Rozprawy doktorskie na temat „Lubricated journal bearings”

The provision of helical grooves on the surface of a plain journal bearing can improve the stability of a rotor-bearing system. However, the improvement depends on the arrangement of the grooves along the axial length of the bearing. In order to verify this improved stability three types of helical groove bearing and a reference plain journal bearing were investigated. The helical groove journal bearings were: a symmetrical, an asymmetrical and a partial grooved bearing. The bearing test rig was used to measure the oil flow rate, load carrying capacity, power losses, bearing surface temperatures, and stability characteristics. A theoretical model was developed to calculate the load carrying capacity, stiffness and damping coefficients, and stability characteristics of the various types of bearing. The experimental and theoretical results show that at the expense of a reduced load capacity the helical groove bearings are more stable particularly at low eccentricity ratios. However, the experimental observations showed that the partial helical groove bearing is not a practical bearing because the bearing becomes misaligned above certain load. For a given eccentricity ratio and speed the symmetrical bearing ran hotter and with greater power losses in comparison to the other three bearings. At the same eccentricity ratio and speed, the asymmetrical bearing ran at about the same temperature as the plain journal bearing.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2000.
Includes bibliographical references (p. 203-208).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Numerical simulations of gas-lubricated journal bearings for microfabricated machines are performed with specialized tools. To maximize flexibility, an orbit method formulation is chosen for the primary tool. Its pseudospectral fluid equation solver enables run-time resolution adjustment while maintaining the efficiency advantage of spectral methods. A design framework is established for microfabricated bearings, including several new charts that reflect the unique constraints of MEMS. A duality between applied load and imbalance level is demonstrated and a method for experimentally determining appropriate loads for unknown imbalance is suggested. A large-amplitude whirling mode is shown to exist on both sides of the fixed-point threshold speed, in agreement with experimental observation. A quasi-static method for calculating shock tolerance is suggested and evaluated against unsteady simulations. Simulations of loads applied via non-circumferentially-uniform pressure at the bearing end are shown to increase the attitude angle and decrease the allowable nondimensional mass compared to the equivalent gravity-loaded case. Furthermore, the associated axial pressure gradients are shown to produce a hydrostatic stiffness via inertial effects. A nondimensional model is constructed for this stiffness and its dependence on various parameters is studied. It is shown that the load capacity advantage reported in the literature for noncircular bearings can be canceled by microfabrication constraints. The stability advantage, however, survives. Tapered axial clearance is shown to have an extremely deleterious effect on performance while bowed clearance proves less detrimental. Navier-Stokes solutions of infinite-length bearings with unity inertial parameters are performed using a second specially-built tool. Little change is found in the steady-state results from inertial and curvature effects in the MIT microengine’s parameter space.
by Edward Stanley Piekos.
Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 439-441).
The outboard bearings that support shafts in naval ships and submarines present unique challenges to designers, shipbuilders, and operators. Such bearings must operate continuously and reliably in demanding environments at speeds that vary from below 1 rpm to well over 100 rpm. Water-lubricated bearings typically used for these applications operate hydrodynamically and are prone to adverse effects at lower speeds such as increased abrasive and adhesive wear as well as stick-slip shaft motion. This project focuses on developing a hybrid journal bearing capable of operating with hydrostatic pump pressure at lower rpm, while still maintaining the capability for hydrodynamic operation at higher rpm. Benefits of such a system include extending the periodicity between outboard bearing replacements, less abrasion and scoring damage to the propulsion shaft, and preventing stick-slip shaft motion. To enable the in-water replacement of bearings without removal of the propulsion shaft, a partial arc (<180 degree wrap) configuration is required. This partial arc constraint introduces several unique manufacturing difficulties. To address this, a novel manufacturing process has been developed that enables the rapid fabrication of high precision bearings with diameter and roundness errors of less than 0.001" (25.4 microns) on a nominal diameter of 3.24" as measured with a Coordinate Measuring Machine - greatly exceeding the published tolerances of conventional methods. A unique experimental test rig was designed and built in order to measure the performance of 15 different prototype bearing designs. The rig is capable of submerged bearing testing in both hydrostatic and hydrodynamic modes of operation, with fundamental parameters such as speed, torque, loads, pressures, flow rates, and shaft position recorded. The operating characteristics of the bearings were then analyzed to identify key features and variables affecting bearing performance. Certain bearing designs were found to be inherently stable for side loading conditions, without the use of compensation typically used in hydrostatic bearings. This finding led to bearings designed with simplified hydrostatic features and fluid supply systems. Such designs were found to have minimal degradation in hydrodynamic performance, making them particularly suitable for use as hybrid bearings. The key design drivers identified in this work are combined with ancillary factors to discuss the feasibility of hybrid bearings for use in marine applications.
by Brian Douglas Heberley.
Ph.D.

