<p>A novel homopolar electrodynamic bearing, together with a suitable permanent magnet drive, have been developed for high-speed applications where low losses and high reliability are essential and exclude the use of ball bearings, and yet where active magnetic bearings offer a too complex system solution. Considered applications are small turbomolecular vacuum pumps, and maintenance free flywheels for energy storage in remote telecom and satellite systems. Other upcoming areas where these bearings offer interesting technical and economic solutions are compressors for fuel cells and heat pumps, applications which normally suffer from short bearing lifetime.</p><p>Unlike active magnetic bearings, forces are produced in electrodynamic bearings without any control electronics, thanks to stabilizing eddy currents induced by permanent magnets. In the novel homopolar concept eddy current losses are reduced to a minimum using a homopolar design with ring magnets instead of multipole or Halbach arrays.</p><p>Currents and forces are simulated using steady state 3D-FEM analysis, which can take velocity into account using an implemented Minkowski transform. From these results an analytical model has been developed, and the results are compared. The results are converted into useful rotordynamic data that is easily understood by machine engineers.</p><p>The bearing has been experimentally tested in a rebuilt turbomolecular vacuum pump up to 90,000 rpm. Bearing forces have been accurately measured on a specially designed spring suspended scales, in which the bearing rotor is powered with the permanent magnet drive. Comparison of measured data with results from the 3D-FEM analysis shows excellent agreement.</p>

A novel homopolar electrodynamic bearing, together with a suitable permanent magnet drive, have been developed for high-speed applications where low losses and high reliability are essential and exclude the use of ball bearings, and yet where active magnetic bearings offer a too complex system solution. Considered applications are small turbomolecular vacuum pumps, and maintenance free flywheels for energy storage in remote telecom and satellite systems. Other upcoming areas where these bearings offer interesting technical and economic solutions are compressors for fuel cells and heat pumps, applications which normally suffer from short bearing lifetime. Unlike active magnetic bearings, forces are produced in electrodynamic bearings without any control electronics, thanks to stabilizing eddy currents induced by permanent magnets. In the novel homopolar concept eddy current losses are reduced to a minimum using a homopolar design with ring magnets instead of multipole or Halbach arrays. Currents and forces are simulated using steady state 3D-FEM analysis, which can take velocity into account using an implemented Minkowski transform. From these results an analytical model has been developed, and the results are compared. The results are converted into useful rotordynamic data that is easily understood by machine engineers. The bearing has been experimentally tested in a rebuilt turbomolecular vacuum pump up to 90,000 rpm. Bearing forces have been accurately measured on a specially designed spring suspended scales, in which the bearing rotor is powered with the permanent magnet drive. Comparison of measured data with results from the 3D-FEM analysis shows excellent agreement. / QC 20101026

What is bearing management? It can be defined as follows¡G To achieve the best quality of the rotary machinery, the supervisor in charge shall possess the comprehensive knowledge, such as, to make the plan schedule and teamwork through the management method, to review the design and selection constantly, to do the problem analysis and the proper decision making in time. The purpose is to maintain the bearing in its good condition, and accordingly, to lower the emergency shut-down and man-power loss. At the year of 2011, CSC will encounter the strike of imbalanced structure of manpower caused by the trend of retirement. Since the consistent quality of maintenance is one of the enterprise¡¦s operation costs, and is also the foundation for the profit gaining and competition with others for survival, therefore, how to efficiently pass on and refine the technical expertise to cope with this foreseeable scenario becomes one the most importance challenges for CSC at this moment. To face the above-mentioned circumstances, the Plant Engineering & Maintenance Dept in CSC is determined to take up the bearing management as one of the crucial strategy. Some steps are adopted, such as, to set up the bearing seminars and establish the disciplinary knowledge through superior-subordinate communication and coordination, and meanwhile, to set up the benchmark to regulate the Bearing Consumption Rate (BCR), to regularly assess the use of bearing basing upon the tonnage of raw steel production, and then to execute the necessary methods to modify any possible problematic situation. The objective is clear, both in financial improvement and production efficiency. The target audiences of this research are from the members who completed the course in the seminars, they now also work as the front line personnel to facilitate in the field of bearing management. Meanwhile, some in-depth interviews with the maintenance superintendents are also applied. Some detections of the outcome are as follows¡G I. It is efficient to convey the bearing education and training via the events of bearing management. II. The support from the superintendent is the direct impact on the bearing management, and also is the vital factor to improve the efficiency. III. The content of curriculum for the training and education is another impact to the improvement of efficiency and success. IV. The lecturers must be qualified, capable and knowledgeable, and acknowledged by the fellow members. V. While the motive is clear and definite, the outcome can be much more enhanced. VI. Suitable location and environment with appropriate facilities are the basis requirement to set up the training program. According to the above-mentioned outcome, this research project has made some conclusions as suggested below¡G I. Staff of managerial level must fully support the bearing management and educational training. II. The empirical exemplification and the practical exercise are the main focus in the training progress, and shall also be the criterion as for the methodology in the other field of maintenance. III. To set a solid and objective goal to get a better result. IV. To set up an operational team to establish the task of the bearing maintenance training. V. The appropriate reward will be granted for any effective cases in the maintenance of bearing. VI. Launch the website of bearing maintenance, and broadly promote bearing maintenance and educational training via e-learning.

