Assessment of passive drag in swimming by numerical simulation and analytical procedure.

The aim was to compare the passive drag-gliding underwater by a numerical simulation and an analytical procedure. An Olympic swimmer was scanned by computer tomography and modelled gliding at a 0.75-m depth in the streamlined position. Steady-state computer fluid dynamics (CFD) analyses were performed on Fluent. A set of analytical procedures was selected concurrently. Friction drag (D), pressure drag (D), total passive drag force (D) and drag coefficient (C) were computed between 1.3 and 2.5 m · s by both techniques. D ranged from 45.44 to 144.06 N with CFD, from 46.03 to 167.06 N with the analytical procedure (differences: from 1.28% to 13.77%). C ranged between 0.698 and 0.622 by CFD, 0.657 and 0.644 by analytical procedures (differences: 0.40-6.30%). Linear regression models showed a very high association for D plotted in absolute values (R = 0.98) and after log-log transformation (R = 0.99). The C also obtained a very high adjustment for both absolute (R = 0.97) and log-log plots (R = 0.97). The bias for the D was 8.37 N and 0.076 N after logarithmic transformation. D represented between 15.97% and 18.82% of the D by the CFD, 14.66% and 16.21% by the analytical procedures. Therefore, despite the bias, analytical procedures offer a feasible way of gathering insight on one's hydrodynamics characteristics.