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Hydrodynamics of human swimming propulsion
J. Paulo Vilas-Boas, Ph.D
Full Professor, Olympic Coach, Pres.GA Portuguese Swimming Federation, SG-BMS-WCSS
Who I am, and
how do I see myself in swimming ?
Full Professor
Olympic Swimming
Coach
VP for C. Educ.
SG-BMS, WCSS
Myself (also as a biophysicist) in swimming
Swimming research and assessment should
be relevant for practical swimming purposes!
Vilas-Boas family
Hydrodynamics
of swimming
fundamentals for the
understanding of
propulsion
The “theory”
theory” of technique
The rational of the movement
Hydroynamic drag
(pressure, friction, wave)
Hydroynamic propulsion
(drag, lift, vortex)
P+D=m*a
P > D → a is positive
P < D → a is negative
P = D → a = 0 → v = const.
The swimming technique is it important for the elite swimmer?
.
W=D
.
.
W=E
.v
.e
D = ½ ρ CD S v2
.
W = K . v3 (K = ½ ρ CD S)
.
.
W=D v= E
.
.
v = E
di Prampero et al. (1974)
.
.e
p
ep
.
E
D
v
=
D
ep
p
[email protected]
Electronics
development
Swimming biomechanics (research, evaluation & advice)
Swimming physiology (research, evaluation & advice)
Swimming psychology (research, evaluation & advice)
Swimming training (research, evaluation & advice)
Force Plates
dynamometry
16
+Vss
+
2 1
8
AD621AN
3 5
-
Image based
3D Kinematics (APAS,
Peak, SIMI)
+ other kinematics
6
17
Policarbonato
2
COM
30
+15V
GND
10K
+Vss
150K Ω
-Vss
-Vss
Vo
1
100K
1 µF ±5%
7
4
19
AD210BN
14
15
18
29
Ref.
10cm cabos Holter
(2m; 4 x 0.1mm, 7 x multicore)
screened; 85pF/m; 384 /km
Ω
Préamplificador
mV
10.0000
8.00000
6.00000
4.00000
2.00000
0.00000
mV
EMG
10.0000
5.00000
0.00000
-5.00000
-10.0000
ABS
EMG
2.00000
1.00000
mV
envelope
3.00000
0.0000
Direct
Oxymetry + [La-]
5.0000
10.000
15.000
seconds
20.000
25.000
5.00000
4.00000
3.00000
2.00000
1.00000
0.00000
mV/sqrt(s)
2.50000
2.00000
1.50000
1.00000
0.50000
0.00000
-0.50000
mV.s
iEMG
RMS
0.00000
Biophysical approaches
N = 26 (8 Fem, 18 Mal)
110
E-tot (mlO2/Kg/min)
100
90
80
Back
70
Breast
60
Fly
50
Free
40
30
20
10
1.0 m/s
1.2 m/s
1.4 m/s
1.6 m/s
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N=5
3 x 200 (75, 85, 100%)
30 min rest
P = 0.5 ρ CD S v3
EC = f (∆
(∆v/c)
v/c)
Mechanisms for
the production of
hydrodynamic
propulsion
“We don’t know exactly how the
swimming movements propels the
swimming body through the water,
and the complex flow patterns found
in the real conditions make difficult
any mathematical analysis”
Gadd (1963, p. 483)
- theory of non viscous flow
over slender bodies
- theory of quasi-static flow
Static flow (stable flow)
Quasi static flow
Unstable flow (non static flow)
Present theoretical situation:
Propulsive drag theory
Propulsive lift (foil) theory
Propulsive vortex theory
Propulsive drag
theory
Cureton (1930)
Counsilman (1968)
According to the
propulsive drag theory:
Swimmers propelled themselves through
successive propulsive segmental actions
that intend to push water backwards in
relation to the intended direction for entire
body movement
Theoretical background:
Newton's 3th low of motion (action / reaction)
(propulsive ) DRAG force Newtonian equation:
DP = 0.5 ρ CD v2 S
DP = Hydrodynamic (propulsive) drag force
ρ = water specific mass
CD = drag force coefficient
v = relative velocity
S = Maximal cross-sectional area normal to force direction
Shoulder / hand
Hand / water
Shoulder / water
Main reasons for
hydrodynamic drag force theory
popularity
(Barthels, 1977)
- The swimmer perceives his movements as “backward”
oriented movements
- A exterior observer perceives the swimmers’ movements
as “backward” oriented movements
Kinematic references
Photogrametry
Permanent light-trace photography
Anatomic
markers
(actives)
LEDs & lamps
Vilas-Boas (1993); Vilas-Boas & Ferreira da Silva (1993)
Photogrametry
Permanent light-trace
photography
Alves & Vilas-Boas (1992). Kinematical
analysis of freestyle hand-path with and
without hand-paddles
Vilas-Boas (1993)
Vilas-Boas & Ferreira da Silva (1993).
