Xdot and Dr. Swanson's Publications

Evolution and Trend of API 617 Compressor Rotordynamic Criteria.

Pettinato, B.C., Kocur, J.A., Swanson, E.E., 2011
Turbomachinery, Transactions of the Turbomachinery Society of Japan

This paper traces the history of the American Petroleum Institute acceptance standards for compressor machinery dynamics. This examination starts with the 1st edition of the API 617 standard published in 1958 and concluding with the 7th edition of API 617 along with potential modifications proposed for the 8th edition.

Rotordynamic Design Audits of AMB Supported Machinery.

Swanson, E.E., Maslen, E.H., Li, G., Cloud, C.H., 2008
Proceedings of the Thirty-Seventh Turbomachinery Symposium, Turbomachinery Laboratory, Texas A&M University, College Station, Texas

Active Magnetic Bearings (AMBs) are a mature bearing technology that is being applied to many new turbomachines. They have become the bearing of choice for most new turbo-expander applications. They are seen as a key enabling technology for compact, high speed, high power density direct drive generators and turbomachinery. As more and more units are fielded, it will become important that end-users and analysts have the tools and background to evaluate the rotor dynamics of AMB supported machinery.\n\nThis tutorial provides a basic review of AMB subsystems and key issues that need to be considered for a rotordynamic audit. Applicable API and ISO standards are reviewed from the perspective of evaluating the rotordynamic performance of AMB machinery. The tutorial concludes with an example audit of an existing AMB supported machine.

Bump Foil Damping Using a Simplified Model.

Swanson, E.E., 2006
ASME Journal of Tribology

Foil bearings are a key enabling technology for advanced and oil-free rotating machinery. In certain applications, they provide a level of performance that is difficult or impossible to match with other technologies. A number of reasonably successful analytical techniques to predict bearing load capacity, power loss, and stiffness have been developed. Prediction of damping, however, has remained problematic. This work presents a fresh look at the damping problem. Using a simplified representation of a bump foil, this work considers explicitly adding the load dependence of the friction force. This approach is shown to provide a good match to previous experimental data. Parametric study results for the various model parameters are presented to examine the characteristics of this model. It is concluded that the load-dependent frictional force is important to consider for a bump foil damping model.

Rotordynamic Considerations For Foil-Bearing-Supported Rotors Operating Above A Bending Critical Speed.

Chen, H.M., Swanson, E.E., Walter, T.J., 2006
International Joint Tribology Conference, Paper IJTC2006-12118.

In meeting goals for higher energy density and efficiency for micro-turbomachinery, there is a trend towards higher operating speeds. Gas-lubricated foil bearings historically have provided a key enabling technology for this class of machinery due to their low power loss, high-speed capability in very low to very high temperatures, and process compatibility. Foil bearings have demonstrated very good performance in many rigid rotor applications. To meet future needs, however, micro-turbomachinery will be required to operate above a bending critical speed where shaft flexibility plays a dominant role. Some successes with foil bearing rotors operating in this region have been achieved, indicating that foil bearings can be built with the required dynamic characteristics. However, these efforts have been primarily experimentally driven, and published results indicate attention to such issues as bearing internal friction, rotor balance, rate of rotor speed change, and bearing location are crucial to success. This work presents an analytical examination of these issues. Using a modal solution for the bending critical mode of a simple, symmetric rotor, various relationships between foil bearing parameters and machine design elements are explored.

A Practical Review of Rotating Machinery Critical Speeds and Modes.

Swanson, E.E., Powell, C.D., Weissman, S., 2005
Sound and Vibration, May, pp. 10-17.

The goal of this article is to present a practical understanding of terminology and behavior based in visualizing how a shaft vibrates, and examining issues that affect vibration. It is hoped that this presentation will help the nonspecialist better understand what is going on in the machinery, and that the specialist may gain a different view and/or some new examples.

Fixed-Geometry, Hydrodynamic Bearing with Enhanced Stability Characteristics.

