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See detailTrefftz polygonal finite element for linear elasticity: convergence, accuracy, and properties
Hirshikesh; Natarajan, Sundararajan; Ratna Kumar, A. K. et al

in Asia Pacific Journal on Computational Engineering (2017)

In this paper, the accuracy and the convergence properties of Trefftz finite element method over arbitrary polygons are studied. Within this approach, the unknown displacement field within the polygon is ... [more ▼]

In this paper, the accuracy and the convergence properties of Trefftz finite element method over arbitrary polygons are studied. Within this approach, the unknown displacement field within the polygon is represented by the homogeneous solution to the governing differential equations, also called as the T-complete set. While on the boundary of the polygon, a conforming displacement field is independently defined to enforce the continuity of the field variables across the element boundary. An optimal number of T-complete functions are chosen based on the number of nodes of the polygon and the degrees of freedom per node. The stiffness matrix is computed by the hybrid formulation with auxiliary displacement frame. Results from the numerical studies presented for a few benchmark problems in the context of linear elasticity show that the proposed method yields highly accurate results with optimal convergence rates. [less ▲]

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See detailtrend Analysis and interpretation of Luxembourg’s consumption Footprint NFA 2010 edition, data years 2000 – 2007
Hild, Paula UL; Takagi, Aya; Schmitt, Bianca

Report (2012)

The Ecological Footprint methodology by Global Footprint Network measures human consumption of products and services from different ecosystems in terms of the amount of bioproductive land and sea area ... [more ▼]

The Ecological Footprint methodology by Global Footprint Network measures human consumption of products and services from different ecosystems in terms of the amount of bioproductive land and sea area needed to supply these products and services. In other words, the Ecological Footprint calculates the land area needed to produce food, provide resources, produce energy, and absorb the CO2 emissions generated by the supply chains within one year at country level. For the calculations of Luxembourg’s Ecological Footprint, international statistical databases are used to identify the quantities of produced, imported and exported goods and services. Then, Global Footprint Network applies different factors to the quantities to assess the area needed to supply these products and services. Finally, the Consumption Footprint of a nation is divided by the number of inhabitants and compared to other countries at a per capita level (global hectares per capita). This means that the Ecological Footprint can be used as an indicator for the sustainability of a national consumption by assessing human land uses. In the following paragraph, Luxembourg’s Ecological Footprint is discussed in the framework of the environmental indicators of Luxembourg’s competitiveness scoreboard (see Table 9) [MECE, 2010]. Luxembourg’s ranking is rather low for all of the scoreboard indicators: number of ISO 9001 certifications per billion of inhabitants (21 out of 27); number of ISO 14001 certifications per billion of inhabitants (15 out of 27); total greenhouse gas emissions (15 out of 27); renewable energy ration (23 out of 27); quantity of municipal waste per capita per year (24 out of 27); energetic intensity (8 out of 27); transport by car (17 out of 27); Ecological Footprint in gha per capita per year (27 out of 27). Based on the environmental competiveness scoreboard indicators, it can be concluded that in general, Luxembourg’s environmental performance is low compared to the other countries of the European Union. With respect to Luxembourg’s Ecological Footprint, it can be said that Luxembourg’s consumption is not sustainable. The number of planets that would be needed if the world's population lived like the population of Luxembourg in 2007 is about six. However, per year, the biocapacity (bioproductive land) of the planet can only regenerate once. [less ▲]

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See detailA Tutorial on Bayesian Inference to Identify Material Parameters in Solid Mechanics
Rappel, Hussein UL; Beex, Lars UL; Hale, Jack UL et al

in Archives of Computational Methods in Engineering (2019)

The aim of this contribution is to explain in a straightforward manner how Bayesian inference can be used to identify material parameters of material models for solids. Bayesian approaches have already ... [more ▼]

