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See detailAn energy momentum conserving algorithm using the variational formulation of visco-plastic updates
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

in International Journal for Numerical Methods in Engineering (2006), 65(6), 904942

In this paper we use the variational formulation of elasto-plastic updates proposed by Ortiz and Stainier (Comput. Methods Appl. Mech. Eng. 1999; 171:419-444) in the context of consistent time integration ... [more ▼]

In this paper we use the variational formulation of elasto-plastic updates proposed by Ortiz and Stainier (Comput. Methods Appl. Mech. Eng. 1999; 171:419-444) in the context of consistent time integration schemes. We show that such a formulation is well suited to obtain a general expression Of energy momentum conserving algorithms. Moreover, we present numerical examples that illustrate the efficiency of our developments. Copyright (c) 2005 John Wiley [less ▲]

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See detailEnergy Partitioning Between Latent And Sensible Heat Flux During The Warm Season At Fluxnet Sites
Wilson, Kell B.; Baldocchi, Dennis D.; Aubinet, Marc ULg et al

in Water Resources Research (2002), 38(12),

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See detailThe Energy Perspective of Bioclimatic Buildings in North-East India
Singh, Manoj Kumar ULg; Mahapatra, Sadhan

in Energy Manager (2009), 2(5), 34-41

The level of thermal comfort greatly affects human’s physical as well as psychological health. Climate control is of prime importance as it involves maintaining comfortable conditions inside the building ... [more ▼]

The level of thermal comfort greatly affects human’s physical as well as psychological health. Climate control is of prime importance as it involves maintaining comfortable conditions inside the building. In parallel, the energy cost of maintaining comfort conditions will rise. Therefore it is desirable to design climate-responsive buildings by incorporating appropriate solar passive features. [less ▲]

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See detailEnergy Plantage, Leeuwarden: Look and feel
Attia, Shady ULg; Huffschmid, Daniel

in Dam, van,, F.; Noorman (Eds.) Grounds for Change:Bridging energy Planning and spatial design strategies (2005)

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See detailEnergy requirements and solar availability in suburban areas: the influence of built density in an existing district
Marique, Anne-Françoise ULg; De Meester, Tatiana; Reiter, Sigrid ULg

in Proceedings of the International Conference CISBAT 2011 - Clean Tech for sustainable buildings - From Nano to urban scale (2011) (2011, September)

Although the environmental impacts of urban sprawl and their associated energy consumptions are now well documented, it remains a concern in many regions. In the current context of growing interest in ... [more ▼]

Although the environmental impacts of urban sprawl and their associated energy consumptions are now well documented, it remains a concern in many regions. In the current context of growing interest in environmental issues, local authorities become aware of this concern and are now trying to limit the development of new low-density suburban districts while households still continue to promote dispersed individual housing types located outside city centres. In this context, the paper proposes to investigate the influence of an increase in built density, in existing suburban neighbourhoods. The idea is to favour a higher built density in existing neighbourhoods instead of building new low-density neighbourhoods on unbuilt areas. The impacts of four renewal strategies dealing with the density are assessed, at the neighbourhood scale, for three indicators: (1) the potential energy savings for heating houses, (2) the solar energy received by the facades and roofs, as dispersed individual housing types are known to be those that receive most solar gains and (3) the potential area of land savings. [less ▲]

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See detailEnergy requirements for growth in young tortoises (Testudo hermanni boettgeri Mojsisovic 1889)
Justet, Delphine; Rotat, Christelle; Lhoest, Estelle et al

in Iben, C. (Ed.) Proceedings of the 12th ESVCN Congress (2008)

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See detailEnergy requirements of characteristic urban blocks
Maïzia, Mindjid; Sèze, Claire; Berge, Sébastien et al

in Proc. of CISBAT 2009 - Renewables in a changing climate - From Nano to urban scale (2009, September)

The present article analyses energy requirements for heating and cooling typical urban blocks in the Region Ile de France. The analysis has been designed to be applicable at the agglomeration level in ... [more ▼]

The present article analyses energy requirements for heating and cooling typical urban blocks in the Region Ile de France. The analysis has been designed to be applicable at the agglomeration level in France through an automatic classification of urban blocks. It provides a contrasted view on the incidence of compactness and urban organisation upon energy requirements and potential solar gains. [less ▲]

