Endüstri Mühendisliği
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Browsing Endüstri Mühendisliği by Author "Ağralı, Semra."
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Item A lot sizing problem in deliberated and controlled co-production systems(Thesis (M.A.) - Bogazici University. Institute for Graduate Studies in the Social Sciences, 2018., 2018.) Pamuk, Bahadır.; Taşkın, Zeki Caner.; Ağralı, Semra.Deliberated and controlled co-production can be defined as the production of different products simultaneously where production parameters are known and co production is deliberate. We study an extension of the lot sizing problem in a deliber ated and controlled co-production system, and show that it is NP-Hard. We investigate special cases of the problem for which it is polynomially solvable, and propose solution techniques for those special cases. We propose four mixed integer programming model formulations based on single item uncapacitated lot sizing and simple plant location formulations. We show that solution spaces of the linear relaxations of the proposed formulations are equal. We propose valid inequalities for the problem and show that our proposed valid inequalities added to the model with a separation algorithm improve the linear relaxation lower bound by more than %20 for all test instances. We propose a pattern fitting heuristic that aims to find initial feasible solutions for a commercial solver. We propose another heuristic based on Wagner-Whitin’s algorithm to create integer feasible solutions from fractional solutions. We show that the average optimal ity gap is reduced by at least %10 with proposed improvements to MIP formulations. We also show that the quality of integer feasible solutions is increased within a given time limit.Item Mathematical programming approaches for a generation expansion planning problem in a carbon-constrained environment(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2016., 2016.) Terzi, Fulya.; Taşkın, Zeki Caner.; Ağralı, Semra.In this thesis, we study a Generation Expansion Planning (GEP) problem in a carbon-constrained environment from the perspective of a private electricity generating company. The company plans to enter the partially regulated electricity generation market, in which carbon emission permits are traded. Hence, the government requires the company to obey a limit for the total carbon emission. The company determines the amount of installed capacity for di erent types of power plants, which may or may not include carbon capture and storage (CCS) technology over a predetermined planning horizon. The company's aim is to maximize the net present value of the total pro t. The market and the company have some restrictions on the investments. The amount of installed capacity is limited by a maximum and a minimum value for each period for all power plant types. The government constrains the market share of the company in order to prevent monopoly. On the other hand, the company aims to reach certain levels of market share at certain time periods. Moreover, the company restricts the percentage of each type of power plant investments in the portfolio by some upper bound to distribute the investment risk. We rst formulate the problem as a deterministic mixed integer linear programming model assuming that all data are known in advance and xed. Then, we use multi-stage stochastic programming approach to include uncertainties in the parameters. We implement these models for a hypothetical company operating in Turkey. We apply sensitivity analysis in our deterministic model to determine the e ects of parameters on the optimal decision.Then, in stochastic model, we analyze the problem by creating scenarios for uncertain parameters.