Many researchers have compared predicted stiffness and damping coefficients for tilting-pad journal bearings (TPJBs) to measurements. Most have found that direct damping is consistently overpredicted. The thrust of this research is to explain the difference between measured and predicted stiffness and damping coefficients for TPJBs, and to provide some confidence to designers that TPJB dynamic coefficients can be accurately predicted. Most analytical models for TPJBs are based on the assumption that explicit dependence on pad motion can be eliminated by assuming harmonic rotor motion such that the amplitude and phase of pad motions resulting from radial and transverse rotor motions are predicted by rotor-pad transfer functions. In short, these transfer functions specify the amplitude and phase of pad motion (angular, radial, translational, etc.) in response to an input rotor motion. A new pad perturbation model is developed including the effects of angular, radial, and circumferential pad motion and changes in pad clearance due to pad bending compliance. Though all of these pad variables have previously been included in different analyses, there are no publications containing perturbations of all four variables. In addition, previous researchers have only perturbed the journal, while both the bearing and journal motions are perturbed in the present analysis, and the applicability of comparing rotor-perturbed bearing impedance predictions to impedances measured on a bearing-perturbed test rig is discussed. This perturbation model was implemented in a Reynolds-based TPJB code to predict the frequency-dependent bearing impedances and rotor-pad transfer functions. Direct measurements of pad motion during test excitation were recorded to produce measured transfer functions between rotor and pad motion, and a comparison between these measurements and predictions is given. Motion probes were added to the loaded pad (having the static load vector directed through its pivot) of a 5-pad TPJB to obtain accurate measurement of pad radial and tangential motion, as well as tilt, yaw, and pitch. Strain gages were attached to the side of the loaded pad to measure static and dynamic bending strains, which were then used to determine static and dynamic changes in pad curvature (pad clearance). Good agreement was found between the amplitude of the measured and predicted transfer functions concerning radial and transverse pad motions throughout the range of speeds and loads tested, while pad tilt was moderately underpredicted. For the bearing investigated, radial pad motions resulting from pivot compliance were as large as 60% of the radial component of shaft motion when operating at 4400 rpm under heavily loaded conditions. Hence, if a dynamic load applied to the shaft resulted in a shaft displacement of 25 microns (1 mil), the pad would displace radially 15 microns (0.6 mils), and the fluid film height would only decrease by 10 microns (0.4 mils). The consequence of this pad motion is that fluid film stiffness and damping forces produced by relative rotor-pad motions are significantly reduced, resulting in a bearing having significantly less direct stiffness and damping than predicted. A similar effect occurs when shaft motions produce significant changes in pad clearance due to pad compliance. For the pad tested here, the measurements show that predicting TPJB stiffness and damping coefficients without accounting for pad and pivot compliance will produce large errors, and is not advised. Transverse pad motion was predicted and observed. Based on phase measurements, this motion is lightly damped, and appears to be caused by pivot deflection instead of slipping. Despite observing a lightly damped phase change, an increase in magnitude at this natural frequency was not observed. Predicted direct stiffness and damping for unit loads from 0-3200 kPa (0-450 psi) fit through 1.5× running speed are within 18% of measurements at 4400 rpm, while predictions at 10200 rpm are within 10% of measurements. This is a significant improvement on the accuracy of predictions cited in literature. Comparisons between predictions from the developed bearing model neglecting pad, pivot, and pad and pivot flexibility show that predicted direct stiffness and damping coefficients for a model having a rigid pad and pivot are overestimated, respectively, by 202% and 811% at low speeds and large loads, by 176% and 513% at high speeds and high loads, and by 51% and 182% at high speeds and light loads. While the reader is likely questioning the degree to which these predictions are overestimated in regard to previous comparisons, these predictions are based on measured operating bearing clearances, which are 20-30% smaller than the cold bearing clearances that previous comparisons were based on. The effect of employing a full bearing model (retaining all of the pad degrees of freedom) versus a reduced bearing model (where only journal degrees of freedom are retained) in a stability calculation for a realistic rotor-bearing system is assessed. For the bearing tested, the bearing coefficients reduced at the frequency of the unstable eigenvalue (subsynchronously reduced) predicted a destabilizing cross-coupled stiffness coefficient at the onset of instability within 1% of the full model, while synchronously reduced coefficients for the lightly loaded bearing required 25% more destabilizing cross-coupled stiffness than the full model to cause system instability. This overestimation of stability is due to an increase in predicted direct damping at the synchronous frequency over the subsynchronously reduced value. This increase in direct damping with excitation frequency was also seen in highly loaded test data at frequencies below approximately 2×running speed, after which direct damping decreased with increasing excitation frequency. This effect was more pronounced in predictions, occurring at all load and speed combinations. The same stability calculation was performed using measured stiffness and damping coefficients at synchronous and subsynchronous frequencies at 10200 rpm. It was found that both the synchronously measured stiffness and damping and predictions using the full bearing model were more conservative than the model using subsynchronously measured stiffness and damping. This outcome contrasts with the comparison between models using synchronously and subsynchronously reduced impedance predictions, which showed the subsynchronously reduced model to be the most conservative. This contrast results from a predicted increase in damping with increasing excitation frequency at all speeds and loads, while this increase in damping with increasing excitation frequency was only measured at the most heavily loaded conditions.

