Effects of Mechanical Preloads on the Rotordynamic Performance of a Rotor Supported on Three-Pad Gas Foil Journal Bearings

2014 ◽  
Vol 136 (12) ◽  
Author(s):  
Kyuho Sim ◽  
Bonjin Koo ◽  
Jong Sung Lee ◽  
Tae Ho Kim
Keyword(s):  
Test Data ◽  
High Speed ◽  
Experimental Tests ◽  
Journal Bearings ◽  
Test Results ◽  
Performance Measurements ◽  
Displacement Sensors ◽  
Single Top ◽  
Speed Up ◽  
The One

This paper presents the rotordynamic performance measurements and model predictions of a rotor supported on three-pad gas foil journal bearings (GFJBs) with various mechanical preloads. The rotor with its length of 240 mm, diameter of 40 mm, and weight of 19.6 N is supported on two GFJBs and one pair of gas foil thrust bearings (GFTBs), being a permanent magnet rotor of a high speed electric motor. Each bearing pad consisting of a top foil and a bump-strip layer is installed on a lobed bearing housing surface over the arc length of 120 deg along the circumference. Test three-pad GFJBs have four different mechanical preloads, i.e., 0 μm, 50 μm, 70 μm, 100 μm with a common radial nominal clearance of 150 μm. A series of speed-up tests are conducted up to 93 krpm to evaluate the effects of increasing mechanical preloads on the rotordynamic performance. Two sets of orthogonally positioned displacement sensors record the rotor horizontal and vertical motions at the thrust collar and the other end. Test results show that the filtered synchronous amplitudes change little, but the onset speed of subsynchronous motions (OSS) increases dramatically for the increasing mechanical preloads. In addition, test bearings with the 100 μm preload show a higher OSS in load-on-pad (LOP) condition than that in load-between-pads (LBP) condition. A comparison with test results for a one-pad GFJB with a single top foil and bump-strip layer reveals that three-pad GFJB has superior rotordynamic performance to the one-pad one. Finally, the test data benchmark against linear rotordynamic predictions to validate a rotor-GFJB model. In general, predicted natural frequencies of the rotor-bearing system and synchronous rotor motions agree well with test data. However, stability analyses underestimate OSSs recorded during the experimental tests.

Effects of Mechanical Preloads on the Rotordynamic Performance of a Rotor Supported on 3 Pad Gas Foil Journal Bearings

2014 ◽  
Author(s):  
Kyuho Sim ◽  
Bonjin Koo ◽  
Jong Sung Lee ◽  
Tae Ho Kim
Keyword(s):  
Test Data ◽  
High Speed ◽  
Experimental Tests ◽  
Journal Bearings ◽  
Test Results ◽  
Performance Measurements ◽  
Displacement Sensors ◽  
Single Top ◽  
Speed Up ◽  
The One

The paper presents the rotordynamic performance measurements and model predictions of a rotor supported on three-pad gas foil journal bearings (GFJBs) with various mechanical preloads. The rotor with its length of 240 mm, diameter of 40 mm, and weight of 19.6 N is supported on two GFJBs and one pair of gas foil thrust bearings (GFTBs), being a permanent magnet rotor of a high speed electric motor. Each bearing pad consisting of a top foil and a bump strip layer is installed on a lobed bearing housing surface over the arc length of 120 deg along the circumference. Test three-pad GFJBs have four different mechanical preloads, i.e., 0 μm, 50 μm, 70 μm, 100 μm with a common radial nominal clearance of 150 μm. A series of speed-up tests are conducted up to 93 krpm to evaluate the effects of increasing mechanical preloads on the rotordynamic performance. Two sets of orthogonally positioned displacement sensors record the rotor horizontal and vertical motions at the thrust collar and the other end. Test results show that the filtered synchronous amplitudes change little, but the onset speed of sub-synchronous motions (OSS) increases dramatically for the increasing mechanical preloads. In addition, test bearings with the 100 μm preload show a higher OSS in load-on-pad (LOP) condition than that in load-between-pads (LBP) condition. A comparison to test results for a one-pad GFJB with a single top foil and bump strip layer reveals that three-pad GFJB has superior rotordynamic performance to the one-pad one. Finally, the test data benchmark against linear rotordynamic predictions to validate a rotor-GFJB model. In general, predicted natural frequencies of the rotor-bearing system and synchronous rotor motions agree well with test data. However, stability analyses underestimate OSSs recorded during the experimental tests.

