Modeling in Engineering
Year:2017 | Volume:15 | Issue:49 |Papers Count:24

The buoyancy-driven fluid flow and heat transfer in a square cavity with partially active side walls filled The buoyancy-driven fluid flow and heat transfer in a square cavity with partially active side walls filled which the length is equal to half of height and width is 0.1 of height respectively so that it contains Al_2 O_3 a water nanofluid which variable properties, has been investigated numerically. The active parts of the left and the right side walls of the cavity are maintained at temperatures Th and Tc , respectively, with Th>Tc . The enclosureas top and bottom walls as well as the inactive parts of its side walls are kept insulated. The governing equations in the two-dimensional space are discretized using the control volume method. A proper upwinding scheme is employed to obtain stabilized solutions. Using the developed code, a parametric study is undertaken, and the effects of the Rayleigh number, the locations of the active parts of the side walls and the volume fraction of the nanoparticles on the fluid flow and heat transfer inside the cavity are investigated. It is observed from the results that the average Nusselt number increase with increasing the Rayleigh number and decrease with increasing the volume fraction of the nanoparticles. Moreover, the maximum average Nusselt number for the high and the low Rayleigh numbers occur for the bottoma middle locations of the thermally active parts, respectively.

Today the air pollution is one of the biggest problem specially in mega cities and it effects directly on human health and environment. in this article pollution dispersion for the light gas pollutant around a building in turbulent 3D incompressible flow using a hybrid turbulence model has been investigated. Pollution around a building in low speed wind may aggregate in some regions and make special problems for pedestrian and environment. Turbulent wind flow over buildings due to the complexity like sharp corners, ground effect, different vortexes and other factors is one of the best choices to evaluate efficiency and accuracy of turbulence methods. DES is hybrid RANS-LES models for simulating turbulent flow which for their characteristic, treat near wall as RANS and farther the wall act as LES model. Consequently computational time will decrease compared to traditional LES models. To evaluate DES model, DES results has been compared with smagorinsky and one-equation model. Also to validate, the simulation results are compared with experimental data. The DES results show good agreement with experiment and LES models and this hybrid model has a good potential for large scale wind engineering problems.

In this paper, the position tracking problem of a magnetic levitation system with the external disturbance and uncertainties is investigated. The dynamic of a magnetic levitation is governed by a SISO third-order nonlinear differential equation and only the position measurement is available for control. In this paper, the combination of the feedback linearization and Back-stepping techniques is used as a new control method for this system. Feedback linearization and back-stepping techniques are introduced as methods for linearization of a system with coordinate transformation and nonlinear designing, respectively. In other hand, nonlinear disturbance observer has a good ability to estimate disturbances and nonlinear dynamics, so it is combined with designed controller to increase performance of the controller, reducing the effects of disturbances and system uncertainties by estimating them. Simulation results show that the proposed method has a good ability in the position tracking and a good performance in elimination of the external disturbance and uncertainties.

The main propose of the present article is to study the second law of thermodynamics over a stretching permeable surface in the presence of the uniform vertical magnetic field in the slip nano-fluid regime. In this study, four types of nanoparticles i.e. Copper , Copper oxide , Aluminum oxide , and Titanium dioxide and also water as the base fluid are considered. Entropy generation equations, for the first time in this problem, are derived as a function of velocity and temperature gradients. Velocity profile as well as temperature distribution and averaged entropy generation are obtained using Homotopy Analysis Method (HAM). An excellent agreement exists between the present result and the other researchers’ result. The obtained result of present study presents that by decreasing magnetic parameter, nanoparticle volume fraction parameter, suction parameter, Reynolds number, Brinkman number, and Hartmann number as well as increasing the slip velocity parameter, the generated entropy reduces.

