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Breugnot A.,EGIS Geotechnique | Breugnot A.,Grenoble Universites | Gotteland Ph.,Grenoble Universites | Villard P.,Grenoble Universites
Numerical Methods in Geotechnical Engineering - Proceedings of the 7th European Conference on Numerical Methods in Geotechnical Engineering | Year: 2010

This paper investigates modelling of granular material submitted to high energy impact due to block impact. An original combined discrete - continuum method is proposed which permits to use discrete element method to model precisely the complex behaviour of granular material in the vicinity of the impacted zonewhile a continuum approach is used in farther areas. Coupled methods proposed are validated through simple static and dynamic tests and, finally used to simulate high energy impact of a cubic impactant on a gravel layer. © 2010 Taylor & Francis Group, London.


Gast N.,CNRS Informatics Laboratory of Grenoble | Gast N.,Grenoble Universites | Gaujal B.,CNRS Informatics Laboratory of Grenoble | Gaujal B.,French Institute for Research in Computer Science and Automation
Theoretical Computer Science | Year: 2010

This paper studies infinite unordered d-ary trees with nodes labeled by {0, 1}. We introduce the notions of rational and Sturmian trees along with the definitions of (strongly) balanced trees and mechanical trees, and study the relations among them. In particular, we show that (strongly) balanced trees exist and coincide with mechanical trees in the irrational case, providing an effective construction. Such trees also have a minimal factor complexity, hence are Sturmian. We also give several examples illustrating the inclusion relations between these classes of trees. © 2009 Elsevier B.V. All rights reserved.


Artikis A.,Greek National Center For Scientific Research | Paliouras G.,Greek National Center For Scientific Research | Portet F.,Grenoble Universites | Skarlatidis A.,Greek National Center For Scientific Research | Skarlatidis A.,University of Aegean
Proceedings of the 4th ACM International Conference on Distributed Event-Based Systems, DEBS 2010 | Year: 2010

Today's organisations require techniques for automated transformation of the large data volumes they collect during their operations into operational knowledge. This requirement may be addressed by employing event recognition systems that detect activities/events of special significance within an organisation, given streams of 'low-level' information that is very difficult to be utilised by humans. Numerous event recognition systems have been proposed in the literature. Recognition systems with a logic-based representation of event structures, in particular, have been attracting considerable attention because, among others, they exhibit a formal, declarative semantics, they haven proven to be efficient and scalable, and they are supported by machine learning tools automating the construction and refinement of event structures. In this paper we review representative approaches of logic-based event recognition, and discuss open research issues of this field. © 2010 ACM.


Stanculescu L.,University of Lyon | Stanculescu L.,Grenoble Universites | Chaine R.,University of Lyon | Cani M.-P.,Grenoble Universites | And 2 more authors.
Computers and Graphics (Pergamon) | Year: 2013

Solid shape is typically segmented into surface regions to define the appearance and function of parts of the shape; these regions in turn use curve networks to represent boundaries and creases, and feature points to mark corners and other shape landmarks. Conceptual modeling requires these multi-dimensional nested structures to persist throughout the modeling process, an aspect not supported, up to now, in free-form sculpting systems. We present the first shape sculpting framework that preserves and controls the evolution of such nested shape features. We propose a range of geometric and topological behaviors (such as rigidity or mutability) applied hierarchically to points, curves or surfaces in response to a set of typical free-form sculpting operations, such as stretch, shrink, split or merge. Our method is illustrated within a free-form sculpting system for self-adaptive quasi-uniform polygon meshes, where geometric and topology changes resulting from sculpting operations are applied to points, edges and triangular facets. We thus facilitate, for example, the persistence of sharp features that automatically split or merge with variable rigidity, even when the shape changes genus. Sculpting nested structures expands the capabilities of most conceptual design workflows, as exhibited by a suite of models created by our system. © 2013 Elsevier Ltd.


Bourrier F.,IRSTEA | Kneib F.,IRSTEA | Chareyre B.,Grenoble Universites | Fourcaud T.,CIRAD - Agricultural Research for Development
Ecological Engineering | Year: 2013

The analysis of the influence of the roots on the shear resistance of the soil requires identifying the effectof the different root-soil interaction processes depending on soil and roots properties. For that purpose,a numerical model of direct shear tests of non-rooted and rooted granular soils based on the DiscreteElement Method was developed. The soil is modeled as an assembly of locally interacting spheres andthe roots are modeled as deformable cylinders in the soil matrix. The model allows accounting for theroot tensile loading until breakage, the root bending loading, the root-soil adhesive links until adhesionbreakage, the root slippage associated with a frictional resistance at the root-soil interface.The study focuses on identifying the different root-soil interaction mechanisms depending on the soiltype. Both frictional and cohesive granular soil types were used in the simulations. The effects of the rootsmechanical properties - tensile, bending modulus and root-soil interfacial friction angle - and of the rootnumber were also analyzed for the different soil types.The results first show that the effect of the roots strongly depends on the shear strain for any soil type.For frictional soils, an increasing shear strain induces progressively a pure tensile loading of the rootsuntil slippage of the root-soil interface. For cohesive granular soils, the pure tensile loading of the rootsis followed by a progressive breakage of the adhesive root-soil links and by a complete slippage of theroots. The results show that the influence of the root number is significant if the prevailing processesare root tensile loading combined with slippage whereas it is less important if root loading is combinedwith progressive breakage of the adhesive links for the root configurations explored. Finally, the resultsshow that the shear strain range associated with the different processes strongly depends on the relativerigidities of the roots and soil matrix.The model developed was shown of great interest to analyze the shear resistance of the rooted soilassemblies depending on the shear strain. Such an approach could therefore be used to test the differentassumptions done in the analytical models. Developing analytical models of slope stability based on thecalculation of the shear resistance of rooted soil depending not only on soil and root properties but alsoon shear strain intensity also constitutes a perspective for the use of the model developed. © 2013 Elsevier B.V.


