Capacity Optimization in Dynamically Routing Computer Network Systems

A computer network system is a complex system with a great number of dynamic components. There are many devices in the system, such as computers, routers, lines, hubs, and switches. In addition to these hardware systems, many protocols are integrated to set the rules and provide the way of communication. Due to the nature of the system, it is hard to formulate and solve problems analytically without making any assumptions. One of the prominent problems that occur in computer systems is the line capacity assignment problem. In the previous mathematical models, message routes were predetermined and the dynamic nature of the system was neglected. This study deals with the line capacity assignment problem under a dynamically routing policy. Four different computer network topologies are used and solved by two heuristic algorithms via simulation. A dynamic search approach based on the occupancy rate of lines is used to define the consecutive routes of messages. The performances of harmony search and genetic algorithms via simulation are compared with the results of OptQuest, one of the optimization packet programs embedded in simulation software Arena®

The Problem of Sustainable Intermodal Transportation: A Case Study of an International Logistics Company, Turkey

Environmental and social concerns force logistics firms to evaluate various risk factors for intermodal transportation systems. In this context, this paper takes into account economic, social, and ecological risk factors that have attracted considerable attention toward sustainable transportation. In this paper, the allocation of export containers to transportation modes, by incorporating social and ecological risks with a main focus on the minimization of transportation costs, was examined. A mixed-integer-programming-based mathematical model was proposed to decide how the containers can be allocated to different transportation modes. In addition, a fuzzy-based approach was performed to determine the social and ecological risk weights of the transportation modes within the decision process. Each mode was evaluated with social risks (e.g., human accidents and deaths) and ecological risks (e.g., emission values and noise pollution) by decision makers via the assignment of numerical scores. The obtained results show that optimal transportation modes more economical and environmentally friendly were provided by the proposed methods

Improving Materials Handling Systems via Simulation Approach for a Woodworking Manufacture Company

Üretim içi malzeme taşıma sistemleri, üretimin hem iş sağlığı ve güvenliğine uygun yürütülmesi hem de sürekliliğinin sağlanması açısından kritik öneme sahiptir. Özellikle yüksek hacim ve ağırlıktaki nesnelerin iş merkezleri arasında transferi oldukça sorunludur. Bu çalışmada, ağaç ürünleri üretimi yapan bir işletmede üretim sahasındaki iş merkezleri arasındaki malzeme taşıma sistemi ele alınmış ve taşıma alternatifleri kesikli olay simülasyonu yaklaşımıyla değerlendirilmiştir. Sonuçlara göre, konveyör sistemlerinin kullanımının istatistiksel olarak anlamlı olduğu görülmüştür. Yatırım kararları göz önüne alındığında da konveyör sistemlerinin kullanımının uzun dönemde daha uygun olduğu görülmüştürEnsuring both of the production sustainability and working with suitable conditions to occupational health and safety makes in-bound material handling systems critically important. Especially, transferring objects having high volume and weight between work centers causes a lot of problems. In this study, the material handling system between the work centers on a production site for a woodworking manufacturer is considered and the transportation alternatives are evaluated via discrete event simulation approach. According to results, using conveyor systems is found statistically significant. When investment costs are considered, using conveyor systems are more suitable in long ter

A New Dynamic Pricing Model for the Effective Sustainability of Perishable Product Life Cycle

Perishable products run their life cycle in a short period of time due to the shortness of their shelf lives. Product efficiency falls when especially non-recyclable products are thrown away without being used. Furthermore, this kind of products that unnecessarily occupy shelves of supermarkets cause supermarkets to follow an insufficient stock management policy. Unconscious and unplanned use of our limited natural resources will deteriorate the product portfolio for future generations. Such unconscious production and consumption patterns will disrupt natural balance and damage sustainability of products. In addition to creating very high costs for producers, sellers and consumers alike, these unsold or stale products lead to environmental problems due to such pricing policies. In other words, although the products have to be thrown away without being sold is attributed by many managers to be attributable to the unplanned over-orders, the actual reason is something else. The real contributor of the problem is changing purchase attitudes of customers because of wrong pricing policies of wholesaler. In addition, limited resources are also consumed fast and in unnecessary amounts. The imbalance in respect to the sustainability of these products leads to increase in the production costs, procurement costs and failure to achieve balance among products to be kept in storage houses as some of the products occupy stocks unnecessarily. In the present study, a new pricing policy is developed for product stock whose shelf lives are about to expire and generally become waste to increase salability of these products in reference to fresher stocks of these products. The present study, which is designed to reduce the above-mentioned losses, will seek to minimize the cost of waste, maximize the profit earned by supermarkets from the product, maximize product utilization rates and ensure sustainability of products and stocks as well. Fulfillment of these objectives will increase productivity and enhance the significance of product efficiency and nature-friendly attitudes

