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See detailComputation of nonlinear normal modes through continuation methods
Renson, Ludovic ULg; Kerschen, Gaëtan ULg

Conference (2013, May)

In mechanical engineering, performance enhancement usually results in lighter and more flexible structures and pushes the limits of the system operating envelope. Nonlinearity is therefore becoming a ... [more ▼]

In mechanical engineering, performance enhancement usually results in lighter and more flexible structures and pushes the limits of the system operating envelope. Nonlinearity is therefore becoming a frequent occurrence and linear design tools show their limitations. To overcome these issues, nonlinear normal modes (NNMs) were introduced in structural dynamics as a direct extension of linear normal modes to nonlinear systems. Our contribution reviews the history and the new trends for the computation of NNMs in mechanical engineering. Specifically, algorithms for the continuation of periodic solutions were first developed. Such algorithms are now well-established and applicable to large-scale systems such as real-life aerospace structures. To further extend the concept of NNMs to nonconservative systems, the definition of an NNM as an invariant manifold in the system’s phase space was introduced. Again, continuation techniques are particularly well suited for computing these invariant manifolds. The geodesic level set method developed by Krauskopf and Osinga [1] as well as the “PDE formulation” method of Guckenheimer and Vladimirsky [2] are both considered. [1] Krauskopf, B. and H. Osinga (2003). "Computing Geodesic Level Sets on Global (Un)stable Manifolds of Vector Fields." SIAM Journal on Applied Dynamical Systems 2(4): 546-569. [2] Guckenheimer, J. and A. Vladimirsky (2004). "A Fast Method for Approximating Invariant Manifolds." SIAM Journal on Applied Dynamical Systems 3(3): 232-260. [less ▲]

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See detailComputation of Nonlinear Normal Modes using Numerical Continuation Techniques
Peeters, Maxime ULg; Viguié, Régis ULg; Serandour, Guillaume et al

in International Confernce on Advanced Computational Methods in Engineering, Liège, 2008 (2008)

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See detailCOMPUTATION OF NONLINEAR NORMAL MODES, PART I: NUMERICAL CONTINUATION IN MATLAB
Peeters, Maxime ULg; Viguié, Régis ULg; Serandour, Guillaume et al

in Sixth EUROMECH Nonlinear Dynamics Conference, Saint Petersbourg, 2008 (2008)

The concept of nonlinear normal modes (NNMs) is discussed in the present paper and its companion, Part II. Because there is virtually no application of the NNMs to large-scale engineering structures ... [more ▼]

The concept of nonlinear normal modes (NNMs) is discussed in the present paper and its companion, Part II. Because there is virtually no application of the NNMs to large-scale engineering structures, these papers are an attempt to highlight one aspect that might drive their development in the future. Specifically, we support that numerical methods for the continuation of periodic solutions pave the way for an effective and practical computation of NNMs. In this context, we show that the NNM computation is possible with limited implementation effort. The proposed algorithm, implemented in MATLAB, relies on two main techniques, namely a shooting procedure and a method for the continuation of NNM motions. The algorithm is demonstrated using a 2DOF nonlinear system. A comparison with the results given by the AUTO software is achieved in Part II. [less ▲]

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See detailComputation of nonlinear normal modes, part II: numerical continuation in Auto
Serandour, Guillaume; Peeters, Maxime ULg; Kerschen, Gaëtan ULg et al

in Sixth EUROMECH Nonlinear Dynamics Conference, Saint Petersbourg, 2008 (2008)

The concept of nonlinear normal modes (NNMs) is discussed in the present paper and its companion, Part I. Because there is virtually no application of the NNMs to large-scale engineering structures, these ... [more ▼]

The concept of nonlinear normal modes (NNMs) is discussed in the present paper and its companion, Part I. Because there is virtually no application of the NNMs to large-scale engineering structures, these papers are an attempt to highlight one aspect that might drive their development in the future. Specifically, we support that numerical methods for the continuation of periodic solutions pave the way for an effective and practical computation of NNMs. In this context, we show that the NNMs computation is possible using an existing continuation software, namely AUTO07. This is demonstrated using a 2DOF nonlinear system. The results are compared with those obtained with the Matlab algorithm described in Part I. [less ▲]

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See detailComputation of photoelectron spectra and evidences of SAMO in C60 and C70
Mignolet, Benoît ULg

Poster (2012, October 26)

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See detailThe computation of prismatic structures, applied to naval architecture
Rigo, Philippe ULg

in Marine Structures (1992)

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See detailComputation of simultaneous available transfer capability under thermal and voltage security constraints
Capitanescu, Florin ULg; Van Cutsem, Thierry ULg

(2002, September)

This paper proposes a method to compute the Available Transfer Capability (ATC) of a power system under both thermal and voltage security constraints. The objective is to determine, in some optimal manner ... [more ▼]

