Path Planning for Cooperative Routing of Air-Ground Vehicles

We consider a cooperative vehicle routing problem for surveillance and reconnaissance missions with communication constraints between the vehicles. We propose a framework which involves a ground vehicle and an aerial vehicle; the vehicles travel cooperatively satisfying the communication limits, and visit a set of targets. We present a mixed integer linear programming (MILP) formulation and develop a branch-and-cut algorithm to solve the path planning problem for the ground and air vehicles. The effectiveness of the proposed approach is corroborated through extensive computational experiments on several randomly generated instances

Topology-Constrained Network Design

International audienc

The ring/κ-rings network design problem: Model and branch-and-cut algorithm

This article considers the problem of designing a two-level network where the upper level consists of a backbone ring network connecting the so-called hub nodes, and the lower level is formed by access ring networks that connect the non-hub nodes to the hub nodes. There is a fixed cost for each type of link, and a facility opening cost associated to each hub. The number of nodes in each access ring is bounded, and the number of access rings connected to a hub is limited to κ, thus resulting in a ring/κ-rings topology. The aim is to decide the hubs to open and to design the backbone and access rings to minimize the installation cost. We propose a mathematical model, give valid inequalities, and describe a branch-and-cut algorithm to solve the problem. Computational results show the algorithm is able to find optimal solutions on instances involving up to 40 nodes within a reasonable time. © 2016 Wiley Periodicals, Inc. NETWORKS, Vol. 68(2), 130–140 2016. © 2016 Wiley Periodicals, Inc

Applications of satellite technology to broadband ISDN networks

Two satellite architectures for delivering broadband integrated services digital network (B-ISDN) service are evaluated. The first is assumed integral to an existing terrestrial network, and provides complementary services such as interconnects to remote nodes as well as high-rate multicast and broadcast service. The interconnects are at a 155 Mbs rate and are shown as being met with a nonregenerative multibeam satellite having 10-1.5 degree spots. The second satellite architecture focuses on providing private B-ISDN networks as well as acting as a gateway to the public network. This is conceived as being provided by a regenerative multibeam satellite with on-board ATM (asynchronous transfer mode) processing payload. With up to 800 Mbs offered, higher satellite EIRP is required. This is accomplished with 12-0.4 degree hopping beams, covering a total of 110 dwell positions. It is estimated the space segment capital cost for architecture one would be about $190M whereas the second architecture would be about$250M. The net user cost is given for a variety of scenarios, but the cost for 155 Mbs services is shown to be about $15-22/minute for 25 percent system utilization

IST Austria Thesis

This thesis considers two examples of reconfiguration problems: flipping edges in edge-labelled triangulations of planar point sets and swapping labelled tokens placed on vertices of a graph. In both cases the studied structures – all the triangulations of a given point set or all token placements on a given graph – can be thought of as vertices of the so-called reconfiguration graph, in which two vertices are adjacent if the corresponding structures differ by a single elementary operation – by a flip of a diagonal in a triangulation or by a swap of tokens on adjacent vertices, respectively. We study the reconfiguration of one instance of a structure into another via (shortest) paths in the reconfiguration graph. For triangulations of point sets in which each edge has a unique label and a flip transfers the label from the removed edge to the new edge, we prove a polynomial-time testable condition, called the Orbit Theorem, that characterizes when two triangulations of the same point set lie in the same connected component of the reconfiguration graph. The condition was first conjectured by Bose, Lubiw, Pathak and Verdonschot. We additionally provide a polynomial time algorithm that computes a reconfiguring flip sequence, if it exists. Our proof of the Orbit Theorem uses topological properties of a certain high-dimensional cell complex that has the usual reconfiguration graph as its 1-skeleton. In the context of token swapping on a tree graph, we make partial progress on the problem of finding shortest reconfiguration sequences. We disprove the so-called Happy Leaf Conjecture and demonstrate the importance of swapping tokens that are already placed at the correct vertices. We also prove that a generalization of the problem to weighted coloured token swapping is NP-hard on trees but solvable in polynomial time on paths and stars

Development of analytical-numerical methods for dynamic analysis of geared transmission systems

