Reassignments of common-use check-in counters following airport incidents

The aim in this research is to develop a model that will assist in the reassignment of flights to common-use check-in counters following airport incidents. The model is formulated as a zero-one integer program. To develop a solution method that will efficiently solve the large problems that occur in the real world, we employ a decomposition technique, where a series of two relaxations of the original model are solved repeatedly. Numerical tests are performed based on a hypothetical incident that is mainly based on data from a Taiwan airport. The obtained results show that the model and the solution method could be useful for the airport authority in actual operations.     

Use counters to model the addition of integers

<正>HANDS-ON LAB You can use positive and negative counters to model the addition of integers.The counter + represents 1,and the counter - represents-1.Remember that addition means combining two sets.ACTIVITY Work with a partner.     

A heuristic approach for airport gate assignments for stochastic flight delays

To make good flight to gate assignments, not only do all the relevant constraints have to be considered, but stochastic flight delays that occur in actual operations also have to be taken into account. In past research, airport gate assignments and stochastic disturbances have often been handled in the planning and the real-time stages separately, meaning that the interrelationship between these stages, as affected by such delays, has been neglected. In this research, we develop a heuristic approach embedded in a framework designed to help the airport authorities make airport gate assignments that are sensitive to stochastic flight delays. The framework includes three components, a stochastic gate assignment model, a real-time assignment rule, and two penalty adjustment methods. The test results are based on data supplied by a Taiwan international airport, and show that the proposed framework performs better than the current manual assignment process and the traditional deterministic model.     

An airline scheduling model and solution algorithms under stochastic demands

When setting a good flight schedule airlines not only have to consider their fleet supply and related operations, as well as market share, but also stochastic variations caused by daily passenger demands in actual operations. Most of the past research on short-term flight scheduling has used the average passenger demand as input to produce the final timetable and schedule, which means that daily passenger variations that occur in actual operations are neglected. To consider such stochastic disturbances we developed a stochastic-demand scheduling model. We employed arc-based and route-based strategies to develop two heuristic algorithms that can be used to solve the model. The test results, based on a major Taiwan airline’s operation, show the good performance of the model and the solution algorithms.     

Airport noise modelling and aircraft scheduling so as to minimize community annoyance

A mathematical model of the annoyance created at an airport by aircraft operations is developed. The model incorporates population distribution considerations around an airport and the annoyance caused by aircraft noise. The objective function of this model corresponds to seeking to minimize total population annoyance created by all aircraft operations in a 24-hour period. Several factors are included in this model as constraint relationships. Aircraft operations by type and time period are upper bounded. Demand for flight services is incorporated by including lower bounds on the number of operations by type of aircraft, runway used and time period. Also upper bounds on the number of operations for each runway are included. The mathematical model as formulated is recognized as corresponding to a nonlinear integer mathematical programming problem.The solution technique selected makes use of a successive linear approximation optimization algorithm. An especially attractive feature of this solution algorithm is that it is capable of obtaining solutions to large problems. For example, it would be feasible to attempt the solution of problems involving several thousand variables and over 500 linear constraints. This suggested solution algorithm was implemented on a computer and computational results obtained for example problems.     

Modelling handling operations in grocery retail stores: an empirical analysis

Shelf stacking represents the daily process of manually refilling the shelves with products from new deliveries. For most retailers, handling operations are labour-intensive and often very costly. This paper presents an empirical study of the shelf-stacking process in grocery retail stores. We examine the complete process at the level of individual sub-activities and study the main factors that affect the execution time of this common operation. Based on the insights from different sub-activities, a prediction model is developed that allows estimating the total stacking time per order line, solely on the basis of the number of case packs and consumer units. The model is tested and validated using real-life data from two European grocery retailers and serves as a useful tool for evaluating the workload required for the usual shelf-stacking operations. Furthermore, we illustrate the benefits of the model by analytically quantifying the potential time savings in the stacking process, and present a lot-sizing analysis to demonstrate the opportunities for extending inventory control rules with a handling component.     

空中交通流量管理中的改航策略研究

针对在恶劣天气下出现的大规模航班延误情况,根据机场和航路段的动态容量约束,建立了改航策略模型,并提出求解该模型的有效算法.选择全国航班时刻表进行仿真,仿真结果表明:该模型提供了在恶劣天气下更安全、更经济的航班改航策略,可为战术级流量管理提供辅助决策.     

