You need to know where the sound comes from and how it is produced, in order to be able to eliminate it. And a decibel meter alone is not going to solve that. Noise pollution is becoming an ever-greater problem. This is exactly what Sorama aims to do: "We make sound visible in order to make appliances quieter. The new insights and tools can help make engineered devices that generate complex forces like animals do quieter. Making drones quieterĪlthough it was not the focus of this study, the knowledge gained may also help improve aircraft and drone rotors as well as laptop and vacuum cleaner fans. It predicts the sound that flapping wings radiate, not only the hum of the hummingbird, but also the woosh of other birds and bats, the buzzing and whining of insects and even the noise that robots with flapping wings generate. The researchers finally managed to condense all these results in a simple 3D acoustic model, borrowed from the world of airplanes and mathematically adapted to flapping wings. In this way, you avoid the possibility that a small distortion in the measurements changes the outcome." The solution to this so-called inverse problem resembles what a police facial composite artist does: using a few clues to make the most reliable drawing of the suspect. Wijnings: "We developed an algorithm for this that can interpret a 3D acoustic field from the measurements, and this enabled us to determine the most probable sound field of the hummingbird. student, and co-first author, Patrick Wijnings. The researchers tackled this challenge harnessing artificial intelligence, the research of TU/e Ph.D. Once the wing location, the corresponding sound and the pressure differences are precisely aligned for each video frame, the researchers were confronted with the complexity of interpretating high volume data. Scholte: "Because light travels so much faster than sound, we had to calibrate each frame separately for both the cameras and the microphones, so that the sound recordings and the images would always correspond exactly." Because the cameras, microphones and sensors were all in different locations in the room, the researchers also had to correct for that. The researchers wanted to know exactly which wing position produced which sound and how this related to the pressure differences. The terabytes of data then had to be synchronized. We had to develop a new instrument for that." During a follow-up experiment, six highly sensitive pressure plates finally managed to record the lift and drag forces generated by the wings as they moved up and down, a first. We also needed to measure the aerodynamic forces the hummingbird's wings generates in flight. Lentink says, "But that's not end of story. For that, Stanford's twelve high-speed cameras came into play, capturing the exact wing movement frame-by-frame. To interpret the 3D sound images, it is essential to know what motion the bird's wing is making at each sound measurement point. A hummingbird wing is similar to a beautifully tuned instrument," Lentink explains. "The distinctive sound of the hummingbird is perceived as pleasant because of the many 'overtones' created by the varying aerodynamic forces on the wing. The model not only provides biological insight into how animals generate sound with their flapping wings, it also predicts how the aerodynamic performance of a flapping wing gives the wing sound its volume and timbre. The researchers combined all measurements in a 3D acoustic model of bird and insect wings. Hummingbirds and insects are noisier because they do so twice per wingbeat." Mosquitoes whine, bees buzz, hummingbirds hum, and larger birds 'woosh." Most birds are relatively quiet because they generate most of the lift only once during the wingbeat at the downstroke. Professor David Lentink of Stanford University says, "This is the reason why birds and insects make different sounds. The difference between whining, humming, buzzing and wooshing Whereas both pressure differences due to the lift and drag force acting on the wing contribute, it turns out that the upward lifting pressure difference is the primary source of the hum. Unlike wings of other species of birds, a hummingbird wing generates a strong upward aerodynamic force during both the downward and upward wing stroke, so twice per wingbeat. These pressure differences over the wing are essential, because they furnish the net aerodynamic force that enables the hummingbird bird to liftoff and hover. The hummingbird's hum originates from the pressure difference between the topside and underside of the wings, which changes both in magnitude and orientation as the wings flap back and forth. The team of engineers succeeded in measuring the precise origin of the sound generated by the flapping wings of a flying animal for the first time.
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