A Modified Conical Beam Element Based on Finite Element Analysis: Experimental Correlations

Abstract

A portion of the results from a previous investigation into the structural behavior of hollow conical sections has been used to develop a method of correcting the conical beam element used in modern rotordynamic programs. The modification is made by altering the local value of the Young’s modulus so that the equations used in the conical element produce a bending flexibility which corresponds to that determined from detailed, three-dimensional finite element models. The use of this modification produces substantial improvement in the prediction of the first five natural frequencies of a hollow nonrotating shaft containing two opposed conical sections, for a range of wall thicknesses. The modification exhibits a length dependency which appears to be a main cause of the remaining discrepancies, though it is pointed out that the procedure is only a partial implementation of a more complete hybrid element to be presented later. Static experiments are also discussed, and the verification of a unique behavior characteristic of steep tapered sections is reported.