Platform exploitation in the sharing economy

We model a revenue sharing contract between a sharing economy platform and a freelance service provider, where the latter hides revenue from the former by canceling some assignments and performing them for cash (“platform exploitation”). The platform counters this via costly, imperfect audits with endogenous success probability, and a variable payment. We show that at equilibrium, all agent types except the highest, indulge in revenue falsification. This problem is exacerbated by the principal's ability to extract restitution from the agent.     

Multiple-Service Costing

The problems of costing, and pricing periodic demands for services, known as the peak load problem, has been widely studied, with relatively little success, largely within the framework of the marginal costing approach of micro-economics. The paper reports the application of a new method called Multiple-Service Costing, to the internal fixed cost allocation procedures within an airline. This new method of allocating the fixed costs of services, to the demands, is based on considering the interacting system of supply and demand as a whole. An illustrative example of the method applied to charging computer time is described. The actual use of the method in an airline, for the calculation of flight check-in charges is reported.     

A modified gating logic to improve the speed of operation of double rank counters

The speed of operation of double rank counters can be increased by a suitable modification of the gating logic now being used. The improvement in speed, predicted on theoretical grounds, has been experimentally verified. The prescribed logic enables the use of both the ranks of the counter to advantage, one rank counting in the normal, and the other in the reverse fashion.     

Check-in computation and optimization by simulation and IP in combination

This paper presents and investigates a check-in problem for a twofold reason:

• (i)as a problem of practical and novel scientific interest in itself and
• (ii)as a problem which requires both a stochastic (simulation) and deterministic (integer programming) approach.

First, simulation is used to determine minimal numbers of desks in order to meet a service level for each separate flight. Next, integer programming formulations are provided to minimize the total number of desks and the total number of desk hours under the realistic constraint that desks for one and the same flight should be adjacent. Both opening intervals with constant and variable capacities will be studied.A numerical example of real world order shows a triple win in waiting time performance, in number of desks and in number of desk hours (staffing). As simulation and integer programming tools are widely available, this combination of simulation and integer programming can thus be regarded as an illustration of a ‘new’ practical OR-tool for optimization.     

Conditions for the existence of continuous schedules of duration five

Each device must perform one operation with each of two demands assigned to it. The assignments are such that the maximum number of operations for one demand equals five, the partial precedence limitations are missing, simultaneous servicing of two or more demands by the same device or of one demand by two or more devices is forbidden, and the duration of each operation equals a unit. The necessary and sufficient conditions are obtained for the existence of a schedule of duration five conforming to the specified assignments and such that each device performs its operations during two consecutive intervals of unit duration. Hence follows the polynomial solvability of the problem under discussion.     

A large scale machine loading problem in flexible assembly

Flexible manufacturing is characterized by versatile work stations with minimum change over times and a versatile material handling system. The loading problem in flexible manufacturing is to assign tools, material, operations and jobs to work stations in order to minimize the total number of job-to-work station assignments. In this paper, we describe a special case of the general loading problem applied to flexible assembly and develop a discrete optimization model. We then discuss approaches for obtaining good heuristic solutions and present results for a large scale study.     

A multi-objective genetic algorithm for robust flight scheduling using simulation

Traditional methods of developing flight schedules generally do not take into consideration disruptions that may arise during actual operations. Potential irregularities in airline operations such as equipment failure are not adequately considered during the planning stage of a flight schedule. As such, flight schedules cannot be met as planned and their performance is compromised, which may eventually lead to huge losses in revenue for airlines. In this paper, we seek to improve the robustness of a flight schedule by re-timing its departure times. The problem is modeled as a multi-objective optimization problem, and a multi-objective genetic algorithm (MOGA) is developed to solve the problem. To evaluate flight schedules, SIMAIR 2.0, a simulation model which simulates airline operations under operational irregularities, has been employed. The simulation results indicate that we are able to develop schedules with better operation costs and on-time performance through the application of MOGA.     

