage process. Cost efficiency can use inputs, as well as their cost and values in order to calculate the efficiency. We investigate the cost efficiency of the stages and whole process, and we also determine returns to scale. One of the advantages of the models is the reduction of computational time. Green Supply Chain Management (GSCM) is an approach to improve environmental performance. GSCM will increase its economic and environmental performance. Hence, GSCM's assessment is very important for every company. One of the techniques which can be used to evaluate GSCM is Data Envelopment Analysis (DEA). In order to achieve our goals in this study, we use network Data Envelopment Analysis (DEA) to investigate 9 GSCM Iranian Drinking Company.

Due to high energy consumption and pollution rate caused by fossil fuels, in the world, hydrogen has been considered by many researchers as a clean fuel. Therefore, process of hydrogen separation can also be very important in this regard. Among various methods of hydrogen separation, membrane processes have been proposed as one of the promising methods for hydrogen purification. One the other hand, among several hydrogen selective membranes, inorganic membranes have also been considered more applicable owing to their high temperature tolerance. Meanwhile, in 2014, graphene membrane was first introduced for hydrogen separation, which showed a high selectivity over other inorganic membranes. Therefore, in this research, the performance of graphene membrane is evaluated using a CFD based model and the impact of important operating parameters such as pressure, temperature, membrane surface area and membrane selectivity on its performance have been investigated. According to the model results, the graphene membrane (with a 7% error) has the best performance at 293 K, while by increasing temperature up 373 K, H2 / CO2 selectivity is decreased from 2800 to 200 and permeances of hydrogen and carbon dioxide are indicated 2*10-7 mole /m2.Pa.s and 1.5*10-10 mole / m2.Pa.s, respectively. On the other hand, increasing the pressure and surface area values also show negative effects on hydrogen selectivity of graphene membranes.

One of main problems of power systems with doubly fed induction generators (DFIG)-based wind farms is their capability of fault ride through (FRT) and output power fluctuations. If these generators provide considerable amounts of power, their outage can lead to system instability. According to the new needs of network codes, wind farms should remain in the network when a fault causes the voltage drop across the generator terminals. To solve this problem, the superconducting fault current limiter (SFCL) is used for limiting the fault current and superconducting magnetic energy storage (SMES) is used for injecting/withdrawing power to reduce power fluctuations. This article carries out the coordinated control of DFIG, SFCL, and SMES by employing the HBB-BC optimization algorithm. Its objective functions include minimization of the required storage core capacity, energy reduction, improvement of generators bus voltage, fault current limiting, reducing power fluctuations, and the generators angular velocity. Simulation results show the ability of this optimal controller in achieving the above indicated objectives.

In data warehouses , some of query responses are stored to accelerate the response time of analytical queries . Materialized views are the response of queries stored in data warehouses . Materialized views should be changed according to changes in basic relations . Different view maintenance expressions have been presented for maintaining materialized views. In this paper a new algorithm is presented to produce the improved view maintenance expression . The proposed algorithm consists of two parts . In the first part , the algorithm constructs a tree to reduce the number of accesses to big data sources and in the second part an improved view maintenance expression is presented according to the constructed tree and the amount of changes in data sources . Experimental results show that the improved view maintenance expression reduces the data warehouse maintenance time and the data warehouse maintenance cost in comparison with previous methods .

In this paper an efficient method for defining multi-variable functions using expression templates for array computations in computational fluid dynamics simulations in C++ is introduced. The method is implemented using variadic templates which is a new feature in C++. One of the advantages of the method is its easy of use for users of computational fields. The user can define and use his own function with any number of input arguments without having knowledge of templates programming concepts. The present method may replace conventional expression templates in developing numerical libraries. For three different functions, including arithmetic operations and trigonometric functions, the efficiency of the proposed method for arrays of different sizes is compared with that of the conventional expression templates, two different C++ syntax and Fortran language. Furthermore, the performance of the method in terms of the compilation time and executable file size is demonstrated. A similar comparison on Graphic Processing Units (GPU) using CUDA is made and the efficiency of the method is shown. The results indicate that, for any array size, the present method has a very good performance in terms of computational time, compilation time and executable file size. Finally, as an application of the proposed method, a numerical simulation is done.

