Category: Papers

Generalized Entities: A Modern Framework For Rotor Dynamics Software

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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.

Abstract

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.

Demonstration Of Powder Shear Damping Applied To Plates

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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.

Abstract

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.

A Test Stand For Dynamic Characterization Of Oil-Free Bearings For Modern Gas Turbine Engines

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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.

Abstract

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.

Thermal Features Of Compliant Foil Bearings – Theory And Experiments

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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.

Abstract

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.

On The Application Of Powder Shear Damping To A Structural Element

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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.

Abstract

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.

Capabilities Of Large Foil Bearings

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Capabilities Of Large Foil Bearings

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

Abstract

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.

A Gas Turbine Engine Backup Bearing Operating Beyond 2.5 Million DN

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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.

Abstract

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.

The Integration Of Structural And Fluid-Film Dynamic Elements In Foil Bearings Part II: A New Approach To The Problem

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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

Abstract

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.

Bearing Test Rig Dynamics Problem Identification And Model Tuning

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Bearing Test Rig Dynamics Problem Identification And Model Tuning

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

Abstract

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.

A 35,000 RPM Test Rig For Magnetic, Hybrid And Back-Up Bearings

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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

Abstract

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.