Extensive research has been conducted in the area of journal bearings over many years for various operating conditions and geometry, effects of different types of lubricants (oil and water), different numbers (zero, one and three) and positions of grooves and the flow of lubricant between the shaft and bearing. One area of research has been developing methods to minimize the experimental time and cost of predicting the performance of journal bearings operating over a wide variety of conditions. This has led to numerical methods being developed and utilised for this purpose. Numerical methods are an important foundation for the development of Computational Fluid Dynamics (CFD). CFD method has proved to be a very useful tool in this research field. This project uses a CFD (specifically FLUENT) approach to simulate the fluid flow in a water lubricated journal bearing with equal spaced axial grooves. Water is fed into the bearing from one end. The lubricant is subjected to a velocity induced flow, as the shaft rotates and a pressure induced flow, as the water is pumped from one end of the bearing to the other. CFD software is used to simulate the fluid flow phenomenon that occurs during the process. Different parameters such as eccentricity ratio, number of grooves and groove orientation to the load line were examined. Lubricant pressure and velocity profiles were obtained and compared with available theoretical and experimental results. Two dimensional studies showed that the predicted maximum pressure and load carrying capacity from CFD were similar to the results from theoretical calculations. A small percentage difference (1.78% - 3.76%) between experimental and theoretical results was found. The pressure distribution in the lubricant shows that grooves decrease the pressure and load carrying capacity of the bearing. Swirl or turbulence does occur in the groove is affected by the viscosity of the lubricant. Three dimensional studies show that the pressure drops linearly from one end of the bearing to the other for no groove, concentric and three grooves cases. As the eccentricity increases, for one groove cases, the shape of the pressure profile changes to parabolic shape at positive region while the other pressure profiles drop linearly. The magnitude of the velocity it the bearing gap increased from 0.8 m/s to about 2.9 m/s when the shaft speed increased from zero to 5.5 m/s for a concentric and no groove case, similar changes were noted for all other cases. An interesting observation occurs when implementing the pressure profiles along the bearing. At cases such as zero and one groove condition and e = 0.4 and 0.6, lubricant flow back is observed at both inlet and outlet i.e. at certain area of the inlet, lubricant flowed out of the bearing against the supply pressure, a similar situation occurred at the exit of the bearing.

