AMIRKABIR
Year:2005 | Volume:16 | Issue:61-B|Papers Count:12

This paper proposes a mathematical model to solve facility layout problem in CMS. Its objective is to solve both inter-cell and intra-cell facility layout problems simultaneously, so that the material handling costs are minimized. It has been assumed that the demand rate varies over the product life cycle. Due to the complexity of the case, an improved simulated annealing algorithm has been developed to provide the optimal solution to this problem. This algorithm can always generate a neighborhood configuration that satisfies all of the zoning constraints. The results indicated that the proposed approach can yield satisfactory solutions within reasonable time.  

This paper presents an integer mathematical programming model for manpower scheduling problems. This can be considered as a type of set covering problem, which is to assign a work pattern considering system's requirements and associated workforces. The objective 'function is to minimize the costs of absent, disobeyed degree of significant for each work shift, and uncovered demands. It is so difficult to solve such problems in a reasonable computational time by using conventional optimization tools. Thus, in this paper a special design of tabu search (TS) is employed as a well-known meta-heuristic method to solve such hard problems. To show the efficiency of the proposed method, ten different test problems are solved and the associated solutions are compared to the solution obtained by the Lingo package.    

Nowadays, scheduling and mixed-model assembly line balancing with multi objectives are significant issues in major industries. In this paper, the problem of sequencing in mixed-model assembly line with the objective function of leveling part usage and minimizing line length is studied. This problem is formulated as an integer non-linear programming model. From the viewpoint of computational complexity, such a scheduling problem belongs to a class of NP-hard problems. Accordingly to solve the above model, a special design of genetic algorithms is used. To evaluate the efficiency of the proposed algorithm, we use the real data taken from three trimming shops in an automotive manufacturing company. For each trimming shop, five different problems (runs) are generated compromising several values of weighted importance factor in the objective function. Then solutions obtained by genetic algorithms are compared with solutions reported by Lingo 6 software. The final solutions are approximately optimal and computational time for achieving the best result is very small showing that the proposed algorithm is a quite suitable tool for solving the problem.    

In the present article, the stress analysis in a special missile motor is studied. This missile motor consists of a steel cylinder which concludes the star grain of solid propellant. The steel cylinder behavior is elastic, but the inner solid propellant exhibits the viscoelastic behavior. The fact confirms this assumption. The problem's solution is performed by finite element method. Since solid propellant bums, the problem shape is dependent on time. On the other hand the behavior of viscoelastic materials is varied by time. Thus, in the analysis of this problem, time has a principle role. This problem which has the moving band is solved by a 'step by step' time method. In each time step, the necessary variations are given to the problem by modifying of the stiffness matrix and the load vector and the problem is solved again. The routine is done until last step. Therefore stress value and distribution are obtained in every location of solid propellant grain and cylinder. This analysis has an important role in solid propellant grain and cylinder design. In this way, cracks of propellant are controlled and insuring of correct function of missile motor can be obtained.    

This paper describes a strategy for predicting the extent of internal damage in a laminated composite structure, when subjected to low velocity impact. The success of the predictions is validated by experiments. Delamination as a result of low-velocity impact loading is a major cause of failure in fiber-reinforced composites. The delamination size was obtained when the' transverse shear force rate reached interlaminar fracture toughness. Post-impact examination of damage is carried out by visual inspection. The impact loading is treated as an equivalent static loading by assuming the impactor to be semi-spherical and the contact to obey Hertzian law. An analytic solution which includes both transverse shear and contact deformation is presented. A First shear deformation theory is employed and solutions for the loads, displacements and strains are obtained using Fourier series expansions. Subsequently, the Tresca criterion is used to detect the zones of failure. It is demonstrated that for given specimens lay-up the materials subjected to impact load whit low rang of energy suffer damage according to the magnitude of the both impactor mass and velocity.    

It is about three decades that operating doctrine under inflation and time-value of money is considered, but a few activities under non-deterministic conditions are provided. The empirical evidence shows difficulty of assuming the inflation rate as well known and constant. Therefore in this paper internal and external inflation rates are stochastic. The developed model can be used any probability density function (p.d.f.) for inflation rates and deteriorating items with shortages. Finally, a numerical example is given to illustrate the theoretical results and a sensitivity analysis of parameters at the optimal solutions is performed.      

The goal of this paper is presenting the optimal formulas and calculation of cutting forces and torque in drilling process. The presented mathematical models are developed to predict the thrust and torque forces at the different regions of cutting on a twist drill. The geometry of the drilling process (chipload, cutting angles,..) was exploited for developing this models. The input to the model is the machining conditions and the tool geometry and the model predicts the thrust and torque profile along the cutting lips and the chisel edge of the twist drill.    

Inventory control and planning can provide a continuous supply of products as well as JIT inventory. It is costly by using up some resource. Traditionally, inventory models have included a cost coefficient to each resource and thus created a single cost-oriented equation to be minimized with or without constraints. Nowadays, the concept of supply chain in inventory control models is widely extended. This paper considers inventory control problems in supply chain as multi criteria - multi decision makers inventory model in a non-serial supply chain with stochastic demands holding uniform distribution. In this developed model, we consider the supply chain in four companies in which there is only one' independent decision maker in each company. Finally, this multi-criteria inventory control problem considering three criteria in a stochastic demand is solved for each company. These criteria are as follows: average inventory capital, number of orders per year, and risk of stockouts.    

Over the past decade, new changes in competition environment have led to fundamental changes in structure of local markets. The market has changed from one focused on the optimization of manufacturing performance around quality' cost and delivery objectives to one with multifaceted performance requirements where customers demand products and services that are increasingly specific to their needs and wants. In order to survive in this volatile competitive environment, companies are striving to improve their manufacturing performance. Their success largely depends on their ability to quickly practice and adopt state-of-the-art manufacturing strategies. A new manufacturing paradigm is needed to take advantage of new requirements of the market. Agile manufacturing is a new paradigm to cope with changes in various dimensions of an organization such as market' competition' technology and social factors, also to choose competitive strategies. An attempt has been made in this research to: I) review the published literature on agile manufacturing with the objective to identify key related concepts of AM, II) develop a framework for the development of agile manufacturing systems. The research concludes by discussing two case studies in detail and identifying and proposing some key steps.    

In this paper, the optimal routing problem for transportation of hazardous materials is studied. Routing for the purpose of reducing the risk of transportation of hazardous materials has been studied and formulated by many researchers and several routing models have been presented up to now. These models can be classified into two categories: the models for routing a single movement and the models for routing multiple movements. In this paper, according to the current rules and regulations of road transportation of hazardous materials in Iran, a routing problem is designed. In this problem, the routes for several independent movements are simultaneously determined. To examine the model, the problem of transportation of two different dangerous materials in the road network of Mazandaran province in the north of Iran is formulated and solved by applying Integer programming model.    

Determination of the time lag caused by utilization of different tubes to measure pressure on the surface of a wind tunnel model is an important problem in the field of aerodynamic especially for unsteady measurements where the pressure signature changes continuously with time. In this investigation the time required for the applied pressure at one end of different tubes to reach its original value (applied pressure) at the other end has been measured. Three plastic tubes and two polyethylene tubes with different lengths and different inner diameters; L=2, 5 and 10 m, d=1, 2 and 4 mm, were used to study the time lag. Experimental data show that the response time in a pressure measuring system is a function of applied pressure, system volume, viscosity, tube length, and tube diameter. As the tube diameter increases, or its length decreases, the required time for the pressure at the end of the tube to reach its initial value reduces significantly.