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Gas bearings in oil-free micro-turbomachinery for process gas applications and for power generation (< 400 kW) must offer adequate load capacity and thermal stability, reliable rotordynamic performance at high speeds and temperatures, low power losses and minimal maintenance costs. The metal mesh foil bearing (MMFB) is a promising foil bearing technology offering inexpensive manufacturing cost, large inherent material energy dissipation mechanism, and custom-tailored stiffness and damping properties. This dissertation presents predictions and measurements of the dynamic forced performance of various high speed and high temperature MMFBs. MMFB forced performance depends mainly on its elastic support structure, consisting of arcuate metal mesh pads and a smooth top foil. The analysis models the top foil as a 2D finite element (FE) shell supported uniformly by a metal mesh under-layer. The solution of the structural FE model coupled with a gas film model, governed by the Reynolds equation, delivers the pressure distribution over the top foil and thus the load reaction. A perturbation analysis further renders the dynamic stiffness and damping coefficients for the bearing. The static and dynamic performance predictions are validated against limited published experimental data. A one-to-one comparison of the static and dynamic forced performance characteristics of a MMFB against a Generation I bump foil bearing (BFB) of similar size, with a slenderness ratio L/D=1.04, showcases the comparative performance of MMFB against a commercially available gas foil bearing design. The measurements of rotor lift-off speed and drag friction at start-up and airborne conditions are conducted for rotor speeds up to 70 krpm and under identical specific loads (W/LD =0.06 to 0.26 bar). The dynamic force coefficients of the bearings are estimated, in a ‘floating bearing’ type test rig, while floating atop a journal spinning to speeds as high as 50 krpm and with controlled static loads (22 N) applied in the vertical direction. The parameter identification is conducted in the frequency range of 200-400 Hz first, and then up to 600 Hz using higher load capacity shakers. A finite element rotordynamic program (XLTRC2) models a hollow rotor and two MMFBs supporting it and predict the synchronous rotor response for known imbalances. The predictions agree well with the ambient temperature rotor response measurements. Extensive rotor response measurements and rotor and bearing temperature measurements, with a coil heater warming up to 200 ºC and placed inside the hollow rotor, reveal the importance of adequate thermal management. The database of high speed high temperature performance measurements and the development of a predictive tool will aid in the design and deployment of MMFBs in commercial high-speed turbomachinery. The work presented in the dissertation is a cornerstone for future analytical developments and further testing of practical MMFBs.

