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See detailModelling of the squeeze film air damping in MEMS
Barroso, Juan José Gómez; Bruls, Olivier ULg; Berli, Claudio et al

in Proceedings of the ENIEF Conference (2009)

We propose a formulation for modeling the squeeze film air damping in micro-plates typical of micro-electromechanical devices for micro switch applications. A special finite element is developed, in which ... [more ▼]

We propose a formulation for modeling the squeeze film air damping in micro-plates typical of micro-electromechanical devices for micro switch applications. A special finite element is developed, in which the nonlinear Reynolds equation for compressible film is used to analyze the air pressure field, whereas a standard linear elastic model is used for the displacement field. The formulation is based on a finite element discretization of both the pressure and displacement fields. The coupled equations of motion are established and, for harmonic oscillations, we show that the resulting damping matrix depends on the frequency. The typical dimensions and properties of the MEMS device are in the order of hundred micrometers length and some micrometers (3-8 micrometers) thick, with a separation from the substrate of also some micrometers (e.g. 3-5 micrometers). For these dimensions, the influence of damping owing to the surrounding air cannot be neglected, having an important contribution to the quality factor of the device. The influence of plate holes, which are necessary because of the fabrication process, determines also the dynamic behavior of the plate. Examples are presented, with comparisons to results of the bibliography. [less ▲]

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See detailModelling of the squeeze film air damping in MEMS
Bruls, Olivier ULg

Report (2008)

This document proposes a formulation of the squeeze film air damping in micro-plates. The nonlinear Reynolds equation for compressible film is used to analyze the air pressure field, whereas a standard ... [more ▼]

This document proposes a formulation of the squeeze film air damping in micro-plates. The nonlinear Reynolds equation for compressible film is used to analyze the air pressure field, whereas a standard linear elastic model is used for the displacement field. The formulation is based on a finite element discretization of both the pressure and displacement fields. The coupled equations of motion are established and, for harmonic oscillations, we show that the resulting damping matrix depends on the frequency. [less ▲]

Detailed reference viewed: 33 (5 ULg)
Peer Reviewed
See detailModelling of the underground coal gasification process at Thulin on the basis of thermodynamical equilibria and isotopic measurements
Dufaux, Anne; Gaveau, Bénédicte; Létolle, René et al

in Fuel (1990), 69

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See detailModelling of the Unsaturated Flow in Porous Media; Handling of the 3D Behaviour with uncoupled 1DV/2DH Richards Equations
Paulus, Raphaël ULg; Dewals, Benjamin ULg; Erpicum, Sébastien ULg et al

in Proceedings of the 5th International Confrence on Advanced Computational Methods in Engineering (2011, November)

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See detailModelling of the wave propagation, the coastal currents and the induced topographic changes
Fraikin, Catherine; Archambeau, Pierre ULg; Erpicum, Sébastien ULg et al

in Proceedings of the 9th International Symposium on River Sedimentation (2004)

This paper models the sea bottom evolution. This model is built up on three main parts. The first one describes the wave propagation, taking simultaneously into account the refraction, the diffraction and ... [more ▼]

This paper models the sea bottom evolution. This model is built up on three main parts. The first one describes the wave propagation, taking simultaneously into account the refraction, the diffraction and the reflection but also the energy dissipation caused by wave breaking. This model is solved by the numerical method of the finite volumes, using an iterative resolution (the GMRES method). Several validations of this model have been carried out on many examples such as harbors of various geometries and depths, beaches,… The wave induced currents are computed in the second part based on the concept of the radiation stresses describing the excess of the flux momentum caused by the waves. A model based on the complete Navier-Stokes equations integrated on the depth and associated with appropriated forcing and friction terms is used. This model is computed as an update of WOLF software (HACH, ULg) and is applied to some examples such as beaches with or without coastal structures. Finally, the third part is about the sediment transport. It exhibits the topographic modifications of the coastal sea bottom caused by the waves and their currents. A loop execution of these three models ends this work. It gives us an operational tool to describe the topographic evolution of the coastal areas caused by the incident waves, the induced currents and then the resulting sediment transport, fulfilling the objectives of this paper. [less ▲]