By increasing the speed of data generation, need to process, store and analyze of Big Data becomes increasing. Related work has been done to create real-time data warehouse, but according to current unstructured data in Big Data, data warehouse with the old structure, it doesn't answer new management requirements of this type of Data. Recently, Data Lake has been proposed for unstructured data (with BASE properties). However, existence of important structured data (with ACID properties) and less sensitive unstructured big data on the other hand, causing new problems in the management of Big Data by using of this methods. In this paper we will offer a solution which is able to store structured data and unstructured data simultaneously and it can response to user’s queries in real-time. As one of the important results of this research, after comparing the data warehouse and Data Lake concluded that the lake is not a replacement for a data warehouse, and data warehouse has particular use, especially in financial data; because the data warehouse compliance ACID theory, and Data Lake cater requirements of BASE theory.  The raised idea in this paper has three main advantage: 1- Simultaneous use of data warehouse and Data Lake to meet the needs of the organization data with the benefits of them. 2- Separating new data from old data to achieve real-time. 3- Development parallelism, thus synchronization loading data and query processing to reduce the cost of time.

Most Datasets related to data mining and machine learning contain data with missing values. How to deal with missing values and to provide solutions based on estimating missing values lead to a very important issue in the field of machine learning and data mining. Among data mining algorithm, the C4.5 algorithm has been used repeatedly because of performance being used in various applications and also ability in working and estimating missing values in data sets. Researchers have presented various methods for deal with missing values and estimating it’s amount in a C4.5 data sets which any of their method causes an increase in accuracy of decision tree and there for produce a more effective and efficient decision. In this paper, for estimating missing values in data sets, at the first, we review the previous methods then the proposed approach as a displacement properties method and in the end the accuracy of proposed methods for deletion and average will be comparing.

Optimal operation of hybrid energy systems has been motivated in developed countries, by decreasing operation costs and pollutions, and increasing use of renewable energy resources. This paper presents a new energy management scheme for utilization of batteries and diesel generators, to decrease operation costs and pollutions, while increase reliability simultaneously. The capacity of the system components is firstly optimized by HOMER software. Then, diesel generator capacity is optimized by particle swarm optimization (PSO) algorithm, taking into account the environmental and outage costs. In the proposed control strategy, due to the variation of power generation and power consumption in hybrid systems, different charge / discharge limits are applied for each hour of the day, instead of conventional fixed upper and lower bands for the state of charge (SOC) of battery. The results show the effectiveness of the proposed strategy on reducing the cost of power generation, the reliability and the environmental issues.

Due to difficulties in formal implementation of swarm robotic systems, controlling software of such systems is developed in an ad-hoc manner and with trial and error. So, it is hard to reuse these systems for other similar problems. Moreover, testing, analyzing and verifying the correctness of the controller are difficult too. There is no guarantee that the implementation matches the specifications. To address these problems, supervisory control theory as a formal approach is suggested. In this paper, probabilistic and timed supervisory control theory (ptSCT) is implemented on ARGoS platform in swarm robotic. The proposed approach automatically calculates ptSCT, and then generates the equivalent controlling software codes. The generated controlling software can be used for both simulation and running on real robots without any changes. For comparison purposes, two tasks namely obstacle avoidance and synchronization of robots are designed using both SCT and proposed ptSCT. The approach is successfully validated in both tasks using up to 64 E-Puck robots. The experimental results show the advantages of the ptSCT, in terms of simplicity, reusability, and automatic code generation.

In this paper, a second order sigma delta modulator is presented that is suitable for medical applications. Using the amplifier and comparator circuits with low power consumption, which are utilized in integrator and comparator, respectively, the power consumption of this modulator has significantly decreased; as one of essential requirements for medical devices. SNDR of the proposed modulator is obtained 102.44 dB which is equal to 16.72 bit implying a high accurate structure. System level analysis and circuit level simulation of the modulator are performed at Matlab and Cadence software, respectively. 180nm CMOS technology is utilized for simulation of the circuit. Comparing the proposed Sigma-Delta modulator with similar works reveals the superior performance of this proposed architecture considering the power consumption and accuracy. In order to accomplish a comprehensive comparison and achieve an overall insight into the performance of the circuit a figure of merit (FOM) is presented including modulator's total power consumption, effective number of bits and bandwidth.

