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See detailAn Iterative Learning Approach for Signal Control in Urban Traffic Networks
Huang, Wei; Viti, Francesco UL; Tampere, Chris M.J.

in Proceedings of IEEE-ITS Conference (2013)

Traffic signal control influences route choice in traffic networks, and may even determine whether a traffic system settles in equilibrium or destabilizes into oscillatory patterns. Ideally, a stable ... [more ▼]

Traffic signal control influences route choice in traffic networks, and may even determine whether a traffic system settles in equilibrium or destabilizes into oscillatory patterns. Ideally, a stable equilibrium flow pattern should result from the interaction between control and route choice on a long-term horizon. This paper proposes an iterative learning approach for designing signal controls able to attract the system to equilibrium in an acceptable convergence speed. The traffic assignment model and combined traffic assignment and control problem are first introduced. An iterative learning control (ILC) based signal control is formulated and a basic model inversion method is analyzed. To deal with the nonlinearity of traffic system, a Newton based ILC algorithm is applied. Test in an example network verifies the effectiveness of the ILC method in achieving stable equilibrium in the traffic system. [less ▲]

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See detailAn iterative Mixed Integer Linear Programming Approach to pursuit evasion problems in polygonal environments
Thunberg, Johan UL; Ögren, P.

in Proceedings of the 2010 IEEE International Conference on Robotics and Automation (ICRA) (2010)

In this paper, we address the multi pursuer version of the pursuit evasion problem in polygonal environments. It is well known that this problem is NP-hard, and therefore we seek efficient, but not ... [more ▼]

In this paper, we address the multi pursuer version of the pursuit evasion problem in polygonal environments. It is well known that this problem is NP-hard, and therefore we seek efficient, but not optimal, solutions by relaxing the problem and applying the tools of Mixed Integer Linear Programming (MILP) and Receding Horizon Control (RHC). Approaches using MILP and RHC are known to produce efficient algorithms in other path planning domains, such as obstacle avoidance. Here we show how the MILP formalism can be used in a pursuit evasion setting to capture the motion of the pursuers as well as the partitioning of the pursuit search region into a cleared and a contaminated part. RHC is furthermore a well known way of balancing performance and computation requirements by iteratively solving path planning problems over a receding planning horizon, and adapt the length of that horizon to the computational resources available. The proposed approach is implemented in Matlab/Cplex and illustrated by a number of solved examples. [less ▲]

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See detailIterative optimization for adaptive anticipatory control in urban traffic networks
Huang, Wei; Viti, Francesco UL; Tampere, Chris M.J.

Scientific Conference (2015, July)

Detailed reference viewed: 61 (1 UL)
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See detailA Joint Day-to-Day Mode and Within-Day Departure Time Choice Model for the Analysis of Dynamic Ridesharing
Viti, Francesco UL; Corman, Francesco

Scientific Conference (2014, June 19)

Sharing travels is an effective way to increase car occupancy rates and to reduce the total number of cars for the same distances travelled. A potentially attractive service based on the sharing concept ... [more ▼]

Sharing travels is an effective way to increase car occupancy rates and to reduce the total number of cars for the same distances travelled. A potentially attractive service based on the sharing concept is dynamic ridesharing (DRS), where a service provider matches up driver and passenger with similar itineraries and time schedules with an automated program. To analyse how modal shift from single passenger use of the car to high occupancy one can be realized and what are the demand management solutions that can effectively be recommended, we deal with a theoretically interesting basic model structure of a single-link case, in which we study the complex interaction of multiple factors involved in the dynamic ridesharing problem, and the joint sensitivity to the most relevant parameters involved in this behavioural process. The main contribution of this study is therefore a unified framework that is able to model the dynamics of the departure time, characterized as a within-day process, while keeping the mode choice as a day-to-day process, and characterizing explicitly the matching process of DRS. [less ▲]

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See detailKE Tableaux for Public Announcement Logic
de Boer, Mathijs UL

Scientific Conference (2007, September 06)

Public announcement logic (PAL) is a simple dynamic epistemic logic extending reasoning about knowledge of agents with a modal operator for simultaneous and transparent knowledge updates. This logic is no ... [more ▼]

Public announcement logic (PAL) is a simple dynamic epistemic logic extending reasoning about knowledge of agents with a modal operator for simultaneous and transparent knowledge updates. This logic is no more expressive than epistemic logic (EL) without updates, but exhibits compact representation of a number of complex epistemic situations. A labeled tableau proof system to reason with these updates directly is presented here. This system can analyse and present well-known epistemic puzzles like `muddy children' and `three wise men'. Using the KE tableau system as a basis, the modal and propositional characteristics of epistemic updates can be separated. [less ▲]

