Agnes Muszynska

Bio: Agnes Muszynska is an academic researcher from Dynamics Research Corporation. The author has contributed to research in topic(s): Rotor (electric) & Bearing (mechanical). The author has an hindex of 14, co-authored 35 publication(s) receiving 1050 citation(s).

Whirl and whip—Rotor/bearing stability problems

Abstract: A mathematical model of an unloaded symmetric rotor supported by one rigid and one fluid lubricated bearing is proposed. The rotor model is represented by generalized (modal) parameters of its first bending mode. The rotational character of the bearing fluid force is taken into account. The model yields synchronous vibrations due to rotor unbalance as a particular solution of the equations of motion, rotor/bearing system natural frequencies and corresponding self-excited vibrations known as “oil whirl” and “oil whip”. The stability analysis yields rotative speed threshold of stability. The model also gives the evaluation of stability of the rotor synchronous vibrations. In the first balance resonance speed region two more thresholds of stability are encountered. The width of this stability region is directly related to the amount of rotor unbalance. The results of the analysis based on this model stand with very good agreement with field observations of rotor dynamic behavior and the experimental data.

Chaotic responses of unbalanced rotor/bearing/stator systems with looseness or rubs

Abstract: The first part of this paper presents results of numerical simulation of the dynamic behavior of a one-lateral-mode unbalanced and radially side-loaded rotor with either a loose pedestal (looseness in a stationary joint), or with occasional rotor-to-stator rubbing. The nonlinearities of these systems (variable stiffness, impacting, and friction) are associated with the rotor intermittent contacts with the stationary element. The results, based on a newly developed local impact model [P. Goldman and A. Muszynska, Analytical and experimental simulation of loose pedestal dynamic effects on a rotating machine vibrational response, Rotating Machinery Dynamics, DE-Vol. 35, ASME, Miami, Florida, pp. 11–17 (1991); P. Goldman and A. Muszynska, Analytical model of the impact between rotating and nonrotating elements and its application in rotor-to-stator rubbing, BRDRC Report 1, (1992); P. Goldman and A. Muszynska, Chaotic behavior of rotor-to-stator systems with rubs, ASME Turbo EXPO Conference, 93-GT-34, Cincinnati, Ohio, Transactions of the ASME (to appear); P. Goldman and A. Muszynska, Dynamic effects in mechanical structures with gap and impacting: Order and chaos, Trans. of ASME, J. Vibration and Acoustics (1994)] exhibit regular periodic vibrations of synchronous (1×) and subsynchronous ( 1 2 ×, 1 3 × , …) orders, as well as chaotic vibration patterns of the rotor, all accompanied by higher harmonics. The second part of the paper presents experimental vibration characteristics of rotors with looseness or rubs, obtained from rotor rigs. The results display similar patterns as those obtained analytically.

Stability of whirl and whip in rotor/bearing systems

Abstract: The paper presents a continuation of the analysis of lateral vibrations of the lightly loaded rotor/bearing system discussed in reference [1] In the present paper, it is shown that the rotor self-excited vibrations (known as oil whirl and oil whip) due to fluid dynamic forces generated in the oil-lubricated bearing, can exhibit multiple regimes These regimes were observed experimentally and were reported from the machinery field data The analysis of stability of the self-excited vibrations of the whirl- and whip-type is outlined in this paper It is shown that after the threshold of stability, the pure rotational motion of the shaft becomes unstable and the whirl regime is stable With increasing rotational speed the whirl smoothly transforms into whip At a certain speed, determined by the system parameters, whip may disappear and either with a “jump” in frequency and amplitude becomes replaced by the second mode whirl, or the rotor motion stabilizes for a limited range of the rotational speeds, and then the second mode whirl starts again These phenomena were observed experimentally The analysis is based on the four-degree-of-freedom model of the rotor (the first bending mode and two rotor modal masses taken into account) and on the rotating fluid dynamic forces in the bearing

Frequency-swept rotating input perturbation techniques and identification of the fluid force models in rotor/bearing/seal systems and fluid handling machines

Abstract: Perturbation techniques used for identification of rotating system dynamic characteristics are described. A comparison between two periodic frequency-swept perturbation methods applied in identification of fluid forces of rotating machines is presented. The description of the fluid force model identified by inputting circular periodic frequency-swept force is given. This model is based on the existence and strength of the circumferential flow, most often generated by the shaft rotation. The application of the fluid force model in rotor dynamic analysis is presented. It is shown that the rotor stability is an entire rotating system property. Some areas for further research are discussed.

Chaotic Behavior of Rotor/Stator Systems With Rubs

Abstract: This paper outlines the dynamic behavior of externally excited rotor/stator systems with occasional, partial rubbing conditions. The observed phenomenon have one major source of a strong nonlinearity: transition from no contact to contact state between mechanical elements, one of which is rotating. This results in variable stiffness and damping, impacting, and intermittent involvement of friction. A new model for such a transition (impact) is developed. In case of the contact between rotating and stationary elements, it correlates the local radial and tangential ("super ball") effects with global behavior of the system. The results of numerical simulations of a simple rotor/stator system based on that model are presented in the form of bifurcation diagrams, rotor lateral vibration time—base waves, and orbits. The vibrational behavior of the considered system is characterized by orderly harmonic and subharmonic responses, as well as by chaotic vibrations. A new result (additional subharmonic regime of vibration) is obtained for the case of heavy rub of an anisotropically supported rotor. The correspondence between numerical simulation and previously obtained experimental data supports the adequacy of the new model of impact.

Dynamics of rotating machines

Abstract: 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.

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

Abstract: Multi-component extraction is an available method for vibration signal analysis of rotary machinery, so a novel method of rubbing fault diagnosis based on variational mode decomposition (VMD) is proposed. VMD is a newly developed technique for adaptive signal decomposition, which can non-recursively decompose a multi-component signal into a number of quasi-orthogonal intrinsic mode functions. The equivalent filtering characteristics of VMD are investigated, and the behavior of wavelet packet-like expansion is first found based on fractional Gaussian noise via numerical simulations. VMD is then applied to detect multiple rubbing-caused signatures for rotor–stator fault diagnosis via numerical simulated response signal and practical vibration signal. A comparison has also been conducted to evaluate the effectiveness of identifying the rubbing-caused signatures by using VMD, empirical wavelet transform (EWT), EEMD and EMD. The analysis results of the rubbing signals show that the multiple features can be better extracted with the VMD, simultaneously.

Stick-Slip Whirl Interaction in Drillstring Dynamics

Abstract: 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.

Rotating Machinery Vibration: From Analysis to Troubleshooting

Abstract: 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

Cracked shaft detection and diagnostics: A literature review

Abstract: 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.