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The prefailure detection of faults in operating plant can effect major rewards in both safety and economy. A successful on-condition maintenance philosophy would pay great dividends particularly in the offshore oil industry where -until recently, only token methods have been employed. Many techniques are available for monitoring mechanical plant and several of these are considered in general terms. Industrial methods are subsequently evaluated on reciprocating compressor and rolling element bearing faults. Bearing fault analysis is considered in two stages. Initially, a series of vibration based techniques are evaluated on a large relatively noise free rotating machine. The techniques of greatest worth carrier spectra, autospectra, time signature analysis and statistical assessments - are then applied to bearings in the hostile environment of a reciprocating machine. It is shown that while discrete faults often produce predictable periodic vibrational patterns, a monitoring system aimed solely at such vibrational phenomena cannot be relied upon. To this end, a diagnostic system must encompass a series of techniques, including carrier spectrum, time signature and statistical analyses. A series of valve and piston faults in reciprocating machines are also studied. By using a number of monitoring techniques, a catalogue of fault characteristics is constructed, and the methods of greatest worth are high-lighted. It is noted that due to the complexities of a reciprocating machine, fault characteristics vary with load, and this must be borne in mind when interpreting the various parameter displays. No single technique can provide a complete cover for all compressor faults, and it is shown that those of greatest worth are acoustic emission, combined pressure and vibration plots, temperature and performance analysis. An indication of compressor temperature and internal cylinder pressure can greatly ease the detection and diagnostic process, and for the latter, bolt load determinations may be a valuable aid.

Foil bearings are widely used for oil-free micro turbomachinery. One of the critical technical issues related to reliability of the foil bearings is a coating wear on the top foil and rotor during start/stops. Bearing cooling is also mandatory for certain applications because the foil bearings can generate significant amount of heat depending on operating conditions. Usually axial flow is used through the space between the top foil and bearing sleeve. In this thesis, a hybrid air foil bearing with external pressurization is introduced. The hybrid operation eliminates the coating wear during start-up/shut down, and also reduces drag torque during starts. Furthermore, this hybrid foil bearing does not need cooling system. An experimental test with a loaded bearing under hydrostatic mode demonstrates the high potential of hybrid air foil bearings. The load capacity of the hybrid foil bearing was measured at 20,000 rpm, and compared with that of hydrodynamic foil bearing. The hybrid foil bearing has much higher load capacity than the hydrodynamic foil bearing. The starting torque was also measured and compared with hydrodynamic bearing. A simple analytical model to calculate top foil deflection under hydrostatic pressurization has been developed. Predictions via orbit simulations indicate the hybrid air foil bearings can have a much higher critical speed and onset speed of instability than the hydrodynamic counter part. Major benefits of the hybrid foil bearings also include very low starting torque, reduced wear of the top foil and rotor, and very effective cooling capability by the pressurized air itself. This new concept of hybrid air foil bearings are expected to be widely applied to the oil free turbomachinery industry, especially for heavily loaded and/or high temperature applications.

Foil bearings are widely used for oil-free micro turbomachinery. One of the critical technical issues related to reliability of the foil bearings is a coating wear on the top foil and rotor during start/stops. Bearing cooling is also mandatory for certain applications because the foil bearings can generate significant amount of heat depending on operating conditions. Usually axial flow is used through the space between the top foil and bearing sleeve. In this thesis, a hybrid air foil bearing with external pressurization is introduced. The hybrid operation eliminates the coating wear during start-up/shut down, and also reduces drag torque during starts. Furthermore, this hybrid foil bearing does not need cooling system. An experimental test with a loaded bearing under hydrostatic mode demonstrates the high potential of hybrid air foil bearings. The load capacity of the hybrid foil bearing was measured at 20,000 rpm, and compared with that of hydrodynamic foil bearing. The hybrid foil bearing has much higher load capacity than the hydrodynamic foil bearing. The starting torque was also measured and compared with hydrodynamic bearing. A simple analytical model to calculate top foil deflection under hydrostatic pressurization has been developed. Predictions via orbit simulations indicate the hybrid air foil bearings can have a much higher critical speed and onset speed of instability than the hydrodynamic counter part. Major benefits of the hybrid foil bearings also include very low starting torque, reduced wear of the top foil and rotor, and very effective cooling capability by the pressurized air itself. This new concept of hybrid air foil bearings are expected to be widely applied to the oil free turbomachinery industry, especially for heavily loaded and/or high temperature applications.