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See detailModelling of uses microorganisms in the degradation of natural polymers.
Thonart, Philippe ULg; Cotes, A. M.; Campos, D. et al

in Production and utilization of lignocellulosics (1991)

Detailed reference viewed: 8 (1 ULg)
See detailModelling on Multiple Scales
Bullinger, Eric ULg

Scientific conference (2012, June 19)

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See detailModelling phytoplankton succession and nutrient transfer along the Scheldt estuary (Belgium, The Netherlands)
Gypens, N.; Delhez, Eric ULg; Vanhoutte-Brunier, A. et al

in Journal of Marine Systems (2013), 128

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See detailModelling plant diseases impact with the Belgium Crop Growth Monitoring System.
El Jarroudi, Moussa ULg; Kouadio, Amani Louis ULg; Martin, Bertrand ULg et al

in Wery, Jacque; Shili-Touzi, I.; Perrin, A. (Eds.) PROCEEDING OF AGRO2010 the XIth ESA Congress (2010, September)

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See detailModelling rapidly rotating stars
Reese, Daniel ULg

in Journal of Physics: Conference Series (2008, October 01), 118

Recent interferometric observations have drawn attention to the effects of rapid rotation on stellar structure. Consequently, a number of 2D models and pulsation codes have been and are being developed in ... [more ▼]

Recent interferometric observations have drawn attention to the effects of rapid rotation on stellar structure. Consequently, a number of 2D models and pulsation codes have been and are being developed in order to gain a better understanding of such stars. These have shed light on effects like centrifugal deformation, gravity darkening, differential rotation and the transport of chemical elements and angular momentum. Pulsation modes within these stars have a different geometrical structure, characterised by a new organisation of the frequency spectrum, as shown by eigenmode calculations and ray dynamics. [less ▲]

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See detailModelling realized niche of metallophyte species along copper and cobalt gradients on Katanga copper hills
Boisson, Sylvain ULg; Seleck, Maxime ULg; Guillaume, Arielle et al

Poster (2012, February 10)

In South Central Africa were identified more than 650 plant species tolerant to heavy metals, several of which endemic to Katanga and critically endangered by mining activities. These metallophyte are ... [more ▼]

In South Central Africa were identified more than 650 plant species tolerant to heavy metals, several of which endemic to Katanga and critically endangered by mining activities. These metallophyte are distributed over a hundred hills containing high copper and cobalt concentrations (20 to 10000 mg/kg for copper and 2 to 1000 mg/kg for cobalt). To understand the response of metallophyte to heavy metals, the ecological niches of 80 cupro-cobaltophytes were modeled with general additive models (GAM). Results show that (1) three groups of species were identified according to their optimum along a metal concentrations gradient and (2) a positive relationship exists between niche amplitude and optimum copper concentration. [less ▲]

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See detailModelling Route Choice Decisions of Car Travellers Using Combined GPS and Diary Data
Ramaekers, Katrien; Reumers, Sofie; Wets, Geert et al

in Networks & Spatial Economics (2013), 13(3), 351-372

The aim of this research is to identify the relationship between activity patterns and route choice decisions. The focus is twofold: on the one hand, the relationship between the purpose of a trip and the ... [more ▼]

The aim of this research is to identify the relationship between activity patterns and route choice decisions. The focus is twofold: on the one hand, the relationship between the purpose of a trip and the road categories used for the relocation is investigated; on the other hand, the relationship between the purpose of a trip and the deviation from the shortest path is studied. The data for this study were collected in 2006 and 2007 in Flanders, the Dutch speaking and northern part of Belgium. To estimate the relationship between the primary road category travelled on and the corresponding activity-travel behaviour a multinomial logit model is developed. To estimate the relationship between the deviation from the shortest path and the corresponding activity-travel behaviour a Tobit model is developed. The results of the first model point out that route choice is a function of multiple factors, not just travel time or distance. Crucial for modelling route choices or in general for traffic assignment procedures is the conclusion that activity patterns have a clear influence on the road category primarily driven on. Particularly, it was shown that the likelihood of taking primarily through roads is highest for work trips and lowest for leisure trips. The second model shows a significant relationship between the deviation from the shortest path and the purpose of the trip. Furthermore, next to trip-related attributes (trip distance), also socio-demographic variables and geographical differences play an important role. These results certainly suggest that traffic assignment procedures should be developed that explicitly take into account an activity-based segmentation. In addition, it was shown that route choices were similar during peak and off-peak periods. This is an indication that car drivers are not necessarily utility maximizers, or that classical utility functions in the context of route choices are omitting important explanatory variables. [less ▲]