Detailed reference viewed: 64 (1 UL)
See detailKnowledge Based Systems
Blessing, Lucienne UL

in CAD/CAM Handbook (1990)

Detailed reference viewed: 11 (0 UL)
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See detailL2-gain of double integrators with saturation nonlinearity
Goncalves, Jorge UL

in IEEE Transactions on Automatic Control (2002), 47(12), 2063-2068

This note uses quadratic surface Lyapunov functions (SuLFs) to efficiently check if a double integrator in feedback with a saturation nonlinearity has L -gain less than > 0. We show that for many such ... [more ▼]

This note uses quadratic surface Lyapunov functions (SuLFs) to efficiently check if a double integrator in feedback with a saturation nonlinearity has L -gain less than > 0. We show that for many such systems, the L -gain is nonconservative in the sense that this is approximately equal to the lower bound obtained by replacing the saturation with a constant gain of 1. These results allow the use of classical analysis tools like -analysis or integral quadratic constraints to analyze systems with double integrators and saturations, including servo systems like some mechanical systems, satellites, hard disks, compact disk players, etc. [less ▲]

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See detailL2-gain of double integrators with saturation nonlinearity
Goncalves, Jorge UL

in Proceedings of the 15th IFAC World Congress (2002)

This paper uses quadratic surface Lyapunov functions to efficiently check if a double integrator in feedback with a saturation nonlinearity has L2-gain less than gamma > 0. We show that for many of such ... [more ▼]

This paper uses quadratic surface Lyapunov functions to efficiently check if a double integrator in feedback with a saturation nonlinearity has L2-gain less than gamma > 0. We show that for many of such systems, the L2-gain is non-conservative in the sense that they are approximately equal to the low erbound obtained by replacing the saturation with a constant gain of 1. These results allow the use of classical analysis tools like mu -analysis or IQCs to analyze systems with double integrators and saturations, including servo systems like some mechanical systems, satellites, hard-disks, CD players, etc. [less ▲]

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See detailLab Testing Beyond Usability: Challenges and Recommendations for Assessing User Experiences
Lallemand, Carine UL; Koenig, Vincent UL

in Journal of Usability Studies (2017), 12(3), 133-154

In the “third wave” of human-computer interaction (HCI), the advent of the conceptual approach of UX broadens and changes the HCI landscape. Methods approved before, mainly within the conceptual approach ... [more ▼]

In the “third wave” of human-computer interaction (HCI), the advent of the conceptual approach of UX broadens and changes the HCI landscape. Methods approved before, mainly within the conceptual approach of usability, are still widely used, and yet their adequacy for UX evaluation remains uncertain in many applications. Laboratory testing is undoubtedly the most prominent example of such a method. Hence, in this study, we investigated how the more comprehensive and emotional scope of UX can be assessed by laboratory testing. In this paper, we report on a use case study involving 70 participants. They first took part in user/laboratory tests and then were asked to evaluate their experience with the two systems (perceived UX) by filling out an AttrakDiff scale and a UX needs fulfillment questionnaire. We conducted post-test interviews to better understand participants’ experiences. We analyzed how the participants’ perceived UX depends on quantitative (e.g., task completion time, task sequence, level of familiarity with the system) and qualitative aspects (think aloud, debriefing interviews) within the laboratory context. Results indicate that the laboratory setting has a strong impact on the participants’ perceived UX, and support a discussion of the quality and limitations of laboratory evaluations regarding UX assessment. In this paper, we have identified concrete challenges and have provided solutions and tips useful for both practitioners and researchers who seek to account for the subjective, situated, and temporal nature of the UX in their assessments. [less ▲]

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See detailLarge Eddy Simulations of the Influence of Piston Position on the Swirling Flow in a Model Two-Stroke Diesel Engine
Obeidat, Anas UL; Schnipper, Teis; Ingorsen, Kristian M. et al

in International Journal of Numerical Methods for Heat & Fluid Flow (2014), 24(2), 325-241

Detailed reference viewed: 82 (4 UL)
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See detailLarge scale phase field model of fracture and cutting in soft tissues
Ziael-Rad, Vahid; Hale, Jack UL; Maurini, Corrado et al

Scientific Conference (2015, July)

The phase field method has proven to be an important tool in computational mechanics in that it is able to deal naturally with crack nucleation and branching [1]. In this contribution, we demonstrate a ... [more ▼]

