Browsing by Author "Kirk, R. Gordon"

Now showing 1 - 20 of 45
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    Active Magnetic Bearings used as an Actuator for Rotor Health Monitoring in Conjunction with Conventional Support Bearings
    Bash, Travis Joel (Virginia Tech, 2005-06-27)
    This thesis describes the test rig and results from a project expanding the field of rotor health monitoring by using Active Magnetic Bearings (AMBs) as actuators for applying a variety of known force inputs to a spinning. Similar to modal analysis and other nondestructive evaluation (NDE) techniques which apply input signals to static structures in order to monitor responses; this approach allows for the measurement of both input and output response in a rotating system for evaluation. However, unlike these techniques, the new procedure allows for multiple forms of force input signals to be applied to a rotating structure. This technique is used on a rotating shaft supported in conventional bearings with an AMB actuator added to the system. This paper presents the results from this project including shaft rub and notch. An EDM notch was also tested to attempt a breathing scenario similar to breathing cracks.
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    Advanced analysis of rotor-bearing systems for stability and response
    Ramesh, Krishnaswamy (Virginia Tech, 1996)
    Rotor dynamics has become an integral part in the analysis and design of industrial turbo machinery. Rotor dynamics deals predominantly with the evaluation of the stability and damped critical speeds, and the response to an unbalance excitation, of turbomachinery. The majority of the industries which deal with rotor dynamics use the conventional and proven transfer matrix methods to solve the dynamics. However, the recent advances in computer technology and the distinct advantages of the finite element method make it an attractive tool to model complex rotor bearing systems. This research has developed a PC-based finite element analysis program capable of modeling rotors supported not only on fluid film bearings, but also on Active Magnetic Beatings (AMB). Methods are described by which the non-synchronous bearing properties can be used to evaluate the stability of the rotors supported on AMB. The effect of sensor noncollocation on general elliptic orbit response and stability has also been studied, as compared to the circular response of the existing programs. A design procedure for the stability of rotors supported on squeeze film dampers has been outlined. The unbalance response of rotors supported on squeeze film dampers can be predicted using the new iterative solution method which accounts for the nonlinear behavior of the damper. Multilevel analysis, essential for systems such as aircraft jet engines and certain other classes of turbo machinery, can be performed using this new computer program. A post processor for viewing/animating the damped mode-shapes and force:d response of a rotor, in 3-dimensions, has been developed. This ability to view the animated complex modes of forward, backward, and mixed forward-backward whirl of the rotor adds a new dimension in understanding the dynamics of rotating machinery. With the increasing demand for more accurately predicting the dynamic response and stability of high performance critical path turbomachinery, it is essential to develop advanced capability computer programs. The new PC-based finite element program developed in this research has the advanced capabilities required to model such complex rotating machinery.
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    Analysis of a Split-Path Gear Train with Fluid-Film Bearings
    Wolff, Andrew Vincent (Virginia Tech, 2004-05-06)
    In the current literature, split path gear trains are analyzed for use in helicopter transmissions and marine gearboxes. The goal in these systems is to equalize the torque in each path as much as possible. There are other gear trains where the operator intends to hold the torque split unevenly. This allows for control over the gearbox bearing loading which in turn has a direct effect on bearing stiffness and damping characteristics. Having control over these characteristics is a benefit to a designer or operator concerned with suppressing machine vibration. This thesis presents an analytical method for analyzing the torque in split path gear trains. A computer program was developed that computes the bearing loads in various gearbox arrangements using the torque information gathered by the analytical method. A case study is presented that demonstrates the significance of the analytical method in troubleshooting an industrial gearbox that has excessive vibration.