A Mathematical Modeling Approach for Materials Requirements Planning in Remanufacturing

Remanufacturing has become an ever more important topic due to a growing need for environmentalfriendly production strategies and an efficient use of resources. Traditional materials requirements planning (MRP) methods need to be adjusted in line with these new manufacturing environments where both manufacturing and remanufacturing are involved. In this study, a mathematical programming model is formulated for materials requirements planning decision in a multi-product, multi-period remanufacturing system where the assembly of final product is done both through use of parts procured from the disassembly of returned (used) (core) products and by ordering new (unused) parts. The decisions regarding the purchase and disassembly of new parts or used products as part of materials requirements planning are made for the purpose of minimizing the costs. The developed model takes into account, in a deterministic manner, the quality of the product to be disassembled, disposal cost of defective cores, lead time for purchasing new parts, disassembly bill of materials, disassembly capacity and disassembly time of each part. The mathematical model is illustrated through application to a sample problem, and an experimental design is provided in order to identify the ways in which different conditions in a manufacturing environment affect the total cost of the systemRemanufacturing has become an ever more important topic due to a growing need for environmentalfriendly production strategies and an efficient use of resources. Traditional materials requirements planning (MRP) methods need to be adjusted in line with these new manufacturing environments where both manufacturing and remanufacturing are involved. In this study, a mathematical programming model is formulated for materials requirements planning decision in a multi-product, multi-period remanufacturing system where the assembly of final product is done both through use of parts procured from the disassembly of returned (used) (core) products and by ordering new (unused) parts. The decisions regarding the purchase and disassembly of new parts or used products as part of materials requirements planning are made for the purpose of minimizing the costs. The developed model takes into account, in a deterministic manner, the quality of the product to be disassembled, disposal cost of defective cores, lead time for purchasing new parts, disassembly bill of materials, disassembly capacity and disassembly time of each part. The mathematical model is illustrated through application to a sample problem, and an experimental design is provided in order to identify the ways in which different conditions in a manufacturing environment affect the total cost of the syste

Analysis of price-discounted stochastic inventory policies for perishable items using simulation

Bu çalışmada bozulabilen fiyat indirimli mallar için stok kontrolü problemi ele alınmıştır. Problemde (S,s) envanter sistemini baz alarak sistemde peryodik gözden geçirme stok kontrolü uygulanmıştır. Problemin çözümünde simülasyon tekniğini kullanarak bu karmaşık problemin sistem davranışını araştırmak amacıyla farklı envanter seviyeleri ve farklı yeniden sipariş verme noktaları için sistem test edilmiştir. Elde edilen simülasyon sonuçları, uygun istatiksel optimizasyon tekniği kullanarak analiz edilmiş ve en iyi envanter politikası belirlenmiştir. Basit ESM modelindeki optimum çözüm, ele alınan stokastik envanter modelindeki elde edilen en iyi çözümden daha kötü olduğu görülmüştür.In this study we have investigated inventory control problem for perishable items with price quantity discounts. An (S,s) periodic review system is used to control inventory level at the end of each day. The behavior of this stochastic inventory system is analyzed using simulation experiments for varying reorder points (s) and reorder levels (S). Resulting simulation output is fed to the statistical optimization method to determine the optimum inventory policy based on the total cost. Simple EOQ (Economic Order Quantity) solution has been shown to be worse than that of the statistical optimization