The phase field method has proven to be an important tool in computational mechanics in that it is able to deal naturally with crack nucleation and branching [1]. In this contribution, we demonstrate a large scale phase field model of fracture and cutting of soft tissues undergoing non-linear deformations with a material law defined by a hyperelastic energy density functional. We will also provide some initial thoughts on the how the effect of a porous medium can be incorporated into the phase field model. We implement this work using the FEniCS project and PETSc software packages [2, 3]. [less ▲]

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See detailLegal Ontology for Nexus: Water, Energy and Food in EU Regulations
Rahman, Md Mizanur UL

Doctoral thesis (2016)

Objectives of the thesis are – (a) to identify the problems in water-energy-food nexus from ICT and Law point of view and to propose theoretically a legal knowledge framework for water-energy-food nexus ... [more ▼]

Objectives of the thesis are – (a) to identify the problems in water-energy-food nexus from ICT and Law point of view and to propose theoretically a legal knowledge framework for water-energy-food nexus in order to reduce those problems technologically, (b) to construct and implement legal ontology for nexus extracted from EU water, energy and food Regulations in OWL 2 language, which is a part of the grater work of implementing legal knowledge framework for water-energy-food nexus pro-posed through the compilation of objective (a). Considering these objectives, this thesis presents total five chapters. Chapter 1 is dedicated to fulfill the requirement of objective (a) and the rest chapters are devoted for objective (b). More particularly chapter four presents technical descriptions of the legal ontology for nexus, while chapter two and three articulate methodological aspect of it. Chapter five evaluates legal ontology for nexus. Additionally, besides the list of references, annex 1 delivers all asserted restrictions used in this ontology and annex 2 provides the links of all modules and documentations of legal ontology for nexus. [less ▲]

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See detailLeveraging GIS Data and Topological Information to Infer Trip Chaining Behaviour at Macroscopic Level
Carrese, Filippo; Fusco, Gaetano; Cantelmo, Guido et al

Scientific Conference (2019, June)

One of the open challenges in transport modelling is to estimate within-day demand flows that reflect the complexity of individual activity-travel behaviour. While disaggregate (Activity-Based) demand ... [more ▼]

One of the open challenges in transport modelling is to estimate within-day demand flows that reflect the complexity of individual activity-travel behaviour. While disaggregate (Activity-Based) demand models can recreate realistic daily mobility patterns at an individual level, they usually require an accurate knowledge of individual user behaviour (i.e. via travel surveys), which is not always available. As a result, practitioners often turn to aggregate demand models, that have the advantage of being less demanding in terms of data but typically under represent the demand for secondary activities. In this work, we take research on within-day demand modelling one step forward by proposing a framework that combines traditional methodologies with heterogeneous data sources in order to explicitly represent trip chaining at an aggregated level. We show that the combination of web-based crowd sensed data, network data and behavioural constraints allows to capture complex spatial and temporal correlations between demand patterns. The methodology is applied on the classical Gravity model to show how to incorporate within-day dynamics. Yet, any alternative demand model can be adopted. In our case, Generation and Attraction are used to estimate the systematic demand, that is enriched of information about individual activity patterns, and then a novel definition of impedance function based on Hagestraand ellipse theory plays a central role in spatially distributing locations of trips using geographic relationships and constraints deriving from space-time behaviour. A case study for Luxembourg City has been presented to show the potential of the methodology: the choice of using data from a different spatial context to account for the temporal dimension has been validated through comparisons with official statistics. The results of simulating a workplace relocation show the advantages of this new approach in representing demand related to secondary activities. [less ▲]

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See detailLEXU II „Low Exergy Wall & Air Tempering for Building Refurbishment“
Schmidt, Christoph Wilhelm; Scholzen, Frank UL

Scientific Conference (2018, April 20)

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See detailLifetime prediction for solder joints with the extended finite element method
Menk, Alexander; Pearce, Chris J.; Lanier, Olivier et al

in Proceedings of 12th Int. Conf. on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, EuroSimE 2011 (2011)

Predicting the lifetime of solder joints undergoing thermal cycling is crucial for the electronics industry in order to guarantee a certain performance of their products in the field. Semi-empirical ... [more ▼]

