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Dive into the research topics where Ramón García-Rojo is active.

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Featured researches published by Ramón García-Rojo.


Wind Engineering | 2004

Algorithm for the Estimation of the Long-term Wind Climate at a Meteorological Mast Using a Joint Probabilistic Approach

Ramón García-Rojo

A new automatic method of calculation of a long-term representative wind climate is proposed. The procedure is based on the calculation of the joint probability distribution of the wind at a local station and at a long-term reference meteorological mast. The results obtained with this algorithm are compared with estimations of the long-term climate obtained with a Measure-Correlate-Predict method. The agreement found is good, even for very different periods of measurement.


Physical Review E | 2006

Transport Coefficients for dense hard-disk systems

Ramón García-Rojo; Stefan Luding; J. Javier Brey

A study of the transport coefficients of a system of elastic hard disks based on the use of Helfand-Einstein expressions is reported. The self-diffusion, the viscosity, and the heat conductivity are examined with averaging techniques especially appropriate for event-driven molecular dynamics algorithms with periodic boundary conditions. The density and size dependence of the results are analyzed, and comparison with the predictions from Enskogs theory is carried out. In particular, the behavior of the transport coefficients in the vicinity of the fluid-solid transition is investigated and a striking power law divergence of the viscosity with density is obtained in this region, while all other examined transport coefficients show a drop in that density range in relation to the Enskogs prediction. Finally, the deviations are related to shear band instabilities and the concept of dilatancy.


Physical Review E | 2005

Characterization of the material response in granular ratcheting

Ramón García-Rojo; Fernando Alonso-Marroquin; Hans J. Herrmann

The existence of a very special ratcheting regime has recently been reported in a granular packing subjected to cyclic loading. In this state, the system accumulates a small permanent deformation after each cycle. The value of this permanent strain accumulation becomes independent of the number of cycles after a short transient regime. We show in this paper that a characterization of the material response in this peculiar state is possible in terms of three simple macroscopic variables. The definition of these variables is such that they can be easily measured both in the experiments and in the simulations. A thorough investigation of the micro- and macromechanical factors affecting these variables has been carried out by means of molecular-dynamics simulations of a polydisperse disk packing, as a simple model system for granular material. Biaxial test boundary conditions with periodically varying load were implemented. The effect on the plastic response of the confining pressure, the deviatoric stress, and the number of cycles has been investigated. The stiffness of the contacts and friction has been shown to play an important role in the overall response of the system. Especially illustrative is the influence of the peculiar hysteretical behavior in the stress-strain space on the accumulation of permanent strain and the energy dissipation.


Physical Review E | 2005

Indeterminacy and the onset of motion in a simple granular packing

Sean McNamara; Ramón García-Rojo; Hans J. Herrmann

We examine the relatively simple problem of a disk placed in a symmetric V-shaped channel, and subjected to gravity and a torque. We obtain analytic predictions of the contact forces and disk motion using two different models. In the first model, the disk is assumed to be perfectly rigid, leading to force indeterminacy. In the second model, the disk is assumed to interact with the walls of the channel via linear springs, leading to a unique solution for the contact forces. The results of these two models are compared. It is shown that there are two possible ways motion can occur--through the appearance of a null eigenvector of the stiffness matrix, or through an instability. When motion occurs through an instability, the first model cannot predict when the disk will rotate; it is necessary to know the undetermined forces in order to predict the motion of the disk. It is also shown how indeterminacy in the first model is linked to memory in the second. The analytical results are also compared with numerical simulations using two different methods, each related to one of the models.


Physical Review E | 2002

Transversal inhomogeneities in dilute vibrofluidized granular fluids

J. Javier Brey; M. J. Ruiz-Montero; F. Moreno; Ramón García-Rojo

The spontaneous symmetry breaking taking place in the direction perpendicular to the energy flux in a dilute vibrofluidized granular system is investigated, using both a hydrodynamic description and simulation methods. The latter include molecular dynamics and direct Monte Carlo simulation of the Boltzmann equation. A marginal stability analysis of the hydrodynamic equations, carried out in the WKB approximation, is shown to be in good agreement with the simulation results. The shape of the hydrodynamic profiles beyond the bifurcation is discussed.


POWDERS AND GRAINS 2009: PROCEEDINGS OF THE 6TH INTERNATIONAL CONFERENCE ON MICROMECHANICS OF GRANULAR MEDIA | 2009

Investigation of the Critical State in Soil Mechanics Using DEM

Andrés A. Peña; Ramón García-Rojo; Fernando Alonso-Marroquin; Hans J. Herrmann

The existence and uniqueness of the so‐called critical state in soil mechanics is validated in our DEM simulations of irregular polygonal particles. For different particle shape characteristics, the critical state is independent of the initial stress and density conditions. We retain low stress levels, since we do not take into account the crushing of particles. In biaxial test simulations isotropic particles evolve toward a limiting state in which the system reaches a critical void ratio and deforms with constant volume, deviatoric stress, fabric anisotropy, and mechanical coordination number. The last one has been found to be the first variable to attain a critical value making possible for the rest of micro‐and‐macro‐mechanical variables the convergence to the critical state. In periodic shear cell tests, for large shear deformations samples with anisotropic particles reach at the macro‐mechanical level the same critical value for both shear force and void ratio. At the micro‐mechanical level the compo...


Granular Matter | 2007

Influence of particle shape on sheared dense granular media

Andrés A. Peña; Ramón García-Rojo; Hans J. Herrmann


Granular Matter | 2005

Shakedown of unbound granular material

Ramón García-Rojo; Hans J. Herrmann


Physical Review E | 2001

Hydrodynamic Maxwell demon in granular systems.

J. Javier Brey; F. Moreno; Ramón García-Rojo; M. J. Ruiz-Montero


Particle & Particle Systems Characterization | 2007

Powder Flow Testing with 2D and 3D Biaxial and Triaxial Simulations

Ciprian T. David; Ramón García-Rojo; Hans J. Herrmann; Stefan Luding

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F. Moreno

University of Seville

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C.T. David

University of Stuttgart

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