Discussionon several important issues in measurement and indirect verification of nonlinear galloping self-excited forceson rectangular cylinders

The nonlinear galloping self-excited forces on a 3:2 rectangular cylinder were measured via wind tunnel tests of a spring-suspended sectional model with synchronous measurements on dynamic force and vibration displacement by using miniature dynamic force balances elaborately developed. The measurement accuracy of the self-excited force was verified indirectly through comparing the time histories of the nonlinear galloping displacement of the sectional model reconstructed by using the measured time histories of the self-excited force with the corresponding measured ones. The importance of considering the nonlinearities of the effective damping and stiffness parameters of the sectional model system in such verification was discussed. The percentages of both the non-wind-induced and wind-induced self-excited forces in the total measured dynamic forces were also evaluated as well as the influences of neglecting the nonlinearities of the non-wind-induced additional aerodynamic damping and inertial forces on the measurement accuracy of galloping self-excited force. It can then be found that for the 3:2 rectangular cylinder the portion of the non-wind-induced self-excited force in the measured total dynamic force exceeds that of the wind-induced self-excited force, and therefore, the non-wind-induced self-excited force should be deducted when extracting the wind-induced self-excited force from the measured total dynamic force. The nonlinearities of the non-wind-induced damping and inertial forces exert some influence on the measurement accuracy of the galloping self-excited force, and deserve to be considered. The nonlinearities of the equivalent damping and stiffness parameters of the sectional model system result in a significant influence on the reconstruction accuracy of the galloping displacement time histories of the sectional model system, and thus, it should also be taken into account in the indirect verification of the measurement accuracy of the galloping self-excited force.