No announcement yet.

Tethered swimming and work in cyclic motion

This topic is closed.
  • Filter
  • Time
  • Show
Clear All
new posts

  • Tethered swimming and work in cyclic motion

    Dear Biomch-L,
    There have been plenty of thoughtful discussions on the work
    done by the tethered swimmer. I agree with Paolo de Leva and some
    others, the work done by the tethered swimmer on water per cycle
    is not equal to zero and is positive generally. The work can be
    calculated, as we often did in the studies of aquatic animal
    locomotion, if you know hydrodynamic forces acting on the swimmer
    (basically the fluid pressure field near the swimmer) at any
    instant. Multiplying the distributive hydrodynamic force by
    the corresponding differential displacement, and summerizing
    (integrating) it over the whole body surface and over one cycle
    give a value, negative of which is the work done by the swimmer
    on surrounding fluid and is supplied by the mechanical energy
    produced by muscle contraction. But this method probably won't
    help much in solving the problem posted by the originator of
    the debate. The reason is that, I believe, little about the
    fluiddynamics of human swimming has been known. I would expect
    that the fluid flow around a normal adult human swimmer is
    associated with large or middle Reynolds numbers (during swimming).
    Thus the hydrodynamic forces acting on the body or body parts at
    any instant is path dependent and even history dependent
    (we need to know complete kinematics in order to obtain
    the hydrodynamic forces).
    I would say that many arguments about the fluid flow in
    previous posting are wrong, but this can be excused as those
    people probably have not much backgroud in the mechanics
    of continuous media.
    For those of you interested in swimming, I have listed below
    some of our work on aquatic animal swimming. These studies
    include hydrodynamics, swimming mechanics, and dynamics of
    locomotor system. We can quantify the mechanical energy
    generated by muscle contraction, and its partition into
    water for propulsion, to deform internal soft tissues,
    and maintaining cyclic motions of the body parts.

    Cheng J-Y., Zhuang L-X., Tong B-G., Analysis of swimming three-dimensional
    waving plates, J. Fluid Mech., Vol .232: 341-355, 1991
    Blickhan R. & Cheng J-Y., Energy storage by elastic mechanisms in the
    tail of large swimmers-- a re-evaluation, J. Theor. Biol., Vol.168:315-321,
    Cheng, J-Y & Blickhan R., Bending moment distribution along swimming
    fish, J. Theor. Biol., Vol.168:337-348, 1994
    Cheng, J-Y & Blickhan R., Note on the calculation of propeller
    efficiency using elongated body theory, J. Experimental Biology, Vol.192:
    p169-177, 1994
    Cheng, J-Y., DeMont, M.E., Jet propelled swimming in scallops:
    swimming mechanics and ontogenic scaling, Canadian Journal of Zoology
    Cheng, J-Y., DeMont, M.E., Hydrodynamics of scallop locomotion:
    unsteady fluid force acting on clapping shells, J. Fluid Mech.
    Cheng, J-Y., Davison, I & DeMont, M.E., Dynamics and energetics
    of scallop swimming, J. Experimental Biology, (submitted)


    Jianyu Cheng
    Biology Dept, STFX University, Canada