The optimal locating of facilities has large effects on economic benefits, providing satisfactory service and levels of customer satisfaction. The decision of facilities location mostly is a long-term and strategic decision of the large private and public companies and reliability is important to make this strategic decision so that the system continues to operate with the least damage in case of stop working or failure of one of the components. This paper at the first time proposes a nonlinear integer model for reliable single allocation hub location problem that considers backup hub, alternative routes, and also uses fortification approach to improve the network reliability, while there is the possibility of direct connection between non-hub nodes. Due to the NP hard nature of the model, genetic algorithm is use in order to solve the defined problem and the numerical results illustrate the genetic algorithm has better performance than the GAMS in terms of speed, it also shows great quality answers. The results of the sensitivity analysis show that considering the protection approach has reduced the total cost.

In most past studies on hub Location Problem (HLP), failure probability is limited to a constant value; however, in reality, it depends on various factors including natural disasters such as floods and earthquakes, commodity ow, institutional elements (strikes), etc. This paper looks into the problem of the hub network design through a new model. The problem is to maximize network reliability and minimize the total routing cost simultaneously. In order to provide a more realistic model, the hub's failure probabilities were considered as a function of the hub's incoming traffic. Reserve hub elements were also taken into account in the model with the aim of increasing network reliability. To solve the model, a Non-dominated Sorting Genetic Algorithm (NSGA-II) was presented. The parameters of the algorithm were tuned using Taguchi method. The proposed solution was then carried out in a case study where the results confirmed the acceptable performance of the model; moreover, sensitivity analysis was performed in order to describe the effects of critical parameters on objective functions.

The optimal locating of facilities has large effects on economic benefits, providing satisfactory service and levels of customer satisfaction. One of the new topics discussed in location problems is hub location and hub facilities are subject to unpredictable disruptions. This paper proposes a nonlinear integer model for reliable single allocation hub location problem that considers backup hub, alternative routes, and also uses fortification approach to improve the network reliability. Due to the NP hard nature of the model, we use genetic algorithm in order to solve the defined problem and the numerical results illustrate the applicability of the proposed model as well as the efficiency of solution procedure.

In recent years, performance of the Mobile Ad-Hoc Network (MANET) has become an important research area in the wireless networks community. MANET consists of clusters of Mobile Nodes (MNs) on the access network that could be connected to other clusters through a fixed backbone of routers. The access link contention can severely constrain the end-to-end throughput of the path between a pair of source and destination MNs connected through the backbone. In this paper, we propose an integrated routing system for MANET that includes the backbone paths and the ad-hoc paths formed as a result of direct communication among MNs without going through the backbone. In our proposed routing system, an alternative ad-hoc path can be used only when the primary backbone path is severely constrained due to access links contention. We also propose a scheme for making the MN aware of link quality measures, and incorporate throughput metric in the core of AODV. We implemented the proposed routing system in the OPNET simulator, and evaluated the performance of our scheme under a variety of conditions. Simulation results show that the alternative ad-hoc path is effective in delivering higher throughput when the backbone path is severely constrained.

This paper proposes a novel day-ahead energy hub scheduling framework aimed at improving resiliency. Accordingly, an energy hub including combined heat and power (CHP), boiler, electric-heat pump (EHP), absorption and electric chillers, energy storages and renewable sources is considered. This energy hub is equipped with smart grid (SG) infrastructures, making it possible to implement demand response (DR) programs and optimally operate energy storages. The hub is connected to the electricity and natural gas networks. Outage of input energy carriers causes failure of devices in the energy hub, loss of electrical loads, failure in cooling and heating and thus reduced resiliency. Maintaining the security of the hub consumers’ power supply system in the event of such severe disturbances is essential. Therefore, a new strategy based on the use of backup electric energy storages (EES) and DR program is proposed in this paper to improve resiliency. In addition, a numerical index is used to accurately calculate and evaluate resiliency. Numerical studies show that the proposed strategy improves resiliency during the outage of power and gas networks by 12.02% and 14.23% respectively when backup energy storages and DR program are implemented simultaneously.

In a hub location problem network, the flow originated from an origin and shipped to a destination via some selected intermediate nodes called hub nodes since using a discount factor of hubs. The hub nodes are fully interconnected in the traditional hub location problem. In any origin-destination path there exists at least one hub element. Rather than directly connecting any pair of locations, all the paths are handled by the hub node. In this paper, a general configuration of hub location problems is considered. The model is presented for hub location-routing problem which any network topology can be structured. This model application is in the public transportation, telecommunication systems and financial networks. Incomplete hub network is designed in the model. Furthermore, location and routing decisions are considered simultaneously in the model besides multiple allocation strategy. Moreover, non-hub nodes can be connected directly. Objective function of this model minimizes transshipment cost of flows and cost of constructing the network. Family of valid inequalities and some preprocessing are proposed to strengthening the model linear relaxation lower bound and improving solution time. Computational results over test problems driven from the literature show that using all valid inequalities and preprocessing perform better than using each of them separately and solve the model in a reasonable solution time.

In this paper we consider the reverse backup 2-median problem with variable coordinates of vertices in Rk. Let n points be given, then in the reverse backup 2-median problem we want to change the coordinates of these points with a limited budget such that the two given points become the backup 2-median. We present a mathematical model for this problem and then solve a spatial case of this problem by a meta-heuristic method.