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Accepted Manuscripts

BASIC VIEW  |  EXPANDED VIEW
research-article  
Xiaomeng Tong, Alan Palazzolo and Junho Suh
Appl. Mech. Rev   doi: 10.1115/1.4037216
The Morton effect (ME) is a thermally induced instability that typically appears in rotating shafts with large overhung masses and fluid film bearings. The time-varying thermal bow due to the asymmetric journal temperature distribution may cause intolerable synchronous vibrations with a hysteresis behavior with respect to rotor speed. Discovered by Morton in the 1970s and theoretically analyzed by Keogh and Morton in the 1990s, the ME is still not fully understood. Traditional rotordynamic analysis generally fails to predict the existence of ME induced instability in the design stage or troubleshooting process. The induced excessive rotor vibrations cannot be effectively suppressed through conventional balancing due to the continuous fluctuation of vibration amplitude and phase angle. A quickly growing number of case studies of ME have sparked academic interest in analyzing the causes and solutions of ME, and engineers have moved from an initial trial and error approach to more research inspired modifications of the rotor and bearings. The current review is intended to provide a comprehensive summary of ME in terms of symptoms, causes, prediction theories and solutions. Published case studies in the past are also analyzed for ME diagnosis based on both the conventional view of critical speed, separation margin and the more recent view of the rotor thermal bow and instability speed band shifting. Although no universal solutions of ME are reported recommendations to help avoid the ME are proposed based on both theoretical predictions and case studies.
TOPICS: Separation (Technology), Engineers, Bearings, Design, Rotor vibration, Rotors, Vibration, Errors, Fluid films, Temperature distribution
Discussion  
Patrick S. Keogh
Appl. Mech. Rev   doi: 10.1115/1.4037217
The authors present a timely review of rotor thermal bending and its potential instability through the Morton effect, which is associated with hydrodynamic fluid film journal bearings. They describe the viscous shearing origin of the heat source and its symptoms through to the rotor dynamics. There then follows an overview of the modeling approaches to predict the coupled fluid-thermal-rotor dynamics and their stability/instability. These are related to the prediction of high and hot spots and their phase difference. Experimental methods are then covered followed by parameter influences and options to avoid the Morton effect, some of which may conflict with the original rotor dynamic design specification. In some cases the sensitivity of the parameter variations may be significant. This discussion article will consider some of the questions on the predictive capabilities for the Morton effect. The inherent asymmetric shaft heating mechanism that drives rotor thermal bending is also related to other phenomena in other rotating machines and systems.
TOPICS: Dynamics (Mechanics), Stability, Heat, Fluids, Machinery, Design, Experimental methods, Modeling, Rotordynamics, Rotors, Fluid films, Shearing (Deformation), Heating, Journal bearings, Die cutting
Review Article  
Andreas Steinboeck, Andreas Ettl and Andreas Kugi
Appl. Mech. Rev   doi: 10.1115/1.4037177
In flat rolling, the lateral position of the product in the rolling mill and the camber (curvature of the product centerline seen in top view) are key process variables. We explore how their evolution can be analytically modeled based on nonlinear geometric relations, material derivatives, balance equations, constitutive equations for the material flow in the roll gap, and a change of coordinates to obtain a time-free formulation. Based on example problems, we verify the developed novel model and further illustrate the mechanisms behind it. Finally, a literature review on models in this field reveals that there is not yet a consensus on the correct analytical model of the evolution of the camber in flat rolling. The literature review shows that most published models are special cases of the model developed in this paper.
TOPICS: Flow (Dynamics), Rolling mills, Constitutive equations

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