Agnes Muszynska

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

Whirl and whip: Rotor/bearing stability problems

Abstract: A mathematical model of a 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 yielded. 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 results.

Estimation of Vibration at Critical Locations Using Available Measurements and Machine Configuration Data

Abstract: This paper discusses one of the problems associated with establishing acceptable vibration levels for rotating machinery related to non collocation of critical vibration and available measurement locations. A critical vibration location is any point along the rotor which has a reduced clearance or a high potential for rubbing, such as seal locations. Non collocation occurs because the physical and/or environmental conditions at the critical locations prohibit the installation of suitable measurement transducers at those points. This leads to the dilemma of correlating the critical and measured vibration responses so the machine can be protected at the critical locations using the known responses at the measurement positions. This paper presents a method for estimating the vibration amplitudes and phases, either synchronous or nonsynchronous, at the critical locations using the known vibration responses at the measurement points, the current operating speed, the machine configuration data, and optimization techniques. A computer program has been developed for a personal computer running Windows 3.1 under DOS 5.0 which uses finite element modeling of the rotor to create a calculated rotor response and a data acquisition system to get the actual measured responses. A local convergence algorithm is then implemented to minimize the error between the calculated and measured vibration responses at the measured locations. The calculated responses at the critical locations then become the estimated vibration response for these points. To evaluate the accuracy of the technique, experiments were conducted using a rotor rig in which the vibration responses at both the critical and measurement locations were measured.The computer program was then used to estimate the vibration responses at the critical locations. The estimated vibration responses were then compared with the measured responses at the same location to evaluate the effectiveness of the technique.The results of these experiments are also included in this paper.© 1993 ASME

Comments on 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.

Specifics of Damping Evaluation in Rotating Machines

Abstract: Focused on rotor lateral modes, the paper discusses specifics of damping evaluation in rotating machines. Rotors force the fluid trapped in small rotor-to-stator radial clearances to rotate in circumferential fashion. The fluid in circumferential motion generates a tangential force acting in feedback on the rotor. This force direction is opposite to that of damping force. The “effective damping” is, therefore, reduced or even nullified by the fluid interaction effects. The classical measures of damping in mechanical structures, such as Logarithmic Decrement and Amplification Factor, which are used to evaluate machine susceptibility to instability based on documented vibration data, have to be adjusted to include the fluid interaction effects. These measures now represent the measures of Quadrature Dynamic Stiffness (QDS). It is shown that they contain the expression defined as Stability Margin (or Nondimensional Stability Margin), derived from the stability condition of the rotor system. A simple model of isotropic rotor lateral vibrations is used to obtain the QDS measures.Copyright © 1996 by ASME

Revisiting Rotor Rigid Body Modes: Parametric Study of Stability

Abstract: This paper presents an analytical model of a rigid rotor supported in two fluid film bearings with an emphasis on predicting the instability threshold speed The factors contributing to the stability of the rotor are discussed and presented graphically using root locus plots The parametric study of the stability starts from the discussion of the rotor/bearing system with “mirror symmetry” Three basic cases are considered:

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.

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.