References of "2009"
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See detailBearing capacity of steel fiber reinforced concrete flat slabs
Michels, Julien UL

Doctoral thesis (2009)

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See detailZur Rotationskapazität von Verbundanschlüssen bei der Bemessung nach dem Fließgelenkverfahren
Hahn, Christoph UL

Doctoral thesis (2009)

The present work deals with the load bearing and rotational behaviour of composite connections in steel and concrete constructions. For typical buildings, composite connections are assumed to be rigid or ... [more ▼]

The present work deals with the load bearing and rotational behaviour of composite connections in steel and concrete constructions. For typical buildings, composite connections are assumed to be rigid or pinned. This assumption can lead to uneconomic structures. A design concept for the estimation of the available rotation capacity, the initial stiffness and the moment bearing capacity of semi-rigid connections is presented. On the basis of the plastic hinge theory diagrams were developed to prove the load carrying capacity and the serviceability of composite beams with semi-rigid connections. The presented design model is based on the evaluation of 9 self conducted tests and on the evaluation of 74 tests on composite connections from all over Europe. The availability of the model was proved by intensive nonlinear finite element simulations. [less ▲]

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

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

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

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

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See detailNumerical integration over arbitrary surfaces in partition of unity finite elements
Natarajan, Sundararajan; dal Pont, Stefano; Hung, Nguyen-Xuan et al

Scientific Conference (2009, September)

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See detailThe smoothed extended finite element method for strong discontinuities
Natarajan, S.; Bordas, Stéphane UL; Rabczuk, Timon

Scientific Conference (2009, June)

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See detailA novel numerical integration technique over arbitrary polygons
Natarajan, Sundararajan; Mahapatra, D Roy; Bordas, Stéphane UL et al

Scientific Conference (2009, April)

In this paper, a new numerical integration technique [1] on arbitrary polygons is presented. The polygonal do- main is mapped conformally to the unit disk using Schwarz-Christoffel mapping [2] and a ... [more ▼]

In this paper, a new numerical integration technique [1] on arbitrary polygons is presented. The polygonal do- main is mapped conformally to the unit disk using Schwarz-Christoffel mapping [2] and a midpoint quadrature rule defined on the unit circle is used. This method eliminates the need for a two level isoparametric mapping usuall required [3]. Moreover the positivity of the Jacobian is guaranteed. We present numerical results for a few benchmark problems in the context of polygonal finite elements that show the effectiveness of the method. [less ▲]

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See detailAdaptive support domain implementation on the Moving Least Squares approximation for Mfree methods applied on elliptic and parabolic PDE problems using strong-form description
Bourantas, Georgios UL; Skouras, Eugene; Nikiforidis, George

in Computer Modeling in Engineering & Sciences (2009), 43

The extent of application of meshfree methods based on point collocation (PC) techniques with adaptive support domain for strong form Partial Differential Equations (PDE) is investigated. The basis ... [more ▼]

The extent of application of meshfree methods based on point collocation (PC) techniques with adaptive support domain for strong form Partial Differential Equations (PDE) is investigated. The basis functions are constructed using the Moving Least Square (MLS) approximation. The weak-form description of PDEs is used in most MLS methods to circumvent problems related to the increased level of resolution necessary near natural (Neumann) boundary conditions (BCs), dislocations, or regions of steep gradients. Alternatively, one can adopt Radial Basis Function (RBF) approximation on the strong-form of PDEs using meshless PC methods, due to the delta function behavior (exact solution on nodes). The present approach is one of the few successful attempts of using MLS approximation [Atluri, Liu, and Han (2006), Han, Liu, Rajendran and Atluri (2006), Atluri and Liu (2006)] instead of RBF approximation for the meshless PC method using strong-form description. To increase the accuracy of the MLS interpolation method and its robustness in problems with natural BCs, a suitable support domain should be chosen in order to ensure an optimized area of coverage for interpolation. To this end, the basis functions are constructed using two different approaches, pertinent to the dimension of the support domain. On one hand, a compact form for the support domain is retained by keeping its radius constant. On the other hand, one can control the number of neighboring nodes as the support domain of each point. The results show that some inaccuracies are present near the boundaries using the first approach, due to the limited number of nodes belonging to the support domain, which results in failed matrix inversion. Instead, the second approach offers capability for fully matrix inversion under many (if not all) circumstances, resulting in basis functions of increased accuracy and robustness. This PC method, applied along with an intelligent adaptive refinement, is demonstrated for elliptic and for parabolic PDEs, related to many flow and mass transfer problems. [less ▲]

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See detailWhite Manipulation in Judgment Aggregation
Grossi, Davide; Pigozzi, Gabriella UL; Slavkovik, Marija UL

Scientific Conference (2009)

Distributive systems consisting of autonomous and intelligent components need to be able to reason and make decisions based on the information these components share. Judgment aggregation investigates how ... [more ▼]

