Computational Methods in Engineering

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In this work the effects of various methods of agitation on the properties of electroless Ni-P-MoS2 composite coatings were investigated. Magnetic stirring as well as purging the solution with gas (Air, Oxygen, Nitrogen) were used. Plating rate, chemical composition, MoS2 distribution, and hardness of the deposit were measured. Topography of coating was studied with metallography and scanning electron microscopy. It was concluded that purging the solution with air produced optimum results, i.e. high rate of deposition, uniform distribution of MoS2 particles and appropriate surface morphology.

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Bilevel programming, a tool for modeling decentralized decision problems, consists of the objective of the leader at its first level and that of the follower at the second level. Bilevel programming has been proved to be an Np-hard problem. Numerous algorithms have been developed for solving bilevel programming problems. These algorithms lack the required efficiency for solving a real problem. In this paper, attempts have been made to develop an algorithm based on Simulated Annealing (SA) Approach. This algorithm is efficient enough to find a near optimal solution. The proposed method is compared with the one developed by Mathieu et al [1] through application of both to a number of different problems.

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Bus network design is an important problem in public transportation. A main step to this design is determining the number of required terminals and their locations. This is a special type of facility location problem, which is a time-consuming, large scale, combinatorial problem. In a previous attempt by the authors, this problem had been solved by GAMS, based on a branch and bound algorithm. In this research, different techniques for solving the problem are investigated to choose the best one. One of these methods is Simulated Annealing (SA), which is an efficient algorithm for solving complex optimization problems. SA’s parameters vary from one problem to another. Here, for the bus terminal location problem, SA’s parameters are determined, then the problem is solved. Another algorithm is the Implicit Enumeration method. In this paper, the results obtained from the above 3 techniques are compared. The criteria for this comparison are the CPU time and the accuracy of the solution. In all the cases studied, SA gave the most accurate results. Its CPU time is lower than the others, too. Solving the bus terminal location problem for the Mashhad network shows that SA is about 150 times faster than GAMS and 50 times faster than Implicit Enumeration. Moreover, bus terminal location problem for the network of the city of Tehran, which is a more difficult problem, has been solved by the SA algorithm successfully. Keywords: Bus network, Lacation problem, Heuristic, Simulated Annealing, Implicit Enumeration

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This research proposes a vigorous methodology based on the fuzzy set theory to improve the facility layout process. Using natural language, the fuzzy set theory is an appropriate tool for controlling complex systems such as facility planning. The closeness rating between departments in a plant depends on qualitative and quantitative factors. Some of these factors may have a greater effect on the closeness rating. Thus, analytical hierarchy process (AHP) is used to find the weight of these factors. In this paper, a computer program, called FDARC, is developed to generate quantitative activity relationship charts. These charts are used by FLAYOUT to develop the layouts. The procedure is compared with two other recent methods. Computational results are used to demonstrate the effectiveness and efficiency of the method proposed.

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

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: In this research, dimensionless temperature and entropy generation for the steady state flow in the stagnation point of incompressible nanofluid impinging on an infinite cylinder have been investigated. The impinging free stream is steady with a constant strain rate  k. Similarity solution of the Navier-Stokes equations and energy equation is derived in this problem. A reduction of these equations is obtained using appropriate transformations introduced in this research. The general self similar solution is obtained when the heat flux on the cylinder wall is constant. All solutions brought above are presented for Reynolds numbers  Re=ka^2/2vf that range from 0.1 to 1000 and the selected values of particle fractions, where a is the radius of the cylinder and υ_f  is the kinematic viscosity of the base fluid. Results show that for Reynolds numbers examined, as the particle fraction increases, the depth of diffusion of the fluid velocity field in axial direction decreases, whereas Nusselt number is raised. Also, the maximum value of entropy generation has been calculated.