Swanson, E.E., 2005
Tribology Transactions, 48, pp. 82-92.

This article presents the results of a successful bearing optimization study aimed at identifying a fixed-geometry, hydrodynamic journal bearing that does not suffer from the low load instability typical of this class of bearings. This goal was met through optimization of a fairly simple objective function based on the rigid rotor whirl-speed ratio, using a constrained, nonlinear algorithm based on sequential quadratic programming. In the interests of reducing computational time, a two-dimensional isoviscous formulation of the Reynolds equation was used for this work. The equation was solved using a finite element approach.This article includes a discussion of the optimization approach, the finite element solution approach, the resulting bearing design, and its performance characteristics. It concludes with an application example comparing the optimized bearing's predicted performance to a tilting-pad bearing's predicted performance for a centrifugal compressor-like rotor. The mismatch between shaft and bearing stiffness due to the rigid rotor optimization makes the optimized bearing less desirable from an unbalance response point of view. However, the optimized bearing is shown to have very good stability characteristics, which compare favorably to a tilting-pad bearing.

Testing of a Centrifugal Blood Pump with a High Efficiency Hybrid Magnetic Bearing.

Locke, D., Swanson, E., Walton, J., Willis, J.P., Heshmat, H., 2003
ASAIO Journal, 49, pp. 737-743.

The purpose of this article is to present test results for a second generation, high efficiency, nonpulsatile centrifugal blood pump that is being developed for use as a left ventricular assist device (LVAD). The LVAD pump uses a hybrid passive-active magnetic bearing support system that exhibits extremely low power loss, low vibration, and high reliability under transient conditions and varying pump orientations. A unique feature of the second generation design configuration is the very simple and direct flow path for both main and washing blood flows. The pump was tested in both vertical and horizontal orientations using a standard flow loop to demonstrate the performance and durability of the second generation LVAD. Steady state and transient orientation pump operating characteristics including pressure, flow, speed, temperatures, vibration, and rotor orientation were measured. During the tests, pump performance was mapped at several operating conditions including points above and below the nominal design of 5 L/min at 100 mm Hg pressure rise. Flow rates from 2 to 7 L/min and pressure rises from 50 to 150 mm Hg were measured. Pump speeds were varied during these tests from 2,500 to 3,500 rpm. The nominal design flow of 5 L/min at 100 mm Hg pressure rise was successfully achieved at the design speed of 3,000 rpm. After LVAD performance testing, both 28 day continuous duty and 5 day transient orientation durability tests were completed without incident. A hydrodynamic backup bearing design feasibility study was also conducted. Results from this design study indicate that an integral hydrodynamic backup bearing may be readily incorporated into the second generation LVAD and other magnetically levitated pump rotors.

A Test Stand for Dynamic Characterization of Oil-Free Bearings for Modern Gas Turbine Engines.

Swanson, E.E., Walton, J.F., II, Heshmat, H., 2002
ASME Paper GT-2002-30005.

A multi-purpose rotor-bearing dynamic simulator was designed and fabricated for the purpose of experimentally evaluating and validating performance of advanced oil-free and back-up bearings under realistic dynamic conditions.  The rotor-bearing dynamic test rig is capable of operation to 25,000 RPM, has a 54 kg test rotor, is designed to simulate a medium size aero gas turbine engine rotor, and incorporates an electromagnetic loader/shaker capable of applying both static and dynamic loads to the rotating shaft.   Testing was completed with the rotor fully supported by magnetic bearings, compliant foil bearings, hybrid foil/magnetic and Zero Clearance Auxiliary Bearings.  These tests demonstrated numerous advances in oil-free bearing technology.  The first ever achievements include: operation of a rotor with a mass in excess of 50 kg supported solely by foil bearings, operation of  hybrid foil/magnetic bearings to high speed, continued operation following simulated magnetic bearing failures for a fully hybrid foil/magnetic bearing support system, and operation of a rotor supported solely by Zero Clearance Auxiliary Bearings.  Data from several tests of the bearing systems are presented.