Extensive research has been conducted in the area of journal bearings over many years for various operating conditions and geometry, effects of different types of lubricants (oil and water), different numbers (zero, one and three) and positions of grooves and the flow of lubricant between the shaft and bearing. One area of research has been developing methods to minimize the experimental time and cost of predicting the performance of journal bearings operating over a wide variety of conditions. This has led to numerical methods being developed and utilised for this purpose. Numerical methods are an important foundation for the development of Computational Fluid Dynamics (CFD). CFD method has proved to be a very useful tool in this research field. This project uses a CFD (specifically FLUENT) approach to simulate the fluid flow in a water lubricated journal bearing with equal spaced axial grooves. Water is fed into the bearing from one end. The lubricant is subjected to a velocity induced flow, as the shaft rotates and a pressure induced flow, as the water is pumped from one end of the bearing to the other. CFD software is used to simulate the fluid flow phenomenon that occurs during the process. Different parameters such as eccentricity ratio, number of grooves and groove orientation to the load line were examined. Lubricant pressure and velocity profiles were obtained and compared with available theoretical and experimental results. Two dimensional studies showed that the predicted maximum pressure and load carrying capacity from CFD were similar to the results from theoretical calculations. A small percentage difference (1.78% - 3.76%) between experimental and theoretical results was found. The pressure distribution in the lubricant shows that grooves decrease the pressure and load carrying capacity of the bearing. Swirl or turbulence does occur in the groove is affected by the viscosity of the lubricant. Three dimensional studies show that the pressure drops linearly from one end of the bearing to the other for no groove, concentric and three grooves cases. As the eccentricity increases, for one groove cases, the shape of the pressure profile changes to parabolic shape at positive region while the other pressure profiles drop linearly. The magnitude of the velocity it the bearing gap increased from 0.8 m/s to about 2.9 m/s when the shaft speed increased from zero to 5.5 m/s for a concentric and no groove case, similar changes were noted for all other cases. An interesting observation occurs when implementing the pressure profiles along the bearing. At cases such as zero and one groove condition and e = 0.4 and 0.6, lubricant flow back is observed at both inlet and outlet i.e. at certain area of the inlet, lubricant flowed out of the bearing against the supply pressure, a similar situation occurred at the exit of the bearing.

Des études internes à Liebherr-Aerospace France, concernant la conception de nouveaux compresseurs lubrifiés par gaz réfrigérant, ont montré que dans des conditions de fonctionnement spécifiques, un mélange de vapeur et de liquide apparaît au sein du compresseur, au lieu d'une phase vapeur seule. De ce fait, le comportement des paliers à feuilles lubrifiés au gaz réfrigérant est étudié, y compris la possibilité d'un écoulement diphasique du lubrifiant. L'étude porte sur le comportement du lubrifiant uniquement, dans des conditions de fonctionnement qui sont celles des paliers à feuilles. L'approche Thermo-Hydrodynamique décrit les caractéristiques du lubrifiant telles que la pression, la densité, la viscosité et la température. Dans ce modèle, une équation de Reynolds généralisée pour écoulement turbulent, une équation d'état non-linéaire pour écoulement diphasique et une équation de l'énergie tridimensionnelle pour film-mince et écoulement turbulent sont utilisées. Les paramètres globaux du palier sont calculés en régime permanent
Internal experiments at Liebherr-Aerospace FRANCE on new refrigerant-lubricated compressor designs have shown that under specific operating conditions, a mixture of vapor and liquid appears in the compressor, instead of a single-phase vapor flow. Therefore, refrigerant-lubricated foil bearings behavior is studied, including the likelihood of two-phase flow in the lubricant. We focus on the lubricant behavior only, in the operating conditions of foil bearings. The Thermo-Hydrodynamic approach describes lubricant characteristics such as pressure, density, viscosity, and temperature. It involves the use of a generalized Reynolds equation for turbulent flow, a nonlinear cubic equation of state for two-phase flow and a 3D turbulent thin-film energy equation. Journal bearing global parameters are calculated for steady-state conditions

