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unknown user
09-05-2005, 07:27 AM
Dear List Members-

Thank you for the references and interest you sent in response to my original
posting 'swimming and hydrodynamics'. I have included a copy of the original
posting and a summary of the responses below in two categories: reference
referrals and interest.

Generally speaking the question boiled down to:

extra stress = extra drag = rho * axial velocity * rotational velocity
(rho is the density of the fluid); extra stress and extra drag being related
since the water flowing around the object has to move in more than one direction

Thanks again!
Bethany Larsen

Arizona State University
Department of Kinesiology, Biomechanics
Tempe, AZ 85287
Bethany.Larsen@asu.edu

REFERENCES:
You may want to communicate directly with Prof Tim Pedley, Cambridge
(UK). I don't have his e-mail address handy, but I saw him give a
lecture on swimming/water locomotion in Vail this summer for the Second
Frontiers in Biomechanics Symposium, for which I acted as co-chair. He
may be able to provide you with some insights. Good luck!

David A. Vorp, Ph.D.

Associate Professor of Surgery and Bioengineering
University of Pittsburgh

---------------------------
the following article by some colleagues of mine:
The swimming flume at Otago could certainly be used to address such
questions as the one you pose.

Vennell, R., D. Pease, & B. Wilson (2005). Wave Drag on Human
Swimmers, In press Journal Biomechanics.


Dr Chris Button
Director of the Human Performance Centre
University of Otago, School of PE


---------------------------
This idea has been investigated by Counsilman(1955) by comparing the towing
forces of subject while rotating and in stationary prone and back positions.
You can find it in Research Quarterly at the same year.

Roozbeh Naemi
PhD student
Centre for Aquatics Research and Education
University of Edinburgh

---------------------------
In response to your request, I would have a look at the work from Dr
Andrew Lyttle in Australia. He has done some great work, especially
looking at drag changes at different kick amplitudes, glide depths,
dolphin vs flutter and body position.

This is a link (paste in your browser) to 'his' page with his employer:
www.wais.org.au/SiteTemplate-WAIS/scripts/viewoverview_contact.asp?NID=2
810

and his old college:
http://www.hmes.uwa.edu.au/about/research/publications


Lee Nicholson
Sports Scientist - Biomechanics
Athlete & Coach Support Services
Queensland Academy of Sport

---------------------------

INTEREST:
No, but it seems that generating any sort of axial angular momentum is going
to require some lift generation, which always comes with drag.

I'm not an engineer, just a doctor and a swimmer, and I probably have no
idea what I'm talking about, but I also sail and when you think about
hydrofoils, there is no lift without drag, period. So there might be more
and less efficient ways of rotating, but they will all incur some drag,
because rotation requires differential lift somewhere on the body. So I
would assume one should come off the wall in as close to the proper
rotational angle as possible, provided that doesn't slow the rest of the
turn down any. How much drag rotation generates as compared to other things
(e.g. Hand position) is difficult to say.

Sorry, no knowledge of articles or studies on the subject. Cool topic,
though. Good luck.

Rgds,
Karl Wittnebel
Washington, dc

---------------------------
Interesting post - I cannot help with the literature, but I will provide my
two cents based on personal experience. From a (now-retired) competitive
swimmer's standpoint I think that although additional drag may be apparent
during a rotating streamline, turning onto the front after the flip (ie.
while still on the wall) is typically much slower. I've found most
competitive swimmers do maybe a 30-45 degree rotation as part of their flip
turn such that their feet land on the wall already rotated, they then
require much less rotation as part of their streamline. The rotation need
not occur all at once, rather I think it is preferable to rotate gradually
during streamlining. In addition, if still on a slight angle at the end of
the underwater streamline, the lower arm position can achieve a very strong
pull for the initial freestyle stroke.


Matthew R. Walker, MSc, CSCS
Biomechanical Engineer
Motion Analysis Laboratory
Shriners Hospitals for Children, Erie, PA
mrwalker@shrinenet.org
http://www.shrinershq.org/research/erie

---------------------------

Interesting question. I don't have a study to offer, but from a practical
standpoint, I do have a question: does this imply that the time saved by
pushing off in the supine position is offset by the drag created by rotation
during the transition to prone position while maintaining a streamlined body
orientation?

This doesn't seem practical. That is, if a swimmer reorients the body
position after making the turn, then pushes off, that would result in less
drag and higher acceleration during the push off since rotation of the body
is eliminated?

From a former swim coach, a faster turn is accomplished if the swimmer
pushes off in the supine position, then rotates. I don't have the numbers,
but the angular velocity of the rotation is, relatively speaking, not very
high given the proper push off (i.e., there is plenty of time to rotate
during the glide phase before the stroke begins).

This is a fluid dynamics problem that someone in engineering (at your
university) could answer for you. It could be calculated (i.e., the
additional fluid drag for an object rotating perpendicular to the direction
of travel). But also, this would be "skin drag" and not "form
drag" or
"pressure drag" that is associated with the cross sectional area
exposed to
the oncoming flow. That would not change unless the body was rotating along
some axis not parallel to the direction of travel (i.e., the area changes as
the swimmer rotates).

I'd be interested in knowing what you find out. Good luck with the thesis.

R.D. Clark, Ph.D.
Dept. of Kinesiology
California Polytechnic State University