فصلنامه مدل سازی در مهندسی
پیاپی 46 (پاییز 1395)

Forced convection heat transfer in metal foams in the presence of radiation heat transfer is studied using the homotopy perturbation method (HPM). To see wall effects, Darcy-Brinkman model for the flow in porous media is used. A constant heat flux is imposed at the wall and the radiation heat transfer is modeled by a temperature-dependent conductivity. In the present study the case of conjugate convection and radiation heat transfer is analyzed by a semi-analytical approach for the first time. Effects of the radiation parameters (λ, Tr) and porous medium shape parameter (s) on the Nusselt number and dimensionless temperature profile are investigated. Moreover, a discussion on the accuracy and limitations of the HPM method will be presented.

The problem of designing sewing machines is known as a difficult task due to the existence of complex mechanisms and various solutions. The stitch quality in these machines is certainly most influenced by the effect of parameters of the needle drive mechanism. The needle heat generated during sewing process as well as the needle contact force are directly related to needle velocity in penetration zone which in turn depends on the needle driver mechanism of sewing machine. Unfortunately, despite the importance of this issue from practical point, very little publications have focused especially on the optimization of needle lever mechanism. Therefore, we first introduce a new needle derive mechanism for which an optimization procedure based on the genetic algorithm is followed to achieve minimum needle velocity during penetration. In addition, further modification of the objective function with respect to the variation of needle acceleration is applied to assure smooth movement of the needle during sewing process.

One of useful methods for strengthening for reinforced concrete frames, is to use steel prop and crub in connections, alone or combined with beam's revival steel sheets and column jacketing with steel sheets or profiles. In this paper, after modeling and verifying application of model, behavior of RC frames, strengthened with this method was studied. For this purpose, a RC frame has been strengthened in 4 general ways (crub and prop, crub and prop with revival sheet among two beam’s crub, crub with column jacketing in the bottom of column’s crub region, combination of three mentioned moods) with three different prop’s sectional area. Results showed that using crub and prop increases stiffness and strength of frame, significantly. If crub and prop are used with column jacketing for strengthening RC frames, frames’ strength increase up to 3.3 times of ordinary frame. Adding beam revival sheet to crub and prop, causes sooner yielding and bulking in compressive prop.

In this paper, buckling analysis of cylindrical panels made of functionally graded material under the action of three types of thermal loads is investigated. At first, Governing equations of panels are obtained based on the second Piola-Kirchhoff stress tensor using three dimensional theory of elasticity. Stability equations of the shells subjected to thermal loading based on the Donnell shell theory are considered. Two methods of solution are employed. In the first method governing equations obtained by benchmark solution are discretized and solved using differential quadrature method. Then the closed form solution is presented for the buckling equations based on the Donnell shell theory. It is assumed that material properties of the shell vary continually through the thickness according to a power law distribution of the volume fraction of constituent materials, while the Poisson’s ratio is constant. The effects of various parameters including the power law exponent, panel angle, different thermal load conditions and geometric ratios on the buckling behavior of functionally graded cylindrical panels are studied.

In this article, triangular optimizer algorithm optimization method is presented for minimizing the weight of the truss structures. Triangular optimizer algorithm is a new metaheuristic method which is inspired of triangle. In this method, the initial vector of design variables is considered as the base of the triangle (first row). Then the objective functions are calculated and the best and the worst response are identified. The worst response is removed from the current population and the remaining population after some modifications is defined the second row. This process continues till reaching the apex of triangle, the optimal solution of this triangle. In the second iteration (second triangle), a certain number of the initial design variables are retrieved by the optimal solution of the previous triangle and the remaining of this population are created in the initial interval for escape from local optimums. So base of the second optimal triangle is formed. Then the mentioned algorithm is performed until optimum response of second triangle is achieved. These operations are continued until the convergence condition being satisfied. To prove the capabilities of the proposed algorithm shaping and sizing-shaping optimization of four truss structures are considered. The obtained statistical results of truss structures optimization show that the TOA is able to managed to achieve better optimal solutions compared to different optimization techniques.

In this paper, the bearing capacity of ring footing is investigated. Ring footings are more economical in comparison with circular footings since less material is used in their construction. However, less investigation regarding the behavior and the bearing capacity of ring footings exits in the literature. The method of characteristics is applied in the present research in order to find the bearing capacity factors, which have been introduced in the so-called Terzaghi’s bearing capacity equation. The ring footing is assumed to be located on the horizontal ground surface, which carries vertical and centric load. The roughness between the footing base and the ground is ignored. The soil is assumed frictional-cohesive, which obeys Mohr-Coulomb yield criterion. The values of the bearing capacity factors are obtained for a wide range of soil friction angle (0~50 deg) and for different ring geometries in terms of the ratio of internal to outer ring radii (n), where n = 0, 0.2, 05, 0.7, and 0.9. The variations of the factors with n are presented in the forms of tables, graphs, and mathematical equations. The magnitude of the obtained factors is compared with the available data published in the literature. Comparisons show that there is good agreement between the results. In the end, by using some optional examples, it is shown that using the proposed bearing capacity equation for a ring footing is safe and conservative in comparison to applying a direct and rigorous plastic analysis.

