Molecular Dynamics Simulation of Flow at Nano Scale

1
Molecular Dynamics Simulation of Flow at Nano
Scale

• Tao Yang
• Department of Mechanical Engineering,
• IUPUI
• Faculty Advisor Dr. Andrew T. Hsu

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Emerging of Nano Technology

• The construction of things, one-atom-at-a-time,
  becomes possible, and nano-scale becomes
  accessible to technology.
• Classical theories fail down at nano scale.
• In fluid mechanics, continuum assumption is no
  longer valid at nano-scale
• New method is needed to simulate the flow at nano
  scale.

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Molecular Dynamics

• Molecular Dynamics Simulation is a method to
  simulate the motion of molecules, molecule by
  molecule,and then get its macroscopic properties.
• Two basic tasks for Molecular Dynamics
• To find the force acting on a molecule
• To integrating the equation of motion to find the
  velocity and displacement of the molecule

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Molecular Dynamics

• It derives directly from the basic laws of
  physics, such as Newtons second of law of
  motion Fma
• No assumptions for the macroscopic, such as
  continuum assumption, is assumed.

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Lennard-Jones Potential

• Lennard-Jones Potential was used to calculate the
  forces between atom pairs.

• ? and ? are characteristic energy and diameter,
  respectively.
• ? and ? are determined by the properties of atom.
  
• In the case of liquid argon

L-J Potential
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Algorithm and Time Step

• A fifth-order accuracy Gear Prediction and
  Correction algorithm was employed to integrate
  the equation of motion.
• The integration was carried out with a time step
  ?t0.005?,where ?(m ?2/ ?)1/2 is the
  characteristic time of the Lennard-Jones
  potential.
• A general simulation usually require a time
  period of about 100 ?

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The Settings of Simulation
U
Graphite structure

• h varies from about 3 nm to 6 nm

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Velocity Profile ( h16? U1 ?/? )
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Velocity Profile ( h8? U1 ?/? )
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Animation Projection of a X-Z Plane
(6?ltylt7?)
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Animation Projection of a x-y plane (Near the
still plate)
(0ltzlt1.5?)
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Animation Projection of a X-Y plane (Near the
moving wall)
(14.5ltzlt16?)
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Animation Projection of a X-Y plane
(In the middle)
(7.5 ? ltzlt8.5?)
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Conclusion

• From the result we can find that the flow at nano
  scale is quite different with that at macro
  scale.
• The simulation demonstrated that Molecule
  Dynamics is a viable way to simulate flow at nano
  scale.
• Investigation of boundary condition at nano scale
  will be helpful in this area.