A new foil bearing with compression springs is designed, built, analyzed, and tested. This foil gas bearing uses a series of compression springs as a compliant structure instead of corrugated bump foils. A spring model to estimate the stiffness of compression springs was developed and showed a good level of agreement with the experimental results. The spring dynamics model was combined with a non-linear orbit simulation to investigate the non-linear behavior of foil gas bearings. The approach could also predict the structural loss factor given the geometry of the underlying springs. A series of rotor-bearing orbit simulations using the compression spring with stiffness of the free-free case, predicted the critical speed and the onset speed of instability at around 7500 rpm and 14,500 rpm with a WFR ~ 0.5. The low critical speed was due to the relatively soft support. The hydrodynamic rotor instability was predicted under the equivalent viscous damping extracted from the spring dynamics, implying the viscous damping alone within the spring cannot suppress hydrodynamic instability of the foil gas bearings. The load capacity of the compression spring foil gas bearing was measured at 20,000 rpm with and without air cooling, to demonstrate the feasibility of the new foil bearing. The constructed bearing with rather soft springs showed a small load capacity of 96N at 20,000 rpm under no cooling. The developed cooling method using direct air supply holes machined on the bearing sleeve, proved to be very effective in cooling the test bearing. The measured level of structural stiffness and damping evidenced the existence of a necessary level of damping for stable bearing operation. The structural stiffness was highly nonlinear and showed different behavior for static loading and the sinusoidal dynamic loading. The measured equivalent viscous damping coefficients increased with the applied load amplitude. A series of parametric design studies were performed to investigate the effects of various design parameters on the bearing stiffness and overall rotordynamic performance. Rotor-bearing orbit simulations showed there is a range of spring stiffness for high onset speeds of instability. Increasing the pitch of the spring while maintaining the same stiffness increased the structural loss factor slightly, manifesting a smaller number of coils is better in terms of damping. The onset speed of instability increases slightly with the rotor mass due to increased static eccentricity and presumably smaller cross-coupled stiffness. However, increasing the rotor mass in order to render a high eccentricity was not effective in increasing the onset speed of instability because of reduced natural frequency and increased inertia. Instead, orbit simulations confirmed that small rotor mass with external loading is the most effective way to increase the bearing stability.

Project Thesis (D. Min.)--Denver Conservative Baptist Seminary, 1984. / Includes bibliographical references (leaves 86-96).

The amount of carbon trapped in hydrates is estimated to be larger than in conventional oil and gas reservoirs, thus methane hydrate is a promising energy resource. The high water pressure and the relatively low temperature needed for hydrate stability restrict the distribution of methane hydrates to continental shelves and permafrost regions. Stability conditions add inherent complexity to coring, sampling, handling, testing and data interpretation, and have profound implications on potential production strategies. New guidelines are identified for sampling equipment and protocols. Then a novel technology is developed for handling, transfering, and testing of natural hydrate bearing sediments without depressurization in order to preserve the sediment structure. Natural samples from the Nankai Trough, Japan, are tested as part of this study. In-situ testing prevents dissociation and the consequences of sampling and handling disturbance. A new multi-sensor in-situ characterization tool is designed and prototyped as part of this research. The tool includes advanced electronics and allows for automated stand-alone operation. Finally, a robust analytical model is developed to estimate the amount of gas that can be recovered from hydrate bearing sediments using depressurization driven dissociation. Results highlight the complexity of gas extraction from deep sediments, and inherent limitations.

This thesis explores the notion of testimony as a theological concept. The task of this thesis is twofold: first, to analyze several exemplary instances of appropriating philosophical resources in the construction of the concept of testimony in biblical and theological writings, and to consider the aptness of these attempts in terms of the effects they produce when recounting the event of Jesus’ resurrection; second, using the dogmatic and systematic ideas of Karl Barth and Wolfhart Pannenberg, to explore the possible conceptual structure and substance apposite to a theological understanding of testimony. Accordingly, the argument put forward in this thesis is twofold. First, philosophies of witness tend to establish the existence of witness around the natural human capacity of memory, imagination and reflection. Divine agency in the constitution and continuous operation of witness is consistently missing from these models. Their infiltration into biblical studies and theology has resulted in a failure to generate a stable and perspicuous theological meaning of Jesus’ resurrection, and has brought about a circumvention of the event’s historicity. Second, Barth’s theological construal of testimony, in contrast to Pannenberg and the philosophical models sampled in this study, lays stress on the self-witness of the triune God as the ontological ground of human testimony. This ontology is repeatedly underscored by Barth as he explicates the reality, history and transmission of Christian witness. A theological understanding of Christian witness must begin with the selftestimony and agency of God, in contrast to an understanding that pitches testimony as an independent species of epistemology.

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