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1
Al, Jughaiman Bader K. "Static and dynamic characteristics for a two-axial-groove bearing and a pressure-dam bearing." [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1816.
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Gunduz, Aydin. "Multi-Dimensional Stiffness Characteristics of Double Row Angular Contact Ball Bearings and Their Role in Influencing Vibration Modes." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1326397623.
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Swanson, Erik Evan. "Design and Evaluation of an Automated Experimental Test Rig for Determination of the Dynamic Characteristics of Fluid-Film Bearings." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30727.
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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
Skjæret, Nina. "Weight-bearing characteristics during standing in adults with Cerebral Palsy." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for bevegelsesvitenskap, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-13165.
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Aim: The aim of this study was to investigate weight-bearing characteristics in young adults with CP compared to young healthy adults in both quiet and relaxed standing. Methods: Two standing conditions were tested, one minute quiet standing (QS) and one minute relaxed standing (RS) in both groups. Data were collected with two Kistler force plates and a video camera. Weight-bearing asymmetries, shifts in weight bearing and CoP movements under each foot were calculated in Matlab, and PSAW Statistics was used for statistical analysis. Results: There were large individual differences in weight bearing characteristics between feet in both CP participants and control participants. In the QS condition, the CP group had equal weight on both feet in average across the trial, a trend towards a higher asymmetrical weight bearing index (p=.08), and larger movements of CoP under each foot than the control participants. In the RS condition, the CP group had no difference in weight bearing between the feet, more shifts in weight bearing in the form of steps, and less asymmetrical weight bearing index than the control group. Also, the CP participants had more CoP movements on their non-affected side than the controls had on their dominant side, and less CoP movements on their affected side than the controls had on their non-dominant side. Conclusion: CP participants have several different strategies for maintaining upright standing posture, varying from largely relying on their non-affected side for weight support, to standing almost symmetrical, to supporting more weight on their affected leg. Even though CP participants have more asymmetrical weight bearing in quiet standing compared to controls, this is not the case in relaxed standing where controls are more asymmetrical. This study provides more insight into relaxed standing and the strategies CP patients use to maintain an upright standing posture. Future studies should investigate the prevalence of postural asymmetry in a larger sample of patients, for a longer period of time, and how possible findings can be used in treatment of this patient group. Key words: Cerebral palsy, quiet standing, relaxed standing, weight-bearing asymmetries, shifts in weight-bearing, center of pressure.
5
Guo, Jenq-Shan. "Characteristics of the nonlinear hysteresis loop for rotor-bearing instability." Case Western Reserve University School of Graduate Studies / OhioLINK, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=case1062688989.
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Kucuk, N. C. "Modelling and identification of dynamic characteristics of a squeeze-film bearing." Thesis, University of Strathclyde, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382252.
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Jones, Andrew Christopher. "An investigation of the performance characteristics of isothermal calorimeters." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264979.
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Erdemir, Ali. "A study of surface metallurgical characteristics of tin coated bearing steels." Diss., Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/20134.
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9
Ha, Duc Nhin. "The floating and dynamic characteristics of a squeeze-film air bearing." Thesis, Brunel University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422456.
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Sianaki, A. H. "Parametric identification of squeeze-film bearing characteristics : a continuous time approach." Thesis, University of Edinburgh, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.661888.
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Gebretsadik, Daniel Woldegebriel. "Tribological characteristics of some multi-layered Pb-free engine bearing materials." Doctoral thesis, Luleå tekniska universitet, Maskinelement, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-62495.
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Lead (Pb) containing alloys such as white metals and Cu-Pb-Sn (lining) with Pb-based overlay plating have been extensively used as materials for internal combustion engine bearings during the last several decades. However, owing to environmental and health concerns, the use of Pb containing materials in automotive engine components is being restricted. In view of this, attempts are under way to develop and replace Pb-containing materials with Pb–free bearing materials. The tribological characteristics of these recently developed Pb-free bearing materials have, however, not been fully investigated and only a limited results about their tribological performance are available in open literature. This thesis therefore focuses on investigating the tribological performance of some recently developed Pb-free engine bearing materials. Although engine bearings are designed to operate in full film lubrication conditions yet they also operate in mixed and boundary lubrication regimes where the material properties do affect their tribological performance. There is thus a need to study the tribological behaviour of these new Pb-free bearing materials in mixed and boundary lubrication conditions vis a vis that of conventional Pb-containing bearing linings and overlays. This work has therefore aimed at investigating the tribological characteristics such as friction and wear, seizure behaviour, interaction with different oil formulations and embeddability behaviour of some selected Pb-free engine bearing materials. Friction and wear properties of Pb-free bearing materials Al-Sn based lining without overlay, bronze lining coated with Polyamide-Imide (PAI) based overlay containing MoS2 and graphite, bronze lining coated with Al-Sn based and PAI based overlay containing MoS2 and graphite, bronze lining coated with Sn-based overlay, and bismuth (Bi) containing bronze lining coated with Sn-based overlay have been studied using a block-on-ring test configuration under unidirectional sliding conditions in mixed and boundary lubrication regimes. The conventional Pb-containing bearing material was also studied as a reference material. Al-Sn based material showed considerably higher friction compared to the other bearing materials. The bearing material with PAI based overlay containing MoS2 and graphite showed superior friction and wear properties compared to all other materials. Sn-based overlay coated materials resulted in comparable friction and wear properties to that of Pbbased overlay. Wear mechanism in Al-Sn based material is mainly adhesive and abrasive in case of Sn based overlay. Seizure behaviour of the bearing materials were also studied using the block-on-ring test configuration in dry as well as lubricated conditions using pure base oil and a fully formulated engine oil. The PAI based overlay containing MoS2 and graphite showed no sign of seizure even at the highest test load in dry as well as lubricated conditions. Al-Sn based lining without overlay seizes at relatively lower load in dry condition compared to the other bearing materials. Adhesion or wear debris smearing onto the counter surface is the main causes of seizure in dry condition. In lubricated condition, seizure occurred at relatively higher load and the conventional Pb-containing material was found to have better seizure performance compared to the Al-Sn based and Sn-based overlay plated materials. Tribological compatibility of Pb-free bearing materials with different oil formulations was studied using a ball-on-bearing specimen test configuration in boundary lubrication under reciprocating sliding conditions. Four different bearing materials were investigated using different lubricants with and without oil additives. In general, the bearing materials lubricated with pure PAO base oil showed higher friction compared to those lubricated with oils containing additives. Lubricants containing additives improved wear properties of the bearing materials except in the case of Al-Sn based lining without overlay. It was also observed that the anti-wear additive level did not significantly influence the wear performance of bearing overlays. The embeddability behaviour of Pb-free bearing materials was studied using a fully formulated engine oil contaminated with SiC particles. Pb-free bearing materials with Snbased overlay, Bi-based overlay, PAI-based overlay containing MoS2 and composite overlay containing PAI, Al, PTFE were investigated. Tests at different rotational speeds (i.e. different oil film thickness) and a constant load were carried out using a journal bearing test rig. It was found that material removal from bearing and shaft surfaces due to abrasive wear is influenced by the lubricant film thickness. The steel counter surface showed lower wear in tests using Sn based overlay and a PAI, Al and PTFE containing composite overlay compared to Bi-based overlay and PAI-based overlay containing MoS2.
12
Gandra, Sachin. "The effect of reservoir characteristics on methane production from hydrate bearing formations." Morgantown, W. Va. : [West Virginia University Libraries], 2006. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4763.
