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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Static and dynamic characteristics for a two-axial-groove bearing and a pressure-dam bearing

Al Jughaiman, Bader K. 02 June 2009 (has links)
This thesis compares experimental static and dynamic force characteristics for a two-axial-groove bearing and a pressure-dam bearing without a relief track. The thesis also compares experimental results to predictions from a numerical analysis. The tested pressure-dam bearing has s θ= 130°, ' k =3.4~4.2, and d L − =0.75. The test results show that eccentricity for both bearings decreases as Sommerfeld number increases. However, the pressure-dam bearing maintains a minimum eccentricity of about 0.5 at high speeds. The results also show that the attitude angle for both bearings increases as Sommerfeld number increases. The maximum attitude angle for the axial-groove bearing is 90° at noload. However, the attitude angle for the pressure-dam bearing increases above 90° at no-load as speed increases. A dynamic test shows that the pressure-dam bearing has higher direct stiffness and damping at high Sommerfeld number because of the increase in eccentricity. However, as Sommerfeld number decreases, the difference between stiffness and damping coefficients of both bearings diminishes. The dynamic test also shows that both bearings have significant added mass coefficients in the laminar flow region that decrease as eccentricity increases. The estimated axial-groove bearing whirlfrequency ratio (WFR) from experimental results is 0.45. The WFR of the pressure-dam bearing reduces to 0.41 at high Sommerfeld numbers. Numerical analysis shows that the pressure-dam bearing can have lower WFR if the dam arc length is increased to 150°. Numerical analysis also shows that stability can be improved further by adding a relief track. Generally, the numerical analysis under predicts the bearings’ eccentricity and dynamic force coefficients with better agreement at low Sommerfeld numbers.
2

Rotordynamic coefficients for a load-between-pad, flexible-pivot tilting pad bearing at high loads

Hensley, John Eric 30 October 2006 (has links)
The dynamic and static performance of a flexure-pivot tilting pad bearing is presented at a load between pad configuration for various load and speed combinations. A similar work performed on the same bearing at lower loads ranging from 0-1 MPa (0-150 psi) by Al-Ghasem was tested, whereas the current work investigates effects in the load range between 1-2.2 MPa (150-320 psi). The bearing design parameters include: 4 pads with pad arc angle 72º and 50% pivot offset, pad axial length 0.0762 m (3 in), pad radial clearance 0.254 mm (0.010 in), bearing radial clearance 190.5 µm (0.0075 in), preload 0.25, and shaft nominal diameter of 0.11684 m (4.600 in). An important distinction between the two sets of tests is the difference in experimental bearing radial clearance, which for this case measured 208 µm (0.00082 in), and for Al-Ghasem’s was 165.1 µm (0.0065 in). The rotordynamic coefficients are determined experimentally using a test rig equipped with motion and load sensors. The rig is modeled using Newton’s laws, which is converted from the time to frequency domain using Fourier Transform to give complex dynamic stiffnesses. From the resulting complex dynamic stiffnesses the associated real and imaginary components are plotted as a function of excitation frequency and curve fitted via linear regression to give the rotordynamic coefficients. The primary objectives were to determine whether the real component of the complex dynamic stiffnesses could be better modeled with or without the mass coefficient and to contrast the rotordynamic coefficients with an analytical model. Only in the load range of 1 to 2.2 MPa were the unloaded direct mass coefficients near or at 0, which would allow for a [K][C] model to be used. The remaining real components are better represented with the mass term. The analytical model generally overpredicted the stiffness, damping and mass coefficients, especially for the direct components; the trends were generally consistent.
3

Design and Evaluation of an Automated Experimental Test Rig for Determination of the Dynamic Characteristics of Fluid-Film Bearings

Swanson, Erik Evan 23 September 1998 (has links)
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. / Ph. D.
4

A Fault Diagnosis System for Rotary Machinery Supported by Rolling Element Bearings

Hasanzadeh Ghafari, Shahab January 2007 (has links)
The failure of rolling element bearings is one of the foremost causes of breakdown in rotary machinery. So far, a variety of vibration-based techniques have been developed to monitor the condition of bearings; however, the role of vibration behavior is rarely considered in the proposed techniques. This thesis presents an analytical study of a healthy rotor-bearing system to gain an understanding of the different categories of bearing vibration. In this study, a two degree-of-freedom model is employed, where the contacts between the rolling elements and races are considered to be nonlinear springs. The analytical investigations confirm that the nature of the inner ring oscillation depends on the internal clearance. A fault-free bearing with a small backlash exhibits periodic behavior; however, bearings categorized as having normal clearance oscillate chaotically. The results from the numerical simulations agree with those from the experiments confirming bearing’s chaotic response at various rotational speeds. Bearing faults generate periodic impacts which affect the chaotic behavior. This effect manifests itself in the phase plane, Poincare map, and chaotic quantifiers such as the Lyapunov exponent, correlation dimension, and information entropy. These quantifiers serve as useful indices for detecting bearing defects. To compare the sensitivity and robustness of chaotic indices with those of well-accepted fault detection techniques, a comprehensive investigation is conducted. The test results demonstrate that the Correlation Dimension (CD), Normalized Information Entropy (NIE), and a proposed time-frequency index, the Maximum Approximate Coefficient of Wavelet transform (MACW), are the most reliable fault indicators. A neuro-fuzzy diagnosis system is then developed, where the strength of the aforementioned indices are integrated to provide a more robust assessment of a bearing’s health condition. Moreover, a prognosis scheme, based on the Adaptive Neuro Fuzzy Inference System (ANFIS), in combination with a set of logical rules, is proposed for estimating the next state of a bearing’s condition. Experimental results confirm the viability of forecasting health condition under different speeds and loads.
5

