Research on variational mode decomposition and its application in detecting rub-impact fault of the rotor system

This book equips the reader to understand every important aspect of the dynamics of rotating machines. Will the vibration be large? What influences machine stability? How can the vibration be reduced? Which sorts of rotor vibration are the worst? The book develops this understanding initially using extremely simple models for each phenomenon, in which (at most) four equations capture the behavior. More detailed models are then developed based on finite element analysis, to enable the accurate simulation of the relevant phenomena for real machines. Analysis software (in MATLAB) is associated with this book, and novices to rotordynamics can expect to make good predictions of critical speeds and rotating mode shapes within days. The book is structured more as a learning guide than as a reference tome and provides readers with more than 100 worked examples and more than 100 problems and solutions.

/pdf/dynamics-of-rotating-machines-499re2kizd.pdf

Dynamics of rotating machines

A Stick-slip Whirl Model is presented which is a simplification of an oilwell drillstring confined in a borehole with drilling fluid. The disappearance of stick-slip vibration when whirl vibration appears is explained by bifurcation theory. The numerical results are compared with the experimental data from a full-scale drilling rig.

http://www.mate.tue.nl/mate/pdfs/1928.pdf

Stick-Slip Whirl Interaction in Drillstring Dynamics

Part I: Primer on Rotor Vibration Vibration Concepts and Methods One-Degree-of-Freedom Model Multi-DOF Models Modes, Excitation, and Stability of Multi-DOF Models Lateral Rotor Vibration Analysis Models Simple Linear Models Formulations for RDA Software Insights into Linear LRVs Nonlinear Effects in Rotor Dynamical Systems Torsional Rotor Vibration Analysis Models Rotor-Based Spinning Reference Frames Single Uncoupled Rotor Coupled Rotors Semidefinite Systems Part II: Rotor Dynamic Analyses RDA Code for Lateral Rotor Vibration Analyses Unbalance Steady-State Response Computations Instability Self-Excited-Vibration Threshold Computations Additional Sample Problems Bearing and Seal Rotor Dynamics Liquid-Lubricated Fluid-Film Journal Bearings Experiments to Measure Dynamic Coefficients Annular Seals Rolling Contact Bearings Squeeze-Film Dampers Magnetic Bearings Compliance Surface Foil Gas Bearings Turbo-Machinery Impeller and Blade Effects Centrifugal Pumps Centrifugal Compressors High-Pressure Steam Turbines and Gas Turbines Axial Flow Compressors Part III Monitoring and Diagnostics Rotor Vibration Measurement and Acquisition Introduction to Monitoring and Diagnostics Measured Vibration Signals and Associated Sensors Vibration Data Acquisition Signal Conditioning Vibration Severity Guidelines Casing and Bearing Cap Vibration Displacement Guidelines Standards, Guidelines, and Acceptance Criteria Shaft Displacement Criteria Signal Analysis and Identification of Vibration Causes Vibration Trending and Baselines FFT Spectrum Rotor Orbit Trajectories Bode, Polar, and Spectrum Cascade Plots Wavelet Analysis Tools Chaos Analysis Tools Symptoms and Identification of Vibration Causes Part IV Trouble-Shooting Case Studies Forced Vibration and Critical Speed Case Studies HP Steam Turbine Passage through First Critical Speed HP-IP Turbine Second Critical Speed through Power Cycling Boiler Feed Pumps: Critical Speeds at Operating Speed Nuclear Feed Water Pump Cyclic Thermal Rotor Bow Power Plant Boiler Circulating Pumps Nuclear Plant Cooling Tower Circulating Pump Resonance Generator Exciter Collector Shaft Critical Speeds Self-Excited Rotor Vibration Case Studies Swirl Brakes Cure Steam Whirl in a 1300 MW Unit Bearing Unloaded by Nozzle Forces Allows Steam Whirl Misalignment Causes Oil Whip/Steam Whirl "Duet" Additional Rotor Vibration Cases and Topics Vertical Rotor Machines Vector Turning from Synchronously Modulated Rubs Air Preheater Drive Structural Resonances Aircraft Auxiliary Power Unit Commutator Vibration-Caused Uneven Wear Impact Tests for Vibration Problem Diagnoses Bearing Looseness Effects Tilting-Pad versus Fixed-Surface Journal Bearings Base-Motion Excitations from Earthquake and Shock Parametric Excitation: Nonaxisymmetric Shaft Stiffness Rotor Balancing Index

