Simple Equation of Motion

The reason why the effective dynamics above are implemented rather than the simple Newton's equation of motion

$$\frac{{\rm d}\bm{U}}{{\rm d}t} = -\bm{F}_{\text{stokes}} +\bm{F}_{\text{ext}} ,$$ (2.19)

where St is the true Stokes number and $\bm{F}_{\text{stokes}} = \bm{R}\cdot\bm{U}$, is that the latter gives similar behavior in the massless dynamics due to the strong (diverging) resistance in the lubrication. [17]

** I'll implement this dynamics soon. **