The aim of this contribution is to explain in a straightforward manner how Bayesian inference can be used to identify material parameters of material models for solids. Bayesian approaches have already been used for this purpose, but most of the literature is not necessarily easy to understand for those new to the field. The reason for this is that most literature focuses either on complex statistical and machine learning concepts and/or on relatively complex mechanical models. In order to introduce the approach as gently as possible, we only focus on stress–strain measurements coming from uniaxial tensile tests and we only treat elastic and elastoplastic material models. Furthermore, the stress–strain measurements are created artificially in order to allow a one-to-one comparison between the true parameter values and the identified parameter distributions. [less ▲]

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See detailA tutorial on multiple crack growth and intersections with XFEM
Sutula, Danas; Bordas, Stéphane UL

Presentation (2015, May 12)

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See detailA two-dimensional Isogeometric Boundary Element Method for elastostatic analysis
Simpson, R. N.; Bordas, Stéphane UL; Trevelyan, J. et al

in Computer Methods in Applied Mechanics & Engineering (2012), 209-212

The concept of isogeometric analysis, where functions that are used to describe geometry in CAD software are used to approximate the unknown fields in numerical simulations, has received great attention ... [more ▼]

The concept of isogeometric analysis, where functions that are used to describe geometry in CAD software are used to approximate the unknown fields in numerical simulations, has received great attention in recent years. The method has the potential to have profound impact on engineering design, since the task of meshing, which in some cases can add significant overhead, has been circumvented. Much of the research effort has been focused on finite element implementations of the isogeometric concept, but at present, little has been seen on the application to the Boundary Element Method. The current paper proposes an Isogeometric Boundary Element Method (BEM), which we term IGABEM, applied to two-dimensional elastostatic problems using Non-Uniform Rational B-Splines (NURBS). We find it is a natural fit with the isogeometric concept since both the NURBS approximation and BEM deal with quantities entirely on the boundary. The method is verified against analytical solutions where it is seen that superior accuracies are achieved over a conventional quadratic isoparametric BEM implementation. © 2011 Elsevier B.V. [less ▲]

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See detailA TWO-STEP APPROACH FOR THE CORRECTION OF THE SEED MATRIX IN THE DYNAMIC DEMAND ESTIMATION
Cantelmo, Guido UL; Viti, Francesco UL; Tampère, Chris M.J. et al

in Transportation Research Record: Journal of the Transportation Research Board (2014), 2466

In this work deterministic and stochastic optimization methods are tested for solving the Dynamic Demand Estimation problem. All the adopted methods demonstrate the difficulty in reproducing the correct ... [more ▼]

In this work deterministic and stochastic optimization methods are tested for solving the Dynamic Demand Estimation problem. All the adopted methods demonstrate the difficulty in reproducing the correct traffic regime, especially if the seed matrix is not sufficiently close to the real one. Therefore, in this paper a new and intuitive procedure to specify an opportune starting seed matrix is proposed: it is a two-step procedure based on the concept of dividing the problem into small-size problems, focusing on specific OD pairs in different steps. Specifically, the first step focuses on the optimization of a subset of OD variables (the ones who generate the higher flows or the ones who generate the bottlenecks on the network). In the second step the optimization works on all the OD pairs, using as starting matrix the matrix derived from the first step. In this way is possible to use a more performance optimization method for every step, improving the performance of the method and the quality of the result with respect to the classical “one-step” approach. The procedure has been tested on the real network of Antwerp, Belgium, demonstrating its efficacy in combination with different optimization methods. [less ▲]

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See detailA two-steps dynamic demand estimation approach sequentially adjusting generations and distributions
Cantelmo, Guido UL; Viti, Francesco UL; Cipriani, Ernesto et al

in Proceedings of IEEE-ITS Conference (2015, September)

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See detailUnderstanding dynamics using sensitivity analysis: caveat and solution
Perumal, Thanneer Malai UL; Gunawan, Rudiyanto

in BMC Systems Biology (2011), 5

BACKGROUND: Parametric sensitivity analysis (PSA) has become one of the most commonly used tools in computational systems biology, in which the sensitivity coefficients are used to study the parametric ... [more ▼]

