The Navier-Stokes equations were used to simulate two laterally driven microcomb structures in this study. The total quality factors predicted numerically agree quite well with the experimental data. The numerical results show that the bottom surface of the oscillating structure contributes about 66% of the total damping and is very close to that predicted by the Couette flow model. The top, side, and edge surface each contributes about 10-12%. The flow above the oscillating structure is far from the Stokes flow due to the curvilinear fluid motion generated by the pumping and sucking motions of the oscillating structure. Lifting the gap between the oscillating structure and the substrate is an effective way to reduce the total damping, and its effectiveness was investigated. The magnitude of the amplitude of the oscillating structure was found to have very minor effect on the damping. The slip effect was also included in this study. The slip effect reduces the viscous damping on the bottom surface of the oscillating structure by about 7%. (C) 2004 Elsevier Ltd. All rights reserved.