CIVINS
The outboard bearings that support shafts in naval ships and submarines present unique challenges to designers, shipbuilders, and operators. Such bearing must operate continuously and reliably in demanding environments at speeds that vary from below 1 rpm to well over 100 rpm. Water-lubricated bearings typically used for these applications operate hydrodynamically and are prone to adverse effects at lower speeds such as increased abrasive and adhesive wear as well as stick-slip shaft motion. This project focuses on developing a hybrid journal bearing capable of operating with hydrostatic pump pressure at lower rpm, while still maintaining the capability for hydrodynamic operation at higher rpm. Benefits of such a system include extending the periodicity between outboard bearing replacements, less abrasion and scoring damage to the propulsion shaft and preventing stick-slip shaft motion. To enable the in-water replacement of bearings without removal of the propulsion shaft, a partial arc (<180 degree wrap) configuration is required. This partial arc constraint introduces several unique manufacturing difficulties. To address this, a novel manufacturing process has been developed that enables the rapid fabrication of high precision bearings with diameter and roundness errors of less that 0.001" (25.4 microns) on a normal diameter of 3.24" as measured with a Coordinate Measuring Machine - greatly exceeding the published tolerances of conventional methods. A unique experimental test rig was designed and built in order to measure the performance of 15 different prototype bearing designs. The rig is capable of submerged bearing testing in both hydrostatic and hydrodynamic modes of operation, with funddamental parameters such as speed, torque, loads, pressures, flow rates, and shaft position recorded. The operating characteristics of the bearing were then analyzed to identify key features and variables affecting bearing performance. Certain bearing designs were found to be inherently stable for side loading conditions, without the use of compensation typically used in hydrostatic bearings. This finding led to bearing designed with simplified hydrostatic features and fluid supply systems. Such designs wre found to have minimal degradation in hydrodynamic performance, making them particularly suitable for use as hybrid bearings. The key design drivers identified in this work are combined with ancillary factors to discuss the feasiblity of hybrid bearings for use in marine applications.

Grease-lubricated journal bearings are widely used in heavy duty applications, such as construction equipment, agriculture- and forest machines. The main purpose of the grease-lubricated journal bearing is solely to create sustainable rotation of a given application. However, purpose seldom decides complexity of journal bearing design. Depending on application, parameters such as Load , Material  and Lubrication immensely increase complexity of the design. Tribology is a highly interdisciplinary subject, which requires knowledge concerning physics, chemistry, metallurgy and solid mechanics. Tribological aspects of a design are frequently regarded as irrelevant. Tribological issues are commonly enlightened in combination with structural design weaknesses. The main aim of the thesis was to analyze two cylinder joints found in a Komatsu Forest 951 crane and establish root cause to the structural and tribological issues. Outline of the approach was divided into three main targets: 1. Investigate mechanical and tribological aspects of the crane design. 2. Understand how these aspects influence the life time of the bearings. 3. Summarize the analysis and suggest improvements based on the discovery. Fundamental structural and tribological design guidelines regarding grease-lubricated journal bearings have been presented in this thesis. Damaged components such as cylinders, pins and journal bearings have been examined at Komatsu Forest’s factory in Umeå. Further, a scanning electron microscopy study has been done at Luleå University of Technology, to determine predominant wear mechanisms in the harvester crane joints. A non-linear finite element model of the crane has been designed to represent pressure distribution in the contact between bearing and pin. The finite element analysis gives a good approximation of the contact but leaves room for further refinements. Temperatures, in the contacts, have not been identified and will be measured outside the time frame of the master’s thesis. Design changes, with respect to discovered structural and tribological issues have been suggested. The suggested improvements can potentially increase the life time of lift cylinders, pins and journal bearings.

碩士
國立中興大學
機械工程學系
90
Abstract This paper applies Reynolds equation to analyze the lubrication performance of the journal bearing. Darcy's law is used to describe the pressure distribution of the porous media. A nonlinear coupled equation are then used to analyze the characteristics of the porous journal bearings Three dimensionless parameters, namely, the permeability factor K, the bearing numberΛ, and the eccentricity ratioε,are employed to characterize the bearing performance. The results of the compressible air bearing compared with that of the equivalent incompressible bearing are proposed in this analysis. The results show that the positive pressure solutions are uniformly distributed on the bearing surface of the porous air-lubricated journal bearing. The loading capacity of the porous air bearings is lower than that of an equivalent incompressible bearing. The attitude angles of the porous air-lubricated bearing appear to be a constant value as the loads of the air bearing vary. The pressure distributions and hence the loading capacity of the porous air-lubricated bearings increase when low permeability of the porous media and high rotational speed of the bearing are used.