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See detailModelling seasonal variations in nitrate and sulphate concentrations in a vulnerable alluvial aquifer
Peeters, Luk; Haerens, Bruno; Van der Sluys, Jan et al

in Environmental Geology (2004), 46(6-7), 951-961

The Eisden-Meeswijk region in Belgium has been affected by mining subsidence due to the deep coal mining activities. Groundwater levels in the alluvial plain of the Meuse River are maintained below the ... [more ▼]

The Eisden-Meeswijk region in Belgium has been affected by mining subsidence due to the deep coal mining activities. Groundwater levels in the alluvial plain of the Meuse River are maintained below the ground surface by drainage installations and municipal well fields. A correlation between the water level in the Meuse River and the variation in nitrate and sulphate concentrations in the aquifer has been observed. A transient groundwater model is developed for the period May 1998-May 2002 and advective transport simulations have been carried out using this model. During dry periods, the major groundwater flow is directed towards the Meuse River, thereby feeding the river. During wet periods, however, groundwater flows in the opposite direction. Due to these variations in groundwater flow direction and to the extraction of groundwater, zones of higher solute concentration exist of which the position and extension vary both spatially and temporally. [less ▲]

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See detailModelling sediment transport over partially non-erodible bottoms
Rulot, François ULg; Dewals, Benjamin ULg; Erpicum, Sébastien ULg et al

in International Journal for Numerical Methods in Fluids (2012), 70(2), 186-199

In depth- and cross section-averaged morphodynamic models, based on explicit time integration, it may happen that the computed bed level becomes lower than the top level of a non-erodible layer (e.g ... [more ▼]

In depth- and cross section-averaged morphodynamic models, based on explicit time integration, it may happen that the computed bed level becomes lower than the top level of a non-erodible layer (e.g. concrete, bedrock or armoured layer). This is a standard pitfall which has been addressed in different ways. In this paper, we present an original approach for avoiding computation of non-physical bed levels, using an iterative procedure to correct the outward sediment fluxes. The procedure is shown to be computationally efficient while it achieves a high accuracy in terms of mass conservation. We compare our original approach with the existing Struiksma’s method and with a reformulation of the problem in terms of mathematical optimization of a linear or non-linear objective function under linear constraints. The new procedure has been incorporated into an existing finite volume morphodynamic model. It has been validated with several 1D benchmarks leading to configurations with sediment transport over non-erodible bottom. The computation time has been verified not to increase by more than 15% compared to runs without non-erodible bottom. [less ▲]

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See detailModelling seed dispersal and tropical forest regeneration :application to Staudtia kamerunensis in the WWF Lake Tele-Tumba Landscape in DR Congo
Coos, William ULg; Dury, Marie ULg; Trolliet, Franck ULg et al

Poster (2014, June)

Unsustainable hunting and slash-and-burn farming in tropical forests can lead to the empty forest syndrome. It is characterized by the loss of key species essential in the maintenance and regeneration of ... [more ▼]