Fatigue is one of the most important failure sources of material that is caused by repeatedly applied loads. It is a progressive and localized structural damage that occurs when a material is subjected to cyclic loading. The experimental results of fatigue tests on Al-alloy 2024-T3 in double shear lap joints were used to estimate (model) fatigue life with artificial neural networks (ANN). Artificial neural networks with experimental data processing can find the knowledge or law lies behind the data, and unlike mathematical models, itas not necessary to determine the mathematical relation between inputs and outputs. To model by artificial neural network, one of the experimental data of fatigue life randomly selected for validation and two other were selected for testing, the rest of the data were used to find the optimal values of weights and bias. After being ensured of the model accuracy, it was used to predict the fatigue life at different loads in the working phase that had not been tested. Comparison of experimental results and the results of the model shows that a 3-layer artificial neural network with less than 10% error could be used to predict the fatigue life at different loads.

Heat transfer and pressure drop in Al2O3-water nanofluid flow through an internally ribbed pipe is studied numerically. The governing conservation equations in cylindrical coordinates for laminar incompressible flow are solved using well-known SIMPLE algorithm based on finite-volume method. The effects of flow parameters, the distance between the pipe ribs, and the volume fraction of nanoparticles, on heat transfer and friction coefficient are investigated. The obtained results illustrate that increasing nanoparticles volume fraction makes the thermal entrance length decrease, and consequently, the heat transfer gets increased. It also reveals that 5% of increment in nanoparticles volume fraction may lead to 28-percent rise in local Nusselt number and about 11-percent rise in average Nusselt number. In this case, the friction factor will also increase about 1.5 times in comparison with the pure fluid ones. The results also show that increasing the pipe ribs distance by five times in Re=100, will make the average Nusselt number increase by 2.45 times.

This paper presents a numerical study on the natural convection in a square cavity, with two pair of heat source and sink and filled with a alumina-water nanofluid. heat source and sink have Th and Tc temperatures respectively. For this purpose, we used a Fortran program based on Finite Volume Method and SIMPLE algorithm. The effects of parameters such as volume fraction for 0 to 0.05 percent, Rayleigh number for 103, 104, 105 and 106 and location of two pair of source-sink on the flow and temperature fields and heat transfer rate have been examined. The obtained results show that by increasing the Rayleigh number and the volume fraction of the nanoparticles, the rate of heat transfer is increased. Also, The results show that, increasing the nanoparticles volume fraction at low Rayleigh numbers (103, 104) has the more enhancement effect on the local and average Nusselt number in compared to the high Rayleigh anumbers(105,106).

In this study, a numerical approach to evaluate and predict the natural frequencies of a functional graded material plate resting on single-parameter elastic foundation, has been presented. In order to avoid nonlinear effects, the elastic foundation, Winkler considered. To investigate FGM Plate, Classic Plate Theory of thin plate is used. The plate is modeled using differential quadrature element method. By decomposing the system into a series of subdomain and elements any discontinuity in loading, geometry, material property and even elastic foundation can be considered. Applying the differential quadrature element method to the governing equations of the plate and the corresponding and boundary and compatibility conditions, they are transformed into an algebraic system of eigenvalue problem. Solving the resulted eigenvalue problem, the natural frequencies of functional graded material plate resting on Winkler foundation are calculated. The proposed method is verified by observing excellent agreements to those are available in literatures. The results show that proposed method can predict well.

Chip removing in the machining processes is done through the forces. Therefore, prediction of the forces and estimation of required energy is very important for determination of the efficiency of these operations. In this investigation first, by using Hooputrsa’s shear damage model in the ABAQUS/Explicit code, a number of conventional machining processes such as plane milling, straight turning, face turning, and drilling are simulated. By performing the simulations, variations of the force acting on the tool, maximum force, and also chip formation mechanism in each of the above processes are predicted. Then, in order to evaluate the shear damage model and material properties, the simulation results are compared with the results of theoretical and experimental relations. Comparison of the numerical and empirical results reveal that the Hooputraa’s shear damage model can well predict the damage initiation and evolution, chip formation, and forces acting on the tool in the machining processes.

