Vortex-excited vibrations and galloping of slender elements

Vortex-excited vibrations and galloping instability are very important phenomena for slender structures or elements. A mathematical model for predicting the vortex-excited vibration has been developed taking into account the increasing correlation length of the exciting force with increasing vibration amplitude, called ''the correlation length model''. The predicted amplitudes have been verified with full-scale measurements within the past 15 years and the agreement is very good. This model has been included into German DIN-standards and into the draft of Eurocode ENV 1991-2-4 ''Wind Action''. The practical calculation of the galloping phenomenon is restricted to prediction of the instability point, the so-called ''onset velocity''. The key point is the knowledge of the correct instability parameter, -delta c(y)/delta alpha, which mostly has been taken from static model test investigations in the past. This quasi-static values ignore the aerolastic effect to the c(y)(alpha)-curve. Model tests with aeroelastic models of different cross sections have been made by the authors and more realistic galloping instability parameters have been analysed from the tests. This values will be presented. Examples of application for vortex shedding as well as for galloping will be presented.