Sharif Digital Repository

This work considers scheduling problems minding the setup and removal times of jobs rather than processing times. For some production systems, setup times and removal times are so important to be considered independent of processing times. In general, jobs are performed according to the automatic machine processing in production systems, and the processing times are considered to be constant regardless of the process sequence. As the human factor can influence the setup and removal times, when the setup process is repetitive the setup times decreases. This fact is considered as learning effect in scheduling literature. In this study, a bi-criteria m-identical parallel machines scheduling... 

An effective facility layout implies that departments with high flow are laid adjacent. However, in the case of a very narrow boundary length between the neighbouring departments, the adjacency would actually be useless. In traditional layout design methods, a score is generally assigned independent of the department’s boundary length. This may result in a layout design with a restricted material flow. This article proposes a new concept of adjacency in which the department pairs are laid adjacent with a wider path. To apply this concept, a shop with unequal rectangular departments is contemplated and a mathematical programming model with the objective of maximizing the sum of the adjacency... 

The main propose of this research is providing a tool for suitable modeling, increase efficiency and decrease construction cost of solar absorption chiller. At first, the solar absorption chiller is modeled by the thermodynamic laws. Then, this model is converted to the new standard mathematical programming model with considering all technical and economic constrains. This mathematical model is optimized by Genetic algorithm (GA). After applying GA, optimized parameters of chiller heat exchanger designing and its electricity consumption are calculated. These parameters consist of heat exchanger effectiveness, heat transfer cross section area, heat transfer coefficient, efficiency of pump and... 

We present a new approach for emergency response planning to the injured on a multi-type transportation network. We consider a three-type transportation network with separate connection links simultaneously: road, rail and air networks. In this study, a circle-based approach is presented where using concentric circles with various radiuses, different levels of the effect of a disaster are considered. After formulating the relations, we present an integer nonlinear programming model for the problem. The model is to determine the locations for establishment of temporary aid stations among the candidate locations, the type of aid stations, the percentage of the injured allocated to each... 

In this study a new version of adjacency, which provides a more flexible layout design, is proposed. In the proposed version, departments which are nonadjacent yet close to each other are considered to be adjacent with a smaller adjacency rating. It is shown that the proposed adjacency is a generalized version of the traditional adjacency. A mathematical programming model is developed for the proposed facility layout problem. To show the flexibility and efficacy of the proposed model, a computational study is conducted. The solution of an illustrative example as well as the solutions of several test problems, reveal flexibility and efficacy of the proposed model  

As part of its Paris Agreement commitment, Iran pledged to decrease 4 % of its carbon dioxide (CO2) emissions from 2020 to 2030. About 29% of total emission in Iran belongs to electricity supply while energy consumption in other sectors (transport, household, and industry) have a lower share in CO2 emission. The main concern here is finding the optimal mix of power plants in the electricity supply system that should be deployed to meet Iran’s mentioned respective targets and considering simultaneously interests of consumers and producers in this energy system. So, we developed a non-linear mathematical programming model for Iran’s electricity system to address this concern with changing... 

In this paper, the problem of scheduling commercial messages during the peak of viewing time of a TV channel is formulated as a combinatorial auction-based mathematical programming model. Through this model, a profitable and efficient mechanism for allocating the advertising time to advertisers is developed by which the revenue of TV channels is maximised while the effectiveness of advertising is increased. We developed a steady-state genetic algorithm to find an optimal or a near optimal solution for the proposed problem. A computational experiment was conducted for evaluating the efficiency of the proposed algorithm. A set of test problems with different sizes were generated, using the... 

This paper studies the scheduling problem in transit networks in order to decrease transfer waiting time. Transfer waiting time is calculated based on headway and departure time of intersecting routes and is divided into two parts. The first part can be reduced by changing departure times and was studied by the authors previously. The focus of the present research, however, is to minimize the second part of the transfer waiting time, dependent on the headways. The proposed optimization model in this paper includes both parts and is a nonlinear mathematical programming model. The model is decomposed to the departure time setting model (DSM) and the headway setting model (HSM). A solution... 

In this manuscript, a vehicle allocation problem involving a heterogeneous fleet of vehicles for delivering products from a manufacturing firm to a set of depots is considered. Each depot has a specific order quantity and transportation costs consist of fixed and variable transportation cost. The objective is to assign the proper type and number of vehicle to each depot route to minimize the total transportation costs. It is assumed that the number of chartering vehicle types is limited. It is also assumed that a discount mechanism is applied to the vehicles renting cost. The discount mechanism is applied to the fixed cost, based on the number of vehicles to be rented. A mathematical... 

Single floor facility layout problem (FLP) is related to finding the arrangement of a given number of departments within a facility; while in multi-floor FLP, the departments should be imbedded in some floors inside the facility. The significant influence of layout design on the effectiveness of any organization has turned FLP into an important issue. This paper presents a three- (two-) stage mathematical programming method to find competitive solutions for multi- (single-) floor problems. At the first stage, the departments are assigned to the floors through a mixed integer programming model (the single floor version does not require this stage). At the second stage, a nonlinear programming... 

The problem of allocating different types of vehicles for transporting a set of products in an existing transportation network, to minimize the total transportation costs, is considered. The distribution network involves a heterogeneous fleet of vehicles each with the given capacity and with a variable transportation cost and a fixed cost with a discounting mechanism. Due to nonlinearity of the discounting mechanism, a nonlinear mathematical programming model is developed. A prioritized K-mean clustering encoding is introduced to designate the distribution depots distances, their demands, and the vehicles’ capacity. Using this priority clustering, a heuristic routine is developed by which... 

This paper presents a facility layout design for a cellular manufacturing system (CMS), with the automated guided vehicles (AGVs) as the transportation device, to minimize the total material handling costs. A new concept of assigning the workstations to the non-overlapping closed zones, by which independent AGVs are allocated for internal transfer of materials/parts in each zone, is proposed. To handle this problem, a mathematical programming model is developed. The problem has been shown to be NP-hard. This computational difficulty has led us to consider suboptimal solutions generated by a Tabu search with three algorithmic variants. To evaluate the efficiencies of these algorithms, an... 

Continuity of supply plays a significant role in modern distribution system planning and operational studies. Accordingly, various techniques have been developed for reliability assessment of distribution networks. However, owing to the complexities and restrictions of these methods, many researchers have resorted to several heuristic optimization algorithms for solving reliability-constrained optimization problems. Therefore, solution quality and convergence to global optimality cannot be guaranteed. Aiming to address this issue, two salient mathematical models are introduced in this paper for topology-variable-based reliability evaluation of both radial and radially-operated meshed... 

Municipal solid waste (MSW) directly impacts community health and environmental degradation; therefore, the management of MSW is crucial. Medical waste is a specific type of MSW which is generally divided into two categories: infectious and non-infectious. Wastes generated by coronavirus disease 2019 (COVID-19) are classified among infectious medical wastes; moreover, these wastes are hazardous because they threaten the environment and living organisms if they are not appropriately managed. This paper develops a bi-objective mixed-integer linear programming model for medical waste management during the COVID-19 outbreak. The proposed model minimizes the total costs and risks, simultaneously,...