This paper proposes a method to compute the Available Transfer Capability (ATC) of a power system under both thermal and voltage security constraints. The objective is to determine, in some optimal manner, the ATC of several simultaneous transactions, such that any postulated contingency does not cause voltage instability nor thermal overloads. Thermal constraints are derived for every branch likely to be overloaded in post-contingency states. Voltage security constraints are derived from voltage unstable post-contingency scenario, obtained by Quasi Steady- State simulation, a fast time-domain method. The paper also addresses the discrimination problem, i.e. the fact that the computed ATC might favor some trades to the detriment of others. Variants will be discussed to deal with such situations. The method is illustrated on an 80-bus test system. [less ▲]

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See detailComputation of Source for Non-Meshed Coils in a Reduced Domain with A–V Formulation
Ferrouillat, Pauline; Guérin, Christophe; Meunier, Gérard et al

in IEEE Transactions on Magnetics (in press), 52

The discretized source magnetic vector potential Aj, projected from source field Hs with H(curl,Ω) semi-norm, is studied for non-meshed coils with magnetic vector potential A and electric scalar potential ... [more ▼]

The discretized source magnetic vector potential Aj, projected from source field Hs with H(curl,Ω) semi-norm, is studied for non-meshed coils with magnetic vector potential A and electric scalar potential V formulation. As a novelty, source potential Aj is computed in a reduced domain Ωred instead of the complete domain Ω. For domains with fixed and moving parts, potential Aj can be computed on each part, for each of the related current sources, with no need to ensure its continuity between these parts. [less ▲]

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See detailComputation of Source for Non-Meshed Coils in a Reduced Domain with A–V Formulation
Ferrouillat, Pauline; Guérin, Christophe; Meunier, Gérard et al

in Proceedings of COMPUMAG 2015 (2015, June)

The discretized source magnetic vector potential Aj, interpolated from source field Hs with H(curl,Ω) semi-norm, is studied for non-meshed coils with magnetic vector potential A and electric scalar ... [more ▼]

The discretized source magnetic vector potential Aj, interpolated from source field Hs with H(curl,Ω) semi-norm, is studied for non-meshed coils with magnetic vector potential A and electric scalar potential V formulation. As a novelty, source potential Aj is computed in a reduced domain Ωred instead of the complete domain Ω. For domains with fixed and moving parts, potential Aj can be computed on each part, for each of the related current sources, with no need to ensure its continuity between these parts. [less ▲]

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See detailComputation of the flow field resulting from dam failure
Pirotton, Michel ULg

Conference (1991, April 08)

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See detailComputation of the Malpasset dam break with a 2D conservative flow solver on a multiblock structured grid
Erpicum, Sébastien ULg; Archambeau, Pierre ULg; Dewals, Benjamin ULg et al

in Proceedings of the 6th International Conference of Hydroinformatics (2004)

In the global framework of safety, the study of the hydraulic consequences of a dam breaking, sudden and instantaneous for concrete structures, gradual for earth ones, is of major interest in the scope of ... [more ▼]

In the global framework of safety, the study of the hydraulic consequences of a dam breaking, sudden and instantaneous for concrete structures, gradual for earth ones, is of major interest in the scope of prevention policies or protection plans for populations and goods. Suitable numerical models, coupled with contemporary computational possibilities, allow engineers to forecast these complex situations with a great reliability. In this field, WOLF 2D is an efficient analysis and optimisation tool, which has been completely developed by the Applied Hydrodynamics and Hydraulic Constructions team (HACH – http://www.ulg.ac.be/hach) of the University of Liege. It is part of WOLF free surface flows computation package, which includes in the same development environment the resolutions of the 1D Saint-Venant equations, the 2D shallow-water equations as well as a physically based hydrological model and powerful optimisation capabilities based on Genetic Algorithms. The interactive and unique user-interface, with high performance pre- and post-processing, allows monitoring 3-D large-scale runs graphically while they proceed, as well as generation of 3D videos. Each code handles general multiblock meshes, dealing with natural topography and mobile bed simultaneously, for any unsteady situation with mixed regimes and moving hydraulic jumps. By this way, WOLF deals with all free surface hydraulic phenomena, from hydrological runoff and river propagation to extreme erosive flows on realistic mobile topography, such as gradual dam breaching processes. It has moreover proved its efficiency and reliability for years by numerous real applications. The first part of this paper covers a brief description of the 2D multiblock flow solver WOLF 2D and the underlying mathematical model. The second part depicts the application of WOLF computation capabilities to the well-known Malpasset dam break (France, 1959), which induced a catastrophic almost instantaneous release of 48 millions m³ of water in the Reyran river valley down to the town of Frejus and the Mediterranean sea. Data available thanks to the CADAM EU-project are used to assess the results. [less ▲]

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See detailComputation of the sensitivity matrix used for Elasto-plastic material parameter identification by inverse methods
Cooreman, Steven; Bouffioux, Chantal ULg; Lecompte, David et al

in Congress on theoretical and applied Mechanics, Mons, Belgium, May 2006 (2006)

