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Modeling And Performance Evaluation Of Machining Spindle With Active Magnetic Bearings, Jerzy T. Sawicki, Eric H. Maslen, Kenneth R. Bischof Dec 2012

Modeling And Performance Evaluation Of Machining Spindle With Active Magnetic Bearings, Jerzy T. Sawicki, Eric H. Maslen, Kenneth R. Bischof

Jerzy T. Sawicki

Active magnetic bearings (AMBs) are increasingly employed in the machine tool industry to exploit their advantages over classical bearings such as high speed capability, rotation accuracy, high stiffness, and accurate displacement tracking capability. Furthermore, the possibility of on-line monitoring of the machining process (e.g., cutting force measurement, tool wear) makes AMB spindles very appealing to the High-Speed Machining (HSM) industry. Despite significant progress already reached in HSM technology, there remain numerous open challenges in modeling and control of magnetic bearings as applied to machining spindles. These include optimum control given AMB magnetic saturation levels, management of nonlinear effects, reduction ...


Structural Damage Detection Using Modal Norms, W. Gawronski, Jerzy T. Sawicki Nov 2012

Structural Damage Detection Using Modal Norms, W. Gawronski, Jerzy T. Sawicki

Jerzy T. Sawicki

No abstract provided.


Comments On Response Errors Of Non-Proportionally Lightly Damped Structures, W. Gawronski, Jerzy T. Sawicki Nov 2012

Comments On Response Errors Of Non-Proportionally Lightly Damped Structures, W. Gawronski, Jerzy T. Sawicki

Jerzy T. Sawicki

Letters to the editor authors reply


Diophantine Type Fractional Derivative Representation Of Structural Hysteresis, Part I: Formulation, Joe Padovan, Jerzy T. Sawicki Nov 2012

Diophantine Type Fractional Derivative Representation Of Structural Hysteresis, Part I: Formulation, Joe Padovan, Jerzy T. Sawicki

Jerzy T. Sawicki

Based on a diophantine representation of the operational powers, a fractional derivative modelling scheme is developed to simulate frequency dependent structural damping. The diophantine set of powers is established by employing the curvature properties of the defining empirical data set. These together with a remezed least square scheme are employed to construct a Chebyschev like optimal differintegro simulation. Based on the use of the rational form resulting from the diophantine representation, a composition rule is introduced to reduce the differintegro simulation to first order form. The associated eigenvalue/vector properties are then explored. To verify the robustness-stability accuracy of the ...


Vibration Based Crack Detection In A Rotating Disk: Part 1—An Analytical Study, Andrew L. Gyekenyesi, Jerzy T. Sawicki, George Y. Baaklini Nov 2012

Vibration Based Crack Detection In A Rotating Disk: Part 1—An Analytical Study, Andrew L. Gyekenyesi, Jerzy T. Sawicki, George Y. Baaklini

Jerzy T. Sawicki

This paper describes the analytical results concerning the detection of a crack in a rotating disk. The concept of the approach is based on the fact that the development of a disk crack results in a distorted strain field within the component. As a result, a minute deformation in the disk’s geometry as well as a change in the system’s center of mass occurs. Finite element analyses were conducted concerning a notched disk in order to define the sensitivity of the method. The notch was used to simulate an actual crack and will be the method utilized for ...


System Identification Methods For Dynamic Testing Of Fluid-Film Bearings, Jerzy T. Sawicki, M. L. Adams, R. J. Capaldi Nov 2012

System Identification Methods For Dynamic Testing Of Fluid-Film Bearings, Jerzy T. Sawicki, M. L. Adams, R. J. Capaldi

Jerzy T. Sawicki

There are various system identification approaches typically used to extract the rotordynamic coefficients from simultaneously measured dynamic force and motion signals. Since the coefficient values extracted can vary significantly as a function of the system identification approach used, more attention is needed to treat this issue than is typically included in the rotor dynamics literature. This paper describes system identification and data reduction methods used for extracting rotordynamic coefficients of fluid-film journal bearings. Data is used from a test apparatus incorporating a double-spoolshaft spindle which permits independent control over the journal spin speed and the frequency of an adjustable-magnitude circular ...