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Thesis (M.S.)--West Virginia University, 2006.Title from document title page. Document formatted into pages; contains x, 72 p. : ill. (some col.), maps. Includes abstract. Includes bibliographical references (p. 69-72).
13
Smith, Andrew J. J. "Effects of Age on Knee Activation Characteristics during Weight Bearing and Directional Loading." Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/22718.
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We developed a novel approach that requires subjects to produce and finely tune ground reaction forces (GRFs) while standing. Using this method we were able to identify specific contributions of individual muscles and how these contributions change with the effects of age. One of the aims of this investigation was to determine whether electromyographic data in our findings was due to random muscle activation or representative of a neuromuscular control strategy. Ten healthy young adults (5 male, 5 female) with their dominant foot fixed within a boot mounted to a force platform participated twice in a target matching protocol, requiring subjects to control both the direction and magnitude of GRF along the horizontal plane while maintaining constant inferior-superior loads of 50% body-weight. Subjects were asked to manoeuvre a cursor with their dominant leg to match a series of targets projected on a screen. Targets appeared at random one at-a-time, separated by 30o around a circular trajectory. Subjects applied loads to the force platform in various horizontal directions to move the cursor while also controlling body weight. A successful target match required subjects to maintain 50% body weight and 30% of their peak horizontal load for one second. Electromyography (EMG) of eight muscles that cross the knee joint, ground reaction forces, and kinematic data were recorded for each successful match. EMG was normalized to percent maximum voluntary isometric contractions collected on an isokinetic dynamometer. Each target matching session was separated by two-three days. A random model, single measures intra-class correlation analysed the reliability for both test-retest and intra-day results, in addition to intersubject reliability. We observed moderate to high ICC values (0.60 – 0.993) for most muscles in most directions, indicating low within-subject variance. In addition, moderate to high between-subject reliability was observed in all eight muscle activation profiles, indicating subjects used similar neuromuscular control strategies to achieve the desired GRFs. Our findings support that groups who have undergone the same number of testing sessions can be compared, and that a single testing session is all that is required to compare neuromuscular control strategies used by a group to achieve target locations.
The second aim of this investigation was to evaluate age related differences in neuromuscular control about the knee joint using our target match protocol. Thirty-three healthy adults (17 younger 24 years ±2, 16 older 59 years ±5), completed the same protocol evaluated above. The mean magnitude of muscle activity, specificity index, and mean direction of muscle activity were calculated in each target direction. Older adults presented with significantly lower strength in knee flexion and extension, hip abduction, and ankle plantar flexion. Significantly (p<0.25) higher mean activation magnitudes in the rectus femoris, vastus lateralis, vastus medialis, biceps femoris, semitendinosus, medial gastrocnemius, and tensor facia lata were also observed. Intraclass correlations (ICC) magnitudes indicate the percentage of global variance that can be explained by within subject and between trial variability. Muscle activation patterns were found to be similar in all muscles (ICC≤0.82). Similar patterns are supported by non-significant differences in mean direction of activation and muscle activation specificity. These results indicated that healthy older adults utilise different activation magnitudes for stabilising the knee while maintain similar muscle activation synergies in all muscles to younger adults.
14
Prase, Björn. "Characteristics of hydrodynamic plain bearings with bonded coating." Technische Universität Chemnitz, 2018. https://monarch.qucosa.de/id/qucosa%3A21228.
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Increasing ecological and economic pressures, as well as increased technical requirements, have given rise to the need for research into alternative wear layers for hydrodynamic plain bearings. Previous investigations have tested and researched the bonded coating GL92. It has been possible to demonstrate that the bonded coating (plastic base) is a viable alternative to a conventional white metal alloy.
However, this coating was not able to address all the issues experienced by industrial users, for example the behaviour of the system (changes to operating properties) during penetration of particles, or behaviour in a mixed friction area. The literature has not – or not sufficiently – answered the questions relating to damage patterns and damage tolerance. Therefore, regardless of the proven benefits, industrial use of this coating is currently not possible or is connected with significant risks.
In the study, tests were carried out in the mixed friction area (start-stop testing, emergency testing without oil, insufficient lubrication tests) as well as in the hydrodynamic area. The comparative tests were performed on different wear layer materials. This paper demonstrates and discusses the results for both a conventional white metal alloy bearing and for the bearing with bonded coating (GL92).
Depending on the operating point, the bearing systems exhibit significant differences at the maximum bearing load, lubricating film pressure distribution and maximum bearing temperature. The investigation has proven that GL92 is a technically useful alternative to conventional wear layers.
15
Butler, Shannon Catherine. "Early diet modifies small intestinal morphological characteristics and IgA-bearing cells in the BB rat." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ40032.pdf.
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Palmer, Mark. "Experimental investigation of the dynamic characteristics of a three lobe bearing at high rotational speeds." Thesis, Cranfield University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391575.
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Rahmanzadeh-Asl, Mahmoud. "Effect of inlet port position on the static and dynamic characteristics of a journal bearing." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/47737.
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Kwan, Y. B. P. "Processing and fluid flow characteristics of hot isostatically pressed porous alumina for aerostatic bearing applications." Thesis, Cranfield University, 1996. http://dspace.lib.cranfield.ac.uk/handle/1826/3690.
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Despite their well known superior load and stiffness characteristics, the wide-spread use of porous aerostatic bearings in preference to other bearing types has been hampered by difficulties in controlling the permeability of the porous material during manufacture and machining, in addition to instability problems caused by the additional volume of air trapped amongst the pores. Recent development in porous aerostatic bearings centres around the use of a thin dense surface layer to overcome the stability problem. The production of single and two-layered porous ceramic structures for aerostatic bearing applications have been investigated using the free-capsule hot isostatic pressing process, and in conjunction with slip and tape castings. The influence of various process parameters on open porosity, and the empirical relationships between porosity, particle size and the resulting fluid flow and structural properties were determined from experimental data. The measurement accuracy and uniformity of temperature within the furnace are identified as the most important factors affecting consistency and predictability of the permeability of the porous substrate. Prototype bearings were produced and tested, based on the above materials. The single-layer bearing was, not unexpectedly, found to be unstable over a wide operating range. The use of a two-layeredb earingm ateriale liminatedth e stabilityp roblem. Initial measurements of the slip coefficient of the porous material in air and at small gaps indicated significant deviation from the Beavers' theory. The effect of velocity slip was found to be significant in both test bearings, and was allowed for by the addition of an equivalent clearance to the bearing gap. The value of the equivalent clearance was deduced from experimental data. The static load characteristics and the pressure profile of both test bearings agreed well with published theories, once the above-mentioned correction for slip was applied.
19
Hobbs, Robert Anthony. "Solidification characteristics, microstructural stability and creep behaviour of advanced ruthenium-bearing nickel-base single crystal superalloys." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604115.
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The principal objective of this thesis is to identify the mechanism(s) by which Ru retards topologically close-packed (TCP) precipitation and to assess its influence on single crystal solidification and intermediate to high temperature creep, with the aim of improving the casting yield of next generation single crystal turbine blades whilst maintaining creep resistance and long term microstructural stability. The effect of Ru on single crystal solidification was found to be negligible, suggesting its concentration may be adjusted to levels necessary to improve other properties, such as microstructural stability, without great determent to the solidification characteristics of the alloy. Ru was confirmed to be a potent microstructural stabilising element with respect to TCP precipitation. The effect appears predominantly thermodynamic in nature due to a combination of γ’ destabilisation and an affinity between Re and Ru atoms decreasing the enthalpy of mixing in the γ phase which effectively increases the solubility limits of Re in the matrix. The marked decrease in TCP nucleation rate seems to be a secondary effect of this reduced driving force for TCP precipitation. Ru enhanced the creep rupture properties throughout the intermediate to high temperature creep regimes. Its potency as a solid solution strengthener decreased with rising temperature whereas its effectiveness as a stabilising element increased with temperature. It is postulated that the reduction in γ’ volume fraction upon the addition of Ru, which is central to its effectiveness as a stabilising element, is the principal cause of its diminishing strengthening contribution at elevated temperatures.
