No abstract

Air transport contributes significantly to the globalization and world economic. With the increasing demand for both passengers and air cargo, future airspace may encounter unprecedented traffic pressure. To ensure the flying safety is always the paramount commitment of air transport. In the face of increasing traffic demand, it is pertinent to investigate how to reduce en-route collision risk without compromising the traffic demand. In this paper, we propose a multiobjective optimization based method to reduce the technical vertical risk (TVR) by controlling en-route air traffic speed. The suggested method simultaneously optimizes two objectives. The first one aims to minimize the TVR while the second tries to minimize the traffic delay. As the modeled optimization problem is concave and the two objectives conflict with each other, we therefore introduce two well-known multiobjective evolutionary algorithms named NSGA-II and NSGA-III and modify some of their operators to solve the proposed optimization problem. Finally, we carry out experiments on sixteen real-world daily traffic sample data that cover en-route flights within the Singapore flight information region (FIR). Experiments demonstrate that by optimizing the proposed problem using the introduced algorithms we obtain a set of speed control suggestions each of which can reduce the TVR for the Singapore FIR. This work will contribute both to strategical and tactical air traffic management as the aviation players can make the preferred choices based on the solutions yielded by the introduced algorithms.

Air traffic is playing a leading role in the global economical growth. Air traffic is indispensable from airport networks which accommodate the traffic demands. Note that airport networks are confronted with intractable uncertainties such as severe meteorological conditions, random mechanical failures of aircraft instruments, terrorist attacks, etc., which give rise to the failures of the components of airport networks. It is of great significance to improve the robustness of airport networks to component failures as the failures can cause staggering economical losses. Existing works either employ network rewire mechanism or add more links to an airport network to enhance the robustness of the given network. In this paper, we provide a counter-intuitive way to enhance the robustness of airport networks. Specifically, we propose to remove links from a given airport network to improve its robustness in face of perturbations. To do so, we develop a single-objective genetic algorithm to locate the links of an airport network whose removal will increase its robustness. Experimental studies on six realworld airport networks validate the feasibility of the proposed research idea. This work provides a new perspective for aviation decision makers to manage airports and air routes, and therefore sheds new light towards robust airspace design.

Air traffic is operated in an air traffic network (ATN) environment. It is of great significance to improve the robustness of ATNs as they are frequently exposed to manifold uncertainties which can break down the functioning components of an ATN. Existing studies on improving the robustness of ATNs either rewire the links of a network or add more links to the network. In this paper we suggest a Braess's Paradox inspired method. Specifically, we propose to improve the robustness of an ATN by removing some of its edges. In order to determine the edges whose removal can improve the robustness of a given ATN, we develop a bi-objective optimization model with one objective maximizing the network's robustness and the other one minimizing the number of links to be removed. We further apply and modify a non-dominated sorting genetic algorithm (NSGA-II) to optimize the developed model. In order to validate the effectiveness of the proposed idea, we carry out experiments on nine real-world ATNs. We also compare the modified NSGA-II algorithm against NSGA-III, and MODPSO, which are famous and efficient multiobjective evolutionary algorithms. Experiments indicate that NSGA-II outperforms the compared algorithms and that the robustness of an ATN indeed can be improved by just removing a small amount of its edges. For the tested ATNs, three networks have their robustness improved by 100% by removing less than six edges while the remaining six get an improvement of around 10%. This work provides a new perspective for aviation decision makers to better design and manage ATNs.

Numerous studies have been carded out in recent years to gain a better understanding of the structural integrity of the interfaces in modern composite systems. These problems are complicated by the fact that at the bimaterial interface crack tip, the tensile and shear effects are coupled, and the fracture resistance of the interface will generally depend on the degree of this mode mixity. Several test specimens have been proposed (see, e.g., Hutchinson and Suo [1]) for determining the interface fracture toughness and crack propagation characteristics of dissimilar isotropic materials. In the study of the fracture behaviour of layered materials, however, beam-type specimens, such as the double cantilever beam (DCB) specimen and the end-loaded-split (ELS) specimen are usually used. These two specimens are commonly employed for the determination of the mode I and mode II fracture toughness of, for example, composite laminates. In these cases, homogenised in-plane elastic constants are generally assumed, and calibration expressions giving the strain energy release rates for completely homogeneous, isotropic as well as orthotropic specimens have been obtained [2]- [5].Recently, the present authors [6] have obtained, using the Boundary Element Method (BEM), calibration results for the interface crack between two orthotropic layers of thickness h in DCB and ELS specimen set-ups. They relate the stress intensity factors, K 1 and K 2, and the strain energy release rates, G, to the normalised crack-length a/h. The material system treated was one in which an orthotropic, transversely isotropic layer was bonded to another layer of equal thickness made of the same material, but the latter being in the plane of transverse isotropy. The effects of the material properties were analysed with respect to two parameters, rll and r12, which correspond to the purely imaginary roots of the characteristic equation for the material. These parameters are related to the commonly used engineering constants as follows:(1) Int Journ of Fracture 72 (1995)