Transient Response Of Rotor On Rolling-Element Bearings With Clearance, David P. Fleming, Brian T. Murphy, Jerzy T. Sawicki, J. V. Poplawski Nov 2012

Transient Response Of Rotor On Rolling-Element Bearings With Clearance, David P. Fleming, Brian T. Murphy, Jerzy T. Sawicki, J. V. Poplawski

Jerzy T. Sawicki

Internal clearance in rolling element bearings is usually present to allow for radial and axial growth of the rotor-bearing system and to accommodate bearing fit-up. The presence of this clearance also introduces a “dead band” into the load-deflection behavior of the bearing. Previous studies demonstrated that the presence of dead band clearance might have a significant effect on synchronous rotor response. In this work, the authors investigate transient response of a rotor supported on rolling element bearings with internal clearance. In addition, the stiffness of the bearings varies nonlinearly with bearing deflection and with speed. Bearing properties were accurately calculated ...


Balanced Dissipative Controllers For Flexible Structures, W. Gawronski, Jerzy T. Sawicki Nov 2012

Balanced Dissipative Controllers For Flexible Structures, W. Gawronski, Jerzy T. Sawicki

Jerzy T. Sawicki

A balanced approach to shaping the closed-loop properties of the dissipative controllers for flexible structures is presented. In the balanced representation the properties of flexible structures are introduced, and a simple method of designing of the dissipative controllers is obtained. It relates the controller gains with the closed-loop pole locations. The examples illustrate the accuracy of the design method.


Diophantinized Fractional Representations For Nonlinear Elastomeric Media, Joe Padovan, Jerzy T. Sawicki Nov 2012

Diophantinized Fractional Representations For Nonlinear Elastomeric Media, Joe Padovan, Jerzy T. Sawicki

Jerzy T. Sawicki

This paper explores the use of diophantinized fractional fits for the nonlinear constitutive representation of elastomeric media. These are caste in terms of either the principal stretches or the strain invariants. Both polynomial and rational forms are considered. To construct the requisite complete and physically admissible basis space, the diophantinized set of fractional powers is bound by the curvature properties of the experimental data set. This set is then employed in conjunction with a remezed least square scheme to obtain an optimal fit. To verify the scheme a sample application case is presented.


Diophantine Type Fractional Derivative Representation Of Structural Hysteresis, Part Ii: Fitting, Computational Mechanics, Jerzy T. Sawicki, Joe Padovan Nov 2012

Diophantine Type Fractional Derivative Representation Of Structural Hysteresis, Part Ii: Fitting, Computational Mechanics, Jerzy T. Sawicki, Joe Padovan

Jerzy T. Sawicki

Part I of this series introduced the diophantinized fractional model and the decompositional formulation. The various important properties of fractional continuum formulation and its decomposed version were developed. In Part II the dynamic properties of the diophantine representation are investigated. The model fitting scheme will be developed to handle an arbitrary frequency dependent structural hysteriesis. This is followed up with the results of benchmark studies which demonstrate the effectiveness of fitting.


Review Of Rotordynamics, Jerzy T. Sawicki Nov 2012

Review Of Rotordynamics, Jerzy T. Sawicki

Jerzy T. Sawicki

Book Review of Rotordynamics, by Agnieszka (Agnes) Muszynska. CRC Press, Taylor & Francis Group, Boca Raton, FL, 2005, 1128 pp., ISBN: 0-8247-2399-6


Rigid Finite Element Model Of A Cracked Rotor, Zbigniew Kulesza, Jerzy T. Sawicki Nov 2012

Rigid Finite Element Model Of A Cracked Rotor, Zbigniew Kulesza, Jerzy T. Sawicki

Jerzy T. Sawicki

The article introduces a new mathematical model for the cracked rotating shaft. The model is based on the rigid finite element (RFE) method, which has previously been successfully applied for the dynamic analysis of many complicated, mechanical structures. In this article, the RFE method is extended and adopted for the modeling of rotating machines. An original concept of crack modeling utilizing the RFE method is developed. The crack is presented as a set of spring–damping elements of variable stiffness connecting two sections of the shaft. An alternative approach for approximating the breathing mechanism of the crack is introduced. The ...