Freshwater generation is always one of the most important issues in human communities coincided with population increase in different areas, using water desalination technology can be one of the most effective and useful method in utilizing power plants heat recovery. Iran has a high potential to use this technology due to the shortage of fresh water resources on the one hand and several thermal power plants in the coastal areas of North and South on the other hand. In this study, exergy destruction rate in different components of the cycle and also the rate of profit and loss resulting from coupling desalination to Neka power plant were studied according to the project of Caspian Sea water transfer to the central plateau of Iran and the necessity of water desalination before transferring. Results showed that the maximum exergy destruction cost occurred in the thermo-compressor and then in condenser. also if the flow of low pressure turbine used in MED-TVC can product 7215m3/day freshwater but this decrease in LP turbine flow, decreased 6.67% of the total power and 0.9 % thermal efficiency of a power plant.

In this research, the nonlinear rolling motion of ships is studied. After obtaining the governing equation of roll motion, the method of multiple scales perturbation technique is applied to solve the nonlinear differential equation. The ship response is studied with and without harmonic excitation. In order to validate the responses obtained by the method of multiple scales, the response was compared with the numerical solution. Finally, the effects of damping coefficient and restoring arm on the frequency response function and resonance frequency have been studied.

This paper investigates the sensorless operation of the brushless DC permanent magnet (BLDC-PM) motors based on the line to line flux function. The three dimensional sensitivity analysis of the line to line flux function is provided. This analysis reveals the influence of the measurement error and motor parameters variation on the electrical torque and motor efficiency. Moreover, the dependency of the method to speed and load variation is studied. The effectiveness of the mentioned method is demonstrated through simulation results

Eccentrically braced frames (EBFs) combine the high elastic stiffness of concentrically braced frames with the ductility and stable energy dissipation of moment resisting frames. In these types of frames energy often dissipated through links that vary from short shear yielding to long flexural yielding link. Link-to-column connections in eccentrically braced frames must transmit large moments and shear forces to facilitate link rotation. Previous researches has shown that link-to-column connections in long links are prone to failure at low drift levels due to their susceptibility to fracture at the link flange-to-column connections and they arena t applicable in sever seismic environments. To overcome this problem it is necessary to keep away stress and strain concentration from the ends of link connections. The use of link with reduced section can transmit plastic zone to reduced part and prevent connection failure. This paper investigates the application of RBS method in long links and studies the behavior of reduced long link to column connections. The analysis is conducted using the ABAQUS FEM software package. The analytical results show that this technique keeps away stress and strain concentration from the end of link beam near the face of column to some extent and improve the connection behavior.

Ground surface with irregular topography is one of the reasons of complex seismic responses, which are mainly due to the seismic wave scattering at ground surface. More investigation is needed for understanding the influence of wave scattering in specific places of ground surface. In this paper, the surface soil assumed homogeneous, isotropic, and elastic. At first, SH wave propagation equations in a two dimensional field by the scaled boundary finite element method have been presented. This method has been developed by combining advantages of the finite element and boundary element methods. In this method, only the boundary is discretized and no fundamental solution or Green's function is required. Then a semi-circular hill has been analyzed by using this method. The results of this analysis compared with other analytical and numerical methods and good agreement is achieved.

In this study, evaluation on lateral resistance and seismic response modification factor-R of strap-braced cold-formed steel shear walls is presented. Also, the results are compared with the prescibed values by the codes and standards. The structural parameters that are taken into account include: cross section of bracing straps, aspect ratio of the frames and studsa spacing. In this study, the effects of nonlinear behavior of steel, geometric imperfection of cold formed sections and residual stresses induced by cold forming process are considered. The lateral strength and displacement of the frames will be determined by ANSYS finite element software. The results of the analysis show that the increase in strapsa cross-sections area and the ratio of width to height of the frame lead to increase of the frame capacity but changing the distances between the studs have no significant impact on the capacity of the frame. Also the response modification factors (R factors) of the studied frames are calculated in the range of 5.31 and 6.39. The results show that the prescribed R factors by the codes are conservative and can be improves, slightly.