Rotordynamic Performance Measurements and Predictions of a Rotor Supported on Multilayer Gas Foil Journal Bearings for Microturbomachinery

2016 ◽  
Author(s):  
Jongsung Lee ◽  
Young Min Kim ◽  
Moon Sung Park ◽  
Tae Ho Kim ◽  
Kyoung Ku Ha ◽  
...  
Keyword(s):  
Damping Ratio ◽  
Operation Time ◽  
Journal Bearings ◽  
Displacement Sensor ◽  
Radial Clearance ◽  
Performance Measurements ◽  
Displacement Sensors ◽  
Model Predictions ◽  
Type C ◽  
Time Required

This paper presents rotordynamic performance measurements of multilayer gas foil journal bearings (GFJBs) supporting the rotor of oil-free microturbomachinery, and a comparison with the model predictions. A series of rotor coast-down tests from 60 krpm were conducted to compare the rotordynamic performances of three previously developed multilayer GFJBs: types A, B, and C. During the tests, two sets of orthogonally positioned displacement sensors recorded the horizontal and vertical rotor motions, and an axially positioned displacement sensor measured the thrust of the runner axial motion. The test results revealed that the type C GFJBs have a superior rotordynamic capability over the other types. The additional coast-down tests from 100 krpm for the type C showed that the synchronous motions of the rotor are dominant at up to ∼50 krpm, but that large amplitudes of subsynchronous motion associated with the natural frequency of a rotor-GFJB system occur above this speed. Thermal transient response measurements were conducted using four k-type thermocouples at increasing rotor speeds of 20 to 100 krpm with increments of 10 krpm. The operation time required to establish steady-state temperatures was approximately 25 min for each speed. For most of the speeds tested, the front GFJB near the rotor impeller end showed the lowest temperatures, and both the rear GFJB near the thrust runner end and the permanent magnet (PM) motor showed the highest temperatures. The GFTB showed the lowest temperature at low speeds of below 50 krpm, and the highest temperature at the top speed of 100 krpm owing to the increasing axial load caused by the impeller force. The measured impeller pressure and motor output power increased nonlinearly with the increasing rotor speed and fits best with the second-order and third-order polynomial equations, respectively. The measured axial displacement revealed that the rotor moved axially up to ∼ 270 μm toward the impeller side as the speed increased to 100 krpm. Further experiments using a decrease in radial clearance of 30 μm demonstrated a suppression of the large amplitude of the subsynchronous rotor motion to a certain degree. In addition, the onset speed of the subsynchronous motions increased to 80 krpm for the type C GFJBs with the decrease in the radial clearance. Rotordynamic model predictions with the predicted GFJB stiffness and damping coefficients were benchmarked against the test data. The predicted natural frequencies, onset speed of instability (OSI) where the damping ratio became negative, and synchronous rotor response versus speed agreed reasonably with the measured whirl frequencies of the subsynchronous motions, the onset speed of subsynchronous motions (OSS), and the filtered synchronous rotor motion versus speed, respectively. The predictions also showed that the OSI increased from 50 krpm to 80 krpm with a decrease in the radial clearance, thus validating the present rotordynamic model.

Nonlinear Vibration and Bifurcation Analysis for Rotor-Seal-Bearing Systems of Centrifugal Compressors

2007 ◽  
Author(s):  
Yuefang Wang ◽  
Yong Li ◽  
Yong Zhang ◽  
Xiaoyan Wang
Keyword(s):  
High Speed ◽  
Labyrinth Seal ◽  
Journal Bearings ◽  
Coupling Vibration ◽  
Oil Film ◽  
Disc Center ◽  
Multiple Parameters ◽  
Jeffcott Rotor ◽  
Vibration Responses ◽  
The One

This paper presents the nonlinear coupling vibration and bifurcation of a high-speed centrifugal compressor with a labyrinth seal and two journal bearings. The rotor system is modeled as a Jeffcott rotor. The Muszynska’s model is used to express the seal force with multiple parameters. For the journal bearings, the model proposed by Zhang is adopted to express the excitation of unsteady oil-film force. The Runge-Kutta method is used to determine the vibration responses at the disc center and the two bearings. With parameters of rotation speed and pressure difference of the seal, bifurcation diagrams are presented to demonstrate the complexity in the rotor motions. Multiple periodic bifurcations are pointed out using two seal pressure differences. The intricate bifurcation behavior shows inherent interactions between forces of oil-film and seal, which reflect much more complicated rotor dynamics than the one with either of the excitations alone.