Inverse methods offer a powerful tool for the determination of the elasto-plastic material properties. Contrary to standard tests, these methods can deal with heterogeneous stress and strain-fields which ... [more ▼]

Inverse methods offer a powerful tool for the determination of the elasto-plastic material properties. Contrary to standard tests, these methods can deal with heterogeneous stress and strain-fields which have a larger information contents and hence allow the simultaneous identification of several material parameters. Moreover, it is expected that the obtained material parameters are more accurate, since these heterogeneous deformation fields are much closer to those occurring in real (metal) forming operations. The principle of the inverse method for the identification of material parameters presented in this paper is to compare an experimentally measured strain field to that computed by a Finite Element (FE) model. The material parameters in the FE model are iteratively tuned in such a way that both strain fields match each other as closely as possible. One of the building blocks in this identification procedure is the updating algorithm for the material parameters in the FE model. The key problem of this updating algorithm is the determination of the sensitivity matrix, which expresses the sensitivities of the strains with respect to the material parameters. This paper presents an analytical method for the calculation of this sensitivity matrix in case of simple tensile tests. [less ▲]

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See detailComputation of worst operation scenarios under uncertainty for static security management
Capitanescu, Florin; Wehenkel, Louis ULg

in IEEE Transactions on Power Systems (2013), 28(2), 1697-1705

This paper deals with day-ahead static security assessment with respect to a postulated set of contingencies while taking into account uncertainties about the next day system conditions. We propose a ... [more ▼]

This paper deals with day-ahead static security assessment with respect to a postulated set of contingencies while taking into account uncertainties about the next day system conditions. We propose a heuristic approach to compute the worst-case under operation uncertainty for a contingency with respect to overloads. We formulate this problem as a non-convex nonlinear bilevel program that we solve approximately by a heuristic approach which relies on the solution of successive optimal power flow (OPF) and security-constrained optimal power flow (SCOPF) problems of a special type. The method aims at revealing those combinations of uncertainties and contingencies for which the best combination of preventive and corrective actions would not suffice to ensure security. Extensive numerical results on a small, a medium, and a very large system prove the interest of the approach. [less ▲]

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See detailComputational advances in quasi-optimal domain decomposition methods for time-harmonic electromagnetic wave problems
Marsic, Nicolas ULg; Vion, Alexandre ULg; Geuzaine, Christophe ULg

Conference (2015)

In this talk we will present recent advances in the construction of quasi-optimal domain decomposition methods for time-harmonic electromagnetic wave problems. In particular, we will discuss the parallel ... [more ▼]

In this talk we will present recent advances in the construction of quasi-optimal domain decomposition methods for time-harmonic electromagnetic wave problems. In particular, we will discuss the parallel implementation and computational efficiency of sweeping-type preconditioners, as well as the use of high order finite element discretizations, potentially mixing orders for the volume and interface formulations. Results on several large scale test cases will be analysed. [less ▲]

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See detailComputational benchmarking for ultrafast electron dynamics: wavefunction methods vs density functional theory
Oliveira, Micael J. T.; Mignolet, Benoît ULg; Kus, Tomasz et al

in Journal of Chemical Theory and Computation (2015), 11

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See detailComputational biology — Modeling of primary blast effects on the central nervous system
Moore, David; Jérusalem, Antoine; Nyen, Michelle et al

in NeuroImage (2009), 47(Sup. 2), 10-20

Objectives Recent military conflicts in Iraq and Afghanistan have highlighted the wartime effect of traumatic brain injury. The reason for the prominence of TBI in these particular conflicts as opposed to ... [more ▼]

Objectives Recent military conflicts in Iraq and Afghanistan have highlighted the wartime effect of traumatic brain injury. The reason for the prominence of TBI in these particular conflicts as opposed to others is unclear but may result from the increased survivability of blast due to improvements in body armor. In the military context blunt, ballistic and blast effects may all contribute to CNS injury, however blast in particular, has been suggested as a primary cause of military TBI. While blast effects on some biological tissues, such as the lung, are documented in term of injury thresholds, this is not the case for the CNS. We hypothesized that using bio-fidelic models, allowing for fluid-solid interaction and basic material properties available in the literature, that a blast wave would interact with CNS tissue and cause a possible concussive effect. Methods The blast shockwave on CNS tissue was modeled using a coupled computational fluid-solid dynamic simulation. The model included a complex finite element mesh of the head and intra-cranial contents. The effects of threshold and 50% lethal blast lung injury were compared with concussive impact injury using the full head model allowing know upper and lower bounds of tissue injury to be applied using pulmonary injury as the reference tissue. Results The effects of a 50% lethal dose blast lung injury (LD50) were comparable with concussive impact injury using the DVBIC – MIT full head model. Interpretation CNS blast concussive effects were found to be similar between impact mild TBI and the blast field associated with LD50 lung blast injury sustained without personal protective equipment. With the ubiquitous use of personal protective equipment this suggests that blast concussive effects may more readily occur in personnel due to enhanced survivability in the current conflicts. [less ▲]

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