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    Analysis of tilting-pad oil seals for high pressure centrifugal compressors
    Salem, Khlifi (Virginia Tech, 1988-12-05)
    Oil ring seals are one major source of instability in high pressure centrifugal compressors. This thesis presents a method for analysis of an improved seal concept that has been used in very high pressure designs (900 PSI). The improved design uses a combination of ring seals and tilting pad bearing elements. The stable tilting pad is used to center the heavily grooved seal element. The eight stiffness and damping coefficients which represent the hydrodynamic forces between the journal and the seal assembly are computed by an automated computer code for evaluation of both the standard ring seal and the tilting pad elements. Both synchronous and nonsynchronous steady state characteristics have been included in the analysis. The nonsynchronous whirl of the rotor and its effects on the stiffness and damping coefficients of a 5 tilting pad seal have been given in the form of design curves. The effect of pad inertia which has been neglected in many bearing analysis codes has been incorporated in this seal analysis, and allowed the determination of the exact cross coupling stiffness and damping coefficients.
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    Cage positioned tilting pad bearing
    (United States Patent and Trademark Office, 2016-07-19)
    A tilting pad bearing for a high speed rotary machines, such as a turbocharger for an internal combustion engine, comprises a cage and a plurality of tilting pads. The cage is formed by two annular rings separated by spacers machined from a single billet of high-temperature metal. The bearing pads are inserted between the spacers of the cage. One or more O-rings retain the bearing pads within the cage during assembly of the bearing but are not required after installation of the bearing. When retained in the final assembly and installation of the bearing, the O-rings allow tilting movement of the pads within the cage. The outer surfaces of the spacers have a plurality of grooves, and outer surfaces of each of the pads have matching grooves. One of the grooves is an oil groove, wherein the oil groove of the spacers communicating with and oil inlet holes in the spacers. At least one of the other grooves receives an O-ring that hold the pads in place in the cage during installation. When two O-rings are used on either side of the oil groove in the final assembly, the O-rings serve to direct oil to the oil groove and prevent or reduce oil leakage.
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    Computational Fluid Dynamic and Rotordynamic Study on the Labyrinth Seal
    Gao, Rui (Virginia Tech, 2012-06-14)
    The labyrinth seal is widely used in turbo machines to reduce leakage flow. The stability of the rotor is influenced by the labyrinth seal because of the driving forces generated in the seal. The working fluid usually has a circumferential velocity component before entering the seal; the ratio of circumferential velocity and shaft synchronous surface velocity is defined as pre-swirl rate. It has been observed that pre-swirl rate is an important factor affecting driving forces in the labyrinth seal thus affecting the stability of the rotor. Besides the pre-swirl, the eccentricity, the clearance, and the configuration of tooth locations are all factors affecting the rotordynamic properties of the labyrinth seal. So it is of interest to investigate the exact relationships between those factors and the seal's rotordynamic properties. In this research, three types of labyrinth seals have been modeled: the straight eye seal, the stepped eye seal, and the balance drum seal. For the straight eye seal, a series of models were built to study the influence of eccentricity and clearance. The other two seals each have only one model. All models were built with Solid Works and meshed with ANSYS-ICEM. Flows in those models were simulated by numerically solving the Reynolds-Averaged Navier-Stokes (RANS) equations in the ANSYS-CFX and then rotordynamic coefficients for each seal were calculated based on the numerical results. It had previously been very difficult to generate a pre-swirl rate higher than 60% in a numerical simulation. So three ways to create pre-swirl in ANSYS-CFX were studied and finally the method by specifying the inlet velocity ratio was employed. Numerical methods used in this research were introduced including the frame transfer, the k-ε turbulence model with curvature correction, and the scalable wall function. To obtain the optimal mesh and minimize the discretization error, a systematical grid study was conducted including grid independence studies and discretization error estimations. Some of the results were compared with previous bulk-flow or experimental results to validate the numerical model and method. The fluid field in the labyrinth seal must be analyzed before conducting rotordynamic analysis. The predicted pressure distributions and leakages were compared with bulk-flow results. A second small vortex at the downstream edge of each tooth was found in the straight eye seal. This has never been reported before and the discovery of this small vortex will help to improve seal designs in the future. The detailed flows in discharged region and in chambers were also discussed. Radial and tangential forces on the rotor were solved based on the fluid field results. It is shown that the traditional first-order rotordynamic model works well for low pre-swirl cases but does not accurately reflect the characteristics for high pre-swirl cases. For example compressor eye seals usually have pre-swirl rates bigger than 70% and the second order model is required. Thus a second-order model including inertia terms was built and applied to the rotordynamic analysis in this research. The influence of pre-swirl, eccentricity and clearance were studied using the straight eye seal model. The rotordynamic characteristics of the stepped eye seal and the balance drum seal were studied considering high pre-swirl rates. Some relationships between influencing factors and the four rotordynamic coefficients were concluded. The results also showed that for all the three seals higher pre-swirl leads to higher cross-coupled stiffness which is one of the main factors causing rotor instability. The rotor stability analysis was conducted to study the influence of drum balance seal on the stability. The rotor was designed with typical dimensions and natural frequencies for a centrifugal compressor rotor. The parameters for bearing and aerodynamic force were also set according to general case in compressors to minimize the effects from them. The result shows that the high pre-swirl rate in balance drum seal leads to rotor instability, which confirmed the significant effect of pre-swirl on the seal and the rotor system.
