Modeling Vortex-Excited Vibrations of Axially Varying Cylindrical Structures in Non-Uniform Flow Fields

摘要

Theoretical investigations have shown that wake-oscillator formulations of the vortex shedding process arise naturally as a consequence of weakly nonlinear and nonparallel instability modes in wake flows. We wish to explore the extension of wake-oscillator formulations to the modeling of vortex-excited vibrations of axially varying cylindrical structures in non-uniform flow fields. The issues to be addressed are threefold: (1) how best to incorporate axial diffusion of vorticity in wake-oscillator formulations; (2) what effect does the inclusion of axial diffusion of vorticity have on predicted structural responses; and, (3) how well do these predicted responses compare with available experimental data and with what generality. We intend to study first the behavior of a diffusive van der Pol oscillator as representative of the vortex shedding process from a cylindrical structure in a non-uniform flow field. The purpose of this investigation is to develop, through comparison with experimental results, a functional relationship between the diffusivity of vorticity and the shear in the flow field. Once this functional relationship has been developed, we intend to model vortex-excited vibrations of axially uniform cylindrical structures in non-uniform flow fields and to compare the predicted responses with experimental observations. This latter objective requires the development of a forced, diffusive van der Pol oscillator coupled to the structural equations of motion.