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See detailEnergy savings in methanol synthesis: Use of heat integration techniques and simulation tools.
Maréchal, François; Heyen, Georges ULg; Kalitventzeff, Boris ULg

in Computers & Chemical Engineering (1997), 21(Suppl. S), 511-516

Starting with a classical process for producing methanol using the reforming and synthesis steps, a combined approach applying simulation models and a new synthesis strategy, named Effect Modelling and ... [more ▼]

Starting with a classical process for producing methanol using the reforming and synthesis steps, a combined approach applying simulation models and a new synthesis strategy, named Effect Modelling and Optimisation (EMO), has been used to optimise the energy efficiency of the process. The method allows to identify different ways of improving the energy efficiency of the process. The modifications concern the synthesis reactor and the reforming reactor designs, the exploitation of the purge stream as fuel gas to satisfy the process requirement and its integration to a gas turbine system. The EMO approach allows to target the impact of a process modification at the global level of the energy cost of the process, including the combined production of heat and mechanical power in a gas turbine and the steam network. Starting with a classical methane conversion of 60% for the classical system, we identify solutions with up to 93% of the overall methane conversion when we transform the net mechanical power produced into methane savings at the country level. The interest of the approach is the possibility of computing the impact of the process modifications suggested by the analysis of the shape of the heat cascade on the overall energy balance of the plant without having to simulate in many details the steam and the heat exchanger network. [less ▲]

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See detailEnergy spectrum and point spread function comparison of pin-hole and parallel-hole collimators for 90Y bremsstrahlung imaging
Walrand, Stephan; Hesse, Michel; Seret, Alain ULg et al

Poster (2013, May 25)

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See detailThe energy the auroral electrons in Saturn's atmosphere : remote sensing and thermal consequences
Gérard, Jean-Claude ULg; Gustin, Jacques ULg; Grodent, Denis ULg et al

Poster (2011, October)

Saturn’s north aurora has been observed between January and May 2011 with the Hubble Space Telescope. The objective was to collect spatially resolved spectra at the different local time from dawn to dusk ... [more ▼]

Saturn’s north aurora has been observed between January and May 2011 with the Hubble Space Telescope. The objective was to collect spatially resolved spectra at the different local time from dawn to dusk and compare them with laboratory or synthetic spectra. For this purpose, HST was programmed to slew from mid-latitudes through the auroral oval up to above the limb while collecting data in the timetag mode. The spectra show signatures of absorption by hydrocarbons present above the peak of the auroral emission. The amount of absorption and implications in terms of penetration of the auroral electron beam into Saturn’s atmosphere will be discussed and compared with other determinations of the altitude of the aurora. The effects of the auroral heat import on the thermal structure of the atmosphere both at high and low altitudes will be examined in the light of these results. [less ▲]

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See detailEnergy Transfer and Dissipation in a Duffing Oscillator Coupled to a Nonlinear Attachment
Viguié, Régis ULg; Peeters, Maxime ULg; Kerschen, Gaëtan ULg et al

in Journal of Computational and Nonlinear Dynamics (2009), 4(4),

The dynamics of a two-degree-of-freedom nonlinear system consisting of a grounded Duffing oscillator coupled to an essentially nonlinear attachment is examined in the present study. The underlying ... [more ▼]

The dynamics of a two-degree-of-freedom nonlinear system consisting of a grounded Duffing oscillator coupled to an essentially nonlinear attachment is examined in the present study. The underlying Hamiltonian system is first considered, and its nonlinear normal modes are computed using numerical continuation and gathered in a frequency-energy plot. Based on these results, the damped system is then considered, and the basic mechanisms for energy transfer and dissipation are analyzed. [DOI: 10.1115/1.3192130] [less ▲]

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See detailAn energy transfer study of homopolymer localization in block copolymers
Rharbi, Yahya; Zhang, Jian-Xin; Spiro, John G et al

in Macromolecules (2003), 36(4), 1241-1252

We have investigated the localization of homopolystyrene (hPS) in its blends with poly(styrene-b-butyl methacrylate) (PS-b-PBMA), at 140 degreesC, measuring the quantum efficiency of direct energy ... [more ▼]

