Scientia Iranica
Volume:27 Issue: 3, May-Jun 2020

Hub facility location problems involve the establishment of strategic hub facilities and allocation of demand nodes to them. Meanwhile, with the emergence of new transport and distribution networks with multi-level structures, the design of such networks has been evolved. The diversity in transportation system has added multimodality to these problems. Considering the strategic nature and long-term implications of decision-making in this field, the decisions shall be of high reliability. The present study is an attempt to consider reliability of communication paths in proportion to the volume of transaction through them while covering all of the above-mentioned issues in hub location problems at the same time. Incorporating hierarchical characteristics of the problem into the model, one can obtained a significantly enhanced model in terms of multimodality and reliability. A Lagrangian solution method was developed considering the strategic level of the problem and the importance of the solution accuracy. The model was then validated in terms of time and quality.

The increasing importance of these two subjects, maintenance and cleaner environment, beside the relations between them, encourages us to investigate a mathematical Markovian model for Condition Based Maintenance problem while considering environmental effects. In this paper, the problem of proposing maintenance optimal policy for a partially observable, stochastically deteriorating system is studied, in order to maximize the average profit of the system with consideration of sustainability aspects. The modeling of this Condition Based Sustainable Maintenance (CBSM) problem is done using mathematical methods such as Partially Observable Markov Decision Process (POMDP) and Bayesian theory. A new exact method named Accelerated Vector Pruning method and other popular estimating and exact methods are applied and compared in solving the presented CBSM model and several managerial conclusions were obtained.

Shop floor control (SFC) is one of the main concepts in manufacturing resource planning (MRPII) and production scheduling is a key element in SFC. This paper studies the hybrid flow shop scheduling problem where jobs are multiprocessor. The objective is to minimize total completion time. Although there are several papers considering hybrid flow-shop scheduling problem with multiprocessor tasks, but none propose a mathematical model for this problem. At first, the two problems (fixed and selective cases) are mathematically formulated by mixed integer linear programming models. Using commercial software, the model is used to solve the small instances of the problems. Moreover, an elephant herding optimization is developed to solve large instances of the problems. To numerically evaluate the proposed algorithm, it is compared with two available algorithms in the literature, simulated annealing and shuffled frog-leaping algorithm in the literature.

Services are increasingly important in the modern economy, for both service and manufacturing firms, yet inventory literature has been focused mainly on physical goods and, only a few studies have included services in optimization. On the other side, traditional service management literature relies on an extremely narrow definition of inventory that excludes services, because they are perishable. Thus, there is a lack of research in the link between inventory optimization and service management. However, according to a new service inventory approach, businesses components such as tasks or information, as different from physical goods, can be performed and stored in anticipation of service demand as a form of service inventory—that is, inventorying by anticipation rather than delaying the service. This article aims to contribute to this lack of research by proposing a service inventory optimization model that integrates a service orientation to optimize tasks and information to be performed in advance. In contrast with traditional inventory models, where the objective is to optimize physical items, in this approach physical products whenever included, constitute only mechanisms for service provision. This service inventory model contributes to optimize the quantity of tasks or information to be anticipated and thus provides benefits for customers.

Control chart is one of the important tools in statistical process control (SPC) that plays a significant role in monitoring and identifying disturbances of any production process. The Shewhart, cumulative sum (CUSUM) and exponentially weighted moving average (EWMA) are commonly used control charts for detecting process shifts. CUSUM and EWMA chart are more sensitive in detecting smaller shifts whereas the typical Shewhart chart is known to be only sensitive to large process shifts. The present study incorporates ratio-type estimators based on auxiliary information in CUSUM structure as a substitute of simple mean estimator for monitoring process location. These estimators are more efficient than the simple mean estimator in the presence of high correlation between the study and the auxiliary variables. Average run length (ARL), standard deviation of run length (SDRL) and extra quadratic loss (EQL) are used to measure the performances of the proposed charts. The performance comparison of the proposed chart with the existing CUSUM, CUSUM-FIR and many other control charts are made by using out-of-control ARL. The comparison revealed the superiority of the suggested charts over the other existing charts. An illustrative example is also provided for the performance evaluation of the proposed charts.

