This study examines the effects of acceleration on fluid forces acting on the hand in swimming and presents a new pressure method to predict fluid forces acting on the accelerating hand.
Swimmers and coaches require accurate information about swimmers� fluid forces, propulsion and drag, in order to improve performance. In general, swimmers are likely to generate propulsion mainly with their hands in the front crawl stroke, butterfly and back crawl stroke. Researchers have attempted to estimate the fluid forces on the hands with various techniques including a cinematographic method (a "quasi-static" approach), a pressure method and a numerical method of computational fluid dynamics. However, the effect of accelerations on fluid forces acting on the hand has not yet been well quantified. Understanding of the effect of acceleration on fluid forces on the hand can provide useful information to enhance swimming performance. Also the developments of a method to predict fluid forces acting on the accelerating hand in swimming can be used to evaluate swimming performance more accurately. The present study used a hand model attached to a load cell to measure forces in three orthogonal directions and pressure sensors to measure pressures on the hand model rotated in the flume. The model position was measured by a potentiometer fixed to the axis of the model rotation.
The quantification of the effect of acceleration was based on a simple theoretical understanding for fluid mechanics, using the inertia coefficients and the coefficients of fluid forces, that is widely accepted in other disciplines. The quantification was focused mainly in the direction tangential to the model rotation because the magnitude of the velocity changed in this direction. The overall effect of acceleration on fluid forces on the hand model was that the inertia coefficients increased rapidly in the early phase of the model movement, then in the final deceleration phase of model movement the inertia coefficients decreased to a negative value and then became small. The inertia coefficient increased in the impulsive start of the hand model, indicating that fluid forces acting on the hand increased as accelerations of the hand increased. This result was consistent with the simple theoretical understanding to induce additional fluid forces on the hand, that is, fluid forces on the hand increased as accelerations increased. However, the inertia coefficient decreased and reached large negative values in the late phase of the model movement involving decelerated motion, indicating that fluid forces on the hand increased as acceleration of the hand decreased to negative values (decelerations). That result was not consistent with the simple theoretical understanding to induce additional fluid forces on the hand because the simple theoretical understanding cannot take account of the preceding history of the fluid motion around the hand model associated with the formation of vortices. Thus, more sophisticated theory is needed. The dynamic pressure measured by the pressure sensors implied that the induced fluid forces might be due to large attached vortices behind the hand model.
The hand was considered as a blunt body when the angle of attack was large (maximum = 90�) and an aerofoil shape when the angle of attack was small. The inertia coefficients became large when the hand model was set at the large angles of attack, indicating that the effect of accelerations on the hand model increased when the hand surface was directed to the on-coming flows (blunt body).
For the development of the new pressure method, a regression analysis was used to build a single best-fit equation to predict fluid forces acting on the accelerating hand model. The single best-fit equation was acquired for various orientations of the hand model. The accuracy of prediction of fluid forces acting on the accelerating hand model was checked by a root mean square (RMS) difference. The RMS difference by the pressure method was approximately half of the RMS difference by the "quasi-static" approach that has been a major method to predict fluid forces exerted by the hand in swimming.
The present study has quantified the effect of acceleration on fluid forces acting on the hand in swimming and developed a new pressure method including acceleration effects to predict fluid forces acting on the accelerating hand.
| Identifer | oai:union.ndltd.org:ADTP/217849 |
| Date | January 2007 |
| Creators | Kudo, Shigetada, n/a |
| Publisher | University of Otago. School of Physical Education |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://policy01.otago.ac.nz/policies/FMPro?-db=policies.fm&-format=viewpolicy.html&-lay=viewpolicy&-sortfield=Title&Type=Academic&-recid=33025&-find), Copyright Shigetada Kudo |
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