Unsustainable hunting and slash-and-burn farming in tropical forests can lead to the empty forest syndrome. It is characterized by the loss of key species essential in the maintenance and regeneration of the forest. Indeed the main mechanism of this regeneration is seed dispersal, which for tropical trees is usually driven by animals, and the alteration of this process through a reduction of the disperser population may have serious consequences on forest composition. Computer models are powerful tools to study these processes, not only towards a better understanding of the key mechanisms controlling tropical forest regeneration, but also with the aim of optimising forest management and exploitation to reach a better equilibrium between tropical tree species and their seed dispersers. This study describes a seed dispersal module ultimately developed to analyze the regeneration of the rainforest in the WWF Lake Tele – Lake Tumba Landscape in RD Congo (BIOSERF project funded by Belgian Science Policy). The module has been developed to upgrade the CARAIB dynamic vegetation model, which is used in the BIOSERF project. Data are derived from a field study in which we analyzed seed dispersal of a common tree species (Staudtia kamerunensis) and we determined the community of its main dispersers (largely dominated by the hornbill Bycanistes albotibialis). Additional data (density of S. kamerunensis, habitat use and retention time in the digestive tract of hornbills to simulate dispersal kernel) were obtained from literature and satellite images. Different simulations were performed to represent seed rain over time and a survival rate was applied to show the regeneration. The module was able to provide a percentage of recolonization of degraded places. In the end, this result was compared to field studies, which provide close percentage of recolonization [less ▲]

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See detailModelling serial offenders’ spatial behaviours: new assumptions for geographic profiling
Trotta, Marie ULg

Doctoral thesis (2014)

The geographic profiling is amethodology of investigation which uses the crime sites of a criminal series in order to delineate prior areas for searching the offender. Its implementation is currently ... [more ▼]

The geographic profiling is amethodology of investigation which uses the crime sites of a criminal series in order to delineate prior areas for searching the offender. Its implementation is currently limited by too simplistic assumptions that are difficult to assess during an investigation or even not corroborated at an individual level of observation. This thesis studies the predictive capacities of geographic profiling in the context of Belgium, a dense country where the road network is not suitable for classical algorithmimplemented with Euclidean or Manhattan distances. More precisely, the thesis has for first objective to integrate space anisotropy with two improvements: (1) the integration of the road network in the journey-to-crime and (2) the integration of the structure of opportunities for series of sexual offences. Beyond this objective, the thesis questions a hypothesis underlying this type of research methodology: the kind of spatial relationship between the offender’s residence and the crime sites. An alternative to the distance decay effect is developed, minimising the variance in travelled distances between the offender anchor point and the initial contact sites of the offences (MOV hypothesis). The sensitivity of this methodology is measured and its effectiveness is compared to the one of the distance decay effect. A major result of the thesis is that the share of behaviours than can be modelled by this new hypothesis is similar to the one of the distance decay effect. However, a large number of series did not meet the required conditions to implement an efficientmethodology given the multiplicity of offender’s residences or the scarcity of sites composing the series; those applicability criteria are analysed in this work. Nevertheless, theMOV hypothesis is particularly valuable for long series of offences. Then, the thesis analyses the impact of the geometry of crime series locations on the effectiveness of the chosen spatial assumption (distance decay effect orMOV) with graph theory. It highlights the superiority of the MOV hypothesis for offenders travelling in some preferred direction. The analysis also shows that both hypotheses are not mutually exclusive but can be combined to build offender geographic profiles. Finally, this thesis focuses on the modelling of neutral areas in terms of criminal attractiveness on the Belgian territory. The work presents the originality of analysing data on a whole country, integrating both urban and non-urban areas. The objective of the modelling is the integration of the opportunity structure of sexual offences in the geographic profile and the estimation of the perturbing effect of a differentiated attractiveness. In order to assess this perturbation, we propose a two-steps process. Firstly, a regression model combining factors fromthe crime pattern and social disorganisation theories models the spatial distribution of crimes. The regression model identifies a centre-periphery relationship in the spatial distribution of crime locations. Still, the model underestimates the number of positive sectors, omitting some attractors. Then, the impact of attractive location (i.e. presenting the favourable factors for crime concentration)is evaluated for the series of sexual offences. In fine, the two spatial hypotheses do not seem affected by the attractors identified by the modelling except when the contact sites are clustered in attractive areas. In addition, the share of serial offenders committing their offences in the most attractive locations is smaller than that of single offenders. This observation strengthens the need for working on spatial distribution models instead of calibrated functions with solved cases. [less ▲]

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