The work substantiates a technical solution for improving the working conditions for the thermal factor in the extraction of oil by the thermoshaft method using the mine refrigeration technology. The review of manufacturers and technical characteristics of refrigeration technology in Russia, CIS countries and Western Europe was conducted. For the selected set, the economic efficiency of the project was assessed and a conclusion was made about the feasibility of implementing this project solution. It was shown that the use of a water cooling machine in the mine air conditioning system will reduce the air temperature in the oil production gallery to the required values and will allow to abandon the long-term construction of a surface stationary refrigeration station. Normalization of the thermal regime reduces the costs of benefits and compensation for work in harmful labor conditions and improves the quality of service of production wells by operators. The project for the introduction of air conditioning has a high level of profitability, and its payoff will occur in the second year of operation.

Due to high competition, companies tend to improve their market share by applying different selling mechanisms such as online to offline commerce as an efficient selling mechanism in which the companies sells their products via both online and real stores. This study deals with a selling problem for two complementary supply chains including a supplier and a shopping center where the commodities are sold by a virtual and a traditional shopping center who present items as complementary shopping centers. It is assumed that market demand depends on price and service level so that they can purchase the item via both shopping centers based on their priorities. Also to analyze the reactions of the chain’s partners, different games such as Nash and Stackelberg game are deemed. The aim is to obtain the closed-form solutions of the decision variables of the networks’ members in order to maximize their profits where the prices of different selling periods at each echelon of the chains are the decision variables of the model. The closed-form solutions are derived and the solutions are examined by a numeric example. In following, several sensitivity analyses on key factors are performed to determine efficient ones on the variables and profits.

We study a multi-time, multi-product and multi-echelon supply chain aggregate procurement, production and distribution planning problem and discuss the implications of formulating a tri-level model to integrate procurement, production and distribution, maintaining the existing hierarchy in the decision process. In our model, there are three different decision makers controlling the procurement, production and the distribution processes in the absence of cooperation because of different optimization strategies. First, we present a hierarchical tri-level programming model to deal with decentralized supply chain problems. Then, an algorithm is presented to solve the proposed model. A numerical illustration is provided to show the applicability of the optimization model and the proposed algorithm. In order to evaluate the application of the model and the proposed algorithm, ten sets of small and large problems are randomly generated and tested. The experimental results show that our proposed fuzzy-stochastic simulation based hierarchical interactive particle swarm optimization (Sim-HIPSO) performs well in finding good approximate solutions within reasonable computation times.

The aim of this paper is to introduce interval trapezoidal neutrosophic set which is a combination of trapezoidal fuzzy numbers and interval neutrosophic set. The paper presents some operational rules, the score and accuracy functions of interval trapezoidal neutrosophic numbers. Then, some aggregating operators under interval trapezoidal neutrosophic information which are called interval trapezoidal neutrosophic number weighted arithmetic averaging (ITNNWAA) operator and interval trapezoidal neutrosophic number weighted geometric averaging (ITNNWGA) operator, are proposed, and their properties are investigated in detail. Furthermore, based on these operators a multi-attribute decision making method is developed. Finally, a numerical example is presented to illustrate the application and effectiveness of the proposed method.

In this paper, we present a numerical method based on septic B-spline function for nonlinear singular second-order two-point boundary value problems, which depend on different physiological processes as thermal explosions problem and the steady state oxygen diffusion in a spherical cell with Michaelis–Menten uptake kinetics and distribution of heat sources in the human head. Septic B-spline method has a truncation error of O(h^8) and converges to the exact solution with O(h^6). The numerical problems show that our method is very effective. The resulting sets of differential equations are modified at the singular point and are treated by using septic B-spline for finding the numerical solution. The maximum absolute errors and the absolute residual errors are acceptable.