Dynamics Of Rotors On Refrigerant Lubricated Gas Foil Bearings

The gas foil bearing (GFB) technology is a key factor for the transition to oil-free rotating machinery. Among numerous advantages, GFBs offer the unique ability to be lubricated with working fluids such as refrigerants. However, the computational analysis of refrigerant-lubricated GFB–rotor systems represents an interdisciplinary problem of enormous complexity. This work pushes forward existing limits of feasibility and establishes a new strategy that enables stability and bifurcation analyses.

This book reports on cutting-edge experimental and numerical findings related to the application of active bearings, including smart ones, in rotating machinery. It discusses their role in improving stability and control of rotor systems and reports in depth on the corresponding modeling and control approaches. Chapters are based on peer-reviewed contributions to the 1st Workshop on Active Bearings in Rotating Machinery (ABROM 2022), held on June 29- 30, 2022, in Athens, Greece, and organized in collaboration between the School of Mechanical Engineering of The National Technical University of Athens (NTUA) and the Faculty of Mechanical Engineering of Karlsruhe Institute of Technology (KIT). In connection with the increasing digital transformation of machine elements, this book offers a timely perspective and extensive information on testing methods and experimental procedures involved in the development of intelligent rotors for industrial applications.

This work considers dampers that do not solely focus on a single strategy but instead combine them. The capabilities of conventional dry friction dampers are expanded by taking into account piecewise defined contact geometries. This leads to friction dampers that change their behavior depending on the amplitude of the oscillations. The vibration damping device in this work, introduces damping at high oscillation amplitudes and takes advantage of absorption at low oscillation amplitudes.

A discussion of models for the behaviour of gas bearings, particularly of the aspects affecting the stability of the system. The text begins with a discussion of the mathematical models, identifying the stiffness and damping coefficients, and describing the behaviour of the models in unstable regions. It then turns to apply these results to bearings: static characteristics and stability of various rotor systems and an extensive discussion of air rings.

The Third Revised And Enlarged Edition Of The Book Presents An In-Depth Study Of The Dynamic Behaviour Of Rotating And Reciprocating Machinery. It Evolved Out Of Lectures Delivered At Different Universities Over The Last Two Decades. The Book Deals With Torsional And Bending Vibrations Of Rotors, Stability Aspects, Balancing And Condition Monitoring. Closed Form Solutions Are Given Wherever Possible And Parametric Studies Presented To Give A Clear Understanding Of The Subject. Transfer Matrix Methods Is Extensively Used For General Class Of Rotors For Both Bending And Torsional Vibrations.Special Attentions Are Given To Transient Analysis Of The Rotors Which Is Becoming An Essential Part Of The Design Of High Speed Machinery. Systems With Fluid Film Bearings, Cracked Rotors And Two Spool Rotors Are Also Presented.A First Course On Theory Of Vibration Is A Prerequisite To This Study. Analysis Used Is Fairly Simple, But Sufficiently Advanced To The Requisite Level Of Predicting Practical Observations. As Far As Possible, Practical Examples Are Illustrated, So That The Book Is Also Useful To Practising Engineers.A Special Feature Of This Book Is Diagnostics Of Rotating Machinery Using Vibration Signature Analysis And Application Of Expert Systems To A Field Engineer In Trouble Shooting Work.

Flexible-surface thrust and journal foil-bearings of novel design were fabricated, and their performance was convincingly demonstrated, both individually and jointly as a unified rotor-support system. A versatile rig was constructed and instrumented, and experimental results are copiously documented with graphs and oscilloscopic data of trajectories, waveforms, and scans of amplitude response. The thrust bearings combine advantages of surface compliance with the superior load capacity of the spiral-groove configuration. The flexible supports provide means of deliberate control of clearance topography, in contrast to bearings in which the formation of the lubricating wedge is casual and incidental. At speeds of 40,000 to 45,000 rpm and a mean clearance of the order of 15 to 20 micrometers (600 to 800 micro in.), the resilient, air-lubricated, spiral-groove thrust bearings comfortably support a load of 127 N (29 lb; 13 kgf), equivalent to 3.0 N/sq. cm. (4.5 lb/sq in, 0.31 kgf/sq cm). The construction of journal foil-bearings is extremely simple. In one design, a coiled ribbon of plane foil and a retaining cartridge constitute the only components. In another design, the plane foil is integral with a section preformed to an open octagon with rounded vertices. A radical departure from operational characteristics of rigid gas bearings is achieved.