Browsing by Subject "Vehicle routing problem."

Now showing 1 - 4 of 4

Open Access
An exact algorithm for the vehicle routing problem with backhauls
(2001) Geloğulları, Cumhur Alper
We consider the Vehicle Routing Problem with Backhauls, in which a eet of vehicles located at a central depot is to be used to serve a set of customers partitioned into two subsets of linehaul and backhaul customers. The ob jective of the problem is to minimize the total distance traveled by the entire eet. The problem is known to be N P-hard in the strongest sense and nds many practical applications in distribution planning. We present an exact algorithm for the Asymmetric Vehicle Routing Problem with Backhauls based on solving a relaxation of the problem. In a cutting plane fashion, the algorithm iteratively solves the relaxation while at each iteration, infeasible solutions are identi ed and seperated from the feasible set of the relaxation. The procedures to identify infeasible solutions are presented, and a set of cuts to eliminate these solutions is proposed. Local search procedures are incorporated to improve the algorithm. Computational tests on randomly generated instances, involving up to 90 customers, are given. The results show the e ectiveness of the proposed approach.
Open Access
A heuristic algorithm for an integrated routing and scheduling problem with stops en-route
(2009) Uzun, Emre
In this study, we examine an integrated routing and scheduling problem that arises in the context of transportation of hazardous materials. The purpose of the problem is to find a minimum risk route between an origin and a destination point on a given network and to build a schedule on this route that determines where and how long to stop for a truck carrying hazardous materials. The objective is to minimize the risk imposed to the society while completing the path within a given time limit. The risk is defined as the expected population exposure in the presence of an accident which varies different times in a day. There are exact algorithms available in the literature that solve the problem. However, these algorithms are not capable of solving large sized networks due to memory constraints. Our aim is to develop a heuristic procedure that can handle larger networks. We separate the problem into two independent components, routing and scheduling, and propose solution algorithms which would communicate each other when running the algorithm. For the routing component we define a neighborhood structure that can be used to generate several paths around a given path on a network. The search procedure takes an initial path and improves it by generating different paths in the defined neighborhood. For the scheduling component, we discuss mixed integer programming, dynamic programming and heuristic approaches. We run the proposed heuristic algorithm on several test networks and compare its performance with the optimal solutions. We also present the application of the heuristic procedure on a large sized Turkey Road Network.
Open Access
Mobile blood donation logistics : case for Turkish Red Crescent
(2012) Şahinyazan, Feyza Güliz
Blood transfusion is one of the most critical operations in various medical interventions. Currently, the only authorized way of securing the required blood for transfusion is through voluntary donations. For this reason, reorganizing blood donation operations to create an operable and efficient system is of utmost importance. In this study, a mobile blood collection system is designed for Turkish Red Crescent (TRC) to increase blood collection levels. This design also takes into account operational costs as a second objective so as to aim the collection of large amounts of blood at reasonable cost. In the current system, TRC has bloodmobiles that perform independent direct tours to certain activities (fairs, college fests etc.), but at the end of each day, they bring the collected blood to a designated depot to prevent its spoilage. Considering blood’s considerably short shelf-life of 24 hrs, these direct tours may seem justifiable yet they are not efficient in terms of logistics costs. The proposed system consists of classic bloodmobiles and a new vehicle – called the shuttle – which visits the bloodmobiles in the field and transfers the collected blood to the blood centers, so that bloodmobiles can continue their tours without having to make daily returns to the depot. A mathematical model is developed to determine the stops of bloodmobiles, the duration of each visit as well as the tours of the bloodmobiles and the shuttle. In the literature, a study that covers all these decisions does not exist. Therefore, a new extension of Selective Vehicle Routing Problem (SVRP) is defined, called SVRP with Integrated Tours. Also, a 2-stage IP based heuristic algorithm is developed for the same problem. The performances of these methodologies are tested on the data set obtained from past blood donation activities in Ankara. In addition, GIS data of the European part of Istanbul is used as a constructed test case. The Pareto set of optimum solutions is generated based on blood amounts and logistics costs, and finally a sensitivity analysis on some important design parameters is conducted.
Open Access
Mobile health services for rubal areas in Turkey : a case study for Burdur
(2013) Kurugöl, Damla
Currently, healthcare services in urban areas are provided by family health centers coordinated by community health centers. By the application of family physician based system, it is planned to provide mobile healthcare services (MHS) for the people living in the rural areas which have difficulties to reach those health centers in urban areas. In the scope of these ongoing studies, family physicians procure primary health services to the determined villages in between defined time periods. The aim of this project is to schedule a working plan by using family physicians’ mobile healthcare service times effectively. In this context, when the problem was examined, we realized that it has similarities with the periodic vehicle routing problem (PVRP). We proposed several different solution approaches to the PVRP in the context of the mobile healthcare services application that we are interested in. We tested the implementation of our proposed solution approaches using both simulated data and extended data obtained from the villages of Burdur city