Browsing by Author "Pettinato, Brian C."

Now showing 1 - 9 of 9
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    Balancing three-bearing rotors
    (Turbomachinery Laboratory, Texas A&M Engineering Experiment Station, 2020) Wang, Qingyu; Pettinato, Brian C.
    Multistage cryogenic pump rotors are vertically oriented and supported radially by three bearings. However, while the rotors are oriented vertically and supported in three planes, they are balanced horizontally in two-plane balancing machines. Since the balancing machines are designed for two planes of support, a third support usually at the far end, is needed to support the rotor. There are two major issues that may affect the quality of balancing a three-bearing rotor as compared to a two-bearing rotor: The first issue is runout, which is essentially eccentricity that can contribute to unbalance. The shaft runout should be measured with the rotor supported at two locations. For rotors that will have short length ball bearings added after the balancing operation, the two support locations of the balancing machine is typically used, and the far end is left without support. The measurement on the far end could be large, and it is easily mistaken as sag and left without correction. The second issue is how to adjust the position of the third support when preparing to balance. The support is usually a two-roller device, and the regular adjustment method is to place it under the 3rd bearing location and raise it gradually to touch the rotor such that when the rotor is spun, both rollers are spinning. The result of this adjustment, however, is for the far end to be in a deflected sagged condition, which is different from the operating condition where all three bearings are aligned. This paper explains the difference between runout and sag, and presents a method to adjust the support such that the rotor can be correctly balanced. The influence of the support adjustment is shown with an example.
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    Bearing Metal Temperature Considerations in Tilting Pad Journal Bearings
    (Turbomachinery Laboratory, Texas A&M Engineering Experiment Station, 2023) Thorat, Manish R.; Li, Wei; Pettinato, Brian C.
    This paper specifically focuses on flooded design tilting pad journal bearings which still have predominant use in the industry
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    Bearing Metal Temperature Considerations in Tilting Pad Journal Bearings
    (Turbomachinery Laboratory, Texas A&M Engineering Experiment Station, 2023) Thorat, Manish R.; Li, Wei; Pettinato, Brian C.
    This paper specifically focuses on flooded design tilting pad journal bearings which still have predominant use in the industry
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    Bearing Metal Temperature Considerations in Tilting Pad Journal Bearings
    (Turbomachinery Laboratory, Texas A&M Engineering Experiment Station, 2023) Thorat, Manish R.; Li, Wei; Pettinato, Brian C.
    This paper specifically focuses on flooded design tilting pad journal bearings which still have predominant use in the industry
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    Rotordynamic Tests Of A Flexible Rotor On Flexure Pivot Journal Bearings And Stability Correlation With Frequency Dependent Characteristics.
    (Texas A&M University. Turbomachinery Laboratories, 2002) Pettinato, Brian C.; De Choudhury, Pranabesh; Turbomachinery Symposium (31st : 2002)
    A series of performance, unbalance response, and stability tests were performed on a flexible rotor incorporating two flexure pivot tilt-pad journal bearings, followed by a theoretical correlations using synchronous and frequency dependent bearing characteristics. The test data consisting of Bode plots and frequency cascade plots are presented along with measured bearing performance data, including peak temperatures at different speeds. Unbalance tests consisted of applying a midspan unbalance. Effects of oil inlet flowrate and oil inlet temperature are examined. The measured peak responses are compared to the theoretical in five measurement planes. Stability tests consisted of running the balanced rotor up in speed to provide a high flexibility ration and reduced logarithmic decrement. For these cases, the motion of the rotor was measured in five planes and results are presented in the form of cascade diagrams. The tests were conducted under a series of operation conditions by varying the speed, oil inlet temperature, and flowrates. High amplitude resonant whip instability did not occur; however, how amplitude limit cycle instability did occur, which aided in determining the stability threshold. Correlation of the test results to the theoretical logarithmic decrement was performed using both synchronous and nonsynchronous bearing coefficients, both with and without pivot rotational stiffness. Bases on the results of the study, the theoretical model with the nonsynchronous bearing coefficients best represents the rotorbearing system. Pivot rotational stiffness had little effect.
