Torsional Instability of Cantilevered Bars Subjected to Nonconservative Loading

Cantilever bar torsional instability under nonconservative compression loadin

The role of aerodynamic forces in a mathematical model for suspension bridges

In a fish-bone model for suspension bridges studied by us in a previous paper we introduce linear aerodynamic forces. We numerically analyze the role of these forces and we theoretically show that they do not influence the onset of torsional oscillations. This suggests a new explanation for the origin of instability in suspension bridges: it is a combined interaction between structural nonlinearity and aerodynamics and it follows a precise pattern. This gives an answer to a long-standing question about the origin of torsional instability in suspension bridges

Periodic solutions and torsional instability in a nonlinear nonlocal plate equation

A thin and narrow rectangular plate having the two short edges hinged and the two long edges free is considered. A nonlinear nonlocal evolution equation describing the deformation of the plate is introduced: well-posedness and existence of periodic solutions are proved. The natural phase space is a particular second order Sobolev space that can be orthogonally split into two subspaces containing, respectively, the longitudinal and the torsional movements of the plate. Sufficient conditions for the stability of periodic solutions and of solutions having only a longitudinal component are given. A stability analysis of the so-called prevailing mode is also performed. Some numerical experiments show that instabilities may occur. This plate can be seen as a simplified and qualitative model for the deck of a suspension bridge, which does not take into account the complex interactions between all the components of a real bridge.Comment: 34 pages, 4 figures. The result of Theorem 6 is correct, but the proof was not correct. We slightly changed the proof in this updated versio

Graphite composite truss welding and cap section forming subsystems. Volume 1: Executive summary

A rolltrusion process was developed for forming of a hybrid, single-ply woven graphite and glass fiber cloth, impregnated with a polysulfone resin and coated with TI02 pigmented P-1700 resin into strips for the on-orbit fabrication of triangular truss segments. Ultrasonic welding in vacuum showed no identifiable effects on weld strength or resin flow characteristics. An existing bench model cap roll forming machine was modified and used to roll form caps for the prototype test truss and for column test specimens in order to test local buckling and torsional instability characteristics

Torsional instability of hinged flanges stiffened by lips and bulbs

Based on torsional instability theory, buckling charts are presented for determining the critical strain of hinged flanges stiffened by idealized lip and bulb elements

Torsional Instability Of Cooling Tower Fan During Induction Motor Startup

Case StudyTorsional instability during starting of an induction motor has caused excessive torque oscillation and eventual failure of gearbox pinion teeth of a cooling tower fan train. A torsional instability appeared due to a steep slope of the induction motor starting torque curve, combined with a torsionally soft driveshaft and a large moment of inertia of the driven fan. In this paper, mechanisms of torsional instability occurrence during startup of an induction motor in a cooling tower fan train are discussed, as well as details of the investigation outcomes of troubleshooting activities, including field measurements. The methods of modeling and analysis are also described. To examine the mechanism of torsional instability occurrence, in addition to transient torsional analysis, the concept of torsional stability analysis is introduced. Practical engineering guidelines to avoid this type of problem, such as a motor selection guideline, are also addressed