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    Cracked shaft detection rig
    Kavarana, Farokh H. (Virginia Tech, 1994-06-15)
    The ever-growing interest of the modern-day rotor dynamicist in the early detection of rotor cracks in turbomachinery has been the direct result of multiple catastrophic experiences that industry has had to face in recent times due to cracked rotors. The complete failure of the rotor due to crack propagation is easily recognized as one of the most serious modes of plant failure. Even so, this aspect has without question not received the attention it warrants. The last decade has, however, witnessed some laudable attempts that have been moderately successful in detecting cracked rotors. This work presents the design and set-up of a complete test rig that can be used for experimental research on response characteristics of cracked rotors. The results of this research will permit increased confidence in detecting the presence of rotor cracks in turbomachinery. The designed rig is capable of testing cracked shafts under the effect of lateral and coupled lateral-torsional vibrations. The conventional vibration signature analysis approach has been employed for the purpose of test rig evaluation and condition monitoring. The test rig has been shown to be essentially functional and the experimental data generated with the test rig are compared to appropriate analyses and published results.
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    Design and Evaluation of an Automated Experimental Test Rig for Determination of the Dynamic Characteristics of Fluid-Film Bearings
    Swanson, Erik Evan (Virginia Tech, 1998-08-07)
    Hydrodynamic journal bearings are applied in a wide range of both old and new, advanced rotating machinery designs. To maintain existing machinery, as well as to design new, state of the art machines, validated analytical models for these bearings are needed. This work documents the development and evaluation of an automated test rig for the evaluation of hydrodynamic journal bearings to provide some of the needed experimental data. This work describes the test rig in detail, including the results of experimental characterization of many of the test rig subsystems. Experimental data for a two axial groove bearing and a pressure dam bearing under steady load conditions are presented for a range of loads at two different shaft speeds. Experimental data and analytical results for dynamic loading are also discussed. The work concludes with a summary of the state of the test rig and recommendations for further work.
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    Development of the second-generation IMTS (Intelligent Monitoring and Trending System) and WOT (Wizard of Tech) expert system for rotating machinery
    Pawtowski, E. C. (Virginia Tech, 1996)
    IMTS and WOT form a PC-based hardware and software system designed to continuously monitor large numbers of rotating machinery, evaluate each machine's condition through a series of user-definable standards, and alert operators to potential problems. This system requires a rack of data acquisition equipment located near the machines being monitored and a PC that can be located remotely. This system has been tested under actual plant conditions at the Virginia Tech Power Plant. The software operates under Windows 3.1, and allows data to be acquired and evaluated simultaneously. This thesis discusses the development of this system over earlier versions and the installation procedures and first runs at the Power Plant. It discusses in detail the operation of some of the main programs that comprise the Intelligent Trending and Expert System.
