Controle de vibrações induzidas pelo vento por alteração do padrão superficial em uma viga cantilever
Paladini, Andre Luis Aguiar
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In the present work, the study of an aeroelastic problem referring to cantilever beams with surface notches exposed to wind is presented, as well as a design of a control system whose purpose is to maintain a desired vibration level for one of the beams, by the action of a bulkhead in exposing its carved surface, given the variation in wind speed. For this purpose, 17 types of surface were proposed and compared, through an analysis of structural dynamics via experimental impact tests and theoretical models validated by their tests, in order to determine the purely structural influence related to the presence of each type of notch on the surface. Next, the beams were subjected to an experiment in which an aerodynamic excitation was provided by a centrifugal fan capable of controlling the wind speed. Thus, the vibration for each beam was measured and compared in terms of their RMS values associated with the vibration signal power, as well as the power distributions along the frequency band. In this way, the beam with superficial notches with the highest RMS value was selected and subjected to a new test, which had a bulkhead that gradually covered a portion of its surface, in fixed distance steps. In this experiment, the same analyzes regarding the power and its RMS values were performed, however, by varying the bulkhead positions and the wind speed. A function that correlates the RMS values with the wind speed and the instantaneous position of the bulkhead was obtained from the interpolation of the results in order to contribute to the control system plant model, which also relied on the results of the analysis of structural dynamics. With the plant model determined, a control system was designed based on two PID controllers in cascade, with a loop to control the position of the actuation system, referring to the position of the bulkhead, and another, to control the vibration levels, given an RMS value. The results for the control system were simulated computationally, with the help of MatLab® and Simulink®, and responses were obtained that stabilized themselves around the reference value, given the variation in wind speed. It was concluded that, by obtaining theoretical and experimental information about the proposed aeroelastic problem, it was possible to carry out an application of the studied concepts by the design of a control system capable to stabilize the vibration levels of a cantilever beam.
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