Machines operating in dusty environments, such as mining and civil works, are prone to premature failure, leading to production losses. To address this problem, this research project examines the interaction between solid contaminants and the bearing micro-geometry, in lubricated surface contacts. In particular, it seeks to identify anti-wear additives that are effective in reducing wear under abrasive conditions, making machine elements more dirt tolerant. In general, the influence of antiwear additive is so small that it is difficult to isolate it. Manufactures often make claims about their antiwear products, which are difficult to verify. Hence, there is a need to characterising the antiwear additives available with a well-defined parameter, making it easier for consumers to compare the efficacy of various additives, and be able to select the most suitable additive for a given environment. Effect of micro-geometry parameters such as radial clearance, out-of-roughness and surface roughness was examined and a Film Shape Factor (FSF) – also termed gamma ratio – has been proposed for ensuring adequate separation of journal bearings operating in hydrodynamic lubrication regime, where the out-of-roundness values are higher than the surface roughness values. In this research, an experimental study has been conducted on journal bearings, to examine the influence of five antiwear additives on the bearing wear and micro-geometry. The test additives were provided by the industry partner without revealing their chemical identity or composition; however, these included some of the most commonly used antiwear additives. The tests were performed under three conditions: pure base oil, base oil containing contaminants, and base oil containing contaminants treated with five different additives. The experiments were aimed at choosing one wear measuring technique that evaluates the performance of an individual additive reliably, and based on this technique the additives were characterised. To achieve these objectives, a multi-wear parameter approach (MWPA) was developed, which employed three main wear measurement methodologies, i.e. weight loss, micro-geometry and particle counts –to examine the effect of the antiwear additives. Minimum oil film thickness was also measured to study the lubrication status in the bearing contacts. The MWPA helped in comparing different wear measuring methods, and in selecting the most reliable one. This approach also helped in developing short duration wear tests, thereby saving time, while still getting reliable results without repeating these. Wear experiments were performed on seven sets of bronze bearings and steel sleeve shafts. The test contaminant was 16 micron Aluminium oxide Al2O3 powder mixed in oil with 4% concentration by weight. These solid contaminants were treated with five different antiwear additives to study their influence on the bearings. Bearings were operated such that the minimum oil film thickness in the bearing was equal to the size of the contaminants. These tests were run for a constant sliding distance of 7536m. The results showed that most of the wear measuring techniques do not suit heavily contaminated test conditions. However, the out-of-roundness technique proved to be the most reliable and practical. Based on this technique a methodology was developed which gave a wear characteristic number (N). A unique value of N can be derived for each additive, thereby ranking the additives for their efficacy. The finding of this research provides a better understanding of the methodologies used for measuring wear in journal bearings subjected to dusty environments, and examines the efficacy of each one of these. The wear characteristic number (N) can be used by manufacturers with support from international standards organisations, so that the users can confidently choose the most appropriate antiwear additive for their application. Machines operating in a dusty environment, such as mining industry and civil works are prone to premature failure with subsequent production losses. In response to this problem, this research project examines the interaction between solid contaminant particles and the lubricant film micro-geometry in lubricated surface contacts. In particular, it seeks to identify lubricant anti-wear additives, which are effective in reducing wear under abrasive conditions and thus making machine elements more dirt tolerant.

There has been little attention to the question as to whom the NT documents speak of as being actively involved in declaring God among the nations, although some scholars recently have paid heed to this theme in the Pauline letters. Also, scholarly work on the question has generally not been carried out in the light of verbal declaration by God's people in the OT, because there is a prevailing idea among scholars that missionary proclamation by God's people simply is not found in the OT. With these in mind, our study first explores whether the OT does or does not deal with verbal declaration by God's people for the sake of leading the nations to him. This leads us to find that some OT passages do indeed concern missionary proclamation by God's people among the nations. Thereafter, our study examines the motif of verbal declaration by the Church in the NT. We focus on the identity of those who are verbal declarers among the nations, considering the relationship between verbal declaration by God's people in the OT and the same by the Church in the NT. Our study argues that, in the identified NT passages, verbal declaration by believers is portrayed in line with the treatment of the same theme, concerning the faithful Israel, in OT documents and that it is believers as a whole who are spoken of as declaring God among the nations for the purpose of bringing them to him.

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