Identification of Mistuning Characteristics of Bladed Disks From Free Response Data

Abstract

The focus of the present investigation is on the estimation of the dynamic properties, i.e. masses, stiffnesses, natural frequencies, mode shapes and their statistical distributions, of turbomachine blades to be used in the accurate prediction of the forced response of mistuned bladed disks. As input to this process, it is assumed that the lowest natural frequencies of the blades alone have been experimentally measured, for example in a broach block test. Since the number of measurements is always less than the number of unknowns, this problem is indeterminate in nature. Two distinct approaches will be investigated to resolve the shortfall of data. The first one relies on the imposition of as many constraints as needed to insure a unique solution to this identification problem. Specifically, the mode shapes and modal masses of the blades are set to their design/tuned counterparts while the modal stiffnesses are varied from blade-to-blade to match the measured natural frequencies. The second approach, based on the maximum likelihood principle, yields estimates of all the structural parameters of the blades through the minimization of a specified “cost function”. The accuracy of these two techniques in predicting the forced response of mistuned bladed disks will be assessed on simple dynamic models of the blades.

Robust dynamic analysis of detuned-mistuned rotating bladed disks with geometric nonlinearities

“…This technology has intensively been studied in the framework of the linear dynamic analysis (see for instance, [4,5,6,7,8,9,10,11,12,13,14]), for which the mistuning effects have been modeled using either parametric probabilistic approaches (see for instance, [15,16,17,18,19]), or using the nonparametric probabilistic approach ( [20,21,22]), and for which the optimization of alternating patterns has been studied (see for instance, [23,24,25,26]).…”

Mistuning Identification and Model Updating of an Industrial Blisk

“…The issue is then how to model the variations of structural properties (mistuning) to achieve this goal. As pointed out by Mignolet et al [22] among others, assuming small perturbations, an accurate knowledge of all structural parameters is not always necessary to get good predictions of global responses. Rather, the identification of modal characteristics can be sufficient.…”

“…To solve the final mistuning problem defined by (22), a least square fit strategy is used (which is quite usual in model updating techniques and was also used in other mistuning identification techniques [13]). The aim is to determine parameters p i , so they are isolated in a vector p:…”

Nonparametric Modeling of Random Uncertainties for Dynamic Response of Mistuned Bladed Disks

“…In this case, blade eigenfrequencies are mistuned through the stiffness parameters but the corresponding eigenmodes remain unchanged with respect to the tuned case. Recently, Mignolet et al [13,14] introduced a probability model which is experimentally identified using the maximum likelihood principle in order to include blade-modal-shape mistuning or not. This model exhibits differences with respect to the parametric probability model currently used.…”