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See detailEfficient modeling of random heterogeneous materials with an uniform probability density function (slides)
Paladim, Daniel; Kerfriden, Pierre; Moitinho de Almeida, José et al

Scientific Conference (2014)

Homogenised constitutive laws are largely used to predict the behaviour of composite structures. Assessing the validity of such homogenised models can be done by making use of the concept of “modelling ... [more ▼]

Homogenised constitutive laws are largely used to predict the behaviour of composite structures. Assessing the validity of such homogenised models can be done by making use of the concept of “modelling error”. First, a microscopic “faithful” -and potentially intractable- model of the structure is defined. Then, one tries to quantify the effect of the homogenisation procedure on a result that would be obtained by directly using the “faithful” model. Such an approach requires (a) the “faithful” model to be more representative of the physical phenomena of interest than the homogenised model and (b) a reliable approximation of the result obtained using the ”faithful” and intractable model to be available at cheap costs. We focus here on point (b), and more precisely on the extension of the techniques devel- oped in [3] [2] to estimate the error due to the homogenisation of linear, spatially random composite materials. Particularly, we will approximate the unknown probability density function by bounding its first moment. In this paper, we will present this idea in more detail, displaying the numerical efficiencies and computational costs related to the error estimation. The fact that the probability density function is uniform is exploited to greatly reduce the computational cost. We will also show some first attempts to correct the homogenised model using non-conforming, weakly intrusive microscopic patches. [less ▲]

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See detailAttitude consensus using networks of uncalibrated cameras
Thunberg, Johan UL; Hu, X.

in The proceedings of the 33rd Chinese Control Conference (2014)

This paper addresses the problem of consensus on SO(3) for networks of uncalibrated cameras. Under the assumption of a pinhole camera model, we prove convergence to the consensus manifold for two types of ... [more ▼]

This paper addresses the problem of consensus on SO(3) for networks of uncalibrated cameras. Under the assumption of a pinhole camera model, we prove convergence to the consensus manifold for two types of kinematic control laws, when only conjugate rotation matrices KRK-1 are available among the agents. In these conjugate rotations, the rotation matrices are distorted by the (unknown) intrinsic parameters of the cameras. For the conjugate rotations, we introduce distorted versions of well known local parameterizations of SO(3) and show consensus by using three types of control laws. The control laws are similar to the standard consensus protocol used for systems of agents with single integrator dynamics, where pairwise differences between the states of neighboring agents are used. By considering the restriction to the planar case (when all the rotations have the same rotational axes), we weaken the assumptions on the cameras in the system and consider networks where the camera matrices differ between agents. [less ▲]

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See detailInference of switched biochemical reaction networks using sparse bayesian learning
Pan, Wei UL; Yuan, Y.; Sootla, A. et al

in The proceedings of the 7th European Conference on Machine Learning and Principles and Practice of Knowledge Discovery in Databases (ECML/PKDD) (2014)

This paper proposes an algorithm to identify biochemical reaction networks with time-varying kinetics. We formulate the problem as a nonconvex optimisation problem casted in a sparse Bayesian learning ... [more ▼]

This paper proposes an algorithm to identify biochemical reaction networks with time-varying kinetics. We formulate the problem as a nonconvex optimisation problem casted in a sparse Bayesian learning framework. The nonconvex problem can be efficiently solved using Convex-Concave programming. We test the effectiveness of the method on a simulated example of DNA circuit realising a switched chaotic Lorenz oscillator. [less ▲]

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See detailDistributed reconstruction of nonlinear networks: An ADMM approach
Pan, Wei UL; Sootla, Aivar; Stan, Guy-Bart

in Proceedings of the 19th World Congress of the International Federation of Automatic Control (IFAC 2014) (2014)

In this paper, we present a distributed algorithm for the reconstruction of large-scale nonlinear networks. In particular, we focus on the identification from time-series data of the nonlinear functional ... [more ▼]

In this paper, we present a distributed algorithm for the reconstruction of large-scale nonlinear networks. In particular, we focus on the identification from time-series data of the nonlinear functional forms and associated parameters of large-scale nonlinear networks. In (Pan et al. (2013)), a nonlinear network reconstruction problem was formulated as a nonconvex optimisation problem based on the combination of a marginal likelihood maximisation procedure with sparsity inducing priors. Using a convex-concave procedure (CCCP), an iterative reweighted lasso algorithm was derived to solve the initial nonconvex optimisation problem. By exploiting the structure of the objective function of this reweighted lasso algorithm, a distributed algorithm can be designed. To this end, we apply the alternating direction method of multipliers (ADMM) to decompose the original problem into several subproblems. To illustrate the effectiveness of the proposed methods, we use our approach to identify a network of interconnected Kuramoto oscillators with different network sizes (500∼100,000 nodes). [less ▲]

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See detailExperimental and Numerical Evaluation of the Residence Time Characteristics on a Forward Acting Grate
Peters, Bernhard UL; Dziugys, A.; Hunsinger, H.

in Condensed Matter 2014 (2014)

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See detailProceedings of the 2014 Workshop on Socio-Technical Aspects in Security and Trust, STAST 2014
Bella, Giampaolo; Lenzini, Gabriele UL

Scientific Conference (2014)

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See detailNetwork Reconstruction from Intrinsic Noise: Non-Minimum-Phase Systems
Hayden, David; Yuan, Ye; Goncalves, Jorge UL

in The proceedings of the The 19th World Congress of The International Federation of Automatic Control (2014)

This paper considers the problem of inferring the structure and dynamics of an unknown network driven by unknown noise inputs. Equivalently we seek to identify direct causal dependencies among manifest ... [more ▼]

This paper considers the problem of inferring the structure and dynamics of an unknown network driven by unknown noise inputs. Equivalently we seek to identify direct causal dependencies among manifest variables only from observations of these variables. We consider linear, time-invariant systems of minimal order and with one noise source per manifest state. It is known that if the transfer matrix from the inputs to manifest states is minimum phase, then this problem has a unique solution, irrespective of the network topology. Here we consider the general case where the transfer matrix may be non-minimum phase and show that solutions are characterized by an Algebraic Riccati Equation (ARE). Each solution to the ARE corresponds to at most one spectral factor of the output spectral density that satisfies the assumptions made. Hence in general the problem may not have a unique solution, but all solutions can be computed by solving an ARE and their number may be finite. [less ▲]

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See detailIMPROVING THE CONVERGENCE OF BOUNDS FOR EFFECTIVE ELASTIC PARAMETERS OF HETEROGENEOUS MATERIALS
Heaney, Claire; Kerfriden, Pierre; Bordas, Stéphane UL

Scientific Conference (2014)

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See detailIsogeometric finite element analysis using polynomial splines over hierarchical T-meshes
Nguyen-Thanh, Nhon; Nguyen-Xuan, Hung; Bordas, Stéphane UL et al

in IOP Conference Series: Materials Science and Engineering (2014), 10(1),

Isogeometric finite element analysis has become a powerful alternative to standard finite elements due to their flexibility in handling complex geometries. One major drawback of NURBS based isogeometric ... [more ▼]

Isogeometric finite element analysis has become a powerful alternative to standard finite elements due to their flexibility in handling complex geometries. One major drawback of NURBS based isogeometric finite elements is their less effectiveness of local refinement. In this study, we present an alternative to NURBS based isogeometric finite elements that allow for local refinement. The idea is based on polynomial splines and exploits the flexibility of T-meshes for local refinement. The shape functions satisfy important properties such as non-negativity, local support and partition of unity. We will demonstrate the efficiency of the proposed method by two numerical examples. [less ▲]

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See detailH2 Norm Based Network Volatility Measures
Huang, Qingqing; Yuan, Ye; Goncalves, Jorge UL et al

in The proceedings of the American Control Conference (2014)

Motivated by applications in biology and economics, we propose new volatility measures based on the H2 system norm for linear networks stimulated by independent or correlated noise. We identify critical ... [more ▼]

Motivated by applications in biology and economics, we propose new volatility measures based on the H2 system norm for linear networks stimulated by independent or correlated noise. We identify critical links in a network, where relatively small improvements can lead to large reductions in network volatility measures. We also examine volatility measures of individual nodes and their dependence on the topological position in the network. Finally, we investigate the dependence of the volatility on different network interconnections, weights of the edges and other network properties. Hence in an intuitive and efficient way, we can identify critical links, nodes and interconnections in network which can shed light in the network design to make it more robust. [less ▲]

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See detailNetwork Reconstruction from Intrinsic Noise
Hayden, David; Yuan, Ye; Goncalves, Jorge UL

in The proceedings of the American Control Conference (2014)

This paper considers the problem of inferring the structure and dynamics of an unknown network driven by unknown noise inputs. Equivalently we seek to identify direct causal dependencies among manifest ... [more ▼]

This paper considers the problem of inferring the structure and dynamics of an unknown network driven by unknown noise inputs. Equivalently we seek to identify direct causal dependencies among manifest variables only from observations of these variables. We consider linear, time-invariant systems of minimal order and with one noise source per measured state. If the transfer matrix from the inputs to manifest states is known to be minimum phase, this problem is shown to have a unique solution irrespective of the network topology. This is equivalent to there being only one spectral factor (up to a choice of signs of the inputs) of the output spectral density that satisfies these assumptions. Hence for this significant class of systems, the network reconstruction problem is well posed. [less ▲]

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See detailFinite-time road grade computation for a vehicle platoon
Yang, Tao; Yuan, Ye; Li, Kezhi et al

in IEEE (2014)

Given a platoon of vehicles traveling uphill, this paper considers the finite-time road grade computation problem. We propose a decentralized algorithm for an arbitrarily chosen vehicle to compute the ... [more ▼]

Given a platoon of vehicles traveling uphill, this paper considers the finite-time road grade computation problem. We propose a decentralized algorithm for an arbitrarily chosen vehicle to compute the road grade in a finite number of time-steps by using only its own successive velocity measurements. Simulations then illustrate the theoretical results. These new results can be applied to real-world vehicle platooning problems to reduce fuel consumption and carbon dioxide emissions. [less ▲]

