PARAMETRIC-INSTABILITY OF SPINNING PRETWISTED BEAMS SUBJECTED TO SINUSOIDAL COMPRESSIVE AXIAL LOADS

The equations of motion of a spinning pretwisted beam under pulsating compressive axial loads are formulated using Euler beam theory and the assumed mode method. Unstable regions of flutter instability are foun d to exist for beams with non-zero pretwist angles, within the stable critical speed zones; The narrower regions of flutter instability sepa rate the stable critical speed zones into smaller stable sub-regions. The compressive axial force is assumed to consist of a steady slate va lue and a time-dependent portion. The multiple scale method is used to determine the regions of instability due to the resulting parametric excitations. As the spin speed varies within the stable sub-regions, c onsistent shifts and widening of unstable regions due to axial load pe rturbation are observed. Widths of the unstable regions are found to d ecrease with decreasing pretwist angle and compressive axial force as well as increasing aspect ratio towards unity. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.