794 Mathematical Modelling Reports

parameters were needed, according to some criteria, for one segment of data which fitted the bell-shaped spectrum of the APs. However, close to 30 parameters were needed to track the low-frequency component of the MUs firing rate, when averaging the reconstructed spectra for 100 segments. (This order can be reduced using special methods.)

With local muscular fatigue, the first AR parameter n,, the first reflection coefficient k,, and the normalized energy of the model error VP, all decline with time. There is then a decline of the similarity of the signal to white noise and it tends to a lower frequency band as observed in the past. During central fatigue-induced by severe sleep deprivation-no consistent changes were observed in the SEMG spectrum or the parameters of its AR model.

J. Sound Vibr Vol. 117, No. 2, pp. 277-288, 1987

A COMPONENT MODE METHOD FOR MODELLING THE DYNAMICS OF TURBO-GENERATOR SETS

A. CRACKS,

Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2G8

Abstract-The paper gives details of a procedure for forming a complete model for the dynamics of a turbo-generator set on a desk-top computer. A reduction procedure is used on each of the principal rotating components in turn, extracting the important information and eliminating unwanted degrees of freedom before assembling into the global system. Finite element models of the high pressure and intermediate turbine rotors, the low pressure rotor and the generator are presented. The degrees of freedom retained are such that they can be measured at the on-site situation and this is an important feature of the method. Because the sub-components are related to real physical entities, the predicted characteristics of these can be checked against some simple test data, which can be used to enhance the model if necessary. There are three important uses for the model: performing a stability analysis, aiding in the balancing process, and in-health monitoring of the rotating parts. While the stability evaluation demands a good model for bearing and foundations, the balancing process can be carried out without knowing these properties. It is to providing a reliable rotor model to aid in the balancing process that is the principal thrust of this paper. The method is illustrated by applications to 350 and 500 MW sets.

Im. J. Solids Srrucr. Vol. 23, No. 6. pp. 733-750. 1987

CONSTITUTIVE MODEL WITH STRAIN SOFTENING

G. FRANTZISKONIS and C. S. DE~AI

Department of Civil Engineering and Engineering Mechanics, University of Arizona, Tucson, AZ 85721. U.S.A.

Abstract-The aim of this paper is to propose a simple yet realistic model for the mechanical behavior of geologic materials such as concrete and rock. The effect of structural changes in such materials is addressed and incorporated in the theory through a tensor form of a damage variable. It is shown that formation of damage is responsible for the softening in strength observed in experiments, for the degradation of the elastic shear modulus, and for induced anisotropy. A generalized plasticity model is incorporated for the so-called topical or continuum part of the behavior, whereas the damage part is represented by the so-called stress-relieved behavior. The parameters required to define the model are identified and determined from multiaxial testing of a concrete. The predictions are compared with observed behavior for a number of stress paths. The model shows very good agreement with the observed response.