A Fault Diagnosis System for Rotary Machinery Supported by Rolling Element Bearings

Hasanzadeh Ghafari, Shahab January 2007 (has links)
The failure of rolling element bearings is one of the foremost causes of breakdown in rotary machinery. So far, a variety of vibration-based techniques have been developed to monitor the condition of bearings; however, the role of vibration behavior is rarely considered in the proposed techniques. This thesis presents an analytical study of a healthy rotor-bearing system to gain an understanding of the different categories of bearing vibration. In this study, a two degree-of-freedom model is employed, where the contacts between the rolling elements and races are considered to be nonlinear springs. The analytical investigations confirm that the nature of the inner ring oscillation depends on the internal clearance. A fault-free bearing with a small backlash exhibits periodic behavior; however, bearings categorized as having normal clearance oscillate chaotically. The results from the numerical simulations agree with those from the experiments confirming bearing’s chaotic response at various rotational speeds. Bearing faults generate periodic impacts which affect the chaotic behavior. This effect manifests itself in the phase plane, Poincare map, and chaotic quantifiers such as the Lyapunov exponent, correlation dimension, and information entropy. These quantifiers serve as useful indices for detecting bearing defects. To compare the sensitivity and robustness of chaotic indices with those of well-accepted fault detection techniques, a comprehensive investigation is conducted. The test results demonstrate that the Correlation Dimension (CD), Normalized Information Entropy (NIE), and a proposed time-frequency index, the Maximum Approximate Coefficient of Wavelet transform (MACW), are the most reliable fault indicators. A neuro-fuzzy diagnosis system is then developed, where the strength of the aforementioned indices are integrated to provide a more robust assessment of a bearing’s health condition. Moreover, a prognosis scheme, based on the Adaptive Neuro Fuzzy Inference System (ANFIS), in combination with a set of logical rules, is proposed for estimating the next state of a bearing’s condition. Experimental results confirm the viability of forecasting health condition under different speeds and loads.
6

Lift-off performance in flexure pivot pad and hybrid bearings

Mertz, David Hunter 15 May 2009 (has links)
Three flexure pivot pad bearings (FPBs) with different preloads are evaluated for use in high performance applications by comparing them to a hybrid hydrostatic bearing (HHB). One application of these bearings is in turbopumps for liquid rocket engines. To evaluate bearing performance, the lift-off speed of the shaft from the bearing surface is experimentally determined. Experimental data of lift-off are collected using a circuit running through the shaft and the designed bearing. Other methods for measuring liftoff speeds were attempted but did not yield consistent results. Water is used as a lubricant to simulate a low viscosity medium. In comparison to load-capacity-based predictions for FPBs, the experimental results showed lower lift-off speeds, higher load capacities, higher eccentricity ratios, and lower attitude angles. The bearings’ predicted load capacity determined lift-off speed predictions, but the experimental results show no clear trend relating lift-off speed to load capacity. This was for a range of running speeds, with the design speed defined as the final speed in a particular test case. At 0.689 bar supply pressure and for a design speed of 3000 rpm, the HHB showed greater load capacities and lower eccentricities than the FPBs, but the FPBs had lower lift-off speeds and attitude angles. In fact, the FPBs in the load-between-pad orientation outperformed the HHB in the load-on-pocket orientation with lower lift-off speeds for the shaft weight-only case. An increased supply pressure lowered the lift-off speeds in the HHB tests. If the load in the bearing application remains relatively small, a FPB could be substituted for an HHB.
7

High-speed performance of a hydrostatic thrust bearing

Ashman, D. January 1987 (has links)
The programme of research reported in this dissertation was undertaken with the aim of improving the high-speed performance of a multi-recessed hydrostatic thrust bearing. A theoretical analysis of the quasi-static behaviour and isothermal frictional power consumption is developed using the basic equations governing viscous fluid flow. The effects of high peripheral speeds are discussed and how recently proposed bearing modifications, in the form of grooved lands and changes in recess geometry, are used to reduce the frictional power consumption, lower operating temperatures, and reduce unwanted hydrodynamic and fluid inertia induced pressure variations. The steady state temperature distribution, frictional power consumption and operating clearance when one bearing member is rotating, and dynamic loading performance are predicted by several specially developed Fortran computer programs. One section concentrates on the design, development and instrumentation of an experimental multi-recessed hydrostatic thrust bearing, which had a facility for changing the pocket geometry using recess inserts. The bearing plate. which had an outside diameter of 200 mm, was operated at rotational speeds between 1000-5000 rpm to give peripheral speeds between 10.5 - 52.5 m/s. A chapter deals with an experimental investigation of the high-speed performance of a multi-recessed hydrostatic thrust bearing, principally the quasi-static loading and flow rate characteristics, temperature and pressure distributions and frictional power consumption. Furthermore, the dynamic response of the test bearing arrangement was investigated experimentally for a range of excitation frequencies between 0- 70 Hz- Finally, the theoretical predictions of characteristics such as quasi-static loading and flow rate, steady state operating conditions and dynamic response are compared with the corresponding experimental results.
8

Modelling and identification of dynamic characteristics of a squeeze-film bearing

Kucuk, N. C. January 1987 (has links)
No description available.
9

Mathematical modelling of vibrations in spindle bearing assemblies

Rahman, Aminur Khosru January 1998 (has links)
No description available.
10

Structure-property relations in some bearing alloys

Busby, A. K. January 1986 (has links)
No description available.

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