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See detailReducing the Mesh-burden and Computational Expense in Multi-scale Free Boundary Engineering Problems
Bordas, Stéphane UL; Kerfriden, Pierre; Hale, Jack UL et al

Presentation (2014, May 12)

We present recent results aiming at affording faster and error-controlled simulations of multi scale phenomena including fracture of heterogeneous materials and cutting of biological tissue. In a second ... [more ▼]

We present recent results aiming at affording faster and error-controlled simulations of multi scale phenomena including fracture of heterogeneous materials and cutting of biological tissue. In a second part, we describe methodologies to isolate the user from the burden of mesh generation and regeneration as moving boundaries evolve. Results include advances in implicit boundary finite elements, (enriched) isogeometric boundary elements and extended finite element methods for multi-crack propagation. ABOUT THE PRESENTER In 1999, Stéphane Bordas joined a joint graduate programme of the French Institute of Technology (Ecole Spéciale des Travaux Publics) and the American Northwestern University. In 2003, he graduated in Theoretical and Applied Mechanics with a PhD from Northwestern University. Between 2003 and 2006, he was at the Laboratory of Structural and Continuum Mechanics at the Swiss Federal Institute of Technology in Lausanne, Switzerland. In 2006, he became permanent lecturer at Glasgow University’s Civil Engineering Department. Stéphane joined the Computational Mechanics team at Cardiff University in September 2009, as a Professor in Computational Mechanics and directed the institute of Mechanics and Advanced Materials from October 2010 to November 2013. He is the Editor of the book series “Advances in Applied Mechanics” since July 2013. In November 2013, he joined the University of Luxembourg as a Professor in Computational Mechanics. The main axes of his research team include (1) free boundary problems and problems involving complex geometries, in particular moving boundaries and (2) ‘a posteriori’ discretisation and model error control, rationalisation of the computational expense. Stéphane’s keen interest is to actively participate in innovation, technological transfer as well as software tool generation. This has been done through a number of joint ventures with various industrial partners (Bosch GmbH, Cenaero, inuTech GmbH, Siemens-LMS, Soitec SA) and the release of open-source software. In 2012, Stéphane was awarded an ERC Starting Independent Research Grant (RealTcut), to address the need for surgical simulators with a computational mechanics angle with a focus on the multi-scale simulation of cutting of heterogeneous materials in real-time. [less ▲]

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See detailReflective Practice: Lessons Learnt by Using Board Games as a Design Tool for Location-Based Games
Jones, Catherine UL; Konstantinos, Papangelis

in Kyriakidis, P; Hadjimitsis, D; Skarlatos, D (Eds.) et al Geospatial Technologies for Local and Regional Development (2019)

Location-based gaming (LBG) apps present many challenges to the design process. They have very different requirements compared to games that are aspatial in nature. They take place in the wild and this ... [more ▼]

Location-based gaming (LBG) apps present many challenges to the design process. They have very different requirements compared to games that are aspatial in nature. They take place in the wild and this brings unique challenges to the practicalities of their design. There is a need to balance the core game play with the spatial requirements of location-aware technologies as well as considering the overall theme and objectives of the game together with the motivations and behaviours of players. We reflect upon this balancing act and explore an approach to creative paper prototyping through the medium of board games to co-design LBG requirements. We examine two case studies of location-based games with different goals. The first case study discusses the CrossCult Pilot 4 app built to trigger reflection on historical stories through thoughtful play. Whilst the second case study uses the City Conquerer app designed and played in Suzhou, China with a view to exploring notions of territoriality. The paper considers how spatial, social and interaction metaphors are used to simulate location-based games in a board game and discusses the lessons learned when transforming the paper game into a digital prototype. It forms part of a thinking by doing approach. By comparing the board games to the technical counterparts, we consider how effective are the features and activities implemented in the technology prototypes. We propose a set of 11 design constraints that developers must be mindful of when transitioning from paper to digital prototypes. [less ▲]

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See detailRegions of stability for limit cycle oscillations in piecewise linear systems
Goncalves, Jorge UL

in IEEE Transactions on Automatic Control (2005), 50(11), 1877-1882

Oscillations appear in numerous applications from biology to technology.However, besides local results, rigorous stability and robustness analysis of oscillations are rarely done due to their intrinsic ... [more ▼]

