Computational Analysis of Fluid-Wall Interactions in Micro- and Nano-Domains

2003 ◽  
Author(s):  
C. Channy Wong ◽  
David R. Noble
Keyword(s):  
Fluid Dynamics ◽  
Molecular Dynamics ◽  
Flow Behavior ◽  
Multiple Length Scales ◽  
Micro Channels ◽  
Macro Scale ◽  
Coupling Strategy ◽  
Dynamics Simulations ◽  
Dynamics Problems ◽  
Wall Interactions

In many micro-scale fluid dynamics problems, molecular-level processes can control the interfacial energy and viscoelastic properties at a liquid-solid interface. This leads to a flow behavior that is very different from those similar fluid dynamics problems at the macro-scale. Presently, continuum modeling fails to capture this flow behavior. Molecular dynamics simulations have been applied to investigate these complex fluid-wall interactions at the nano-scale. Results show that the influence of the wall crystal lattice orientation on the fluid-wall interactions can be very important. To address those problems involving interactions of multiple length scales, a coupled atomistic-continuum model has been developed and applied to analyze flow in channels with atomically smooth walls. The present coupling strategy uses the molecular dynamics technique to probe the non-equilibrium flow near the channel walls and applies constraints to the fluid particle motion, which is coupled to the continuum flow modeling in the interior region. We have applied this new methodology to investigate Couette flow in micro-channels.

Interface Conditions for Coupled Atomistic and Continuum Models of Solids for Dynamics Problems at Finite Temperature

2006 ◽  
Vol 978 ◽  
Author(s):  
Xiantao Li ◽  
Weinan E
Keyword(s):  
Molecular Dynamics ◽  
Boundary Conditions ◽  
Finite Temperature ◽  
Langevin Equations ◽  
Continuum Models ◽  
Interface Conditions ◽  
System Temperature ◽  
Dynamics Simulations ◽  
Dynamics Problems ◽  
Generalized Langevin Equations

AbstractWe will present a general formalism for deriving boundary conditions for molecular dynamics simulations of crystalline solids in the context of atomistic/continuum coupling. These boundary conditions are modeled by generalized Langevin equations, derived from Mori-Zwanzig's formalism. Such boundary conditions are useful in suppressing phonon reflections, and maintaining the system temperature.

Heat Transfer Predictions for Micro/Nano-Channels at Atomistic Level Using Combined Molecular Dynamics and Monte Carlo Techniques

2007 ◽  
Author(s):  
S. V. Nedea ◽  
A. J. Markvoort ◽  
A. A. van Steenhoven ◽  
P. A. J. Hilbers
Keyword(s):  
Molecular Dynamics ◽  
Heat Flux ◽  
Boundary Conditions ◽  
Wall Effects ◽  
Characteristic Parameters ◽  
Monte Carlo Techniques ◽  
Dilute Gas ◽  
Effective Coefficients ◽  
Dynamics Simulations ◽  
Wall Interactions

The thermal behavior of a gas confined between two parallel walls is investigated. Wall effects like hydrophobic or hydrophilic wall interactions are studied, and the effect on the heat flux and other characteristic parameters like density and temperature is shown. For a dilute gas, the dependence on gas-wall interactions of the temperature profile between the walls for the incident and reflected molecules is obtained using Molecular Dynamics. From these profiles, the effective accomodation coefficients for different interactions and different mass fluid/wall ratio are derived. We show that MC with Maxwell boundary conditions based on the accomodation coefficient gives good results for heat flux predictions when compared to pure Molecular Dynamics simulations. We use these effective coefficients to compute the heat flux predictions for a dense gas using MD and MC with Maxwell-like boundary conditions.

