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Rafiqul A. Tarefder (University of New Mexico, USA), Jielin Pan (University of New Mexico, USA) and Mohammad I. Hossain (Bradley University, USA)

Source Title: Handbook of Research on Advanced Computational Techniques for Simulation-Based Engineering

Copyright: © 2016
|Pages: 30
DOI: 10.4018/978-1-4666-9479-8.ch013

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TopMD simulation computes, using a computer, the motion of a series of atoms, their co-ordinates in three-dimensional space, and their connectivity in a system as a function of time. It solves the classical equations of motion of *N* atoms interacting via a potential *U*, the sum of the pair potential of all the atoms. In Cartesian coordinates, the equation of motion is simply Newton’s second law of motion:

In general, the above equations of motion are solved using Verlet integration algorithm. The most widely used for integrating molecular dynamics equations is the velocity Verlet algorithm, which gives positions, velocities and accelerations at the same time and does not compromise precision (Leach, 2001). This method is used in this study. The position and velocity of atom *i* at the next step in time is determined by the following equations:

Moisture Damage: Moisture damage causes the debonding of asphalt-aggregate mixture, which also causes the rheological property changes of asphalt such as viscosity.

Molecular Dynamics Simulation: This is a computational method used to simulate the physical movements of atoms and molecules depending on time and force field chosen under different conditions, such as temperature, pressure, and force.

Monte Carlo Algorithm: It is a randomized algorithm which uses a degree of randomness as part of its logic to run under certain time until one of the runs produces an output that can be verified to be correct.

Functional Groups: Functional groups are specific groups of atoms in molecules that are responsible for the characteristic chemical reactions and properties of those molecules.

Potential Energy: This is the energy stored in an object due to its position in a force field. In a system, potential energy refers to the configuration of the system in a force field.

Force Field: Force field in chemistry is used to describe the potential energy of a system of molecules and atoms in the form of mathematical functions and parameters of mathematical functions.

Asphalt Oxidative Aging: Asphalt oxidative aging is an inevitable oxidation process when asphalt is exposed to the atmospheric oxygen, since asphalt is a natural organic end product of ancient living organisms which is subject to chemical oxidation. Oxidative aging causes hardening of asphalt which leads to embrittlement of asphalt pavement.

Composition of Asphalt: Asphalt is composed of saturates, aromatics, resins, and asphaltenes, four fractions, with an increase of polarity. The four fractions are mainly comprised of carbon and hydrogen with heteroatoms such as oxygen, nitrogen, and sulfur. Except for saturate fraction, the other three fractions are aging fractions.

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