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## Publications

Publications (31)

A model of physiological age, accompanied by non-linear diffusion in space, is studied analytically and numerically, and is shown to develop non-stationary traveling population waves. A window of intermediate growth rates is found where collective supercycles are formed from individual (stochastic) life cycles. Supercycle periods can be considerabl...

A granular gas in gravity heated from below develops a certain stationary density profile. When the heating is switched off, the granular gas collapses. We investigate the process of sedimentation using computational hydrodynamics, based on the Jenkins-Richman theory, and find that the process is significantly more complex than generally acknowledg...

A reversible algorithm [enforced energy conservation (EEC)] that enforces total energy conservation for microcanonical simulations is presented. The key point is the introduction of the discrete-gradient method to define the forces from the conservative potentials, instead of the direct use of the force field at the actual position of the particle....

We show that 2D clustering with constant restitution coefficient is qualitatively well described by a compressible Navier-Stokes like system. Shock capturing highly accurate methods are needed to resolve well shock waves in the cluster formation phase. Numerical results agree with qualitative predictions on clustering.

We perform two-dimensional hydrodynamic simulations on a paradigmatic
problem of granular dynamics, the Faraday instability, using two
different approximations to the Navier-Stokes granular equations: the
constitutive equations and kinetic coefficients derived from the
assumption of vanishing inelasticity (Jenkins-Richman approach) obtained
by solv...

A numerical study is presented to analyze the thermal mechanisms of unsteady,
supersonic granular flow, by means of hydrodynamic simulations of the
Navier-Stokes granular equations. For this purpose a paradigmatic problem in
granular dynamics such as the Faraday instability is selected. Two different
approaches for the Navier-Stokes transport coeff...

The evolution of a force-free granular gas with a constant restitution coefficient is
studied by means of granular hydrodynamics. We numerically solve the hydrodynamic
equations and analyze the mechanisms of cluster formation. According to our findings, the
presently accepted mode-enslaving mechanism may not be responsible for the latter
phenomenon...

The invention relates to a hand-held medical instrument, in particular a hand-held surgical or dental instrument, compris-ing a component that generates mechanical vibrations during operation, and a particle damping element which has at least one hollow space that is designed to receive the mechanical vibrations and is filled at least in part with...

We discuss several models for granular particles commonly used in Molecular Dynamics simulations of granular materials, including spheres with linear dashpot force, vis-coelastic spheres and adhesive viscoelastic spheres. Starting from the vectorial interaction forces we derive the coefficients of normal and tangential restitution as functions of t...

A numerical hydrodynamic model of a vibrated granular bed in 2D is elaborated based on a highly accurate Shock Capturing scheme applied to the compressible Navier-Stokes equations for granular flow. The hydrodynamic simulation of granular flows is numerically difficult, particularly in systems where dilute and dense regions occur at the same time a...

The aim of this article is to present the results of the lattice Boltzmann method (LBM) application as computational fluid dynamics solvers. After of short review of the basic theory and using the two-dimensional model with 9 velocities (D2Q9), the Poiseuille flow is modelled and validated the results with the analytical solutions. Also, the Lid-dr...

A force-free granular gas was considered with an impact-velocity-dependent coefficient of restitution as it followed from the model of viscoelastic particles. Structural formation in this system was studied by means of three independent methods: event-driven molecular dynamics (MD), numerical solution of the hydrodynamic (HD) equations, and linear...

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 met...

With the assumption of viscoelastic particle deformation, it is demonstrated that naive scaling modifies the properties of granular systems such that the original system and the scaled system might reveal quite different dynamic properties. To guarantee equivalent dynamical properties of the original and the scaled systems, material properties are...

The onset of surface fluidization of granular material in a vertically vibrated container, z = A cosωt
, is studied experimentally. Recently, for a column of spheres it has been theoretically found (see T. Pöschel, T. Schwager,
C. Salue na, Phys. Rev. E 62, 1361 (2000)) that the particles lose contact if a certain condition for the acceleration amp...

For the experimental investigation of large scale phenomena in the laboratory such as in geophys- ical 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 orig...

When granular material is shaken vertically one observes convection, surface fluidization, spontaneous heap formation, and other effects. There is a controversial discussion in the literature as to whether there exists a threshold for the Froude number Gamma=A(0)omega(2)(0)/g, below which these effects cannot be observed anymore. By means of theore...

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...

Simulation models in space industry may allocate a few mesh points for such fine details as granular dampers embedded in mechanical parts. As a result, collective dynamics of grains inside dampers cannot be adequately resolved. A hierarchical approach to modeling and design has been explored by practitioners to study this phenomenon. Available mode...

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...

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 gas-like regimes. The behavior of effective damping decrement in the s...

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 con...

We have analyzed the viscoelastic behavior of a suspension of ferromagnetic particles. The dynamics of the correlations of the magnetic moment of the particle follows from the corresponding Smoluchowski equation, which generates a hierarchy of equations coupling the consecutive moments. Different decoupling approximations are proposed and studied....

The viscosities of a dilute suspension of ferromagnetic rod-like particles are computed in a general situation in which a homogeneous stationary flow and a magnetic field are imposed on the system. For this purpose, the corresponding Smoluchowski equation giving the probability density for the orientations of the particle has been solved. After usi...

Here we analyze the viscosities of a ferrofluid composed of elongated magnetic particles. Starting from the Smoluchowski equation, we compute the elongational and shear viscosities, assessing their behavior as functions of the magnetic field.

We obtain the expression for the viscosity tensor of a ferrofluid under external flow. The system is modeled as a suspension of rigid dumbbells with a dipole moment in the direction of their bond vector. Our starting point is the Kramers–Kirkwood expression for the stationary viscous pressure tensor whose average is computed with the stationary sol...

We analyze the effect of an external flow on the rheological and magnetic properties of a suspension of non-interacting magnetic dipoles in a Newtonian non-polar fluid (ferrofluid). The friction for a dipole moving through this fluid, which is in a state of elongational flow, is computed. A continuum approach is used to derive relaxation equations...

Here we analyze transport phenomena in suspensions of magnetic dipoles in a Newtonian nonpolar solvent (ferrofluid). A continuum or mean field approximation is used to derive hydrodynamic equations for the system and the expression for a new transport coefficient: the rotational viscosity, which is shown to be proportional to the volume fraction. F...

We compute nonequilibrium correlation functions about the stationary state in which the fluid moves as a consequence of tangential stresses on the liquid surface, related to a varying surface tension (thermocapillary motion). The nature of the stationary state makes it necessary to take into account that the system is finite. We then extend a previ...