On a hot summer day,Lund University生物学家克里斯托弗·约翰逊（Christoffer Johansson）和亨宁森（Per Henningsson）穿过瑞典学校野战站附近草地的草地和野花。他们安静而故意朝着哈密瓜色的昆虫的短暂扑动，准备使用软织物网收集它。
The capture of silver-washed fritillary butterflies is far more than just a summer hobby for Johansson and Henningsson. They use slow-motion cameras and high-speed flow measurements to determine what gives these butterflies their distinct flight pattern. This discovery not only helps scientists better understand the life of this insect but could also help inform the design of next-generation drones.
确定什么使这些蝴蝶它们独特的飞行方式也可以帮助告知下一代无人机的设计。
约翰逊说，这项工作并不总是那么容易，回想起草地狩猎期间残酷的热量或在其实验性风洞中重新捕获标本的疯狂搜索，但总是很有趣。
“We normally spend most of the time in the lab,” says Johansson. “In this case, we actually spent a few days out in the meadows, capturing butterflies… But I would say the most fun and frustrating part is during the actual experiments in the wind tunnel. Even though we place the butterfly in a specific place, once it takes off, it can quickly move around the tunnel and disappear, only to reappear atop of the head of the researchers.”
君主的奥秘
Butterflies can fly not only in short bursts from flower to flower, but also in sustained migratory flights over long distances. The monarch’s migration, for example, from the U.S. to Mexico is more than 4,800 km (3,000 miles) one way.
And that’s not the only thing that makes butterfly flight unusual, says Johansson. They also have a body size–to-wing ratio unlike that of other insects, with unusually large wings for their small body size.
约翰逊和他的同事们希望提供新的数据来帮助回答蝴蝶飞行机制的问题，研究人员一直在努力理解近50年。
约翰逊说：“与其他飞行动物相比，蝴蝶是极端的。”“它们的机翼载荷非常低，翅膀的纵横比低，这意味着与其他飞行动物相比，机翼本质上是大，短而宽的。”
Butterfly takeoff with downstroke used for weight support and upstroke used to generate thrust. (Image credit: L. C. Johansson and P. Henningsson)
在1970年代，科学家认为，蝴蝶可能通过在上风顶部的顶部拍手翅膀时创建空气飞机来实现这一多功能飞行，以推动它们向前推动。但是，研究人员一直在努力确认这种机制已有近50年的历史，因为在实验室条件下，量化自由飞行活动，而不是在实验室条件下束缚飞行，说起来容易做起来难。Johansson和Henningsson在他们的研究中提供了新数据，以帮助回答蝴蝶飞行机制的问题，并了解如何在其他应用程序中使用。
约翰逊说：“通常很难想象最终将要使用什么基础研究，但是在这种情况下，无人机有直接的应用。”“有今天飞行的无人机that use a clap mechanism to generate forces. It could be interesting for them to look into this proposed butterfly mechanism to improve drone wing flexibility and maximize the efficiency and force of the clapping.”
Capturing Butterfly Flight
研究小组将六枚银色洗薯条蝴蝶引入了隆德大学的循环风洞中，使用蜂蜜水喂食器吸引昆虫起飞。这条风隧道是独一无二的。它最初是为了研究鸟类飞行而建造的。隧道中的一个大风扇以每秒两米（4.5 mph）的速度循环空气，以防止蝴蝶太容易地远离球队的尺寸设置。
The team uses four high-speed cameras to record the air motion caused by the butterflies and another two cameras to capture the butterflies’ motion. The flow measurement technique, called tomographic particle image velocimetry, enables the researchers to create a 3D model of fluid flow; the team can then study the aerodynamic forces to understand how butterfly wings propel their flight. In this research, the focus was the jets of wind created when the butterflies clap their wings.
Tiny aerosol particles, only about 1 micrometer in size, are suspended in the wind tunnel. The high-speed cameras capture the motion of these particles as the butterflies fly through them in front of a sheet illuminated by laser light. In total, the team captured 25 sequences with one to three wingbeats each.
约翰逊说，团队使用了MATLAB®用于数据分析，包括使用他为矢量分析设计的用户界面来研究蝴蝶飞行的流体动力学。
Johansson说：“我们的研究领域在技术上和数字上都要求很高，没有一个可以按照我们想要的方式进行所有分析的单一软件。”“因此，我们需要自己创建大部分代码。”
“MATLAB was, by far, our most useful tool on this project.”
隆德大学生物学家Christoffer Johansson
在上风和拍打蝴蝶时产生的推力大约2毫秒-1。（图片来源：L。C. Johansson和P. Henningsson）
Mathworks的教育客户成功工程师Sagar Zade说：“ MATLAB被用来可视化流程并绘制实验的结果。”
Johansson和Henningsson还使用MATLAB来计算空气动力，确定拍手的空气动力，并使用Monte Carlo模拟估算背景功率。
Zade补充说：“这些实验发现的结果对于未来的研究人员来说非常有价值，他们希望使用MATLAB使用复杂的Navier Stokes方程来数值对流体动力学进行建模。”
除了测量蝴蝶飞行所产生的喷气流外，该团队还分析了翅膀的形态如何在上风上创造出杯形的形状，以改善这些喷头。他们使用这些数据来创建机械蝴蝶翅膀，以隔离柔性翅膀的效果和杯形形状对拍手性能的影响。
Johansson says these mechanical wings are simple, right-angled triangles made of balsa wood and a latex membrane controlled by a servo engine and an Arduino®board. A hinge along the side of the wings enables them to rotate and clap together. The flexible membrane forms a cupped shape during the clap while the stiff balsa wood does not, allowing for comparisons of performance and investigation of the effect of the cupped shape alone. Between the biologists’ work in the tunnel and the work in the lab with the mechanical wings, Johansson says they gained some key insights into the dynamics of butterfly flight and how it could be recreated. One discovery, he says, was that a flexible membrane wing outperformed the balsa wing in impulse and efficiency by 25% during the clap. They also determined that a butterfly’s upstroke and downstroke serve two unique purposes in flight.
约翰逊说：“下沉的人会产生垂直力，而上冲和拍手产生推力。”“与大多数飞行一样，垂直力占主导地位。在这种特殊情况下，垂直力是推力的9.4倍。”
灵活的机翼提高了机翼拍手的力和效率。（图片来源：L。C. Johansson和P. Henningsson）
该团队的完整研究发表在Journal of the皇家学会界面。
由于Johansson和Henningsson在Matlab没有进行正规培训，因此Johansson说，该软件的可访问性，其灵活性和易用性是这项工作的巨大资产。
“MATLAB was, by far, our most useful tool on this project,” says Johansson.
超越蝴蝶
After the success of using this approach to capture butterfly flight, Johansson is interested in seeing how it applies more generally to model flight in other creatures, ranging from birds and bats down to microscopic organisms.
大自然的完善飞行时间比任何人都长得多。通过研究这些生物实现这一目标的无数方式，工程师可以建造更高效，动态的飞行，甚至游泳。这些无人机可能有一天可以将杂货运送到您的前门，或者在深处进行研究以研究海洋生物。
约翰逊说：“有人建议蝴蝶使用书中的所有技巧飞行。”“要弄清楚这是否真的以及不同的条件如何影响这些机制，还有很多研究要做。”
