Browsing by Author "Yildirim, Gonca"

Now showing 1 - 3 of 3

Citation - WoS: 1
Citation - Scopus: 1
Cycle Cost Considerations in a Continuous Review Inventory Control Model
(Taylor & Francis Ltd, 2021) Yildirim, Gonca; Konur, Dincer; 45908; 01. Çankaya Üniversitesi; 06. Mühendislik Fakültesi; 06.04. Endüstri Mühendisliği
In this study, the continuous review order-quantity-re-order point (Q, R) model is analysed with cycle cost considerations. First, we formulate the maximum cycle cost of a given (Q, R) policy using a distribution-free approach. Then, two approaches are introduced to minimize the maximum cycle cost: (i) adjusting R of a given (Q, R) policy and (ii) designing a new (Q, R) policy. Optimum inventory control decisions are characterized for each approach. A set of numerical studies is presented to compare the outcomes of both approaches to three long-term cost minimization approaches, namely the cost minimizing (Q, R) policy, the distribution-free minmax (Q, R) policy, and the distribution-free (Q, R) policy based on the maximum entropy principle. Our numerical results demonstrate the viability of the two approaches introduced and discuss implications of penalty costs and lead time demand's coefficient of variation. Later, we formulate a bi-objective model with the objectives of expected cost and maximum cycle cost minimizations and propose a bi-directional method to approximate the set of Pareto efficient solutions. Numerical examples are presented to illustrate the algorithm and demonstrate the Pareto front.
Citation - WoS: 1
Citation - Scopus: 1
Designing an Annual Leave Scheduling Policy: Case of a Financial Center
(Amer inst Mathematical Sciences-aims, 2022) Aydemir-Karadag, Ayyuce; Yildirim, Gonca; 45908; 116059; 01. Çankaya Üniversitesi; 06. Mühendislik Fakültesi; 06.04. Endüstri Mühendisliği
Providing annual leave entitlements for employees can help allevi-ate burnout since paid-time off work directly affects the health and productivity of workers as well as the quality of the service provided. In this paper, we de-velop realistic vacation scheduling policies and investigate how they compare from both the employer and the employees' perspectives. Among those poli-cies, we consider one that is used in practice, another that we propose as a compromise which performs very well in most cases, and one that is similar to machine scheduling for benchmarking. Integer programming models are for-mulated and solved under various settings for workload distribution over time, substitution and unit of time for vacations. We use three performance mea-sures for comparisons: penalty cost of unused vacation days, percent vacation granted and level of employee satisfaction. We provide a real-life case study at a bank's financial center. Numerical results suggest that an all-or-nothing type of vacation policy performs economically worse than the others. Attrac-tive annual leave scheduling policies can be designed by administering vacation schedules daily rather than weekly, ensuring full cover for off-duty employees, and offering employees some degree of choice over vacation schedules.
Citation - WoS: 3
Citation - Scopus: 5
A General Production and Financial Planning Model: Case of a Poultry Integration
(Springer Heidelberg, 2020) Satir, Benhur; Yildirim, Gonca; 45908; 54700; 01. Çankaya Üniversitesi; 06. Mühendislik Fakültesi; 06.04. Endüstri Mühendisliği
We propose a general linear programming formulation for a poultry integration to facilitate decision making in production and financial planning. The formulation is motivated by a medium-size application and by involving practitioners from the industry. It is a realistic and strategic model since we incorporate all divisions in a complex poultry integration, (including, but not limited to, feed mill, breeder coops, incubation house, broiler coops, slaughterhouse and distribution centers) as well as the interrelations among these divisions. The horizon we consider is in years, which makes the plan a strategic level plan in this fast-paced industry. Through extensive experimentation with various end-customer demand scenarios, we found out that the quantity of breeder chicks to buy at certain times during the planning horizon is the robust key decision variable in the overall system.