Sharif Digital Repository

The design process always has some known or unknown uncertainties in the design variables and parameters. The aim of robust design is minimization of performance sensitivity to uncertainties. Tolerance allocation process can significantly affect quality and robustness of the product. In this paper, a methodology to minimize a product's sensitivity to uncertainties by allocating manufacturing tolerances is presented. The robust tolerance design problem is formulated as a multi-objective optimization based on the combined function-uncertainty-cost model. Genetic algorithm is utilized to solve the multi-objective optimization and a case study is presented to illustrate the methodology  

During the last decade, the importance of process development has persuaded researchers to propose a great number of optimization models on "production planning" and "production scheduling" for different productive processes. Although many scheduling and planning models are proposed in the past decade, there are few models that handle various applicable goals. In this paper the main objective is developing and extending the traditional scheduling formulations to accommodate optimization of utility (especially energy barriers) demands and supplies. In the context of optimization, the final formulation takes the form of a mixed-integer programming. For this purpose a mathematical model is... 

In this paper, optimal production and maintenance planning of a flexible manufacturing system under a time variant demand is considered. There is a preventive maintenance plan to reduce the failure rate of the machine. It is assumed that the failure rate of the machine is a function of its age and its maintenance rate. It is, also, assumed that the demand of the manufacturing product is time dependent and its rate depends on the level of the advertisement on that product, The objective is to maximize the expected discounted total profit of the firm over an infinite time horizon. To solve this optimization problem, first, an optimal control is characterized by a set of Hamilton-Jacobi-Bellman... 

On-line optimization for the base case of the Tennessee Eastman (TE) challenge problem is presented; furthermore, an interesting operating condition near base case has been obtained, which results in a lower cost function. The proposed method is based on the estimation of the internal states and the time varying parameters of the process model based on an Extended Kalman filter. The sequential quadratic programming method has been used to accomplish the non-linear programming (NLP) task. The objective function is the operational cost while the constraints are the reactor mass balance, safe operation of the process equipment, and the conditions that satisfy the product quality and flow. The... 

A methodology is presented for optimization of the dynamic response of concentrically braced steel frames subjected to seismic excitation, based on the concept of uniform distribution of deformation. In order to obtain the optimum distribution of structural properties, an iterative optimization procedure has been adopted. In this approach, the structural properties are modified so that inefficient material is gradually shifted from strong to weak areas of a structure. This process is continued until a state of uniform deformation is achieved. It is shown that the seismic performance of such a structure is optimal, and behaves generally better than those designed by conventional methods. In... 

Response surface methodology (RSM) was applied to optimize the process of biodiesel production from Iranian bitter almond oil. Design of experiments was performed by application of a 5-level-3-factor central composite design in order to study the effect of different factors on the product yield, biodiesel yield and biodiesel purity. These factors were reaction temperature (30-70°C), catalyst concentration (0.3-1.7% w/w) and methanol to oil molar ratio (4.4-13.6 mol/mol). A quadratic model was suggested for the prediction of the biodiesel yield. Analysis of variance revealed that the factors were significant on the production process of biodiesel. For each factor, the optimum value was... 

This study investigates optimal strategies for price, warranty length, and production rate of a new product in which both static markets for non-durable and dynamic markets for durable products are involved. The mathematical model incorporates both the demand and the cost functions including production, warranty length, and inventory costs. Using the maximum principle approach, the optimal strategies and interactions among price, warranty length, and production rate in both markets are analyzed using some propositions. The analysis shows that to maximize profits in all cases, the price, the warranty length, and the production rate all must go up simultaneously, or one of them must increase... 

This paper discusses the studies carried out for the optimal production of enzyme l-asparaginase (l-asparagine amidohydrolase, EC 3.5.1.1) from Escherichia coli (ATCC 11303). It was found that inoculum age of 18 h and inoculum size of 10% were the most favorable operating conditions for enzyme production. Lactose, yeast extract and KH 2PO 4 were found to be the best carbon, nitrogen and ion sources, respectively. Statistical method was used to survey how various medium conditions affect the enzyme production. By response surface methodology, the values of lactose, tryptone, yeast extract, KH 2PO 4 and l-asparagine concentration were investigated to obtain the maximum enzyme activity. The... 

This paper studies simultaneous lot sizing and scheduling problem in a job shop environment over a finite number of periods. The machines are flexible such that the production manager is able to change their working speeds. Also, the production schedule of the items over machines should be in consistence with technological precedence relationships. The problem is formulated as an integer linear program. Then, a number of valid inequalities are developed based on the problem structures. The proposed valid inequalities are added to the problem formulation in a "cut and branch" manner to accelerate the search process by common solvers. Finally, performance of the valid inequalities is... 

Production optimization is defined as the process of maximizing oil production over the long term while minimizing total production costs. The overall goal is to achieve the optimum profitability from the well or field. In this process, the reservoir system can be considered as a multiple input–output system. In this complex system injection and production wells are known as inputs and outputs. The output of the system is often affected by various parameters consisting reservoir conditions, petrophysics, and PVT data. The optimization of the injector rates and number and installation of submersible pumps are the main issues which have been studied in this paper. Determining the factor with... 

