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    <item>
      <title>"Hochpumpvortrieb" während Kraulschwimmen</title>
      <pubDate>Tue, 01 Jan 2002 03:05:27 +0100</pubDate>
      <link>https://sponet.de/sponet/Record/3034478</link>
      <guid>https://sponet.de/sponet/Record/3034478</guid>
      <author>Toussaint, H. M.</author>
      <author>Berg, C. van den</author>
      <author>Beek, W. J.</author>
      <dc:format>Artikel</dc:format>
      <dc:subject>Schwimmen</dc:subject>
      <dc:subject>Kraulschwimmen</dc:subject>
      <dc:subject>Vortrieb</dc:subject>
      <dc:subject>Hydrodynamik</dc:subject>
      <dc:subject>Biomechanik</dc:subject>
      <dc:format>Artikel</dc:format>
      <dc:creator>Toussaint, H. M.</dc:creator>
      <dc:creator>Berg, C. van den</dc:creator>
      <dc:creator>Beek, W. J.</dc:creator>
      <content:encoded><![CDATA[Zielstellung:
1. Erweiterung der Theorie zum Vortrieb während Kraulschwimmen unter dem Aspekt der dynamischen Wirkungen der Armrotation.
2. Experimentelle Visualisierung der Richtung der Wasserströmung während des Schwimmens. über Quasten (aus schwarzer Wolle).
Methoden:
Mittels Quasten aus schwarzer Wolle wurden die Strömungsrichtungen um den Arm und die Hand während der Einwärts- und Auswärtszugphase (insweep und outsweep) untersucht. In einem zweiten Experiment wurde der Druck während des Zuges an verschiedenen Punkten des Armes und der Hand gemessen.
Ergebnisse:
Die Strömung während der Insweep- und teilweise der Outsweep-Phase war sehr unstetig.
Die Armbewegungen waren in hohem Maße rotierend. 
Während der Insweep- und Outsweepphase wurde eine deutliche axiale Strömungskomponente nicht in Richtung der Armbewegung beobachtet.
Schlussfolgerungen:
Die Untersuchung zeigte die Rotations- und unstetigen Wirkungen beim Kraulschwimmen. Es wird angenommen, dass die beobachtete axiale Strömung während der Outsweepphase einen vortriebserhöhende Wirkung durch Anstieg der Druckdifferenz über der Hand hat.]]></content:encoded>
      <slash:comments>0</slash:comments>
    </item>
    <item>
      <title>"Hochpumpvortrieb" während Kraulschwimmen</title>
      <pubDate>Tue, 01 Jan 2002 03:05:27 +0100</pubDate>
      <link>https://sponet.de/sponet/Record/4006809</link>
      <guid>https://sponet.de/sponet/Record/4006809</guid>
      <author>Toussaint, H. M.</author>
      <author>van den Berg, C.</author>
      <author>Beek, W. J.</author>
      <dc:format>Artikel</dc:format>
      <dc:subject>Biomechanik</dc:subject>
      <dc:subject>Hydrodynamik</dc:subject>
      <dc:subject>Kraulschwimmen</dc:subject>
      <dc:subject>Schwimmen</dc:subject>
      <dc:subject>Vortrieb</dc:subject>
      <dc:format>Artikel</dc:format>
      <dc:creator>Toussaint, H. M.</dc:creator>
      <dc:creator>van den Berg, C.</dc:creator>
      <dc:creator>Beek, W. J.</dc:creator>
      <content:encoded><![CDATA[PURPOSE: It is currently held that propulsion in human front crawl swimming is achieved by lift and drag forces predominantly generated by the hands. Calculation of these propulsive forces relies on the quasi-steady assumption that the fluid dynamic behavior of a hand model in a flow channel (constant velocity and orientation) is similar to that of a hand of a real swimmer. However, both experimental and theoretical analyses suggest that this assumption is questionable and that unsteady and rotational propulsion mechanisms play a significant role. Theoretical considerations suggest that arm rotation could lead to a proximodistal pressure gradient, which would induce significant axial flow along the arm toward the hand. METHODS: To gain insight into such mechanisms, we used tufts to study the flow directions around the arm and hand during the front crawl, which consists of a glide, an insweep, and an outsweep phase. In a second experiment, we measured pressure during the stroke at various points along the arm and hand. RESULTS: It was observed that 1) the flow during insweep and part of the outsweep was highly unsteady; 2) the arm