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首页> 外文期刊>American Zoologist >Upstroke thrust, drag effects, and stroke-glide cycles in wing-propelled swimming by birds
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Upstroke thrust, drag effects, and stroke-glide cycles in wing-propelled swimming by birds

机译：鸟类通过机翼推动的游泳中的上冲推力，阻力效应和中风滑行周期

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A number of bird species swim underwater by wing propulsion. Both among and within species, thrust generated during the recovery phase (upstroke) varies from almost none to more than during the power phase (downstroke). More uneven thrust and unsteady speed may increase swimming costs because of greater inertial work to accelerate the body fuselage (head and trunk), especially when buoyant resistance is high during descent. I investigated these effects by varying relative fuselage speed during upstroke vs. downstroke in a model for wing-propelled murres which descend at relatively constant mean speed. As buoyant resistance declined with depth, the model varied stroke frequency and glide duration to maintain constant mean descent speed, stroke duration, and work per stroke. When mean fuselage speed during the upstroke was only 18% of that during the downstroke, stroke frequency was constant with no gliding, so that power output was unchanged throughout descent. When mean upstroke speed of the fuselage was raised to 40% and 73% of mean downstroke speed, stroke frequency declined and gliding increased, so that power output decreased rapidly with increasing depth. Greater inertial work with more unequal fuselage speeds was a minor contributor to differences in swimming costs. Instead, lower speeds during upstrokes required higher speeds during downstrokes to maintain the same mean speed, resulting in nonlinear increases in drag at greater fuselage speeds during the power phase. When fuselage speed was relatively higher during upstrokes, lower net drag at the same mean speed increased the ability to glide between strokes, thereby decreasing the cost of swimming.
机译：许多鸟类通过机翼推进在水下游泳。在种间和种内，恢复阶段（上冲程）产生的推力几乎没有变化，而在动力阶段（下冲程）则变化更大。更大的不均匀推力和不稳定速度可能会增加游泳成本，这是因为加大了惯性工作以加速机身（头部和躯干），特别是在下降过程中浮力较高时。我通过在以相对恒定的平均速度下降的机翼推进的微流模型中，通过改变上冲程与下冲程之间的相对机身速度来研究这些影响。随着浮力阻力随着深度的增加而下降，该模型会改变冲程频率和滑行持续时间，以保持恒定的平均下降速度，冲程持续时间和每冲程功。当上冲程期间的平均机身速度仅为下冲程期间的平均速度的18％时，冲程频率保持恒定且无滑行，因此功率输出在整个下降过程中均保持不变。当机身的平均上冲程速度提高到平均下冲程速度的40％和73％时，冲程频率下降而滑行增加，因此功率输出随着深度的增加而迅速下降。更大的惯性功和不平等的机身速度是造成游泳成本差异的一个小因素。取而代之的是，在上冲程期间较低的速度需要在下冲程期间较高的速度以维持相同的平均速度，从而导致在功率阶段在较高的机身速度下阻力非线性增加。当在上冲程期间机身速度相对较高时，在相同的平均速度下较低的净阻力会增加冲程之间的滑行能力，从而降低游泳成本。

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