Optimiranje pakiranja paleta u distribucijskom centru pomoću obojenih Petrijevih mreža

The pallet packing process is a critical supply chain component for many distribution centers. Most pallet loading optimization tools provide very good solutions when boxes’ dimensions are practically quite uniform, which is the case of most production industrial systems, since they are used to work with a reduced number of master boxes. However, there are other systems such as distribution centers characterized by a high diversity of boxes to be fitted altogether in the same pallet. In this paper a Coloured Petri Net model that formalizes the Pallet Loading problem and its optimization by integrating evaluation methods with search methods will be presented. The model developed provides very good results by using certain heuristics that avoids the analysis of the whole search space, simulating only the best scenarios. The proposed approach can be used to integrate warehouse layout configuration, storage policy, distribution policy together with picking policy. As a result of the proposed strategy, considerable savings on transport resource costs can be achieved.Proces pakiranja paleta kritična je faza opskrbnog lanca u distribucijskim centrima. Većina alata za optimiranje pakiranja paleta daje vrlo dobre rezultate kada su dimenzije kutija ujednačene, što je često slučaj u industrijskim distribucijskim centrima, ali ne daju dobre rezultate u distribucijskim centrima s velikom neujednačenošću dimenzija kutija koje treba upakirati u jednu paletu. U radu su primijenjene obojene Petrijeve mreže, koje formaliziraju proces pakiranja palete i njegovu optimizaciju integracijom evaluacijskih metoda i metoda pretraživanja. Razvijeni model daje vrlo dobre rezultate uz primjenu određene heuristike kojom se pretraživanje svodi samo na najbolje scenarije umjesto pretraživanja čitavog prostora. Predloženi pristup može se koristiti za integraciju organizacije skladišta, strategije spremanja, strategije distribucije i strategije pakiranja, čime se mogu postići značajne uštede u transportnim troškovima

Coloured Petri net-based traffic collision avoidance system encounter model for the analysis of potential induced collisions

The Traffic Alert and Collision Avoidance System (TCAS) is a world-wide accepted lastresort means of reducing the probability and frequency of mid-air collisions between aircraft. Unfortunately, it is widely known that in congested airspace, the use of the TCAS may actually lead to induced collisions. Therefore, further research regarding TCAS logic is required. In this paper, an encounter model is formalised to identify all of the potential collision scenarios that can be induced by a resolution advisory that was generated previously by the TCAS without considering the downstream consequences in the surrounding traffic. The existing encounter models focus on checking and validating the potential collisions between trajectories of a specific scenario. In contrast, the innovative approach described in this paper concentrates on quantitative analysis of the different induced collision scenarios that could be reached for a given initial trajectory and a rough specification of the surrounding traffic. This approach provides valuable information at the operational level. Furthermore, the proposed encounter model can be used as a test-bed to evaluate future TCAS logic changes to mitigate potential induced collisions in hot spot volumes. In addition, the encounter model is described by means of the coloured Petri net (CPN) formalism. The resulting state space provides a deep understanding of the cause-and-effect relationship that each TCAS action proposed to avoid an actual collision with a potential new collision in the surrounding traffic. Quantitative simulation results are conducted to validate the proposed encounter model, and the resulting collision scenarios are summarised as valuable information for future Air Traffic Management (ATM) systems.Peer ReviewedPostprint (author's final draft

From Single Aircraft to Communities: A Neutral Interpretation of Air Traffic Complexity Dynamics

Present air traffic complexity metrics are defined considering the interests of different management layers of ATM. These layers have different objectives which in practice compete to maximize their own goals, which leads to fragmented decision making. This fragmentation together with competing KPAs requires transparent and neutral air traffic information to pave the way for an explainable set of actions. In this paper, we introduce the concept of single aircraft complexity, to determine the contribution of each aircraft to the overall complexity of air traffic. Furthermore, we describe a methodology extending this concept to define complex communities, which are groups of interdependent aircraft that contribute the majority of the complexity in a certain airspace. In order to showcase the methodology, a tool that visualizes different outputs of the algorithm is developed. Through use-cases based on synthetic and real historical traffic, we first show that the algorithm can serve to formalize controller decisions as well as guide controllers to better decisions. Further, we investigate how the provided information can be used to increase transparency of the decision makers towards different airspace users, which serves also to increase fairness and equity. Lastly, a sensitivity analysis is conducted in order to systematically analyse how each input affects the methodology.Comment: 21 pages, 30 figures, 2 tables, submitted to Research Transportation Part

Spatiotemporal graph indicators for air traffic complexity analysis

There has been extensive research in formalising air traffic complexity, but existing works focus mainly on a metric to tie down the peak air traffic controllers workload rather than a dynamic approach to complexity that could guide both strategical, pre-tactical and tactical actions for a smooth flow of aircraft. In this paper, aircraft interdependencies are formalized using graph theory and four complexity indicators are described, which combine spatiotemporal topological information with the severity of the interdependencies. These indicators can be used to predict the dynamic evolution of complexity, by not giving one single score, but measuring complexity in a time window. Results show that these indicators can capture complex spatiotemporal areas in a sector and give a detailed and nuanced view of sector complexity

Support to Design for Air Traffic Management: An Approach with Agent-Based Modelling and Evolutionary Search