We have investigated the localization of homopolystyrene (hPS) in its blends with poly(styrene-b-butyl methacrylate) (PS-b-PBMA), at 140 degreesC, measuring the quantum efficiency of direct energy transfer (Phi(ET) of DET) between hPS randomly labeled with phenanthrene moieties and PS-b-PBMA labeled at the junction with anthracene. The molecular weight of hPS was similar to the molecular weight of the PS block of PS-b-PBMA, and the hPS content was kept to a maximum of 26 vol %, to preserve the lamellar morphology of PS-b-PBMA. We have found very low rates of DET, which implies that hPS is almost totally localized between the PS brushes of PS-b-PBMA. In addition to the experimental measurements, we also calculated Phi(ET) values by simulating fluorescence decay curves, based on Vavasour and Whitmore's numerical self-consistent-field (NSCF) formalism. The latter theory confirmed that we were dealing with a "dry brush" situation, but the NSCF results suggested a higher level of penetration of hPS than the experiments. We attribute this discrepancy to uncertainties about inputs to the simulations, particularly the Flory-Huggins chi parameter and the Kuhn length for the PBMA block. [less ▲]

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See detailEnergy transfers in a system of two coupled oscillators with essential nonlinearity: 1 : 1 resonance manifold and transient bridging orbits
Kerschen, Gaëtan ULg; Vakakis, Alexander F.; Lee, Young S. et al

in Nonlinear Dynamics (2005), 42(3), 283-303

The purpose of this study is to highlight and explain the vigorous energy transfers that may take place in a linear oscillator weakly coupled to an essentially nonlinear attachment, termed a nonlinear ... [more ▼]

The purpose of this study is to highlight and explain the vigorous energy transfers that may take place in a linear oscillator weakly coupled to an essentially nonlinear attachment, termed a nonlinear energy sink. Although these energy exchanges are encountered during the transient dynamics of the damped system, it is shown that the dynamics can be interpreted mainly in terms of the periodic orbits of the underlying Hamiltonian system. To this end, a frequency-energy plot gathering the periodic orbits of the system is constructed which demonstrates that, thanks to a 1:1 resonance capture, energy can be irreversibly and almost completely transferred from the linear oscillator to the nonlinear attachment. Furthermore, it is observed that this nonlinear energy pumping is triggered by the excitation of transient bridging orbits compatible with the nonlinear attachment being initially at rest, a common feature in most practical applications. A parametric study of the energy exchanges is also performed to understand the influence of the parameters of the nonlinear energy sink. Finally, the results of experimental measurements supporting the theoretical developments are discussed. [less ▲]

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See detailEnergy Transition from a Linear Oscillator to an Attached Mass through an Essential Nonlinearity
Quinn, D. Dane; Kerschen, Gaëtan ULg; Vakakis, Alexander F. et al

in 11th Nonlinear Vib., Stability and Dynamics of Structures Conf., Blacksburg, 2006 (2006)

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See detailEnergy Type Liapunov-like direct criteria for rapid transient stability analysis
Ribbens-Pavella, Mania; Van Cutsem, Thierry ULg; Dhifaoui, R. et al

Scientific conference (1985)

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See detailAn Energy-Based Variational Model of Ferromagnetic Hysteresis for Finite Element Computations
François-Lavet, Vincent ULg; Henrotte, François; Stainier, Laurent ULg et al

in Journal of Computational & Applied Mathematics (2013), 246

This paper proposes a macroscopic model for ferromagnetic hysteresis that is well-suited for finite element implementation. The model is readily vectorial and relies on a consistent thermodynamic ... [more ▼]

This paper proposes a macroscopic model for ferromagnetic hysteresis that is well-suited for finite element implementation. The model is readily vectorial and relies on a consistent thermodynamic formulation. In particular, the stored magnetic energy and the dissipated energy are known at all times, and not solely after the completion of closed hysteresis loops as is usually the case. The obtained incremental formulation is variationally consistent, i.e., all internal variables follow from the minimization of a thermodynamic potential. [less ▲]

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See detailThe energy-conserving and energy-dissipating processes in mitochondria isolated from wild type and nonripening tomato fruits during development on the plant.
Almeida, A.; Navet, R.; Jarmuszkiewicz, W. et al

in Journal of Bioenergetics & Biomembranes (2002), 34(6), 487-498

Bioenergetics of tomato (Lycopersicon esculentum) development on the plant was followed from the early growing stage to senescence in wild type (climacteric) and nonripening mutant (nor, non-climacteric ... [more ▼]