Optimal control of terrorism and global reputation: A case study with novel threshold behavior

A control model is presented which studies optimal spending for the fight against terrorism. Under the assumptions that economic damages are larger the greater the number of terrorists and that the success of counter terror operations depends on public opinion, it is demonstrated that a so-called DNSS threshold may exist, separating the basin of attraction of optimal paths.     

Assigning arriving flights at an airport to the available gates

Unexpected changes in the flight schedules may disrupt the initial aircraft-gate assignments, and result in congestions and delays in getting aircraft onto gates. A mathematical model is developed to assign the flights with the minimum range of unutilised time periods of gates, subject to the level of service offered to passengers and other physical and managerial considerations. (The assignments are expected to be flexible enough to absorb the minor modifications in the flight schedules.) Interactive optimum and heuristic procedures, both utilising lower bounds on the ranges of future solutions, are proposed to cope with the major changes in disrupting the initial gate-assignments. Over randomly generated schedules, 74 flights can be optimally assigned to seven gates within 17 seconds when the gates are re-utilised within 30 minutes after each departure. The heuristic reaches the optimal solution after evaluating at most 20 partial solutions at one level. Over data obtained from Riyadh’s International Airport, the heuristic outperforms the existing practice: On average, 72.03% and 54.28% improvements are obtained on the number of remote served aircraft and towed aircraft, respectively.     

An optimization approach for planning daily drayage operations

Daily drayage operations involve moving loaded or empty equipment between customer locations and rail ramps. Our goal is to minimize the cost of daily drayage operations in a region on a given day. Drayage orders are generally pickup and delivery requests with time windows. The repositioning of empty equipment may also be required in order to facilitate loaded movements. The drayage orders are satisfied by a heterogeneous fleet of drivers. Driver routes must satisfy various operational constraints. We present an optimization methodology for finding cost-effective schedules for regional daily drayage operations. The core of the formulation is a set partitioning model whose columns represent routes. Routes are added to the formulation by column generation. We present numerical results for real-world data which demonstrate that our methodology produces low cost solutions in a reasonably short time.     

Flight gate scheduling with respect to a reference schedule

This paper considers the problem of assigning flights to airport gates. We examine the general case in which an aircraft serving a flight may be assigned to different gates for arrival and departure processing and for optional intermediate parking. Restrictions to this assignment include gate closures and shadow restrictions, i.e., the situation where certain gate assignments may cause blocking of neighboring gates. The objectives include maximization of the total assignment preference score, a minimal number of unassigned flights during overload periods, minimization of the number of tows, maximization of a robustness measure as well as a minimal deviation from a given reference schedule. We show that in case of a one period time horizon this objective can easily be integrated into our existing model based on the Clique Partitioning Problem. Furthermore we present a heuristic algorithm to solve the problem for multiple periods.     

基于多目标规划的飞机路径恢复最优化算法研究

本文针对同一机场中同机型的多架飞机受到干扰后, 飞机路径恢复的多目标最优化问题进行研究。首先根据航空公司实际航班调整的常用原则和航班干扰管理的基本思想, 基于连接网络建立多目标规划模型, 其中两个目标按照优先级排列:第一个目标为最小化航班的最大延误时间, 第二个目标为最小化参与交换的飞机数量。然后根据该问题的航班波结构特点, 结合求解多目标规划的分层序列法, 分析优化问题的若干最优性质, 并基于快速排序算法和最小费用路算法设计出多项式算法。最后用算例验证了算法的有效性。该研究结果可以为航空公司减少航班延误提供理论和技术支持。     

Self-organizing lists and independent references: A statistical synergy

Let R₁,…, R_n be a linear list of n elements. We assume the independent reference model, with a fixed but unknown access probability vector. We survey briefly the problem of reorganizing the list dynamically, on the basis of accrued references, with the objective of minimizing the expected access cost. The counter scheme (CS) is known to be asymptotically optimal for this purpose. The paper explores the CS, with the aim of reducing its storage requirements. We start with a detailed exposition of its cost function and then point out that it interacts with the access model to produce some remarkable synergistic effects. These make it possible to use very effective “truncated versions” of the CS, which have very modest space requirements. The versions we consider are: (i) the “limited-counters scheme”, which bounds each of the frequency counters to a maximal value c; (ii) the original CS with a bound on the number of references during which the scheme is active. The bound is chosen so as to achieve a desired level of performance compared with the optimal policy.