Distributive systems consisting of autonomous and intelligent components need to be able to reason and make decisions based on the information these components share. Judgment aggregation investigates how individual judgments on logically connected propositions can be aggregated into a collective judgment on the same propositions. It is the case that seemingly reasonable aggregation procedures may force the group to hold an inconsistent judgment set. What happens when the agents realize that the group outcome will be inconsistent? We claim that, in order to avoid an untenable collective outcome, individuals may prefer to declare a non-truthful, less preferred judgment set. Thus, the prospect of an individual trying to manipulate the social outcome by submitting an insincere judgment set is turned from being an undesirable to a “virtuous” (or white) manipulation. We define white manipulation and present the initial study of it as a coordinated action of the whole group. [less ▲]

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See detailProjection-based reduction of fluid-structure interaction systems using monolithic space-time modes
Zilian, Andreas UL; Dinkler, D.; Vehre, A.

in Computer Methods in Applied Mechanics & Engineering (2009), 198(47-48), 3795-3805

The focus of this work is the development of reduced models for engineering applications in complex bidirectional fluid-structure interaction. In the simultaneous solution procedure, velocity variables ... [more ▼]

The focus of this work is the development of reduced models for engineering applications in complex bidirectional fluid-structure interaction. In the simultaneous solution procedure, velocity variables are used for both fluid and solid, and the whole set of model equations is discretized by a stabilized time-discontinuous space-time finite element method. Flexible structures are modeled using a three-dimensional continuum approach in a total Lagrangian setting considering large displacements and rotations. In the flow domain the incompressible Navier-Stokes equations describe the Newtonian fluid. A continuous finite element mesh is applied to the entire spatial domain, and the discretized model equations are assembled in a single set of algebraic equations, considering the two-field problem as a whole. The continuous fluid-structure mesh with identical orders of approximation for both solid and fluid in space and time automatically yields conservation of mass, momentum and energy at the fluid-structure interface. A mesh-moving scheme is used to adapt the nodal coordinates of the fluid space-time finite element mesh to the structural deformation. The computational approach for strongly coupled fluid-structure interaction is used to create suitable reduced models of generic nonlinear problems. Reduction is performed with monolithic projection-based space-time modes, ensuring strong coupling of fluid and structure in the reduced model. The contribution discusses results using proper orthogonal decomposition (POD) for determination of monolithic space-time modes in the reduction of fluid-structure systems. © 2009 Elsevier B.V. All rights reserved. [less ▲]

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See detailNumerical integration over arbitrary polygonal domains based on Schwarz-Christoffel conformal mapping
Natarajan, S.; Bordas, Stéphane UL; Roy mahapatra, D.

in International Journal for Numerical Methods in Engineering (2009), 80(1), 103-134

This paper presents a new numerical integration technique on arbitrary polygonal domains. The polygonal domain is mapped conformally to the unit disk using Schwarz-Christoffel mapping and a midpoint ... [more ▼]

This paper presents a new numerical integration technique on arbitrary polygonal domains. The polygonal domain is mapped conformally to the unit disk using Schwarz-Christoffel mapping and a midpoint quadrature rule defined on this unit disk is used. This method eliminates the need for a two-level isoparametric mapping usually required. Moreover, the positivity of the Jacobian is guaranteed. Numerical results presented for a few benchmark problems in the context of polygonal finite elements show that the proposed method yields accurate results. © 2009 John Wiley & Sons, Ltd. [less ▲]

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See detailOn time integration in the XFEM
Fries, T.-P.; Zilian, Andreas UL

in International Journal for Numerical Methods in Engineering (2009), 79(1), 69-93

The extended finite element method (XFEM) is often used in applications that involve moving interfaces. Examples are the propagation of cracks or the movement of interfaces in two-phase problems. This ... [more ▼]

The extended finite element method (XFEM) is often used in applications that involve moving interfaces. Examples are the propagation of cracks or the movement of interfaces in two-phase problems. This work focuses on time integration in the XFEM. The performance of the discontinuous Galerkin method in time (space-time finite elements (FEs)) and time-stepping schemes are analyzed by convergence studies for different model problems. It is shown that space-time FE achieve optimal convergence rates. Special care is required for time stepping in the XFEM due to the time dependence of the enrichment functions. In each time step, the enrichment functions have to be evaluated at different time levels. This has important consequences in the quadrature used for the integration of the weak form. A time-stepping scheme that leads to optimal or only slightly sub-optimal convergence rates is systematically constructed in this work. © 2009 John Wiley & Sons, Ltd. [less ▲]

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See detailAdaptive-gain Extended Kalman Filter: Extension to the Continuous-discrete Case
Boizot, Nicolas UL; Busvelle, Eric; Gauthier, Jean-Paul

Scientific Conference (2009)

In the present article we propose a nonlinear observer that merges the behaviors 1) of an extended Kalman filter, mainly designed to smooth off noise , and 2) of high-gain observers devoted to handle ... [more ▼]

In the present article we propose a nonlinear observer that merges the behaviors 1) of an extended Kalman filter, mainly designed to smooth off noise , and 2) of high-gain observers devoted to handle large perturbations in the state estimation. We specifically aim at continuous-discrete systems. The strategy consists in letting the high-gain self adapt according to the innovation. We define innovation computed over a time window and justify its usage via an important lemma. We prove the general convergence of the resulting observer. [less ▲]

