Browsing by Subject "Location routing"

Now showing 1 - 4 of 4

Open Access
Location-location routing problem and its application on refugee camps
(2019-05) Kumcu, Gül Çulhan
In the classical Location Routing Problem (LRP), the customers are at xed and known locations. Given the known customer locations, in LRP models, decisions are taken for distribution center locations and corresponding vehicle routes. However; for some public applications the locations of customers can also be decision variables coming from a discrete set. In this study we consider such an application where the locations of demand nodes will be determined while considering the distribution center location(s) and corresponding vehicle routes. To the best of our knowledge this variant of LRP has not been de ned in the location literature before. We refer this problem as Location-Location Routing Problem(L-LRP). We observe that, refugee camp location and management problem is a direct application of the L-LRP. In refugee camps certain public services are required to protect health, safety, dignity, etc. of the refugees. Thus, authorities should plan regular public service visits to the refugee camps to provide these services. In the refugee camp location problem authorities decide the locations of hosting institutions and routes of service providers originated from these institutions. Actually, in addition; authorities also decide the locations of these refugee camps. For the L-LRP, a linear mixed integer mathematical formulation is developed. To obtain results in shorter times with preserving solution qualities, a two-stage math-heuristic algorithm is presented. The computational analysis of mathematical formulation and heuristic algorithm are conducted on a real data set obtained from Southern part of Turkey.
Open Access
A mobile ammunition distribution system design on the battlefield
(2010) Toyoğlu, Hünkar
Ammunition has been the most prominent factor in determining the outcome of combat. In this dissertation we study a military logistics problem in which ammunition requirements of the combat units, which are located on the battle- field, are to be satisfied in the right amount when and where they are needed. Our main objective is to provide a decision support tool that can help plan ammunition distribution on the battlefield. We demonstrate through an extensive literature review that the existing models are not capable of handling the specifics of our problem. Hence, we propose a mathematical programming model considering arc-based product-flow with O(n 4 ) decision variables and constraints. The model is a three-layer commodity-flow location routing formulation that distributes multiple products, respects hard time windows, allows demand points to be supplied by more than one vehicle or depot, and locates facilities at two different layers. We then develop a new mathematical programming model with only O(n 3 ) decision variables and constraints by considering node-based product-flow. We derive several valid inequalities to speed up the solution time of our models, illustrate the performance of the models in several realistically sized scenarios, and report encouraging results. Based on these mathematical models we propose two three-phase heuristic methods: a routing-first location-second and a location- first routing-second heuristic. The computational results show that complex real world problems can effectively be solved in reasonable times with the proposed heuristics. Finally, we introduce a dynamic model that designs the distribution system in consecutive time periods for the entire combat duration, and show how the static model can be utilized in dynamic environments.
Open Access
A new selective location routing problem: educational services for refugees
(2022-07) Demir, Şebnem Manolya
Syrian War has forced 5.5 million Syrians to seek for asylum. Turkey hosts 3.7 million Syrian refugees, 47% of whom are children. Even though the schooling rate of Syrian refugee children has steadily increased, currently, there are still more than 400 thousand children distanced from education. Turkey’s initial plans were not accounting for a refugee crisis going on for a decade. In this study, we first identify the availability and accessibility challenges posed by the country’s existing plans of integrating refugees to the national education system. Then, to reinforce schooling access for the refugee children in Turkey, we develop a planning strategy that is aligned with the local regulations. To improve school enrollment rates among Syrian refugee children without burdening the existing infrastructure of the host country, we formulate Capacitated Maximal Covering Problem with Heterogenity Constraints (CMCP-HC) and two extensions: Cooperative CMCP-HC (CCMCP-HC) to improve the current schooling access in Turkey and Modular CCMCP-HC to provide a guide for early planning in the case of a future crisis. As lack of school accessibility has been identified as one of the significant challenges hampering the school attendance rates, we incorporate routing decisions. To ease children’s transportation to schools, we propose a new Selective Location Routing Problem (SLRP) that corresponds to a novel formulation, where the location decisions impact the selective nature of the routing problem. For cases with further scarcity of the resources, we introduce Attendance-based SLRP (A-SLRP) and represent children’s attendance behaviors as a gradual decay function of distance. For the solution of these two complex problems, we offer a 2-Stage Solution Approach that yields optimal solutions for A-SLRP. Results of our computational analysis with the real-life data of the most densely refugee populated Turkish province illustrate that CCMCPHC and Modular CMCP-HC improve schooling enrollment rates and capacity utilizations compared to status quo. Moreover, SLRP and A-SLRP enable approximately twice as many children’s continuation to education, compared to the benchmarking formulation. Overall, this study analyzes Turkey’s experience and lessons learned over a decade to provide a road-map based on operations research methodologies, for potential similar situations in the future.
Open Access
Periodic location routing problem : an application of mobile health services in rural area
(2017-06) Savaşer, Sinem
Lack of sufficient healthcare services in rural areas has been a considerable problem throughout the world for a long time. One of the alternative ways to address and solve this problem is providing mobile healthcare services in which the providers are traveling and visiting patients. These services have been obligatory in Turkey since 2010 and there are certain requirements that are enforced by Ministry of Health, such as having multiple routinized visits, having alternative visiting rules and dedicating doctors to specified villages. Based on the characteristics of this problem, it is categorized under Periodic Location Routing Problem (PLRP) literature. The common characteristic of the solution methodologies in the PLRP literature is to predefine a set of alternative schedules and select the best one among those. Unlike the other approaches that have been already studied, the developed integer programming model determines the schedules of the doctors via its constraints, dedicates each doctor to same villages through the planning horizon and satisfies certain visiting rules. The performance of the model is tested by utilizing the data set of Burdur. The proposed model is solved to optimality in reasonable times for the small instances; however, significant optimality gaps remain at the end of predefined time limits of the larger instances. In order to obtain prominent results in shorter durations, a \cluster first, route second" based heuristic algorithm is developed. Based on the computational experiments, it is observed that the solution times are significantly improved and optimal or near-optimal solutions are obtained with the heuristic approach.