## Prof. Dr. Clara Salueña

**Research Projects**

**Function**

Postdoctoral researcher

**Info**

Departament de Enginyeria Mecànica, Universitat Rovira i Virgili, Tarragona, Spain

Postdoctoral researcher

Departament de Enginyeria Mecànica, Universitat Rovira i Virgili, Tarragona, Spain

New Journal of Physics **19**, 013001

(2017)

Physical Review E **91**, 062214

(2015)

New Journal of Physics **15**, 043044

(2013)

AIP Conference Proceedings **1501**, 993-1000

(2012)

J. Fluid Mech., **597**, 119-144

(2008)

The goal of this study is to demonstrate numerically that certain hydrodynamic systems, derived from inelastic kinetic theory, give fairly good descriptions of rapid granular flows even if they are way beyond their supposed validity limits. A numerical hydrodynamic solver is presented for a vibrated granular bed in two dimensions. It is based on a highly accurate shock capturing state-of-the-art numerical scheme applied to a compressible Navier-Stokes system for granular flow. The hydrodynamic simulation of granular flows is challenging, particularly in systems where dilute and dense regions occur at the same time and interact with each other. As a benchmark experiment, we investigate the formation of Faraday waves in a two-dimensional thin layer exposed to vertical vibration in the presence of gravity. The results of the hydrodynamic simulations are compared with those of event-driven molecular dynamics and the overall quantitative agreement is good at the level of the formation and structure of periodic patterns. The accurate numerical scheme for the hydrodynamic description improves the reproduction of the primary onset of patterns compared to previous literature. To our knowledge, these are the first hydrodynamic results for Faraday waves in two-dimensional granular beds that accurately predict the wavelengths of the two-dimensional standing waves as a function of the perturbation’s amplitude. Movies are available with the online version of the paper.

European Journal of Environmental and Civil Engineering **12**, 827-870

(2008)

We discuss several models for granular particles commonly used in Molecular

Dynamics simulations of granular materials, including spheres with linear dashpot force, viscoelastic

spheres and adhesive viscoelastic spheres. Starting from the vectorial interaction

forces we derive the coefficients of normal and tangential restitution as functions of the

vectorial impact velocity and of the material constants. We review the methods of

measurements of the coefficients of restitution and characterize the coefficient of normal

restitution as a fluctuating quantity. Moreover, the scaling behavior and the influence of

different force laws on the dynamical system behavior are discussed. The powerful method of

event-driven Molecular Dynamics is described and the algorithmic simulation technique is

explained in detail. Finally we discuss the limitations of event-driven MD.

Physical Review Letters, **93**, 134301

(2004)

A force-free granular gas is considered with an impact-velocity-dependent coefficient of restitution as it follows from the model of viscoelastic particles. We analyze structure formation in this system by means of three independent methods: molecular dynamics, numerical solution of the hydrodynamic equations, and linear stability analysis of these equations. All these approaches indicate that structure formation occurs in force-free granular gases only as a transient process.

SPIE, **3045**

(2002)

The properties of dense granular systems are analyzed from a hydrodynamical point of view, based on conservation laws for the particle number density and linear momentum. We discuss averaging problems associated with the nature of such systems and the peculiarities of the sources of noise. We perform a quantitative study by combining analytical methods and numerical results obtained by ensemble-averaging of data on creep during compaction and molecular dynamics simulations of convective flow. We show that numerical integration of the hydrodynamic equations gives the expected evolution for the time-dependent fields.

Continuous and Discontinuous Modelling of Cohesive Frictional Materials (P. A. Vermeer, S. Diebels, W. Ehlers, H. J. Herrmann, S. Luding, and E. Ramm (eds.)), 173-184, Springer, Berlin

(2001)

Given an assembly of viscoelastic spheres with certain material properties, we raise the question how the macroscopic properties of the assembly will change if all lengths of the system, i.e. radii, container size etc., are scaled by a constant. The result leads to a method to scale down experiments to lab-size.

Physical Review E, **64**, 011308

(2001)

Powders & Grains'2001 (Kishino), 439-442, Balkema, Rotterdam

(2001)

For the experimental investigation of large scale phenomena in the laboratory such as in geophysical or industrial applications one has to scale down all length in the system, e.g. particle size, container size. We show that besides length scaling one as to scale the material properties too to achieve identical behavior of the scaled and the original systems. We provide the scaling laws for a system of viscoelastic spheres.

European Physical Journal, **4**, 233-239

(2001)

The onset of surface fluidization of granular material in a vertically vibrated container, z=A cos(ω t), is studied experimentally. Recently, for a column of spheres it has been theoretically found that the particles lose contact if a certain condition for the acceleration amplitude d²z/dt² = Aω²/g = f(ω) holds. This result is in disagreement with other findings where the criterion (d²z/dt² = d²z/dt²)_crit = const. was found to be the criterion of fluidization. We show that for a column of spheres a critical acceleration is not a proper criterion for fluidization and compare the results with theory.

European Physical Journal E, **1**, 55-59

(2000)

In horizontally shaken granular material different types of pattern formation have been reported. We want to deal with the convection instability which has been observed in experiments and which recently has been investigated numerically. Using two dimensional molecular dynamics we show that the convection pattern depends crucially on the inelastic properties of the material. The concept of restitution coefficient provides arguments for the change of the behaviour with varying inelasticity.

Proceed. ICTAM, Chicago

(2000)

When dealing with dense granular flows (not far above the fluidization point of the granular material), which cannot be regarded as granular gases, multiple unresolved questions arise. Many of them are related to the necessity of constructing the right framework to handle the dynamics of void occupation, which governs granular flow athigh densities. This is a formidable task. However, hydrodynamic fields such as density, velocity, pressure and granular temperature, are easy to produce and study in numerical simulations of particles.

Physical Review E, **62**, 1361-1367

(2000)

When granular material is shaken vertically one observes convection, surface fluidization, spontaneous heap formation and other effects. There is a controversial discussion in literature whether there exists a threshold for the Froude number Γ=(A_0ω_0^2)/g below which these effects cannot be observed anymore. By means of theoretical analysis and computersimulation we find that there is no such single threshold. Instead we propose a modified criterion which coincides with critical Froude number Γ_c=1 for small driving frequency ω_0

Physical Review E, **59**, 4422-4425

(1999)

We investigate collective dissipative properties of vibrated granular materials by means of molecular-dynamics simulations. Rates of energy losses indicate three different regimes or phases in the amplitude-frequency plane of the external forcing,namely solid, convective, and gaslike regimes. The behavior of effective damping decrement in the solid regime is glassy. Practical applications are discussed.

Proceedings of the SPIE's Conference on Smart Structures and Materials, Passive Damping and Isolation, **3327**, 19 - 26

(1998)

We investigate collective dissipative properties of vibrated granular materials by means of molecular dynamics simulations. The rate of energy loss indicates three di®erent phases in the amplitude-frequency plane of the external forcing, namely solid, convective and gas-like regimes. The behavior of the e®ective damping decrement is consistent with the glassy nature of granular solids. The gas-like regime is most promising for practical applications.

Powders and Grains'97 (R. P. Behringer and J. T. Jenkins), 341-344, Balkema, Rotterdam

(1997)

We analize the properties of dense granular systems by assuming a hydrodynamical description, based on conservation laws for the particle number density and linear momentum. We combine analytical methods and experimental and numerical results obtained by ensemble-averaging of data on creep during compaction and molecular dynamics simulations of convective flow.