MOLECULAR DYNAMICS STUDIES OF FLOW AND SWIMMING AT MICROSCOPIC SCALES

00:00 13-05-2008
<p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">Recent applications of molecular dynamics (MD) simulation</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">to complex hydrodynamical phenomena are described.   The first case</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">involves spontaneous pattern formation  in externally driven fluids,</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">modeled at the discrete-particle level using MD.   Two examples are</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">considered, Rayleigh-Benard convection  in  a  thin layer  where an</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">almost perfect array of hexagonal convection  cells  develops,  and</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">Taylor-Couette vortex formation  in an annular container where even</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">quantitative  agreement  with  continuum  theory  is  obtained. The</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">second case deals  with  self-propelled motion (swimming) of fluid-</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">immersed microscopic bodies,  a problem of growing interest because</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">of  its  relevance  to  nanotechnology, again modeled using MD. The</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">advantage of the atomistic approach is  that the detailed level  of</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">description  allows  complete  freedom  in  specifying  the swimmer</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">design and its coupling to the fluid.  A variety of two-dimensional</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">swimmers employing  propulsion  mechanisms  motivated by biological</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">and microrobotic design are investigated,  including  moving  limbs,</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">changing body shapes  and  fluid  jets.  The  efficiencies  of  the</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">mechanisms  and  the  nature  of  the  induced, time-dependent flow</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">fields  differ  widely  among  swimmers.   The corresponding three-</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">dimensional problem  is  also  mentioned.   The cost of  the highly</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">detailed MD approach  is the relatively extensive computations that</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">are sometimes necessary,  even  though  the actual system sizes are</font></span></p> <p class="MsoNormal" style="MARGIN: 0in 0in 0pt"><span style="FONT-FAMILY: 'Courier New'"><font face="Arial, Helvetica, sans-serif" size="2">microscopic.</font></span></p>