AMIRKABIR
Year:2006 | Volume:17 | Issue:64-B (TOPICS IN: MECHANICAL ENGINEERING & INDUSTRIAL ENGINEERING)|Papers Count:10

In this research effects of surface roughness on turbulent flow field (2-D) in a rectangular duct are investigated by Direct Roughness Simulation (DRS) for the first time. In traditional methods, wall functions are normally corrected and applied for considering surface roughness. However, in present method Direct. Roughness Simulation (DRS) without using roughness modeling. In this way, the wall surface roughness scheme is considered like a saw tooth with triangular shape and random height. Reynolds stresses which appear in the Navier-Stock equations are modeled with RSTM method (with corrective coefficients) and solved with the SIMPLE method, using the FLUENT software. The fluctuating components of fluid velocity are determined by CFWN model.In compare with the traditional methods, the present method results for fluctuating components of fluid velocity are more compatible with experimental data.

Controlling system state is a purpose in system automation. Monitoring of tool wear is the same in machining process. Dimensional accuracy, surface quality of work, machining economy, machine tools life and machining forces were influenced by tool wear. So estimating the tool wear without stopping the operation can be a monitoring method. In this paper an on-line multisensoring approach for tool wear estimation in face milling proposed. Measuring of forces and motor current simultaneously is used. Many experimental tests have been done in different machining conditions and a back propagation neural network (bp) has been designed. This neural network can estimate the tool wear amount with a high accuracy by measuring of machining forces and motor current simultaneously. This method can be used in controlling and monitoring of machining process.

in this paper, the TVD method is applied to the numerical solution of the flow over axisymmetric steady hypersonic viscous flow using TLNS equations over blunt cone. In the TVD schemes, the artificial viscosity is implemented using entropy condition. For hypersonic flow, Yee entropy condition has better stability and convergence rate. This paper presents a new entropy condition for increasing the accuracy and convergence rate of the TVD scheme which does not have the difficulty associated with Yee entropy condition for viscous flow in the hypersonic regime. The numerical solution has been compared, with the Beam & Warming shock fitting approach which shows that this approach has better convergence rate and accuracy.

The effect of carbon on oxidation behaviour of austenitic heat resistant steels (20% Ni 25% Cr) has been evaluated in the temperature range (1000-1300°C).The results indicate that the addition of carbon causes the poor oxidation resistance due to spelling of protective chromium oxide on the surface of alloy. Also addition of carbon causes spinel oxide to form on alloy replacing the protective, continuous Cr2O3 type oxide. Because produced carbides allocate a lot of chromium of matrix, the oxidation resistant of steel was decreased. Carbon does't change the behaviour of oxidation rate constant but increase it and these alloys obey the parabolic law.

Problem of Resource Constrainted allocation and leveling in multi-stage, multi-product and multiperiod production planning is one of the most difficult and important-decision making problems. Variuos heuristic and optimal algorithms have been provided to solve the problem. In this paper, an effective approach is proposed to solve the problem for lot-size determination. This approach, through the Resource Constrainted allocation based on Lagrange multiplier, decomposes a mutli-product production planning problem to a single product production planning problem. After solving the single product mathematical model for each product, by comparing the allocated and required capacity for each product, total remained capacity is calculated and resource leveling is performed. Accordingly, after several stages, leveling of the remained capacities does not affect the problem solution. In this case, the primary problem solution is obtained. Experiments designed in this paper indicate the optimal usage of the Resource Constrainted by this approach and its superiority over Genetic Algorithm and Linear Programming methods.

A search of available literature didn't reveal any empirical studies about application of tools, techniques, concepts and factors relating to TQM in management practices of Iranian pioneer industries.The purpose of this research is a survey on the understanding & application of critical factors and concepts relating to TQM in management practices of Iranian pioneer industries.The survey was sent to quality directors and middle managers of top 100 Iranian companies (IMI-100) from abroad spectrum of industries. Statistical analysis of the data reveal the mean amount of understanding and application of each tools, factors and concepts relating to TQM in Iranian pioneer industries and through a comparative study this result has been compared with American pioneer industries. Then by doing a gap analysis the difference between current situation and the desired condition is discussed.

In this paper, a method is developed to minimize the expected warranty servicing cost per item sold. In this method, to be decided to repair or replace a failed item. These kinds of items work in multi-state deteriorating and they may fail in every state. The last decades some researches for minimizing the expected warranty servicing cost under one-dimensional (Time) and nonrenewable warranty policy have been published. But here, the warranty policy has two-dimensions (Time & Usage). The decision to repair or replace a failed item depends on two parameters, the deterioration degree of the item and the length of the residual warranty period. The optimality of these two parameters for minimizing the expected warranty servicing cost are examined by two methods, analytically and simulation. Then an offered algorithm is used as an approximating method for performing the warranty policy.

Predicting the motion of particles in a quiescent liquid is a key problem in fluid mechanics that has a bearing on wide range of applications in multiphase flow modeling. A significant part of the paper is devoted to an evaluation of gravity, drag, added mass and history force on the motion of high-Reynolds number particles. In this study, the motion of metallic and plastic particles of 5 and 10 mm diameters in liquid media during their sedimentation toward a plate was studied experimentally. Variation of the sphere size and density allow measurements at Reynolds numbers, based on terminal velocity, between 1000 and 95000. The comparison is made by solving the equation of particle motion based on Lagrangian approach. The results showed if gravity is sufficient to describe the particle trajectory in a gas, this is not the case in a liquid where drag and added mass force are important but not sufficient: the history force is shown to be non-negligible. For the small particles, the history force has a (t-t)-1/2 behavior as predicted by Odar and Hamilton and as observed in numerical simulation. Finally, comparison of the dynamics of particles of different diameters for the same density shows that the diameter has a significant role in treatment of particle sedimentation and that large particles show transitory oscillations in velocity profile.