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Model Scale (model + scale)

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Engineering40%

Selected Abstracts

SCALES: a large-scale assessment model of soil erosion hazard in Basse-Normandie (northern-western France)

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2010
P. Le Gouée
Abstract The cartography of erosion risk is mainly based on the development of models, which evaluate in a qualitative and quantitative manner the physical reproduction of the erosion processes (CORINE, EHU, INRA). These models are mainly semi-quantitative but can be physically based and spatially distributed (the Pan-European Soil Erosion Risk Assessment, PESERA). They are characterized by their simplicity and their applicability potential at large temporal and spatial scales. In developing our model SCALES (Spatialisation d'éChelle fine de l'ALéa Erosion des Sols/large-scale assessment and mapping model of soil erosion hazard), we had in mind several objectives: (1) to map soil erosion at a regional scale with the guarantee of a large accuracy on the local level, (2) to envisage an applicability of the model in European oceanic areas, (3) to focus the erosion hazard estimation on the level of source areas (on-site erosion), which are the agricultural parcels, (4) to take into account the weight of the temporality of agricultural practices (land-use concept). Because of these objectives, the nature of variables, which characterize the erosion factors and because of its structure, SCALES differs from other models. Tested in Basse-Normandie (Calvados 5500,km2) SCALES reveals a strong predisposition of the study area to the soil erosion which should require to be expressed in a wet year. Apart from an internal validation, we tried an intermediate one by comparing our results with those from INRA and PESERA. It appeared that these models under estimate medium erosion levels and differ in the spatial localization of areas with the highest erosion risks. SCALES underlines here the limitations in the use of pedo-transfer functions and the interpolation of input data with a low resolution. One must not forget however that these models are mainly focused on an interregional comparative approach. Therefore the comparison of SCALES data with those of the INRA and PESERA models cannot result on a convincing validation of our model. For the moment the validation is based on the opinion of local experts, who agree with the qualitative indications delivered by our cartography. An external validation of SCALES is foreseen, which will be based on a thorough inventory of erosion signals in areas with different hazard levels. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Gelifluction: viscous flow or plastic creep?

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2003
Charles Harris
Abstract This paper reports results from two scaled centrifuge modelling experiments, designed to simulate thaw-related geli,uction. A planar 12° prototype slope was modelled in each experiment, using the same natural ,ne sandy silt soil. However two different scales were used. In Experiment 1, the model scale was 1/10, tested in the centrifuge at 10 gravities (g) and in Experiment 2, the scale was 1/30, tested at 30 g. Centrifuge scaling laws indicate that the time scaling factor for thaw consolidation between model and prototype is N2, where N is the number of gravities under which the model was tested. However, the equivalent time scaling for viscous ,ow is 1/1. If geli,uction is a viscosity-controlled ,ow process, scaling con,icts will therefore arise during centrifuge modelling of thawing slopes, and rates of displacement will not scale accurately to the prototype. If, however, no such scaling con,icts are observed, we may conclude that geli,uction is not controlled by viscosity, but rather by elasto-plastic soil deformation in which frictional shear strength depends on effective stress, itself a function of the thaw consolidation process. Models were saturated, consolidated and frozen from the surface downwards on the laboratory ,oor. The frozen models were then placed in the geotechnical centrifuge and thawed from the surface down. Each model was subjected to four freeze,thaw cycles. Soil temperatures and pore water pressures were monitored, and frost heave, thaw settlement and downslope displacements measured. Pore water pressures, displacement rates and displacement pro,les re,ecting accumulated shear strain, were all similar at the two model scales and volumetric soil transport per freeze,thaw cycle, when scaled to prototype, were virtually identical. Displacement rates and pro,les were also similar to those observed in earlier full-scale laboratory ,oor experiments. It is concluded therefore that the modelled geli,uction was not a time-dependent viscosity-controlled ,ow phenomenon, but rather elasto-plastic in nature. A ,rst approximation ,,ow' law is proposed, based on the ,Cam Clay' constitutive model for soils. Copyright © 2003 John Wiley & Sons, Ltd. [source]