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Straub, D'Arcy Winston. "Iron-bearing minerals--relationships to the near infrared and radiothermal emissivity characteristics of the Venusian surface." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/58027.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1993.Includes bibliographical references (p. 208-214).
by D'Arcy Winston Straub.
Ph.D.
21
Rowan, D. "Design and development of a high-speed test facility and the measurement of the fluid film characteristics of journal bearings." Thesis, Cranfield University, 1998. http://dspace.lib.cranfield.ac.uk/handle/1826/11357.
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In the theoretical analysis of high speed rotor bearing systems, it is common to use
four displacement and four velocity based coefficients, which characterise the
behaviour of the lubricating fluid film. Although a great deal of work has been
published establishing theoretical models of all types of hydrodynamic journal bearings,
the large amount of experimental work has centred on relatively low speed conditions.
This work presents a contribution to the experimental study of the static and dynamic
characteristics of oil films in journal bearings used in high-speed rotating machinery.
The main objectives of the work are:
• To devise new experimental techniques for the measurement of dynamic
coefficients suitable for use at high rotational speeds
• To design, manufacture, assemble and commission a test facility to measure
the static and dynamic characteristics of journal bearings at speeds up to
30000 rpm
• To determine the static and dynamic characteristics of a 5 Pad Tilting Pad
Journal Bearing Unit of 80 mm diameter at speeds up to 25 000 rpm using the
said test facility.
New techniques are particularly necessary for the measurement of velocity coefficients
because these invoke the necessity of imposing a velocity on to the bearing housing
and previous techniques have utilised synchronous motion of the bearing.
Consequently a new experimental procedure for measuring the four velocity or
damping coefficients of an oil film journal bearing from imposed dynamic "orbits" has
been devised called the "double pulse" technique. All four velocity coefficients are
derived from one imposed journal centre dynamic orbit and, therefore may be regarded
as being obtained at the same time. The method requires the production of a "cross-
over" point similar to that of a "figure of eight" shaped orbit and utilises the "cross-over"
point therein.
Coefficients are initially evaluated in a co-ordinate system, which is chosen to align with
the designated parts of the measured orbit. Each coefficient is then evaluated from
single values of instantaneous imposed force and resulting journal centre velocity.
Coefficients are them converted into any other desired axes system. The result is a
simpler experimental procedure, with reduced uncertainty compared to hitherto existing
methods.
The use of non-sinusoidal excitation of the oil film was explored, in the form of applying
a step-pulse train load pattern to produce a cross-over pattern in the journal
displacement ·orbit'.
Experimental tests were completed on a tilting pad bearing at speeds up to 15 000 rpm
inclusive. At speeds above this, the bearing exhibited a vibrational response, which
precluded the accurate measurement of journal centre displacement.
22
Sjökvist, Thobias. "Influence of Ferrochromium and Ferromanganese Additions on Inclusion Characteristics of Steel." Doctoral thesis, KTH, Materials Science and Engineering, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3150.
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Wang, Chao. "Static, dynamic and levitation characteristics of squeeze film air journal bearing : designing, modelling, simulation and fluid solid interaction." Thesis, Brunel University, 2011. http://bura.brunel.ac.uk/handle/2438/5832.
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Bearings today need to be able to run at very high speed, providing high positional accuracy for the structure that it supports, and requiring very little or no maintenance. For this to happen, bearings must have tight tolerances and very low or zero friction during operation. This pushes many traditional contact-type bearings to their limits as they often fail due to friction, generating heat and causing wear. By comparison, existing non-contact bearings fare better because of their very low or zero friction. But some have their own problem too. For example, the fact that aerostatic bearings require an air supply means having to use a separate air compressor and connecting hoses. This makes the installation bulky. Aerodynamic and hydrodynamic bearings cannot support loads at zero speed. Both hydrodynamic and hydrostatic bearings may cause contamination to the work-pieces and the work environment because of the use of lubricating fluid. A potential solution to the above-mentioned problems is the new squeeze film air bearing. It works on the rapid squeeze action of an air film to produce separation between two metal surfaces. This has the benefit of being compact with a very simple configuration because it does not require an external pressurized air supply, can support loads at zero speed and is free of contamination. For this research, two squeeze film air journal bearings, made from material of Al 2024 - T3 and Cu - C101 with the same geometry, were designed. The bearing is in the shape of a round tube with three fins on the outer surface and the journal, a round rod. When excited at a certain normal mode, the bearing shell flexes with a desirable modal shape for the squeeze film action. The various modes of vibration of Al bearing were obtained from a finite-element model implemented in ANSYS. Two Modes, the 13th and 23rd, at the respective frequencies of 16.320 kHz and 25.322 kHz, were identified for further investigation by experiments with respect to the squeeze film thickness and its load-carrying capacity. For Cu bearing, the two Modes are also 13th and 23rd at the respective frequencies of 12.184 kHz and 18.459 kHz. In order to produce dynamic deformation of the bearings at their modes, a single layer piezoelectric actuator was used as a driver. The maximum stroke length and the maximum blocking force of the single layer piezoelectric actuator were determined using manual calculation and ANSYS simulation. In the coupled-field analysis, the single layer piezoelectric actuator was mounted on the outside surface of the bearing shell and loaded with an AC and a DC voltage in order to produce the static and dynamic deformation. For the static analysis, the maximum deformation of Al bearing shell is 0.124 μm when the actuators are driven at the DC of 75 V. For the dynamic analysis, the actuators are driven at three levels of AC, namely 55, 65 and 75V with a constant DC offset of 75V and the driving frequency coincided with the modal frequency of the bearing. The maximum dynamic deformation of Al bearing shell is 3.22μm at Mode 13 and 2.08μm at Mode 23 when the actuators were driven at the AC of 75 V and the DC of 75 V. Similarly, the FEA simulation was used for analyzing Cu bearing. Furthermore, the dynamic deformation of both Al and Cu bearing at Mode 13 and 23 are validated by experiments. This research developed two theoretical models that explain the existence of a net pressure in a squeeze film for the levitation. The first model uses the ideal gas law as first approximation whilst the second uses the CFX simulation to provide a more exact explanation. In terms of the load-carrying capacity, Mode 13 was identified to be better than Mode 23 for both bearings. However, at Mode 13, Al bearing has a higher load-carrying capacity than Cu bearing. This is due to Al bearing having a higher modal frequency and amplitude. Finally, the coupled-field analysis for fluid solid interaction (FSI) was studied at both Mode 13 and 23 for Al bearing. The findings are that: a) the fluid force in the squeeze film can affect the dynamic deformation of the bearing shell, especially at high oscillation frequency, more at Mode 13 than at Mode 23 due to the relatively high pressure end-leakage in the latter; b) the dynamic deformation of the bearing shell increases with the gap clearance in a logarithmic manner at Mode 13; and c) the micron levels of gap clearance provide a damping effect on the dynamic deformation of the bearing shell at Mode 13 and at Mode 23, though much less dominant.