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See detailTemperature Fields Induced by Low Power Focused Ultrasound in Soft Tissues During Gene Therapy. Numerical Predictions and Experimental Results
Gambin, Barbara; Kujawska, Tamara; Kruglenko, Eleonora et al

in Archives of Acoustics (2009), 34(4), 445459

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See detailMeasure and Failure Cost Analysis: Selecting Risk Treatment Strategies
Gericke, Kilian UL; Klimentew, Lars; Blessing, Lucienne UL

in Proceedings of the 17th International Conference on Engineering Design (2009)

Project Risk Management is used to prevent projects to fail. Despite its proven use, barriers still exist that hinder implementation and use by inexperienced persons. One barrier is the additional effort ... [more ▼]

Project Risk Management is used to prevent projects to fail. Despite its proven use, barriers still exist that hinder implementation and use by inexperienced persons. One barrier is the additional effort required by the process of Project Risk Management itself. An additional barrier is the lack of systematic support of important steps like the selection of an appropriate risk treatment strategy. The decision which strategy to select is a challenging task due to the uncertain character of the addressed issue. The trade-off of the perceived additional efforts caused by a method must be addressed by an enhancement of the cost-benefit ratio of the applied methods and implemented risk treatment measures. Decision making using the proposed Measure and Failure Cost Analysis (MFCA) method enables the Risk Manager to compare the arising costs of different risk treatment strategies caused by an occurring risk and risk treatment measures. It is based on a de-escalation principle which analyzes the course of the impact of an event. The method compares the reaction rate of different strategies and proposes the favorite one. [less ▲]

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See detailA localized mixed-hybrid method for imposing interfacial constraints in the extended finite element method (XFEM)
Zilian, Andreas UL; Fries, T.-P.

in International Journal for Numerical Methods in Engineering (2009), 79(6), 733-752

The paper proposes an approach for the imposition of constraints along moving or fixed immersed interfaces in the context of the extended finite element method. An enriched approximation space enables ... [more ▼]

The paper proposes an approach for the imposition of constraints along moving or fixed immersed interfaces in the context of the extended finite element method. An enriched approximation space enables consistent representation of strong and weak discontinuities in the solution fields along arbitrarily-shaped material interfaces using an unfitted background mesh. The use of Lagrange multipliers or penalty methods is circumvented by a localized mixed hybrid formulation of the model equations. In a defined region in the vicinity of the interface, the original problem is re-stated in its auxiliary formulation. The availability of the auxiliary variable enables the consideration of a variety of interface constraints in the weak form. The contribution discusses the weak imposition of Dirichlet- and Neumann-type interface conditions as well as continuity requirements not fulfilled a priori by the enriched approximation. The properties of the proposed approach applied to two-dimensional linear scalar- and vector-valued elliptic problems are investigated by studying the convergence behavior. © 2009 John Wiley & Sons,Ltd. [less ▲]

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See detailLocal vs. Global Search Strategies in Evolutionary GRID-based Conformational Sampling & Docking
Horvath, Dragos; Brillet, Lorraine; Roy, Sylvaine et al

in 2009 IEEE CONGRESS ON EVOLUTIONARY COMPUTATION, VOLS 1-5 (2009)

Conformational sampling, the computational prediction of the experimental geometries of small proteins (folding) or of protein-ligand complexes (docking), is often cited as one of the most challenging ... [more ▼]

Conformational sampling, the computational prediction of the experimental geometries of small proteins (folding) or of protein-ligand complexes (docking), is often cited as one of the most challenging multimodal optimization problems. Due to the extreme ruggedness of the energy landscape as a function of geometry, sampling heuristics must rely on an appropriate trade-off between global and local searching efforts. A previously reported "planetary strategy", a generalization of the classical island model used to deploy a hybrid genetic algorithm on computer grids, has shown a good ability to quickly discover low-energy geometries of small proteins and sugars, and sometimes even pinpoint their native structures - although not reproducibly. The procedure focused on broad exploration and used a tabu strategy to avoid revisiting the neighborhood of known solutions, at the risk of "burying" important minima in overhastily set tabu areas. The strategy reported here, termed "divide-and-conquer planetary model" couples this global search procedure to a local search tool. Grid nodes are now shared between global and local exploration tasks. The phase space is cut into "cells" corresponding to a specified sampling width for each of the N degrees of freedom. Global search locates cells containing low-energy geometries. Local searches pinpoint even deeper minima within a cell. Sampling width controls the important trade-off between the number of cells and the local search effort needed to reproducibly sample each cell. The probability to submit a cell to local search depends on the energy of the most stable geometry found within. Local searches are allotted limited resources and are not expected to converge. However, as long as they manage to discover some deeper local minima, the explored cell remains eligible for further local search, now relying on the improved energy level to enhance chances to be picked again. This competition prevents the system to waste too much effort in fruitless local searches. Eventually, after a limited number of local searches, a cell will be "closed" and used - first as "seed", later as tabu zone - to bias future global searches. Technical details and some folding and docking results will be discussed. [less ▲]

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See detailGeographical Modelling with Cellular-Automata
Caruso, Geoffrey UL

Presentation (2009)

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