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See detailPOD-based model order reduction for the simulation of strong nonlinear evolutions in structures: Application to damage propagation
Kerfriden, P.; Gosselet, P.; Adhikari, S. et al

in IOP Conference Series: Materials Science and Engineering (2014), 10(1),

In this paper, we develop a bridge between POD-based model order reduction techniques and the classical Newton-Krylov solvers to derive an efficient solution procedure for highly nonlinear problems ... [more ▼]

In this paper, we develop a bridge between POD-based model order reduction techniques and the classical Newton-Krylov solvers to derive an efficient solution procedure for highly nonlinear problems undergoing strong topological changes. [less ▲]

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See detailSpace-time reduced basis approximation and goal-oriented a posteriori error estimation for wave equation
Hoang, Khac Chi; Kerfriden, Pierre; Bordas, Stéphane UL

in Theory and Application of Model Order Reduction (2013, December)

We study numerically the linear second order wave equation with an output quantity of interest which is a linear functional of the field variable using reduced basis approximation methods in the space ... [more ▼]

We study numerically the linear second order wave equation with an output quantity of interest which is a linear functional of the field variable using reduced basis approximation methods in the space-time domain. The essential new ingredient is the a posteriori error estimation of the output quantity of interest. The technique, which is based on the well-known dual-weighted residual (DWR) method is deployed within a reduced basis approximation context. First, we introduce the reduced basis recipe - Galerkin projection onto a space spanned by the reduced basis functions which are constructed from the solutions of the governing PDE at several selected points in the parameter space. Second, in order to construct these basis functions we propose a new “goal-oriented” Proper Orthogonal Decomposition (POD)-Greedy sampling procedure, which is based on these new a posteriori error estimations. Finally, this a posteriori error estimation is also used to evaluate approximately the quality of many output computations in the online stage within the reduced basis procedure. [less ▲]

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See detailA Meshless Method for the Reissner-Mindlin Plate Equations based on a Stabilized Mixed Weak Form
Hale, Jack UL; Baiz, P. M.

Scientific Conference (2013, September)

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See detailEvaluation of V2me: A Virtual Coaching System for Loneliness Prevention and Intervention
Roelofsma, Peter; Ferring, Dieter UL; Aleksic, Gabrijela UL

in Medicine 2.0: Social Media, Mobile Apps and Internet/Web 2.0 (2013, September)

One out of three persons in our society suffers from social or emotional loneliness. This percentage is even higher in the population of people who suffer from chronic diseases. Loneliness has pervasive ... [more ▼]

One out of three persons in our society suffers from social or emotional loneliness. This percentage is even higher in the population of people who suffer from chronic diseases. Loneliness has pervasive effects on mental health but it also has negative effects on physical well-being. The aim of this paper is to present a series of pilot studies evaluating the development of an ambient virtual coaching system. This system, called V2me (Virtual Coach reaches Out to Me) offers a friendship enrichment course for people in need for improving their social network. Several pilot studies were performed with about 50 participants in total who evaluated the system that was developed using a living lab approach. In this approach new health media was developed from a user-centered process that allows frequent iterations of user evaluation and involvement. The paper presents the results of the first five iterations. The reactions on receiving the system and experiences during instruction were increasingly positive over these iterations of the system development phase. Over time the system has passed the user’s choice selection criteria. Participants have been expressing a clear interest for choosing and wanting to use the system in their daily lives. However, the system did not pass the persistent use selection criteria when the system was brought and left for independent use. It appeared that participants did not use it very much during the day as expected. Moreover, participants did not perform all the tasks (i.e., messaging, Skyping) that they were asked to achieve on a daily basis. The final goal of the V2me system, i.e. establishing social relations between elderly persons, was not achieved as well, although this might be due to the limited time space of using the system and its facilities. Given these observation, it is concluded that more iterations in the system development are needed for the system in order to pass the habitual use criteria which is needed for its effectiveness. [less ▲]

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See detailA multiscale partitioned reduced order model applied to damage simulation
Goury, Olivier; Kerfriden, Pierre; Bordas, Stéphane UL

Scientific Conference (2013, July)

Simulating fracture in realistic engineering components is computationally expensive. In the context of early-stage design, or reverse engineering, such simulations might need to be performed for a large ... [more ▼]

Simulating fracture in realistic engineering components is computationally expensive. In the context of early-stage design, or reverse engineering, such simulations might need to be performed for a large range of material and geometric parameters, which makes the solution to the parametric problem of fracture unaffordable. Model order reduction, such as the proper orthogonal decomposition (POD), is one way to reduce significantly the computational time by reducing the number of spatial unknowns. The solution is searched for in a reduced space spanned by a few well-chosen basis vectors only. In the context of solid mechanics involving structural softening, the strong topological changes in the zone where damage localises are extremely sensitive to variations of the parameters, which requires reduced spaces of prohibitively large dimensions in order to approximate the solution with a sufficiently high degree of accuracy. Introduced in [1], partitioned model order reduction is an alternative to global model order reduction that essentially divides up the problem into smaller regions. Each region can then be tackled using a reduced model of appropriate size, if at all, depending on the local material non-linearities in the region. In the context of multiscale homogenization, simulations of representative volume elements (RVE) have to be performed to obtain the material properties in the different elements of a coarse mesh. When considering a nonlinear material, those multiple RVE simulations can be com- putationally very expensive. They however only differ by the history of boundary conditions applied. This contribution proposes to apply partitioned model order reduction to those RVEs with reduced bases parametrized by the boundary conditions. REFERENCES [1] P. Kerfriden, O. Goury, T. Rabczuk, S. Bordas, A partitioned model order reduction approach to rationalise computational expenses in nonlinear fracture mechanics, Computer Methods in Applied Mechanics and Engineering, 256:169–188, 2013. [less ▲]

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See detailSensitivity Analysis and Shape Optimisation through a T-spline Isogeometric Boundary Element Method
Lian, Haojie; Simpson, Robert; Bordas, Stéphane UL

Scientific Conference (2013, March 25)

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See detailSensitivity Analysis and Shape Optimisation through a T-spline Isogeometric Boundary Element Method
Lian, Haojie; Simpson, Robert; Bordas, Stéphane UL

Scientific Conference (2013, March)

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See detailTowards Effective Shell Modelling with the FEniCS Project
Hale, Jack UL; Baiz, P. M.

Scientific Conference (2013, March)

Fast and efficient simulations of shell structures are required in a wide range of engineering fields such as fluid-structure interaction and structural optimisation. Because of its expressive high-level ... [more ▼]

Fast and efficient simulations of shell structures are required in a wide range of engineering fields such as fluid-structure interaction and structural optimisation. Because of its expressive high-level form language UFL the FEniCS project is in an ideal position to tackle tough problems such as large deformations of non-isotropic shells. In this talk we will discuss some aspects of achieving this goal; generalised mixed formulations, reduction and projection operators for eliminating shear and membrane locking, the general shell model vs classical models and the recent work by Rognes et al. on manifolds. [less ▲]

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See detailA goal-oriented reduced basis method for the wave equation in inverse analysis
Hoang, Khac Chi; Kerfriden, Pierre; Bordas, Stéphane UL

in International Conference on Computational Mechanics CM13 Proceedings (2013, March)

In this paper, we extend the reduced-basis methods developed earlier for wave equations to goal-oriented wave equations with a ne parameter dependence. The essential new ingredient is the dual (or adjoint ... [more ▼]

In this paper, we extend the reduced-basis methods developed earlier for wave equations to goal-oriented wave equations with a ne parameter dependence. The essential new ingredient is the dual (or adjoint) problem and the use of its solution in a sampling procedure to pick up “goal-orientedly” parameter samples. First, we introduce the reduced-basis recipe — Galerkin projection onto a space YN spanned by the reduced basis functions which are constructed from the solutions of the governing partial di erential equation at several selected points in parameter space. Second, we propose a new “goal-oriented” Proper Orthogonal Decomposition (POD)–Greedy sampling procedure to construct these associated ba-sis functions. Third, based on the assumption of a ne parameter dependence, we use the o ine-online computational procedures developed earlier to split the computational procedure into o ine and online stages. We verify the proposed computational procedure by applying it to a three-dimensional simulation dental implant problem. The good numeri-cal results show that our proposed procedure performs better than the standard POD–Greedy procedure in terms of the accuracy of output functionals. [less ▲]

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See detailDesign Automation With the Characteristics Properties Model and Property Driven Design for Redesign
Qureshi, Ahmed Jawad UL; Eisenbart, Boris UL; Dantan, Jean-Yves et al

in Abramovici, Michael, Stark, Rainer (Ed.) Smart Product Engineering (2013)

This paper presents a framework consisting of a mathematical model and an algorithm for representation, analysis and exploration of the design space in redesign problems. The framework develops and ... [more ▼]

This paper presents a framework consisting of a mathematical model and an algorithm for representation, analysis and exploration of the design space in redesign problems. The framework develops and extends the existing formalism of the Characteristics Properties Model (CPM) and Property Driven Design (PDD). A platform independent quantitative model based on formal log-ic is presented to map the characteristics and properties, as well as the relations and dependencies between them, along with the necessary conditions for solu-tion evaluation. The model is based on generalization of existing mathematical design models and is supported by the development of an algorithm enabling property driven design. The resulting framework offers a rich and flexible syn-tax and vocabulary along with a mathematical and computational tool applica-ble to mechanical product redesign. [less ▲]

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See detailTravel-sharing in multimodal systems: a behavioural modelling approach
Viti, Francesco UL

Scientific Conference (2013)

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See detailRobust Signal-Structure Reconstruction
Chetty, Vasu; Hayden, David; Goncalves, Jorge UL et al

in The proceedings of the IEEE 52nd Annual Conference on Decision and Control (2013)

This paper focuses on the reconstruction of the signal structure of a system in the presence of noise and nonlinearities. Previous results on polynomial time reconstruction in this area were restricted to ... [more ▼]

This paper focuses on the reconstruction of the signal structure of a system in the presence of noise and nonlinearities. Previous results on polynomial time reconstruction in this area were restricted to systems where target specificity was part of the inherent structure, [5]. This work extends these results to all reconstructible systems and proposes a faster reconstruction algorithm along with an improved model selection procedure. Finally, a simulation study then details the performance of this new algorithm on reconstructible systems. [less ▲]