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Snyder, Troy Alan. "On Hydrodynamic Lubrication using Perturbed Reynolds equation and CFD-FSI: Static and Dynamic Characteristics of Compliant Marine Bearings." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron157552061871739.
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Rahal, M. Dwayne. "Genesis of a "Null" lymphocyte population with natural killer cell characteristics in bone marrow of normal and tumor-bearing mice." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74371.
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Mouse bone marrow was shown to contain a population of null lymphocytes which lack molecular markers of both B and T lineages ($ mu sp-,$ B220$ sp-,$ Thyl$ sp-).$ Null cells represent 12-14% of all bone marrow small lymphocytes. Studies on population dynamics have revealed that these null cells turnover rapidly with a production rate almost 1/3 as great as that of B lymphocytes. Some newly-formed null lymphocytes express natural killer (NK) cell-associated markers, including NK1.1. Some small lymphocytes in the bone marrow express low intensities of Thyl. These Thyl$ sp{ rm lo}$ cells are also rapidly renewing and some express NK1.1, suggesting that these cells, in addition to null lymphocytes, form part of the rapidly generated lineage of NK cells. During growth of a transplantable tumor, there were marked increases of limited duration in the numbers of null, NK1.1$ sp+,$ and Thyl$ sp{ rm lo}$ cells in the bone marrow. The increase in null cells was further enhanced in tumor-bearing mice given indomethacin. These findings suggest that the production of null small lymphocytes in the bone marrow includes the neogenesis of NK cells, possibly playing an important role against naturally occurring malignancies.
26
Raharjo, Parno. "An investigation of surface vibration, airbourne sound and acoustic emission characteristics of a journal bearing for early fault detection and diagnosis." Thesis, University of Huddersfield, 2013. http://eprints.hud.ac.uk/id/eprint/19034/.
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High power machinery such as steam turbines, large pumps and motors often use journal bearings as rotor supports. This type of bearing is simple, low cost and with high load carrying capacity. However, abnormal operating conditions in the journal bearings will degrade machine performance, increase operating cost and may cause unexpected sudden failure which is dangerous in both engineering and safety terms. Bearing condition monitoring can detect faults at an early stage and prevent the occurrence of such failures which can be catastrophic. Monitoring techniques that have been used for monitoring of journal bearing are lubricant analysis, vibration analysis, noise and acoustic emission analysis. Lubricant analysis has been used effectively for condition monitoring for a long time but cannot be implemented in real time. Many researchers have studied the use of the vibration and sound signals and acoustic emissions generated by the hydrodynamic journal bearing for detecting and diagnosing faults. The studies give relatively little information regarding surface vibration and airborne sound characteristics for self-aligning spherical journal bearings, nor has comprehensive condition monitoring been implemented for a particular self-aligning spherical bearing journal. Surface vibration, airborne sound analysis and acoustic emission monitoring can be used simultaneously to detect any signal emitted from the bearing at very wide frequency range. Sound vibration occurs in solid structure, liquid and gases transmitted to air surrounding create airborne sound. This study has conducted a thorough review of theoretical and experimental studies. The research began with designing and building a test rig consisting of a drive system, radial loading system, torsion loading system, the bearing testing system itself and control, data acquisition and measurement instrumentation systems include encoder, pressure transducers, thermocouples, load cells, vibration transducer, acoustic and acoustic emission sensors. Preliminary experiments were conducted to ensure all equipment and instrumentation worked well and also to test measurement repeatability. Preliminary experiment results showed that all the equipment either driving, loading, data acquisition and measurement system works well. Experimental analysis of the surface vibration, airborne sound and acoustic emission analysis responses in time domain and frequency domain analysis include RMS value, Kurtosis and mean value showed good repeatability. The AE measurement response showed the best repeatability, followed by surface vibration and airborne response. Theoretical study shows that the self-aligning spherical journal bearing system under radial load generated surface vibration, airborne sound and acoustic emission responses that originated from external force excitation such as fluctuating loads due to system misalignment or unbalance and internal excitation such as asperity in boundary or mixed operation. These excitations generate structure-borne vibration and acoustic emission. The structure-borne vibration dynamic responses then radiated airborne sound. Airborne sound also originated from oil pressure fluctuation and flow turbulence. The surface vibration and airborne sound frequency responses occur at frequencies < 100kHz and the acoustic emission frequency responses appear at high frequencies >100kHz. The amplitude and frequency of surface vibration, airborne sound and acoustic emission is influence by radial load, shaft speed and surface quality of journal and bearing components themselves. The quality of asperity contact between journal and bearing may be due to manufacturing defect, lubricant and surface deterioration over time during operation. The experiments and analysis of the surface vibration, airborne sound and acoustic emission characteristics of the self-aligning spherical journal bearing indicate that there is a positive correlation between the spectrum mean value of surface vibration, airborne sound and acoustic emission with radial load and speed. Meanwhile, when use higher lubricant viscosity creates lower surface vibration, airborne sound and acoustic emission mean amplitude. Investigation of lubricant deterioration due to water contaminant indicated that when use higher concentration contaminant in the lubricant generates higher spectrum mean value of surface vibration, airborne sound and acoustic emission responses. The surface deterioration experiment showed that there is a clear significant different in the frequency domain of surface vibration, airborne sound and acoustic emission between a scratched surface and a normal surface journal bearing. The surface vibration, airborne sound and acoustic emission frequency characteristic for scratches and lubricant deterioration creates different peak amplitudes and different frequency. The larger the scratch generate the greater the amplitude and higher frequency. From of the three measurement systems used, acoustic emission is the most sensitive and a better detect of the bearing fault than followed by vibration and air-born sound measurement system. Therefore the acoustic emission measurement technique can be integrated with surface vibration, airborne sound for rotating machinery/engine condition monitoring. Using surface vibration, airborne sound and acoustic emission monitoring the symptoms of early damage at low, medium or high frequency can be detected and more severe and catastrophic failure can be prevented, and finally very high maintenance costs can be eliminated.
27
Harris, Joel Mark. "Static characteristics and rotordynamic coefficients of a four-pad tilting-pad journal bearing with ball-in-socket pivots in load-between-pad configuration." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-3194.
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Doostmohammadi, Hamid. "A Study of Slag/Metal Equilibrium and Inclusion Characteristics during Ladle Treatment and after Ingot Casting." Doctoral thesis, KTH, Materialvetenskap, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11596.
