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第104期:如何阻止建筑摇晃

来源:可可英语 编辑:hoy   可可英语APP下载 |  可可官方微信:ikekenet

For this video Lego sent me some of their Saturn V rocket sets.

为了制作这个视频,乐高公司寄给我一些他们的土星五号运载火箭套装。
But this isn't a video about space - I actually want to talk about the physics of how to keep tall things from shaking,
但这不是一个关于空间的视频——实际上我想讲的是如何防止高物晃动的物理学,
like how to keep skyscrapers from swaying too much in the wind, or in an earthquake.
比如如何防止摩天大楼在风中或地震中过度摇晃。
The taller something is, the more liable it is to sway back and forth,
东西越高,就越容易前后摇摆,
so to demonstrate this, the Saturn V seemed by far like the best and coolest Lego set for the job (even if not the most realistic).
所以为了证明这一点,土星五号似乎是迄今为止最好和最酷的乐高套装(即使不是最现实的)。
If you don’t your tall thing to sway, either because you’re worried it’ll fall apart or you’re worried it’ll freak out the people inside,
如果你不想让你的高大的东西摇晃,要么是因为你担心它会破碎,要么是因为你担心它会吓坏里面的人,
you could just make it stiffer – either by adding more stuff or using more rigid materials –
你可以让它变得更硬,通过加入更多的材料或者使用更硬的材料
this isn’t always the most elegant solution, and gets expensive fast.
这并不总是最优雅的解决方案,而且成本增加地很快。
But there’s another, clever solution.
但还有另一个聪明的解决办法。
From a physics perspective, a tall thing like a building is really an upside-down pendulum -
从物理学的角度来看,像建筑物这样的高东西实际上是一个倒立的钟摆,
when it gets bent a little bit to one side, the building’s natural stiffness pulls it back the other way, and so on.
当它稍微向一边弯曲时,建筑的自然硬度会把它往另一边拉,等等。
And there's a neat phenomenon that happens with pendulums when you attach two of them together with a spring:
当你用弹簧把两个钟摆连在一起时,钟摆就会产生一种奇妙的现象:
they start swapping energy back and forth – first one oscillates,
它们开始来回交换能量,第一个振动,
then both together, then the other has all the oscillations, then the first again, and so on.
然后两者都在一起,然后另一个有所有的振动,然后第一个又一次振动,如此类推。
The same thing happens with solid blocks and springs, too, or any two oscillating things that are coupled together.
同样的事情也发生在固体块和弹簧上,或者任何两个耦合在一起的振动物体上。
In a perfect frictionless simulation this energy swapping will go on forever.
在完美无摩擦的模拟中,这种能量交换将永远进行下去。
But in the real world there's friction and air resistance and the spring itself might heat up,
但在现实世界中,存在摩擦和空气阻力,而且弹簧本身可能会升温,
causing the objects to lose energy, and the oscillations dampen over time.
导致物体失去能量,振荡随时间减弱。
And this phenomenon is what you can use to ‘discourage’ your upside-down pendulum from shaking in ways you don’t want it to.
你可以用这种现象来“阻止”倒立的钟摆以你不想要的方式晃动。
A big tall object is going to want to sway back and forth at its own natural frequency of swaying (which depends on its height, weight, and stiffness).
一个高大的物体会想要以它自己的固有摆动频率来回摆动(这取决于它的高度、重量和刚度)。
If you then attach a smaller object to it that can sway to and fro,
如果你在上面放一个可以来回摇摆的小物体,
and add a little bit of friction, then any time the big object trades its energy to the little object,
加上一点摩擦力,在任何时候大的物体把能量交换给小的物体时,
the little object loses the energy to friction rather than trading it back to the big object, and this dampens out the big object's oscillations.
小物体会由于摩擦而失去了能量,而不是把它交换回大物体,这就减弱了大物体的振动。
In practice, you normally put the little object inside the big object, which looks more like this, but the principle is the same.
在实践中,你通常把小物体放在大物体里面,它看起来更像这样,但原理是相同的。

如何阻止建筑摇晃.png

And you don’t want to use just any old little object and any old spring.

你不希望使用任何旧的小物体和任何旧的弹簧。
It turns out that for a given big thing, there’s an optimal combination of weight and friction and spring strength for the little object.
事实证明,对于一个特别大的物体,与之相配的小物体的重量,摩擦和弹簧强度有一个最佳组合。
And only with your setup perfectly tuned will you get the fastest possible loss of energy and the best slowing down of the shaking.
只有你的设置完美的调谐,你才能得到最快的可能的能量损失和最好的减缓晃动。
That’s why this setup is called a “tuned mass damper” – “damper” because it dampens the swaying,
这就是为什么这个装置被称为“调谐质量阻尼器”——“阻尼器”,因为它减弱了摇摆,
and “tuned” because the little object is specifically tuned to steal energy from this particular big thing’s natural tendency to swing.
之所以称之为“调谐”,是因为这个小物体的调谐是专门用来从这个大物体摆动的自然倾向中窃取能量的。
Which brings us to the Lego Saturn V rockets: in one of the rockets I’ve put a weighted pendulum in the place the lunar module should go,
这让我们想到乐高土星五号火箭:在其中一个火箭里,我在登月舱应该去的地方放了一个加重的钟摆,
while the other just has the weights stuck in place.
而另一个只是把重量固定在这个位置上。
If all goes well, and if I’ve done my math right, then when I bump the table,
如果一切顺利,如果我没算错,那么当我撞到桌子时,
the rocket with the pendulum should sway a lot less than the rocket without.
有摆锤的火箭应该比没有摆锤的火箭摇摆得少。
As you can see, the tuned mass damper does actually help! (though it’s a bit subtle).
正如你所看到的,调谐质量阻尼器确实有所帮助!(尽管有点不易察觉)。
Here’s a graph of the motion of the rocket in each case, which makes it more obvious.
这是每个例子中火箭运动的图表,这使它更加明显。
And though tuned mass dampers definitely weren’t used in the saturn V rocket in this way (since this is where the lunar module went),
虽然调谐质量减震器在土星5号火箭上肯定不是这样使用的(因为这里是登月舱的位置),
they are used in skyscrapers and even in other things that aren’t buildings (though they’re usually hard to notice).
它们被用于摩天大楼,甚至是其他非建筑的东西(尽管它们通常很难被注意到)。
For example, if you look closely at power lines, a lot of them have this little dumbbell thing on them,
例如,如果你仔细观察输电线,很多电线上都有一个小哑铃,
which is a tuned mass damper that keeps the lines from shaking too vigorously in the wind.
这是一个调谐质量阻尼器,防止线在风中剧烈晃动。
And tuned mass dampers have been used to reduce unwanted vibrations in airplane engines, formula 1 racing cars, and audio speaker cones.
调谐质量阻尼器已用于减少飞机发动机、一级方程式赛车和音响喇叭锥的不必要振动。
So there you go – the tuned mass damper, aka the physics of how to use little things to keep big things under control!
这就是调谐质量阻尼器,也就是如何使用小物体来控制大物体晃动的物理学!

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