Chemistry Reference
In-Depth Information
Molecular Dynamic
Region
Finite Element
Region
FE mesh is scaled to
meet molecular sites
Figure 2.2
MAAD handshake region (FE/MD) [49].
the molecular sites in a fluid move constantly throughout the domain (thermal mo-
tion/diffusion) even if the fluid is at rest. Coupling between fluid domains requires
an interface between the two that allows for the movement of molecules. For
solids, the validity of the continuum equations can be extended, as the molecules
are within a rigid structure and they move little, if at all, allowing the continuum
laws to be valid at smaller scales. In fluids, however, the dynamic molecular struc-
ture cannot be treated in the same way. Garcia
et al.
[50] developed the coupling
between the Navier-Stokes equations and direct simulation Monte Carlo (DSMC)
models for dilute gases by using a Chapman-Enskog velocity distribution-based
current generation scheme. This model considers only the scattering of molecules
due to collisions; it is the diffusion that is vital to the model, as opposed to the
simulation of cracks and solid systems, where diffusion is negligible and position
is important. The method they developed is based around an adaptive mesh and
algorithm refinement (AMAR) base, where they use DSMC to enhance the ac-
curacy of the final stage of refinement (Figure 2.3). The simulation is detailed as
follows. The continuum region covers the whole domain of the simulation, even
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