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Today, there is a high demand on clean steel for high performance materialproperties. Thus, steel producers try to deliver a steel product with the highestquality and cleanliness to the market. The number of parameters that affect thesteel cleanliness may vary depending on the required material properties of thefinal product. However, the non-metallic inclusion characteristics represent one ofthe most important parameters. More specifically, the composition, size, numberand morphology affect steel cleanliness. In this work, selected parameters affectingthe inclusion characteristics were studied using the following methods: i)thermodynamic calculations (including computational thermodynamiccalculations), ii) inclusion determinations using a cross sectional (CS) method (2Dinvestigations) and iii) inclusion determinations using an electrolytic extraction(EE) method (3D investigations). The computational thermodynamic calculations of the slag-steel and inclusion-steelequilibriums were carried out using the Thermo-Calc software. With the help ofthese calculations, the influence of the slag carryover on the top slag, aluminumcontent in steel and sulfur distribution ratio as well as predictions of stable phasesof inclusions were studied. In addition, inclusion determinations of tool steel gradesamples collected during various stages of the ladle treatment in a scrap-based steelplant were carried out using both 2D and 3D methods. Furthermore, inclusiondeterminations of bearing steel grade samples from a runner system after ingotcasting were performed using a 2D metallographic method (CS-method). Also, theINCAFeature software was used, when using cross sectional method, in order tocollect more statistics of the inclusion characteristics. It was found that slag carryover has a large influence on the composition of theactual top slag as well as the aluminum content in the steel as well as the sulfurdistribution ratio. In addition, steel and slag were found to be in “near”-equilibriumconditions, after the completion of the vacuum degassing operation. Furthermore,the composition of small-size inclusions in samples taken from tool steel was foundto be very scattered. Moreover, the composition of the large-size inclusions wasfound to be less scattered. Furthermore, closer to the top slag composition insamples collected after vacuum degassing. Finally, the accuracy of the inclusioncomposition determinations of tool steel samples using the electrolytic extractionmethod was found to be better than for the cross sectional method. The worseaccuracy of the CS-method is due to a considerable effect of matrix elements oninclusion composition.QC 20100709
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Červenec, Adam. "Parní turbína pro pohon kompresoru." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-401526.
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The purpose of the diploma thesis is the design of condensing steam turbine for driving a compressor with mechanical power of 14,5 MW and operating speed 6800 rotations per minute on the compressor clutch. The main part is the thermodynamic calculation of the blade canal, which is verified with strength calculation to meet the requirements of the standart API 612. The next part is a basic design of gland sealing system, including a piston which is leveling the axial force with reusage of steam back to the blade canal. This thesis includes a calculation of axial and radial forces including the choice of suitable bearing, which both support the turbine. In the end there is an operating characteristics and function reliability of rising rotating speed on the total stress of blades.
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Kern, Colin. "Betriebsverhalten von thermisch und mechanisch hoch beanspruchten kunststoffbeschichteten Radial-Mehrflächengleitlagern." Doctoral thesis, Universitätsbibliothek Chemnitz, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-71977.
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Die vorliegende Arbeit verfolgte die Zielstellung der Substitution des etablierten Weißmetalls als Laufschicht von hydrodynamischen Mehrflächengleitlagern durch neuartige Kunststoffschichten. Dazu wurden vergleichende Bauteilversuche an Mehrflächengleitlagern mit verschiedenen Laufschichten und Bohrungsformen vorgenommen. Eine Zinnbasislegierung als Laufflächenbeschichtung diente dabei als Referenzwerkstoff. Zur Durchführung des Versuchsprogrammes kam ein vorhandener, messtechnisch neu konditionierter Turbinenlagerprüfstand zum Einsatz. Die Versuchsreihen haben durchweg positive Beurteilungen der Lagerkennwerte im untersuchten Betriebsbereich der neuen Lagervarianten ergeben. Die neuartigen Laufschichtvarianten erfüllten die hohen tribologischen und thermischen Anforderungen. Einzelne Abweichungen der ermittelten Kennwerte wurden zahlenmäßig dokumentiert und können mit bereits verfügbaren physikalischen Modellen beschrieben werden. Die Ergebnisse erwiesen sich als unabhängig von der Lagerbauform aber abhängig von der gewählten Schichtvariante. Die Untersuchungen zum Betriebsverhalten unter hydrodynamischer Dauerbelastung sowie im Mischreibungsgebiet und im Notlaufbetrieb führten zu teilweise unterschiedlichen Ergebnissen. Im Mischreibungsgebiet wiesen die untersuchten Lager kaum Unterschiede im Betriebsverhalten auf. Im Dauerversuch zeigten die Lager mit Weißmetall, Gleitlack und Keramikschicht hervorragende Eigenschaften. Die Variante Klüberplast besaß eine ungenügende Bindefestigkeit und führte zu plastischen Verformungen der Schicht infolge der hydrodynamischen Drücke. Im Notlaufbetrieb übertrafen die untersuchten Kunststoffvarianten die Standzeiten des Referenzwerkstoffs WeißmetallThe aim of this study was to identify and test an alternative liner material instead of common liner materials such as white alloy for multi-lobe radial bearings. For this purpose comparative tests with different radial bearings were carried out. The white alloy material was taken as a reference. In preparation for these test series, the measurement system of the turbine bearing test rig was upgraded. Experiments showed beneficial performances of the bearings with a plastic liner by evaluating the static and dynamic properties of different bearing geometries and liner thicknesses under a wide range of operating conditions. The new bearings fulfilled the high tribological and thermal requirements. Observed deviations of the determined parameters were documented in number and can be described with available physical models. The results were independent of the bearing type and depending on the selected liner material variant. The studies on operating performance in continuous operation in the mixed friction area and in dry running operation led to partially different results. The mixed friction tests showed little difference in the examined stock performance. The bearings with white alloy, ceramic layer and bonded coating showed excellent fatigue properties of long-term experiment. On Klüberplast insufficient bonding strength and plastic deformation of the layer due to the hydrodynamic pressure was found. In the dry running operation the investigated polymers exceeded the lifetime of the referencematerial white alloy
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Netscher, Heather Gayle. "The neuro-muscular and musculo-skeletal characterization of children with joint hypermobility." Queensland University of Technology, 2009. http://eprints.qut.edu.au/30295/.
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In children, joint hypermobility (typified by structural instability of joints) manifests clinically as neuro-muscular and musculo-skeletal conditions and conditions associated with development and organization of control of posture and gait (Finkelstein, 1916; Jahss, 1919; Sobel, 1926; Larsson, Mudholkar, Baum and Srivastava, 1995; Murray and Woo, 2001; Hakim and Grahame, 2003; Adib, Davies, Grahame, Woo and Murray, 2005:). The process of control of the relative proportions of joint mobility and stability, whilst maintaining equilibrium in standing posture and gait, is dependent upon the complex interrelationship between skeletal, muscular and neurological function (Massion, 1998; Gurfinkel, Ivanenko, Levik and Babakova, 1995; Shumway-Cook and Woollacott, 1995). The efficiency of this relies upon the integrity of neuro-muscular and musculo-skeletal components (ligaments, muscles, nerves), and the Central Nervous System’s capacity to interpret, process and integrate sensory information from visual, vestibular and proprioceptive sources (Crotts, Thompson, Nahom, Ryan and Newton, 1996; Riemann, Guskiewicz and Shields, 1999; Schmitz and Arnold, 1998) and development and incorporation of this into a representational scheme (postural reference frame) of body orientation with respect to internal and external environments (Gurfinkel et al., 1995; Roll and Roll, 1988). Sensory information from the base of support (feet) makes significant contribution to the development of reference frameworks (Kavounoudias, Roll and Roll, 1998). Problems with the structure and/ or function of any one, or combination of these components or systems, may result in partial loss of equilibrium and, therefore ineffectiveness or significant reduction in the capacity to interact with the environment, which may result in disability and/ or injury (Crotts et al., 1996; Rozzi, Lephart, Sterner and Kuligowski, 1999b).
Whilst literature focusing upon clinical associations between joint hypermobility and conditions requiring therapeutic intervention has been abundant (Crego and Ford, 1952; Powell and Cantab, 1983; Dockery, in Jay, 1999; Grahame, 1971; Childs, 1986; Barton, Bird, Lindsay, Newton and Wright, 1995a; Rozzi, et al., 1999b; Kerr, Macmillan, Uttley and Luqmani, 2000; Grahame, 2001), there has been a deficit in controlled studies in which the neuro-muscular and musculo-skeletal characteristics of children with joint hypermobility have been quantified and considered within the context of organization of postural control in standing balance and gait. This was the aim of this project, undertaken as three studies.