The main objective of the present research activity is the study of geared transmission system dynamics, which is basically represented by a system of nonlinear differential equations. First of all, the different approaches to study the nonlinear dynamics of gears are qualitatively presented. Afterwards, the realization of a lumped parameter model is discussed by analyzing two different modeling strategies linked to two different numerical resolution techniques. The first modeling strategy is based on time integration techniques and enhances the employment of a commercial software to speed-up the modeling set-up phase. The proposed method rely on a block diagram technique and it is developed in Simcenter AMESim, a commercial software widely used in industries. By starting from the single gear pair model, detailed guidelines are given to construct any type of ordinary transmission layout by connecting some pre-programmed devices between them. In order to demonstrate the reliability of the approach, an experimental validation on industrial use case is proposed with excellent outcomes. The second modeling strategy rely on a frequency domain solution technique able to capture unstable solution branches in multi-valued frequency response regions. In particular, it proposes the Asymptotic Numerical Method combined to the Harmonic Balance Method as a valuable approach to solve the nonlinear dynamics of gear pairs. Thanks to a quadratic recast of the equation of motion, the Taylor and Fourier series can be computed in a very efficient way and each step produces a continuous representation of the solution branch making the continuation very robust. Effectiveness and reliability of the method are proved by comparing the numerical outcomes with that obtained from the Runge-Kutta time integration scheme. As a result, this technique provides for excellent computational performance despite additional time is needed for the quadratic recast of the equations system. Once a detailed analysis on the modeling strategy has been conducted, rattle noise and whine noise occurrence are investigated. Regarding the rattle noise, the research activity has conducted to the introduction of a new analytical parameter as a novelty to the current state of the art. A rattle index formulation is retrieved by starting from the classical 6-DOFs equation system defining the nonlinear dynamics of a gear pair. The proposed formulation may be applied to single or multiple branch geartrain, both in idle or loaded condions. The reliability of the analytical formulation is proved by numerical experiments which demonstrate the capability of the proposed index to instantaneously describe the vibro-impacts events related to any gear pair of the driveline. In addition its magnitude may be a measure of the tooth impact severity and it is shown to be a proper indicator of the potential presence of mutual interactions between different gear pairs pertaining to the same driveline. Finally, the investigation of whine noise occurrence addresses to an analytical formulation able to forecast the main overall direction and magnitude of bearing reaction forces on idler gear. By starting from the definition of meshing forces by means of Fourier series development, idler gear bearing forces are obtained under the hypothesis of quasi-static motion. This procedure demonstrates that the alternating component of bearing forces on idler gear describes an elliptical trajectory as the prime mover rotates over a pitch angle. The formulation directly links the bearing forces elliptical trajectory with the gear spatial position, the meshing phase and the amplitude of meshing forces. By properly setting the over-mentioned parameters one may be able to control the magnitude and direction of the overall idler bearing reaction forces. Numerical experiments were performed and the obtained results confirm the author intuitionL’obiettivo principale della presente attività di ricerca riguarda lo studio della dinamica non lineare degli ingranaggi che, di fatto, è rappresentata da un sistema di equazioni differenziali. Prima di tutto, viene presentata un ‘analisi qualitativa finalizzata a valutare i diversi approcci per studiare tale fenomeno. Successivamente, viene descritto lo sviluppo di un modello a parametri concentrati analizzando due diverse strategie di modellazione basate su metodi di risoluzione numerica diversi. Il primo approccio propone l’utilizzo di un software commerciale per velocizzare la fase di set-up del modello ed è basato su tecniche di integrazione temporale. Questa strategia di modellazione è sviluppata in Simcenter AMESim, un software commerciale distribuito da Siemens. Partendo dal modello di una singola coppia di ruote, viene dettagliata una procedura per costruire qualsiasi tipo di treno di ingranaggi grazie alla tecnica dei diagrammi a blocchi. Per dimostrare l’efficacia di tale tecnica, il metodo viene applicato ad un caso industriale ottenendo un’ottima correlazione numerico-sperimentale. Il secondo approccio si basa su tecniche di risoluzione numerica nel dominio della frequenza in grado di calcolare i rami instabili della risposta dinamica. Il metodo propone la combinazione del “Asymptotic Numerical Method” con il “Harmonic Balance Method” utilizzando una formulazione quadratica del sistema di equazioni differenziali. Grazie a tale formulazione, sia la serie di Taylor che quella di Fourier possono essere sviluppate in una maniera molto efficiente rendendo la continuazione della soluzione periodica molto robusta. L’affidabilità di questa tecnica è stata dimostrata confrontando i risultati con quelli ottenuti dal metodo di Runge-Kutta, basato sull’integrazione temporale. In più, tale tecnica garantisce performance computazionali eccellenti, anche se la riformulazione quadratica del sistema iniziale non è sempre facile da ottenere. Una volta analizzate le strategie di modellazione e le tecniche numeriche risolutive, lo studio si concentra su i fenomeni di rattle e whine noise. Riguardo il rattle noise, l’attività di ricerca ha portato all’introduzione di un nuovo parametro analitico come novità rispetto allo stato dell’arte. Partendo dal sistema di equazioni che governa il moto di una coppia di ruote dentate, è stato definito un indice analitico denominato “rattle index”. Tale indice può essere applicato a qualsiasi tipo di treno di ingranaggi, a uno o più rami, sia in condizioni di trasmissione di potenza che in folle. La sua affidabilità è supportata da simulazioni numeriche che dimostrano la capacità del “rattle index” di descrivere istantaneamente la perdita di contatto tra qualsiasi coppia di ruote di una trasmissione. Infine, la sua ampiezza è un indice della severità degli urti e permette di identificare l’esistenza di mutue interazioni tra le ruote della driveline. Infine, lo studio del whine noise ha portato ad una formulazione analitica capace di prevedere la direzione e l’ampiezza delle forze sui cuscinetti delle ruote oziose. Tale formulazione viene ottenuta partendo dalla definizione delle forze di ingranamento tramite lo sviluppo in serie di Fourier e ricavando le forze sui cuscinetti sotto l’ipotesi di moto quasi-statico. Questa procedura dimostra che le componenti alterne delle forze sui cuscinetti seguono una traiettoria ellittica quando il movente ruota di un passo angolare. La formulazione mette in relazione la traiettoria delle forze sui cuscinetti con la posizione delle ruote nel piano, la fase di ingranamento e l’ampiezza delle forze di ingranamento. Agendo sui parametri descritti, è possibile pilotare e controllare la direzione delle forze sui cuscinetti delle ruote oziose. La trattazione analitica è supportata da simulazioni numeriche con un ottimo riscontro