BACKGROUND: Parametric sensitivity analysis (PSA) has become one of the most commonly used tools in computational systems biology, in which the sensitivity coefficients are used to study the parametric dependence of biological models. As many of these models describe dynamical behaviour of biological systems, the PSA has subsequently been used to elucidate important cellular processes that regulate this dynamics. However, in this paper, we show that the PSA coefficients are not suitable in inferring the mechanisms by which dynamical behaviour arises and in fact it can even lead to incorrect conclusions. RESULTS: A careful interpretation of parametric perturbations used in the PSA is presented here to explain the issue of using this analysis in inferring dynamics. In short, the PSA coefficients quantify the integrated change in the system behaviour due to persistent parametric perturbations, and thus the dynamical information of when a parameter perturbation matters is lost. To get around this issue, we present a new sensitivity analysis based on impulse perturbations on system parameters, which is named impulse parametric sensitivity analysis (iPSA). The inability of PSA and the efficacy of iPSA in revealing mechanistic information of a dynamical system are illustrated using two examples involving switch activation. CONCLUSIONS: The interpretation of the PSA coefficients of dynamical systems should take into account the persistent nature of parametric perturbations involved in the derivation of this analysis. The application of PSA to identify the controlling mechanism of dynamical behaviour can be misleading. By using impulse perturbations, introduced at different times, the iPSA provides the necessary information to understand how dynamics is achieved, i.e. which parameters are essential and when they become important. [less ▲]

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See detailUnderstanding human need fulfilment to support the design of secure experiences
Distler, Verena UL

in Proceedings of NordiCHI' 18 Doctoral Consortium (2018)

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See detailUnderstanding the differences between how novice and experienced designers approach design tasks
Ahmed, S.; Wallace, K. M.; Blessing, Lucienne UL

in Research in Engineering Design (2003), 14(1), 1-11

Research was undertaken to understand how to provide the most appropriate support for novice designers in engineering design. However, how designers apply their experience and knowledge is not understood ... [more ▼]

Research was undertaken to understand how to provide the most appropriate support for novice designers in engineering design. However, how designers apply their experience and knowledge is not understood and further research in this area is required. This paper describes an observational study to understand how novice and experienced designers approach design tasks. [less ▲]

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See detailUndesirable Consequences and Social Contexts of Technology Use: A Micro-analysis of Embodied User Interaction
Jungmann, Manuela UL; Cox, Richard

in Interacting with Computers (2017), 29(4), 481493

The focus of this paper is on the unexpected and undesirable consequences of social interaction with technological innovations, which we analyse with the support of two frameworks to better comprehend ... [more ▼]

The focus of this paper is on the unexpected and undesirable consequences of social interaction with technological innovations, which we analyse with the support of two frameworks to better comprehend their social implications. The first, techno-social framework, consists of Allenby and Sarewitz's taxonomy of technological social function. In the second, cognitive, framework, we introduce concepts from dual-systems theory. The frameworks provide a lens through which to view techno-cultural examples. This sets the stage for our case study in which we investigate an interactive game installation. Using data analytics, we uncover hidden effects due to the social interactions between the players and to their physical attributes. We conclude that there is a pressing need for innovators to broaden the scope of their evaluations to not just evaluate innovative technologies at the initial engineering/design phase but also to conduct evaluations at later phases of adoption and appropriation that focus on social contexts-of-use. [less ▲]

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See detailA unified enrichment approach addressing blending and conditioning issues in enriched finite elements
Agathos, Konstantinos; Chatzi, Eleni; Bordas, Stéphane UL

in Computer Methods in Applied Mechanics and Engineering (2019), 349

We present a combination of techniques to improve the convergence and conditioning properties of partition of unity (PU) enriched finite element methods. By applying these techniques to different types of ... [more ▼]

