Computationally efficient estimation of high-dimension autoregressive models : with application to air pollution in Malta

The modelling and analysis of spatiotemporal behaviour is receiving wide-spread attention due to its applicability to various scientific fields such as the mapping of the electrical activity in the human brain, the spatial spread of pandemics and the diffusion of hazardous pollutants. Nevertheless, due to the complexity of the dynamics describing these systems and the vast datasets of the measurements involved, efficient computational methods are required to obtain representative mathematical descriptions of such behaviour. In this work, a computationally efficient method for the estimation of heterogeneous spatio-temporal autoregressive models is proposed and tested on a dataset of air pollutants measured over the Maltese islands. Results will highlight the computation advantages of the proposed methodology and the accuracy of the predictions obtained through the estimated model.peer-reviewe

Increasing the design strength of glass - fractography and stress testing

p. 867-880Brittleness is the unintended, but inevitable consequence of producing a transparent ceramic for architectural applications such as the soda-lime glass. Its tensile strength is particularly sensitive to surface imperfections, such as that from natural weathering and malicious damage. Although a significant amount of testing of new glass has been carried out, there has been surprisingly little testing on weathered glass. Due to the variable nature of the causes of surface damage, the lack of data on weathered glass leads to a considerable degree of uncertainty in the long-term strength of exposed glass. This paper presents the results of recent tests on weathered annealed glass which has been exposed to natural weathering for more than 20 years. The tests include experimental investigations using the co-axial ring setup as well as optical and atomic force microscopy of the glass surfaces. The experimental data from these tests is subsequently used to extend existing fracture mechanics-based models to predict the strength of weathered glass. It is shown that using an automated approach based directly on finite element analysis results can give an increase in effective design strength in the order of 70 to 100% when compared to maximum stress methods. It is also shown that by combining microscopy and strength test results, it is possible to quantitatively characterise the damage on glass surfaces.Zammit, K.; Overend, M. (2010). Increasing the design strength of glass - fractography and stress testing. Editorial Universitat Politècnica de València. http://hdl.handle.net/10251/695

On e-constraint based methods for the generation of Pareto frontiers

Over the years, a number of methods have been proposed for the generation of uniform and globally optimal Pareto frontiers in multi-objective optimization problems. This has been the case irrespective of the problem definition. The most commonly applied methods are the normal constraint method and the normal boundary intersection method. The former suffers from the deficiency of an uneven Pareto set distribution in the case of vertical (or horizontal) sections in the Pareto frontier, whereas the latter suffers from a sparsely populated Pareto frontier when the optimization problem is numerically demanding (ill-conditioned). The method proposed in this paper, coupled with a simple Pareto filter, addresses these two deficiencies to generate a uniform, globally optimal, well-populated Pareto frontier for any feasible bi-objective optimization problem. A number of examples are provided to demonstrate the performance of the algorithm.peer-reviewe

Towards optimized profile descents at Malta International Airport through revised approach procedures

The work presented in this paper was conducted as part of the CLEAN-FLIGHT project which is financed by the Malta Council for Science and Technology through the National Research and Innovation Programme 2011 (Grant Agreement R&I-2011-021).Traditionally, aircraft descend from cruise level towards the aerodrome in a stepped manner as directed by Air Traffic Control to ensure safe separation between aircraft, particularly in the terminal area. A descent methodology that is now being preferred is that of optimised profile descents (OPD). In OPDs, the aircraft descends from the top-of-descent (TOD) point towards the aerodrome following a smooth, continuous descent profile that is optimal from an operational perspective of choice, until it intersects the final approach glide path such as that of the Instrument Landing System (ILS). OPDs are advantageous because they consume less fuel and generate fewer emissions than their stepped counterparts. This paper presents a proposal of new approach procedures for use in the approaches to Malta International Airport (MIA) that will facilitate the introduction of OPDs. With around 28,000 aircraft movements per annum at MIA, this can be achieved by giving Air Traffic Control Officers (ATCOs) a selection of approach procedures on which to direct in-trail inbound and outbound aircraft without imposing altitude constraints. The discussion includes a study of current procedures, a statistical analysis of historical radar plots, the presentation of the proposed approaches, and a forecast of the potential gains in terms of fuel burn and emissions expected through fast-time simulation.peer-reviewe

