PLANNING FOR TRUCK FLEET SIZE IN THE PRESENCE OF A COMMON-CARRIER OPTION

This paper considers a class of network optimization problems in which certain directed arcs must be covered by a set of cycles. Our study was motivated by a distribution planning problem of a commercial firm that had to make deliveries over several origin-destination pairs (directed arcs) and that could service any demand arc by using a vehicle in its own fleet or by paying a common carrier. The problem is to determine an optimal fleet size and the resulting vehicle routes while satisfying maximum route-time restrictions. We formulate the problem, describe some approximate solution strategies, and discuss important implementation issues.     

Adaptation of some vehicle fleet mix heuristics

Standard models used for the combined vehicle routing and vehicle fleet composition problem use the same value for the unit running cost across vehicles. In practice such a parameter depends on several factors and particularly on the capacity of the vehicle. The purpose of this paper is to show simple modifications of some well known methods to allow for variable running costs; and also to assess the effect of neglecting such variability. Interesting numerical results, measured in terms of changes in total cost or/and fleet configuration, are found at no extra computational effort.     

Mixed-fleet single-terminal bus scheduling problem: Modelling,solution scheme and potential applications

Reducing pollutant emissions and promoting sustainable mobility solutions, including Public Transport (PT), are increasingly becoming key objectives for policymakers worldwide. In this work we develop an optimal vehicle scheduling approach for next generation PT systems, considering the instance of mixed electric / hybrid fleet. Our objective is that of investigating to what extent electrification, coupled with optimal fleet management, can yield operational cost savings for PT operators. We propose a Mixed Integer Linear Program (MILP) to address the problem of optimal scheduling of a mixed fleet of electric and hybrid / non-electric buses, coupled with an ad-hoc decomposition scheme aimed at enhancing the scalability of the proposed MILP. Two case studies arising from the PT network of the city of Luxembourg are employed in order to validate the model; sensitivity analysis to fleet design parameters is performed, specifically in terms of fleet size and fleet composition. Conclusions point to the fact that careful modelling and handling of mixed-fleet conditions are necessary to achieve operational savings, and that marginal savings gradually reduce as more conventional buses are replaced by their electric counterparts. We believe the methodology proposed may be a key part of advanced decision support systems for policymakers and operators that are dealing with the on-going transition from conventional bus fleets towards greener transport solutions.     

Vehicle Procurement Policy for Humanitarian Development Programs

This article aims to identify optimal vehicle procurement policies for organizations engaged in humanitarian development programs and to derive general insights on the characteristics of these policies. Toward that end, we follow an inductive approach. First, we study the operations of the International Committee of the Red Cross (ICRC) in three representative countries: Sudan, Afghanistan, and Ethiopia. Using a linear programming (LP) model primed with field data provided by the ICRC, we calculate the optimal vehicle fleet size and compare it with the policies actually implemented. Second, drawing from results of the LP model, we develop a stylized quadratic control model and use it to characterize the general structure of the optimal policy under different demand scenarios and operational constraints. After demonstrating that the results of the control model are consistent with those of the LP model in the specific context analyzed, we discuss the optimal policies and the applicability of the former as a practical tool for strategic asset planning.     

MODEL FORMULATION FOR FLEET SIZE ANALYSIS OF A UNIVERSITY MOTOR POOL

A GPSS/360 model was developed to investigate the behavior of a university's motor pool dispatch fleet. Time-series data were collected and frequency distributions were constructed for vehicle request patterns and trip-duration times. Regression analysis was performed to formulate trip mileage generators as functions of service time. Appropriate statistical goodness-of-fit tests were conducted to ascertain the extent of congruence between actual system behavior and expectations based on a number of theoretical distributions. Analysis of simulated response variables indicates that the model's internal structure reproduces reality to a high degree. Fifteen years of simulated experience were generated for six alternative fleet size configurations; results suggest that reductions in existing fleet capacity could be realized without effecting undue impairment in service levels.     

带时间窗装卸货问题的改进多策略分组编码遗传算法

通过研究求解PDPTW的分组编码遗传算法（GGA）及多策略分组编码遗传算法（MSGGA），改进了GGA中的交叉算子及MSGGA中的路径调整策略，提出了易位组合交叉算子、单车路径重排策略及需求对换策略。求解了400个客户点的标准算例集，其中4个算例lc2_4_3、lrc1_4_1、lrc2_4_2和lrc2_4_3的行驶总路程有所减少。     

Optimal replacement strategies in network infrastructures under quality penalties

As a consequence of liberalization, electric utilities have developed different asset management strategies with the aim of reducing total maintenance costs by prolonging replacement cycles. A cost-minimizing network operator has to optimize the trade-off between costs for early replacement and quality penalties he faces in the case of outages (due to a resulting higher number of failures). The basic purpose of this paper is to identify the optimal decisions for a network operator under output-based quality regulation and to determine the main drivers for his decisions. In order to derive general insights, an analytical framework is chosen for this paper. This work builds on the foundations of optimal maintenance and replacement strategies as developed across Operations Research, Production Economics and Engineering Production Theory. As main results we are able to analytically derive optimal replacement strategies for network components depending on the characteristics of their failure distributions linked to the equipment’s cost, respective replacement cost, and quality penalties.     