Bioenergetics of tomato (Lycopersicon esculentum) development on the plant was followed from the early growing stage to senescence in wild type (climacteric) and nonripening mutant (nor, non-climacteric) fruits. Fruit development was expressed in terms of evolution of chlorophyll a content allowing the assessment of a continuous time-course in both cultivars. Measured parameters: the cytochrome pathway-dependent respiration, i.e., the ATP synthesis-sustained respiration (energy-conserving), the uncoupling protein (UCP) activity-sustained respiration (energy-dissipating), the alternative oxidase(AOX)-mediated respiration (energy-dissipating), as well as the protein expression of UCP and AOX, and free fatty acid content exhibited different evolution patterns in the wild type and nor mutant that can be attributed to their climacteric/nonclimacteric properties, respectively. In the wild type, the climacteric respiratory burst observed in vitro depended totally on an increse in the cytochrome pathway activity sustained by ATP synthesis, while the second respiratory rise during the ripening stage was linked to a strong increase in AOX activity accompanied by an overexpression of AOX protein. In wild type mitochondria, the 10-microM linoleic acid-stimulated UCP-activity-dependent respiration remained constant during the whole fruit development except in senescence where general respiratory decay was observed. [less ▲]

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See detailAn Energy-Dissipative Momentum-Conserving Time Integration Algorithm for Viscoplastic Hyperelastic Models Based on the Variational Updates Framework
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

(2007)

Traditional time integration algorithms for finite-element discretization are numerically stable only for linear models. To overcome that drawback, a new class of "Energy Momentum Conserving Algorithms ... [more ▼]

Traditional time integration algorithms for finite-element discretization are numerically stable only for linear models. To overcome that drawback, a new class of "Energy Momentum Conserving Algorithms" or EMCA and ``Energy-Dissipative Momentum-Conserving'' or EDMC algorithms, verifying the conservation/dissipation laws in the non-linear range, was recently developed. They consist in a mid-point scheme with an adequate evaluation of the internal forces, which strongly assume the existence of an energy potential. Following the variational visco-plastic constitutive updates formalism, a general energy-dissipative momentum-conserving algorithm for hyperelastic-based formulation is proposed. The main feature of this variational formulation is that the stress tensor always derives from an incremental potential, even if plastic deformations occur, allowing to use it in the above integration algorithms. [less ▲]

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See detailEnergy-flux relationship in the FUV Jovian aurora deduced from HST-STIS spectral observations
Gustin, Jacques ULg; Gérard, Jean-Claude ULg; Grodent, Denis ULg et al

in Journal of Geophysical Research. Space Physics (2004), 109(A10),

[1] Far ultraviolet spectral observations of the Jovian aurora have been made since 1997 with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope at low spectral resolution ... [more ▼]

[1] Far ultraviolet spectral observations of the Jovian aurora have been made since 1997 with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope at low spectral resolution. The combination of the spectral resolution with the intensity variation along the STIS slit provides information on the latitudinal variation of the precipitating auroral electron energy flux and the mean electron energy, from which the electron current density at the top of the atmosphere can also be deduced. It is found that the mean electron energies associated with the main oval lie in the range 30 - 200 keV and show a tendency to increase with the precipitating energy flux. The current densities lie in the range similar to 0.04 - 0.4 muA m(-2), consistent with previous estimates, and are also positively correlated with the energy flux. The observed relationship between the auroral time-integrated energy fluxes and the electron energies in the main oval is compatible with that expected from Knight's theory of field-aligned currents. The best agreement between the observed data and the Knight curves is obtained for an electron temperature of T-e = 2.5 keV and a source density N = 0.003 cm(-3), that is within the range of values observed in the equatorial plane during the Voyager flybys. No systematic dependence of the electron energy with magnetic local time is found, but the morning sector around 0800 MLT shows greater variability than other regions of the oval. Analysis of time-tagged data shows that the main oval energy flux usually varies steadily over the several minute intervals of observation and that the mean electron energy usually undergoes correlated variations such that the current density remains relatively constant. It is shown that these overall properties are also consistent with Knight's theory of auroral electron acceleration associated with field-aligned current flow, from which it is inferred that the temporal variations observed are often due to slow changes in the magnetospheric "source'' electron parameters in the presence of near-steady magnetosphere-ionosphere coupling currents. By contrast, time-integrated emissions in the polar region are found to be associated with similar mean electron energies to the main oval but with typically smaller energy fluxes and current densities. Pressure balance arguments are advanced, which indicate that the brighter of these emissions must be associated with an auroral acceleration mechanism perhaps similar to that operative in the main oval, while it remains possible that the weaker emissions could result from precipitation from a quasi-isotropic hot magnetospheric electron source. [less ▲]

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