Demonstration of Powder Shear Damping Applied to Plates.

Pulitzer, S.W., Swanson, E.E., and Heshmat, H., 2002
Boundary and Mixed Lubrication: Science and Applications D. Dowson, et. al. (eds), Elsevier Science B.V. pp. 547-553.

Thin powder films have been proposed as a damping medium to overcome the thermal and frequency limitations of viscoelastic materials. In previous work, a fundamental characterization of the stiffness and damping of constrained powder layers was conducted. To assess concept feasibility, constrained powder layers were integrated into a metal beam, and theoretical and experimental analyses showed that such layers are a viable damping mechanism. In this paper, the application of powder shear dampers to a plate will be presented. A novel method for fabricating a high temperature plate with constrained layer powder damping will be discussed, and the results of dynamic testing will be reviewed. A generic plate was designed and modeled using finite elements. Mode shapes and frequencies were identified analytically and correlated with experimental results. The theoretically optimum locations for damping on the plate were identified and treated with shear powder dampers.

Generalized Entities: A Modern Framework for Rotor Dynamics Software.

Swanson, E.E., and Pulitzer, S.W. III, 2002
Presented at the 2002 IFToMM Sixth International Conference on Rotor Dynamics.

Traditionally, the organization of the data for rotor dynamics software has been centered about the needs of the analysis routines. This paper offers a new approach based on a self-organizing description of the rotor(s) and stator(s). The strategy is straightforward to implement and understand, and provides a more intuitive way to model a rotor system. The concept of a Generalized Entity forms the core of the approach. Within the proposed framework, the various components that comprise rotor systems, such as point masses and bearings, are represented as similar objects with different parameters. All of the information describing how an entity interacts with the user and the model is encapsulated within in. As a result, the code is inherently modular, and newly defined entities can be added with very little programming effort. Additionally, complicated entities such as those with mixed degrees-of-freedom (e.g. mechanical and electrical) or nonlinearities can be included with few changes to the master code. This paper demonstrates the approach by discussing three examples in detail: a point mass, a conical element, and a linear bearing. It is shown how this approach can be used as the basis for a modern, self-organizing, modular rotor dynamic code.

Oil-Free Foil Bearings as a Reliable, High Performance Backup Bearing for Active Magnetic Bearings.

Swanson, E.E., Heshmat, H., 2002
ASME Paper GT-2002-30291.

Gas turbine engines and other high speed rotating machinery supported by magnetic bearings require some form of backup bearing to ensure reliable and safe operation. To date, this backup capability has been provided by either rolling element bearings or solid lubricated bushings. Both of these solutions have drawbacks - must notably limited life and uncertain dynamic performance. In many cases, the backup bearing system requires substantial maintenance following an activation event. An alternative approach investigated in this work is the use of a compliant foil bearing as a backup bearing. This work discusses tests of this concept on a test rig with a 63 kg rotor. In this application, the foil bearing demonstrated smooth, stable operation during a variety of simulated magnetic bearing failure events, and allowed for continued operation of the rotor following the simulated failures.

Performance of a Foil-Magnetic Hybrid Bearing.

Swanson, E.E., Heshmat, H., Walton, J.F. II, 2002
ASME Journal of Engineering for Gas Turbine and Power, 124, 2002, pp. 375-382.

To meet the advanced bearing needs of modern turbomachinery, a hybrid foil-magnetic hybrid bearing system was designed, fabricated and tested in a test rig designed to simulate the rotor dynamics of a small gas turbine engine (31 kN to 53 kN thrust class).  This oil-free bearing system combines the excellent low and zero-speed capabilities of the magnetic bearing with the high load capacity and high speed performance of the compliant foil bearing.  An experimental program is described which documents the capabilities of the bearing system for sharing load during operation at up to 30,000 RPM and the foil bearing component’s ability to function as a back-up in case of magnetic bearing failure.  At an operating speed of 22,000 RPM, loads exceeding 5300 N were carried by the system.  This load sharing could be manipulated by an especially designed electronic control algorithm.  In all tests, rotor excursions were small and stable.  During deliberately staged magnetic bearing malfunctions, the foil bearing proved capable of supporting the rotor during continued operation at full load and speed, as well as allowing a safe rotor coast-down.  The hybrid system tripled the load capacity of the magnetic bearing alone and can offer a significant reduction in total bearing weight compared to a comparable magnetic bearing.