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See detailNetwork reconstruction using knock-out and over-expression data
Hayden, David; Yuan, Ye; Goncalves, Jorge UL

in The proceedings of the 2013 European Control Conference (ECC) (2013)

This paper outlines necessary and sufficient conditions for network reconstruction of linear, time-invariant systems using data from either knock-out or over-expression experiments. These structural ... [more ▼]

This paper outlines necessary and sufficient conditions for network reconstruction of linear, time-invariant systems using data from either knock-out or over-expression experiments. These structural system perturbations, which are common in biological experiments, can be formulated as unknown system inputs, allowing the network topology and dynamics to be found. We assume that only partial state measurements are available and propose an algorithm that can reconstruct the network at the level of the measured states using either time-series or steady-state data. A simulated example illustrates how the algorithm successfully reconstructs a network from data. [less ▲]

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See detailReal-time Fault Diagnosis for Large-Scale Nonlinear Power Networks
Pan, Wei UL; Yuan, Ye; Sandberg, Henrik et al

in The proceedings of the IEEE 52nd Annual Conference on Decision and Control (2013)

In this paper, automatic fault diagnosis in large scale power networks described by second-order nonlinear swing equations is studied. This work focuses on a class of faults that occur in the transmission ... [more ▼]

In this paper, automatic fault diagnosis in large scale power networks described by second-order nonlinear swing equations is studied. This work focuses on a class of faults that occur in the transmission lines. Transmission line protection is an important issue in power system engineering because a large portion of power system faults is occurring in transmission lines. This paper presents a novel technique to detect, isolate and identify the faults on transmissions using only a small number of observations. We formulate the problem of fault diagnosis of nonlinear power network into a compressive sensing framework and derive an optimisation-based formulation of the fault identification problem. An iterative reweighted ℓ1-minimisation algorithm is finally derived to solve the detection problem efficiently. Under the proposed framework, a real-time fault monitoring scheme can be built using only measurements of phase angles of nonlinear power networks. [less ▲]

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See detailDistributed Kalman Filter with minimum-time covariance computation
Thia, Jerry; Yuan, Ye; Shi, Ling et al

in The proceedings of the IEEE 52nd Annual Conference on Decision and Control (2013)

This paper considerably improves the well-known Distributed Kalman Filter (DKF) algorithm by Olfati-Saber (2007) by introducing a novel decentralised consensus value computation scheme, using only local ... [more ▼]

This paper considerably improves the well-known Distributed Kalman Filter (DKF) algorithm by Olfati-Saber (2007) by introducing a novel decentralised consensus value computation scheme, using only local observations of sensors. It has been shown that the state estimates obtained in [8] and [9] approaches those of the Central Kalman Filter (CKF) asymptotically. However, the convergence to the CKF can sometimes be too slow. This paper proposes an algorithm that enables every node in a sensor network to compute the global average consensus matrix of measurement noise covariance in minimum time without accessing global information. Compared with the algorithm in [8], our theoretical analysis and simulation results show that the new algorithm can offer improved performance in terms of time taken for the state estimates to converge to that of the CKF. [less ▲]

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See detailCentralized and decomposed anticipatory Model Predictive Control for network-wide Ramp Metering
Rinaldi, Marco UL; Tampere, C. M. J.; Himpe, W. et al

in Proceedings of the 16th International IEEE Conference on Intelligent Transportation Systems: Intelligent Transportation Systems for All Modes, ITSC 2013 (2013)

The problem of determining Ramp Metering control rates, taking into account routing response, is addressed in this paper. We develop Model Predictive Control based Anticipatory control schemes, featuring ... [more ▼]

The problem of determining Ramp Metering control rates, taking into account routing response, is addressed in this paper. We develop Model Predictive Control based Anticipatory control schemes, featuring both centralized and decomposed optimization problems, with focus on real-life deployability. We then evaluate the aforementioned schemes' performances in comparison to simpler, non-anticipatory control techniques, by means of software simulation based on purpose-built experimental scenarios. © 2013 IEEE. [less ▲]

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See detailEquilibrium in capacitated network models with queueing delays, queue-storage, blocking back and control
Smith, Mike J.; Huang, Wei; Viti, Francesco UL

in Procedia Social and Behavioral Sciences (2013), 80

This paper considers a steady-state, link-based, fixed (or inelastic) demand equilibrium model with explicit link-exit capacities, explicit bottleneck or queuing delays and explicit bounds on queue ... [more ▼]

This paper considers a steady-state, link-based, fixed (or inelastic) demand equilibrium model with explicit link-exit capacities, explicit bottleneck or queuing delays and explicit bounds on queue storage capacities. The (spatial queueing) model at the heart of this equilibrium model takes account of the space taken up by queues both when there is no blocking back and also when there is blocking back. The paper shows in theorem 1 that a feasible traffic assignment model has an equilibrium solution provided prices are used to impose capacity restrictions and utilises this result to show that there is an equilibrium with the spatial queueing model, provided queue-storage capacities are sufficiently large. Other results are obtained by changing the variables and sets in theorem 1 suitably. These results include: (1) existence of equilibrium results (in both a steady state and a dynamic context) which allow signal green-times to respond to prices and (2) an existence of equilibrium result which allow signal green-times to respond to spatial queues; provided this response follows the P0 control policy in Smith (1979, 1987). These results show that under certain conditions the P0 control policy maximises network capacity. The spatial queueing model is illustrated on a simple network. Finally the paper includes elastic demand; this is necessary for long-run evaluations. Each of the steady state models here may be thought of as a stationary solution to the dynamic assignment problem either with or without blocking back. [less ▲]

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See detailDie Extended Discrete Element Method (XDEM) für multiphysikalische Anwendungen
Peters, Bernhard UL; Besseron, Xavier UL; Estupinan Donoso, Alvaro Antonio UL et al

Scientific Conference (2013)

A vast number of engineering applications include a continuous and discrete phase simultaneously, and therefore, cannot be solved accurately by continuous or discrete approaches only. Problems that ... [more ▼]

A vast number of engineering applications include a continuous and discrete phase simultaneously, and therefore, cannot be solved accurately by continuous or discrete approaches only. Problems that involve both a continuous and a discrete phase are important in applications as diverse as pharmaceutical industry e.g. drug production, agriculture food and processing industry, mining, construction and agricultural machinery, metals manufacturing, energy production and systems biology. <br />A novel technique referred to as Extended Discrete Element Method (XDEM) is developed, that offers a significant advancement for coupled discrete and continuous numerical simulation concepts. XDEM treats the solid phase representing the particles and the fluidised phase usually a fluid phase or a structure as two distinguished phases that are coupled through heat, mass and momentum transfer. An outstanding feature of the numerical concept is that each particle is treated as an individual entity that is described by its thermodynamic state e.g. temperature and reaction progress and its position and orientation in time and space. The thermodynamic state includes one-dimensional and transient distributions of temperature and species within the particle and therefore, allows a detailed and accurate characterisation of the reaction progress in a fluidised bed. Thus, the proposed methodology provides a high degree of resolution ranging from scales within a particle to the continuum phase as global dimensions. <br />These superior features as compared to traditional and pure continuum mechanics approaches are applied to predict drying of wood particles in a packed bed and impact of particles on a membrane. Pre- heated air streamed through the packed bed, and thus, heated the particles with simultaneous evaporation of moisture. Water vapour is transferred into the gas phase at the surface of the particles and transported to the exit of the reactor. A rather inhomogeneous drying process in the upper part of the reactor with higher temperatures around the circumference of the inner reactor wall was observed. The latter is due to increased porosity in conjunction with higher mass flow rates than in the centre of the reactor, and thus, augmented heat transfer. A comparison of the weight loss over time agreed well with measurements. <br />Under the impact of falling particles the surface of a membrane deforms that conversely affects the motion of particles on the surface. Due to an increasing vertical deformation particles roll or slide down toward the bottom of the recess, where they are collected in a heap. Furthermore, during initial impacts deformation waves are predicted that propagate through the structure, and may, already indicate resonant effects already before a prototype is built. Hence, the Extended Discrete Element Method offers a high degree of resolution avoiding further empirical correlations and extends the knowledge into the underlying physics. Although most of the work load concerning CFD and FEM is arranged in the ANSYS workbench, a complete integration is intended that allows for a smooth workflow of the entire simulation environment. [less ▲]

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See detailSignal control strategies in day-to-day dynamic process of combined traffic assignment and control
Huang, Wei; Viti, Francesco UL; Tampere, Chris M.J.

Scientific Conference (2013)

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See detailDevice-free indoor localization using ambient radio signals
Popleteev, Andrei UL

in UbiComp-2013 Adjunct proceedings (2013)

This paper investigates feasibility of device-free indoor localization using single passive receiver. Instead of local wireless nodes sharing one frequency channel, this work leverages multiple ambient FM ... [more ▼]

This paper investigates feasibility of device-free indoor localization using single passive receiver. Instead of local wireless nodes sharing one frequency channel, this work leverages multiple ambient FM radio stations. Experimental results demonstrate feasibility of the proposed approach and highlight the role of frequency diversity for passive localization. [less ▲]

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See detailAnalytical solutions to feedback systems on the special orthogonal group SO(n)
Markdahl, J.; Thunberg, Johan UL; Hoppe, J. et al

in the proceeding of the 52nd Annual Conference on Decision and Control (2013)

This paper provides analytical solutions to the closed-loop kinematics of two almost globally exponentially stabilizing attitude control laws on the special orthogonal group SO(n). By studying the general ... [more ▼]

This paper provides analytical solutions to the closed-loop kinematics of two almost globally exponentially stabilizing attitude control laws on the special orthogonal group SO(n). By studying the general case we give a uniform treatment to the cases of SO(2) and SO(3), which are the most interesting dimensions for application purposes. Working directly with rotation matrices in the case of SO(3) allows us to avoid certain complications which may arise when using local and global many-to-one parameterizations. The analytical solutions provide insight into the transient behaviour of the system and are of theoretical value since they can be used to prove almost global attractiveness of the identity matrix. The practical usefulness of analytical solutions in problems of continuous time actuation subject to piece-wise unavailable or discrete time sensing are illustrated by numerical examples. [less ▲]

