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Tools For Engine Diagnostics Under The Nasa Aviation Safety Program, George Baaklini, Andrew Gyekenyesi, K. Smith, Jerzy Sawicki, L. Brasche

Jerzy T. Sawicki

No abstract provided.

Response Errors Of Nonproportionally Lightly Damped Structures, W. Gawronski, Jerzy Sawicki

Jerzy T. Sawicki

No abstract provided.

Rotor Fault Diagnosis Utilizing Active Magnetic Bearings, Jerzy Sawicki, Andrew Gyekenyesi, George Baaklini

Jerzy T. Sawicki

6176-09, Session 2 This paper conducts an analytical modeling effort and an experimental system design in order to assess the feasibility of utilizing active magnetic bearings (AMB) for rotor fault diagnosis. Mathematical models are developed in order to gain an understanding of the interaction between the rotor system and the AMBs (both conical and radial). The rotor system is in the form of a Jeffcott rotor, therefore, the set-up involves a rigid disk located mid-span on a flexible shaft with rigid supports (i.e., traditional ball bearings providing support). Based on the modeling results, the AMBs are located along the shaft …

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 of …

Nonlinear Vibrations Of Fractionally Damped Systems, Joe Padovan, Jerzy Sawicki

Jerzy T. Sawicki

This paper deals with the harmonic oscillations of periodically excited nonlinear systems where hysteresis is simulated via fractional operator representations. Employing a diophantine version of the fractional operational powers, the energy constrained Lindstedt–Poincaré perturbation procedure is utilized to establish the harmonic solution. The constrained perturbation procedure was employed since it allows for the handling of strong damping and exciting forces over the full span of the driving frequency range. Based on the approach taken, the long time behavior of the fractionally damped Duffing's equation is studied in detail. Of special interest is the determination of the influence of fractional order …

Analysis Of Transient Response Of Cracked Flexible Rotor, Jerzy Sawicki, Andrew Gyekenyesi, George Baaklini

Jerzy T. Sawicki

No abstract provided.

Analytical Solutions Of Piston Ring Lubrication Using Mass Conserving Cavitation Algorithm, Jerzy Sawicki, Biao Yu

Jerzy T. Sawicki

A novel analytical approach for piston ring lubrication solution is presented by taking proper account of mass conservation in the cavitated region (JFO boundary conditions). A system of five nonlinear equations is employed to calculate such parameters as oil film thickness, frictional force, power loss, and oil flow rate. For an enclosed cavitation pattern in piston-ring assembly it was found, that JFO boundary conditions give much better accounting of the estimation of friction force, power loss and flow rate. To show the effectiveness of the undertaken approach, the widely accepted Jeng's approach (Jeng, 1992a) was selected, in which the pressure …

Structural Damage Assessment Of Propulsions System Components By Impedance Based Health Monitoring, Richard Martin, Andrew Gyekneyesi, Jerzy Sawicki, George Baaklini

Jerzy T. Sawicki

No abstract provided.

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

Jerzy T. Sawicki

No abstract provided.

Finite Element Analysis Of Coupled Lateral And Torsional Vibrations Of A Rotor With Multiple Cracks, Xi Wu, Jerzy Sawicki, Michael Friswell, George Baaklini

Jerzy T. Sawicki

The coupling between lateral and torsional vibrations has been investigated fora rotor dynamic system with breathing crack model. The stiffness matrix has been developed for the shaft element which accounts for the effect of the crack and all six degrees of freedom per node. Since the off-diagonal terms of the stiffness matrix represent the coupling of the respective modes, the special attention has been paid on accurate determination of their values. Based on the concepts of fracture mechanics, the variation of the stiffness matrix over the full shaft revolution is represented by the truncated cosine series where the fitting coefficient …

Static And Dynamic Analysis Of Bearings For Truck Brake Compressor, Biao Yu, Jerzy Sawicki, V. Dunaevsky

Jerzy T. Sawicki

Mobility method is used to analyze the steady-state performance of crankshaft and connecting rod bearings which are subjected to loads whose magnitude and direction both vary in time. The steady-state characteristics include journal center orbit, minimum film thickness, maximum film pressure, effective temperature, flow through the bearing, etc. To extract the stiffness and damping coefficients over the load cycle, linear analysis method based on a short-bearing approximation is employed. In addition, the oil flow through the main and connecting rod bearings is investigated. Sufficient lubrication conditions for these bearings are discussed. This combined analysis is supported by numerical simulations.

