The independent effects of e.rcitation frequency and escitariorr n~agnitltde on esperin~entally derived hearing coeficier~ts for a highly preloaded three-lobe jo~rrnal hearing were studied. The effect of escitation fieq~ret~cy was determined by applying e,~ternal dynamic forces at half-synchronous, synckrono~ts, and twice synchronorrsfrequencies with respect to the operatitlg speed. Effect of e,vcitation nlcrgninrde ~l a s independently deternzirled by applying either three or forrr dtfferent an~plitudes of e.vcitatiort force to the hearing resulritrg in orbit sizes ranging tip to 30% of clearance. Applying static forces to the hearing housing controlled the Somniet$elrl nrm~her, and thus, the static operating position. Data
Presented as a Society of Tribologists and Lubrication EngineersPaper at the STLEIASME Tribology Conference in San Francisco, CA October 21-24,2001 Final manuscript approved June 12,2001 Review led by Gregory Kostrzewsky was reduced as linear dynaniic coefficients, and presented relative to excitation frequency and excitation niagtiilude over a range of Sonlnlerfeld numbers from 0.2 to 3.0 and operating eccentricities from 0.3 to 0.9. In general, neither excitation frequency nor e.rcitatioti magttitrtde was shown to have a nieasurahle efSEct over the ranges studied.
To validate a new squeeze film damper (SFD) bearing design introduced in [1], a pair of 3.5 inch SFD bearings were manufactured and tested. Static spring compression test was conducted to prove the spring design stiffness calculated through the geometry parametric spring model. High cycle loading fatigue testing of the spring was conducted to validate the design spring fatigue limit. The entire SFD bearing assembly was inspected and checked through a SFD centering bench test before the rotor dynamic test.
Unbalance response correlation and logarithmic decrement (Log. Dec.) measurement using the operational modal analysis (OMA) method were employed for the rotor-dynamic tests. An agreement was seen between the analysis and the experimental measurement. It was seen that the SFD bearing provided the extra damping as expected to suppress the unbalance vibration when passing through the critical speed and also improve the stability (Log. Dec.) of the rotor. It was found that the measured SFD damping was closer to the full film damping model when the squeeze oil film was sealed with O-rings. The SFD improved the logarithmic decrement of the rotor-bearing system from 0.07 to more than 0.21 as compared to the system without SFD.
In a rotor-bearing system, there are usually some under- or unmodeled components, such as foundations and seals. Identifying the dynamic characteristics of these components often requires both an analytical model and test data due to the working conditions, such as running speed above the first bending mode and non-collocation measurements. The existing methods always identify the dynamic characteristics by solving the equations of motion at discrete frequencies of the measured frequency response functions (FRFs). They have two problems: first, the physical background of the identification is buried in the equation solving process, and second, there is no quality estimation of the identified result. This paper discusses the first problem which is the equation solving process. The second problem, quality estimation, is discussed in a subsequent paper [1]. This paper reveals that model-based identification is the interconnection of certain transfer functions. These transfer functions are either generated from an analytical model (the common model-based method), or directly measured (direct measurement method). The process of both these methods is then illustrated by use of experimental data. A novel seal test design is proposed based on the idea of the direct measurement method. Identification under complex situations is also considered as complementary to the main content, such as different input/output locations. The conditions for identifiability are given.
The predicted and measured bearing metal temperatures of tilting-pad journal bearings are examined. All bearings are a five-pad design with load-between-pad orientation. The two loaded pads in each bearing are instrumented with a resistance temperature detector (RTD). The bearing pad metal temperatures are measured as a part of the ISO 10439 (API 617) mechanical test requirement. Bearing pad metal temperatures are predicted using the thermoelastohydrodynamic (TEHD) analysis method. One particular bearing size 4 in. (101.6 mm) in diameter and 1.54 in. (39.12 mm) in the axial length is examined with respect to the tolerance range influence on the predicted pad metal temperatures including the effect of bearing assembled clearance and preloads. A range of loads and speeds are investigated. The temperature variation observed for this bearing size is compared against the variation in the measured temperature data for three other bearing sizes (bearing sizes are denoted by diameter × axial length) 2.95 in. (74.9 mm) × 1.02 in. (25.9 mm), 6 in. (152.4 mm) × 3 in. (76.2 mm), and 8 in. (203.2 mm) × 7 in. (177.8 mm).
The paper discusses the redesign of a high-speed turbocharger for improved bearing life and mechanical operation. The bearings were changed from a pair of combination journal/thrust bearings to a pair of redesigned journal bearings with double acting thrust bearing at the center of the unit. Internal oil passages, drain cavities, and seals were also revised. These modifications resulted in reduced oil leakage across end seals, reduced coke buildup at the turbine, increased thrust load capacity, and improved rotordynamics. Both the analytical and experimental results, which consisted of bearing performance and vibration data of original and modified systems are presented.
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