The Role of High Performance Foil Bearings in an Advanced, Oil-Free, Integral Permanent Magnet Motor Driven, High-Speed Turbo-Compressor Operating Above The First Bending Critical Speed.

Swanson, E.E., Heshmat, H., Shin, J.S., 2002
ASME paper GT-2002-30579.

The demand for high power density, reliable, low maintenance, oil-free turbomachinery imposes significant demands on the bearing system.  The full benefits of high speed, permanent magnet driven machines, for example are realized at speeds exceeding the capabilities of rolling element bearings.  The high speeds, and a desire for oil-free operation also make conventional liquid lubricated bearings an undesirable alternative.  The modern, oil-free foil bearing provides an excellent alternative,  providing low power loss, adequate damping for supercritical operation, tolerance of elevated temperatures and long life.  In this paper, the application of modern foil bearings to a high speed, oil-free turbo-compressor is discussed.  In this demanding application, foil bearings support a 24 pound, multi-component rotor operating at 70,000 RPM with a bending critical speed of approximately 43,000 RPM.  Stable and reliable operation over the full speed range has been demonstrated.  This application also required low bearing start-up torque for compatibility with the constant torque characteristic of the integral permanent magnet motor.  This work discusses the rotor bearing system design, the development program approach, and the results of testing to date.  Data for both a turbine driven configuration, as well as a high speed integral motor driven configuration are presented.

Thermal Features of Compliant Foil Bearings - Theory and Experiments.

Salehi, M., Swanson, E., and Heshmat, H., 2001
ASME Journal of Tribology, 123, pp. 566-571.

The paper presents an analytical and experimental investigation aimed at eliciting the thermal characteristics of air lubricated compliant foil bearings. A Couette approximation to the energy equation is used in conjunction with the compressible Reynolds equation to obtain a theoretical temperature distribution in the air used as a lubricant. The effect of temperature on the thermal properties of the working fluid is included. In parallel, an experimental program was run on a 100 mm diameter foil bearing operating at speeds up. to 30000 rpm employing cooling air across the bearing. The temperature rise of the cooling air provided an indication of the amount of heat energy conducted across the top foil of the bearing from the hydrodvnamic film. The temperatures resulted from some tests are compared with the temperatures predicted by the analysis, and maximum over-prediction of about 19 percent was obtained. This simplified approach provides us with reasonably predicted temperatures. By comparing the theoretical heat dissipation obtained from the analytical predicted temperatures with the amount of heat carried away by the cooling air it was possible to arrive at the relative quantities of heat transferred from the bearing by convection via side leakage and by conduction via the top foil. From these comparisons it was deduced that about an average of 80 percent of the heat energy is carried away by conduction. The transient temperatures of the foil bearing in conducted tests for various speeds and loads are also presented.

A Gas Turbine Engine Backup Bearing Operating Beyond 2.5 Million DN.

Swanson, E.E., Walton, J.F. II, Heshmat, H., 2000
ASME Paper 2000-GT-622.