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    Shop Acceptance Testing Of Compressor Rotordynamic Stability And Theoretical Correlation
    (Texas A&M University. Turbomachinery Laboratories, 2010) Pettinato, Brian C.; Cloud, C. Hunter; Campos, Rogerio S.; Turbomachinery Symposium (39th : 2010)
    This paper presents the rotordynamic stability testing of a nine-stage centrifugal compressor used for hydrogen recycle service. The machine tested was of a basic design and employed no damper bearings, damper seals, shunts or swirl brakes to generate very high logarithmic (log) decrements as in previous papers. The test was performed using an electromagnetic shaker as part of the shop order. Results include the forward and backward mode’s stability and frequencies. Two log decrement estimation techniques were employed: One based in the time domain that does not require measurement of the shaker force and the classic ones based in the frequency domain. Examination of the results benchmarks the original equipment manufacturer’s (OEM’s) stability analysis methods versus the measurements. It also provides benchmarking of purchaser’s acceptance criteria, which can be tailored to each specific OEM.
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    Torsional Natural Frequencies: Measurement Vs. Prediction
    (Texas A&M University. Turbomachinery Laboratories, 2012) Wang, Qingyu; Feese, Troy D.; Pettinato, Brian C.; Turbomachinery Symposium (41st : 2012)
    Excessive torsional vibration can cause damage or failure to rotating equipment trains thereby resulting in costly shutdowns. A comprehensive torsional vibration analysis is the typical method of designing a torsional system that avoids such problems. Requirements of a torsional system design are commonly based on the API Standards (API 617, 2002 and API 684, 2005). These standards require torsional natural frequencies (TNFs) to have at least 10% separation margin (SM) from any excitation frequency. If the recommended SM cannot be achieved, then the torsional system design must be shown to be acceptable by stress analysis. The validity of the predicted TNF and any stress analysis is dependent on the accuracy of the model. Some degree of uncertainty is always present within the analytical data, the modeling techniques, and the assumptions for excitation and damping. This paper provides an uncertainty study of more than ten (10) torsional systems. Major sources of uncertainty in torsional modeling are identified. The effect of variation in mass-elastic data is examined, and a comparison between measured and predicted TNFs for numerous cases is presented. Based on the studies and measurements, a reasonable SM range is presented, and 5% SM for measured TNFs is proposed.
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    Torsional Natural Frequencies: Measurement Vs. Prediction
    (Texas A&M University. Turbomachinery Laboratories, 2013) Wang, Qingyu; Pettinato, Brian C.; Feese, Troy D.; Turbomachinery Symposium (42nd : 2013)
    Excessive torsional vibration can cause damage or failure to rotating equipment trains thereby resulting in costly shutdowns. A comprehensive torsional vibration analysis is the typical method of designing a torsional system that avoids such problems. Requirements of a torsional system design are commonly based on the API Standards (API 617, 2002 and API 684, 2005). These standards require torsional natural frequencies (TNFs) to have at least 10% separation margin (SM) from any excitation frequency. If the recommended SM cannot be achieved, then the torsional system design must be shown to be acceptable by stress analysis. The validity of the predicted TNF and any stress analysis is dependent on the accuracy of the model. Some degree of uncertainty is always present within the analytical data, the modeling techniques, and the assumptions for excitation and damping. This paper provides an uncertainty study of more than ten (10) torsional systems. Major sources of uncertainty in torsional modeling are identified. The effect of variation in mass-elastic data is examined, and a comparison between measured and predicted TNFs for numerous cases is presented. Based on the studies and measurements, a reasonable SM range is presented, and 5% SM for measured TNFs is proposed.
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    Torsional Rotordynamics of Machinery Equipment Strings
    (Turbomachinery Laboratories, Texas A&M Engineering Experiment Station, 2016) Corbo, Mark A.; Pettinato, Brian C.; Leader, Malcolm E.; Kulhanek, Chris D.; Turbomachinery Symposium (45th : 2016)