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List of Responses to Swim and Hydrodynamics

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  • List of Responses to Swim and Hydrodynamics

    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

    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:

    and his old college:

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


    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.

    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


    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

    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