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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 detailDealing with interfaces in partitioned model order reduction for application to nonlinear problems
Goury, Olivier; Kerfriden, Pierre; Bordas, Stéphane UL

Scientific Conference (2013)

We propose a reduced order modelling technique based on a partitioning of the domain of study in the context of para- metric nonlinear problems. A formulation of the reduction of the displacement and of ... [more ▼]

We propose a reduced order modelling technique based on a partitioning of the domain of study in the context of para- metric nonlinear problems. A formulation of the reduction of the displacement and of the interface tractions linking subdomains to each others will be performed in a FETI context. [less ▲]

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See detailStable extended finite element method: Convergence, Accuracy, Properties and Diffpack implementation
Paladim, Daniel; Natarajan, Sundarajan; Bordas, Stéphane UL et al

in International Conference on Extended Finite Element Methods - XFEM 2013, September 11 – 13, 2013, Lyon, France (2013)

Problems involving singularities and moving boundaries, especially when they involve discontinuities, create difficulties for the finite element method. On another, albeit related, front, two diametrally ... [more ▼]

Problems involving singularities and moving boundaries, especially when they involve discontinuities, create difficulties for the finite element method. On another, albeit related, front, two diametrally opposed approaches are attempting to simplify the CAD to Analysis pipeline: isogeometric methods on the one hand [1] aim at coupling the geometry and field approximations, whilst implicit boundary definition-based methods attempt to decouple them [3,4,5]. We examine in this paper one instance of the latter approach, and rely on partition of unity enrichment of the field variable to capture discontinuities along material interface or domain boundaries. We study in particular the stable generalized finite element method of Babuˇka and Banerjee [6] for higher order approximations in two and three dimensions and propose a generic implementation within the C++ library Diffpack from inuTech GmbH [7]. In a companion paper, the implementation of enrichment within Diffpack is presented in more detail. We will present results obtained with our 3D implementation of partition of unity enrichment within Diffpack. This implementation represents the interfaces through level-sets and palliates blending problems using various approaches. We study here the stabilisation approach proposed in [6] in more detail and pay particular attention to the global convergence rate of the approach and to the stability and the local flux converence close to the interfaces. [less ▲]

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See detailNumerical Modelling of Piezoelectric Energy Harvesting Devices
Ravi, Srivathsan UL; Zilian, Andreas UL

Scientific Conference (2013)

This paper introduces a monolithic approach that provides simultaneous modeling and analysis of the coupled energy harvester, which involves surface-coupled fluid-structure interaction, volume-coupled ... [more ▼]

This paper introduces a monolithic approach that provides simultaneous modeling and analysis of the coupled energy harvester, which involves surface-coupled fluid-structure interaction, volume-coupled piezoelectric mechanics and a controlling energy harvesting circuit for applications in energy harvesting. The weak form of the governing equations is discretized by the space-time finite element method based on a mixed velocity-stress/rate form of the potential-dielectric displacement framework. The results will be compared to the simple cases with closed-form solution available from literature. [less ▲]

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See detailNumerical Modelling of Piezoelectric Energy Harvesting Devices
Ravi, Srivathsan UL; Zilian, Andreas UL

in 2nd ECCOMAS Young Investigators Conference (YIC 2013) (2013)

This paper introduces a monolithic approach that provides simultaneous solution to the coupled system which involves volume-coupled piezoelectric mechanics and a controlling energy harvesting circuit for ... [more ▼]

This paper introduces a monolithic approach that provides simultaneous solution to the coupled system which involves volume-coupled piezoelectric mechanics and a controlling energy harvesting circuit for applications in energy harvesting. The weak form of the governing equations is discretized by space-time nite element method based on mixed velocity-stress/ rate of potential-dielectric displacement setting. The results will be compared to the simple cases with closed-form solution available from literature. [less ▲]

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See detailEquilibrium and sensitivity analysis of dynamic ridesharing
Viti, Francesco UL; Corman, Francesco

Scientific Conference (2013)

Sharing travels is an effective way to increase car occupancy rates and to reduce the number of cars for the same distances traveled. This is a problem involving operations research (how to best match ... [more ▼]

Sharing travels is an effective way to increase car occupancy rates and to reduce the number of cars for the same distances traveled. This is a problem involving operations research (how to best match travels in time and space, what level of similarity for the routes,…) and behavior challenges (on which conditions users choose to share travels, which type of users is willing to share the travel, what is the accepted detour and rescheduling, …). This research aims at filling the gap in the latter aspect by proposing an equilibrium modeling approach for (dynamic) ridesharing. By using a Nested logit model, , greater insight into the impact of different policies, behavioral factors and matching criteria can be presented. We deal with a theoretically interesting basic model structure of a single-link case, in which we study the complex interaction of multiple factors, and the joint sensitivity to the most relevant parameters. This allows us to derive some basic recommendations from the equilibrium states reached. [less ▲]

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See detailCombining demand management and merge control in an equilibrium network model
Viti, Francesco UL; Huang, Wei; Smith, Mike J.

Scientific Conference (2013)

Equilibrium models under congested traffic conditions, and especially those addressing blocking back, are very useful to estimate the demand conditions that ITS policies should be able to manage, for ... [more ▼]

Equilibrium models under congested traffic conditions, and especially those addressing blocking back, are very useful to estimate the demand conditions that ITS policies should be able to manage, for instance to maintain congestion within controlled areas and avoiding that they further spillback and cause more serious and/or less controllable congestion states. The objective of this paper is to supplement the equilibrium model, developed by the authors in recent research, with a more thorough analysis of merge behaviour, especially in cases of blocked nodes. Regulating the merger behaviour together with the demand pattern can lead to certain desired stationary states. It has a great practical significance when congestion is inevitable, while demand management and merge control are able to retain queues and spill-backs within the local area. [less ▲]

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See detailQuantifying partial observability in network sensor location problems
Viti, Francesco UL; Rinaldi, Marco; Corman, Francesco

Scientific Conference (2013)

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See detailA Null-Space metric for the analysis of partial network observability in sensor location problems
Rinaldi, Marco; Viti, Francesco UL; Corman, Francesco

Scientific Conference (2013)

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See detailInteractions between residential and daily mobility: Luxembourg case study in the MOEBIUS project (extended abstract)
Gerber, Philippe; Caruso, Geoffrey UL; Cornélis, Eric et al

in Hesse, Markus; Caruso, Geoffrey; Gerber, Philippe (Eds.) et al Proceedings of the BIVEC-GIBET Transport Research Days 2013 (2013)

We present the modelling strategy of the research project MOEBIUS, which aims at simulating future urbanisation and commuting mobility, including modal split, under various planning conditions. MOEBIUS is ... [more ▼]

We present the modelling strategy of the research project MOEBIUS, which aims at simulating future urbanisation and commuting mobility, including modal split, under various planning conditions. MOEBIUS is similar in its objectives to a Land Use and Transport Interaction (LUTI) model, although very modular in its implementation and with ability to deal with very fine spatial resolution inputs and outputs. We simulate (i) the future potential urbanisation in Luxembourg, (ii) the population and its spatial distribution, and (iii) the daily mobility (commuting pattern and travel mode choice) at a disaggregated level. [less ▲]

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See detailOn the impacts of transport policies and urban form on traffic-induced air pollution (extended abstract)
Schindler, Mirjam UL; Caruso, Geoffrey UL

in Hesse, Markus; Caruso, Geoffrey; Gerber, Philippe (Eds.) et al Proceedings of the BIVEC-GIBET Transport Research Days 2013 (2013)

Air pollution is a major concern in urban areas worldwide. It is not only a hazard to the environment but also on human health. Many argue that a compact city is the desirable urban form in the context of ... [more ▼]

Air pollution is a major concern in urban areas worldwide. It is not only a hazard to the environment but also on human health. Many argue that a compact city is the desirable urban form in the context of sustainability due to shorter travelling distances and reduced conversion of land. If considering not only the environmental pillar of sustainability in terms of total emissions but also the social one comprising human exposure and social well-being, the argumentation might change. The question we ask is whether selected common transport policies are efficient solutions to overcome the environmental and social challenge? In order to investigate this question, we developed a modelling system in order to test the impacts of different transport policies, either on the urban structure itself or on traffic flows and respectively on air quality. [less ▲]

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See detailPotentials for Realising a Consistent Transition Between Function Modelling with the IFM Framework and Early System Simulation
Eisenbart, Boris UL; Dohr, Fabio; Gericke, Kilian UL et al

in Proceedings of 19th International Conference on Engineering Design (2013)

Conceptual design is considered one of the most demanding design tasks requiring a joint effort of the involved designers, particularly in interdisciplinary design. Sound decision-making across ... [more ▼]

Conceptual design is considered one of the most demanding design tasks requiring a joint effort of the involved designers, particularly in interdisciplinary design. Sound decision-making across disciplines on alternative solution concepts may be considerably facilitated through early system simulation. A consistent transition of the available information in function modelling to early system simulation may thus support designers in this task. The IFM framework intends to support cross-disciplinary collaboration of involved designers by providing an integrated function modelling approach. In the paper it is analysed in how far a consistent transition from the IFM framework to established modelling techniques for simulation may be realised. The paper compares the information required for early system simulation in an interdisciplinary design context to the specific information conveyed in the different views of the IFM framework. The analysis identifies specific potentials and barriers for a consistent transition between them. Finally, the implications of the derived insights are discussed. [less ▲]

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See detailAdapting the IFM Framework to Functional Approaches Across Disciplines
Eisenbart, Boris UL; Gericke, Kilian UL; Blessing, Lucienne UL

in Proceedings of 19th International Conference on Engineering Design (2013)

Conceptual design is considered one of the most demanding design tasks requiring a joint effort of the involved designers, particularly in interdisciplinary design. The IFM framework intends to support ... [more ▼]

