Fig. 3.
Frequencies of the first six flexural modes σ̂n as functions of the imposed torsional moment Û0 for periodic (left) and clamped (right) boundary conditions. On both plots the solid black lines correspond to the frequencies in the limit η → 0 and the symbols represent the frequencies for η = 0.05 (the circle ○ and triangle ▽ represent, respectively, the in-plane and out-of-plane mode frequencies). The labels ”ip” and ”op” denote the in-plane and out-of-plane frequency branches for the first two modes (the other modes are ordered similarly). Finally, the numbers in the gray circles indicate the indices of the modes.