Oscillations appear in numerous applications from biology to technology.However, besides local results, rigorous stability and robustness analysis of oscillations are rarely done due to their intrinsic nonlinear behavior. Poincarémaps associated with the system cannot typically be found explicitly and stability is estimated using extensive simulations and experiments. This paper gives conditions in the form of linear matrix inequalities (LMIs) that guarantee asymptotic stability in a reasonably large region around a limit cycle for a class of systems known as piecewise linear systems (PLS). Such conditions, based on recent results on impact maps and surface Lyapunov functions (SuLF), allow a systematic and efficient analysis of oscillations of PLS or arbitrarily close approximations of nonlinear systems by PLS. The methodology applies to any locally stable limit cycle of a PLS, regardless of the dimension and the number of switching surfaces of the system, and is illustrated with a biological application: a fourth-order neural oscillator, also used in many robotics applications such as juggling and locomotion. [less ▲]

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See detailRegions of Stability for Limit Cycles of Piecewise Linear Systems
Goncalves, Jorge UL

in Proceedings of the 42th IEEE Conference on Decision and Control (2003)

This paper starts by presenting local stability conditions for limit cycles of piecewise linear systems (PLS), based on analyzing the linear part of Poincare maps. Local stability guarantees the existence ... [more ▼]

This paper starts by presenting local stability conditions for limit cycles of piecewise linear systems (PLS), based on analyzing the linear part of Poincare maps. Local stability guarantees the existence of an asymptotically stable neighborhood around the limit cycle. However, tools to characterize such neighborhood do not exist. This work gives conditions in the form of LMIs that guarantee asymptotic stability of PLS in a reasonably large region around a limit cycle, based on recent results on impact maps and surface Lyapunov functions (SuLF). These are exemplified with a biological application: a 4th-order neural oscillator, also used in many robotics applications like, for example, juggling and locomotion. [less ▲]

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See detailRemoving the saturation assumption in Bank-Weiser error estimator analysis in dimension three
Bulle, Raphaël UL; Chouly, Franz; Hale, Jack UL et al

in Applied Mathematics Letters (2020), 107

We provide a new argument proving the reliability of the Bank-Weiser estimator for Lagrange piecewise linear finite elements in both dimension two and three. The extension to dimension three constitutes ... [more ▼]

We provide a new argument proving the reliability of the Bank-Weiser estimator for Lagrange piecewise linear finite elements in both dimension two and three. The extension to dimension three constitutes the main novelty of our study. In addition, we present a numerical comparison of the Bank-Weiser and residual estimators for a three-dimensional test case. [less ▲]

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See detailRepeated anticipatory network traffic control using iterative optimization accounting for model bias correction
Huang, Wei; Viti, Francesco UL; Tampere, Chris

in Transportation Research. Part C : Emerging Technologies (2016)

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See detailRepresenting Structure in Linear Interconnected Dynamical Systems
Yeung, Y.; Goncalves, Jorge UL; Sandberg, H. et al

in The proceedings of the 49th IEEE Conference on Decision and Control (CDC) (2010)

Interconnected dynamical systems are a pervasive component in our modern world's infrastructure. One of the fundamental steps to understanding the complex behavior and dynamics of these systems is ... [more ▼]

Interconnected dynamical systems are a pervasive component in our modern world's infrastructure. One of the fundamental steps to understanding the complex behavior and dynamics of these systems is determining how to appropriately represent their structure. In this work, we discuss different ways of representing a system's structure. We define and present, in particular, four representations of system structure-complete computational, subsystem, signal, and zero pattern structure-and discuss some of their fundamental properties. We illustrate their application with a numerical example and show how radically different representations of structure can be consistent with a single LTI input-output system. [less ▲]

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See detailA review of nature-based solutions for resource recovery in cities
Kisser, Johannes; Wirt, Maria; De Gusseme, Bart et al

in Blue-Green System (2020), 2(1)

Our modern cities are resource sinks designed on the current linear economic model which recovers very little of the original input. As the current model is not sustainable, a viable solution is to ... [more ▼]

Our modern cities are resource sinks designed on the current linear economic model which recovers very little of the original input. As the current model is not sustainable, a viable solution is to recover and reuse parts of the input. In this context, resource recovery using nature-based solutions (NBS) is gaining popularity worldwide. In this specific review, we focus on NBS as technologies that bring nature into cities and those that are derived from nature, using (micro)organisms as principal agents, provided they enable resource recovery. The findings presented in this work are based on an extensive literature review, as well as on original results of recent innovation projects across Europe. The case studies were collected by participants of the COST Action Circular City, which includes a portfolio of more than 92 projects. The present review article focuses on urban wastewater, industrial wastewater, municipal solid waste and gaseous effluents, the recoverable products (e.g., nutrients, nanoparticles, energy), as well as the implications of source-separation and circularity by design. The analysis also includes assessment of the maturity of different technologies (technology readiness level) and the barriers that need to be overcome to accelerate the transition to resilient, self-sustainable cities of the future. [less ▲]