Gas turbine engines and high speed rotating machinery using magnetic bearings require auxiliary and backup bearings for reliability and safety of operation. A 140 mm diameter Zero Clearance Auxiliary Bearing (ZCAB) capable of supporting radial and/or thrust loads of up to 4500 N was designed for an advanced gas turbine engine. The ZCAB was fabricated and tested successfully up to the expected maximum operating speed of 18,000 rpm in a specially configured test rig. The test rig included a 36,000 rpm capable drive motor, a 64 kg rotor which simulates a gas turbine engine shaft dynamics, a damped ball bearing at the drive end and an active magnetic bearing next to the ZCAB. Operation in excess of 240 minutes and 20 transient engagements simulating magnetic bearing failures were completed in the initial tests. Post test inspection revealed minimal wear to the shaft and the ZCAB rollers, whereupon the ZCAB was reassembled for shipment. These preliminary tests confirm the operation and durability of the ZCAB in maintaining rotor support and continued operation even if the primary magnetic bearing support is overloaded or encounters a failure.

Capabilities of Large Foil Bearings.

Swanson, E.E., Heshmat, H., 2000
ASME Paper 2000-GT-387.

An experimental program was conducted on a large compliant surface foil bearing to document its performance.  This large single pad foil bearing is 100 mm in diameter, and was operated at speeds of up to 30,000 RPM.   Operation at 22,000 RPM with a measured load of 4190 N was also demonstrated.  During coastdown runs from 30,000 RPM, maximum amplitudes of shaft vibration did not exceed 7.6 μm while passing through the two rigid shaft modes of the system.  Thermal performance of the bearing was also in accord with previously documented foil bearings.  This testing also demonstrates the practicality of scaling smaller foil bearing designs to the large bearings required for larger turbomachinery. To enhance the practical application of the results, the test rig shaft was designed to simulate a small gas turbine engine rotor.

On The Application of Powder Shear Damping to a Structural Element.

Swanson, E.E., Xu, D.S., Russell, T.E., Walton, J.F. II, Heshmat, H., 2000
ASME Paper 2000-GT-0365.

With the increasing demands placed on modern gas turbine components, improvements in high temperature compatible damping technology are required. The areas of application include turbine airfoils, struts, guide vanes, exhaust ducts, and similar components. The need for improved damping elements is especially acute for integrally bladed disks (""blisks"").  Constrained powder shear dampers, using thin pockets of high temperature compatible powders meets these needs. With damping performance comparable to current visco-elastic elements, shear powder damping elements add the capability of high temperature operation, compatibility with blade heat treatments, good high frequency damping characteristics, and minimal degradation predicted for high centrifugal loads. Building on previous fundamental work, this paper discusses a proof of concept application of powder shear damping to a thin beam.  Both cantilever and free-free configurations are examined.  Comparisons between experimental measurements of undamped, constrained layer visco-elastic damping, and powder shear damped beams are presented. FEA results for the cantilever configuration are also shown to correlate well with the experimental data.

A 35,000 RPM Test Rig for Magnetic, Hybrid and Back-Up Bearings.

Swanson, E.E., Walton, J.F. II, Heshmat, H., 1999
ASME Paper 99-GT-180

Magnetic bearings have long offered the potential for significant turbomachinery system improvements due to their oil-free, non-contact, low loss nature and their ability to actively control shaft dynamic motion. However, end-users and many designers are hesitant to apply this technology. There are two basic stumbling blocks: active magnetic bearings (AMBs) have little overload capacity, and failure of any portion of the AMB system could result in catastrophic damage to the machine. To cope with both of these problems, a secondary back-up bearing must be included in the system. This paper describes a new full scale, high speed test rig which has the capability to test a variety of back-up bearings at speeds of up to 35,000 RPM, and bearing loads of up to 6.7 kN. Preliminary data for two novel back-up bearings are presented as a demonstration of the test rig's capabilities.

Bearing Test Rig Dynamics Problem Identification and Model Tuning.

Swanson, E.E., Kirk, R.G., 1999
Proc. IMAC XVII, SEM, pp. 270-276.

The experimental determination of the dynamic stiffness and damping for fluid-film bearings and seals is an increasingly important research subject in the area of rotating machinery design. During development testing of a new test rig for dynamic characterization of oil lubricated, hydrodynamic bearings, unexpected phase shifts in measured shaft response data were observed. This paper describes the problem that was observed and the ensuing experimental modal investigation of the shaft dynamics. Both traditional impact and scanning doppler laser velocimeter techniques were used to develop a tuned rotor dynamic model which was subsequently used to help understand and explain the unexpected phase shift observations. The results from this analytical study highlight several design issues which should be considered in future test rig designs to avoid similar difficulties.

