New Indirect Method for Calculation of Flow Forces on Immersed Bodies in Molecular Dynamics Simulation

Abstract

In this paper, two different approaches of calculating forces in molecular dynamics simulation are investigated and a new method is presented. Drag force on a carbon nanotube in uniform liquid argon flow is evaluated using these three methods. Nanotube is modeled as a rigid cylinder and all the interactions are calculated by Lennard-Jones potential function. First of all common method of calculating drag by direct summation of forces in flow direction is used to verify the code and simulation. Then the continuum approach of calculating forces using momentum balance and change in flow velocity profile is implemented and investigated. Results of this approach show that the increase in number of bins used for velocity measurement will decrease the difference with direct method about 5%. Nevertheless the continuum approach at the best underestimate the drag force by about 20% of direct summation and confirm the fact that continuum approaches are not necessarily appropriate at nanoscale flows. Finally a molecular momentum balance method is presented and used for calculating drag force. The new presented method works properly and the difference with the direct summation method can be reduced from 30% to less than 1% by increasing the number of time steps used for data averaging.