Macroscopic Real-Time Timetable Rescheduling Approach for High-Speed Railway under Complete Blockages Using a Three-Stage Algorithm

2021 ◽  
pp. 036119812110529
Author(s):  
Bowen Gao ◽  
Decun Dong ◽  
Yusen Wu ◽  
Dongxiu Ou
Keyword(s):  
High Speed ◽  
Mixed Integer ◽  
Activity Time ◽  
Total Delay ◽  
High Speed Railway ◽  
Railway Line ◽  
Optimization Task ◽  
Speed Up ◽  
Milp Model ◽  
The One

The rescheduling of train timetables under a complete blockage is a challenging process, which is more difficult when timetables contain lots of trains. In this paper, a mixed integer linear programming (MILP) model is formulated to solve the problem, following the rescheduling strategy that blocked trains wait inside the stations during the disruption. When the exact end time of the disruption is known, trains at stations downstream of the blocked station can depart early. The model aims at minimizing the total delay time and the total number of delayed trains under the constraints of station capacities, activity time, overtaking rules, and rescheduling strategies. Because there are too many variables and constraints of the MILP model to be solved, a three-stage algorithm is designed to speed up the solution. Experiments are carried out on the Beijing–Guangzhou high-speed railway line from Chibibei to Guangzhounan. The original timetable contains 162 trains, including 29 cross-line trains and 133 local trains. The simulation results show that our model can handle the optimization task of the timetable rescheduling problem very well. Compared with the one-stage algorithm, the three-stage algorithm is proved to greatly improve the solving speed of the model. All instances can get a better optimized disposition timetable within 450 to 600 s, which is acceptable for practical use.

Abrasion Resistance and High Speed Tensile Strength of Elastomers

1966 ◽  
Vol 39 (4) ◽  
pp. 823-840 ◽  
Author(s):  
Ruprecht Ecker
Keyword(s):  
Tensile Strength ◽  
Viscoelastic Properties ◽  
High Speed ◽  
Loss Modulus ◽  
Empirical Relation ◽  
Viscoelastic Behavior ◽  
Experimental Tests ◽  
Test Results ◽  
Resonant Vibrations ◽  
Mechanical Rupture

Abstract In earlier communications, we defined abrasion, especially of tires, as a thermal-oxidative process caused at high velocity of mechanical rupture. Other authors (e.g., Schallamach, Boggs, Zapp etc.), with theoretical and experimental tests, prove the importance of viscoelastic behavior as a characteristic property for abrasion. The results of experiments on six elastomers (NR, IR, BR, SBR, IIR, and EPT) compared in tire tread compounds are communicated and discussed in the present work. Tensile strength was determined over a temperature range of 20° to 140° C at deformation speeds of 10 to 20,000 % elongation per second. Forced, non-resonant vibrations were used to determine viscoelastic properties, e.g., resilience, storage modulus, and loss modulus. As abrasion is a consequence of frictional processes, coefficients of friction, dependent on temperature, were measured on dry, wet, and frosty asphalt/fine concrete track. The apparatus is briefly described. From these test results, an empirical relation established between abrasion, friction, viscoelastic properties, tensile strength at high speed and temperature allows one to predetermine the abrasion behavior of a vulcanizate in the laboratory.

Rotordynamic Coefficients for a Tooth-on-Stator Labyrinth Seal at 70 Bar Supply Pressures — Measurements Versus Theory and Comparisons to a Hole-Pattern Stator Seal

2004 ◽  
Author(s):  
Arthur Picardo ◽  
Dara W. Childs
Keyword(s):  
Test Data ◽  
Control Volume ◽  
Labyrinth Seal ◽  
Test Results ◽  
Flow Models ◽  
Rotordynamic Coefficients ◽  
Volume Model ◽  
Supply Pressure ◽  
Theoretical Predictions ◽  
The One

Rotordynamic and leakage coefficients are presented for a labyrinth seal that was tested at a supply pressure of 70 bar-a and speeds up to 20200 rpm. Tests were conducted at clearances of 0.1mm and 0.2mm, pressure ratios of 0.10, 0.31 and 0.52, and three pre-swirls ratios. Comparisons are made between test data and predictions from one-control-volume and two-control-volume bulk-flow models. Generally, theoretical predictions agree poorly with the test results, with the one-control volume model giving better predictions. The one-control-volume model provides a conservative prediction for effective damping; i.e., this parameter is underestimated. Both models under predict leakage rates. Comparisons are also made between rotordynamic coefficients of labyrinth and hole-pattern seals.

Rotordynamic Performance of Shimmed Gas Foil Bearings for Oil-Free Turbochargers

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Kyuho Sim ◽  
Lee Yong-Bok ◽  
Tae Ho Kim ◽  
Jangwon Lee
Keyword(s):  
Diesel Engine ◽  
Test Data ◽  
Compressed Air ◽  
Radial Clearance ◽  
Bench Test ◽  
Test Results ◽  
Passenger Vehicle ◽  
Performance Measurements ◽  
Foil Bearings ◽  
Model Predictions