The Integration of Structural and Fluid-Film Dynamic Elements in Foil Bearings Part II: A New Approach to the Problem.

Swanson, E.E., Heshmat, H., 1999
Proc. 1999 ASME Design Engineering Technical Conference, Paper DETC/VIB-8270

In Part I of this investigation a survey was made to see how the two-tiered construction of foil bearings, consisting as they do of two generically disparate elements, one hydrodynamic in nature and the other following the laws of elasticity, have been modeled in order to obtain integrated values of bearing stiffness and damping.  Here a series of experiments is reported showing that  serious discrepancies exist between results obtained from conventional dynamic models and test results.  A new approach to the problem is here taken in modeling the two-tiered dynamic system of foil bearings.  For this purpose a series of analytical solutions were obtained for different spring and dashpot arrangements.  A basic approach was taken in considering the foil bearing as consisting of a two-degrees-of-freedom system.  Differences in amplitude of vibration and phase angles were plotted for the different models.  Similar data were obtained separately for the hydrodynamic and structural regimes.  The solutions showed substantial differences in the amplitudes and phase angles between the two domains.  It is concluded that treatment of foil bearing dynamics should be based on a two-degrees-of-freedom model.  Suggestions are made  for an analytical and experimental program to put the technology of foil bearings on a sounder basis than has been the case heretofore.

Survey of Experimental Data for Fixed Geometry Hydrodynamic Journal Bearings.

Swanson, E.E., Kirk, R.G., 1997
ASME Journal of Tribology, 119, pp.704-710.

An extensive survey of the experimental research on the static and/or dynamic characteristics of fixed geometry, hydrodynamic journal bearings available in English, in the open literature is presented.  The type(s) of bearing, size of bearing(s) and range of parameters measured in each work are reported for slightly over 100 published experimental works.  In addition, some general observations about the available experimental data sets are made.  This annotated survey is intended to help the analytical community by providing an extensive list of sources of experimental data for use in analysis verification.  It is intended to help the experimental community by  highlighting the shortcomings of the available literature, as well as by providing a list of sources for appropriate data to help with current and future test rig debugging.

Evaluation of AMB Turbomachinery Auxiliary Bearings.

Kirk, R.G., Raju, K.V.S., Swanson, E.E., 1996
Proc Fifth Colloquium on Turbomachinery, Turbo and Power Machinery Research Center, Seoul National University, Seoul, Korea, May 6-11.

The use of active magnetic bearings (AMB) for turbomachinery has experienced substantial growth during the past two decades. The advantages for many applications make AMBs a very attractive solution for potentially low loss and efficient support for both radial and thrust loads. New machinery must be shop tested prior to shipment to the field for installation on-line. For AMB turbomachinery, one additional test is the operation of the auxiliary drop or overload bearings. A major concern is the ability of the selected auxiliary bearing to withstand the contact forces following an at-speed rotor drop. The proper design of AMB machinery requires the calculation of the anticipated loading for the auxiliary bearings. Analytical techniques to predict the rotor transient response are reviewed. Results of transient response evaluation of a full-size compressor rotor are presented to illustrate some of the important parameters in the design for rotor drop. In addition, selected results for two test rotors used for research and development at the Virginia Tech Rotor Dynamics Laboratory are discussed.

Test Results and Numerical Simulation of AMB Rotor Drop.

Swanson, E.E., Raju, K.V.S., Kirk, R.G., 1996
Proc. 6th Int'l Conf. on Vibrations in Rotating Mach., IMechE, pp. 119-131.