An investigation of pulsatile flow in a model cavo-pulmonary vascular system

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 11 2009
K. Chitra
Abstract The complexities in the flow pattern in a cavo-pulmonary vascular system,after application of the Fontan procedure in the vicinity of the superior vena cava, inferior vena cava, and the confluence at the T-junction,are analysed. A characteristic-based split (CBS) finite element scheme involving the artificial compressibility approach is employed to compute the resulting flow. Benchmarking of the CBS scheme is carried out using standard problems and with the flow features observed in an experimental model with the help of a dye visualization technique in model scale. The transient flow variations in a total cavo-pulmonary connection (TCPC) under pulsatile conditions are investigated and compared with flow visualization studies. In addition to such qualitative flow investigations, quantitative analysis of energy loss and haemodynamic stresses have also been performed. The comparisons show good agreement between the numerical and experimental flow patterns. The numerically predicted shear stress values indicate that the pulsatile flow condition is likely to be more severe than steady flow, with regard to the long-term health of the surgically corrected TCPC. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Gelifluction: viscous flow or plastic creep?

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2003
Charles Harris
Abstract This paper reports results from two scaled centrifuge modelling experiments, designed to simulate thaw-related geli,uction. A planar 12° prototype slope was modelled in each experiment, using the same natural ,ne sandy silt soil. However two different scales were used. In Experiment 1, the model scale was 1/10, tested in the centrifuge at 10 gravities (g) and in Experiment 2, the scale was 1/30, tested at 30 g. Centrifuge scaling laws indicate that the time scaling factor for thaw consolidation between model and prototype is N2, where N is the number of gravities under which the model was tested. However, the equivalent time scaling for viscous ,ow is 1/1. If geli,uction is a viscosity-controlled ,ow process, scaling con,icts will therefore arise during centrifuge modelling of thawing slopes, and rates of displacement will not scale accurately to the prototype. If, however, no such scaling con,icts are observed, we may conclude that geli,uction is not controlled by viscosity, but rather by elasto-plastic soil deformation in which frictional shear strength depends on effective stress, itself a function of the thaw consolidation process. Models were saturated, consolidated and frozen from the surface downwards on the laboratory ,oor. The frozen models were then placed in the geotechnical centrifuge and thawed from the surface down. Each model was subjected to four freeze,thaw cycles. Soil temperatures and pore water pressures were monitored, and frost heave, thaw settlement and downslope displacements measured. Pore water pressures, displacement rates and displacement pro,les re,ecting accumulated shear strain, were all similar at the two model scales and volumetric soil transport per freeze,thaw cycle, when scaled to prototype, were virtually identical. Displacement rates and pro,les were also similar to those observed in earlier full-scale laboratory ,oor experiments. It is concluded therefore that the modelled geli,uction was not a time-dependent viscosity-controlled ,ow phenomenon, but rather elasto-plastic in nature. A ,rst approximation ,,ow' law is proposed, based on the ,Cam Clay' constitutive model for soils. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Providing and verifying advanced IP services in hierarchical DiffServ networks-the case of GEANT

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2004
Athanassios Liakopoulos
Abstract The differentiated services (DiffServ) framework is widely proposed as an efficient method for providing advanced IP services to large-scale networks, with QoS requirements. However, the provisioning of such services in production networks has proved to be more difficult than initially expected, in defining, setting and verifying appropriate Service Level Agreements (SLAs). GEANT, the Gigabit core pan-European research network, on a pilot basis introduced ,Premium IP' service, offering bounded delay and negligible packet loss to the European National Research & Education Networks (NRENs) that it interconnects. However, large scale provisioning of this new service requires the definition of efficient interaction procedures between administrative domains involved and methods for SLA monitoring. This paper focuses on these issues and presents the experience acquired from the early experiments in GEANT, as an example of hierarchical Gigabit multi-domain environment, enabled with QoS provisioning to its constituent NRENs. This model scales more efficiently than the common peering Internet Service provider (ISP) commercial paradigm. Finally, we outline other options that promise QoS, such as Layer 2 VPNs in MPLS backbones, with non-standard (yet) mechanisms. Copyright © 2004 John Wiley & Sons, Ltd. [source]