Mechanical Engineering Commons^™

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 …

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.

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 …

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 …

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 …

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, …

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 …

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 …

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.

Limiting Stiffness And Damping Coefficients Of Foil Bearing, Jerzy Sawicki, T. Rao

Jerzy T. Sawicki

The limiting values of load capacity, stiffness and damping coefficients for a foil bearing are presented. The necessary conditions for high bearing numbers (journal operating at high speed) are obtained by simplifying the compressible Reynolds equation. Linearized stiffness and damping coefficients are obtained using infinitesimal perturbation method. Results of load capacity, stiffness and damping coefficients, for foil bearing are compared with those obtained for a rigid gas journal bearing. The limiting values of dynamic characteristics for a foil bearing are constant for all eccentricity ratios. ©2005 ASME

Lunar Surface Gas Turbine Power Systems With Fission Reactor Heat Sources, Jerzy Sawicki, Albert Juhasz

Jerzy T. Sawicki

No abstract provided.

Modal Uncoupling Of Damped Gyroscopic Systems, Jerzy Sawicki, G. Genta

Jerzy T. Sawicki

A new approach for uncoupling the equations of motion typical for rotordynamical systems is presented. The method does not neglect the speed-dependent e!ects, such as gyroscopic e!ects, and can be particularly valuable in the controller design of actively controlled rotors. In the presence of hysteretic type of damping, the resulting uncoupled gyroscopic systems come with an equivalent viscous damping, equivalent in a sense of yielding the same natural frequency and decay rate. The approach is illustrated through three examples of technical interest: a Je!cott rotor with hysteretic damping, a Stodola}Green rotor, and a rotor of a small gas turbine. The …

The Response Of Rotating Machines On Viscoelastic Supports, Michael Friswell, Jerzy Sawicki, D. Inman, A. Lees

Jerzy T. Sawicki

Damping in the stator of a rotating machine is able to reduce the unbalance response, and increase the speed where the stability limit is reached. A convenient method to introduce damping is to support the bearings on viscoelastic elastomeric supports. This successfully adds damping but makes the analysis considerably more difficult. Viscoelastic materials have properties that depend on frequency and temperature. The determination of the run-up or run-down response of a linear machine at a constant temperature is quite straightforward based on measured material characteristics. However the introduction of transient and non-linear effects, temperature changes and model uncertainties makes the …

Cavitation Effects On The Dynamics Of Journal Bearings, Jerzy Sawicki

Jerzy T. Sawicki

A numerical procedure incorporating cavitation effects on the dynamics of journal bearings is presented. A two-dimensional linear stability analysis considering the fluid flow in both full film and cavitation regions for a plain cylindrical journal bearing and four multi-lobe bearings are presented. The Lund’s infinitesimal perturbation procedure is applied to Elrod’s universal equation for evaluation of unsteady pressure gradients. Based on JFO theory, the pressure distribution, film rupture, and reformation boundaries can be obtained using Elrod’s universal equation, for a given operating position of the journal. In this work, it is assumed that for infinitesimal perturbation of journal about equilibrium …

Pattern Recognition Based Shaft Angle Encoder, Adam Pilat, Jerzy Sawicki

Jerzy T. Sawicki

The aim of this paper is to present the analysis of experimentally collected data acquired from the rotating shaft. The shaft surface was sensed by the non-contacting eddy-current probe using the home made robot. The robot consists of the controlled round table for object positioning and controlled arm for sensor. Two stepper motors are employed to control the movement of the probe in two perpendicular directions. The third motor drives the table with the rotor. The stepper motors are controlled by the micro-controller programmed from the PC. Using the probe and sensing the shaft surface pattern it is possible to …

Fluid Film Bearing For Heavy Loaded Applications – Comparisons And Optimizations, Florin Dimofte, Jerzy Sawicki, Margareta Lambrulescu, Robert Handschuh, Mary Jo Long-Davis

Jerzy T. Sawicki

Fluid film journal bearings for heavily loaded running conditions with specific loads to 24 MPa were analyzed and compared. Four sets of bearings were considered to be used in an aerospace planetary transmission. Both plain and wave bearing geometries were considered, compared, and optimized. Minimum fluid film thickness and oil temperature increase due to the friction force in the bearing are the basic criteria for comparison and optimization. Misalignment capability was also considered. Both laminar and turbulent flow, with and without viscosity correction, were considered in analyses. Power loss in friction and oil flow rate are also taken into account …

Rotor Crack Detection Using Active Magnetic Bearings, Jerzy Sawicki

Jerzy T. Sawicki

Well-established procedures exist to monitor and diagnose fairly severe problems with rotating machinery but little progress has been made in developing techniques to detect subtle changes in machine condition for both improved diagnostics, and to develop prognostic procedures for determining remaining service life. Of all machine faults, crack initiated problems present probably the most significant safety and loss hazard in modern turbomachinery, including aircraft engines and power generation units. Different approaches are used to model, detect, and localize crack-induced damage in rotating structures. This paper presents novel application of active magnetic bearings (AMBs) for on-line rotor crack detection. AMB-actuators provide …

Crack Identification By Multifractal Analysis Of A Dynamic Rotor Response, Grzegorz Litak, Jerzy Sawicki

Jerzy T. Sawicki

Multifractal analysis has been used to diagnose cracked and healthy rotors. Is has been shown that the complexity and regularity criteria of the dynamical systems defined by the multiple scaling of the time series can indicate the damages of the rotating shaft. Relation to the standard power spectrum technique has been also discussed.

Stability Characteristics Of Herringbone Grooved Journal Bearings Incorporating Cavitation Effects, T.V.V.L. Rao, Jerzy Sawicki

Jerzy T. Sawicki

Stabilitycharacteristics of the herringbone grooved journal bearings (HGJBs) are analyzedtaking into account cavitation of the fluid flow. The perturbedvalues of pressure and film thickness from a given equilibriumposition are substituted into the Elrod's universal equation, which considersmass conservation in the complete bearing geometry. In order toanalyze the herringbone groove configuration, the governing equations under steadyand perturbed states are transformed to a rectangular domain usingthe grid transformation techniques. It is assumed that under perturbedconditions, the cavitation extent in the bearing remains unchanged andthe pressure gradients are computed in the full film region.The linearized stiffness and damping coefficients are evaluated in thecomplete …

Auxiliary State Variables For Rotor Crack Detection, Zbigniew Kulesza, Jerzy Sawicki

Jerzy T. Sawicki

In the present study, a new model-based method for rotor crack detection and crack location is proposed. The finiteelement model of the rotor-bearing system accounts for the breathing mechanism of the crack. The model of the rotor system is augmented with an auxiliary single-degree-of-freedom oscillator. The observer is designed and the estimates of its two auxiliary state variables are proposed as crack indicators. The crack location along the shaft is determined by designing a set of observers, which calculate the values of these indicators for different possible crack locations along the shaft. The proposed method is validated numerically and the …