Intermittent Behaviour Of A Cracked Rotor In The Resonance Region, Grzegorz Litak, Jerzy T. Sawicki Nov 2012

Intermittent Behaviour Of A Cracked Rotor In The Resonance Region, Grzegorz Litak, Jerzy T. Sawicki

Jerzy T. Sawicki

Vibrations of the Jeffcott rotor are modelled by a three degree of freedom system including coupling between lateral and torsional modes. The crack in a rotating shaft of the rotor is introduced via time dependent stiffness with off-diagonal couplings. Applying the external torque to the system allows to observe the effect of crack “breathing” and gain insight into the system. It is manifested in the complex dynamic behaviour of the rotor in the region of internal resonance, showing a quasi-periodic motion or even non-periodic behaviour. In the present paper report, we show the system response to the external torque excitation ...


Detecting Cracked Rotors Using Auxiliary Harmonic Excitation, Jerzy T. Sawicki, Michael I. Friswell, Zbigniew Kulesza, Adam C. Wroblewski, John D. Lekki Nov 2012

Detecting Cracked Rotors Using Auxiliary Harmonic Excitation, Jerzy T. Sawicki, Michael I. Friswell, Zbigniew Kulesza, Adam C. Wroblewski, John D. Lekki

Jerzy T. Sawicki

Cracked rotors are not only important from a practical and economic viewpoint, they also exhibit interesting dynamics. This paper investigates the modelling and analysis of machines with breathing cracks, which open and close due to the self-weight of the rotor, producing a parametric excitation. After reviewing the modelling of cracked rotors, the paper analyses the use of auxiliary excitation of the shaft, often implemented using active magnetic bearings to detect cracks. Applying a sinusoidal excitation generates response frequencies that are combinations of the rotor spin speed and excitation frequency. Previously this system was analysed using multiple scales analysis; this paper ...


A Nonlinear Model For Prediction Of Dynamic Coefficients In A Hydrodynamic Journal Bearing, Jerzy T. Sawicki, T.V.V.L. N. Rao Nov 2012

A Nonlinear Model For Prediction Of Dynamic Coefficients In A Hydrodynamic Journal Bearing, Jerzy T. Sawicki, T.V.V.L. N. Rao

Jerzy T. Sawicki

This paper investigates the variation of nonlinear stiffness and damping coefficients in a journal orbit with respect to equilibrium position. The journal orbit is obtained by the combined solution of equations of motion and Reynolds equation. In the linearized dynamic analysis, dynamic pressure is written as a perturbation of static pressure and pressure gradients at equilibrium position. However, in order to obtain nonlinear dynamic coefficients about equilibrium position, the dynamic pressure gradients in the orbit are also written as the first order perturbation of static pressure gradients and higher order pressure gradients for displacement and velocity perturbations. The dynamic coefficients ...


Damage Assessment Of Aerospace Structural Components By Impedance Based Health Monitoring, Andrew L. Gyekenyesi, Richard E. Martin, Jerzy T. Sawicki, George Y. Baaklini Nov 2012

Damage Assessment Of Aerospace Structural Components By Impedance Based Health Monitoring, Andrew L. Gyekenyesi, Richard E. Martin, Jerzy T. Sawicki, George Y. Baaklini

Jerzy T. Sawicki

This paper addresses recent efforts at the NASA Glenn Research Center at Lewis Field relating to the set-up and assessment of electro-mechanical (E/M) impedance based structural health monitoring. The overall aim is the application of the impedance based technique to aeronautic and space based structural components. As initial steps, a laboratory was created, software written, and experiments conducted on aluminum plates in undamaged and damaged states. A simulated crack, in the form of a narrow notch at various locations, was analyzed using piezoelectric-ceramic (PZT: lead, zirconate, titarate) patches as impedance measuring transducers. Descriptions of the impedance quantifying hardware and ...