The Dynamics Of Rotor With Rubbing, Jerzy Sawicki, Joe Padovan, Rabih Al-Khatib

Jerzy T. Sawicki

This paper presents the description of some phenomena associated with dynamic behavior of rotors interacting with stationary components. Numerical simulations show rotor vibration spectrum rich in subharmonic, quasi-periodic, and chaotic vibrations. The nonlinear calculation techniques are applied to demonstrate the changes of the vibration patterns for different operating conditions. Some conclusions are discussed with regard to unique characteristics of rub-induced rotor response, initial conditions, as well as appropriate ranges of system parameters. Of special interest are the changes in the apparent nonlinearity of the system dynamics as rubs are induced at different rotor speeds. In particular, starting with 2nd order …

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

Jerzy T. Sawicki

Letters to the editor authors reply

Analysis Of Elastic Distortions Of A Piston Ring In The Reciprocating Air Brake Compressor Due To The Installation Stresses, V. Dunaevsky, Jerzy Sawicki, J. Frater, H. Chen

Jerzy T. Sawicki

The objective of this paper is to present the results of an investigation of elastic distortions of split piston rings that are used in lubricated and non-lubricated air brake compressors. Concepts of advanced stress analysis and Finite Element Analysis (FEA) have been employed in this study.

The analysis of elastic distortions (twist) of piston rings due to the installation stresses has been quite poorly documented in the technical literature. As a result, unjustifiable engineering assumptions are some time made which result in misleading design solutions.

This paper demonstrates analytically and with the support of FEA the mechanical/geometrical parameters of a …

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 overall …

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 upcoming experiments. …

Frequency Driven Phasic Shifting And Elastic-Hysteretic Partitioning Properties Of Fractional Mechanical System Representation Schemes, Jerzy Sawicki, Joe Padovan

Jerzy T. Sawicki

Based on the Louiville–Riemann fractional formulation of lumped hysteretic mechanical system simulations, asymptotic-type relationships are derived. These are employed to determine how such operators, which act as viscoelastic elements, partition system energy into conservative and nonconservative components. Special emphasis is given to: (a) determine how operator order serves to weigh such a splitting, (b) determine how partitioning affects system phasing and amplitude response, and (c) to establish how conservative and nonconservative effects modulate during a given system cycle. The generality of the undertaken approach is such that multi-element fractional Kelvin Voigt formulations subject to spectrally rich inputs can be handled, …

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

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 …

Recent Advances In Vibration Based Damage Detection Techniques For Cracked Rotors, Jerzy Sawicki, George Baaklini

Jerzy T. Sawicki

In recent years, there has been a growing interest in the development of structural health monitoring for rotating structures, and especially shaft crack detection methodologies and on-line diagnostic techniques. Crack initiated problems present a significant safety and loss hazard in nearly every application of modern turbomachinery, including aircraft engines and power generation units. Different approaches are used to model, sense, and localize crack-induced damage in rotating structures. This presentation will provide an overview of the recent progress in the vibration based health monitoring and rotor crack detection techniques developed by author in recent years. A brief review of the unique …

Experimental And Theoretical Rotordynamic Characteristics Of A Hybrid Journal Bearing, Jerzy Sawicki, R. Capaldi, M. Adams

Jerzy T. Sawicki

This paper describes an experimental and theoretical investigation of a four-pocket,oil-fed, orifice-compensated hydrostatic bearing including the hybrid effects of journalrotation. The test apparatus incorporates a double-spool-shaft spindle which permitsindependent control over the journal spin speed and the frequencyof an adjustable-magnitude circular orbit, for both forward and backwardwhirling. This configuration yields data that enables determination of thefull linear anisotropic rotordynamic model. The dynamic force measurements weremade simultaneously with two independent systems, one with piezoelectric loadcells and the other with strain gage load cells. Theoreticalpredictions are made for the same configuration and operating conditionsas the test matrix using a finite-difference solver of …

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

Jerzy T. Sawicki

No abstract provided.

