Browsing by Author "Kalweit, Marco"
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Item Open Access Collision dynamics of nanoscale Lennard-Jones clusters(American Institute of Physics, 2006-12-11) Kalweit, Marco; Drikakis, DimitrisAn investigation of collision dynamics of nanoparticles for a broad range of impact factors and collision speeds is presented. The investigation is based on molecular dynamics simulations in conjunction with the Lennard-Jones interaction potential thus making the results applicable for a broad range of material properties. Identification criteria are used to classify the collision dynamics into different collision modes and submodes. Detailed analysis of the collision processes reveals the existence of coalescence and stretching separation modes, which are further classified according to their dynamics into sticking; slide-and-locking; droplet; normal stretching separation; stretching separation with satellite droplets; and shearing-off modes. Qualitative and quantitative comparisons with previous molecular dynamic studies and analytical prediction models derived for macroscopic droplet collisions are also discussed. The investigation reveals that the reflexive separation mode, which has been observed in macroscopic droplet collisions, does not occur for nanoparticles consisting of 10 000 (or less) atoms.Item Open Access Mesoscale flow and heat transfer modelling and its application to liquid and gas flows(2009-11-09T00:00:00Z) Asproulis, Nikolaos; Kalweit, Marco; Shapiro, Evgeniy; Drikakis, DimitrisAdvances in micro and nanofluidics have influenced technological developments in several areas, including materials, chemistry, electronics and bio-medicine. The phenomena observed at micro and nanoscale are characterised by their inherent multiscale nature. Accurate numerical modelling of these phenomena is the cornerstone for enhancing the applicability of micro and nanofluidics in the industrial environment. We investigated different strategies for applying macroscopic boundary conditions to microscopic simulations. Continuous rescaling of atomic velocities and velocity distribution functions, such as Maxwell-Boltzmann or Chapman-Enskog, were investigated. Simulations were performed for problems involving liquids and gases under different velocity and temperature conditions. The results revealed that the selection of the most suitable method is not a trivial issue and depends on the nature of the problem, availability of computational resource and accuracy requirement.Item Open Access Molecular modelling of meso- and nanoscale dynamics(Cranfield University, 2008-02) Kalweit, Marco; Drikakis, DimitrisMolecular modelling of meso- and nanoscale dynamics is concerned with length and time scales that are in the transition zone from molecular to continuum models. Molecular simulation methods, in particular molecular dynamics (MD), only allow the simulation of relatively small nanoscale systems. Continuum methods, such as computational fluid dynamics (CFD), are applicable at macroscopic scales but cease to be valid for nanoscales. This thesis is focused on hybrid MD-CFD methods with geometrical decomposition that seek to bridge the gap between molecular and continuum modelling. The hybrid solution interface (HSI) establishes the coupling between the molecular and the continuum domain. In this work, different realisation approaches for the HSI, flux and state coupling, are discussed and compared. A detailed investigation on MD flux boundary conditions, the most crucial part of a flux based HSI, is carried out. Different schemes for the imposition of mass, momentum and energy fluxes through convective and viscous transport are presented: direct and indirect flux imposition for convective fluxes; the imposition of momentum fluxes through reflective walls, external forces and the reverse velocity scheme; and imposition of energy fluxes through external forces and an energy transfer scheme. Different combinations of these schemes are compared for standard flow situations. The momentum and energy transfer by an external force creates a relaxation zone at the MD boundary. The characteristics of this zone is investigated in detail and a theoretical model for the density profile has been derived. The reverse velocity scheme has been created as part of this work to avoid the problems encountered when using the external force for the momentum transfer. It is shown that indirect convective flux imposition in conjunction with the reverse velocity scheme gives the best results for the standard flow situations. The scheme is also tested for liquid flow past Carbon nanotubes.