We present a combination of techniques to improve the convergence and conditioning properties of partition of unity (PU) enriched finite element methods. By applying these techniques to different types of enrichment functions, namely polynomial, discontinuous and singular, higher order convergence rates can be obtained while keeping condition number growth rates similar to the ones corresponding to standard finite elements. [less ▲]

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See detailA unified polygonal locking-free thin/thick smoothed plate element
Katili, Irwan; Maknun, Imam Jauhari; Katili, Andi Makarim et al

in Composite Structures (2019), 219

A novel cell-based smoothed finite element method is proposed for thin and thick plates based on Reissner-Mindlin plate theory and assumed shear strain fields. The domain is discretized with arbitrary ... [more ▼]

A novel cell-based smoothed finite element method is proposed for thin and thick plates based on Reissner-Mindlin plate theory and assumed shear strain fields. The domain is discretized with arbitrary polygons and on each side of the polygonal element, discrete shear constraints are considered to relate the kinematical and the independent shear strains. The plate is made of functionally graded material with effective properties computed using the rule of mixtures. The influence of various parameters, viz., the plate aspect ratio and the material gradient index on the static bending response and the first fundamental frequency is numerically studied. It is seen that the proposed element: (a) has proper rank; (b) does not require derivatives of shape functions and hence no isoparametric mapping required; (c) independent of shape and size of elements and (d) is free from shear locking. [less ▲]

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See detailUniversal health coverage: an urgent need for collaborative learning and technology in primary care
Patel, Kunal D.; Mcloughlin, Clodagh; Lygidakis, Charilaos UL et al

in Education for Primary Care (2017)

Universal health coverage is an achievable goal for all health professionals globally. However, for it to be implemented technology and collaboration are essential. This letter focuses on recently ... [more ▼]

Universal health coverage is an achievable goal for all health professionals globally. However, for it to be implemented technology and collaboration are essential. This letter focuses on recently published recommendations for technology in primary care education in respect to Universal Health Coverage. [less ▲]

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See detailUnpacking Collaboration in Digital History Projects
Kemman, Max UL

Scientific Conference (2017)

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See detailUntersuchungen der instationären Strömungstopologie im Nachlauf einer Seehundvibrisse.
Witte, Matthias; Michael, Mark UL; Brede, Martin et al

in Delgado, A.; Rauh, A.; Lienhart, H. (Eds.) et al Proceedings der 17.GALA-Fachtagung “Lasermethoden in der Strömungsmesstechnik“ (2009)

Die Vibrissen von Seehunden zeichnen sich durch eine komplizierte dreidimensionale Struk- turierung aus. Sie versetzen den Seehund in die Lage, hydrodynamische Nachlaufspuren von Beutefischen zu ... [more ▼]

Die Vibrissen von Seehunden zeichnen sich durch eine komplizierte dreidimensionale Struk- turierung aus. Sie versetzen den Seehund in die Lage, hydrodynamische Nachlaufspuren von Beutefischen zu detektieren. Mit Hilfe von Stereo- μ Piv Messungen an Seehundvibrissen konnte die stationäre Strömungstopologie des Vibrissennachlaufes ermittelt werden. Zum besseren Verständnis der Funktion der Vibrissenstrukturierung ist es notwendig, die instatio- näre Strömungstopologie zu kennen. Durch räumlich und zeitlich hochauflösende numeri- sche Verfahren konnte die instationäre Strömungstopologie im Nachlauf einer Seehund- vibrisse ermittelt werden. [less ▲]

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See detailUsage of Smartphone Data to Derive an Indicator for Collaborative Mobility between Individuals
Toader, Bogdan UL; Sprumont, François UL; Faye, Sébastien UL et al

in ISPRS International Journal of Geo-Information (2017), 6(3), 62

The potential of geospatial big data has been drawing attention for a few years. Despite the larger and larger market penetration of portable technologies (nomadic and wearable devices like smartphones ... [more ▼]

