2. Biomechanics of propulsion and drag in front crawl swimming Huub Toussaint Institute for Fundamental and Clinical Human Movement Sciences Vrije Universiteit, Amsterdam, Holland www.ifkb.nl/B4/indexsw.html H_M_Toussaint@fbw.vu.nl

4. Buoyancy Weight Drag Propulsion

5. How is propulsion generated? Pushing water backwards

6. Viewpoints:

7. Front crawl kinematics Pushing water backwards?

8. Hand functions as hydrofoil

9. Hydrofoil subjected to flow

10. Hand has hydrofoil properties

11. Lift and drag force

12. Adapt  to direct F p forward

13. Quasi-steady analysis

14. Quasi-steady analysis: Combining flow channel data with hand velocity data

15. MAD-system

16. Propulsion: Results Quasi- steady analysis vs MAD-system

17. Does the quasi-steady assumption fail? How to proceed? A brief digression The aerodynamics of insect flight

18. ‘The bumblebee that cannot fly’ l Quasi-steady analysis cannot account for required lift forces l Hence, there must be unsteady, lift-enhancing mechanisms

19. Delayed Stall Unsteady lift-enhancing mechanism Add rotation…. and visualize flow

20. Hovering robomoth

21. 3D leading-edge vortex

22. Delayed stall: the 3D version l Leading-edge vortex stabilized by axial flow l Can account for ~ 50% of required lift force l Key features: –Stalling: high angle of attack (~ 45º) –Axial flow: wing rotation leads to an axial velocity / pressure gradient –Rotational acceleration (?)

23. So what’s the connection?

24. ...back to front crawl swimming l Short strokes & rotations: unsteady effects probably play an important role l Explore by flow visualization l Our first attempt: –Attach tufts to lower arm and hand to record instantaneous flow directions

26. Outsweep

27. Accelerated flow

28. The pumping effect arm rotation  pressure gradient  axial flow

29. Toussaint et al, 2002

31. Buoyancy Weight Drag Propulsion

32. Drag:

33. ship v

34. Divergent waves Transverse waves ship

35. Effect of speed on wave length Wave drag 70% of total drag (of ship)

36. Length of surface wave Hull speed for given length (L) of ship:

37. Height of swimmer 2 m: Hull speed for a swimmer “Pieter” swims > 2 m/s…..

38. Wave drag as % of total drag 12%

39. Summary  humans swim faster than ‘hull’ speed  wave drag matters at competitive swimming speeds but is with 12% far less than that for ships where it is 70% of total drag

40. Interaction length of ship (L) with wave length ( )

41. hull speed reinforcement cancellation reinforcement

42. hull speed

44. Could non-stationary effects reduce wave drag?

45. Takamoto M., Ohmichi H. & Miyashita M. (1985)

46. ‘Technique’ reducing bow wave formation?  Glide phase: arm functions as “bulbous bow” reducing height of the bow wave  Non-stationarity of rostral pressure point prohibits full build-up of the bow wave ship

47. With whole stroke swimming speed increases about 5% without a concomitant increase in stern-wave height. The leg action might disrupt the pressure pattern at the stern prohibiting a full build up of the stern wave

48. THANK YOU FOR YOUR ATTENTION