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See detailA rheological interface model and its space-time finite element formulation for fluid-structure interaction
Legay, A.; Zilian, Andreas UL; Janssen, C.

in International Journal for Numerical Methods in Engineering (2011), 86(6), 667-687

This contribution discusses extended physical interface models for fluid-structure interaction problems and investigates their phenomenological effects on the behavior of coupled systems by numerical ... [more ▼]

This contribution discusses extended physical interface models for fluid-structure interaction problems and investigates their phenomenological effects on the behavior of coupled systems by numerical simulation. Besides the various types of friction at the fluid-structure interface the most interesting phenomena are related to effects due to additional interface stiffness and damping. The paper introduces extended models at the fluid-structure interface on the basis of rheological devices (Hooke, Newton, Kelvin, Maxwell, Zener). The interface is decomposed into a Lagrangian layer for the solid-like part and an Eulerian layer for the fluid-like part. The mechanical model for fluid-structure interaction is based on the equations of rigid body dynamics for the structural part and the incompressible Navier-Stokes equations for viscous flow. The resulting weighted residual form uses the interface velocity and interface tractions in both layers in addition to the field variables for fluid and structure. The weak formulation of the whole coupled system is discretized using space-time finite elements with a discontinuous Galerkin method for time-integration leading to a monolithic algebraic system. The deforming fluid domain is taken into account by deformable space-time finite elements and a pseudo-structure approach for mesh motion. The sensitivity of coupled systems to modification of the interface model and its parameters is investigated by numerical simulation of flow induced vibrations of a spring supported fluid-immersed cylinder. It is shown that the presented rheological interface model allows to influence flow-induced vibrations. © 2010 John Wiley & Sons, Ltd. [less ▲]

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See detailRhythmic regulation of Ca2+ signalling networks
Gardner, M.; Hotta, C.; Hubbard, K. et al

Scientific Conference (2006)

The circadian clock is the internal timekeeper of plants. This clock regulates most aspects of plant physiology providing considerable competitive advantage. We are investigating the role for oscillations ... [more ▼]

The circadian clock is the internal timekeeper of plants. This clock regulates most aspects of plant physiology providing considerable competitive advantage. We are investigating the role for oscillations in the cytosolic free Ca2+ concentration ([Ca2+]cyt) in the circadian control of cellular physiology. We have previously demonstrated that circadian oscillations of [Ca2+]cyt encode photoperiodic information but the precise role of circadian [Ca2+]cyt oscillations remain obscure. We have been taking a systems wide approach to determine the origin and function of circadian oscillations of [Ca2+]cyt. Using pharmacology, bioinformatics and biochemical tools we have new evidence that oscillations of [Ca2+]cyt are generated by the small signalling intermediate, cADPR. Positioning the oscillations of [Ca2+]cyt with respect to the molecular oscillator using reverse genetics indicates that [Ca2+]cyt is an output of the clock. Using a whole genome transcriptional profile we have identified over 1800 circadian-regulated transcripts, many of which encode for Ca2+ signalling elements. The function of circadian-regulated transcripts encoding signalling components is being investigated by reverse genetic screens with automated imaging. Using our extensive data sets describing the circadian regulation of [Ca2+]cyt in different backgrounds and conditions we have constructed a mathematical model. This is being validated using mutant analysis and refined by introducing complexity to the model. Our data and models suggest that [Ca2+]cyt acts an output of the clock that regulates diverse aspects of physiology and has the potential to form a feedback loop with the molecular components of the oscillator. [less ▲]

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See detailRisk-averse Stochastic Nonlinear Model Predictive Control for Real-time Safety-critical Systems
Sajadi Alamdari, Seyed Amin UL; Voos, Holger UL; Darouach, Mohamed

in The 20th World Congress of the International Federation of Automatic Control, IFAC 2017 World Congress, Toulouse, France, 9-14 July 2017 (2017, July 11)

Stochastic nonlinear model predictive control has been developed to systematically find an optimal decision with the aim of performance improvement in dynamical systems that involve uncertainties. However ... [more ▼]

