Torsional flutter and branch characteristics for 2-D rectangular cylinders

Branch switching characteristics for coupled flutter and torsional flutter of structural sections are analyzed using step-by-step (SBS) flutter analysis. In the case of typical coupled flutter instability, prior to the appearance of flutter instability, the torsional branch (TB) controls the instability; although at certain lower velocity ranges after flutter onset, the TB and heaving branch (HB) coexist, with sudden switching in particular velocity ranges. In the vicinity of this velocity range, significant differences in the flutter characteristics are obtained by the conventional complex eigenvalue analysis (CEV) and the SBS methods, but in some velocity ranges, the two methods show good agreement. However, for flutter which is dominated by the TB, such as typical torsional flutter instability as for a 2-D rectangular cylinder with side-ratio B/D of 5 and 1.1 frequency ratio, fϕ0/fη0, the flutter characteristics obtained by CEV and SBS analyses show fairly good agreement at all velocity ranges, where no branch switching is observed.