Active magnetic bearings (AMB) for use in land based turbomachinery has enjoyed substantial growth during the past decade. Their advantages to many applications make them an attractive solution for potentially low loss and efficient support of both radial and thrust loads. New machinery must be shop tested prior to shipment to the field for installation on-line. One necessary test is the satisfactory performance of the emergency overload backup bearings. A major concern treated by this paper is the verification of the calculation of the transient response during rotor drop and estimation of the contact forces on the radial backup bearings. The calculation technique is reviewed and results of transient response evaluation of a fill-size test rotor are compared to the reported test experimental drops. Recommendations will be given to improve the probability of stable operation during rotor drop on the test stand and in the field operating condition.

AMB Rotor Drop Initial Transient on Ball and Solid Bearings.

Swanson, E.E., Kirk, R.G., 1995
Proc. MAG '95, pp. 227-235.

The increasing number of critical path machinery applications using active magnetic bearing (AMB) technology has focused awareness on the necessity for proper design of the auxiliary (backup) bearings.  These emergency bearings are required to support the rotor in the event of control system failure or to provide for operation during momentary overload conditions with the AMB control system still active.  Full-scale testing of production machinery has demonstrated both successful rotor drops as well as limited cases of auxiliary bearing failure.  The reliability required for critical path machinery makes it essential to completely understand what parameters control the nature of the rotor drop transients.  The current research project is intended to help understand the dynamic behavior of the rotor/bearing/support systems in the case of total loss of AMB support. This work presents test results for the initial rotor drop transient for several backup bearing configurations.  The cases reported are: rigidly mounted antifriction bearing, rigidly mounted solid bushings (lubricated and unlubricated), and two soft mounted solid bushing configurations.

Experimental Temperature and Pressure Profiles for Two Steadily Loaded Journal Bearings.

Swanson, E.E., Kirk, R.G., 1995
Tribology Transactions, 38, pp. 601-606.

Experimental temperature and pressure profiles for a steel and a bronze bearing are examined.  The comparisons show systematic differences between these otherwise identical bearings.  These comparisons suggest that there would be merit in including thermal deformation in the analysis if high accuracy is required.  The additional accuracy obtained could be especially important in accurately predicting the characteristics of sensitive high performance turbomachinery.

Simulation of AMB Turbomachinery for Transient Loading Conditions.

Raju, K.V.S., Ramesh, K., Swanson, E.E., Kirk, R.G., 1995
Proc. MAG '95, pp. 227-235.

The increasing number of critical path machinery applications using active magnetic bearing (AMB) technology has focused awareness on the necessity for proper design of the auxiliary (backup) bearings.  These emergency bearings are required to support the rotor in the event of control system failure or to provide for operation during momentary overload conditions with the AMB control system still active.  Full-scale testing of production machinery has demonstrated both successful rotor drops as well as limited cases of auxiliary bearing failure.  The reliability required for critical path machinery makes it essential to completely understand what parameters control the nature of the rotor drop transients.  The current research project is intended to help understand the dynamic behavior of the rotor/bearing/support systems in the case of total loss of AMB support. This work presents test results for the initial rotor drop transient for several backup bearing configurations.  The cases reported are: rigidly mounted antifriction bearing, rigidly mounted solid bushings (lubricated and unlubricated), and two soft mounted solid bushing configurations.

An Experimental Comparison of Two Steadily Loaded Plain Journal Bearings.

Swanson, E.E., Kirk, R.G., 1994
Tribology Transactions, 37, pp. 843-849.

A potentially powerful effect on the characteristics of plain journal bearings is local thermal deformation of the bearing surface.  Although there are a few analyses that consider the effect, it is ignored by most journal bearing codes used by industry.  There is also almost no experimental data in the literature that focuses on this effect.  To generate such data, two ""identical,"" 101 mm dia., 57 mm long bearings - one fabricated from steel and one from bronze - have been tested in a precision journal bearing test rig.  Comparisons between shaft displacement data for steady loading of the two bearings show that the deformations are important to consider.

Rotor Drop Test Stand for AMB Rotating Machinery, Part I: Description of Test Stand and Initial Results.