Análise cinemática da técnica de bruços ondulatório
com recuperação aérea dos membros superiores
Photogrametry
Permanent light-trace
photography
FHUDSP
HiIT =
HiTDSP
HiHD
HA-PHD
IH =
HD
HD
FIT =
HA-PHD
FTUDSP
FHUDSP
HiTDSP
FTUDSP
HiHD
Vilas-Boas & Cunha (1995). Fatigue related technical changes in butterfly swimming.
Vilas-Boas et al. (1996). Movement analysis in simultaneous swimming techniques.
Propulsive lift
(foil) theory
Counsilman (1971)
Schleihauf (1974, 1979, 1984, 1986)
Schleihauf et al. (1983, 1988)
Wood (1979)
Berger (1996)
Berger et al. (1996)
…
Basic assumption:
Part, or the totality, of the
propulsive segments are
able to produce a
hydrodynamic force
perpendicular to its
direction of movement
relative to the fluid.
Lift force:
Defined as a hydrodynamic
force perpendicular to the
body’s direction of motion.
Characteristics of the “in-fluid” moving bodies that allow
the production of a hydrodynamic force perpendicular to
the relative direction of movement:
Nortrip et al. (1974)
- The body has a “aerofoil” shape
- Translation occurs together with a
rotational movement of the body
- The surface of the body is oriented with a
acute angle in relation to its direction of
movement
Bernoulli theorem:
For ideal fluids, there exists an
inverse relationship between
velocity and pressure
Magnus effect
> V; < P
< V; > P
Schleihauf (1974, 1979, 1984, 1986)
Schleihauf et al. (1983, 1988)
Wood (1979)
Berger (1996)
Berger et al. (1996)
The Human hand and forearm are
able to produce hydrodynamic lift
forces due to the similarity of its
shapes with a aerofoil shape.
Production of
hydrodynamic lift
force by a aerofoil
shape object
(propulsive) LIFT force Newtonian equation:
L = 0.5 ρ CL v2 SL
L = Hydrodynamic (propulsive) lift force
ρ = water specific mass
CL = lift force coefficient
v = relative velocity
SL = Maximal cross-sectional area normal to force direction
Thomson theorem:
Into a non-viscous
incompressible flow
submitted to the action
of potential massic
forces, the velocity
circulation along any
close fluid contour is
constant on time.
Is hydrodynamic
LIFT FORCE the...
...only propulsive force in
swimming?
...main propulsive force in
swimming?
L
R
Dp
Critics to the foil theory
X
Critics to the foil theory
Steady flow
Newton vs. Bernoulli
vs.
???
Unsteady flow
Evidencies “pro-foil”
(Schleihauf, 1979)
(Reischle, 1988)
“Tortuosity”
Tortuosity” of limb movements
and prevalence of vertical and
mediummedium-lateral displacements.
Propulsive surfaces are not
hydrodynamic neutral
(Berger, 1996)
Presence of tip vortexes
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Drag force (N)
CFD- Computer Flow Dynamics
Fluent® software
Velocity (m/s)
Marinho, D.A.; Reis, V.M.; Vilas-Boas, J.P.; Alves, F.B.; Machado, L.;
Rouboa, A.I.; Silva, A.J. (2010). Design of a three-dimensional
hand/forearm model to apply Computational Fluid Dynamics. Brazilian
Archives of Biology and Technology, 53 (2): 437-442.