A new computational technique for the generation of optimised aircraft trajectories

A new computational technique based on Pseudospectral Discretisation (PSD) and adaptive bisection ε-constraint methods is proposed to solve multi-objective aircraft trajectory optimisation problems formulated as nonlinear optimal control problems. This technique is applicable to a variety of next-generation avionics and Air Traffic Management (ATM) Decision Support Systems (DSS) for strategic and tactical replanning operations. These include the future Flight Management Systems (FMS) and the 4-Dimensional Trajectory (4DT) planning and intent negotiation/validation tools envisaged by SESAR and NextGen for a global implementation. In particular, after describing the PSD method, the adaptive bisection ε-constraint method is presented to allow an efficient solution of problems in which two or multiple performance indices are to be minimized simultaneously. Initial simulation case studies were performed adopting suitable aircraft dynamics models and addressing a classical vertical trajectory optimisation problem with two objectives simultaneously. Subsequently, a more advanced 4DT simulation case study is presented with a focus on representative ATM optimisation objectives in the Terminal Manoeuvring Area (TMA). The simulation results are analysed in-depth and corroborated by flight performance analysis, supporting the validity of the proposed computational techniques.peer-reviewe

Spatio-temporal analysis of air pollution data in Malta

Air pollution measurements display patterns over space and time allowing for spatio-temporal modelling, through which pollution concentrations and trends can be analysed. In Malta, the MEPA (Malta Environment and Planning Authority) collects monthly averaged data for various pollutants from a network of 123 diffusion tubes located around the Islands (Figure 1). This preliminary study uses data associated with traffic, that is nitrogen dioxide (NO2) and benzene, collected monthly between the period 2004 and 2010 with the objectives to i) develop a computationally efficient method that best describes the data; ii) determine the level of dependency of each site on neighbouring ones and iii) identify any factors that affect the behaviour and patterns of pollution. Results will show that generally there is a low spatial dependency between close sites, thus implying that local sources, rather than diffusion, have a predominant effect on the measurements. This analysis will prove valuable in MEPA’s redistribution exercise of the diffusion tube network to determine which sites are necessary to retain and which sites can be removed without significantly affecting the information gathered.peer-reviewe

A generic framework for multi-parameter optimization of flight trajectories

The project is co-funded by the European Community’s Seventh Framework Programme (FP7/2007-2013) for the Clean Sky Joint Technology Initiative.This paper presents the requirements and design concept of a multi-parameter optimization tool to be used on flight trajectories. The tool, referred to as GATAC, is being developed as part of the EU-funded Clean Sky Joint Technology Initiative (JTI) programme, and a preliminary version is discussed in this paper. The tool has been evaluated and the results obtained confirm the validity of the tool, opening the way for further development. The paper also addresses the architectural design and a number of key features of the tool.peer-reviewe

A quasi-real-time ground-based trajectory optimization tool for greener operations

This paper describes the methodology adopted in designing a quasi-real-time ground-based trajectory optimization tool for use by air traffic control officers. The tool is primarily intended for the optimization of aircraft trajectories during the climb and descent phases in which the user can define the trajectory in four dimensions. The optimized trajectories would then contribute to a reduction in fuel burn and emissions. The designed tool takes into account different aircraft types and sub-types through BADA performance and engine coefficients. A simple case study for an approach in Malta International Airport has also been presented to illustrate the use of the tool.peer-reviewe

A flexible framework for configurable real-time flight simulators

This paper presents the design and development of a Simulation and Integration Framework for use in research and teaching simulators. The design of the framework facilitates the integration of different simulation models of various formats without the need of software programming skills in a simulation environment. This is achieved through a Graphical User Interface (GUI) allowing the user to easily set up a flight simulator utilizing models programmed in different languages and having different interfaces. The framework allows for dynamic parallel processing over a distributed system providing the capability of concurrent model processing.peer-reviewe

GATAC - A generic framework for multi-parameter optimization of flight trajectories

Simulations in different scenarios requires the use of various models, the interfacing of which typically requires extensive effort and programming resources that may not be readily available in most industrial and academic environments. This paper discusses the development of GATAC - a generic framework that was developed for simulation and multiparameter optimization purposes allowing users to easily set up a simulation by making use of models developed using different technologies with different interfaces.peer-reviewe