Nonlinear Prediction Of Rotordynamic Coefficients For A Hydrodynamic Journal Bearing, Jerzy Sawicki, T.V.V.L. Rao

Jerzy T. Sawicki

In the analysis of hydrodynamic journal bearings, linearized stiffness and damping coefficients are widely used for the evaluation of stability and dynamic response characteristics. Under given operating conditions, these coefficients vary along the locus of the orbital response, and are not valid at large amplitudes (40% of the bearing clearance) of the journal motion. The time history of journal bearing motion for large vibrations is accurately predicted herein using nonlinear (time-transient) analysis. This paper discusses the adequacy of bearing analysis based on linearized coefficients and presents the significance of variation of the coefficients under the dynamic conditions. A method to …

Analytical Solution Of Piston Ring Pack Lubrication For Truck Air Brake Compressor, Biao Yu, Jerzy Sawicki, V. Dunaevsky

Jerzy T. Sawicki

This paper presents an analytical solution of piston ring pack lubrication for two-cylinder truck air brake compressor. A system of nonlinear equations with seven variables was developed to describe lubrication phenomena of the piston ring pack for both fully flooded and starvation conditions. The full mass conservation boundary conditions defined by JFO ([ 14 ],[ 15 ]) theory were employed for complete description of the cavitation algorithm with enclosed and open cavitation patterns. Impact of the piston ring design parameters such as offset, crown height, and tension on the oil transport, lubrication conditions and friction losses of the compressor were …

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

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.

High Temperature Fusion Reactor Cooling Using Brayton Cycle Based Partial Energy Conversion, Albert Juhasz, Jerzy Sawicki

Jerzy T. Sawicki

For some future space power systems using high temperature nuclear heat sources most of the output energy will be used in other than electrical form, and only a fraction of the total thermal energy generated will need to be converted to electrical work. The paper describes the conceptual design of such a “partial energy conversion” system, consisting of a high temperature fusion reactor operating in series with a high temperature radiator and in parallel with dual closed cycle gas turbine (CCGT) power systems, also referred to as closed Brayton cycle (CBC) systems, which are supplied with a fraction of the …

Balanced Model Reduction And Control Of Rotor-Bearing Systems, Jerzy Sawicki, W. Gawronski

Jerzy T. Sawicki

Aneffective technique is applied to the suppression of vibrations inflexible rotor-bearing systems with small gyroscopic effects. A balanced linear-quadratic-Gaussian(LQG) controller design procedure is implemented. The size of thecontroller is reduced in two stages by using (i) abalanced model reduction, and (ii) an LQG balanced reduction. Thecondition for a gyroscopic matrix is developed that allows oneto ignore the rotor gyroscopic effects in the process ofthe controller design, although they are included in the rotordynamics. The approach is illustrated on a typical rotor-bearing system represented by a 48 degree-of-freedom finite element model.

Fatigue Life Prediction For Large-Diameter Elastically-Constrained Ball Bearings, Jerzy Sawicki, Samuel Johansson, John Rumbarger, Ronald Sharpless

Jerzy T. Sawicki

Theapplication of large-diameter bearing rings and the thereof inherited lowstiffness make them susceptible to local distortions caused by theirsurrounding structures, which are often under heavy loads. The standardaccepted design criteria for these bearings are based on theestimation of the internal load distribution of the bearing, underthe assumption of rigid circular and flat supporting structures, thatkeep the bearing inner and outer races in circular, flat,i.e., not deformed shapes. However, in the presence of structuraldistortions, the element load distribution can be severely altered andcannot be predicted viathe standard design criteria. Therefore, theapplication of large-diameter ball and roller bearing rings as thecritical components …

Thermodynamic Properties Of Fractional Differ-Integro Type Constitutive Relations, Joe Padovan, Jerzy Sawicki, Arkadi Leonov

Jerzy T. Sawicki

Using the asymptotic properties of Riemann-Liouville form, the intrinsic rate-based first and second laws of thermodynamics properties of fractional differintegro operator type constitutive representations are investigated by illustrating how the conservative and nonconservalive features of the response behavior interact under spectrally rich inputs. Due to the generality of the development, fractional operator representations of any order are considered. This includes the determination of the underlying features giving rise to frequency dependencies in the phasing and amplitude behavior and in this context the irreversible energy release rate process associated with fractional viscoelastic simulations.