Tchiboukdjian M.,French Atomic Energy Commission | Danjean V.,Grenoble Universites | Raffin B.,French Institute for Research in Computer Science and Automation
IEEE Transactions on Visualization and Computer Graphics | Year: 2010

One important bottleneck when visualizing large data sets is the data transfer between processor and memory. Cache-aware (CA) and cache-oblivious (CO) algorithms take into consideration the memory hierarchy to design cache efficient algorithms. CO approaches have the advantage to adapt to unknown and varying memory hierarchies. Recent CA and CO algorithms developed for 3D mesh layouts significantly improve performance of previous approaches, but they lack of theoretical performance guarantees. We present in this paper a O(Nlog N) algorithm to compute a CO layout for unstructured but well shaped meshes. We prove that a coherent traversal of a N-size mesh in dimension d induces less than N/B+O(N/M 1/d) cache-misses where B and M are the block size and the cache size, respectively. Experiments show that our layout computation is faster and significantly less memory consuming than the best known CO algorithm. Performance is comparable to this algorithm for classical visualization algorithm access patterns, or better when the BSP tree produced while computing the layout is used as an acceleration data structure adjusted to the layout. We also show that cache oblivious approaches lead to significant performance increases on recent GPU architectures. © 2006 IEEE.


Lambert S.,IRSTEA | Nicot F.,IRSTEA | Gotteland P.,Grenoble Universites
Geotextiles and Geomembranes | Year: 2011

Cellular structures are widely used in civil engineering. Their design is based on the understanding of the mechanical behavior of geocells. This paper investigates the response of a single geocell to a uniaxial compression test. The geocells were cubic, either 500. mm or 300. mm on a side. The fill materials were sand and scrapped tire and sand mixtures in different mass ratios. The envelope of the geocell was made up of a hexagonal wire netting cage and a containment geotextile. The response of the geocell is discussed based on the axial load and displacement measurements as well as the change in geocell volume.The axial load was found to be globally governed by the interaction between the fill material and the envelope, which depends on the shape of the wire mesh and the volumetric behavior of the fill material. © 2011 Elsevier Ltd.


Bourrier F.,Pierre Mendès-France University | Lambert S.,IRSTEA | Heymann A.,IRSTEA | Gotteland P.,Grenoble Universites | Nicot F.,IRSTEA
Canadian Geotechnical Journal | Year: 2011

Cellular structures are efficient technological solutions for rockfall protection. A multi-scale approach is used to develop a cellular rockfall protection structure model for engineering purposes. The macroscopic structure is composed of mesoscale individual layers made up of rocky particles contained in wire netting cages, fine granular material, and a reinforced embankment. Simple constitutive models were developed for the different mesoscale layers of the structure. Information is gathered from experiments at the layer scale to calibrate the parameters of the constitutive models. The capacities of the model are evaluated by comparisons between simulations and impact experiments on small structures. Despite quantitative differences, the comparative analysis highlights that the structure model can account for the main physical mechanisms occurring during the impact on sandwich structures. This analysis also emphasizes the model's applicability for engineering purposes.


Bourrier F.,IRSTEA | Gotteland Ph.,Grenoble Universites | Heymann A.,IRSTEA | Lambert S.,IRSTEA
Numerical Methods in Geotechnical Engineering - Proceedings of the 7th European Conference on Numerical Methods in Geotechnical Engineering | Year: 2010

A model for the design of rockfall protection sandwich structures is presented and evaluated using results from real-scale experiments. The experiments consist of the impact by a 260 kg spherical projectile on a structure composed of gabion cages filled with coarse materials in the front part and fine granular material in the kernel part. This structure stands against a rigid concrete wall. The model allows accounting for the mechanisms occurring in the individual layers of the structure. The comparison between the simulations and the experiments shows that the model correctly predicts the time evolution of the force on the projectile. However, the model partially accounts for the time evolution of the stress on the rigid concrete wall due to the simplicity of the formulation of the constitutive model used to characterize the kernel layer. © 2010 Taylor & Francis Group, London.


Zhang X.,Grenoble Universites | Gotteland Ph.,Grenoble Universites | Foray P.,Grenoble Universites | Lambert S.,Keller Fondations Speciales | Hatem A.,Keller Fondations Speciales
Numerical Methods in Geotechnical Engineering - Proceedings of the 7th European Conference on Numerical Methods in Geotechnical Engineering | Year: 2010

The ground reinforcement by Mixed Module Columns allows a high increase in bearing capacity and a reduction in settlement. With its high flexibility, the upper part of the Mixed Module Columns (CMM) can absorb most of seismic energy. Numerical modeling was conducted on a shallow foundation lying on a soft clay reinforced by four CMM subjected to static and dynamic horizontal cyclic loading. The numerical results indicate that strength of CMM decreases with increasing height of stone columns. The inertial effect is well demonstrated in the dynamic analyses in comparison to the static ones. © 2010 Taylor & Francis Group, London.

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