The major study (Study One) compared the fundamental neuro-muscular and musculo-skeletal characteristics of 15 children with joint hypermobility, and 15 age (8 and 9 years), gender, height and weight matched non-hypermobile controls. Significant differences were identified between previously undiagnosed hypermobile (n=15) and non-hypermobile children (n=15) in passive joint ranges of motion of the lower limbs and lumbar spine, muscle tone of the lower leg and foot, barefoot CoP displacement and in parameters of barefoot gait. Clinically relevant differences were also noted in barefoot single leg balance time. There were no differences between groups in isometric muscle strength in ankle dorsiflexion, knee flexion or extension.
The second comparative study investigated foot morphology in non-weight bearing and weight bearing load conditions of the same children with and without joint hypermobility using three dimensional images (plaster casts) of their feet. The preliminary phase of this study evaluated the casting technique against direct measures of foot length, forefoot width, RCSP and forefoot to rearfoot angle. Results indicated accurate representation of elementary foot morphology within the plaster images. The comparative study examined the between and within group differences in measures of foot length and width, and in measures above the support surface (heel inclination angle, forefoot to rearfoot angle, normalized arch height, height of the widest point of the heel) in the two load conditions. Results of measures from plaster images identified that hypermobile children have different barefoot weight bearing foot morphology above the support surface than non-hypermobile children, despite no differences in measures of foot length or width.
Based upon the differences in components of control of posture and gait in the hypermobile group, identified in Study One and Study Two, the final study (Study Three), using the same subjects, tested the immediate effect of specifically designed custom-made foot orthoses upon balance and gait of hypermobile children. The design of the orthoses was evaluated against the direct measures and the measures from plaster images of the feet. This ascertained the differences in morphology of the modified casts used to mould the orthoses and the original image of the foot. The orthoses were fitted into standardized running shoes. The effect of the shoe alone was tested upon the non-hypermobile children as the non-therapeutic equivalent condition. Immediate improvement in balance was noted in single leg stance and CoP displacement in the hypermobile group together with significant immediate improvement in the percentage of gait phases and in the percentage of the gait cycle at which maximum plantar flexion of the ankle occurred in gait.
The neuro-muscular and musculo-skeletal characteristics of children with joint hypermobility are different from those of non-hypermobile children. The Beighton, Solomon and Soskolne (1973) screening criteria successfully classified joint hypermobility in children. As a result of this study joint hypermobility has been identified as a variable which must be controlled in studies of foot morphology and function in children. The outcomes of this study provide a basis upon which to further explore the association between joint hypermobility and neuro-muscular and musculo-skeletal conditions, and, have relevance for the physical education of children with joint hypermobility, for footwear and orthotic design processes, and, in particular, for clinical identification and treatment of children with joint hypermobility.
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Sabbagh, F. "Wear characteristics of cast iron and steel under boundary lubricated conditions : A study of boundary lubricated wear of cast iron piston rings and its relation to their wear under engine conditions, with a comparative wear study on roller bearing steel." Thesis, University of Bradford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381032.
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Collins, D. "The vibrational characteristics of oil lubricated plain journal bearings." Thesis, University of Leeds, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373844.
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Chen, Juhn-Horng, and 陳俊宏. "Identification of Linearized Characteristics of Bearings in Rotor-Bearing Systems." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/24464136957993458029.
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Tsai, ChiPing, and 蔡其平. "Characteristics Analysis of Hydrostatic Bearing with capillary Restrictions." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/57920654539967014972.
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碩士東南科技大學
機械工程研究所
100
This study is primarily focusing on the influences of hydrostatic radial bearing on load capacity and static stiffness with different parameters, including number of recess, restriction, recess length ratio, and displacement ratio in capillary restriction. We constructed the flow continuity equations for each recess using Flow Resistance Network (FRN) method, solved the set of equations for pressure ratios, and then further obtained the load capacities and static stiffness. The FRN method establishes the flow rates and interactions within themselves in a multi-recess system based on energy equations. The rates are proportional to the pressure difference between two recesses, but inversely proportional to the flow resistance. The simulation results indicate that the hydrostatic radial bearing of capillary compensator has better performance with increase in the numbers of recess and decrease in recess length ratio. The stiffness is optimized with smaller restriction parameters under heavy load capacity. Moreover, while the number of recess is fixed and displacement ratio is greater than 0.3, the stiffness reaches its optimum with smaller recess length ratio and appropriate restriction parameters.
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OuYang, Chun-Nan, and 歐陽俊男. "The characteristics of CD11b+ cells in tumor-bearing mice." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/32520704959939774515.
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碩士長庚大學
基礎醫學研究所
95
Tumor-associated macrophages (TAMs) are known to be part of inflammatory circuits that promote tumor progression. They are attracted from the circulation into the tumor stroma by the chemokines and differentiate into TAMs. Latent membrane protein-1 (LMP-1) is an Epstein-Barr virus oncoprotein, which is highly associated with malignancies, including nasopharyngeal carcinoma (NPC). It acts as a ligand-independent tumor necrosis factor receptor (TNFR), resulting in cell transformation. In addition, LMP-1 was also shown to upregulate the secretion of several cytokines and chemokines that may attract and activate macrophages. However, the in vivo mechanism how NLMP-1 tumor involves the macrophages in the tumor progression is unclear. Previously, a transplantable tumor model using NLMP-1-transformed BALB/c-3T3 cells (3T3/NLMP-1) has been established in this laboratory. By using this model, this study was to understand the type of macrophages and chemokines involved in the NLMP-1 tumor progression. By flow cytometry, we found that most of tumor-infiltrating leukocytes in the 3T3/NLMP-1 tumor were macrophage; in particular, CD11b+ Gr-1+ CD80+ CXCR3+ macrophages. Further ELISA analysis of culture supernatants of cell lines and tumor mass for the chemokine profile revealed that the proinflammatory chemokines such as MCP-1, MIP-1alpha, IP-10, and RANTES that tend to attract macrophages were produced either from tumor or infiltrates. Furthermore, CT26, a murine colon carcinoma, with NLMP-1 transfection, demonstrated a significant elevated CD11b+ cells infiltration in the tumor mass. Since we have previously found that the in vivo establishment of 3T3/NLMP-1 tumor is strictly stroma-dependent, the present study suggested that NLMP-1 may enhance the process of stroma formation by recruiting specific type of macrophages through the manipulation of chemokines in the microenvironment.
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Hu, Sheng-Yen, and 胡聖彥. "Characteristics Analysis of Constant-flow Valve for Hydrostatic Bearing." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/90621275749942677586.
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碩士中原大學
機械工程研究所
100
Constant-flow valves have been presented in industrial applications or academic studies, which compensate pressures of bearing recesses as load fluctuates. The flow rate of constant-flow valves can be constant in spite of the pressure changes in recesses. However, specific condition of design parameters must be satisfied. This paper utilizes analytical method to study the static and dynamic characteristics of constant-flow valves, three types of constant-flow valve are DDE-type, DSI-type, and spool-type. The static analysis gives the specific relationships among design parameters for constant flow. The dynamic analysis gives the variations around the constant flow rate as the working pressure fluctuates.
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ITOH, Y., T. KAMIMURA, M. HIROHATA, and T. MORI. "DETERIORATION CHARACTERISTICS OF Sn-BEARING STEEL BY ACCELERATED EXPOSURE TESTS." 2013. http://hdl.handle.net/2237/18867.
