Vibration torsional coupling

In a study of methyl-substituted pyridines, the aryl regions of the overtones show a simplified structure having one peak progression for each nonequivalent C-H. The methyl regions of the methylpyridines show complex profiles. The band profile in 3- and 4-methylpyridine is similar to that of toluene because the methyl groups of these compounds are free rotors, and all have a low-energy barrier to rotation. However, the methyl band profiles of 2-methylpyridine are complex, and these patterns indicate that vibration-torsional coupling is an important contribntor to the complex structure." ... 

D Bermejo, J Santos, P Cancio, JM Fernandez, S Montero. Vibrational-torsional coupling. High-resolution stimulated Raman spectrum of the V3 band of ethane ( C2H6). J Chem Phys 97 7055-7063, 1992. 

Softening and cure is examined with the help of a torsional pendulum modified with a braid (65), which supports thermosets such as phenoHcs and epoxies that change from a Hquid to a soHd on curing. Another method uses vibrating arms coupled to a scrim-supported sample to measure storage and loss moduH as a function of time and temperature. An isothermal analytical method for phenoHc resins provides data regarding rate constants and activation energies and allows prediction of cure characteristics under conditions of commercial use (47). 

Very low-frequency vibrations have been observed in proteins (e.g., Brown et al., 1972 Genzel et al., 1976), which must involve concerted motion of rather large portions of the structure. By choosing a suitable set of proteins to measure (preferably in solution), it should be possible to decide approximately what structural modes are involved. Candidates include helix torsion, coupled changes of peptide orientation in /3 strands, and perhaps relative motions of entire domains or subunits. These hypotheses should be tested, because the low-frequency vibrations probably reflect large-scale structural properties that would be very useful to know. 

Ueha proposed a two-vibration-mode coupled type (Fig. 4.1.38), that is, a torsional Langevin vibrator was combined with three multilayer actuators to generate larger longitudinal and transverse surface displacements of the stator, as well as to control their phase difference [62]. The phase change can change the rotation direction. 

Furthermore, we suppose that the bending-torsion coupling and the axial vibration of the beam centerline are negligible and that the components of the displacement field u of the beam are based on the Timoshenko beam theory which, in turn, means that the axial displacement is proportional to z and to the rotation ir x, t) of the beam cross section about the positive y-axis and that the transverse displacement is equal to... 

This phenomenon is caused by self-excitation of the blade and is aero-elastic. It must be distinguished from classic flutter, since classic flutter is a coupled torsional-flexural vibration that occurs when the freestream velocity over a wing or airfoil section reaches a certain critical velocity. Stall flutter, on the other hand, is a phenomenon that occurs due to the stalling of the flow around a blade. 

Lateral vibrations result from the coupling with axial mode of buckling. The lateral vibrations may also result from a coupling with the torsional vibrations. 

Because of the length of these shafts and the flexible couplings or joints used to transmit torsional power, jackshafts tend to flex during normal operation. Flexing results in a unique vibration profile that defines its operating mode shape. 

Fig. 5.19 Low-frequency Fe modes of Fe(TPP)(NO) predicted on the basis of B3LYP calculations. The modes mainly involve porphyrin core translation, Fe-NO torsion, Fe-N-O bending, and Fe out-of-plane motion coupled to doming of the porphyrin core. Arrows representing mass-weighted atomic displacements are 100(my/mFe) longer than the zero-point vibrational amplitude of atom j. Color scheme as in Fig. 5.15 (taken from [101])...

Torsional flexing and related torsion-vibration-coupling effects... 

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