Swimmer Producing A Lot Of Drag
产生很大前进阻力的游泳者
Streamlined Swimmer
流线型的游泳者
Arm Stroke
胳膊的划水
Generally speaking, the arm stroke produces the majority of the thrust. The difference between swimmers is how the arm stroke is used to produce thrust. The best swimmers not only achieve thrust by pushing back on the water, but also by moving their hands and arms like a propeller.
总体来说,胳膊划水产生的推力是主要的推进力量。不同的游泳运动员之间的区别很大一部分就是如何使用手臂的划水来产生前推力。那些最好的运动员在进行手臂向后推水时,不但产生很大的推进力,同时他们移动手掌的方式就像扳动桨叶。
The most obvious production of thrust comes from pushing back on the water like a paddle wheel. For a while it was thought that moving the arms in shorter strokes, like a caterpillar paddle wheel, would increase speed. This was tested using a riverboat equipped with a caterpillar paddle wheel (see figure). Unfortunately for the inventor, the boat practically stood still. The explanation for this can be found in the following quote:
最明显的推力来自于手臂的向后推水,就像圆盘明轮那样。有一段时间人们一度认为手臂的蠕虫状划水(短划水)可以增加前进的速度。这个可以通过一艘装备了蠕虫状推进桨叶的船进行测试(见下面的图)。然而结果让人失望,那艘船几乎不动。这个现象的科学解释可以通过下面引用的资料来解释:
"Maximum efficiency in water is achieved by pushing a large amount of water a short distance rather than by pushing a small amount of water a large distance."
“更好的流体推进效率的获得是通过推动大量的水(哪怕是推动的行程短一些),而那种推动虽然比较长,但推动的水量比较少的方式获得推进效率则比较小。”
To understand this quote, we should look at what is the most efficient arm stroke. The straight arm is brought around in a full circle, with the hand flat (see paddle wheel figure). This way the swimmer is always pushing back on still water. The advantage here is that the still water offers more resistance than the water that is already moving back.
为了理解这个引用的资料,我们应该看看什么样的划手才是最有效率的划手。直臂划手是把手臂绕一个整圈,手平放(就像明轮的图)。在这种划手方式下,游泳者划手时后推的都是原先静止的水,这个划水方式的优点是静止的水给予手臂的反推力要大于那种推水是的水已经是向后流动是产生的反推力(译者注:按照上一段的描述,蠕虫式划水有一段划的水是已经被手推动流动的水了,所以划水效率低。此段描写似乎和目前流行的S形划水不符,S形划水和蠕虫式划水有近似的地方)。
Paddle Wheel Arm Pull
Caterpillar Arm Pull
Interestingly, the paddle wheel or propeller style movement creates lift and thrust. In this case lift adds to thrust. To visualize this better, think of the swimmer's arm like an airfoil (or wing). As the arm plows through the water lift is created which lifts the body closer to the surface of the water. This reduces drag. So, even though the swimmer is moving from right to left, his hand is moving from top to bottom and the lift force adds to the thrust (see figure). Therefore, the swimmers arm stroke becomes similar to an airplane's propeller. Studies of Olympic caliber swimmers show that this is indeed the case.
这个很有意思,明轮推水或者桨叶方式的推水产生了上举力和向前的推力,在这种情况下上升力和推力会叠加在一起。为了更好的看清楚这一点,我们将游泳者的手臂看成是飞机的螺旋桨(或者机翼):当手臂在犁过水面时,浮力产生了,这个浮力会让身体更加贴近水面,所以阻力降低了。那么,即便游泳者是从右往左移动,他的手也是从上往下移动,所以浮力就叠加到前推力上(见图)。因此,游泳者的划手的效果是和飞机的螺旋桨的作用相似,这个结论是基于对那些卓越的奥运高手们的泳姿进行综合研究之后所得出的。 |