The canonical correlation analysis (CCA) is one of the most widely used frequency recognition methods in steady-state visual evoked potential (SSVEP)-based brain computer interface systems. Although the CCA is often associated with good results, but if stimulation frequencies have harmonic relation, this issue will challenge this method. In this paper, the modified CCA method has been proposed that can solve this problem by adding a post-processing step in the standard CCA. For this purpose, visual stimulus ranged from 6-16 Hz with an interval of 0.5 have been generated using Matlab and the psychophysics toolbox. The SSVEP signal was recorded from ten subjects via one electrode placed at Oz. According to the proposed method, after applying CCA and determining the frequency corresponding to the maximum correlation, the difference between the correlation associated to this frequency and the correlation of the corresponding harmonic frequency is calculated. Then, the frequency is recognized by comparing the obtained value with the threshold. The threshold is determined based on the data of each subject during the offline analysis. For eight-second time window, the average recognition accuracy of the standard CCA with choosing two harmonics in constructing the reference signal (N=2) was 74%, while the corresponding value of the proposed method was 81%. Correspondingly, the accuracy was increased from 78% to 83% for four-second time window. For wide frequency range, the proposed method has been able to improve the frequency recognition accuracy compared with the standard CCA, by reducing harmonic recognition error.

The high cost and time of implementation of the bridgeworks necessitate the optimization in the structural design. The optimization can extensively reduce the used steel, reinforcement, concrete and the time of doing project. In this study the effect of design elements in optimization of a bridge have been investigated. By definition of cross section geometry, strength of material, location and number of pre-stressing cables as variable and also using Cuckoo algorithm, the best value of variables are selected and the best geometry of cross area is choice. These variables in fact are calculated based on two regulations AASHTO LRFD-2015 and standard 2002 and the results are compared. The results show that the weight minimalist and economic plan are not depended directly because of the effect of concrete, steel and pre-stressed cables and also the high strength concrete used in long bridge span. Finally, for comparison of the bridge span effect, the optimization is carried out for different lengths from 30 to 70 based on the pointed regulations in above and the results are compared

Plate elements is one of the most important parts of structures specially ships and offshores structures. Pitting corrosion is one of the most important types of deterioration of steel structures. There have been many losses of the merchant vessels due to exposure to large environmentally induced forces. Residual strength assessment of damaged structures subjected to pitting corrosion is essential. Present study investigates the ultimate strength characteristics of plate elements with pit corrosion subjected to axil compressive loads. A series of ABAQUS non-linear FEM analysis of plates with partial depth corrosion pits are carried out, changing geometrical attributes of both pits and plates, i.e., the radius and depth of pits and the slenderness of plates. Simulation results show that the volume of corrosion loss, yielded stress, the loaded dimension have a remarkable influences than the depth and radius of corrosion pits on the ultimate strength of damaged steel plate elements by pitting corrosion.

The most extensive application of raft foundations, with pile when the raft alone can be enough resistance against the incoming load, to avoid large settlements of foundation, prevents the formation of differential settlement, pile group under the raft has been used. In this study, foundation deformation, maximum, average and differential settlements of foundation in piled-raft foundations systems under static loading in sandy soil using finite element modeling to various arrangements of piles and different composite systems regarding connection of raft and piles, has been studied and analyzed. The design of a pile group is usually based on a high safety of factor for the piles and the main design criterion is the group's load capacity. Plaxis 3D foundation finite element software version 1.6 is used to model piled-raft systems. Obtained results indicates that using the connected and disconnected piles as combined leads to very appropriate combined system performance on reduction the maximum and differential settlement of raft foundation.