Stochastic nonlinear model predictive control has been developed to systematically find an optimal decision with the aim of performance improvement in dynamical systems that involve uncertainties. However, most of the current methods are risk-neutral for safety-critical systems and depend on computationally expensive algorithms. This paper investigates on the risk-averse optimal stochastic nonlinear control subject to real-time safety-critical systems. In order to achieve a computationally tractable design and integrate knowledge about the uncertainties, bounded trajectories generated to quantify the uncertainties. The proposed controller considers these scenarios in a risk-sensitive manner. A certainty equivalent nonlinear model predictive control based on minimum principle is reformulated to optimise nominal cost and expected value of future recourse actions. The capability of proposed method in terms of states regulations, constraints fulfilment, and real-time implementation is demonstrated for a semi-autonomous ecological advanced driver assistance system specified for battery electric vehicles. This system plans for a safe and energy-efficient cruising velocity profile autonomously. [less ▲]

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See detailRIVER MORPHOLOGY MONITORING OF A SMALL-SCALE ALPINE RIVERBED USING DRONE PHOTOGRAMMETRY AND LIDAR
Backes, Dietmar UL; Smigaj, Magdalena; Schimka, Marian et al

in The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences (2020, August 12), XLIII-B2-2020 Article Metrics Related articles(1017), 1024

An efficient alternative to labour-intensive terrestrial and costly airborne surveys is the use of small, inexpensive Unmanned Aerial Vehicles (UAVs) or Remotely Piloted Aerial Systems (RPAS). These low ... [more ▼]

An efficient alternative to labour-intensive terrestrial and costly airborne surveys is the use of small, inexpensive Unmanned Aerial Vehicles (UAVs) or Remotely Piloted Aerial Systems (RPAS). These low-altitude remote sensing platforms, commonly known as drones, can carry lightweight optical and LiDAR sensors. Even though UAV systems still have limited endurance, they can provide a flexible and relatively inexpensive monitoring solution for a limited area of interest. This study investigated the applicability of monitoring the morphology of a frequently changing glacial stream using high-resolution topographic surface models derived from low-altitude UAV-based photogrammetry and LiDAR. An understanding of river-channel morphology and its response to anthropogenic and natural disturbances is imperative for effective watershed management and conservation. We focus on the data acquisition, processing workflow and highlight identified challenges and shortcomings. Additionally, we demonstrate how LiDAR data acquisition simulations can help decide which laser scanning approach to use and help optimise data collection to ensure full coverage with desired level of detail. Lastly, we showcase a case study of 3D surface change analysis in an alpine stream environment with UAV-based photogrammetry. The datasets used in this study were collected as part of the ISPRS Summer School of Alpine Research, which will continue to add new data layers on a biyearly basis. This growing data repository is freely available for research. [less ▲]

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See detailRobotic assistants in factory routines - the ethical implications
Klecker, Sophie UL; Hichri, Bassem UL; Plapper, Peter UL

in RACIR 2019 (2019)

This paper is concerned with the problems which arise when humans are working alongside robotic assistants. The main question which appears is how to define the difference between humans and robots in ... [more ▼]

This paper is concerned with the problems which arise when humans are working alongside robotic assistants. The main question which appears is how to define the difference between humans and robots in terms of characteristics, similarities or differences and how to consequently treat humans and robots in the factory routine. Based on a literature analysis, a common ground for the treatment of human and robotic workforce in the manufacturing industry is established. Subsequently, a framework for their cooperation is deduced and an implementation of the solution suggested. [less ▲]

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See detailRobotic Trajectory Tracking: Position- and Force-Control
Klecker, Sophie UL

Doctoral thesis (2019)

This thesis employs a bottom-up approach to develop robust and adaptive learning algorithms for trajectory tracking: position and torque control. In a first phase, the focus is put on the following of a ... [more ▼]