α
CD
CL
0º
0.35
0.18
45º
0.63
0.32
90º
1.10
0.05
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CFD- Computer Flow Dynamics
Fluent® software
1,1
Marinho, D.A.; Barbosa, T.M.; Reis, V.M.; Kjendlie, P.L.; Alves, F.B.; Vilas-Boas,
J.P.; Machado, L.; Silva, A.J.; Rouboa, A.I. (2010). Swimming propulsion forces
are enhanced by a small finger spread. Journal of Applied Biomechanics, 26: 8792.
Fingers "abertos"
Fingers "semiabertos"
Fingers "fechados"
0,9
Fingers
0,7
Lift coefficient
Drag coefficient
0,7
0,5
0,3
Attack angle (degrees)
0,5
0,3
0.64 cm spread
0.32 cm spread
closed
0,1
0
15
30
45
60
Angle of attack (º)
75
90
0,1
0
15
30
45
60
Angle of attack (º)
75
90
Effective hydrodynamic
propulsive force:
The component on the direction of intended body motion, of
the...
...resultant
force (R) of
hydrodynamic propulsive lift (L)
and
hydrodynamic propulsive drag (DP)
forces
L
P
R
Dp
Propulsive segments hydrodynamic configuration:
Orientation relatively to the flow
Inclination relatively to the flow
Angle of attack
(α
α)
Angle of orientation
- Sweepback - (Ψ
Ψ)
Robert Schleihauf Jr. (1979)
CL values
CD values
Finger positions
Tumb positions
Robert Schleihauf Jr. (1979)
Toussaint (2002)
Velocity of
segments
Direction of the successive
phases of the propulsive
pathway of propulsive
segments
Circumstantial
characteristics
of segments
α
Ψ
direction, orientation, intensity
of DP, L and R
Intensity of
P
Adapted from Vilas-Boas (1986)
The kinetic analysis of swimming techniques showed:
Propulsion produced at least from the arms
action is (partly) due to a combination of
propulsive drag and propulsive lift forces.
Circumstantially one or the other of both forces
assumes a more relevant propulsive role.
(Schleihauf, 1974, 1979, 1984, 1986; Wood, 1979; Schleihauf et al.,
1983, 1988; Thayer et al., 1986; Berger, 1996; Berger et al., 1996)
These findings do not exclude the contribution of other
propulsive mechanisms.
General methodology used by Schleihauf
Schleihauf (1974, 1979, 1984, 1986) and Schleihauf et al. (1983, 1988):
To assess CD and CL values for the human hand in
different positions (fingers and thumb) and different
orientations;
To determine the hand pathway, velocity, orientation
and inclination (attack)
To combine both steps for the assessment of L, DP
and R
Kolmogorov e Cappaert (sd). Personal repport
81.33 .308
±12.09 ±0.061
Kolmogorov e Cappaert (sd). Personal repport
Kolmogorov e Cappaert (sd). Personal repport
Kolmogorov e Cappaert (sd). Personal repport
Kolmogorov e Cappaert (sd). Personal repport
Propulsive vortex
theory
Colwin
Ungerecht
Colman
Arellano
Propulsive vortex theory
Specially centred into leg
actions of front crawl,
backstroke and butterfly
Lift force paradox for leg kick
sinusoidal movements
(crawl, back-crawl and butterfly)
(Maglischo, 1982)
Vortex:
mass of
water
animated
of an
organized
rotational
movement
Vortex (flow) visualization:
Water aeration
Water coloration
Extremity
vortices and
propulsive lift
theory
Extremity vortices
aerofoil effect
Ring (or cylinder)
vortices and
unsteady flow
propulsive theory
Unsteady flow
Colwin approach
Colwin approach
Ungerecht approach
Arellano
Synthesis of today
conception of human
swimming propulsion
We are convinced that:
Newtonian action / reaction is present
Bernoullian lift and / or other lift forces are present
Propulsive drag force plays a very important role
Unstable flow situations are determinant
Rotating water plays a determinant role
Thank you very much!
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