A new approach for determining the onset velocity of galloping instability taking into account the nonlinearity of the aerodynamic damping characteristic

Abstract Slim structural designs are known to be induced to vibrate in natural wind. These vibrations are mainly caused by eddies and galloping vibrations. Such oscillations are representing a safety risk and have repeatedly led to damage so that reconstruction has to be undertaken. The aim of this study is the investigation of aerodynamic instabilities in order to predict the response of slender structures in natural wind and to assure their safety. The present study provides aerodynamic coefficients for the calculation of vibrations caused by galloping oscillations either in the vertical mode or torsional mode in natural wind. The investigated section types are slim building components (1/d ⪖ 10) and they correspond to forms common in practical use. The aerodynamic damping characteristics are measured with section models using free decay tests and a forced oscillation method.The stability parameters such as lift and moment coefficients for various on-flow angles, for variations of the degree of turbulence and for different geometric dimensions of the profiles are measured. Within this study the nonlinear relation of the aerodynamic damping of a system and the wind velocity is demonstrated and discussed. Depending on the characteristic of this nonlinear relation two different methods of determining the onset point of galloping vibrations are introduced. Comparisons between observed torsional flutter responses of existing structures and the results of the section model tests are made. Both methods of determining the onset point for galloping vibrations are used in this case of damage and the results are discussed.