Biomechanics of propulsion and drag in front crawl swimming

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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_at_fbw.vu.n
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Buoyancy
Drag
Propulsion
Weight
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How is propulsion generated?
Pushing water backwards
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Viewpoints
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Front crawl kinematics
Pushing water backwards?
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Hand functions as hydrofoil
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Hydrofoil subjected to flow
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Hand has hydrofoil properties
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Lift and drag force
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Adapt ? to direct Fp forward
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Quasi-steady analysis
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Quasi-steady analysis Combining flow channel
data with hand velocity data
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MAD-system
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Propulsion ResultsQuasi- steady analysis vs
MAD-system
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Does the quasi-steady assumption fail?
How to proceed?A brief digressionThe
aerodynamics of insect flight
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The bumblebee that cannot fly

• Quasi-steady analysis cannot account for required
  lift forces
• Hence, there must be unsteady,lift-enhancing
  mechanisms

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Delayed Stall
Unsteady lift-enhancing mechanism
Add rotation. and visualize flow
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Hovering robomoth
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3D leading-edge vortex
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Delayed stall the 3D version

• Leading-edge vortex stabilized by axial flow
• Can account for 50 of required lift force
• Key features
• Stalling high angle of attack ( 45º)
• Axial flow wing rotation leads to an axial
  velocity / pressure gradient
• Rotational acceleration (?)

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So whats the connection?
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...back to front crawl swimming

• Short strokes rotations unsteady effects
  probably play an important role
• Explore by flow visualization
• Our first attempt
• Attach tufts to lower arm and hand to record
  instantaneous flow directions

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Outsweep
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Accelerated flow
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The pumping effect arm rotation ? pressure
gradient ? axial flow
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Toussaint et al, 2002
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Buoyancy
Drag
Propulsion
Weight
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Drag
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v
ship
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ship
Divergent waves
Transverse waves
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Effect of speed on wave length
(of ship)
Wave drag 70 of total drag
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Length of surface wave
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Hull speed for a swimmer
Height of swimmer 2 m
Pieter swims gt 2 m/s..
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Wave drag as of total drag
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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

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Interaction length of ship (L) with wave length
(l)
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hull speed
reinforcement
cancellation
reinforcement
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hull speed
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Could non-stationary effects reduce wave drag?
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Takamoto M., Ohmichi H. Miyashita M. (1985)
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Technique reducing bow wave formation?

• Glide phase arm functions as bulbous bow
  reducing height of the bow wave

ship

• Non-stationarity of rostral pressure point
  prohibits full build-up of the bow wave

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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
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