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Highlights • A polynomial surrogate for the cracked rotor system with UBB parameters is constructed. • The FE rotor analysis model is treated as a black box and only runs at sample points. • Calculation accuracy of the surrogate is validated by comparisons with other methods. • The surrogate method can deal with a large number of uncertain quantities with efficiency. Abstract Uncertain‑but‑bounded (UBB) parameters are used to describe the non-probabilistic uncertainties in rotor systems. A general non-intrusive polynomial surrogate is constructed to quantify the uncertain effects of the UBB quantities on the dynamic responses. The surrogate is convenient to establish and able to deal with a large number of uncertain variables. The zeros of the Chebyshev series are used as sample points and the least square method (LSM) is employed to evaluate the coefficients. At the sample points of the polynomial surrogate, the harmonic balance method is applied to obtain the sample responses (PS-HBM). During the surrogate modeling, the deterministic rotor system with a breathing crack is treated as a black box and no modifications should be made to the deterministic finite element (FE) analysis process. It needs no distribution laws and is especially helpful in small sample sized problems. Numerical simulations of the rotor system with various UBB parameters are carried out to demonstrate the effectiveness of the surrogate. Moreover, its accuracy and efficiency are verified by comparisons with other classic sampling methods. [ABSTRACT FROM AUTHOR]

The hysteresis effect of brush seal is a key factor affecting the sealing performance of the rotor system, so it is particularly important to study the nonlinear behaviors of the rotor-bearing-brush seal system under the hysteresis effect. First, the entire circle of bristle pack is classified according to the position angle and contact condition of single bristle, and the rotor support force, the interaction force between the bristles, the air pressure and the friction of back plate are considered. It is proposed to use the loss rate to calculate the uniform load of the back plate, according to the linear beam theory, the bending force model of bristle under different rotor eccentricity is established. Second, the hysteresis angle is proposed to represent the degree of hysteresis effect of the whole circle of bristle pack, and the seal force model under hysteresis effect is established. Third, considering the interaction of seal force and oil-film force, the dynamic model of Jeffcott rotor-bearing-brush seal system is established. The influence of hysteresis effect on the dynamic characteristics of rotor system is studied by using bifurcation diagram, axis orbit, Poincaré map, spectrum diagram and time history. It is found that the hysteresis effect has different degrees of influence on the nonlinear dynamic characteristics of the rotor system in different rotational velocity intervals. In addition, the influence of seal interference on the motion state of rotor system cannot be ignored. • The bending force of bristle is classified according to the position angle and contact condition. • The rotor support force, bristles interaction force, air pressure and friction of back plate are considered. • The seal force model of brush seal under hysteresis effect is established. • The influence of hysteresis effect on the dynamic characteristics of rotor system is studied. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this paper is to investigate the use of the 2× and 3× super-harmonic frequency components for detecting the presence of a single transverse breathing crack in a non-linear rotor system. This procedure is based on the detection of the super-harmonic frequency components of the non-linear dynamical behaviour at the associated sub-critical resonant peaks. The non-linear behaviour of the rotor system with a breathing crack is briefly analysed numerically: it will be illustrated that the effects of the crack size and location induce the variation of non-linear responses and the emerging of new resonance – antiresonance peaks of the cracked rotor at second, third and fourth harmonic frequency components. Then, the influence of the crack–unbalance interactions and more particularly the relative orientation between the front crack and the unbalance are also undertaken with considerations of various crack depths, and unbalance magnitudes. It is demonstrated that for a given crack depth, the unbalance does not only affect the vibration amplitude of the 1× amplitudes, but also the and sub-critical resonant peaks. Finally, it is illustrated that the emerging of super-harmonic frequency components provides useful information on the presence of cracks and may be used on an on-line crack monitoring rotor system. Using this methodology, the detection of small levels of damage may be easily undertaken. [Copyright &y& Elsevier]