Aeroelasticity studies the interaction of aerodynamic stresses, inertia, and elastic responses in structures, which can produce static and dynamic responses. Unstable dynamic responses can lead to structural failure. Aeroelasticity pertains to designing stable structures subjected to dynamic airflow, including airborne and land-based features. External aerodynamic forces cause mechanical stress in structures, leading to deformation and altering the aerodynamic stress. Inertia gained during deformation can cause oscillation, requiring friction or damping force to slow down the swing. The Tacoma Narrows Bridge’s destruction due to uncontrolled structural vibration in 1940 increased interest and research in aeroelasticity.
Aeroelasticity is the study of the interaction of aerodynamic stresses, inertia and elastic responses in physical structures. Such interactions can produce both static and dynamic responses. Unstable dynamic responses in components can lead to structural failure under certain conditions. Aeroelasticity typically pertains to designing structures to be stable when subjected to dynamic airflow. These structures are often airborne, but can also include bridges, wind turbines, and other land-based features.
Most materials, including metals, exhibit elastic behavior when responding to external stresses. Elastic materials will return to their original size and shape if they are not deformed beyond a critical amount. During deformation, they will stretch or shrink based on the level of stress applied. A metal spring stretches when it is pulled at its edges, but does not become permanently deformed after it is released. In fact, even solid pieces of metal behave this way.
In an airplane, external aerodynamic forces apply mechanical stress to the wings and main body. In terms of aeroelasticity, this stress is similar to a stress applied directly to the material, such as from placing weights on the plane. In response, the aircraft structure will deform slightly due to. This will slightly alter the shape of the aircraft, which in turn will affect the exact aerodynamic stress. In a static scenario, the aircraft’s structural response will reach equilibrium with the new aerodynamic stresses.
As a structure begins to deform due to aerodynamic stresses, it will gain inertia, or momentum, as it moves to change shape. Once it reaches its new “equilibrium” position, it doesn’t stop immediately; rather, it surpasses this position because it has gained momentum. Aerodynamic stresses may tend to return the structure to an equilibrium shape, but oscillation can sometimes occur. It requires friction or some kind of damping force to slow down this swing. In other words, the structure may have an equilibrium shape, but if it picks up too much inertia each time it moves towards that shape, it will be in an unstable equilibrium.
Many people witnessed this important aspect of aeroelasticity on November 7, 1940, when the Tacoma Narrows Bridge in the US state of Washington began to vibrate due to high winds. The natural frequency of the bridge, which is related to how fast the bridge will vibrate, was similar to how fast the wind changed direction. When this happens, the wind can make the bridge vibrate more and more. In the case of the Tacoma Narrows Bridge, uncontrolled structural vibration led to the destruction of the bridge. This event led to an increase in interest and research on aeroelasticity.
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