A New Approximation Algorithm for the Capacitated Vehicle Routing Problem on a Tree

This paper presents a new approximation algorithm for a vehicle routing problem on a tree-shaped network with a single depot. Customers are located on vertices of the tree, and each customer has a positive demand. Demands of customers are served by a fleet of identical vehicles with limited capacity. It is assumed that the demand of a customer is splittable, i.e., it can be served by more than one vehicle. The problem we are concerned with in this paper asks to find a set of tours of the vehicles with minimum total lengths. Each tour begins at the depot, visits a subset of the customers and returns to the depot without violating the capacity constraint. We propose a 1.35078-approximation algorithm for the problem (exactly, ), which is an improvement over the existing 1.5-approximation.     

Designing optimal routing strategies for a manufacturer: A case study

A study of the vehicle transportation system for a manufacturer is presented. An algorithm based on a dynamic programming model is developed so as to find the optimal transportation arrangements referring to the composition of the vehicles as well as the routing of these vehicles. The algorithm is run under the current condition as well as under a number of different scenarios. It is shown the algorithm can solve the problem with reduced computational complexity. The findings and suggestions resulting from the study can help the department manager in reviewing current operations arrangement and determining future operations arrangements.     

新能源汽车闭环供应链的多级契约决策优化

随着环境问题的日益严峻,传统汽车工业面临巨大压力。虽然新能源汽车的绿色低碳为解决大气、水土污染提供了途径,但动力电池若回收不利也将对生态环境造成负面影响。文章着眼于构建新能源汽车销售及动力电池回收的多级供应链网络,在不同回收模式下对电池生产企业主导的闭环供应链进行契约协调。然后,针对动力电池回收体系不完善的社会问题,为政府找到促使销售和回收平衡的最优条件。研究发现:(1)当回收再制造利润空间满足一定条件,电池生产商倾向选择多回收渠道的模式,并且渠道竞争的加剧,对消费者和上游企业都有利;(2)当电池生产商同时参与正向销售、逆向回收上的收益共享时,"联合"共享契约可以实现供应链的协调、有效提高各企业利润;(3)电池的制造、再制造成本对回收价格和企业利润有很大影响,当技术革新、成本下降时,无论是企业还是消费者都可以获得更多的利润,进一步对单、双渠道回收模式进行选择,找出不同成本范围内的最优回收模式;(4)为了提高废旧电池回收率,政府通过征收环境保护税可以有效促进废旧电池的回收,并且最优税额随电池制造成本的增长而降低,随再制造成本的增长而增加。     

A multi-compartment vehicle routing problem arising in the collection of olive oil in Tunisia

We introduce, model and solve to optimality a rich multi-product, multi-period and multi-compartment vehicle routing problem with a required compartment cleaning activity. This real-life application arises in the olive oil collection process in Tunisia, where regional collection offices dispose of a fleet of vehicles to collect one or several grades of olive oil from a set of producers. For each grade, the quantity offered by a producer changes dynamically over the planning horizon. We first provide a mathematical formulation of the problem, along with a set of known and new valid inequalities. We then propose an exact branch-and-cut algorithm to solve the problem. We evaluate the performance of the algorithm on real data sets under different transportation scenarios to demonstrate to our industrial partner the advantages of using multi-compartment vehicles.     

大规模灾害中基于聚类的医疗物资联合运送优化

应急响应中,往往出现救援物资供应节点与需求节点距离太远、关键道路损毁导致难以及时通过车辆运送物资到灾区等情景,此时直升飞机逐渐被用来运送关键应急资源（如医疗物资及医护人员）。然而,大规模灾害中难以使用直升飞机运送医疗物资到每个医疗救助点,通常考虑灾民的聚集性选择一定数量的应急中转点,以接收直升飞机运送的医疗物资,之后采用车辆运送物资到其覆盖的医疗救助点。针对该问题,提出一种基于聚类的两阶段医疗物资联合运输方法：第一阶段根据医疗救助点分布,采用模糊C-均值算法（FCM）进行应急中转点选择和医疗救助点划分,并针对FCM划分中存在的剩余容量不均衡问题,考虑容量约束提出一种改进划分方法（FCMwCC）,构建“直升飞机-车辆”医疗物资联合运输网络结构;第二阶段建立基于聚类的运送路线优化模型,确定从应急中转点到医疗救助点的具体运送路线。数值实验验证了提出方法和算法的有效性。     

同时集散货物的开放式车辆路径问题研究

本文研究了车辆工作时间限制下同时集散货物的多配送中心开放式车辆路径问题,以车辆数和运输里程最小为目标,建立了多目标规划模型,提出了基于拉格朗日松弛技术和禁忌搜索算法的混合求解算法。 该算法首先求出最优解的最大下界,然后采用客户点的分配和调整策略实现解的可行化,其中禁忌搜索引入了4种领域搜索方法,采用了随机变领域搜索方法和重起策略。算例分析表明,该算法能有效地找到满意解,且采用开放式安排路线比闭合式安排路线更加经济合理。     

