Extreme value statistics of flow-induced hydrofoil vibration and resonance

Flow-induced noise and vibration produce cyclic loading on structures such as wind turbines, propellers, and vehicle control surfaces. This cyclic loading can produce fatigue damage in these structures. Additionally, large outlier loads can potentially exceed maximum design levels. Most other works have focused on the extreme value statistics of random loads, and there is limited work which considers the influence of structural resonances. The goal of this work was to study the influence of low order mode responses on extreme response statistics. To accomplish this, the flow-induced vibration response of cantilever fins forced by the wake of an upstream flow obstruction was measured in a closed-circuit water tunnel. The tunnel flow speed was increased, so the wake would excite the first bending mode. A maxima data set was determined from the measured response using the block maxima method, and the generalized extreme value (GEV) distribution was applied to each flow speed. Data were then filtered into stiffness-controlled and damping-controlled responses, and the extreme value analysis was repeated. Results indicated that the extreme response was influenced more by the damping-controlled response than the stiffness-controlled response. When excited, extreme responses from structural resonances must be considered in maximum load design.