This paper presents a methodology to manage the support to design in ATM operations. We propose a workflow for the design of ATM solutions in a performance-based setting. The methodology includes the evaluation of the impact on human behaviour and exploits a combination of different paradigms, such as Agent-Based Modelling and Simulation, and Agent-Based Evolutionary Search. We prove the soundness of the methodology by carrying out a real case study, which is the transition from Direct Routing to Free Routing in the Italian airspace. The validation results exhibit limited errors for the assessment of the performance metrics under evaluation. Furthermore, the optimization of sector collapsing/decollapsing configuration is discussed to demonstrate the effectiveness of the implemented engines

Identification of spatiotemporal interdependencies and complexity evolution in a multiple aircraft environment

To support future automated transitions among the ATM safety nets, this study elaborates identification of the complex traffic scenarios based on the concept of aerial ecosystems. As an extension of the TCAS operational domain and evolving from the separation management towards collision avoidance layer, the concept has been developed as a stepwise algorithm for identification of cooperative aircraft involved in the safety event – detected conflict, and negotiating their resolution trajectories before the ecosystem deadlock event occurs, in which at least one aircraft stays out of a conflict-free resolution. As a response to this threshold, the paper examines generation of both acceptable and candidate resolution trajectories, with respect to the original aircraft trajectories. The candidate trajectories are generated from a set of tactical waypoints and a return waypoint to the original trajectory. Described methodology has been practically implemented to one ecosystem scenario, characterizing its evolution in terms of the intrinsic complexity. By introducing the heading maneuver changes and delay in the resolution process, the results have shown how the scenario complexity is increasing, especially affected by the states of two aircraft in the initial conflict. Furthermore, it has been demonstrated an evolution in the amount of the acceptable and candidate trajectory solutions, for which the minimum complexity value is satisfied. A goal of the study was to explore the lateral resolutions capacity at certain moments and its timely decrement

LAVICAD: LAboratori VIrtual de Comunicacions Analògiques i Digitals

Mitjançant el present ajut s’ha ampliat l’aplicació en xarxa LAVICAD (LAboratori VIrtual de COmunicacions Analògiques i Digitals) que s’ofereix de forma integrada dins de la plataforma d’e-learning COM@WEB. LAVICAD és una eina programada en Java i Matlab i està formada per un conjunt de simuladors de la capa física de sistemes de comunicacions. Tots els simuladors es presenten en xarxa i es poden utilitzar pels estudiants des de qualsevol ordinador sense necessitat d’instal·lació de cap tipus de software especial. Durant el curs 2007 2008 s’han desenvolupat entre d’altres dos línies de treball. D’una banda s’ha programat l’applet que emula la capa física de la televisió digital terrestre, com a referent per a l’ensenyament de sistemes de comunicacions avançats. D’altra banda s’ha treballat en la programació de noves funcionalitats de l’eina LAVICAD, que permeten ajudar als professors en el seguiment i avaluació del treball continuat dels estudiants. En particular s’ha programat la generació d’una base de dades que conté la informació dels usuaris que s’han connectat i els resultats obtinguts a l’executar un determinat simulador. Les dues línies desenvolupades han de permetre durant l’actual curs, consolidar l’ús dels diferents simuladors per a la docència de les assignatures implicades al projecte.Peer Reviewe

TIMSPAT - Reachability graph search-based optimization tool for colored Petri net-based scheduling

We present a reachability graph-based search optimization tool for scheduling.Motivated by the lack of tool support for optimization of TCPNs.Implements an event-driven timed state space with AI heuristic search algorithms.Aimed at supporting flexible decision making process with algorithm portfolio.Comparative study of nine search algorithms on real system demonstrates tool efficiency. The combination of Petri net (PN) modeling with AI-based heuristic search (HS) algorithms (PNHS) has been successfully applied as an integrated approach to deal with scheduling problems that can be transformed into a search problem in the reachability graph. While several efficient HS algorithms have been proposed albeit using timed PN, the practical application of these algorithms requires an appropriate tool to facilitate its development and analysis. However, there is a lack of tool support for the optimization of timed colored PN (TCPN) models based on the PNHS approach for schedule generation. Because of its complex data structure, TCPN-based scheduling has often been limited to simulation-based performance analysis only. Also, it is quite difficult to evaluate the strength and tractability of algorithms for different scheduling scenarios due to the different computing platforms, programming languages and data structures employed. In this light, this paper presents a new tool called TIMSPAT, developed to overcome the shortcomings of existing tools. Some features that distinguish this tool are the collection of several HS algorithms, XML-based model integration, the event-driven exploration of the timed state space including its condensed variant, localized enabling of transitions, the introduction of static place, and the easy-to-use syntax statements. The tool is easily extensible and can be integrated as a component into existing PN simulators and software environments. A comparative study is performed on a real-world eyeglass production system to demonstrate the application of the tool for scheduling purposes.Peer ReviewedPostprint (author's final draft

Performance optimization of a CNC machine through exploration of the timed state space

Flexible production units provide very efficient mechanisms to adapt the type and production rate according to fluctuations in demand. The optimal sequence of the different manufacturing tasks in each machine is a challenging problem that can deal with important productivity benefits