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In multi-stage manufacturing/service systems, quality of final products depends on several decision variables and design factors from several stages of operations as well as environmental and operational nuisance factors. Typically, the... more
In multi-stage manufacturing/service systems, quality of final products depends on several decision variables and design factors from several stages of operations as well as environmental and operational nuisance factors. Typically, the effects of factors in one stage might remain significant at the next stages. Due to high degree of interdependencies among the variables in/between the stages, multistage quality control methods have recently attracted special attentions. Multi-response optimization is a well-grounded method for offline quality design that can consider several inputs and outputs. This study introduces a new multiresponse surface methodology by proposing two different modeling approaches for quality optimization in multistage systems with multiple response variables. Several stochastic parameters, including response surfaces and covariates, are to be considered the proposed models. In order to cope with the uncertainty, multistage stochastic programming is applied w...
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Iranian bread production methods are often unsanitary, in the last decades, different attempts were made to mechanize production of Iranian breads, but a few of them, due to a variety of factors, could succeed. The aim of this study is to... more
Iranian bread production methods are often unsanitary, in the last decades, different attempts were made to mechanize production of Iranian breads, but a few of them, due to a variety of factors, could succeed. The aim of this study is to examine various factors affecting the system of bread production in Iran and to provide effective solutions for the development of mechanized bakeries as the main strategy for improving the quality of bread production. Existence of different factors and the relation between them makes the system of bread production a complex system; therefore, this study uses system dynamics approach to analyze this system and to design solutions. Furthermore, the system of bread production is broken down to three subsystems: knowledge and technology subsystem, economic subsystem, and political and social subsystem.
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Research Interests: Computer Science and CRC
The nature of input materials is changed as long as the product reaches the consumer in many types of manufacturing processes. In designing and improving multi-stage systems, the study of the steps separately may not lead to the greatest... more
The nature of input materials is changed as long as the product reaches the consumer in many types of manufacturing processes. In designing and improving multi-stage systems, the study of the steps separately may not lead to the greatest possible improvement in the whole system, therefore the study of inputs and outputs of each stage can be effective in improving the output quality characteristics. In this study, the double sampling method is applied for inspection where decision variables are the sample size per sampling time and the maximum amount of defective items in the first and second samples in each stage. Furthermore, uncertainty in parameters such as production, inspection, and replacement costs are included in the objective function and handled by a Monte-Carlo based optimization method. In order to show the efficacies of the proposed method, a numerical example has been designed, and further analyses on solutions have been conducted.
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Most of the existing approaches for fuzzy reliability analysis are based on fuzzy probability. The aim of this paper is to describe fuzzy reliability using fuzzy differential equation. The reliability of a system in real world... more
Most of the existing approaches for fuzzy reliability analysis are based on fuzzy probability. The aim of this paper is to describe fuzzy reliability using fuzzy differential equation. The reliability of a system in real world applications is affected by some uncertain parameters. Fuzzy reliability is a way to present the reliability function uncertainly using fuzzy parameters. In the proposed fuzzy differential equation for reliability, two types of fuzzy derivative: Hukuhara derivative and generalized differentiability are used. It is proved that the Hukuhara differentiability is not adequate for fuzzy reliability analysis. Finally, using the fuzzy integration, the concept of fuzzy mean time to failure (FMTTF) will be introduced. Some numerical simulations are presented to show the applicability and validity of generalized differentiability, in comparison with the Hukuhara differentiability results for fuzzy reliability analysis.
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Manufacturers need to evaluate the reliability of their products in order to increase the customer satisfaction. Proper analysis of reliability also requires an effective study of the failure process of a product, especially its failure... more
Manufacturers need to evaluate the reliability of their products in order to increase the customer satisfaction. Proper analysis of reliability also requires an effective study of the failure process of a product, especially its failure time. So, the Failure Process Modeling (FPM) plays a key role in the reliability analysis of the system that has been less focused on. This paper introduces a framework defining an approach for the failure process modeling with censored data in Constant Stress Accelerated Life Tests (CSALTs). For the first time, various types of censoring schemes are considered in this study. Usually, in data analysis, it is impossible to get closed form of estimates of the unknown parameter due to complex and nonlinear likelihood equations. As a new approach, a mathematical programming problem is formed and the Maximum Likelihood Estimation (MLE) of parameters is obtained to maximize the likelihood function. A case study in red Light- Emitting Diode (LED) lamps is a...
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Background and aims: Knowledge of safety attitude is very important for managers of organizations, because it can be used to predict their employee safety behaviors. In this way, a further exploration about safety attitude and knowledge... more
Background and aims: Knowledge of safety attitude is very important for managers of organizations, because it can be used to predict their employee safety behaviors. In this way, a further exploration about safety attitude and knowledge of workers as well as the relationship among the affecting factors is required. This study aimed to investigate the relationship between safety attitude and knowledge of workers and WAI in one of the large hospitals in Tehran. Methods: The research is cross-sectional and has been used of a random sampling method by a sample size of 340 people. In order to measure of safety attitudes and knowledge, Kumar questionnaire has been used, and the Occupational Safety and Health Institute of Finland WAI questionnaire has been used to evaluate WAI. Data analyses are also performed using SPSS 22 statistical analysis package. Results: This study showed that mean of safety attitude and knowledge is 6.1 ± 39.7, and most people (45.3%) are in the category of good WAI. Also, with increasing age and work experience, safety attitude and knowledge and work ability index is reduced. There was no significant relationship between education and work shifts and the safety attitude and knowledge and WAI. Occupational health and safety training courses, increase safety knowledge and attitude and work ability index. Conclusion: WAI has a significant relationship and direct and severe correlation with safety knowledge and attitude. Also educational courses in the field of occupational safety and health can be enhanced employee safety attitudes and knowledge toward safety.