The potential of geospatial big data has been drawing attention for a few years. Despite the larger and larger market penetration of portable technologies (nomadic and wearable devices like smartphones and smartwatches), their opportunities for travel behavior analysis are still relatively unexplored. The main objective of our study is to extract the human mobility patterns from GPS traces in order to derive an indicator for enhancing Collaborative Mobility (CM) between individuals. The first step, extracting activity duration and location, is done using state-of-the-art automated recognition tools. Sensors data are used to reconstruct individual’s activity location and duration across time. For constructing the indicator, in a second step, we defined different variables and methods for specific case studies. Smartphone sensor data are being collected from a limited number of individuals and for one week. These data are used to evaluate the proposed indicator. Based on the value of the indicator, we analyzed the potential for identifying CM among groups of users, such as sharing traveling resources (e.g., carpooling, ridesharing, parking sharing) and time (rescheduling and reordering activities). [less ▲]

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See detailUse of commercial simulation software for analyzing the dynamics of an injection-molding clamp unit
Hostert, Claude UL

Doctoral thesis (2006)

Today, the interest in integrated dynamic analysis of mechatronic systems increases. Different approaches are possible depending on the nature of the system, on the required complexity of the model, or ... [more ▼]

Today, the interest in integrated dynamic analysis of mechatronic systems increases. Different approaches are possible depending on the nature of the system, on the required complexity of the model, or simply on the tools available to the engineer. During this work, the aim was to implement specialized commercial simulation software packages and to combine them in order to simulate the dynamic behavior of mechatronic systems as for example an injection molding machine. The multi-body simulation software is the backbone of the current analysis as it inherently models large non-linear motions. It is possible to account for the flexibility of components in the MBS model if necessary. Furthermore, other simulation codes were used to model the hydraulic and controls systems. The case studies show the interest and the potential of a combined analysis of mechatronic systems. Once the different sub-models, generated with the adequate simulation tool, have been successfully linked and validated by measurements, various scenarios can be simulated and analyzed. The model provides the engineer with an additional insight into the overall system and thus with a better understanding of its dynamic characteristics. The interactions between the subsystems, which may be of very distinctive nature, can be investigated. Generally, it is difficult to predict such relations intuitively. Finally, the model allows to simulate with different design parameters and to asses the effect of modifications to these on the overall performance of the machine. This helps to identify the significant parameters that are crucial for an optimized functioning. [less ▲]

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See detailUsing Bayes' theorem to infer the material parameters of human soft tissue
Hale, Jack UL; Farrell, Patrick; Bordas, Stéphane UL

Presentation (2015, October 21)

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See detailUsing Bayesian inference to recover the material parameters of a heterogeneous hyperelastic body
Hale, Jack UL; Farrell, Patrick; Bordas, Stéphane UL

Scientific Conference (2016)

We present a method for calculating a Bayesian uncertainty estimate on the recovered material parameters of a heterogeneous geometrically non-linear hyperelastic body. We formulate the problem in the ... [more ▼]

We present a method for calculating a Bayesian uncertainty estimate on the recovered material parameters of a heterogeneous geometrically non-linear hyperelastic body. We formulate the problem in the Bayesian inference framework [1]; given noisy and sparse observations of a body, some prior knowledge on the parameters and a parameter-to-observable map the goal is to recover the posterior distribution of the parameters given the observations. In this work we primarily focus on the challenges of developing dimension-independent algorithms in the context of very large inverse problems (tens to hundreds of thousands of parameters). Critical to the success of the method is viewing the problem in the correct infinite- dimensional function space setting [2]. With this goal in mind, we show the use of automatic symbolic differentiation techniques to construct high-order adjoint models [3], scalable maximum a posteriori (MAP) estimators, and efficient low-rank update methods to calculate credible regions on the posterior distribution [4]. [less ▲]

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