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    Dynamic Stability Evaluation of an Automotive Turbocharger Rotor-Bearing System
    Alsaeed, Ali A. (Virginia Tech, 2005-05-03)
    This project was initiated to more fully understand the dynamic stability of an automotive turbocharger rotor-bearing system using both linear and nonlinear analyses. The capabilities of a commercial Finite Element Analysis (FEA) code (computer program) were implemented in the investigation process. Several different hydrodynamic journal bearings were employed in the study of the turbocharger linearized dynamic stability. The research demonstrates how the linear analysis of a turbocharger rotordynamics can be very beneficial for the design evaluation and maintenance purposes.
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    Evaluation of Alternate Bearing Designs in a High Speed Automotive Turbocharger
    Mondscehin, Brian David (Virginia Tech, 2010-05-27)
    Automotive turbochargers experience self-excited instabilities through the majority of their operating speed range. The results of these instabilities can cause damage to the bearings, shafts, and housing walls. Preventing this damage while maintaining or increasing performance characteristics is a huge concern to industry due to the time and money needed to replace vital components. The aim of this research is to determine which characteristics of the bearings have the greatest influence on the damped natural frequencies. It was believed that axial groove bearings could offer an acceptable alternative to the floating ring bearings currently found in automotive turbochargers. DyRoBeS rotor dynamics software was used to determine analytically damped natural frequencies for floating ring bearings, and also for six, eight, and ten axial groove fixed geometry bearings, under different speed and loading conditions. The resulting data were compared to experimental test results from an on-engine turbocharger test stand and presented in this report.
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    Evaluation of the Effectiveness of an Active Magnetic Damper (AMD) in Damping Subsynchronous Vibrations in a Flexible Rotor
    Mendoza, Hector (Virginia Tech, 2000-06-22)
    Subsynchronous vibrations such as those caused by rotor instability represent one of the most harrowing scenarios of rotor vibration. They are related to a great diversity of destabilizing forces and some of them are not well understood yet. Therefore, special attention must be paid to this type of vibration. Active Magnetic Bearings (AMBs) monitor the position of the shaft and change the dynamics of the system accordingly to keep the rotor in a desired position, offering the possibility of being used as dampers for vibration control. In the present work, a single-disk and a three-disk rotor were built to evaluate the effectiveness of an Active Magnetic Damper (AMD) in damping subsynchronous vibrations. An AMD was used to inject a signal simulating a subsynchronous vibration in the rotor, as another AMD was used to perform active control. Two locations of the AMD were considered for each rotor. For the single-disk rotor, experimental data was taken with the AMD located at three-quarters of the rotor-span and with the AMD located at midspan. For the three-disk rotor, experimental data was taken with the AMD located at a quarter-span and with the AMD at two-thirds of the rotor span. An undamped critical speed and a forced response analysis were performed on the rotors in order to predict the dynamic characteristics of the rotors with and without the AMD. It was demonstrated that an AMD is effective in damping subsynchronous vibrations. The addition of an AMD introduces damping and stiffness to the rotor-bearing system resulting in a change in the synchronous response and a consequent increase of the amplitude of vibrations at synchronous frequencies. This effect must be carefully considered when designing a system with an AMD.
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    Experimental evaluation of effective friction coefficient for liquid ring seals
    Dorton, David W. (Virginia Tech, 1991-08-05)
    Rotor dynamic analysis of liquid ring seals depends upon the correct specification of seal dynamic stiffness and damping characteristics. These are in turn dependent upon several parameters, including the friction holding force between the sealing face and the mating retaining ring. Designers currently assume a value for effective friction coefficient in order to utilize methods for prediction of response and stability. This thesis presents the results of testing on twelve actual seal rings of varying configuration at pressures of 689, 1378, 2068, and 2757 kPa in a static seal test rig to experimentally determine values of effective friction coefficient. The results are presented in graphical form as average effective friction coefficient versus eccentricity ratio for forward and backward motion of the rings.