Conceptual design is considered one of the most demanding design tasks requiring a joint effort of the involved designers, particularly in interdisciplinary design. The IFM framework intends to support interdisciplinary collaboration of designers, by linking the different functional modelling perspectives, which are prominent in the different disciplines. The presented analysis aims to answer the question, which particular adaptations are required, in order to enable and improve the application of the IFM framework across disciplines. The paper presents a comparison of the framework with established functional approaches proposed in literature. It is shown, in which ways the specific contents addressed in the individual steps of the reviewed functional approaches can be mapped onto corresponding views in the IFM framework. The findings suggest that the IFM framework is interoperable with the reviewed functional approaches without necessitating fundamental changes. Furthermore, specific potentials for the improvement of its applicability across disciplines are derived. Finally, the paper discusses specific adaptations of the IFM framework, in order to improve its applicability. [less ▲]

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See detailDynamic modeling of VISSIM critical gap parameter at unsignalized intersections
Viti, Francesco UL; Wolput, Bart; Tampere, Chris M.J. et al

Poster (2013)

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See detailImplementation of a XFEM toolbox in Diffpack
Hossain, Md Naim; Paladim, Daniel; Vogel, Frank et al

in International Conference on Extended Finite Element Methods - XFEM 2013, September 11 – 13, 2013, Lyon, France (2013)

The Diffpack Development Framework is an object-oriented software environment for the numerical solution of partial differential equations (PDEs). By its design, Diffpack intends to close the gap between ... [more ▼]

The Diffpack Development Framework is an object-oriented software environment for the numerical solution of partial differential equations (PDEs). By its design, Diffpack intends to close the gap between black-box simulation packages and technical computing environments using interpreted computer languages. The framework provides a high degree of modeling flexibility, while still offering the computational efficiency needed for most demanding simulation problems in science and engineering. Technically speaking, Diffpack is a collection of C++ libraries with classes, functions and utility programs. The numerical functionality is embedded in an environment of software engineering tools supporting the management of Diffpack development projects. Diffpack supports a variety of numerical methods with distinct focus on the finite element method (FEM) but has no inherent restrictions on the types of PDEs and therefore applications to be solved. The key point of partition of unity enriched methods such as XFEM and GFEM is to help capture discontinuities and singularities or large gradients in solutions, which are not well resolved by h or prefinement [1]. The general idea is that the mesh need not conform to the moving boundaries so that minimal or no remeshing is required during the analysis. Our main motivation is to provide a generic implementation of enrichment within a flexible C++ environment, namely the Diffpack platform. The work was inspired by some of our earlier work [6,9] and that of other colleagues [5,7,8]. We demonstrate how object-oriented programming is particularly useful for the treatment of data structures and operations associated with XFEM : mesh-geometry interaction, non-standard integration rules, application of boundary conditions, treatment of level set data [2,6]. We detail the implementation of such features and verify and validate their implementation based on [5]. We show results based on unshifted, shifted [1] and study the behaviour of the stable generalized finite element method (SGFEM) to avoid blending effects and help control the conditioning of the system matrix [4]. For integration of elements cut by interface we use an in-house Delaunay Triangulation algorithm proposed by [3,5] and presented in detail in a companion paper. [less ▲]

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See detailDynamical structure function identifiability conditions enabling signal structure reconstruction
Adebayo, J.; Southwick, T.; Chetty, V. et al

in The proceedings of the 51st IEEE Conference on Decision and Control (CDC) (2012, December)

Networks of controlled dynamical systems exhibit a variety of interconnection patterns that could be interpreted as the structure of the system. One such interpretation of system structure is a system's ... [more ▼]

Networks of controlled dynamical systems exhibit a variety of interconnection patterns that could be interpreted as the structure of the system. One such interpretation of system structure is a system's signal structure, characterized as the open-loop causal dependencies among manifest variables and represented by its dynamical structure function. Although this notion of structure is among the weakest available, previous work has shown that if no a priori structural information is known about the system, not even the Boolean structure of the dynamical structure function is identifiable. Consequently, one method previously suggested for obtaining the necessary a priori structural information is to leverage knowledge about target specificity of the controlled inputs. This work extends these results to demonstrate precisely the a priori structural information that is both necessary and sufficient to reconstruct the network from input-output data. This extension is important because it significantly broadens the applicability of the identifiability conditions, enabling the design of network reconstruction experiments that were previously impossible due to practical constraints on the types of actuation mechanisms available to the engineer or scientist. The work is motivated by the proteomics problem of reconstructing the Per-Arnt-Sim Kinase pathway used in the metabolism of sugars. [less ▲]

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See detailEnergy performance assessment of an existing double-skin façade: measurements and simulation
Carton, Julien UL; Scholzen, Frank UL; Thomas, Sébastien et al

in Energy Forum - Solar Building Skins, 06 - 07 December 2012, Italy (2012, December)

An existing office building with an active double skin façade in Luxembourg has been analyzed. In the first step in-situ measurements have been performed. For this purpose outside, inside and cavity ... [more ▼]

An existing office building with an active double skin façade in Luxembourg has been analyzed. In the first step in-situ measurements have been performed. For this purpose outside, inside and cavity conditions have been measured for representative summer and winter conditions. In a second step, a thermal simulation using TRNSYS was performed. The simulation model has been compared to the time limited series of measurements and thus has been validated for some of the annual meteorological conditions. Then the model has been extrapolated to a whole year in order to assess the energy performance of the given façade. Further a parametric study of alternative façades has been carried out based on the validated simulation model to assess their own performances. For the given case study building, the double skin concept energetically performs well compared to other concepts with non outside (non weather exposed) solar protection, but worse than an external solar protection. The thermal comfort level in the rooms has also been determined by simulation - the calculated room averaged comfort level is quite optimal, but further investigations regarding the local comfort close to the glazed façades still have to be achieved. [less ▲]

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See detailIn-silico Robust Reconstruction of the Per-Arnt-Sim Kinase Pathway using Dynamical Structure Functions
Chetty, V.; Adebayo, J.; Mathis, A. et al

Scientific Conference (2012, October)

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See detailModification of the Shear-Slip Mesh Update Method with Respect to Space-Time Finite Element Discretisation of Fluid Flows
Schippke, Henning; Zilian, Andreas UL

Scientific Conference (2012, April 27)

Space-time discretisations of physical problems involving moving and deforming bodies, boundaries and interfaces have been shown to offer advantageous properties while being methodologically uniform and ... [more ▼]

Space-time discretisations of physical problems involving moving and deforming bodies, boundaries and interfaces have been shown to offer advantageous properties while being methodologically uniform and flexible. Well-known phenomena which are ideally suited to be analysed by space-time methods, are fluid-structure interaction problems in general as well as fluid flows with subdomain phase boundaries or immersed moving objects. In this contribution a short overview of existing mesh- moving techniques is given within the framework of finite element discretisations of the incompressible Navier-Stokes equations in space and time. The investigation is based on a SUPG/PSPG velocity-pressure formulation on the deforming space-time domain. A modification of the shear-slip mesh update method in the framework of space-time finite element discretisation is presented leading to a continuous space-time mesh in the shear-slip layer. The modified mesh moving technique is applied to engineering problems with rotating space-time fluid meshes. Its conservation properties and its quality regarding the approximated solutions on moving and deforming meshes are investigated. [less ▲]

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See detailSensitivity analysis and shape optimisation with the isogeometric boundary element methods
Lian, Haojie; Simpson, Robert; Bordas, Stéphane UL

Scientific Conference (2012, March 27)

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See detailALGEBRAIC COARSE-GRAINING METHODS IN FRACTURE MECHANICS: TACKLING LOCAL LACK OF CORRELATION USING DOMAIN DECOMPOSITION
Goury, Olivier; Kerfriden, Pierre; Rabczuk, Timon et al

Scientific Conference (2012, March)

In this paper, we propose to couple model order reduction techniques with domain decomposition meth- ods for the solution to parametric problems of fracture. The nonlinear nature of the problems requires ... [more ▼]

In this paper, we propose to couple model order reduction techniques with domain decomposition meth- ods for the solution to parametric problems of fracture. The nonlinear nature of the problems requires the use of a system approximation method to speed-up the assembly of the non-linear opreators. We show that the method efficiently computes a solution faster than a full order model for a given accuracy. The speed-up increases with the problem size. [less ▲]

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See detailMachine learning techniques for atmospheric pollutant monitoring
Sainlez, Matthieu UL; Heyen, Georges

Poster (2012, January 27)

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See detailA transformation of the position based visual servoing problem into a convex optimization problem
Wang, Y.; Thunberg, Johan UL; Yu, X.

in Proceedings of the 51th IEEE Conference on Decision and Control (2012)

Here we address the problem of moving a camera from an initial pose to a final pose. The trajectory between the two poses is subject to constraints on the camera motion and the visibility, where we have ... [more ▼]

Here we address the problem of moving a camera from an initial pose to a final pose. The trajectory between the two poses is subject to constraints on the camera motion and the visibility, where we have bounds on the allowed velocities and accelerations of the camera and require that a set of point features are visible for the camera. We assume that the pose is possible to retrieve from the observations of the point features, i.e., we have a Position Based Visual Servoing Problem with constraints. We introduce a two step method that transforms the problem into a convex optimization problem with linear constraints. In the first step the rotational motion is restricted to be of a certain type. This restriction allows us to retrieve an explicit solution of the rotational motion that is optimal in terms of minimizing geodesic distance. Furthermore, this restriction guarantees that the rotational motion satisfies the constraints. Using the explicit solution, we can formulate a convex optimization problem for the translational motion, where we include constraints on workspace and visibility. [less ▲]

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See detailDistributed identification of the Cell Transmission traffic model: A case study
Rinaldi, Marco UL; Capisani, L.; Ferrara, A. et al

in Procedings of the 2012 American Control Conference, ACC 2012 (2012)

The problem of the distributed identification of a macroscopic first-order traffic model, viz. the Cell Transmission Model (CTM), is considered in the paper. The parameters to be identified characterize ... [more ▼]

The problem of the distributed identification of a macroscopic first-order traffic model, viz. the Cell Transmission Model (CTM), is considered in the paper. The parameters to be identified characterize the dynamics of the density in different sections of the freeway (cells). We explore different distributed identification schemes. The purposes of the approach are mainly to obtain good prediction models through the minimization of the one-step ahead prediction error of the densities of the cells, and to reduce the computational time and the effort required to perform the identification. The methodology is validated relying on real-life data measured on a portion of the A12 freeway in The Netherlands. An evaluation of the performance of the identified model used as a set of virtual sensors in different scenarios is presented. © 2012 AACC American Automatic Control Council). [less ▲]

