Flow induced vibrations are observed in many engineering applications. A flexible body located in the wake of an obstacle is usually forced to vibrate by the periodic vortices shedding from the obstacle. Here we focus on the response of the flexible body in the wake. Soap film tunnels are used to provide two-dimensional flow. Cylinders and flexible filaments are employed as obstacles and flexible bodies, respectively. The filaments exhibit lock-in behavior to the wake. Three response modes are found by changing the distance between the filaments and cylinders. The observations are illuminated in terms of waving plate theory.

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