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Chang, Jer-Rong, and 張哲榮. "A Study on Dynamic Characteristics of Geared Rotor-Bearing System." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/83738202872182721874.
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博士國立成功大學
航空太空工程學系
85
This thesis is concerned with the dynamic analysis of a geared rotor-bearing system. A finite element model of the geared rotor-bearing system is developed by taking account of the lateral-torsional coupling effect to obtain the natural frequencies, mode shapes, and the steady-state responses. From the response time histories, the FFT spectra can be obtained to investigate the effects of dynamic coupling terms under different grades of balance quality and spin speeds. In addition, the lateral response due to short circuit torque is examined to be substantial for the turbo-generator set. The nonlinear dynamic behavior of a geared system supported bysqueeze-film dampers is also investigated. The FFT spectra, Poincare maps and bifurcation maps are made to classify the responses whichinclude sub-harmonic, superharmonic, quasi- periodic, and chaotic responses. The hybrid technique of the Harmonic Balance Method and Time Collocation is employed to obtain the stability of the first variation equations with periodic coefficients, which is generatedby the perturbation technique.
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Chen, Chin-An, and 陳金安. "Research on the Dynamic Characteristics of the Aerostatic Spindle Bearing." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/25958333058371263742.
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碩士國立彰化師範大學
工業教育學系
89
The purpose of this research is to analyze the static and dynamic behaviors of air turbine aerostatic spindle thrust bearing with/without grooves. First, in order to calculate the bearing relative behaviors to include load capacity、stiffness and flow by the current applied force using the resistance network method. Then with motion equation, including squeeze film effect to analyze the stability of cutting force. Its motion equation uses integration method to solve it. A thrust bearing set for an air turbine spindle has been designed and proposed. From the research on the behaviors of the air turbine aerostatic spindle bearings, one can obtained the follow- ing conclusions： 1.Grooved bearings have higher load capacity and greater stiffness than bearings without grooves by the theoretically and experimental results prove. 2.Increasing the annular area enhances the stability of the bearing. 3.A thrust bearing set for an air turbine spindle has been designed and proposed.
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Chirathadam, Thomas. "Metal Mesh Foil Bearings: Prediction and Measurement for Static and Dynamic Performance Characteristics." Thesis, 2012. http://hdl.handle.net/1969.1/148301.
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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.
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Wu, Fu-Shin, and 吳馥馨. "Dynamic Stiffness Characteristics Analysis and Testing of a Passive Magnetic Bearing." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/40119919073731861677.
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碩士國立清華大學
動力機械工程學系
95
Turbo molecular pump, an accurate mechanism, is characterized by the small volume and high rotary speed (3,000~60,000rpm). To achieve contact-free rotor spinning in the confined space, passive magnetic bearing system inside the pump must be designed accurately to avoid the unstableness of the rotor, which requires the design of the bearing to attain the preciseness in the micrometer’s level. Thus, the study aims to analyze the dynamic stiffness of passive magnetic bearing and to design the stiffness of the bearing for the system. Two parts are covered in this paper. In the first part, we measured the magnetic flux of passive magnetic bearing and analyzed the magnetic field by the standpoint of magnetic circuits. Besides, we compared the results of multiplayer magnets with different materials. In the second part, I used computer program Ansoft, which is based on finite element method, to analyze magnetic field and force. Furthermore, we analyzed the effect of displacement to magnetic bearing stiffness. Implementing 3D simulation with different parameters, we then discussed what the best design is. Finally, the result of simulation and the experimental data were compared and suggestions were further provided.
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Lo, Wu-Jen, and 羅武仁. "Dynamic Characteristics Analysis and Testing of a Microturbine Rotor-Bearing System." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/61932283777594980230.
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碩士國立清華大學
動力機械工程學系
91
This paper can be divided into two parts, which are numerical analysis and experimental equipment construction and testing. In numerical analysis, we mainly use the finite element method as our basis and MATLAB program design software as our tool, to write the numerical analysis program for a rotor-bearing system. This rotor-bearing system consists of rigid disks, distributed parameter finite rotor elements, and discrete bearings. During modeling of the system, the finite element model includes the effects of translation inertia, rotatory inertia, gyroscopic moments, and shear deformations. In order to verify the numerical analysis program, we choose to analyze the simple uniform rotor. We calculate and compare its natural frequencies, mode shapes, and critical speeds in bending with the theoretical results. After that, we further analyze a more complex system, which contains three disks and two bearings. The influences of the element number, the whirl frequency, the Campbell diagram, and the critical speed versus bearing stiffness diagram were studied. In experimental equipment construction and testing, we continue to progress on the RGT-3600 micro turbine and completed the related works of the equipment construction and testing. It includes the assembly of the hardware, the build of the measurement equipments, the construction of the sub-systems and the test of the sensor elements, the fuel supply, the fuel atomization, the fuel ignition, and the starting motor. We were able to get the micro turbine started properly and shut down safely. In addition, we accumulated many valuable experiences as well as test data.
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Sun, Shi-Mu, and 孫士牧. "Development of a Small Magnetic Bearing and Research on its Characteristics." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/24882604798995780681.
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碩士國立臺灣大學
機械工程學研究所
87
The aim of this thesis is to develop a small magnetic bearing fit for a turbo molecular pump and research on its characteristics. By observing the magnetic behavior between two magnets, three kinds of passive magnetic bearing types are designed. Comparing with these kinds of bearing types, the passive radial magnetic bearing composed of axial magnetized rings is decided because it can produce a magnetic force that keeps the rotor a certain range of the radial direction. For comprehending the characteristics of this magnetic force experiments are carried out. Form these experiments, the magnetic force''s relationships with the properties of magnet, the outer diameter of the rotor and the inner diameter of the stator are obtained, and operating ranges of the rotor in both axial and radial directions are also be decided. To compare with experimental results finite element analysis with ANSYS is applied. And in consideration of the magnetic force decay of a magnet in air the analytical results can approximate with experimental results very well. On the other way, a radial magnetic force equation derived from magnetic circuit theory can calculate the radial magnetic force, and it is suitable for the situation of small axial running offsets. Because the passive radial magnetic bearing can only offer the radial stiffness, it needs to combine with the active axial magnetic bearing to build up a magnetic bearing system and which makes the rotor achieve magnetic levitation.
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Hung, Yu-Hong, and 洪宇宏. "Characteristics Analysis of Hydrostatic Closed-type Bearing Using Double-action Compensations." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/87v2q3.
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碩士中原大學
機械工程研究所
98
This thesis of a serial studies for studying constant and variable compensations of the closed-type hydrostatic flat bearing. In this part, the double-action variable restrictors including cylindrical-spool, conical-spool and membrane types and self-compensation are taken into consideration. Analysis of the recess pressure versus displacement ratio of worktable and load capacity and static stiffness. Characteristics of hydrostatic closed-type bearing using double-action compensations. The static stiffness of will be also determined by the same method as shown in previous parts. Consequently, the usage range of recess pressure and optimal parameters of appropriate compensation type can be obtained according to the smallest gradient of displacement or maximum stiffness.
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Lin, Che-Chuan, and 林哲銓. "Structure and Sedimentary Characteristics of Gas Hydrate-Bearing Sediments off Southwest Taiwan." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/96930402368491057237.