We are concerned with an open shop scheduling problem having sequence-dependent setup times. A novel bi-objective possibilistic mixed-integer linear programming model is presented. Sequence-dependent setup times, fuzzy processing times and fuzzy due dates with triangular possibility distributions are the main constraints of this model. An open shop scheduling problem with these considerations is close to the real production scheduling conditions. The objective functions are to minimize total weighted tardiness and total weighted completion times. To solve small-sized instances for Pareto-optimal solutions, an interactive fuzzy multi-objective decision making (FMODM) approach, called TH... 

Cell culture feeds optimization is a critical step in process development of pharmaceutical recombinant protein production. Amino acids are the basic supplements of mammalian cell culture feeds with known effect on their growth promotion and productivity. In this study, we reported the implementation of the Plackett-Burman (PB) multifactorial design to screen the effects of amino acids on the growth promotion and productivity of a Chinese hamster ovary DG-44 (CHO-DG44) cell line producing bevacizumab. After this screening, the amino acid combinations were optimized by the response surface methodology (RSM) to determine the most effective concentration in feeds. Through this strategy, the... 

This paper considers the modeling and control of a tubular fixed bed reactor with recycle stream for dimethyl ether (DME) production. For simulation purposes, a pseudo homogeneous model has been developed. By reactor simulation under steady state condition, effects of parameters such as feed rate, pressure and shell temperature are investigated. Using the steady state model, an optimizer that maximizes the reactor yield has been developed. For cooling the reactor, a steam drum that uses heat of reactions to produce steam was coupled with the reactor. Through dynamic simulation, system open loop response was obtained and two control loops were considered for controlling the reactor... 

The economic production quantity (EPQ) model is often used in manufacturing environments to assist firms in determining the optimal production lot size that minimizes the overall production-inventory costs. While there are some unrealistic assumptions in the EPQ model that limit its real-world applications, in this research, some of these assumptions such as (1) infinite availability of warehouse space, (2) all of the produced items being perfect, and (3) the existence of one product type are relaxed. In other words, we develop a multi-product EPQ model in which there are some imperfect items of different product types being produced such that reworks are allowed and that there is a... 

In this paper, an Economic Production Quantity (EPQ) model is studied, in which the production defective-rate follows either a uniform or a normal probability distribution. Shortages are allowed and take a backorder state, and the existence of only one machine causes a limited production capacity for the common cycle length of all products. The aim of this research is to determine the optimal production quantity of each product, such that the expected total cost including holding, shortage, production, setup and defective items cost is minimized. The mathematical model of the problem is derived, for which the objective function is proved to be convex. Then, a derivative approach is utilized... 

Imprecise productions with low quality are produced by the incapable manufacturing processes. Prediction of the process capability in the design stage plays a key role to improve the product quality. In this paper, a new method is proposed to optimally reduce the locating error by allocating the minimum adjustments of locators. To quantify the precision of the manufacturing process, a proper tool that is called the geometric capability ratio (GCR) of the manufacturing process is introduced. First, based on a part fixture model, the relationship between the locating error and its sources is developed. Then, using the proposed geometric capability ratio, the manufacturing process capability is... 

Interactive and integrated design and manufacturing can be a useful strategy for designers to reach the efficient design through the cognitive or physical interactions. Process tolerance design is a key tool in the integrated design and manufacturing to reach a product with high quality and low cost. Since the optimal tolerance allocation involves several aspects of the design, manufacturing and quality issues, it is always a time consuming and difficult procedure, especially for complex products. Therefore, to overcome these difficulties, a computer-aided approach for optimal tolerance design of manufacturing process is needed in the design stage. In this paper, a novel interactive... 

Imprecise productions with low quality are produced by the incapable manufacturing processes. Prediction of the process capability in the design stage plays a key role to improve the product quality. In this paper, a new method is proposed to optimally reduce the locating error by allocating the minimum adjustments of locators. To quantify the precision of the manufacturing process, a proper tool that is called the geometric capability ratio (GCR) of the manufacturing process is introduced. First, based on a part fixture model, the relationship between the locating error and its sources is developed. Then, using the proposed geometric capability ratio, the manufacturing process capability is... 

Interactive and integrated design and manufacturing can be a useful strategy for designers to reach the efficient design through the cognitive or physical interactions. Process tolerance design is a key tool in the integrated design and manufacturing to reach a product with high quality and low cost. Since the optimal tolerance allocation involves several aspects of the design, manufacturing and quality issues, it is always a time consuming and difficult procedure, especially for complex products. Therefore, to overcome these difficulties, a computer-aided approach for optimal tolerance design of manufacturing process is needed in the design stage. In this paper, a novel interactive... 

Intense global competition, dynamic product variations, and rapid technological developments force manufacturing systems to adapt and respond quickly to various changes in the market. Such responsiveness could be achieved through new paradigms such as Reconfigurable manufacturing systems (RMS). In this paper, the problem of configuration design for a scalable reconfigurable RMS that produces different products of a part family is addressed. In order to handle demand fluctuations of products throughout their lifecycles with minimum cost, RMS configurations must change as well. Two different approaches are developed for addressing the system configuration design in different periods. Both...