Kirk, R.G., Swanson, E.E., Kavarana, F.H., Wang, X., 1994
Proc. of Fourth International Symposium on Magnetic Bearings, Zurich, pp. 207-212.

The recent increase in the number of critical path rotating machinery applications using active magnetic bearing (AMB) technology has focused awareness and necessity for proper design of the auxiliary or backup bearings. These emergency bearings are essential for protection of the AMB stator in the event of control system failure or limited operation during momentary overload conditions wherein the AMB control system is still active. The current research project is concerned with the former design requirement, which is referred to as rotor drop. The rotor system and the auxiliary bearing support structure are equally important and influence the nature of the resulting rotor drop transient response. Limited testing of production machinery has demonstrated both successful drop tests and limited cases of auxiliary bearing failure. The reliability required for critical path machinery makes it essential to completely understand what parameters control the nature of the rotor drop transients. The design and construction of a full scale research test stand at Virginia Tech will be documented in this paper. The overall goals are summarized and initial test results of rotor drops on the rigidly supported auxiliary bearings are presented.

An Examination and Comparison of the Maximum Film Temperatures in a Journal Bearing for 13 Synthetic, Mineral and Viscosity Index Enhanced Oils.

Swanson, E.E., Kirk, R.G., Mondy, R.E., 1992
Rheology and Tribology of Engine Oils, SAE SP-936, Society of Automotive Engineers, Warrendale, pp. 137-145.

An experimental investigation of the peak film temperatures for 13 different oils has been performed with a precision journal bearing test rig. This study examined the differences between mineral, synthetic and viscosity index enhanced oils with regards to peak oil film temperatures. The oils examined include: three mineral oils (1-ISO 68 and 2-ISO 32), eight synthetic oils (1-ISO 22, 6-ISO 32, 1-ISO 68) and two viscosity index enhanced oils (1-ISO 22 synthetic, 1-ISO 32 mineral). The synthetic oils included both Diester base and Polyalphaolefin base products. Data for each oil were obtained at 6000, 8000, 10800, 12000, and 14000 RPM (100, 133, 180, 200 and 233 Hz); for loads of 670, 1330, 2000, 2670 and 3340 N. These speeds and loads correspond to surface speeds between 16 m/s to 37 m/s and unit loading between 0.5 MPa and 2.6 MPa. A 50.8 mm diameter, 25.4 mm long bearing with the upper portion relieved was used for all tests.

The data obtained tend to confirm the initial expectation that the bulk fluid characteristics are much more important than the lubricant composition with regards to static performance characteristics (i.e., load capacity and peak film temperature) in the thick film operating regime characteristic of a moderately loaded journal bearing. The results showed a 5 to 10 ?C decrease in peak film temperature can be obtained by changing from an ISO 68 to an ISO 32 oil. It was also found that viscosity index enhancers can allow a relatively inexpensive mineral base oil to show the same general level of thermal performance as a synthetic oil. The reduction in peak temperatures was seen in both an enhanced ISO 32 mineral base oil and an enhanced ISO 22 synthetic base oil. These observations suggest that the effect of shear thinning on polymer thickened oils may not be as great as the published analytical investigations would suggest. The reductions in temperature observed should also be of interest with regards to thrust bearings which often experience severe thermal crowning.

Experimental Evaluation of Fluid-Film Bearings Using Electro-Magnetic Shaft Loading and Evidence of Localized Thermal Distortion.

Swanson, E.E., Kirk, R.G., 1992
Proc. 5th Int'l Conf. on Vibrations in Rotating Mach., IMechE, pp. 359-363.

During the preliminary operational verification of a new test rig, a possible source of some of the discrepancy between analytical and experimental results for fluid film bearings, which has not been considered at great length in the literature, was noted. This mechanism is the localized thermal deformation of the bearing bush. To qualitatively demonstrate that such a mechanism may change the static shaft locus for a bearing, results from the VPI & SU test rig and a published work are presented.