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See detailError estimation in quantities of interest for XFEM using recovery techniques
González-Estrada, O. A.; Nadal, E.; Ródenas, J. J. et al

in Yang, Z J (Ed.) 20th UK National Conference of the Association for Computational Mechanics in Engineering (ACME) (2012)

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See detailA Shared Basis for Functional Modelling
Eisenbart, Boris UL; Gericke, Kilian UL; Blessing, Lucienne UL

in Proceedings of Norddesign 2012 (2012)

The presented research aims at contributing to a better understanding of the diverse functional modelling approaches proposed across disciplines, often involving more than one function model. The paper ... [more ▼]

The presented research aims at contributing to a better understanding of the diverse functional modelling approaches proposed across disciplines, often involving more than one function model. The paper presents a review of 41 systematic design approaches from different disciplines, analysing what is addressed by functional modelling at which point in the proposed development process, i.e. in which sequence, if any. The analysis aims at deriving potential commonalities across disciplines, which could support the development of an integrative functional modelling approach. Finally, the results of the analysis are discussed, concluding that while there seems to be no shared sequence in functional modelling across disciplines, a common base can be derived, with regard to what is prominently addressed by functional modelling in the different disciplines. [less ▲]

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See detailEffects of periurban structure on air pollution: coupling CA models to understand the link between urban structure and air pollution
Schindler, Mirjam UL; Caruso, Geoffrey UL

in Pinto N, Dourado J (Ed.) Proceedings of the Symposium on Cellular Automata Models of Urban and Spatial Systems (2012)

Air quality is a major concern in urban areas worldwide not only because of its severe health impacts but also due to its influence on living quality and residential behaviour. The subsequent increasing ... [more ▼]

Air quality is a major concern in urban areas worldwide not only because of its severe health impacts but also due to its influence on living quality and residential behaviour. The subsequent increasing demand for residential areas in the greener fringes of urban agglomerations fuels the discussion about sustainability in future cities. As traffic emissions are acknowledged to be the major source of pollutants in an urban environment this residential trend has triggered research to further understand the influence of urban structure on air quality. In order to meet sustainable growth, many researchers argue that in a global perspective a compact city is the desirable urban form due to less traffic distance, just in contrast to the trend towards urban sprawl. However, quantifying the link between urban structure and air pollution has only been the aim of few research studies so far. Thus, our objective is to deepen the understanding of this link by coupling a micro-economic CA urban growth model with a traffic emission model and a CA air pollution model while focussing on the impact on residential population. [less ▲]

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See detailXFEM coupling of granular flows interacting with surrounding fluids
Pasenow, F.; Zilian, Andreas UL; Dinkler, D.

in ECCOMAS 2012 - European Congress on Computational Methods in Applied Sciences and Engineering, e-Book Full Papers (2012)

In this paper, ideas for the simulation of sliding dry granular materials interacting with surrounding fluids are presented and first results are presented. The compressible granular material is modeled ... [more ▼]

In this paper, ideas for the simulation of sliding dry granular materials interacting with surrounding fluids are presented and first results are presented. The compressible granular material is modeled as a medium which can show solid-like and fluid-like characteristics. Therefore a weighted decomposition of stress tensors of a solid-like and a fluid-like phase is applied. The surrounding incompressible fluids are described with a Newtonian constitutive model. Interface dynamics are handled with the level-set method. The model equations are discretized with the space-time finite element method. Discontinuous solution characteristics across interfaces are captured numerically by the extended finite element method (XFEM). For all discontinuities the space of ansatz functions is enriched with Heaviside functions. [less ▲]

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See detailEquilibrated patch recovery for accurate evaluation of upper error bounds in quantities of interest
González-Estrada, O. A.; Ródenas, J. J.; Nadal, E. et al

in ECCOMAS Thematic Conference - ADMOS 2011: International Conference on Adaptive Modeling and Simulation, An IACM Special Interest Conference (2012)

There is an increasing interest on the use of goal-oriented error estimates which help to measure and control the local error on a linear or non-linear quantity of interest (QoI) that might result ... [more ▼]

There is an increasing interest on the use of goal-oriented error estimates which help to measure and control the local error on a linear or non-linear quantity of interest (QoI) that might result relevant for design purposes (e.g. the mean stress value in a particular area, displacements, the stress intensity factor for fracture problems,⋯). In general, residual-based error estimators have been used to obtain upper and lower bounds of the error in quantities of interest for finite element approximations. In this work, we propose a novel a posteriori recovery technique to obtain an upper error bound of the QoI. We use a recovery procedure based on the superconvergent patch recovery (SPR) technique to obtain nearly statically admissible recovered stress fields for the primal and dual problems. This recovery technique was previously used to obtain upper bounds of the error in energy norm and has been used in this paper to obtain a computable version of the upper bound for the quantity of interest. [less ▲]

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See detailError estimation and error bounding in quantities of interest based on equilibrated recovered displacement fields
Nadal, E.; González-Estrada, O. A.; Ródenas, J. J. et al

in ECCOMAS 2012 - European Congress on Computational Methods in Applied Sciences and Engineering, e-Book Full Papers (2012)

Over the last ten years there has been an increase on the use of goal-oriented error estimates aimed to quantify the local error on a (non)linear quantity of interest (QoI) that might result relevant for ... [more ▼]

Over the last ten years there has been an increase on the use of goal-oriented error estimates aimed to quantify the local error on a (non)linear quantity of interest (QoI) that might result relevant for design purposes. Residual-based error estimators have been used recursively to obtain upper and lower bounds of the error in quantities of interest for finite element approximations. In this paper, we present a recovery technique for 2D linear elasticity problems, based on the superconvergent patch recovery (SPR), which provides recovered displacement and stress fields that are then utilised to evaluate practical upper and lower error bounds in QoI. [less ▲]

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See detailError estimation and error bounding in energy norm based on a displacement recovery technique
Nadal, E.; González-Estrada, O. A.; Ródenas, J. J. et al

in ECCOMAS 2012 - European Congress on Computational Methods in Applied Sciences and Engineering, e-Book Full Papers (2012)

Traditionally, recovery based error estimators in linear elasticity have considered the evaluation of an enhanced stress field obtained from the raw Finite Element (FE) stress solution. Instead of that ... [more ▼]

Traditionally, recovery based error estimators in linear elasticity have considered the evaluation of an enhanced stress field obtained from the raw Finite Element (FE) stress solution. Instead of that, one can also obtain a recovered displacement field from the FE displacements. Herein, we describe a superconvergent patch recovery of the displacement field which considers the local fulfilment of boundary and internal equilibrium equations, Dirichlet constraints and, for singular problems, the splitting of the displacement and stress fields into singular and smooth parts. Numerical tests using problems with known analytical solution have been carried out to validate the proposed technique for error estimation and error bounding in energy norm and quantities of interest. [less ▲]

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See detailFunctional Modelling Perspectives Across Disciplines: A Literature Review
Eisenbart, Boris UL; Blessing, Lucienne UL; Gericke, Kilian UL

in Proceedings of the 12th International Design Conference - DESIGN 2012 (2012)

The research presented in this paper discusses the different understandings of function which hamper shared functional modelling. Function models proposed in literature from various disciplines are then ... [more ▼]

The research presented in this paper discusses the different understandings of function which hamper shared functional modelling. Function models proposed in literature from various disciplines are then analysed, in order to identify the different inherent functional modelling perspectives. The paper concludes that in order to support shared functional modelling and to support cross-disciplinary system development, these different functional modelling perspectives need to be linked. [less ▲]

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See detailA force-based large increment method for 2D continuum solids and the mesh convergence study
Long, D.; Guo, Z.; Liu, X. et al

in AIP Conference Proceedings (2012), 1504

In this paper, a triangular plane stress element is implemented based on the large increment method (LIM) to solve 2D continuum mechanics problems. In the LIM, after the governing equations are ... [more ▼]

In this paper, a triangular plane stress element is implemented based on the large increment method (LIM) to solve 2D continuum mechanics problems. In the LIM, after the governing equations are established using the generalized elemental force variables as primary unknowns, an iteration procedure is employed to obtain an optimised approximate solution of the problem. Two numerical examples are investigated to study the mesh convergence of the proposed triangular LIM element. Structured meshes as well as unstructured meshes with different element densities are generated to illustrate the convergence of the total strain energy in both examples. The numerical results obtained from the LIM (including the total strain energy, the displacement and the stress) are compared with the analytical solutions as well as the results from the commercial FEM software ABAQUS. All the results show that the performance of the LIM is as good as the FEM in linear elastic problems. A simple elastoplastic example suggests that the LIM may obtain better result than the FEM. © 2012 American Institute of Physics. [less ▲]

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See detailMaximum-Entropy Meshfree Method for the Reissner-Mindlin Plate Problem based on a Stabilised Mixed Weak Form
Hale, Jack UL; Baiz, P. M.

