自由泳中打腿提供向前推力的原理

自由泳中打腿提供向前推力的原理
设计流体动力学的请解释清楚些,我不太懂
最好有配图,

以下是我本人翻译的一篇文章,谈到了游泳的流体动力学,但可惜的是这里无法引用图片.这篇文章本来配了很好的图片用于说明的:
Fluid Dynamics of Swimming
游泳的流体动力学
Most people enjoy swimming, especially on a hot summer day. However, the level of swimming skill varies greatly between recreational and competitive swimmers. Even at the competitive level some swimmers are faster than others. The fastest swimmers use the fundamental (basic) principles of fluid dynamics the best. These same principles have been used by anyone who has ever treaded water (keeping your head above water by moving your arms and legs).
很多人都喜欢游泳,特别是在炎热的夏季.然而,这些游泳爱好者的水平则千差万别,不一而足.有的人只是用来娱乐,而有些人则用来参与比赛.即便是那些参加比赛的人中间,也有些人远比其他人有的快.而那些游得最快的人,他们一般都很好的遵循了流体力学的原理.但实际上这些原理每个人都在使用,只要他们会踩水（能够通过手臂和腿的运动将头部维持在水上）.
There are four primary forces acting on a swimmer:
对于一个游泳者,主要有以下四个方面的力：
1. Weight of the swimmer 游泳者的体重；
2. Buoyancy - ability to float 浮力---漂浮的能力；
3. Thrust - arm stroke and kick 推进力---手臂的划水和腿部的打水；
4. Drag - pressure and skin friction 阻力---压力以及皮肤的摩擦力.
The pressure drag comes from the front of the swimmer exposed to the water and the flow separation behind the swimmer. Since the flow is already turbulent (not laminar or smooth) a swimmer must streamline his body to reduce the flow separation even more (see the figures below). Frontal drag is reduced by thrusting and kicking, which brings the body up higher out of the water. Meanwhile, skin friction increases as the body becomes more streamlined. But, pressure drag is the main concern (worry) and if it is reduced then overall drag is reduced.
压力带来的阻力来自于游泳者的前部对水面以及后部流体分层.由于流体已经是紊流了（并非层流或者平滑流体）,那么游泳者应该尽可能地维持身体的流线型,这样可以尽可能的减少流体因身体而导致更多的分层（见下图）.前沿阻力可以由迅捷而有力的前伸和打水来克服,比如前伸和打腿动作能把更大部分的身体前部抬高.这样,由于体位变得更加流线型,那么皮肤摩擦导致的阻力会显得更大一些.但是,压力引起的阻力才是阻力的主要方面,所以如果这个方面的阻力能够减小,那么总体阻力也将会减小.
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.
This same lift force is generated while treading water. While treading water, one does not push down on the water. Instead, one sculls (moves) the hands back and forth near the surface. The legs and feet are making similar movements. This results in the production of lift, which in turn keeps the swimmer's head above water.
当运动员进行踩水的时候也会有相同的上升力产生.当你做踩水动作时,你不会从水面之上向水下压水.实际上,常见的动作是手从靠近水面处的位置上下移动,腿和脚的动作也相似,这样,浮力产生了,这个浮力就可以帮助把游泳者的头部维持在水面之上.
Kick
打腿
The swimmer's kick has two purposes. First, to add thrust and the second to acquire (get) stability. It is important to keep the feet in the water. Each time the swimmer's feet leave and enter the water, air comes along, increasing drag and reducing thrust.
打腿有两个目的.首先,增加前冲力；第二,维持身体的稳定性.这样,维持脚部没于水面就非常重要.无论什么时候,只要游泳者的脚从水面之上打入水中,空气就会随着脚进入水中,这些空气泡会产生阻力,而且还会减少推动力.
The best swimmers go further by moving their feet during the kick to produce the same lift force achieved by their hands. This is much harder to visualize unless you look at the breast stroke kick. The breast stroke kick is most similar to the movements of the legs while treading water. Remember, while treading water, the legs are moved through the water in a similar fashion as the arms to produce a lift force.
那些最好的运动员可以仅仅通过打腿就可以获得足够的浮力,并使自己能够移动得更远,而平常这个浮力是靠手获得的.这个很难通过眼睛观察,除非你在观察蛙泳运动员蹬腿的动作,因为蛙泳的蹬腿动作和踩水是的蹬腿动作最相似.请记住,当你踩水时,腿部的动作和手臂的动作相似,都是做产生浮力的动作.
As the swimmer moves each arm around through the water he must be careful not to twist his body. This increases pressure drag as the body becomes less streamlined. A proper kick helps to keep the body streamlined, thereby reducing the drag (see figure).
当游泳者在水中进行风车式的划臂时,一定要注意维持身体的平顺,即不要扭动,否则由于身体的流线被破坏导致更大的阻力.正确的打腿可以维持身体的良好的流线,那么自然也可以减少阻力.

In the freestyle (breast stroke), there are three types of kicks: The six-beat kick, the two-beat kick, and the two-beat crossover kick. The six beat kick is favored by sprinters (short distance, fast pace), while the variations of the two beat kick are favored by distance swimmers. However, there is no proof that one kick is better than another. However, the six beat kick might help lift the sprinter higher in the water, while the two beat kick retains the stabilizing effect while conserving the energy of the long distance swimmer.
在进行自由泳（蛙泳）时（应该为仰泳,译者注）,目前有三种打腿方式：6次腿、两次腿和两次交叉打腿.6次腿常见于短距运动员（短距离,高速度）,那么两次腿则多见于长距离游泳运动员.然而,并没有证据说明这两种打腿中的一个更好.但是,6次腿显然有助于短距运动员提升在水中的体位,而2次腿则更合适于长距离运动员所需要的稳定地进行能量转换的需求.

The butterfly kick is also known as the dolphin kick since it is similar to the movement of a dolphin tail. The butterfly kick has a stabilizing effect when it is done in time with the stroke. Studies show a remarkable similarity between champion butterfly swimmers and captive dolphins.
蝶泳的打腿还有一个常见的俗名,即海豚踢.这是因为这种打腿方式和海豚尾巴的运动方式非常相似.蝶泳腿在和划水完整的配合时,他还有一个稳定身体的效应.研究表明,那些蝶泳冠军们的打腿和豢养的海豚有着惊人的相似.
Summary
总结
So, as one can see, the gap between champion swimmers and recreational swimmers is the ability to use the basic principles of fluid dynamics to ones advantage. This shouldn't be too difficult, after all, anyone who has ever treaded water knows how to apply these concepts. However, applying them while swimming is another issue. The fastest swimmers don't think about how their hands move through the water, but rather have a feel for the water. Mark Spitz, one of the best swimmers in history, used all of the techniques shown here.
因此,大家可以看到,那些冠军选手和娱乐型的爱好者之间的区别就在于对于流体力学的遵循状况.这个应该并不很难,可以说,每个经过一定训练的游泳者都能够理解如何遵循这些理论.然而,把这些理论真正应用到游泳中去确实另外一个问题.那些有的最快的运动员,他们并不需要去想他们的手臂应该如何移动,他们依靠的是他们的水感!马克斯皮茨---一个历史上最伟大的游泳运动员---他使用了所有列在这里的技术.