movements were largely rotational; 3) a clear axial flow component, not in the direction of the arm movement, was observed during insweep and outsweep; and 4) both the V-shaped "contracting" arrangement of the tufts during the outsweep and pressure recordings point to a pressure gradient along the direction of the arm during the outsweep, as predicted on theoretical grounds. CONCLUSION: Our results demonstrate the reality of the predicted rotational and unsteady effects during front crawl swimming. We hypothesize that the axial flow observed during the outsweep has a propulsion-enhancing effect by increasing the pressure difference over the hand. Further investigation is required to establish more accurately the role of axial flow on propulsion.]]></content:encoded>
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    </item>
    <item>
      <title>Hochgepumpter Vortrieb beim Freistilschwimmen</title>
      <pubDate>Tue, 01 Jan 2002 03:05:27 +0100</pubDate>
      <link>https://sponet.de/sponet/Record/4003159</link>
      <guid>https://sponet.de/sponet/Record/4003159</guid>
      <author>Toussaint, H. M.</author>
      <author>Berg, C. van den</author>
      <author>Beek, W. J.</author>
      <dc:format>elektronische Publikation</dc:format>
      <dc:subject>Biomechanik</dc:subject>
      <dc:subject>Hydrodynamik</dc:subject>
      <dc:subject>Kraulschwimmen</dc:subject>
      <dc:subject>Schwimmen</dc:subject>
      <dc:subject>Vortrieb</dc:subject>
      <dc:format>elektronische Publikation</dc:format>
      <dc:creator>Toussaint, H. M.</dc:creator>
      <dc:creator>Berg, C. van den</dc:creator>
      <dc:creator>Beek, W. J.</dc:creator>
      <content:encoded><![CDATA[It is currently held that propulsion in human competitive swimming is achieved by a mixture of lift and drag forces predominantly  generated by the hands. Calculation of these propulsive forces relies on the quasi-steady assumption that the fluid dynamic behaviour of a hand model in a flow channel (constant velocity and orientation) is similar to that of a hand of a real swimmer swimming the front  crawl. Recently, it has been shown that quasi-steady calculations cannot account for the observed propulsive forces and propelling  efficiency during front crawl swimming , suggesting that significant unsteady mechanisms must be present. To gain insight into the  nature of such unsteady mechanisms, we used woollen tufts to study the flow pattern around the arm and hand during the front crawl  stroke, which consists of a glide -, an insweep - and a powerful outsweep phase. It was shown that: 1) the velocity and movement  direction of the fingertip and elbow varied strongly throughout the insweep and outsweep, 2) the arm movements were largely rotational,   3) the flow direction varied strongly throughout the insweep and outsweep, 4) a strong, accelerating axial flow component, not in the  direction of the arm movement, was observed during the late insweep and the outsweep. These observations discredit the quasi-steady  analysis of front crawl swimming. Furthermore, during most of the stroke the flow direction was inconsistent with circulation around the
hand, and associated lift force production may be assumed to be of secondary importance. Therefore, the notion that the main propulsive forces are generated by conventional hydrofoil action of the hand was abandoned. Instead, we show how rotation of the arm could lead to a proximo-distal pressure gradient, which could account for the observed axial flow. We further demonstrate that such axial flow along the trailing side of the arm could greatly enhance the pressure difference over the hand, thus assisting propulsion by  paddling. Axial flow was also observed during hawkmoth hovering. Therefore, we suggest that axial flow could play an important role wherever a propelling element is rotated (e.g. fins, paddles, wings, legs).
(siehe auch unter http://www.ifkb.nl/B4/PUMPED.html)]]></content:encoded>
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