Scientific Conference (2012)

Meshless methods, such as the Element Free Galerkin (EFG) method, hold various advantages over mesh-based techniques such as robustness in large-deformation problems and high continuity. The Reissner ... [more ▼]

Meshless methods, such as the Element Free Galerkin (EFG) method, hold various advantages over mesh-based techniques such as robustness in large-deformation problems and high continuity. The Reissner-Mindlin plate model is a particularly popular choice for simulating thin structures. It is well known in the Finite Element and Meshless literature that the simplest numerical treatments of the Reissner-Mindlin model lead to shear-locking which in turn produces erroneous results. This is due to the inability of the approximation functions to satisfy the Kirchoff constraint in the thin-plate limit. A recent advance in the area of meshless approximation schemes are Maximum-Entropy (MaxEnt) approximants. MaxEnt schemes provide a weak Kronecker-delta property on convex node sets which allows the direct imposition of Dirichlet (essential) boundary conditions. In this work, we derive a shear-locking free meshless method using MaxEnt approximants by consider- ing a stabilised mixed weak form. We include a scalar parameter which splits the energy from the shear bilinear form into two parts; the first is formed from the displacement fields only and the second from the independently interpolated shear strain field and the displacement fields. This splitting greatly eases the satisfaction of the LBB stability condition. We then eliminate the independently interpolated shear strain field using a localised projection operator, related to the “volume-averaged pressure” technique, which produces a final system of equations in the original displacement unknowns only. We show the good performance of the method for a variety of test problems. [less ▲]

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See detailError estimation of recovered solutions in FE analysis. Higher order h-adaptive refinement strategies
Ródenas, J. J.; Nadal, E.; González-Estrada, O. A. et al

in Pimienta, P M (Ed.) 10th World Congress on Computational Mechanics (WCCM 2012) (2012)

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See detailDistributed attitude synchronization control of multi-agent systems with directed topologies
Thunberg, Johan UL; Song, W.; Hong, Y. et al

in the proceedings of the 10th World Congress on Intelligent Control and Automation (2012)

In the present paper we consider the problem of attitude synchronization for a system of rigid body agents. We provide distributed kinematic control laws for two different synchronization problems. In the ... [more ▼]

In the present paper we consider the problem of attitude synchronization for a system of rigid body agents. We provide distributed kinematic control laws for two different synchronization problems. In the two problems the objective is the same, i.e., to synchronize the orientations of the agents, but what is assumed to be measurable by the agents differs. In problem 1 the agents measure their own orientations in a global reference frame, and obtain the orientations of their neighbors by means of communication. In problem 2 the agents only measure the relative orientations to their neighbors. By using the axis-angle representation of the orientation, we show that simple linear control laws solve both synchronization problems. Moreover we show that our proposed control laws work for directed and connected topologies on almost all SO(3) for problem 1 and on convex balls in SO(3) for problem 2. [less ▲]

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See detailPractical error bounds in energy norm based on a recovered displacement field
Nadal, E.; González-Estrada, O. A.; Ródenas, J. J. et al

in Pimienta, P M (Ed.) 10th World Congress on Computational Mechanics (WCCM 2012) (2012)

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See detailAccurate error estimate in energy norm using a nearly-equilibrated kinematically-admissible displacement recovery technique
Nadal, E.; González-Estrada, O. A.; Ródenas, J. J. et al

in Pimienta, P M (Ed.) 10th World Congress on Computational Mechanics (WCCM 2012) (2012)

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See detailError estimation and bounding in energy norm based on a displacement recovery technique
Nadal, E.; González-Estrada, O. A.; Ródenas, J. J. et al

in Eberhardsteiner, Josef; Böhm, Helmut; Rammerstorfer, F G (Eds.) 6th European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS 2012) (2012)

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See detailAN ANALYSIS OF DESIGN PROCESS MODELS ACROSS DISCIPLINES
Gericke, Kilian UL; Blessing, Lucienne UL

in Proceedings of the 12th International Design Conference - DESIGN 2012 (2012)

This paper presents a comparison of design methodologies and process models from nine disciplines. The evolutionary development of the approaches, which can be traced back to similar roots, lead to ... [more ▼]

This paper presents a comparison of design methodologies and process models from nine disciplines. The evolutionary development of the approaches, which can be traced back to similar roots, lead to process models which are now adapted to specific design disciplines but still have many similarities. Most of the established approaches have not been adapted to many of the challenges of current design practice and represent isolated views on the design process. This comparison is intended to provide a basis for consolidation and reformation of design methodology. [less ▲]

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See detailDecentralised minimal-time dynamic consensus
Yuan, Y.; Liu, J.; Murray, R. M. et al

in The proceedings of the 2012 American Control Conference (ACC) (2012)

This paper considers a group of agents that aim to reach an agreement on individually measured time-varying signals by local communication. In contrast to static network averaging problem, the consensus ... [more ▼]

This paper considers a group of agents that aim to reach an agreement on individually measured time-varying signals by local communication. In contrast to static network averaging problem, the consensus we mean in this paper is reached in a dynamic sense. A discrete-time dynamic average consensus protocol can be designed to allow all the agents tracking the average of their reference inputs asymptotically. We propose a minimal-time dynamic consensus algorithm, which only utilises minimal number of local observations of randomly picked node in a network to compute the final consensus signal. Our results illustrate that with memory and computational ability, the running time of distributed averaging algorithms can be indeed improved dramatically using local information as suggested by Olshevsky and Tsitsiklis. [less ▲]

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See detailRobust network reconstruction in polynomial time
Hayden, D.; Yuan, Y.; Goncalves, Jorge UL

in The proceedings of the 51st IEEE Conference on Decision and Control (2012)

This paper presents an efficient algorithm for robust network reconstruction of Linear Time-Invariant (LTI) systems in the presence of noise, estimation errors and unmodelled nonlinearities. The method ... [more ▼]

This paper presents an efficient algorithm for robust network reconstruction of Linear Time-Invariant (LTI) systems in the presence of noise, estimation errors and unmodelled nonlinearities. The method here builds on previous work [1] on robust reconstruction to provide a practical implementation with polynomial computational complexity. Following the same experimental protocol, the algorithm obtains a set of structurally-related candidate solutions spanning every level of sparsity. We prove the existence of a magnitude bound on the noise, which if satisfied, guarantees that one of these structures is the correct solution. A problem-specific model-selection procedure then selects a single solution from this set and provides a measure of confidence in that solution. Extensive simulations quantify the expected performance for different levels of noise and show that significantly more noise can be tolerated in comparison to the original method. [less ▲]

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See detailDistributed attitude synchronization control of multi-agent systems with time-varying topologies
Song, W.; Thunberg, Johan UL; Hong, Y. et al

in Proceedings of the 10th World Congress on Intelligent Control and Automation (2012)

This paper addresses the attitude synchronization problem of multiple rigid body agents in SO(3) with directed and switching interconnection topologies. Using the axis-angle representation of the ... [more ▼]

This paper addresses the attitude synchronization problem of multiple rigid body agents in SO(3) with directed and switching interconnection topologies. Using the axis-angle representation of the orientation, a distributed controller based on differences between the orientations of agents in a global frame is proposed. In the case of the balanced interconnection graph, the attitude synchronization is achieved with the well-known mild assumption (that is, uniform joint strong connection). To demonstrate the effectiveness of the proposed control scheme, an illustrative example is provided. [less ▲]

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See detailComparison of Machine Learning techniques for atmospheric pollutant monitoring in a Kraft pulp mill
Sainlez, Matthieu UL; Heyen, Georges

Scientific Conference (2011, November)

In this paper, machine learning techniques are compared to predict nitrogen oxide (NOx) pollutant emission from the recovery boiler of a Kraft pulp mill. Starting from a large database of raw process data ... [more ▼]

In this paper, machine learning techniques are compared to predict nitrogen oxide (NOx) pollutant emission from the recovery boiler of a Kraft pulp mill. Starting from a large database of raw process data related to a Kraft recovery boiler, we consider a regression problem in which we are trying to predict the value of a continuous variable. Generalization is done on the worst case configuration possible to make sure the model is adequate: the training period concerns stationary operations while test periods mainly focus on NOx emissions during transient operations. This comparison involves neural network techniques (i.e., static multilayer perceptron and dynamic NARX network), tree-based methods and multiple linear regression. We illustrate the potential of a dynamic neural approach compared to the others in this prediction task. [less ▲]

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See detailA web-based tool for efficient carbon footprint calculations: Lux screen CO2
Hild, Paula UL; Guiton, Mélanie; Pieropan, Julien et al

Scientific Conference (2011, August 30)

Several commercial software tools for Life Cycle Assessment (LCA) are already available on the market and recently included ad-hoc extensions to calculate carbon footprints. Unfortunately, these software ... [more ▼]

Several commercial software tools for Life Cycle Assessment (LCA) are already available on the market and recently included ad-hoc extensions to calculate carbon footprints. Unfortunately, these software tools are often too complex and require too much specific expertise to be used by SMEs, consultants and others. For companies without any experience in the field of environmental assessment, the analysis of company-related CO2 emissions within a regional context is often an impossible task. The presented easy-to-use CO2 screening tool, adapted to their needs, was designed to support these companies. The web-based tool, ‘Lux screen CO2’ is able to assess and report site related direct and indirect greenhouse gas emissions, including the whole supply chain of the company and food-related impacts of the company restaurant. [less ▲]

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See detailInfluence of piston position on the scavenging and swirling flow in two-stroke Diesel engines
Obeidat, Anas UL; Haider, S.; Meyer, K.E. et al

in EUROMECH Colloquium 525 - Instabilities and transition in three-dimensional flows with rotation (2011, June 21)

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See detailSimulation of Shear Deformable Plates using Meshless Maximum Entropy Basis Functions
Hale, Jack UL; Baiz, P. M.