Oil-free turbochargers (TCs) will increase the power and efficiency of internal combustion engines, both sparking ignition and compression ignition, without engine oil lubricant feeding or scheduled maintenance. Using gas foil bearings (GFBs) in passenger vehicle TCs enables compact, lightweight, oil-free systems, along with accurate shaft motion. This paper presents extensive test measurements on GFBs for oil-free TCs, including static load-deflection measurements of test GFBs, rotordynamic performance measurements of a compressed air driven oil-free TC unit supported on test GFBs, and bench test measurements of the oil-free TC driven by a passenger vehicle diesel engine. Two configurations of GFBs, one original and the other modified with three shims, are subjected to a series of experimental tests. For the shimmed GFB, three metal shims are inserted under the bump-strip layers, in contact with the bearing housing. The installation of shims creates mechanical preloads that enhance a hydrodynamic wedge in the assembly radial clearance to generate more film pressure. Simple static load-deflection tests estimate the assembly radial clearance of the shimmed GFB, which is smaller than that of the original GFB. Model predictions agree well with test data. The discrepancy between the model predictions and test data is attributed to fabrication inaccuracy in the top foil and bump strip layers. Test GFBs are installed into a TC test rig driven by compressed air for rotordynamic performance measurements. The test TC rotor, 335 g in weight and 117 mm long, is coated with a commercially available, wear-resistant solid lubricant, Amorphous M, to prevent severe wear during start-up and shutdown in the absence of an air film. A pair of optical proximity probes positioned orthogonally at the compressor end record lateral rotor motions. Rotordynamic test results show that the shimmed GFB significantly diminishes the large amplitude of subsynchronous rotor motions arising in the unmodified GFB. Predicted synchronous rotor amplitudes and rigid body mode natural frequencies agree reasonably well with recorded test data. Finally, the oil-free TC is installed into a passenger vehicle diesel engine test bench. The TC rotor speed is controlled by the vehicle engine. Speed-up tests show dominant synchronous motion (1X) of the rotor. Whirl frequencies of the relatively small subsynchronous motions are associated with the rigid body natural mode of the TC rotor-GFB system as well as (forced) excitation from the four-cylinder diesel engine. The bench test measurements demonstrate a significant reduction in the amplitude of subsynchronous motions for the shimmed GFB, thus verifying the preliminary test results in the TC test rig driven by compressed air.

scholarly journals The Influence of Water and Mineral Oil on Mechanical Losses in a Hydraulic Motor for Offshore and Marine Applications

2020 ◽  
Vol 27 (2) ◽  
pp. 125-135 ◽  
Author(s):  
Paweł Śliwiński
Keyword(s):  
Mathematical Model ◽  
High Speed ◽  
Experimental Studies ◽  
Experimental Tests ◽  
Mineral Oil ◽  
Hydraulic Motor ◽  
Influence Of Water ◽  
Marine Applications ◽  
The One ◽  
The Mathematical Model

AbstractIn this paper, mechanical losses in a hydraulic motor supplied with water and mineral oil (two liquids having significantly different viscosity and lubricating properties) are described and compared. The experimental tests were conducted using a special design (prototype) of a hydraulic satellite motor. The design of the satellite motor is presented. This motor was developed to supply both with water and mineral oil and features a non-circular tooth working mechanism. The paper also characterizes sources of mechanical losses in this motor. On this basis, a mathematical model of these losses has been developed and presented. The results of calculation of mechanical losses according to the model are compared with the experimental results. Experimental studies have shown that the mechanical losses in the motor supplied with water are 2.8 times greater than those in the motor supplied with oil. The work demonstrates that the mechanical losses in both the motor supplied with water and the one supplied with oil are described well by the mathematical model. It has been found that for the loaded motor working at high speed, the simulation results differ from experimental ones by no more than 3% for oil and 4% for water.

Experimental Evaluation of the Markl Fatigue Methods and ASME Piping Stress Intensification Factors

2008 ◽  
Author(s):  
Chris Hinnant ◽  
Tony Paulin
Keyword(s):  
Test Data ◽  
Research Group ◽  
Experimental Evaluation ◽  
Experimental Tests ◽  
Design Codes ◽  
Test Results ◽  
Design Code ◽  
Butt Weld ◽  
Fatigue Data ◽  
Existing Data

Experimental results of ten girth weld and two unreinforced piping intersections recently tested at Paulin Research Group (PRG) are reported. Results are compared to the original Markl work [1–5] and to current ASME piping design code practices [6]. In addition, approximately 800 experimental tests from the literature [7–32] are compared to the new test results and the existing Mark1 equations. Findings indicate that the original mean girth weld equation provided by Mark1, which serves as the basis of the ASME piping codes, does not match trends expected for as-welded fatigue data. Discrepancies are apparent in the low and high cycle regimes. Finally, the new PRG test data and the existing data from literature are used to develop a new mean girth butt weld curve and to modify the existing ASME piping design codes.

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