Person: AKTİN, AYŞE TÜLİN
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AKTİN
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AYŞE TÜLİN
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Publication Metadata only Tedarikçi Seçimi ve Değerlendirmesi Problemine Bir Yaklaşım: Analitik Hiyerarşi Süreci Yöntemi(1995) AKTİN, AYŞE TÜLİN; 109203Publication Metadata only Joint Decision Making for Production and Marketing(1995) Ulusoy, Gündüz; AKTİN, AYŞE TÜLİN; 109203The prosperity of a firm depends highly on the functional integration of its various departments, and in particular the cooperation between the production and the marketing departments appears to have a large impact on the well-being of a firm. The aim of this study is to model an aggregate production planning problem that considers the production and marketing functions in a simultaneous manner. The developed multi-period, multi-product model with the objective of profit maximization reflects the characteristics of both departments. Demand for each product in each period is generated through the use of demand functions. The advertising efficiency and price of the products are determined within the model. The cash outflow for advertising expenditures is approximated by a quadratic cost function, and the production cost exhibits economies of scale. Also, stockouts are taken into consideration in the form of backlogging. A solution methodology consisting of two phases is developed, and cases displaying some important characteristics are generated and solved in order to test the performance of the proposed model. This methodology incorporates linear mixed integer programming which is embedded in two different search techniques, along with a dynamic programming-based heuristic procedure.Publication Metadata only A hierarchical planning approach for a production-distribution system(TAYLOR & FRANCIS LTD, ONE GUNPOWDER SQUARE, LONDON EC4A 3DE, ENGLAND, 1999-11-10) Özdamar, Linet; AKTİN, AYŞE TÜLİN; 57877; 109203A production-distribution model involving production and transportation decisions in a central factory and its warehouses is developed. The model is based on the operating system of a multi-national company producing detergents in a central factory from which products are distributed to geographically distant warehouses. The overall system costs are optimized considering factory and warehouse inventory costs and transportation costs. Constraints include production capacity, inventory balance and fleet size integrity. Here, a hierarchical approach is adopted in order to make use of medium range aggregate information, as well as to satisfy weekly fluctuating demand with an optimal fleet size. Thus, a model which involves an aggregation of products, demand, capacity, and time periods is solved. In the next planning phase, the aggregate decisions are disaggregated into refined decisions in terms of time periods, product families, inventory and distribution quantities related to warehouses. Consistency between the aggregate and disaggregation models is obtained by imposing additional constraints on the disaggregation model. Infeasibilities in the disaggregated solution are resolved through an iterative constraint relaxation scheme which is activated in response to infeasible solutions pertaining to different causes. Here, we investigate the robustness of the hierarchical model in terms of infeasibilities occurring due to the highly fluctuating nature of demand in the refined time periods and also due to the aggregation process itself.Publication Metadata only Sipariş Üzerine Üretimde Ürün Ailelerine Bağlı Bir Üretim Planlama Yaklaşımı(1996) Özdamar, Linet; AKTİN, AYŞE TÜLİN; 109203; 57877Publication Metadata only Capacity Driven Due Date Settings in Make-to-Order Production Systems(1997-03-14) Özdamar, Linet; AKTİN, AYŞE TÜLİN; 57877; 109203Due date setting is a difficult task for make-to-order companies and requires efficient capacity and lead time management. In the job-shop literature, production planning for make-to-order companies is tackled by using shop floor scheduling algorithms coupled with simulation. However, capacity management cannot be realized in the most detailed phase of planning and should be carried out at a higher decision level so that work loads are smoothed over time. A linear capacity planning model is proposed for dealing with problems of load leveling in bottleneck departments over a planning horizon. In this model, end items in each order are conveniently grouped into product families so that the proposed model becomes tractable in terms of practical problem sizes. Capacity constraints are included in the model and covers a number of future periods with known firm orders. The objective is to minimize total backorder and overtime costs. In this context, an order is assumed to be backordered if it is delivered some weeks later than that of its arrival. Actually, the time during which an order is backordered represents the production lead time for that order. Furthermore, the production lead time of each order is constrained by an order specific maximum lead time determined as a company policy. The output of the model conveys weekly order release and delivery times which serve as order due dates. Hence, lead time management and due date setting as well as load leveling are achieved by the proposed model. Since the model does not take family set-up times into consideration, an iterative algorithm which balances over time, the additional capacity demanded by set-up times, is proposed. The production plan developed for the bottleneck department is propagated to the other stages of the production system through a binary LP model whose binary variables are reduced at every stage. The proposed multi-stage planning system is applied for planning production in a manufacturing company which makes/assembles custom kitchen cupboards. The case study demonstrates the advantages of the system.Publication Metadata only An Application of the Analytic Hierarchy Process to the Supplier Selection Problem(1997) Barbarosoğlu, Gülay; AKTİN, AYŞE TÜLİN; 109203