Molecular Dynamics Simulation of Granular Systems: A Study of Segregation Mechanisms

Granular materials such as sand and grains, are large conglomerations of discrete macro-scopic particles that interact with each other through energy-dissipating contact forces [1]. The dynamics of granular materials is one of the most important research topics and was widely studied in the last years in the context of non-linear systems, dissipatives and far from equilib-rium. However, in spite of the intensive effort on theoretical works, experiments and computa-cional simulations for understanding and even-tually controling the complex phenomenology of granular materials, their behavior is still far from being properly understood [2]. The mixture of granular materials has a wide technological interest. For instance, in the phar-maceutical industry, drugs are often manufac-tured by mixing particles with different sizes or not. This mixture is implemented by vibration or rotation of the constitutive elements, but it is common to observe pattern formation and segre-gation of particles [3]. In other words, vibration of granular materials do not always produce a homogeneous mixture. Since there is no comprehensive theory on type of complex, many-body system, numerical simu-lations are commonly used to better understand the behavior of granular materials [4]. In this work, we are interested in the simulation of par-ticles inside a shaking container. A large par-ticle is added at the bottom of the container that oscillates vertically. After a short simula-tion time the large particle moves upward. This phenomenon is known as Brazil Nut Effect [5]. We intend here to investigate segregation mech-anisms in this granular system and to analyze microstructure formation. For this purpose, we performed molecular dynamics (MD) simulations using the softwar