Indiana University-Purdue University Indianapolis (IUPUI)
This thesis concentrates on the study of hybrid gas journal bearings (bearings with externally pressurized mass addition). It differs from most work in that it goes back to “basics” to explore the hydrodynamic phenomena in the bearing gap. The thesis compares geometrically identical bearings with 2 configurations of external pressurization, porous liners where mass-addition compensation is varied by varying the liner’s permeability, and bushings with 2 rows of 6 feedholes where the mass-addition compensation is varied by the feedhole diameter. Experimentally, prototype bearings with mass-addition compensation that spans 2 orders of magnitude with differing clearances are built and their aerostatic properties and mass addition characteristics are thoroughly tested. The fundamental equations for compressible, laminar, Poiseuille flow are used to suggest how the mass flow “compensation” should be mathematically modeled. This is back-checked against the experimental mass flow measurements and is used to determine a mass-addition compensation parameter (called Kmeas) for each prototype bushing. In so doing, the methodology of modeling and measuring the mass addition in a hybrid gas bearing is re-examined and an innovative, practical, and simple method is found that makes it possible to make an “apples-to-apples” comparison between different configurations of external pressurization. This mass addition model is used in conjunction with the Reynolds equation to perform theory-based numerical analysis of virtual hybrid gas journal bearings (CFD experiments). The first CFD experiments performed use virtual bearings modeled to be identical to the experimental prototypes and replicate the experimental work. The results are compared and the CFD model is validated. The ontological significance of appropriate dimensionless similitude parameters is re-examined and a, previously lacking, complete set of similitude factors is found for hybrid bearings. A new practical method is developed to study in unprecedented detail the aerostatic component of the hybrid bearings. It is used to definitively compare the feedhole bearings to the porous liner bearings. The hydrostatic bearing efficiency (HBE) is defined and it is determined that the maximum achievable hydrostatic bearing efficiency (MAHBE) is determined solely by the bearing’s mass addition configuration. The MAHBE of the porous liner bearings is determined to be over 5 times that of the feedhole bearings. The method also presents a means to tune the Kmeas to the clearance to achieve the MAHBE as well as giving a complete mapping of the hitherto misunderstood complex shapes of aerostatic load versus radial deflection curves. This method also rediscovers the obscure phenomenon of static instability which is called in this thesis the “near surface effect” and appears to be the first work to present a practical method to predict the range of static instability and quantify its resultant stiffness fall-off. It determines that porous liner type bearings are not subject to the phenomenon which appears for feedhole type bearings when the clearance exceeds a critical value relative to its mass-addition compensation. The standing pressure waves of hydrostatic and hybrid bearings with the 2 configurations of external pressurization as well as a geometrically identical hydrodynamic bearing are studied in detail under the methodology of the “CFD microscope”. This method is used to characterize and identify the development, growth, and movement of the pressure wave extrema with increased hydrodynamic action (either increasing speed or increasing eccentricity). This method is also used to determine the “cause” of the “near surface effect”. A gedanken experiment is performed based on these results which indicates that a bearing with a “stronger aerostatic strength” component should be more stable than one with a low aerostatic strength component. Numerical instability “speed limits” are found that are also related to the hydrostatic strength of the bearing. The local conditions in the standing waves are characterized in terms of their local Mach number, Knudsen number, Reynolds number, and Taylor Number. It is concluded that low eccentricity bearing whirl can be attributed to the off load-line orientation of the bearing load force caused by the overlay of the hydrodynamic bearing standing wave onto the hydrostatic bearing wave of the hybrid bearing, whereas it is hypothesized that aperiodic and random self-excited vibration which occurs at high eccentricity, as reported in the literature, is probably due to shock waves, turbulence, near surface effect, and slip at local areas of the standing wave.

