Vibration Response Reduction of a Rotor Shaft System Using Viscoelastic Polymeric Supports

Abstract

The main objective of the present work is to determine reduction in the unbalance response of a rotor shaft system by using a suitable polymeric or viscoelastic bearing support. For analysis, a simple rotor system has been taken with the rotor placed in the middle of a massless shaft with linear elastic bearings at the ends, having viscoelastic supports. A procedure is given for determining the frequency dependence of viscoelastic support characteristics so that the frequency of excitation never coincides with any of the undamped natural frequencies of the system, thus giving low unbalance response over a wide frequency range and the support material can be chosen accordingly. IntroductionExternal damping at the supports is found to be useful in controlling dynamic response of rotating systems [1, 2, 3]. The damping in these studies has been taken to be viscous.Squeeze-film dampers at the rotor bearing supports have been used for high speed systems [4]. A comparison of squeeze film type supports with elastomeric or viscoelastic supports has been carried out experimentally and the latter have been seen to offer operational advantages [5]. Preliminary theoretical studies in [6] have indicated that the unbalance response of a rotor system may be reduced significantly by suitable choice of viscoelastic support parameters. For harmonic vibration conditions, the characteristics of a viscoelastic member are represented by complex stiffness K* = K{\ + irj),Kbe\ng in-phase stiffness and i\, the material loss factor [7]. In most available viscoelastic materials, in the useable frequency range, K increases with frequency and ij increases or decreases with frequency depending on the type of material. The influence of frequency dependence has not been included in [6] and the same has been considered in the present work in order to determine suitable support characteristics for reducing the unbalance response of the rotor.

Design of Optimum Support Parameters for Minimum Rotor Response and Maximum Stability Limit

“…If either the primary support stiffness or the primary support damping assumes a very high value, the support tends to be rigid and hence the stabilizing effects of the support damping are not obtained. Therefore, it is observed from the ®gures, as well as supported by references [10,11], that very high values of b 1 and z 1 lowers the stability limit speed. There remains optimum values for each of these parameters corresponding to the maximum stability limit speed.…”

“…Figure 5 shows the variation of DLIMIT of the rotor ± shaft system with respect to different values of z i of the shaft. It is well established [10,11] that the internal damping in the shaft reduces the stability limit speed. The same is true in this case.…”

“…When subjected to sinusoidal excitations, polymeric materials exhibit in-phase stiffness and loss factor both of which vary with the frequency of excitation. Dutt and Nakra [10] utilized this property of the polymeric materials and predicted suitable frequency dependent support characteristics (in terms of in-phase stiffness and loss factor) to avoid resonance due to unbalance excitation for a rotor ±shaft system with single symmetrically placed rotor disc. The procedure followed in reference [10] is dif®cult to apply to continuous multi-rotor multi support systems.…”

A numerical study on vibration control of a nonlinear Jeffcott rotor via Bouc-Wen model

“…Das et al [4] proposed an active vibration control approach to this problem. Vibrational response of rotor using passive support was studied by Dutta et al [5]. Reduction the whirl amplitude using nonlinear springs is studied by Carrella et al [6].…”

Estudo do controle ativo e passivo de vibrações em sistemas rotativos e estruturais

“…Dentre os dispositivos passivos, podem-se citar os squeeze-film dampers [49,147,165,185], os seal-dampers [192], os suportes viscoelásticos [19,39,54,88], os absorvedores dinâmicos pendulares [79,174], os absorvedores dinâmicos de esferas [8,103], e os anéis hidrocompensadores [14,169]. Dentre os dispositivos semi-ativos ou ativos, podem-se citar os squeeze-film dampers híbridos [58], os squeeze-film dampers ativos com fluido magnetorreológico [90,121,208], mancais com sistema ativo de câmaras hidráulicas [9,166,188], os mancais hidrodinâmicos com acumuladores de impedância variável [72], os mancais com atuadores piezoelétricos [5,144], os mancais com atuadores piezoidráulicos [183], os mancais com lubrificação ativa [135,167,168], os mancais hidrostáticos ativos [22,23,146], os mancais ativos com fluido magnetorreológico [142], os amortecedores rotativos com fluido magnetorreológico [182,193,194], os mancais do tipo foil híbridos [75], os mancais de geometria ativa [98,181], e os mancais magnéticos ativos [93,173]…”