Heat Transfer Predictions for Micro-/Nanochannels at the Atomistic Level Using Combined Molecular Dynamics and Monte Carlo Techniques

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
S. V. Nedea ◽  
A. J. Markvoort ◽  
A. A. van Steenhoven ◽  
P. A. J. Hilbers
Keyword(s):  
Molecular Dynamics ◽  
Heat Flux ◽  
Monte Carlo ◽  
Boundary Conditions ◽  
Accommodation Coefficient ◽  
Monte Carlo Techniques ◽  
Effective Coefficients ◽  
Accommodation Coefficients ◽  
Dynamics Simulations ◽  
Wall Interactions

The thermal behavior of a gas confined between two parallel walls is investigated. Wall effects such as hydrophobic or hydrophilic wall interactions are studied, and the effect on the heat flux and other characteristic parameters such as density and temperature is shown. For a dilute gas, the dependence on gas-wall interactions of the temperature profile between the walls for the incident and reflected molecules is obtained using molecular dynamics (MD). From these profiles, the effective accommodation coefficients for different interactions and different mass fluid/wall ratio are derived. We show that Monte Carlo (MC) with Maxwell boundary conditions based on the accommodation coefficient gives good results for heat flux predictions when compared with pure molecular dynamics simulations. We use these effective coefficients to compute the heat flux predictions for a dense gas using MD and MC with Maxwell-like boundary conditions.

Packing Density Insensitive Contact Detection Algorithm for Molecular Dynamics Simulations

2008 ◽  
Author(s):  
A. Munjiza
Keyword(s):  
Molecular Dynamics ◽  
Packing Density ◽  
Detection Algorithm ◽  
Contact Detection ◽  
Dense Gases ◽  
Large Numbers ◽  
Dynamics Simulations ◽  
Interacting Atoms ◽  
Dynamics Problems ◽  
Contact Detection Algorithm

Molecular dynamics problems involve large numbers of interacting atoms requiring CPU and RAM intensive computational simulations. A contact detection algorithm which detects pairs of interacting atoms is a key component of these simulations. This paper presents a contact detection algorithm that is completely insensitive to packing density in terms of both RAM and CPU requirements — thus permitting near vacuum conditions and dense gases or liquids to coexist in the same simulation. In addition, both CPU and RAM requirements are proportional to the total number of atoms.

Hybrid Continuum Mechanics and Atomistic Methods for Simulating Materials Deformation and Failure

MRS Bulletin ◽  
2007 ◽  
Vol 32 (11) ◽  
pp. 920-926 ◽  
Author(s):  
Ronald E. Miller ◽  
Ellad B. Tadmor
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Computational Cost ◽  
Atomic Scale ◽  
Molecular Statics ◽  
Deformation And Failure ◽  
Multiple Length Scales ◽  
Adequate Representation ◽  
Dynamics Simulations ◽  
Critical Regions

AbstractMany aspects of materials deformation and failure are controlled by atomic-scale phenomena that can be explored using molecular statics and molecular dynamics simulations. However, many of these phenomena involve processes on multiple length scales with the result that full molecular statics/molecular dynamics simulations of the entire system are too large to be tractable. In this review, we discuss hybrid models that perform molecular statics/molecular dynamics simulations “without all the atoms,” aimed at retaining atomistic detail at a fraction of the computational cost. These methods couple a fully atomistic model in critical regions to regions described by less-expensive continuum methods where they can provide an adequate representation of the important physics. We give an overview of the challenges such models present, with a focus on recent work to address issues of dynamics and finite (non-zero) temperature.

Metal ions affect the formation and stability of amyloid β aggregates at multiple length scales

2018 ◽  
Vol 20 (13) ◽  
pp. 8951-8961 ◽  
Author(s):  
Myeongsang Lee ◽  
Jae In Kim ◽  
Sungsoo Na ◽  
Kilho Eom
Keyword(s):  
Molecular Dynamics ◽  
Metal Ions ◽  
Neurodegenerative Disease ◽  
Molecular Dynamics Simulations ◽  
Metal Ion ◽  
Amyloid Β ◽  
Length Scales ◽  
Multiple Length Scales ◽  
Dynamics Simulations

The effect of metal ion on the formation of amyloid β (Aβ) aggregates, which are a hallmark for neurodegenerative disease, was studied based on full atomistic molecular dynamics simulations.

