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揽瓜阁俱乐部第二期 Day1 2020.06.15
【社会科学-科技】 Which way a wind turbine turns might not seem to matter （635字 精读 必做篇）
If the hands of dial clocks swept over their faces the other way around, that would be the direction known as “clockwise”. And they would tell the hour just as faithfully. It is convenient to have all clock hands turn in the same direction, but it is an accident of history which direction that is. Similarly, it seems an arbitrary but efficient choice by wind-turbine makers that the blades of almost all of those devices turn clockwise. However, a study presented on May 4th to the General Assembly of the European Geosciences Union (held online, instead of in Vienna, as planned), suggests that in the northern hemisphere, where 96% of these turbines are found, universal clockwiseness may be bad.
For a single turbine it does indeed not matter. But turbines are usually planted in groups. If, in such a group, one turbine is behind another then it does matter, according to Antonia Englberger of the German Aerospace Centre, in Oberpfaffenhofen, and her colleagues. They have built a computer model which simulates the flow of air over a turbine turning in either direction, and then calculates the effect this has on a second turbine, downwind of the first. By day, the team conclude, there is no difference. But at night the power output of the downwind device may be up to 23% higher if its upwind colleague is turning anticlockwise.
The reason lies in the nocturnal behaviour of the bottom few hundred metres of the atmosphere, known as the boundary layer. By day, the sun’s rays heat the ground, which heats the nearby air, which rises in whorls of turbulence, resulting in a well-mixed boundary layer that behaves in the same way at all altitudes. The consequence, for a wind turbine, is that its rotor blades feel the same wind speed and direction whether they are at the top or the bottom of their rotation.
At night, however, the ground cools. The whorls therefore often go away and the boundary layer stops mixing. Friction with vegetation or buildings now means that air close to the ground moves more slowly than air higher up—an effect known as altitude-related wind shear. And the amount of shear, given the blade-span of modern turbines, is large enough for Earth’s rotation to come into play. This pushes moving air to the right in the northern hemisphere and to the left in the southern, a phenomenon called the Coriolis force. The faster the airflow, the larger the deviation. Thus wind shear begets wind veer, a gradual change in direction with height.
That matters for turbine pairs because the air that pushes against the blades of the upwind device, and thus gets them to rotate, say, clockwise, is itself deflected by those blades in the other direction. This turns it into a turbulent wake with a rotation (in this case) going anticlockwise. This anticlockwise rotation conflicts with the Coriolis-induced veering tendency of the undisturbed wind around the wake. And that hampers the wake’s ability to pick up energy from this surrounding, undisturbed wind and then go on to hit the second turbine with renewed vim.
In the case that the first turbine rotates anticlockwise, the wake will be clockwise, thus matching the northern-hemisphere wind veer. This lets it gain energy from the surrounding air to deliver to the next turbine—the opposite of what now happens. And in the southern hemisphere this all works the other way around, so conventional, clockwise turbines do best.
Retooling factories in light of Dr Englberger’s discovery, to make turbines run anticlockwise instead, would certainly be expensive. Whether the extra power that could be squeezed out of the wind by doing so would make that worthwhile would require a lot more investigation. Her result does, however, show neatly how even apparently arbitrary decisions can have unintended consequences.
Source: The Economist
【社会科学-科技】 Internet Cables Could Also Measure Quakes （291字 1分49秒 精听 必做篇）
先做精听再核对原文哦~
In addition to giant crustaceans and creepy anglerfish, the deep oceans hide a vital piece of technology: the cables connecting almost every continent, island and archipelago to the Internet. But it seems those undersea cables can be used for more than just sending cute cat memes around the world.
“We can do a good job picking up earthquakes in offshore cables.”
Jonathan Ajo-Franklin is an applied geophysicist at Rice University and Lawrence Berkeley National Lab. He says that fiber-optic cables are like threads of glass—and there are impurities built in. So when you shoot lasers through the fibers, those impurities backscatter some of the light right back to the laser source.
“We make measurements of the change in the backscattered light over time, which gives you information on the stretch of the cable at each location."
His team took advantage of a brief maintenance period when a particular cable, off the coast of Monterey, California, was not being used for communication. The researchers studied the slight deformations in the cable and were able to sense a small earthquake, pinpoint unmapped faults in the seafloor and observe movements in the water column—all of which might be of interest to oceanographers.
Their work is in the journal Science.
Ajo-Franklin points out that seismometers are pretty sparse in the world’s oceans:
“It’s a big blank spot.”
So these cables could really come in handy. And unlike for this study, you wouldn’t even have to turn off the Internet to do it.
“We’re looking at ways of potentially using just a small section of the spectrum, so you can communicate at the same time you can do sensing on these kinds of cables.”
Which might bring more of the Earth’s deep rumblings online.
Source: Scientific American
【笔记格式要求】
精读笔记格式要求： 1.总结文章中心大意 2.总结分论点或每段段落大意 3.摘抄印象深刻或者觉得优美的句子 4.总结文章中的生词 5.记录阅读时间、总结时间、总时间
精听笔记格式要求： 1.逐句听写整篇文章 2.对照原文修改听写稿，标记出错原因 3.总结文章中心大意 4.总结精听过程中的生词 5.记录听写时间、总结时间、总时间
这里也给大家两点学习小建议哦~ 精读：如遇到读不懂的复杂句，建议找出句子主干，分析句子成分，也可以尝试翻译句子来帮助理解~ 精听：建议每句不要反复纠结听，如果听 5 遍都没听出来，那就跳过，等完成后再回听总结原因，时间宝贵，不要过于执着哦~
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发表于 2020-6-14 20:15:52
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