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Molecular Dynamics Simulation of Nano-Robot Motion in Nano-Scale Flows

Khaledi-Alidusti, Rasool | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 41508 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Abbaspour, Madjid; Darbandi, Massoud
  7. Abstract:
  8. There is a need to achieve a capability for detailed modeling of the physical processes nano-robots at nano-scales that is driven by the growing demands of nanotechnology.. This is regime where behavior runs contrary to the familiar macroscopic world; optimized engineering design may well benefit from insight gained by emulating some of the multitude of architectures and mechanisms to be found in the biological world. Despite the fact that micro-robotics has long captured the imagination, practical implementations are only now starting to become feasible. One class of nano-robot with potential medical applications was considered that made of single wall carbon nanotube; however, long before such devices were conceived, studies of the dynamics of microscopic biological forms, and the theoretical analysis of hydrodynamics at correspondingly low Reynolds numbers— Re ≈ 10−5—made clear that the prevailing fluid environments were unlike those encountered in more familiar circumstances where Re >> 1.0). This is known as Stokes (or creeping) flow, and responsibility for the counterintuitive behavior lies in the absence of inertia from the dynamics. In this study, nonequilibrium molecular dynamics (NEMD) simulations were performed to cross and axial drags calculation on a nanotube in uniform liquid argon and water molecules separately. The behavior of fluids in nano-scale channels is very different from the behavior in microscopic and macroscopic channels. So, getting a formula to estimation cross and axial drags on a nanotube in nano-scale and Re≤1.0 is the main purpose of doing this study. To reaching to this purpose, we simulated (6,0), (8,0) and (10,0) nanotubes in argon flow with different velocities and computed cross drag coefficient against Reynolds number in each simulation. To improve the efficiency of the system simulations, the insertion of molecules using of USHER algorithm was examined, and the molecules remove when pass from the end of the simulation box. According to our results in each simulation, and using of power trend line, we estimated a formula to calculation cross and axial drags on a nanotube. In every simulation, only the first 2 and last 2 rings of the nanotube are frozen. All non-bonded interactions were calculated based on Lennard-Jones potential. Molecular dynamics results were compared with two empirical equations which were based on experiments in macro-scale cylinders. Results show that in slow flows (Re<<1.0), the drags force on a single-walled nanotube calculated from MD simulations were larger than those from the empirical equations. So, classical continuum mechanics cannot be used to calculate drag on a nanotube in Re<<1.0. The difference increased as the flow velocity decreased. And for higher velocity flows, the difference decreased. In addition, in this study we have been examined some properties of water molecules in different conditions. Water molecules are one of the important molecules in nanofluidics. The structure of this molecule can change with Temperature and cutoff distance parameters. Temperature and cutoff distance effects on the behavior of nanoscale water molecules are investigated by molecular dynamics simulations. Many water molecular models have been developed in order to help discover the structure of water molecules. In this study, the flexible three centered (TIP3P-C) water potential is used to model the inter- and intramolecular interactions of the water molecule. In this simulation, we have been studied 512 water molecules in a simulation box with 25 angstrom dimensions. It means the density of water has been supposed 0.99 g/cm3. To examine of accuracy of TIP3P-C model, Radial distribution function of remarkable water model has been compared with experimental data. In this paper, to study temperature effect on water behavior, mentioned system with 300, 450 and 600 K have been considered and compared. The results have showed that with decreasing temperature, the tetrahedrality of the distribution of the water molecules around the central water molecule is enhanced, and the hydrogen bonds become more linear. It is found that as the temperature rises, kinetic energy rises too, and it makes that the average number of hydrogen bonds per water molecule decrease. In addition to Temperature, Cutoff Radius parameter effect have been considered too, and four different Cutoff radiuses 7.5, 9.0, 10.5, and 12 angstrom have been studied
  9. Keywords:
  10. Carbon Nanotubes ; Molecular Dynamics ; Drag Force ; Molecular Dynamic Simulation ; Nanorobot

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