Alexandre Martin

High performance hybrid FEM/DEM simulation tool for numerical analysis of historical structures

The current paper aims at presenting the various aspects of a modeling and simulation framework dedicated to the study of historical structures considered as complex mechanical systems with interactions (contact, friction, cohesion, etc) and multi-physics couplings (thermal effects, diffusion, etc). Based on the proposed framework a simulation tool has been developed, with a complete strategy (pre-processing, simulation, post-processing), making possible to deal efficiently with the numerical modeling of those structures; it is available as an open-source software: LMGC90 [4].

Jamming and flow statistics in a silo geometry

We propose a 2D study of jamming at the outlet of a silo in the metastable state by means of the nonsmooth contact dynamics method. The jamming problem in this geometry can be mapped into the avalanche problem on a granular slope. In this analogy, the size of the opening plays the same role as the slope angle whereas the number of passing particles between two jams corresponds to the avalanche size. We use a simple protocol to break the arch and thus trigger a new avalanche every time an arch is formed. We find that the probability density of avalanche size scaled by the mean avalanche size is a decreasing exponential function independent of the opening. The mean avalanche size increases with the opening and it diverges as a critical opening is approached. This transition to steady flow where the jamming probability vanishes, bears close analogy to transition to steady flow on an inclined plane at the maximum angle of stability. We also present a simple model of passing events as an uncorrelated process. ...

Real-time 3D visualization of DEM combined with a robust DCT based data-hiding method

Using aerial photography, satellite imagery, scanned maps and Digital Elevation Models implies to make storage and visualization strategy choices. To obtain a three dimensional visualization, we have to link these images called texture with the terrain geometry named Digital Elevation Model. These information are usually stored in three different files (One for the DEM, one for the texture and one for the geo-referenced coordinates). In this paper we propose to store these information in only one file. In order to solve this problem, we present a technique for color data hiding of images, based on DC components of the DCT-coeffcients. In our application the images are the texture, and the elevation data are hidden in each block. This method mainly protects against JPEG compression and cropping.