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Articles 61 - 70 of 70
Full-Text Articles in Mechanical Engineering
Application Of Nonlinear Dynamics Tools For Diagnosis Of Cracked Rotor Vibration Signatures, Jerzy T. Sawicki, Xi Wu, Andrew L. Gyekenyesi, George Y. Baaklini
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 plot …
Vibration-Based Crack Diagnosis In Rotating Shafts During Acceleration Through Resonance, Jerzy Sawicki, Xi Wu, George Baaklini, Andrew Gyekenyesi
Vibration-Based Crack Diagnosis In Rotating Shafts During Acceleration Through Resonance, Jerzy Sawicki, Xi Wu, George Baaklini, Andrew Gyekenyesi
Jerzy T. Sawicki
The dynamic response of a cracked Jeffcott rotor passing through the critical speed with constant acceleration is investigated analytically and numerically. The nonlinear equations of motion are derived and include a simple hinge model for small cracks and Mayes' modified funciton for deep cracks. The equations of motion are integrated in the rotating coordinate system. The angle between the crack centerline and the shaft vibaiton (whirl) vector is used to determine the clsoing and opening of the crack, allowing one to study the dynamic response with and without the rotor weight dominance. Vibration phase response is used as one of …
Modeling Disk Cracks In Rotors By Utilizing Speed Dependent Eccentricity, Andrew L. Gyekenyesi, Jerzy T. Sawicki, Wayne C. Haase
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 experimental data. The …
Cavitation Effects On The Stability Of A Submerged Journal Bearing, Jerzy Sawicki, T. Rao
Cavitation Effects On The Stability Of A Submerged Journal Bearing, Jerzy Sawicki, T. Rao
Jerzy T. Sawicki
A computational procedure for the mechanism of shear between the liquid sublayer and air cavity in the cavitation zone of a submerged journal bearing is presented here. Using the mass conservation principle, Elrod's universal equation is modified to take into consideration the shear of the air cavity in the cavitation region. Results of steady state and transient response for the submerged journal bearing using the present approach are compared with the universal equation based on the striated flow in the cavitation region. At steady state, the angular extent of cavitation region predicted by the present approach is higher than that …
Comparison Of Mobility Method And Mass Conservation Method In A Study Of Dynamically Loaded Journal Bearings, Biao Yu, Jerzy T. Sawicki
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 and …
Thermomechanical Behavior Of Rotor With Rubbing, Jerzy T. Sawicki, Alberto Montilla-Bravo, Zdzislaw Gosiewski
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
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 comparison …
Multiresolution Wavelet Analysis Of The Dynamics Of A Cracked Rotor, Jerzy T. Sawicki, Asok K. Sen, Grzegorz Litak
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
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 …
Rotor Model Validation For An Active Magnetic Bearing Machining Spindle Using Mu-Synthesis Approach, Ryan Madden, Jerzy Sawicki
Rotor Model Validation For An Active Magnetic Bearing Machining Spindle Using Mu-Synthesis Approach, Ryan Madden, Jerzy Sawicki
Jerzy T. Sawicki
Model-based identification and l-synthesis are employed for model updating of the rotor for a high-speed machining spindle supported on active magnetic bearings. The experimentally validated model is compared with a nominal engineering model to identify the unmodeled dynamics. The extracted missing dynamics from the nominal rotor model provides engineering insight into an effective model correction strategy. The corrected rotor model is validated by successful implementation of a number of l-synthesized controllers, providing robust and stable levitation of the spindle over its entire operating speed range.