Direct model reference adaptive control for nonlinear hydrodynamic oscillations

摘要

In order to mitigate against extreme vibration conditions, this paper proposes the implementation of active control technology to stabilize the motion of a structure immersed in a flow field. Specifically, a tuned mass damper is attached to the structure. In view of the coupling between the dynamics of this mass and those of the structure-fluid system, moving the mass along a particular path directly affects the dynamics of the structure. The object of this paper, then, is to determine a strategy for actuating the mass damper in order to substantially reduce the vibration of the structure. The control decision will be based on measurements, made in real time, of the structural response, and can therefore be viewed as a feedback strategy. In particular, adaptive control will be utilized in order to allow for uncertainty in the structure of Morisson's equation and the various hydrodynamic coefficients. These have traditionally been measured under specific flow conditions which difer, in general, from actual field conditions. The adaptive control logic used in this paper will automatically update the values of these coefficients, thus providing a novel procedure for estimating them and for validating the application of Morisson's equation to this type of problems. Since the adaptation of these coefficients will be done in real-time, a measure of the validity of the Morisson's model will be established. Specifically, if the estimated parameters reach a steady state value after an initial transient period, this will suggest that the dynamical model used for the vibrations of the structure is valid, and the new set of coefficients is consistent with measurements, otherwise, the error is in the model rather than in the parameters, and a measure of this error with be established by looking at the error in the controlled motion and the estimated parameters.