This thesis employs a bottom-up approach to develop robust and adaptive learning algorithms for trajectory tracking: position and torque control. In a first phase, the focus is put on the following of a freeform surface in a discontinuous manner. Next to resulting switching constraints, disturbances and uncertainties, the case of unknown robot models is addressed. In a second phase, once contact has been established between surface and end effector and the freeform path is followed, a desired force is applied. In order to react to changing circumstances, the manipulator needs to show the features of an intelligent agent, i.e. it needs to learn and adapt its behaviour based on a combination of a constant interaction with its environment and preprogramed goals or preferences. The robotic manipulator mimics the human behaviour based on bio-inspired algorithms. In this way it is taken advantage of the know-how and experience of human operators as their knowledge is translated in robot skills. A selection of promising concepts is explored, developed and combined to extend the application areas of robotic manipulators from monotonous, basic tasks in stiff environments to complex constrained processes. Conventional concepts (Sliding Mode Control, PID) are combined with bio-inspired learning (BELBIC, reinforcement based learning) for robust and adaptive control. Independence of robot parameters is guaranteed through approximated robot functions using a Neural Network with online update laws and model-free algorithms. The performance of the concepts is evaluated through simulations and experiments. In complex freeform trajectory tracking applications, excellent absolute mean position errors (<0.3 rad) are achieved. Position and torque control are combined in a parallel concept with minimized absolute mean torque errors (<0.1 Nm). [less ▲]

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See detailRobotix-Academy Conference for Industrial Robotics (RACIR) 2017
Müller, Rainer; Plapper, Peter UL; Brüls, Olivier et al

Book published by Shaker Verlag - 1st ed (2017)

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See detailRobotix-Academy Conference for Industrial Robotics (RACIR) 2018
Müller, Rainer; Plapper, Peter UL; Brüls, Olivier et al

Book published by Shaker Verlag - 1st ed (2018)

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See detailRobust dynamical network reconstruction
Yuan, Y.; Stan, G. B.; Warnick, S. et al

in The proceedings of the 49th IEEE Conference on Decision and Control (CDC) (2010)

Motivated by biological applications, this paper addresses the problem of network reconstruction from data. Previous work has shown necessary and sufficient conditions for network reconstruction of noise ... [more ▼]

Motivated by biological applications, this paper addresses the problem of network reconstruction from data. Previous work has shown necessary and sufficient conditions for network reconstruction of noise-free LTI systems. This paper assumes that the conditions for network reconstruction have been met but here we additionally take into account noise and unmodelled dynamics (including nonlinearities). Algorithms are therefore proposed to reconstruct dynamical (Boolean) network structure from time-series (steady-state) data respectively in presence of noise and nonlinearities. In order to identify the network structure that generated the data, we compute the smallest distances between the measured data and the data that would have been generated by particular Boolean structures. Information criteria and optimisation technique balancing such distance and model complexity are introduced to search for the true structure. We conclude with biologically-inspired network reconstruction examples which include noise and nonlinearities. [less ▲]

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See detailRobust dynamical network structure reconstruction
Yuan, Ye; Stan, Guy-Bart; Warnick, Stan et al

in Automatica (2011), 47(6),

This paper addresses the problem of network reconstruction from data. Previous work identified necessary and sufficient conditions for network reconstruction of LTI systems, assuming perfect measurements ... [more ▼]

This paper addresses the problem of network reconstruction from data. Previous work identified necessary and sufficient conditions for network reconstruction of LTI systems, assuming perfect measurements (no noise) and perfect system identification. This paper assumes that the conditions for network reconstruction have been met but here we additionally take into account noise and unmodelled dynamics (including nonlinearities). In order to identify the network structure that generated the data, we compute the smallest distances between the measured data and the data that would have been generated by particular network structures. We conclude with biologically inspired network reconstruction examples which include noise and nonlinearities. [less ▲]

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See detailRobust dynamical network structure reconstruction
Yuan, Y.; Stan, G. B.; Warnick, S. et al

Scientific Conference (2010)

Motivated by biological applications, this paper addresses the problem of network reconstruction from data. Previous work has shown necessary and sufficient conditions for network reconstruction of noise ... [more ▼]

Motivated by biological applications, this paper addresses the problem of network reconstruction from data. Previous work has shown necessary and sufficient conditions for network reconstruction of noise-free LTI systems. This paper assumes that the conditions for network reconstruction have been met but here we additionally take into account noise and unmodelled dynamics (including nonlinearities). Algorithms are therefore proposed to reconstruct dynamical (Boolean) network structure from time-series (steady-state) data respectively in presence of noise and nonlinearities. In order to identify the network structure that generated the data, we compute the smallest distances between the measured data and the data that would have been generated by particular Boolean structures. Information criteria and optimisation technique balancing such distance and model complexity are introduced to search for the true structure. We conclude with biologically-inspired network reconstruction examples which include noise and nonlinearities. [less ▲]

Detailed reference viewed: 75 (0 UL)