Predicting the lifetime of solder joints undergoing thermal cycling is crucial for the electronics industry in order to guarantee a certain performance of their products in the field. Semi-empirical methods are often used to predict the average lifetime of the critical joints. However, to get a reliable failure probability the standard deviation must also be addressed. The deviation of the lifetime from the mean value is a consequence of the variation in microstructure found in actual joints. We therefore propose a new methodology that calculates crack growth based on microstructural features of the joint. A series of random microstructures is generated. Crack growth calculations are performed for each of these structures. The structural problem is solved numerically with the extended finite element method which allows a complete automation of the process. The mean crack length and standard deviation are calculated from the crack growth simulations and the result is compared to experimental data. [less ▲]

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See detailLINEAR BUCKLING ANALYSIS OF CRACKED ISOTROPIC PLATES USING THE EXTENDED FINITE ELEMENT METHOD
Baiz, PM; Natarajan, Stéphane; Kerfriden, P. et al

Scientific Conference (2010, March)

The behaviour of plate structures under compressive loads has been of great concern for engineering applications, especially in aeronautical and aerospace structures in which the demanding design of ... [more ▼]

The behaviour of plate structures under compressive loads has been of great concern for engineering applications, especially in aeronautical and aerospace structures in which the demanding design of weight critical applications usually leads to stability problems. In this paper, the linear buckling problem of cracked isotropic plates is studied using the extended finite element method (XFEM). The mixed interpolation technique of the well-established MITC4 quadrilateral finite element with 12 standard degrees of freedom per element is used. The critical buckling load and mode shapes of simply supported square plates are computed as a function of crack length. [less ▲]

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See detailLinear buckling analysis of cracked plates by SFEM and XFEM
Baiz, P. M.; Natarajan, S.; Bordas, Stéphane UL et al

in Journal of Mechanics of Material and Structures (2011), 6(9-10), 1213-1238

In this paper, the linear buckling problem for isotropic plates is studied using a quadrilateral element with smoothed curvatures and the extended finite element method. First, the curvature at each point ... [more ▼]

In this paper, the linear buckling problem for isotropic plates is studied using a quadrilateral element with smoothed curvatures and the extended finite element method. First, the curvature at each point is obtained by a nonlocal approximation via a smoothing function. This element is later coupled with partition of unity enrichment to simplify the simulation of cracks. The proposed formulation suppresses locking and yields elements which behave very well, even in the thin plate limit. The buckling coefficient and mode shapes of square and rectangular plates are computed as functions of crack length, crack location, and plate thickness. The effects of different boundary conditions are also studied. © 2011 by Mathematical Sciences Publishers. [less ▲]

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See detailLinear identification of nonlinear systems: A lifting technique based on the Koopman operator
Mauroy, Alexandre UL; Goncalves, Jorge UL

in Proceedings of the 55th IEEE Conference on Decision and Control (2016, December)

We exploit the key idea that nonlinear system identification is equivalent to linear identification of the socalled Koopman operator. Instead of considering nonlinear system identification in the state ... [more ▼]

We exploit the key idea that nonlinear system identification is equivalent to linear identification of the socalled Koopman operator. Instead of considering nonlinear system identification in the state space, we obtain a novel linear identification technique by recasting the problem in the infinite-dimensional space of observables. This technique can be described in two main steps. In the first step, similar to a component of the Extended Dynamic Mode Decomposition algorithm, the data are lifted to the infinite-dimensional space and used for linear identification of the Koopman operator. In the second step, the obtained Koopman operator is “projected back” to the finite-dimensional state space, and identified to the nonlinear vector field through a linear least squares problem. The proposed technique is efficient to recover (polynomial) vector fields of different classes of systems, including unstable, chaotic, and open systems. In addition, it is robust to noise, well-suited to model low sampling rate datasets, and able to infer network topology and dynamics. [less ▲]

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See detailA Linear Programming Approach to Parameter Fitting for the Master Equation
Martins, N. C.; Goncalves, Jorge UL

in IEEE Transactions on Automatic Control (2009), 54(10), 2451-2455

This technical note proposes a new framework for the design of continuous time, finite state space Markov processes. In particular, we propose a paradigm for selecting an optimal matrix within a pre ... [more ▼]

This technical note proposes a new framework for the design of continuous time, finite state space Markov processes. In particular, we propose a paradigm for selecting an optimal matrix within a pre-specified pencil of transition rate matrices. Given any transition rate matrix specifying the time-evolution of the Markov process, we propose a class of figures of merit that upper-bounds the long-term evolution of any statistical moment. We show that optimization with respect to the aforementioned class of cost functions is tractable via dualization and linear programming methods. In addition, we suggest how this approach can be used as a tool for the sub-optimal design of the master equation, with performance guarantees. Our results are applied to illustrative examples. [less ▲]

Detailed reference viewed: 87 (1 UL)