Cracked Rotor Detection By Recurrence Plots, Grzegorz Litak, Jerzy T. Sawicki, Rafał Kaspereka Nov 2012

Cracked Rotor Detection By Recurrence Plots, Grzegorz Litak, Jerzy T. Sawicki, Rafał Kaspereka

Jerzy T. Sawicki

Recurrence plots (RPs) analysis has been used to distinguish cracked and healthy rotor responses. It has been shown that the recurrence criteria of the dynamical systems defined by the RPs can indicate the damages of the rotating shaft using relatively short time series.


Exploration Of Nde Properties Of Amb Supported Rotors For Structural Damage Detection, Jerzy T. Sawicki, Dmitry L. Storozhev, John D. Lekki Nov 2012

Exploration Of Nde Properties Of Amb Supported Rotors For Structural Damage Detection, Jerzy T. Sawicki, Dmitry L. Storozhev, John D. Lekki

Jerzy T. Sawicki

Recent advancements in actuator technology, power electronics, sensors, and signal processing have created a rapid development of smart machine technologies for rotating machinery. Ranging from machine condition monitoring and diagnostics to full active control of machine behavior, the integration of electrical and computer systems has produced significant advances in machine performance and reliability. Magnetic bearings are a typical mechatronics product. The hardware is composed of mechanical components combined with electronic elements such as sensors and power amplifiers and an information processing part, usually in the form of a microprocessor. In addition, an increasingly important part is software, which specifies the ...


Application Of Nonlinear Dynamics Tools For Diagnosis Of Cracked Rotor Vibration Signatures, Jerzy T. Sawicki, Xi Wu, Andrew L. Gyekenyesi, George Y. Baaklini Oct 2012

Application Of Nonlinear Dynamics Tools For Diagnosis Of Cracked Rotor Vibration Signatures, Jerzy T. Sawicki, Xi Wu, Andrew L. Gyekenyesi, George Y. Baaklini

Jerzy T. Sawicki

The nonlinear model of the cracked Jeffcott rotor is investigated, with the particular focus on study of rotor’s vibrational response using tools of nonlinear dynamics. The considered model accounts for nonlinear behavior of the crack and coupling between lateral and torsional modes of vibrations. Load torque is applied to the rotor which is laterally loadedwith a constant radial force (gravity force) and unbalance excitation. The co-existence of frequencies of lateral modes in the frequency spectra of torsional mode are characteristics of the coupling response of lateral and torsional vibrations. When only the lateral excitations are applied, vibration amplitude bifurcation ...


Modeling Disk Cracks In Rotors By Utilizing Speed Dependent Eccentricity, Andrew L. Gyekenyesi, Jerzy T. Sawicki, Wayne C. Haase Oct 2012

Modeling Disk Cracks In Rotors By Utilizing Speed Dependent Eccentricity, Andrew L. Gyekenyesi, Jerzy T. Sawicki, Wayne C. Haase

Jerzy T. Sawicki

This paper discusses the feasibility of vibration-based structural health monitoring for detecting disk cracks in rotor systems. The approach of interest assumes that a crack located on a rotating disk causes a minute change in the system’s center of mass due to the centrifugal force induced opening of the crack. The center of mass shift is expected to reveal itself in the vibration vector (i.e., whirl response; plotted as amplitude and phase versus speed) gathered during a spin-up and/or spin-down test. Here, analysis is accomplished by modeling a Jeffcott rotor that is characterized by analytical, numerical, and ...


Comparison Of Mobility Method And Mass Conservation Method In A Study Of Dynamically Loaded Journal Bearings, Biao Yu, Jerzy T. Sawicki Oct 2012

Comparison Of Mobility Method And Mass Conservation Method In A Study Of Dynamically Loaded Journal Bearings, Biao Yu, Jerzy T. Sawicki

Jerzy T. Sawicki

The inverse problem of dynamically loaded journal bearings was solved using generalized Reynolds equation coupled with a complete mass conservative cavitation boundary conditions, as outlined by the Jacobsson-Floberg and Olsson (JFO) cavitation theory. In the course of solution, the modified Thomas algorithms was employed, instead of standard Gauss±Jordan reduction method, which fully utilizes the sparse character of the system matrix, and thus greatly reduces computational time. The developed model was tested against the well-known mobility method for the case of journal bearings in a commercial reciprocating air compressor. It was found that the mobility method overestimates minimum film thickness ...