Rotating Machinery Vibration: From Analysis to Troubleshooting

Cracks in shafts have long been identified as factors limiting the safe and reliable operation of turbomachines. They can sometimes result in catastrophic failure of equipment (rotor bursts) and, more often, in costly process upsets, repairs and premature scrapping and replacement of equipment. Cracked shafts still pose a significant and real threat to equipment in spite of the great advances made in the areas of metallurgy, manufacturing and design. In the past two decades, much research and many resources have gone into developing various on-line and off-line diagnostic techniques to effectively detect cracks before they cause serious damage. Because of the enormous amount of ongoing research in this area (more than 500 technical papers have been published in English alone in the past 30 years), there is a real need to periodically condense and summarize the information. This paper reviews literature on cracked shaft detection and diagnostics published after 1990.

Cracked shaft detection and diagnostics: A literature review

Amelioration des modeles de calcul des systemes rotors-paliers ou rotors-joint d'etancheite faiblement charges

Improvements in Lightly Loaded Rotor/Bearing and Rotor/Seal Models

The paper discusses orderly and chaotic dynamic responses of simple mechanical structures with clearances and impacting. Experimental results from a simulator of a rotating machine with one loose pedestal are presented, and a summary of analytical results for this case is given. The orderly and chaotic responses obtained through numerical integration are presented in the form of bifucation diagrams. The second part of the paper discusses an existence of the main and higher order resonances in structures with clearances and impacting, which are excited by external periodic forces. For a one degree of freedom nonlinear system, the application of a discontinuous variable transformation, followed by an averaging method provides analytical formulae describing the system response amplitudes and phases in the proximity fo the main and harmonic resonances

Dynamic Effects in Mechanical Structures with Gaps and Impacting: Order and Chaos

The thermal effects of rotor-to-stator rub, and their influence on the rotor vibrational response, are discussed in this paper. Based on machinery observations, it is assumed in the analysis that velocities of transient thermal effects are considerably lower than that of rotor vibrations, and thermal effects affect only rotor steady-state vibrational responses. These responses would change due to thermally induced bow of the rotor, which can be considered slowly varying in time for the purposes of rotor vibration calculation. Thus uncoupled from the thermal problem, the rotor vibration is analyzed. The major consideration is given to the rotor, which experiences intermittent contact with the stator due to predetermined thermal bow of the rotor, unbalance force, and radial constant load force. In the case of an inelastic impact, this causes an on/off step-change in the stiffness of the system. A specially developed transformation is applied to the system model which contains discontinuities, and an averaging technique is then used to analyze stability of the different resonance regimes of rotor motion that were obtained. These regimes are further used to calculate the heat generated during rotor-to-stator contact stages, as a function of thermal conditions and rotor thermal bow modal parameters. The calculated heat input is used as a boundary condition for the rotor heat transfer problem. The latter is treated as quasi-static, which allows the application of an asymptotic method to the problem. The solution at its first approximation is used to adjust the rotor thermal bow value. As a result of this calculation, an ordinary differential equation with complex variables is obtained for the thermal bow, and it is investigated from the stability standpoint.

/pdf/rotor-to-stator-rub-related-thermal-mechanical-effects-in-389yn4ln54.pdf

Rotor-to-stator, rub-related, thermal/mechanical effects in rotating machinery

This paper presents the results of recent experimental studies on rotor/seal full annular rub, including forward and reverse precession. It was found that reverse precessional full annular rub (dry whip) could occur repeatedly in small clearance cases without any outside disturbance. The rotor rubbed against the seal with almost constant amplitude and frequency, which was higher than the natural frequency of the original rotor system and lower than of that of the coupled rotor/seal system. Once generated, the reverse precessional rub could be sustained over the whole speed range as long as slippage was maintained. Radius-to-clearance ratio varied from 10 to 40. The experimental studies include forward rub jump phenomena, reverse rub triggering mechanism, and effects of mass unbalance, surface lubrication, shaft speed, and seal stiffness. The results of both forward and reverse precession are discussed in detail, with emphasis on the reverse and the transition from the forward to the reverse.

/pdf/full-annular-rub-in-mechanical-seals-part-i-experimental-2t6bw69hnu.pdf

Agnes Muszynska

Papers

Improvements in Lightly Loaded Rotor/Bearing and Rotor/Seal Models

Dynamic Effects in Mechanical Structures with Gaps and Impacting: Order and Chaos

Rotor-to-stator, rub-related, thermal/mechanical effects in rotating machinery

Full Annular Rub in Mechanical Seals, Part I: Experimental Results

Forward and backward precession of a vertical anisotropically supported rotor