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    The Experimental Testing of an Active Magnetic Bearing/Rotor System Undergoing Base Excitation
    Clements, Joshua Ryan (Virginia Tech, 2000-08-25)
    Active Magnetic Bearings (AMB) are a relatively recent innovation in bearing technology. Unlike conventional bearings, which rely on mechanical forces originating from fluid films or physical contact to support bearing loads, AMB systems utilize magnetic fields to levitate and support a shaft in an air-gap within the bearing stator. This design has many benefits over conventional bearings. The potential capabilities that AMB systems offer are allowing this new technology to be considered for use in state-of-the-art applications. For example, AMB systems are being considered for use in jet engines, submarine propulsion systems, energy storage flywheels, hybrid electric vehicles and a multitude of high performance space applications. Many of the benefits that AMB systems have over conventional bearings makes them ideal for use in these types of vehicular applications. However, these applications present a greater challenge to the AMB system designer because the AMB-rotor system may be subjected to external vibrations originating from the vehicle's motion and operation. Therefore these AMB systems must be designed to handle the aggregate vibration of both the internal rotor dynamic vibrations and the external vibrations that these applications will produce. This paper will focus on the effects of direct base excitation to an AMB/rotor system because base excitation is highly possible to occur in vehicular applications. This type of excitation has been known to de-stabilize AMB/rotor systems therefore this aspect of AMB system operation needs to be examined. The goal of this research was to design, build and test a test rig that has the ability to excite an AMB system with large amplitude base excitation. Results obtained from this test rig will be compared to predictions obtained from linear models commonly used for AMB analysis and determine the limits of these models.
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    An expert system for off-line analysis of rotating equipment
    Hoglund, James R. (Virginia Tech, 1989-08-05)
    The analysis of rotating equipment difficulties is currently accomplished by a specialist in rotating equipment examining the signs and symptoms of the equipment, applying his expert judgement, and determining the cause of the machine's difficulty. This thesis covers the development of an off-line expert system that can be used to emulate the expert's ability to interpret the signs and symptoms of the machine, including suggestions of possible further actions to take for repairing the problem or refining the proof for the proposed cause the difficulty. An editor has also been built which will allow an expert to keep the information used by the system current with the state of the art for rotating machinery diagnostics. This thesis documents the development of the PC-based Turbo Prolog expert shell and external knowledge-base editor. The use of the system editor is illustrated by loading current diagnostic table information into a knowledge base. Then the expert program's operation is illustrated by applying the editor-formed database in a typical session. The expert shell and knowledge base can operate as a stand-alone unit for field application. Resident experts in machinery diagnostics can build and update databases for distribution to users in the company to assure full uniform utilization of the current and most correct knowledge.
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    Expert System Source Identification of Excessive Vibration
    Kirk, R. Gordon; Guo, Zenglin (Hindawi, 2003-01-01)
    The importance of vibration data in determining the condition of rotating machinery is well established in both the aircraft and the heavy equipment industries. Installation of noncontact displacement probes for shaft motion and either velocity or acceleration sensors for bearing cap or foundation motion is standard practice for equipment manufacturers. Automation of the diagnostic evaluation of certain simple faults can be easily implemented. The advances in computer languages in recent years have made it diffiucult to keep pace with the graphical capabilities available to the programmers. One major concern is the content of the knowledge base and the method of modifying the knowledge base or the procedure of evaluating the confidence of a given identified possible cause of a problem. This article addresses the application of one such expert system to a recentvibration problem on a 7-megawatt steam turbine–driven generator located at the power plant of Virginia PolytechnicInstitute.