Thermomechanical Behavior Of Rotor With Rubbing, Jerzy T. Sawicki, Alberto Montilla-Bravo, Zdzislaw Gosiewski Oct 2012

Thermomechanical Behavior Of Rotor With Rubbing, Jerzy T. Sawicki, Alberto Montilla-Bravo, Zdzislaw Gosiewski

Jerzy T. Sawicki

This article presents an analytical study of the dynamics and stability of rotors subjected to rubbing due to contact with seals, taking account of associated thermal effects. The seal interaction force acting on the shaft gives rise to a friction force, which is a source of heating and can induce so-called spiral vibrations. A mathematical model that has been developed couples the heat-conduction equation with the equations for motion of the rotor. Numerical simulations have been conducted that show the thermomechanical behavior of the rotor at various operating conditions. A procedure for analyzing the stability of multibearing rotors based on ...


Rotor Model Updating And Validation For An Active Magnetic Bearing Based High-Speed Machining Spindle, Adam C. Wroblewski, Jerzy T. Sawicki, Alexander H. Pesch Oct 2012

Rotor Model Updating And Validation For An Active Magnetic Bearing Based High-Speed Machining Spindle, Adam C. Wroblewski, Jerzy T. Sawicki, Alexander H. Pesch

Jerzy T. Sawicki

This paper presents an experimentally driven model updating approach to address the dynamic inaccuracy of the nominal finite element (FE) rotor model of a machining spindle supported on active magnetic bearings. Modeling error is minimized through the application of a numerical optimization algorithm to adjust appropriately selected FE model parameters. Minimizing the error of both resonance and antiresonance frequencies simultaneously accounts for rotor natural frequencies as well as for their mode shapes. Antiresonance frequencies, which are shown to heavily influence the model’s dynamic properties, are commonly disregarded in structural modeling. Evaluation of the updated rotor model is performed through ...


Multiresolution Wavelet Analysis Of The Dynamics Of A Cracked Rotor, Jerzy T. Sawicki, Asok K. Sen, Grzegorz Litak Oct 2012

Multiresolution Wavelet Analysis Of The Dynamics Of A Cracked Rotor, Jerzy T. Sawicki, Asok K. Sen, Grzegorz Litak

Jerzy T. Sawicki

We examine the dynamics of a healthy rotor and a rotor with a transverse crack, which opens and closes due to its self weight. Using discrete wavelet transform, we perform a multiresolution analysis of the measured vibration signal from each of these rotors. In particular, the measured vibration signal is decomposed into eight frequency bands, and the rms amplitude values of the healthy and cracked rotors are compared in the three lowest-frequency bands. The results indicate that the rms vibration amplitudes for the cracked rotor are larger than those of the healthy rotor in each of these three frequency bands ...


Controlled Deflection Approach For Rotor Crack Detection, Zbigniew Kulesza, Jerzy T. Sawicki Oct 2012

Controlled Deflection Approach For Rotor Crack Detection, Zbigniew Kulesza, Jerzy T. Sawicki

Jerzy T. Sawicki

Atransverse shaft crack is a serious malfunction that can occurdue to cyclic loading, creep, stress corrosion, and other mechanismsto which rotating machines are subjected. Though studied for manyyears, the problems of early crack detection and warning arestill in the limelight of many researchers. This is dueto the fact that the crack has subtle influence onthe dynamic response of the machine and still there areno widely accepted, reliable methods of its early detection. Thispaper presents a new approach to these problems. The methodutilizes the coupling mechanism between the bending and torsional vibrationsof the cracked, nonrotating shaft. By applying an external lateralforce ...