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碩士國立中央大學
地球物理研究所
93
A seismic interpretation study was carried out on a dense grid of multichannel seismic data off SW Taiwan. The study area can be divided into three geological domains on the basis of structure and sedimentary characteristics: the South China Sea (SCS) continental slope domain, the folded domain, and the thrusted domain. The folded and thrusted domains occupy the frontal accretionary prism. The SCS continental slope domain situates between the Taiwan Strait shelf break and the deformation front of the accretionary prism. There are many erosional gullies in the upper slope of this domain, manifesting an erosion dominant region. Beneath the upper slope, the strata are eroded and truncated at the seabed, exposing Pliocene-Pleistocene sediments that are deeply buried in the adjacent shelf. By contrast, in the lower slope, there has developed slope-front fills revealing a deposition dominant region. The region between the deformation front and the fringe of emergent thrusts is the folded domain. Several west-vergent blind thrusts have uplifted the strata and formed a series of anticlines. Seismic facies suggests that the western half of this region is dominated by hemipelagic sedimentation and the eastern half is dominated by the chanelling and deposition of the Penghu submarine canyon system. The thrusted domain lies in between the westernmost emergent thrusts and the Kaoping Canyon. Westward emergent thrusts and anticlines prevail in this area. On top of each thrust sheets, it has developed a slope basin. Seismic facies show that the sedimentation is governed by hemipelagic sediments and/or turbidite deposits. Sedimentation in the eastern half of this region is influenced by the Kaoping and Kaohsiung submarine canyons as evidenced by turbidite levee deposits, channel and canyon infills. In each thrust or anticline, there is an array of unconformities associated with the episodic development of the growing structures. An analysis of the timing for the development of these unconformities suggests that thrusts in the rear of the frontal prism occurred earlier (about 2.3Ma) than that in the region near the deformation front. Thrust activities were frequent in the thrust domain when compared to the folded domain. Bottom simulating reflectors(BSRs), marking the base of hydrate stability zone, exist in the region deeper than c.600m and are commonly observed in thrusted domain, whereas it is less commonly found in the folded domain. The sub-bottom depth of the BSRs increases with icreasing water depths, a characteristic which is governed by the phase diagram of hydrate stability.
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Huang, Chun-Jung, and 黃俊榮. "A STUDY ON DYNAMIC CHARACTERISTICS OF GEARED ROTOR-BEARING SYSTEM WITH CRACK." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/58896036507200956668.
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博士國立成功大學
航空太空工程學系碩博士班
91
In this thesis, the dynamic analysis of a geared rotor-bearing system with an open crack or a breathing crack is discussed. A simple analytic model of a geared rotor system is developed by taking into account the effect of an open transverse surface crack for determination of natural frequencies, critical speeds, and stability of the system. The existing crack results in a local flexibility of the shaft and it is replaced by a set of springs based on the balance of energy. The effect of the crack results in a periodic time-varying system. From the response time histories, the FFT spectra can be obtained for investigating the effects of crack. The Floquet theory is used to examine the stability of the first variation equations with periodic coefficients. Finite element models are developed for geared rotor-bearing system with an open transverse surface crack and with a breathing transverse surface crack for determination of natural frequencies, critical speeds, dynamic response and stability. The results show that additional instability regions of the shaft’s spin speed are observed when a crack occurs on the shaft. The influences of the crack on the stability of the system are significant as the depth increases to an evident value.
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Hwu, Chwan-Jing, and 胡傳菁. "Surface Roughness Effects on the Squeeze Film Characteristics of Partial Journal Bearing." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/18904834786032075178.
Full textAbstract:
碩士中原大學
機械工程學系
88
The present study examines the surface roughness effects on the squeeze film characteristics of a finite partial journal bearing. We can derive the Reynolds’ equation from the momentum equations and the continuity equation and further adopt the stochastic models to develop the stochastic Reynolds’ equation describing the uniform, isotropic roughness. After obtaining the pressure distribution of the squeeze film, we can calculate the surface roughness effects on the squeeze film characteristics. The results of the study show that the surface roughness effects have negative influence both on the load-carrying capacity or the time-height relationship.
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Shen, Sung-Chiang, and 沈頌? "Performance Analysis on Static and Dynamic Characteristics of Porous Media Aerostatic Bearing." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/21654658398746670162.
Full textAbstract:
碩士國立臺灣科技大學
機械工程系
103
This study investigates the performances of the porous-media aerostatic thrust and journal bearings via numerical simulation. Based on the finite-volume method and the pressure-velocity coupling SIMPLE scheme, this work utilizes the CFD software Fluent to solve the three dimensional, compressible Navier-Stokes equations for calculating the pressure and velocity fields inside the bearings. The effects of the air compressibility, the flow resistance of porous medium, the thickness of porous medium insert, the bearing gap, the housing gap, the eccentric ratio, and the rotational speed of the spindle on the characteristics of bearing such as the pressure distribution, the load carrying capacity, the surface average pressure and the stiffness are evaluated. At first, the appropriateness of compressible or incompressible for the analysis on aerostatic bearing is examined carefully. The computed results of thrust bearing reveal that, the compressible approach should be adopted for analyzing the aerostatic bearings. Later, porous graphite and porous alumina are selected for comparing the pressure distribution of thrust bearing. Because the porous graphite’s fluid resistance is larger, so the load capacity of porous-alumina bearing is considerably bigger comparing that of the porous-graphite bearing by 10 to 13 times for various spindle speeds. Additionally, the thickness of porous-medium insert is considered in analyzing its effect on aerostatic bearings. The numerical results illustrate that the load capacity increases about 6% when the thickness of porous medium varies form 10 mm to 4 mm. Subsequently, the simulation approach of the thrust bearing extends to the journal bearings. At first, the analysis on the eccentric ratio of spindle for journal bearing shows that, the stiffness enlarges about 19~39% for a thinner gap. To enhance the practical validity of the simulation, the study also takes into account the ratio of the housing gap to bearing gap. The housing gap is the distance between the inner case surface and spindle surface, and the bearing gap is defined between the bottom surface of the porous-medium insert and spindle surface. The calculations of journal bearing reveal that the average pressure on spindle surface becomes larger when the housing gap is thinner. Also, the average pressure on spindle surface reduces 55% when bearing gap decreases form 10 to 4 μm. These results show the average pressure on spindle surface may reach the peak value when the housing gap is not too thick and the bearing gap is not too thin. In summary, the CFD study considers many parameters for enhancing the pressure and the stiffness of thrust bearing and journal bearing. Also, the physical phenomenon of dynamic-pressure effect inside the porous bearing is analyzed thoroughly for the high-speed spindle case, which can serve as an important design reference for engineering applications.
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Huang, Yi-Xiang, and 黃翊祥. "Characteristics of Worktable Supported by Hydrostatic Planar Bearing Compensated by DSI Valves." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/2tr3q6.
Full textAbstract:
碩士中原大學
機械工程研究所
103
DSI valve was published in AD 1964 by Rippel, its spool is composed of two piston head with a combination of the post, before and after the change by the pressure on the piston and DSI different internal flow resistance of the throttle valve , allowing the flow of oil through the DSI after the throttle bearing oil film has a certain stiffness performance, in order to support oil platform hydrostatic bearing. Equality of the equation by the continuous oil pad and compensator traffic can be derived bearing pressure, hydrostatic oil film thickness platforms, oil platform traffic flow with the relationship between static stiffness platform Therefore this study to establish DSI valve and continuous flow of oil hydrostatic equation platform considerations DSI valve used on oil platforms hydrostatic static characteristics.