In this paper, a new method for generation of artificial earthquake record from the target spectra is proposed. This method uses new model in compression named MFCC analysis and MLFF Artificial Neural Networks and wavelet analysis. This procedure uses the learning capabilities of neural network to expand the knowledge of the inverse recording from response spectra to earthquake accelerogram. In the first step, wavelet analysis is used to decompose earthquake accelerograms to several levels in which each level covers a special range of frequencies, and then for every level a neural network is trained to learn to relate the response spectra to wavelet coefficients. Mel-Frequency Cepstral Coefficient (MFCC) compress signals for better training of neural networks. Finally, the generated accelerogram using inverse discrete wavelet transform is obtained. Some example is presented to demonstrate the effectiveness of the proposed method.

Agent-based negotiation is one of the interesting approaches in the field of automated negotiation in the E-Commerce world. Establishment an automated negotiation needs to develop a mechanism for it and it is obvious that users would accept a mechanism that is close to human methods of negotiation and reliable alternative for negotiating individual. Therefore, the need to developing efficient and reliable agent-based negotiation mechanism is being felt. In this paper we present a multi-issue negotiation mechanism. In contrast to previous studies, we had a multi-disciplinary to the negotiation problem and used micro economics theory to analysis and developing counter offers. In addition, in each round of this mechanism a twofold proposal is presented that caused the time of negotiation decreases while increasing the efficiency of negotiation and probability to reach better solutions. Validity and efficiency of proposed negotiation mechanism is indicated via predefined conditions of literature.

The main goal of reusing software components is to produce new software systems using existing components rather than building it from scratch. Component-based software development is one of the most common approaches found today in different branches of engineering, but in software engineering reusing components is still faced with numerous challenges. In order to increase efficiency and accelerate the adoption of component reuse in software development, quantitative measurement of component reusability is necessary. In this regard, various models and metrics have been proposed, so it is important to review the research literature on this concept fairly and comprehensively. In this paper, we conducted a systematic review to identify and evaluate the methods that have been used for measuring component reusability and provide a new classification. Finally, based on the results of studies carried out, some of the relating challenges and issues have been introduced.

Due to the effective heat transfer in fluidized beds, these systems have been wieldy used in many thermal processes. There are limited published papers in the literature regarding heat transfer in fluidized beds, because of complexities existing in these systems. In the present study, a gas-solid bubbling fluidized bed including the spherical particles with diameter of 280 µm is simulated by a Eulerian-Eulerian Two-Fluid Model incorporating the kinetic theory of granular flow (KTGF). Influence of two important drag models of Gidaspow and Syamlal as well as some hydrodynamics parameters, namely, particle-particle restitution coefficient and solid wall boundary conditions are studied. Both drag models predict the behavior of the bubble passage through the bed reasonably. Although both drag functions show the same trend with the experimental data, Gidaspow drag model predicts the better results than the Syamlal one. The CFD results reveal that the modeling parameters of specularity coefficient, particle-particle and particle-wall restitution coefficients have a significant effect on the heat transfer coefficient between the wall and particles.

Transient instability, voltage instability or a combination of both have been the cause of several power system blackouts all over the world in the recent years. Occurrence of a super-component contingency (SCC) that refers to multiple and simultaneous outages of grid facilities like a power plant or a multi-circuits line may lead to blackout if no remedial action schemes (RAS) are implemented. This paper proposes a new event-based RAS to overcome the transient and voltage instabilities caused by super-component contingencies through optimal generation shedding and load cut. To do this, a new multi objective framework is presented simultaneously optimizing the competing objective functions of transient and voltage stability margins and generation shed and load cut amount. Multi objective decision making is performed using a combination of analytical hierarchy process (AHP), modified augmented  constraint method and technique for order preference by similarity to ideal solution (TOPSIS). The effectiveness of both the proposed model and MODM solution approach is extensively illustrated on a simulated model of Iran’s power system in 2014.

In this paper, a method based on hybrid Volume-Surface Integral Equation (VSIE) formulation in combination with Green's Function is presented to analyze a wide band planar microstrip antenna. Hybrid volume-surface Mixed Potential Integral Equation (MPIE) is used to analyze the structure. This hybrid integral equation is solved with the aid of spatial-domain Method of Moments (MoM) in order to compute surface current in metal faces and volume charge densities in dielectric substrate. The antenna is fed via a coaxial probe which is modeled in the developed code. Accuracy of the presented method is validated by comparing the results obtained from the proposed method with those of CAD simulations and measurements results.