Human progress on prediction of the time and place of release the energy and movement of the inner layers of the earth for prevent of the disaster can be cuased by an earthquake, has been very little. So now the only practical way to deal with this natural phenomenon is the pridicting of damages and then equipping and preparing to reduce the losses and casualties of it. Generally, the purpose of this study was to assess the seismic losses of structures in Hamedan to estimate the vulnerability in order to increase safety and improve conditions .This study, using informations gathered by the Statistics and Information Technology Organization of Hamedan Municipality -like type of structures, number and size of floors, population of each regions, soil types and etc.- and is implemented with the HAZUS method and the risk analysis software ''SELENA ver 6.0". In this method, for calculating the seismic performance of structures, the demand curve of various structures with different damping effects and the response curve based on soil type are crossed together.The outputs of this research include damaged area by the type of structures, probable loss of life and damage to property inflicted by the design earthquake of Iranian Seismic Code (Standard 2800). The results of the analysis indicate that the prediction of the average damage ratio of Hamedan in areas 1, 2, 3 and 4 is 17.9, 16.1, 19.8, 14.4 percent, respectively, and the average damage ratio is 18 percent. GIS 10.2 was used for illustrate the results.

One of the most important problems of irrigation networks is damage to the concrete's canal, which resulted from uplift forces in many cases. The uplift force is created due to the lack of control of the hydrostatic pressure of groundwater on the side wall and the bottom of the canal. The aim of this study is to investigate the position and dimensions of weep hole in the floor and side walls of the concrete channel and its effect on the of reverse leakage flow, uplift forces and hydraulic gradient in different levels of groundwater. For this purpose, a concrete channel with hypothetical geometry over the permeable foundation was simulated by Seep/W software. The variables of the study included dimensions and different positions of weep hole under three different levels of groundwater.The results showed that in all dimensions of weep hole, increasing groundwater depth increase the linear reverse leakage flow rate into the concrete channel and the exist hydraulic gradient. Also, in all weep holes, increasing the diameter reduces the uplift force. If two weep holes are used, the reverse leakage flow into the canal and the uplift forces are respectively more and less than a weep hole. In other words, the placement of two weep holes at positions N=6 and 7 showed a good performance in terms of uplift forces and inverse leakage flow. If two weep holes were placed in positions N=2 and 3, it had the best performance in terms of the exist hydraulic gradient.

Increased use of groundwater resources in arid regions , thereby growing the economy, especially in agriculture , has led to a worsening trend of the aquifer. Thus, a logical and systematic framework for decision- making principles for allocating water resource limit is needed , so as to provide effective and desirable community needs and economic growth will result. This paper uses a conceptual model of the relationship between economic activity in the region of Birjand plain water sources were identified using a systematic approach and the Vensim software environment was simulated . Then, to model different policy packages under six different scenarios were considered and the amount of water volume and rate of value added in alternatives was compared . The results showed that the trend in the state of the economy ( value added) and groundwater resources will worsen. Also, if the water volume does not change and the value added is greater, Also, if the water resources volume does not change and the value added of regional increases. Should initially be invested in non-water based economic activities such as mines and non-water based industries. But it will be realized that while the primary sources of economic activities there are.

Performance prediction of the tunnel boring machine (TBM) is one of the crucial issues for estimating excavation costs and construction time of tunnel projects. TBM performance highly depends on an achieved penetration rate. The aim of this study is to develop TBM penetration rate prediction models using Response surface method (RSM) and then to compare the results obtained from various meta-heuristics optimization techniques including Differential Evolution (DE), Hybrid Harmony Search (HS-BFGS) and Grey Wolf Optimizer (GWO). To achieve this aim, the database uniaxial compressive strength (UCS), intact rock brittleness (BI), the angle between plane of weakness and TBM driven direction and distance between planes of weakness are assembled by collecting data from Queens water tunnel project. According to the results, it can be said that the proposed model is a useful and reliable means to predict TBM penetration rate provided that a suitable dataset exists. From the prediction results the squared correlation coefficient (R2) between the observed and predicted values of the proposed model was obtained 0.939, which shows a high conformity between predicted and actual penetration rate. The performance of different predictor models controlled by Mean Absolute Percentage Error (MAPE), Route Mean Square Error (RMSE), Variance Absolute Relative Error (VARE), Variance Account for (VAF) and Correlation Coefficient (CC). Response surface method based model with higher VAF and CC as well as lower MAPE, RMSE, VARE will show better performance.