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    Impact Damage Resistance of Shape Memory Alloy Hybrid Composite Structures
    Jia, Hongyu (Virginia Tech, 1998-05-26)
    The strain energy absorption of shape memory alloy (SMA) bars and beams under tension and bending loading was studied. A theoretical model is presented that can give quantitative relations between the martensite fraction, the applied load, and the strain energy absorbed in the shape memory alloy (SMA). It was found analytically that the super-elastic SMA demonstrates a high strain energy absorption capability. The closed- form solution of the strain energy absorption capability of SMA bars is a simple and useful tool in the design of energy absorption applications of super-elastic SMA. The nonlinear equations for SMA hybrid composite plates, which can be used for low velocity impact or quasi-static contact loading, are derived. The governing equations include the transverse shear deformation to the first-order, large deformation of the plates, and SMA/epoxy lamina. The equations are derived in the general form with general boundary conditions and general stack of angle ply. The equations can be simplified to special forms in the specific applications. A theoretical study of the impact force and the strain energy absorption of an SMA/graphite/epoxy composite beam under a low-velocity impact has been performed. The contact deformation, the global bending deformation, the transverse shear deformation, and the martensitic phase transformation of the super-elastic SMA fibers are studied. The energy absorbed by the SMA hybrid composite is calculated for each task of the absorption mechanisms: contact deformation, global bending deformation, and The analysis methods and models developed in this dissertation are the first reported research in modeling SMA composite under low velocity impact and quasi-static loading. The models and methods developed here can be used for further study and design of SMA composites for low velocity impact or quasi-static loading in failure process.
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    Induced Unbalance as a Method for Improving the Dynamic Stability of High-Speed Turbochargers
    Kirk, R. Gordon; Alsaeed, Ali A. (Hindawi, 2011-02-06)
    The high-speed diesel engine turbocharger is known to have subsynchronous vibrations for a wide speed range. The bearing fluid-film instability is the main source of the vibration. The nonlinear forces inside the bearings are causing the rotor to whirl in a limit cycle. This study presents a new method for improving the dynamic stability by inducing the turbocharger rotor unbalance in order to suppress the subsynchronous vibration. The finite-element model of the turbocharger with floating-ring bearings is numerically solved for the nonlinear time-transient response. Both compressor and turbine added unbalance are induced and the dynamic stability is computed. The turbocharger model with linearized floating-ring bearings is also solved for eigenvalues to predict the modes of instability. The linear analysis demonstrates that the forward whirling mode of the floating-ring at the compressor end also becomes unstable at the higher turbocharger speeds, in addition to the unstable forward conical and cylindrical modes. The numerical predictions are also compared to the former experimental results of a similar turbocharger. The results of the study show that the subsynchronous frequency amplitude of the dominant first mode is reduced when inducing either the compressor or the turbine unbalance at a certain level.
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    Influence of active magnetic bearing sensor location on the calculated critical speeds of turbomachinery
    Keesee, John Micheal (Virginia Tech, 1989-06-05)
    The calculation of critical speeds for turbomachinery with active magnetic bearings (AMBs) is of great interest due to the increasing number of applications of this new technology. The potential for increased turbomachine performance through improved AMB design has created the need for a more accurate method for predicting the system's undamped critical speeds. This thesis documents the development of a method which improves the accuracy of critical speed calculation by properly accounting for the influence of AMB sensor location on the undamped critical speeds. This investigation includes the development of an AMB modified Jeffcott model. The results from the AMB modified Jeffcott analysis give useful design guidance for the influence of the sensor location on the first and third modes of a symmetric rotor system. A more accurate solution using a transfer matrix method modified to account for AMB sensor locations is presented. The results from the transfer matrix method for an example compressor are presented showing the influence of the sensor placement on a standard undamped critical speed map. The mode shapes with sensor location at a typical design location are given to illustrate the importance of the sensor location.
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    Influence of Induced Unbalance on Subsynchronous Vibrations of an Automotive Turbocharger
    Sterling, John Anthony (Virginia Tech, 2009-06-22)
    Rotordynamic instability is present in most or all automotive turbochargers. High subsynchronous amplitudes can cause a variety of problems in areas such as mechanical failures, emissions regulations and rotor design. Self-excited vibrations from sources of damping can lock in at lateral natural frequencies causing dangerously high vibration levels. The resulting high-amplitude conical and bending modes can be reduced in order to achieve a more robust system. This research focuses on the relationship between synchronous and subsynchronous amplitude levels. It is theorized that an increase in unbalance could cause a reduction in subsynchronous vibration amplitudes. Through the use of a custom turbocharger, a series of unbalances were applied to both the turbine and compressor wheels and the resulting amplitudes were recorded off a modified compressor nut. The resulting data were reduced and are presented at the end of this paper.