In this paper, a 3D nonlinear finite element model of a new moment-resistance connection in precast concrete structures is developed and its behaviors in several different details of connection, under cyclic loading are studied. During the FE modeling performed by Abaqus Software, the results of analysis of related connections under cyclic loads is compared with experimental results. The effect of nonlinearity of material and geometry and contact between different parts of model as well as bond-slip effect of reinforcement bars are considered. It should be noted that three connections, include two precast connections and a monolithic connection, are modeled. For verification of Finite elements model, the hysteresis curves, resistance of connections and failure modes (the cracks pattern and deformation mode) which have been compared with experimental results and show the suitable accordance of outputs of related computerized model with related experimental results.

In this paper the closed-loop supply chain network design problem is modeled and solved in a competitive and uncertain environment. The competition between two supply chains is on the price of products in forward channel and the price of returns (incentives) on the reverse channel. Demand is price sensitive and the amount of returned products is also linearly dependent on the incentives. Fuzzy set theory is used to cope with uncertainty. The proposed bi-level model is proved to be concave then we turn it to a single level model which is also proved to be a concave one. Afterwards, the single level model is solved using the Benders Decomposition approach. Finally, computational results are presented based on data inspired from real case. Results show that the proposed algorithm is converged in reasonable iterations. Increasing the price elasticity coefficient (intensifying competition) leads to less profit and Increasing the rivalas price elasticity coefficient leads to more profits for the existing chain.

In this paper, a comprehensive mathematical model for designing supply chain network via considering integrated flow of forward and reverse of multiple products during multiple periods is proposed. The uncertainty of the parameters includes customer demand, products reverse flows, rates of reverse product recovery and disposal, as well as costs of products transportation, storage and reverse flow management are considered via two stage stochastic programming. An efficient solution algorithm based on the sample average approximation and new accelerated benders decomposition is developed to solve the proposed model. An accelerated Benders decomposition algorithm utilizing efficient acceleration mechanisms based on the priority heuristic and adding the demand constraint to master problem is devised to cope with computational complexity. Computational analysis is also provided by using a phone cell industrial case study to present the significance of the proposed stochastic model versus deterministic one as well as the efficiency of the proposed the accelerated benders decomposition algorithm. In addition, obtained solutions of the stochastic model have a more robustness than solutions of the deterministic model.

Cut-off grade and capacity of processing plant are two factors influencing the design and the feasibility study of mine and calculation of these two plays an important role in mining economy. The main purpose of this study is to optimize the cut of grade and production capacity considering price uncertainty, simultaneously. Slight changes on lane algorithm and its formulation as a nonlinear programming problem were done, leading to design a model that can optimize the both factors simultaneously. A heuristic model similar to geometric Brownian model has been used to consider uncertainty in the model. An assumed copper mine data were used to model verification. Solver plugin in excel for model solving was used. Finally, the recommended values for plantas capacity were in range of between 16 and 17 with mean value of 16.5 million tons. This value for cut of grade is between 0.17 to 0.2 with the mean value of 0.19 percent, and for net present value is between 900 to 1200 with the mean value of 1080 million dollars. The optimum capacity distribution of processing plant has slight negative skewness, optimum cut of grade distribution has slight positive skewness and approximately maximum net present value has normal distribution.

Accurate estimation of software service development effort is a great challenge both in industry and for academia. The concept of effort is an important and effective parameter in process development and software service management. The reliable estimation of effort helps the project managers to allocate the resources better and manage cost and time so that the project will be finished in the determined time and budget. One of the most popular effort estimation methods is analogy base estimation (ABE) to compare a service with similar historical cases. Unfortunately ABE is not capable of generating accurate results unless determining weights for service features. Therefore, this paper aims to make an efficient and reliable model through combining ABE method and DE algorithm to estimate the software services development effort. In fact, the DE algorithm was utilized for weighting features in the similarity function of the ABE method. The proposed hybrid model has been evaluated on a real data set and two artificial datasets. The obtained results were compared with common effort estimation methods. Obtained values indicate 28, 34 and 19 percentage improvement on the three datasets ISBSG, Moderate, and Severe, respectively.