One of the effective parts in providing the hard rigid connections of the beam to the column is continuity plates in the connections panel zone. The continuity plates in providing the connection hardness and its suitable operation play key role. Using continuity plates in the H columns is performable easily but in the box columns since of closing the cross section, its connection had problem. For this reason some times the flows of the steel structures prevented of using them. Installing internal continuity plates is a difficult fabrication task and also a costly procedure, and therefore researchers have tried to improve this type of connection not only by improving the connection details in the presence of internal continuity plates, but also by avoiding internal continuity plates and providing new load paths via external features. In this study to evaluate the performance of the U plates as external continuity plates of box column under cyclic loading. The results showed that in proposed connection with small dimention the plastic hing location is in the beam and stress of the column remains in the elastic limit, but proposed connection with medium and large dimention the plastic hing location is in the column. Therefor the medium and large connection strengthend whit rib plates. The rib plates in the proposed connection caused the plastic hing location is in the beam and the hysteresis curve is regular and stable.

The current research investigated parameters affecting cyclic behaviour of perforated core buckling restrained braces (PCBRB) (e.g. section thickness, materials and geometry of core holes). In the current research, modelling and numerical analysis of 8 specimens of PCBRBs were performed using ABAQUS software under cyclic load. A reference specimen with a thickness of 10 mm modelled and validated exactly based on laboratory specimen, 4 specimens by changing core thickness, 2 specimens by changing core geometry and 1 specimen by changing core material used. Results indicate that by increasing thickness, an increase will be seen in bearing capacity. Due to more hardness, the model with thickness of 15 mm bears a greater force, but for having less ductility, it has a higher resistance drop at tensile region. The model with circular holes performs the best. In comparison to models with elliptic and rectangular holes, this model buckles very later in the pressure zone and it has a higher bearing capacity and energy dissipation. The model with rectangular holes in the core has a low performance; in a way that in the pressure zone of hysteresis curve its performance does not even reach to half of the bearing capacity and ultimate strength of the model with circular core geometry. Aluminium core brace bears less force during loading in contrast to steel core brace, but this shortage is compensated for by later local buckling in the pressure zone.

This paper focuses on the study of Laminar mix convection heat transfer of water-AL2O3 and water-CuO nanofluids whit temperature and nanoparticles concentration dependent thermophyscical properties in a rectangular shallow cavity was investigated numerically. Upper movable lid of the cavity was at a lower temperature compared to the bottom wall. Simulations were performed for Grashof numbers of 104 for Richardson numbers from 0.1 to 4.5, and nanoparticle volume fraction of 0.01-0.04. The two-dimensional governing equations were discretized using a finite volume method and SIMPLE algorithm. The model prediction for very low solid volume fraction were found to be in good agreement whit earlier numerical studies for a base fluid. It is shown that under a wide range of volume fraction of nanoparticles and different Richardson number, the enhancement of heat transfer will be evaluated. The Reynolds number varies due to variation of the Richardson number. Heat transfer was elevated by increasing the concentration of nanoparticles additionally. In this paper investigated the role of nanofluid variable properties in differentially heated enclosures and found that the prediction of heat.

In order to accurately predict the cellular response, it is necessary, along with other factors, to consider the effect of the cell spreading on the substrate. Also, the core tensions, due to the cell spreading, play a crucial role in the fate of a stem cell. Therefore, the exact prediction of these tensions is of particular importance. The effect of the strain stiffening of a mesenchymal cell, in a two-dimensional model, was investigated numerically using finite element method, by exerting a time function displacement, to the cytoplasm boundary. Utilizing Schwartz-Christoffel transformation, a model for cell-spreading was proposed that can be used to achieve accurate cellular responses. Three different models are considered. In the first model, the cell is treated as a non-alive material. That is, the mechanical properties remain constant on the substrate. Two other models, the linear and exponential strain-stiffening, are active models. By comparing the results of these models with the experimental results, it was found that the assumption that the cell is inactive departs the response from the exact amount. Therefore, considering the cell’s living nature, in both linear and exponential models, leads to more similarity of the results, both the tension value and the slope of the variations, with the experimental observations. Furthermore, by increasing the amount of the cell spreading, the difference in the amount of the nucleus stress in active models with the inactive model increases, so that the predicted tension by the linear model reaches 2.3 times that predicted by the non-alive model.

