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How Moths Confuse Bats
When your predators use echolocation to locate you, it pays to have an ultrasonic deterrence. So, many species of ermine moths have structures on their wings known as tymbals. (Image credit: Wikimedia/entomart; research credit: H. Mendoza Nava et al.; via APS Physics) Read the full article
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One of the most dramatic and famous engineering failures of the twentieth century is also one of the most complicated: the collapse of the Tacoma Narrows Bridge. This early suspension bridge earned the name “Galloping Gurtie” from construction workers while it was still being built because its flexibility made it prone to moving up and down under even relatively light winds. That vertical motion was due to vortex-induced vibration. As the wind blew, it shed vortices off the downstream side of the bridge. These vortices alternated, coming off the top and then bottom of the bridge deck. The resulting forces made the bridge shift up and down.
That wasn’t the bridge’s ultimate downfall, though. Shortly before it collapsed, the bridge stopped flexing up and down and instead twisted back and forth. This was a clear sign that the bridge had moved into aeroelastic flutter. In this situation, you get a feedback loop between the bridge’s aerodynamics and its structural dynamics. When the wind twists the bridge deck to a positive angle of attack, it will try to continue forcing the bridge to twist that direction. The internal forces of the bridge will try to twist it back, but when that happens, it can overshoot and end up at a negative angle of attack. At that point, the wind tries to push it further that direction and internal forces twist it back, overshooting the other way. This back-and-forth can create a dangerous feedback loop where the twisting of the bridge keeps getting worse and worse. In fact, that’s exactly what happened -- right up until the bridge collapsed rather than twisting any more. (Video and image credit: Practical Engineering)
Everyone has watched a flag flutter in the breeze, but you may not have given much thought to it. One of the earliest scientists to consider the problem was Lord Rayleigh, who wrote an aside on the mathematics of an infinite flag flapping in a paper on jets (pdf). Today researchers consider the problem in terms of fluid-solid interaction; in other words, to study a fluttering flag, you must consider both the properties of the flag -- its flexibility, length, elasticity, and so on -- and the properties of the fluid -- air speed, viscosity, etc. The combination of these factors governs the complicated shapes taken on by a flag. The image above is a composite of several photos of a string (a 1-d flag) flapping in a flow that moves from left to right. By combining photos, the image highlights the envelope of shapes the flag takes and demonstrates at a glance just how far the flag flutters in either direction along its length. (Image credit: C. Eloy)
Design, Experimental Investigation, Aeroelasticity Modelling and Control of an Aircraft Wing with Bio-inspired Active Morphing Wingtip at University of Birmingham - (Jobs/Scholarships)
Are you passionate about developing next-generation adaptive aircraft that mimic nature? Do you want to contribute to cutting-edge research that will transform aircraft wings from static compromises into actively morphing and efficient structures? Applications are invited for a 3.5-year UK PhD studentship for the project “Design, Experimental Investigation, Aeroelasticity Modelling and Control of…
International Journal of Aeronautical Science & Aerospace Research (IJASAR) is a comprehensive, peer reviewed journal devoted to Aeronautical Science and Aerospace Research. publishes original research, latest developments, review papers, scientific data, editorials from leading scientists and scholars around the world
International Journal of Aeronautical Science & Aerospace Research (IJASAR) ISSN 2470-4415 is a comprehensive, peer reviewed journal devoted to Aeronautical Science & Aerospace Research. IJASAR, published by SciDoc is an open access journal that includes high quality papers, which covers all major areas of Aeronautical Science & Aerospace Research. SciDoc with its Open Access publication model spreads all the day-to-day developments and research to readers around the world.
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Yay first post.
I have been working on simulating a narrow, thin, long ribbon with a crossflow across it’s length.
I am using a 1-D model for the structural deformation there’s only vertical bending (due to lift) and torsional deformations across the span axis. There are no warping considerations. There are some details of the structural model to work out still.
For the aerodynamics I am using the vortex lattice method. At the moment the aerodynamics are steady.Â
There’s still a lot of work to be done but it looks neat.
The ribbon is eventually going to be allowed to autorotate, does anyone know if unsteady VLM would work to model that? I think not, and I plan on using a full CFD model to account for that.
Active Flutter Suppression
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