Catálogo de publicaciones - libros

Particulate or granular materials are an integral part of our environment. Due to their fascinating physical properties and their wide variety of applications in industrial and technological processes, they are the subject of intensive studies and scientific research. The related studies are often based on numerical simulations. It is still considered as challenging to investigate computationally complicated phenomena of dense granular systems and, therefore, parallel computation techniques should be applied. In this study, we investigate particle segregation of dry granular mixtures using a commonly used machine in granular processing: a tumbling screening machine. Screeners are generally considered as sifting units which are rotated as material is fed into their interior. The system under consideration can be modelled as a multibody system which consists basically of the machine itself and the system of the mixed particles. Fine particles usually fall through the sieve openings while oversized particles are ejected out through certain outlets located around the machine body The concept of the discrete element method (DEM) that considers the motion of each single particle individually is applied in this study. Dynamical values of particle positions, velocities and orientations are tracked at each time step of the simulation. Particle-to-particle and particle-to-wall/sieve collisions will appear under the tumbling action of the rotating structure. The soft particle method, which is one of the most common discrete element simulation techniques, is applied. In this method, the normal and frictional forces between particles themselves and particles and machine walls are calculated according to a penalty method. Results from numerical computations are shown and interpreted.

Key words: Discrete element method, granular material, screening, segregation, sorting machine.

Two unilateral models, the first with contact interfaces and the second with continuous damage material (Fremond’s model), are applied on the nonlinear analysis and collapse of masonry arches. The results are compared with the predictions of the classical Heyman theory.

Key words: Unilateral analysis, Fremond damage model, masonry arches, limit analysis, collapse analysis, Heyman theory.

In this article the behavior of buried vaults (arches, tunnels, bridges, etc.) is studied with Discontinuous Deformation analysis, a numerical method that allows for the discontinuity of the structure and bases its physics on contact and friction among blocks. Two vault geometries are studied, the first semicircular and the second similar to that of oval arches. The considered loads are the weight of the structure, those related with lateral filling, with embankment and with concentrated (through a short distribution) forces at the peak. These loads are transformed to side forces with standard contact algorithm (penalty, Coulomb friction) and to point forces applied to the center of gravity with simple formulae from Soil Mechanics.

The analysis results are compared with experimental ones taken from the literature with, for most cases, very good agreement given the uncertainties on the geometry and material properties and given the intrinsic quality dispersion of masonry structures. The comparison is done for collapse load as a function of the number of joints, safety coefficients and limit point loads, including several modes of failure. The geometry of collapse is also compared with that of the experiments, obtaining here very good agreement.

Key words: Masonry, discontinuous numerical methods, contact, friction, experimental, oval arch, vault, collapse, hinge, filling, embankment, point load.