Visualization of Multiscale Processes - Bubble Dynamics in Surface Active Colloids

2015 ◽  
Vol 137 (8) ◽  
Author(s):  
S. Manoharan ◽  
D. Kalaikadal ◽  
R. M. Manglik ◽  
E. Iskrenova-Ekiert ◽  
S. S. Patnaik
Keyword(s):  
Molecular Dynamics ◽  
Surface Tension ◽  
Pure Water ◽  
Dynamic Surface Tension ◽  
Air Flow Rate ◽  
Dynamic Surface ◽  
Multi Scale ◽  
Macro Scale ◽  
Dynamics Simulations ◽  
Adsorption Desorption

The growth dynamics of isolated gas bubbles from a submerged capillary-tube orifice in a pool of aqueous solution of Cetyl Trimethyl Ammonium Bromide (CTAB) was studied by multi-scale modeling. The macro-scale bubble ebullience is controlled by the molecular scale surfactant adsorption/desorption on the liquid-gas interface. Molecular dynamics simulations were carried out to predict the interfacial adsorption/desorption kinetics. The results of the molecular dynamics simulations were input to the volume-of-fluid based macro-scale computations. The size and shape of bubbles from incipience to departure were measured using high speed videography for model validation. Predictions of the multi-scale model agree with the experimental measurements of bubble size evolution and bubble diameter at departure. The surfactant mass transfer and adsorption on the liquid gas interface gives rise to dynamic surface tension. As a result of the surfactant presence, the bubble departure diameters were smaller in CTAB solution compared to pure water. Furthermore, dynamic surface tension behavior of CTAB makes the bubble departure diameter a function of bubble Reynolds number (Re based on the orifice diameter and air flow rate). At low flow rates or low Re, the bubble departure diameters are smaller than those in water. As the air flow rate increases, the bubble departure diameters tend towards those in pure water. The authors gratefully acknowledge funding from AFOSR Thermal Science Program and AFRL DoD Supercomputing Resource Center for computing time and resources.

scholarly journals An Investigation towards Coupling Molecular Dynamics with Computational Fluid Dynamics for Modelling Polymer Pyrolysis

Molecules ◽  
2022 ◽  
Vol 27 (1) ◽  
pp. 292
Author(s):  
Timothy Bo Yuan Chen ◽  
Ivan Miguel De Cachinho Cordeiro ◽  
Anthony Chun Yin Yuen ◽  
Wei Yang ◽  
Qing Nian Chan ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Molecular Dynamics ◽  
Computational Fluid Dynamics ◽  
Polymer Materials ◽  
Combustion Model ◽  
Detailed Chemical Kinetics ◽  
Kinetics Parameters ◽  
Pyrolysis Gas ◽  
Modelling Framework ◽  
Macro Scale

Building polymers implemented into building panels and exterior façades have been determined as the major contributor to severe fire incidents, including the 2017 Grenfell Tower fire incident. To gain a deeper understanding of the pyrolysis process of these polymer composites, this work proposes a multi-scale modelling framework comprising of applying the kinetics parameters and detailed pyrolysis gas volatiles (parent combustion fuel and key precursor species) extracted from Molecular Dynamics models to a macro-scale Computational Fluid Dynamics fire model. The modelling framework was tested for pure and flame-retardant polyethylene systems. Based on the modelling results, the chemical distribution of the fully decomposed chemical compounds was realised for the selected polymers. Subsequently, the identified gas volatiles from solid to gas phases were applied as the parent fuel in the detailed chemical kinetics combustion model for enhanced predictions of toxic gas, charring, and smoke particulate predictions. The results demonstrate the potential application of the developed model in the simulation of different polymer materials without substantial prior knowledge of the thermal degradation properties from costly experiments.

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