Scientific Conference (2011, June)

First-order Shear Deformable Plate Theory (FSDT) is widely used throughout engineering practice to simulate structures with planar dimensions much larger than their thickness. Meshless methods have seen ... [more ▼]

First-order Shear Deformable Plate Theory (FSDT) is widely used throughout engineering practice to simulate structures with planar dimensions much larger than their thickness. Meshless methods have seen use in the literature as a method for discretising the FSDT equations and hold numerous advantages over traditional mesh based techniques. A recent advance in the area of meshless methods are Maximum Entropy approximants (MaxEnt). MaxEnt combines many properties of various prior meshless approximants such as a weak Kronecker-delta property, seamless blending with Delaunay triangulations, high continuity, and convexity. In this work MaxEnt along with other meshless approximants have been implemented in a hybrid object-oriented Python/C++/Fortran computer simulation for the simulation of static deflection, free vibration and linear buckling of FSDT plates. The relative performance and ease of implementation of each of the methods will be discussed. The causes of shear locking along with the merits of various alleviation techniques will be covered, including matching fields method, mixed-variational formulations and construction of higher order polynomial basis via both intrinsic and extrinsic (partition of unity) methods. Convergence results show that MaxEnt provides in most cases similar and in some cases superior behaviour to MLS and RPIM approximants when used to discretise the FSDT equations. [less ▲]

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See detailEnriched Element Free Galerkin Method for Gradient Elasticity
Natarajan, S; Kerfriden, P; Bordas, Stéphane UL et al

Scientific Conference (2011, June)

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See detailRationalised computational time in fracture simulation: adaptive model reduction and domain decomposition
Goury, Olivier; Kerfriden, Pierre; Margetts, Lee et al

Scientific Conference (2011, June)

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See detailApproche neuronale dynamique pour la prédiction de polluants atmosphériques: application à l'industrie papetière.
Sainlez, Matthieu UL; Heyen, Georges; Lumen, Philippe

Scientific Conference (2011, May 27)

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See detailDynamic neural network approach for atmospheric pollutant prediction: A pulp mill case study
Sainlez, Matthieu UL

Scientific Conference (2011, May 27)

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See detailNatural frequencies of cracked isotropic & specially orthotropic plates using the extended finite element method
Natarajan, S; Baiz, P; Mahapatra, D Roy et al

Scientific Conference (2011, April)

In this paper, the linear free flexural vibration of cracked isotropic and specially orthotropic plates is studied using the extended finite element method. The mixed interpolation technique of the well ... [more ▼]

In this paper, the linear free flexural vibration of cracked isotropic and specially orthotropic plates is studied using the extended finite element method. The mixed interpolation technique of the well- established MITC4 [1] quadrilateral finite element with 12 standard degrees of freedom per element is used for this study. The natural frequencies of simply supported square plates are computed as a function of crack length and crack location. [less ▲]

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See detailSupervised learning for a Kraft recovery boiler: a data mining approach with Random Forests.
Sainlez, Matthieu UL; Heyen, Georges; Lafourcade, Sébastien

in Favrat, Daniel; Maréchal, François (Eds.) ECOS 2010 Volume IV (Power plants and Industrial processes) (2011, January 11)

A data mining methodology, the random forests, is applied to predict high pressure steam production from the recovery boiler of a Kraft pulping process. Starting from a large database of raw process data ... [more ▼]

A data mining methodology, the random forests, is applied to predict high pressure steam production from the recovery boiler of a Kraft pulping process. Starting from a large database of raw process data, the goal is to identify the input variables that explain the most significant output variations and to predict the high pressure steam flow. [less ▲]

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See detailThe Genetics Lab: An Innovative Tool for Assessment of Intelligence by Mean of Complex Problem Solving
Hazotte, Cyril; Mayer, Hélène; Djaghloul, Younes et al

Scientific Conference (2011)

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See detailEnhanced recovery techniques for accurate evaluation of error estimates in FE aproximations
González-Estrada, O. A.; Ródenas, J. J.; Bordas, Stéphane UL et al

in Laghrouche, O; El Kacimi, A; Woodwaed, P (Eds.) et al 19th UK National Conference of the Association for Computational Mechanics in Engineering (2011)

When modelling critical structures, it is crucial to rationally assess the outcome of numerical simu- lations. Specifically, error estimation strategies are key tools in critical decision-based processes ... [more ▼]

When modelling critical structures, it is crucial to rationally assess the outcome of numerical simu- lations. Specifically, error estimation strategies are key tools in critical decision-based processes. The development of design tools that enhance performance of the final product and give reliability on the calculations is essential in todays industrial environment, which increasingly seeks to reduce develop- ment times for new products while improving the quality. During the last years there has been an increasing interest on the use of error estimates which help to measure and control the error committed in standard or enriched finite element approximations. The error can be defined in terms of energy norm or in quantities relevant for design purposes (such as the mean stress value in a particular area, displacements, the stress intensity factor for fracture problems). In this work, we discuss the use of different a posteriori recovery techniques to evaluate error estimates for different finite element (FE) approximations. These techniques are based on equilibrated supercon- vergent patch recovery or equilibrated moving least squares procedures and can be used in smooth or singular problems. Numerical results show the capabilities of the proposed techniques to provide good error estimates. [less ▲]

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See detailAccurate evaluation of stress intensity factors using error estimation in quantities of interest based on equilibrated recovery
González-Estrada, O. A.; Ródenas, J. J.; Bordas, Stéphane UL et al

in Oliver, J; Jirasek, M; Allix, O (Eds.) et al Computational Modeling of Fracture and Failure of Materials and Structures. Proceedings of CFRAC 2011 (2011)

During the last years the use of error estimators which measure the error in a quantity of interest defined by the analyst, instead of the energy norm, have become increasingly popular as they provide an ... [more ▼]

During the last years the use of error estimators which measure the error in a quantity of interest defined by the analyst, instead of the energy norm, have become increasingly popular as they provide an error indicator for goal oriented adaptivity procedures. In this paper we propose an a posteriori recovery-based error estimation procedure which considers the stress intensity factor K typical of singular problems as the quantity of interest in finite element (FE) approximations. In general, error estimators in quantities of interest have been based on residual techniques and, although recovery techniques have been often preferred when considering the error in energy norm due to their robustness and simplicity, so far, there is no available procedure which considers an equilibrated recovery technique that can be used in standard FE frameworks. In [1] a standard SPR recovery technique is used to obtain an error measure of the J-integral, which is closely related to the value of the SIF. However, it does not consider any equilibrium constraints or the singularity near the crack tip, thus the obtained recovered stress field is not well suited for this kind of problems. The technique proposed herein relies on the enhanced superconvergent patch recovery technique presented in [2] to evaluate highly accurate recovered stress fields of the primal and dual problems, which are then used to obtain a sharp error estimate. The primal problem is simply the problem under analysis. To formulate the dual problem we consider the linear interaction integral representing K to obtain the applied loads of the dual FE approximation to solve. The high accuracy of the recovered stress fields for both the primal and dual solutions is obtained by decomposing the raw stress field obtained from the finite element approximations into singular and smooth parts, and enforcing the fulfilment of boundary and internal equilibrium equations. The results indicate an accurate estimation of the error in K for benchmark problems with exact solution. [less ▲]

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See detailA Framework for Comparing Design Modelling Approaches Across Disciplines
Eisenbart, Boris UL; Gericke, Kilian UL; Blessing, Lucienne UL

in Proceedings of the 18th International Conference on Engineering Design (2011)

Design models are an important means for the representation of design information in product development processes. Designers use design models to visualise and communicate their ideas to other members of ... [more ▼]

Design models are an important means for the representation of design information in product development processes. Designers use design models to visualise and communicate their ideas to other members of a design team, the project manager or a costumer. Communication between experts from different disciplines using design models is often hindered by different terminology and different ways of modelling. Potential consequences are design flaws, which may lead to time-consuming iterations and – if undetected – to problems during production or use. In order to enhance the communication through design models across disciplines, and to address the mentioned problems, an understanding of similarities as well as differences between modelling approaches needs to be established. For that purpose, this paper discusses different design states which represent a distinct level of available information in the development process. They are derived through comparing different design models proposed in literature and provide the basis of a framework for a detailed comparison of modelling approaches across disciplines. Further, first insights into different ways of modelling are discussed. [less ▲]

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See detailMulti-robot distributed visual consensus using epipoles
Montijano, E.; Thunberg, Johan UL; Hu, X. et al

in Proceedings of the 50th IEEE Conference on Decision and Control and European Control Conference (CDC-ECC) (2011)

In this paper we give a distributed solution to the problem of making a team of non-holonomic robots achieve the same heading (attitude consensus problem) using vision sensors with limited field of view ... [more ▼]

In this paper we give a distributed solution to the problem of making a team of non-holonomic robots achieve the same heading (attitude consensus problem) using vision sensors with limited field of view. The use of cameras with constrained field of view limits the information the robots perceive compared to other omnidirectional sensors. This makes the consensus problem more complicated, because the robots will not always be able to observe other robots. By using structure from motion computed from images, the robots can estimate the difference in their headings from common observations of the environment without the necessity of directly observe each other. In this way, the robots achieve the consensus in their headings while observing the environment instead of each other. The contribution of the paper is a new controller that uses the epipoles computed from pairs of images to estimate the misalignment between neighbor robots. In addition, the control is robust to changes in the topology of the network and does not require to know the calibration of the cameras in order to achieve the desired configuration. To the best of our knowledge, this is the first time that the epipoles are used in multi-robot consensus, putting their properties in value. [less ▲]

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See detailMathematical relationships between representations of structure in linear interconnected dynamical systems
Yeung, E.; Goncalves, Jorge UL; Sandberg, H. et al

in The proceedings of the 2011 American Control Conference (ACC) (2011)

A dynamical system can exhibit structure on multiple levels. Different system representations can capture different elements of a dynamical system's structure. We consider LTI input-output dynamical ... [more ▼]

A dynamical system can exhibit structure on multiple levels. Different system representations can capture different elements of a dynamical system's structure. We consider LTI input-output dynamical systems and present four representations of structure: complete computational structure, subsystem structure, signal structure, and input output sparsity structure. We then explore some of the mathematical relation ships that relate these different representations of structure. In particular, we show that signal and subsystem structure are fundamentally different ways of representing system structure. A signal structure does not always specify a unique subsystem structure nor does subsystem structure always specify a unique signal structure. We illustrate these concepts with a numerical example. [less ▲]

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See detailDistributed attitude synchronization control
Thunberg, Johan UL; Montijano, E.; Hu, X.

in Proceedings of the 50th IEEE Conference on Decision and Control and European Control Conference (CDC-ECC) (2011)

In this paper we consider the problem of constructing feedback control laws for a system of n agents that shall synchronize their attitudes in SO(3). We propose distributed controllers for two ... [more ▼]

In this paper we consider the problem of constructing feedback control laws for a system of n agents that shall synchronize their attitudes in SO(3). We propose distributed controllers for two synchronization problems, in which the objective is the same, to synchronize the orientations, but what the agents can perceive or communicate differs. In the first problem the agents can measure their orientation to a common reference object, and either communicate with the neighbors or estimate the relative orientation to their neighbors. In the second problem the agents can, without communication, only measure the relative orientation to the neighbors. For the first problem we present a controller which will lead to synchronization, provided the neighborhood graph is connected. For the second problem we present a controller that will lead to synchronization provided the neighborhood graph is connected and the agents initially are contained within a geodesic ball of radius π/2, which is the maximal convex set in SO(3). [less ▲]

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