In the medical field, microrobots that use swimming motions to move may make micromanipulations in unreachable environments. 
The equation used for a blood vessel:
where,
: f = oscillation frequency of the microbot swimming motion
: D = blood vessel diameter
: V = unsteady viscoelastic flow
The Strouhal number is used as a ratio of the Deborah number (De) and Weissenberg number (Wi):
The Strouhal number may also be used to obtain the Womersley number (Wo). The case for blood flow can be categorized as an unsteady viscoelastic flow, therefore the Womersley number is
Or considering both equations,