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Galloping is an aeroelastic phenomenon typical of slender structures that can produce large-amplitude oscillations in cross-flow direction. Several structures typical of civil and mechanical engineering applications, e.g. cables and bracings exposed to a flow, may be prone to galloping and their reliability depends on the correct estimation of the critical conditions for which this instability can occur. Usually, the instability condition is characterized in terms of critical flow velocity, which depends on the aerodynamic behavior of the structure, as well as on its mechanical properties. The critical velocity can be estimated, indirectly, from aerodynamic tests involving force or pressure measurements on static bodies or on rigid structures oscillating according to a prescribed motion. This gives rise to large uncertainties due to the experimental conditions that are not perfectly controllable, the observation time that is necessarily limited and the models used to fit the data that do not reproduce perfectly the physics of the problem. These uncertainties reflects into inaccuracies in the evaluation of the critical instability condition. In order to investigate the technical problem described above, an experimental campaign involving pressure measurements on a square cylinder with controlled harmonic motion in a bi-dimensional flow has been carried out. Motion excited forces have been modeled as random variables and characterized by statistical analysis of the experimental data. Finally, the probability of occurrence of the instability condition has been evaluated by propagating the experimental uncertainties through the traditional quasi-steady galloping approach, as well as through an unsteady formulation.

UNCERTAINTY IN THE MOTION-EXCITED FORCES ON A SQUARE PRISM AND PROBABILISTIC ASSESSMENT OF GALLOPING INSTABLITY