Fleet Replacement,Technology Choice,and the Option to Breach a Leasing Contract

We analyze the option to breach a leasing contract when replacing a fleet of ICVs (internal combustion engine vehicles) and EVs (electric vehicles) subject to cost uncertainty. We derive the optimal policy for technology choice and breaching ICV contracts. The decision to breach is shown to offer both cost savings resulting from reduced ICV operating costs and preemptive acquisition, but incurs additional costs arising from the need to compensate for breached vehicles and in the form of opportunity costs. We also demonstrate that the effects of breaching a leasing contract have a ripple effect across the decision horizon, thus amplifying the impact of a single breach. A numerical study based on data from La Poste, the French postal service, shows that breaching a leasing contract in this context offers measurable cost benefits.     

Open Source Development with a Commercial Complementary Product or Service

We examine optimal control decisions regarding pricing, network size, and hiring strategy in the context of open source software development. Opening the source code to a software product often implies that consumers would not pay for the software product itself. However, revenues may be generated from complementary products. A software firm may be willing to open the source code to its software if it stands to build a network for its complementary products. The rapid network growth is doubly crucial in open source development, in which the users of the firm's products are also contributors of code that translates to future quality improvements. To determine whether or not to open the source, a software firm must jointly optimize prices for its various products while simultaneously managing its product quality, network size, and employment strategy. Whether or not potential gains in product quality, network size, and labor savings are sufficient to justify opening the source code depends on product and demand characteristics of both the software and the complementary product, as well as on the cost and productivity of in‐house developers relative to open source contributors. This paper investigates these crucial elements to allow firms to reach the optimal decision in choosing between the open and closed source models.     

Multi-depot vehicle routing problem with time windows under shared depot resources

A new variant of multi-depot vehicle routing problem with time windows is studied. In the new variant, the depot where the vehicle ends is flexible, namely, it is not entirely the same as the depot that it starts from. An integer programming model is formulated with the minimum total traveling cost under the constrains of time window, capacity and route duration of the vehicle, the fleet size and the number of parking spaces of each depot. As the problem is an NP-Hard problem, a hybrid genetic algorithm with adaptive local search is proposed to solve it. Finally, the computational results show that the proposed method is competitive in terms of solution quality. Compared with the classic MDVRPTW, allowing flexible choice of the stop depot can further reduce total traveling cost.     

Cost models for lot streaming in a multistage flow shop

Lot streaming is a technique used to split a processing batch into several transfer batches. In this way, overlapping operations can be performed in different manufacturing stages, and production can be accelerated. This paper proposes two cost models for solving lot streaming problems in a multistage flow shop. The purpose is to determine the optimal processing batch size and the optimal number of transfer batches that minimize the total annual cost in each model. In the first model, a more complete and accurate method is developed to compute the costs of raw materials, work-in-process, and finished-product inventories. The total cost includes the setup cost, the transfer batch movement cost, the three-type inventory holding cost, and the finished-product shipment cost. The second model contains not only the four costs in the first model, but also the imputed cost associated with the makespan time. The total annual cost functions in both models are shown to be convex, and two solution approaches are suggested. An experiment consisting of three phases was conducted to explore the effect on the optimal solution when changing the value of one parameter at a time. The results indicate that three parameters have significant effects on the optimal solution.     

危险品集成物流管理系统选址-选线模型研究

以路网的危险度瓶颈限制为切入点研究了一类危险品集成物流管理系统选址—选线问题,对应于路网危险度瓶颈限制引入安全费用非递减函数,并根据运输工具的安全配置等级构造该等级下的子网络,物流系统的选址—选线结果随着路网的调整而不断变化.危险品集成物流系统的管理存在多个目标,文中首先分析了成本、风险和风险公平性等优化目标,在说明了建模的假设条件后,建立了基于路网危险度瓶颈限制的危险品集成物流系统选址—选线的多目标模型,并根据模型给出了一种启发式算法,最后用一个算例对模型进行了数值演算.     

Distributed algorithms for barrier coverage via sensor rotation in wireless sensor networks

When deploying sensors to monitor boundaries of battlefields or country borders, sensors are usually dispersed from an aircraft following a predetermined path. In such scenarios sensing gaps are usually unavoidable. We consider a wireless sensor network consisting of directional sensors deployed using the line-based sensor deployment model. In this paper we propose distributed algorithms for weak and strong barrier coverage that allow sensors to determine their orientation such that the total number of gaps is minimized. We use simulations to analyze the performance of our algorithms and to compare them with related works.     

缺陷汽车召回所需安排的最优维修店数目

讨论了缺陷汽车产品制造商在汽车召回事件中如何安排最优维修店数目。假设汽车制造商在召回期限内维修几乎全部召回汽车,车主逗留时间和维修时间都服从指数分布,并且假设维修人员会根据库存水平(车位)调整维修速度。选取制造商安排组织的维修店数目为决策变量,利用有限源排队理论建立了成本控制模型。搜索算法确定了最优的维修店数目,使得期望总成本最小。