In this paper, natural convection heat transfer in a closed square cavity with a hot triangular obstacle at temperature TH simulated by Finite Element Method. The top and the bottom walls are insulated while the left and the right walls are maintained at a constant temperature Tc (TH> Tc). The used method is validated against the existing numerical results and an excellent agreement between the results was found. The flow is assumed to be two-dimensional and air is chosen as a working fluid. The effect of different parameters such as Rayleigh number (Ra =103, 104, 105, 106), different position of obstacle inside cavity (H=L=0.1, 0.4, 0.7) and different angle of obstacle (θ'=00, 900, 1800, 2700) at different aspect ratio (AR =0.2, 0.4, 0.6, 0.8) on fluid flow and heat transfer inside the channel are investigated. The results showed that by increasing the Rayleigh number and increment of aspect ratio, the rate of heat transfer is increased. Also, enhancement the distance of obstacle from left and bottom walls of cavity, lead to decrement rate of heat transfer and the maximum values of mean Nusselt number are shown respectively at angles of 0, 90, 270, 180 degrees.

Annihilating of unwanted vibrations of mechanical systems is one of the necessary requirements of designers over years. This current paper investigates dynamical behavior of a clamped-clamped beam attached to a Nonlinear Energy Sink (NES) under the harmonic force with different amplitudes. The nonlinear absorber consists of a linear damper and an essentially nonlinear stiffness. The considered system is a simple model of offshore structures subjected to the external fluid flow. In order to simulate the primary system, Euler-Bernoulli beam theory has been applied. Occurrence of Strongly Modulated Responses (SMR) under sinusoidal load reflects the efficiency of the absorber. Analytical approach (complexification-averaging method) and numerical solution (Runge-Kutta method) are applied for comparison and validation of the results. The boundaries of occurrence of Saddle-node and Hopf bifurcations and relaxation oscillations are obtained. The results show that the NES damping has substantial influence on the NES performance. Furthermore, by approaching the NES location to the beam supports, the probability of occurrence of the SMR decreases and the transient responses of the system lasts longer.

Unglazed transpired solar collectors (UTCs) are solar air heating collectors that used for preheating air in ventilation systems or producing hot air for drying systems. Thermal performance of UTCs is a function of various parameters including incident solar radiation, air approach velocity, diameter and pitch of perforations. Modeling predicts the thermal performance of UTCs over a wide range of design and operating conditions. This paper presents the details of modeling for UTC using heat transfer expressions for the collector components and energy balances. The effects of key parameters on the performance of a UTC were studied by varying the approach velocity, solar radiation, diameter and pitch of perforations and finding their influence on collector thermal efficiency, heat exchange effectiveness and outlet air temperature. Results showed that the UTC thermal efficiency increases by increase in solar radiation and approach velocity, but the efficiency decreases by increasing plate hole diameters and pitch.

Time domain simulation is an essential tool for dynamic security assessment in power system stability studies. Today, computational complexity is the concern that limits online applications of time domain simulation results. This paper proposes an engineering procedure for the use of computational time domain tools for acceleration in the time of estimating voltage instability time. For this purpose, three key parameters in the computational burden which are the computational time step, the reporting time step, and the number of reporting variables are investigated and the results of estimation time are compared for different values of these parameters. The results by an average processor have been shown that implementation of proposed procedure for Nordic32 can lead to a reduction in estimation time more than ninety percent of the instability detection time compared to the real instability time. This achievement gives the operator more time to decide, select and execute appropriate remedial actions.

Given the increased consumption and energy costs, the reduction of fossil fuels and the growing concern for environmental issues and global warming, finding a way to convert energy with high efficiency and low environmental impact is essential. The purpose of this study is to model and evaluate the technical, economical and environmental aspects of the molten carbonate fuel cell compared to the conventional technology of micro turbine gas. According to the estimates made in various capacities, the fuel efficiency of the fuel cell was 23% higher than that of the micro turbine, which would reduce fuel consumption in the fuel cell. In terms of the environment, the amount of carbon dioxide produced in a fuel cell and micro turbine is 377 and 625 grams per kilowatt-hour, which represents 40% lower emissions in fuel cells. In the economic evaluation, various parameters such as carbon taxes, fuel prices and fuel cell stack costs are very influential. According to forecasts, with increasing carbon taxes in the coming years and lowering the cost of fuel cell technology, this technology can be exploited by conventional power generation technologies such as gas micro turbines.