Ozgur Toy | Yasar University (original) (raw)

Papers by Ozgur Toy

Lecture notes in management and industrial engineering, 2023

Springer Proceedings in Energy, 2015

Population and the economic growth are highly correlated with the energy demand. The world popula... more Population and the economic growth are highly correlated with the energy demand. The world population was multiplied by a factor of 1.59 (reaching above 7 billion) from 1980 to 2013, while the total energy consumption of the world was multiplied by 1.84 (getting beyond 155,000 TWh) in the same time interval. Furthermore, the demand for energy is expected to increase even more with an average annual rate of 1.2 % in the near future. However, for the last 30 years, about 85–90 % of the energy demand is supplied by petroleum, natural gas, and coal, even though they are harmful for the environment and estimated to be depleted soon. Hence, building energy policies to satisfy the needs of increasing population and growing economy in a sustainable, reliable, and secure fashion has become quite important. This may involve optimizing the energy supplies, minimizing the environmental costs, promoting the utilization of clean and renewable energy resources and diversifying the type of energy sources. Thus, not only the conventional energy generation technologies must be developed more, but also environmentally friendly alternative energy sources (such as wind, solar, geothermal, hydro, and bio) must become more widespread to sustain the energy needs for the future. However, this requires a significant amount of research on energy technologies and an effective management of the energy sources.

International Journal of Production Economics, 2013

We consider the dynamic lot sizing problem for a warm/cold process where the process can be kept ... more We consider the dynamic lot sizing problem for a warm/cold process where the process can be kept warm at a unit variable cost for the next period if more than a prespecified quantity has been produced. Exploiting the optimal production plan structures, we develop nine rule-based forward solution heuristics. Proposed heuristics are modified counterparts of the heuristics developed previously for the classical dynamic lot sizing problem. In a numerical study, we investigate the performance of the proposed heuristics and identify operating environment characteristics where each particular heuristic is the best or among the best. Moreover, for a warm/cold process setting, our numerical studies indicate that, when used on a rolling horizon basis, a heuristic may also perform better costwise than a solution obtained using a dynamic programming approach.

Lecture Notes in Management and Industrial Engineering, 2021

European Journal of Operational Research, 2008

Naval units are vulnerable to accidents and hazards. Particularly on combat ships, explosive mate... more Naval units are vulnerable to accidents and hazards. Particularly on combat ships, explosive material storages, a complex network of electrical and mechanical systems, and battle stations and living quarters/compartments of the crew intermingle. The space limitations and simultaneous operational tasks combined with the difficult weather and sea conditions create a risky environment, hence extra caution is required for each activity. Decision makers on board may benefit from any tools which could be used to manage the risk for the mitigation of accidents and hazards. This is the first comprehensive work in the Turkish Navy to develop a risk management framework. In this work, we develop procedures and tools for each main stage of the risk management that can be applied by decision-makers at every level in naval units. We also discuss some of the risk analysis methods and their suitability at the stages of risk management process.

Public reporting burden for this collection of information is estimated to average 1 hour per res... more Public reporting burden for this collection of information is estimated to average 1 hour per response, including the tune for reviewing instruction, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1 204, Arlington, V A 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0 188) Washington DC 20503 AGENCY USE ONLY (Leave blank) 2. REPORT DATE September 96 3.

Military Operations …, Jan 1, 1997

, 1215 Jefferson Davis Highway, SuitB 1204, Aringten.VA 22202-4302, and fc> the Office of Managem... more , 1215 Jefferson Davis Highway, SuitB 1204, Aringten.VA 22202-4302, and fc> the Office of Management and Budget, Paperwork Fteouction Project(0704^)188), Washington, DC 20503.

Naval Research Logistics (NRL), Jan 1, 2009

We consider design of control charts in the presence of machine stoppages that are exogenously im... more We consider design of control charts in the presence of machine stoppages that are exogenously imposed (as under jidoka practices). Each stoppage creates an opportunity for inspection/repair at reduced cost. We first model a single machine facing opportunities arriving according to a Poisson process, develop the expressions for its operating characteristics and construct the optimization problem for economic design of a control chart. We, then, consider the multiple machine setting where individual machine stoppages may create inspection/repair opportunities for other machines. We develop exact expressions for the cases when all machines are either opportunity-takers or not. On the basis of an approximation for the all-taker case, we then propose an approximate model for the mixed case. In a numerical study, we examine the opportunity taking behavior of machines in both single and multiple machine settings and the impact of such practices on the design of an X – Q C chart. Our findings indicate that incorporating inspection/repair opportunities into QC chart design may provide considerable cost savings. © 2009 Wiley Periodicals, Inc. Naval Research Logistics 2009

IIE Transactions, Jan 1, 2006

We consider a dynamic lot sizing problem with finite capacity for a process that can be kept warm... more We consider a dynamic lot sizing problem with finite capacity for a process that can be kept warm until the next production period at a unit variable cost ω t only if more than a threshold value has been produced and is cold, otherwise. That is, the setup cost in period t is K t if xt− 1&amp;amp;lt; Q t− 1 and kt, otherwise (0≤ kt≤ K t). We develop a dynamic programming formulation of the problem, establish theoretical results on the structure of the optimal production plan and discuss its computational complexity in the presence of Wagner-Whitin-type cost ...

European Journal of Operational Research, Jan 1, 2008

We consider the dynamic lot-sizing problem with finite capacity and possible lost sales for a pro... more We consider the dynamic lot-sizing problem with finite capacity and possible lost sales for a process that could be kept warm at a unit variable cost for the next period t+ 1 only if more than a threshold value Qt has been produced and would be cold, otherwise. Production with a cold process incurs a fixed positive setup cost, Kt and setup time, St, which may be positive. Setup costs and times for a warm process are negligible. We develop a dynamic programming formulation of the problem, establish theoretical results on the structure of ...