碩士
國立中興大學
機械工程學系
92
This paper analyze the lubrication performance of surrounding oil supply porous journal bearings. Reynolds equation is used to describe the lubrication performance of journal bearing. Darcy’s law is used to describe the pressure distribution inside the porous media. These two coupled equations and applied Reynolds condition are then used to analyze the characteristics of the surrounding oil supply porous journal bearings. This paper analyze the performance of infinite long surrounding oil supply porous bearing by three dimensionless parameters ( the permeability ratio K，the bearing number ，the eccentricity ratio ) which are employed to characterize the bearing performance. The result shows that : porous media have the effect of regulating the pressure between the bearing and porous media，and the rupture point will decrease by the increase of permeability ratio of the porous madia，but increase by the increase of bearing number and the eccentrically ratio.

碩士
中華大學
機械工程學系碩士在職專班
101
This thesis studies the characteristics of hydrostatic bearings lubricating with ferrofluid. The multi-pocket capillary compensated bearings has been studied to simulate lubricant film and to determine the influences of magnetic field, magnetic fluid, couple stress parameters, restrictor and geometry and physical parameters of bearing on the static and dynamic performances and stability of a rotor-bearing system. The modified Reynolds equation is developed by using Stoke couple stress fluid theory as well as Jenkins model. The Reynolds equation is split into the zero-th and first order equations by the method of perturbation. A finite difference method is introduced to solve the zero-th equation for the static pressure and the first order equations for the dynamic pressure distributions of the hydrostatic journal bearing. Static analyses determine the static pressure distribution, load capacity, flow rate and friction coefficient, and dynamic analyses determine the stiffness and damping coefficients. In advance, stability maps of a rotor-bearing system are determined by Routh-Hurwitz method.

碩士
中原大學
機械工程研究所
102
Nowadays, the fluid fluid-lubricated bearings applying in the rotating machines are very widespread. However, these rotor interaction systems need to consider the instability phenomena induced by the lubricated fluid, such as the fluid whirl and fluid whip. The fluid-induced self-excited vibrations of rotor will make the journal rubbing or striking to bearing and may demand the machine parts. By these lights, the research proposed a solution to chance and promote the frequencies of fluid-induced self-excited vibrations by a ferrofluid and an additional magnetic field to avoid the rotating machine operating in the resonance frequencies. In this research, we have established a fluid-dynamic bearing rotor test platform. The system uses the ferrofluid to replace traditional bearing lubricant fluid and provide different types of magnetic fields by the permanent magnets in the outside of bearing to change the lubricated viscously of ferrofluid. From the analyzing results of the different magnetic directions and the corresponding experimental results in the oil bearing system showed that the resonance frequencies of fluid whirl and fluid whip of the oil bearing system had been changed. The experimental results also showed that the magnetic field built by eight has the best performance in these proposed magnetic fields. It can promote the he instability threshold speed of the test system from 3024 RPM to 4480 RPM.

碩士
崑山科技大學
機械工程研究所
101
This study analyzes the tribological performance of the test results of the journal bearing wear tester designed for the simulation of the toggle pin motion in the plastics injection molding machine. The tests were divided into two parts. The first part was to find the optimal operating condition combination among the selected test factors and levels by the Taguchi method. The second part was the durability test of two different kinds of grease. Results showed the optimal operating combination of the selected factors from the tribological viewpoint is valid and can reduce the coefficient of friction to the minimum in the confirmation test. Grease with or without the addition of nano-diamond particles were all tested in the durability tests. It showed that the nano-diamond particles can effectively extend the life of grease in the reciprocating heavy-load and low-speed journal bearing tests. The optimum grease change period can be successfully determined by the Hilbert-Huang Transform (HHT) and fractal analysis. The grease needs to be changed if the fractal dimensional parameter varies with large amplitude on the first IMF (Intrinsic Mode Function) of EMD (Emperical Mode Decomposition) after the HHT of the vibration signals.