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Simultaneous optimization of multiple quality characteristics (responses) of a product or process is required in many real-world problems. Multiresponse optimization (MRO) techniques tries to solve such problems; the ultimate objective of... more
Simultaneous optimization of multiple quality characteristics (responses) of a product or process is required in many real-world problems. Multiresponse optimization (MRO) techniques tries to solve such problems; the ultimate objective of which is to adjust control factors that provides most desired values for the responses. Regression techniques are most commonly used methods to identify and estimate relationships between control variables and responses. Due to the industrial advances and hence the complexity of processes and systems, many relationships between input variables and quality characteristics have become much more complex. In such circumstances, classic regression techniques encounter difficulties to create a well-fitted model which can be easily optimized. The alternative approach proposed in this study is a regression tree method called CART, which is a data mining method. Since the output of CART consists of several if-then terms, NSGA-II algorithm was considered to ...
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Improving quality in today’s complicated industrial systems is gaining more and more importance every day. Since applying these systems costs a lot, companies should try to offer the best outcomes and processes possible. One of the... more
Improving quality in today’s complicated industrial systems is gaining more and more importance every day. Since applying these systems costs a lot, companies should try to offer the best outcomes and processes possible. One of the products most applied is Tailor Welding Blanks, which is widely used in automobile, aerospace, and other industries. One of the best methods of producing Tailor Welding Blanks is Friction Stir Welding. Using this technology, sheets dissimilar in material and thickness can be joined. In this paper, the possibility of welding thin sheets of 5083-H12 and 6061-T6 aluminum alloy by Friction Stir Welding with the thickness of 1.5 mm is examined. To detect the impact of Friction Stir Welding parameters, i.e. rotational speed (r/min), linear speed (mm/ min), shoulder diameter (mm), and tilt angle (°), a Box-Behnken design was used and using multiple Response Surface Methodology values of robust optimization of tensile strength and elongation were derived. The opt...
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ABSTRACT The performance of an engine is one of the major concerns in the automotive industry. Increased emission restrictions on motor vehicles have led to the necessity of more accurate control on the engine performance. The objective... more
ABSTRACT The performance of an engine is one of the major concerns in the automotive industry. Increased emission restrictions on motor vehicles have led to the necessity of more accurate control on the engine performance. The objective of this study is to optimize the injection and ignition system in an automobile internal-combustion engine. In this paper the engine torque, the fuel consumption and the hydrocarbon emissions are considered as the main performance metrics of the engine, and a mathematical model is proposed on the basis of response surface methodology and two-stage stochastic programming. The proposed model encompasses desirability functions with a maximum–minimum operator to convert several responses into a single response and also considers the probabilistic pattern of regression coefficients by some random scenarios. To illustrate application of the proposed approach, it was applied in a real case in an automotive company. The results of this test represent a reasonable performance of the proposed approach.
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... Hakimi (1964;1965) [9] p-center problem Minimize the maximum distance that demand is from its closest facility given that we are locating a pre-determined number of facilities.Hakimi (1964;1965)[9,10] Mladenovic et al. (2003) [11] ...
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In many industrial systems, improvement of quality characteristics is a main step in product design. Design of experiments is a well-grounded approach to optimize quality characteristics (Response variables) in terms of design parameters... more
In many industrial systems, improvement of quality characteristics is a main step in product design. Design of experiments is a well-grounded approach to optimize quality characteristics (Response variables) in terms of design parameters (Factors). The aim of this study is to develop the mathematical model for continuous optimization and analysis of the multiple response surfaces whereas the responses are correlated.
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ABSTRACT To maintain optimal quality characteristics in the defined specification limits is a vital decision for any industry and service system. To avoid nonconformity in outputs, the stream of variations and their potential causes must... more
ABSTRACT To maintain optimal quality characteristics in the defined specification limits is a vital decision for any industry and service system. To avoid nonconformity in outputs, the stream of variations and their potential causes must be identified so that the response variables fall into desirable limits across the manufacturing or service chain. Response surface methodology is considered as a powerful technique to facilitate the analysis of the mentioned problem. This paper presents the general quality chain design problem as a mathematical program and also proposes a method to solve it using multiple response surface methodology. An example of multistage processes is analyzed by the proposed approach to show its efficacies numerically and analytically.
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ABSTRACT In the current competitive business world, viable companies are those that have flexible strategies and long-term plans, by which they can appropriately respond to a dynamic environment. These strategies are used to find the... more
ABSTRACT In the current competitive business world, viable companies are those that have flexible strategies and long-term plans, by which they can appropriately respond to a dynamic environment. These strategies are used to find the optimum allocation of company income to the main sources of development, for the expansion of company activities and for service expansions.This paper presents a new mathematical model for multiple echelon, multiple commodity Supply Chain Network Design (SCND) and considers different time resolutions for tactical and strategic decisions. Expansions of the supply chain in the proposed model are planned according to cumulative net profits and fund supplied by external sources. Furthermore, some features, such as the minimum and maximum utilisation rates of facilities, public warehouses and potential sites for the establishment of private warehouses, are considered. To solve the model, an approach based on a Lagrangian Relaxation (LR) method has been developed, and some numerical analyses have been conducted to evaluate the performance of the designed approach.