PARAMETRIC IDENTIFICATION OF VORTEX-INDUCED VIBRATION OF A CIRCULAR-CYLINDER FROM MEASURED DATA

A non-linear, single-degree-of-freedom model is developed to describe the vortex-induced, transverse vibration of a circular cylinder, elast ically suspended in a wind flow. The model is appropriate for predicti ng the dynamic response during lock-in conditions. The ''linear-in-the parameters'' nature of the model allows the formulation of a relative ly simple and computationally very efficient procedure for estimating all the unknown parameters in the model. The method, based on the use of a state variable filter, enables the parameters to be estimated rec ursively by processing digitized records of the cylinder dynamic respo nse. The technique is validated by applying it to both simulated data, where the parameters are known a priori, and to real data obtained fr om an experimental rig placed in a wind tunnel. For the experimental d ata, which relates to time-varying wind flow conditions, representing the natural wind, it is shown that the estimation technique allows the response during lock-in events to be isolated and treated separately. A reasonably good fit to the experimental data is obtained and the re sulting estimates of the mean values of the parameters are found to co nverge satisfactorily. (C) 1998 Academic Press Limited.