Reza Tavakoli Moghadam; Fariborz Jolai; Somayyeh Ghandi Beygi
Abstract
The parallel machine scheduling problem is an important and difficult problem to be considered in the real-world situations. Traditionally, this problem consists of the scheduling of a set of independent jobs on parallel machines with the aim of minimizing the maximum job completion. In today's manufacturing ...
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The parallel machine scheduling problem is an important and difficult problem to be considered in the real-world situations. Traditionally, this problem consists of the scheduling of a set of independent jobs on parallel machines with the aim of minimizing the maximum job completion. In today's manufacturing systems, in which both early and tardy finishing of job processing are undesired, the objectives related to earliness and tardiness penalties have become increasingly popular. In this paper, two major goals are considered as follows: (1) total weighted earliness; (2) total weighted tardiness. Due to the complexity of such a hard problem, a new multi-objective meta-heuristic method, i.e. multi-objective scatter search (MOSS), is proposed to obtain the locally Pareto-optimal frontier where the simultaneous minimization of the above-mentioned objectives is desired. In order to validate the performance of the proposed MOSS method, in terms of solution quality and diversity level, various test problems are considered and the reliability of this method, based on different comparison metrics, is compared with the Elite Tabu Search (ETS) devised in this paper. The computational results show the high capability of the proposed MOSS method.
Parham Pahlevani; Mahmoud Reza Delavar; Farhad Samad Zadegan
Abstract
Multi-criteria shortest path problems (MSPP) are called as NP-Hard. For MSPPs, a unique solution for optimizing all the criteria simultaneously will rarely exist in reality. Algorithmic and approximation schemes are available to solve these problems; however, the complexity of these approaches often ...
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Multi-criteria shortest path problems (MSPP) are called as NP-Hard. For MSPPs, a unique solution for optimizing all the criteria simultaneously will rarely exist in reality. Algorithmic and approximation schemes are available to solve these problems; however, the complexity of these approaches often prohibits their implementation on real-world applications. This paper describes the development of a geospatial information system (GIS)-based genetic algorithm (GA) approach to MSPP on simple networks with multiple independent criteria. The GA approach is shown to explore the underlying network space, generate large candidate path sets, and evolve high quality approximations to the optimal MSPP solution(s) adequately.
Ahmad Assempour; Sa'eed As'adi
Abstract
In this paper, a mathematical model for symmetrical multi-layer sheet rolling, in which the layers are unbounded before rolling, by using the upper bound method and stream function theorem is proposed. Using this model, we can investigate the plastic deformation behavior of sheets at the roll gap during ...
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In this paper, a mathematical model for symmetrical multi-layer sheet rolling, in which the layers are unbounded before rolling, by using the upper bound method and stream function theorem is proposed. Using this model, we can investigate the plastic deformation behavior of sheets at the roll gap during rolling. Effect of various rolling conditions such as initial and final thickness and flow stress of sheets, friction factors, rolling velocity and etc. on the rolling power and force, the thickness reduction of each layer, the relative length of plastic region in each layer and etc. are discussed. The velocity field derived from the newly proposed stream function can automatically satisfy the volume constancy and velocity boundary conditions within the roll gap. The optimized velocity fields are obtained through the minimization of total power, which is expressed by the function of five pseudo-independent parameters, during the plastic deformation. The analytical predictions from the proposed model were compared with the analytical and experimental results of other investigators and a good agreement is shown. Present model is applicable for simulating and online control applications of the rolling process of multilayer sheets.