Numerical Simulation of Capillary Flows Through Molecular Dynamics

Capillary pore imbibition represents a very challenging field of research because of its crucial role in several physical phenomenona. This paper deals with capillary dynamics in connection with non destructive test technique used to evidence eventual defects present in mechanical parts whose perfect integrity is vital for the reliability of all the systems (car, planes, etc.) which they are part of. For the description of such phenomenona, essentially two different approaches are possible. The first approach consists in considering the fluid motion as a continuum to be described in terms of mathematical models governed by ordinary or partial differential equation. Subsequently, according to the prescribed initial and boundary conditions to these models, the solution can be worked out numerically through one of the available numerical techniques such as finite difference, finite elements, finite volumes, meshless methods, etc. Conversely, the second approach considers the fluid motion as an atomistic ensemble of discrete particles (atoms or molecules), whose macroscopic features are strongly determined by the inner interactions occurring among them. In this context, the two most important conceptual available tools are the Lattice Boltzmann theory, mainly used by physicists and the Molecular Dynamics, MD for the sequel, that jointly with its numerical treatment represents the topic of the present paper. Capillary imbibition represents a specific aspect of the wider area of wetting solid by liquids and its description in terms of MD has revealed to be a very promising approach for the description of the capillary flows alternative to continuous differential models. At the beginning, MD was used to simulate essentially the behavior of biological materials, but over the years MD has proved to be a powerful tool to model and simulate nanotechnology structures. In this paper large scale MD is used in order to model the intrusion of water into a defect of a few given solid materials. Finally numerical results have been obtained for cylindrical defects of Titanium or Aluminum both internally smooth or rough.