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Comprehensive modeling of gas foil bearings (GFBs) anchored to reliable test data will enable the widespread usage of GFBs into novel turbomachinery applications, such as light weight business aircraft engines, hybrid fuel cell-turbine power systems, and micro-engines recharging battery packs for clean hybrid electric vehicles. Pressurized air is often needed to cool GFBs and to carry away heat conducted from a hot turbine in oil-free micro turbomachinery. Side end pressurization, however, demonstrates a profound effect on the rotordynamic performance of GFBs. This dissertation presents the first study that devotes considerable attention to the effect of side end pressurization on delaying the onset rotor speed of subsynchronous motions. GFB performance depends largely on the support elastic structure, i.e. a smooth foil on top of bump strips. The top foil on bump strips layers is modeled as a two dimensional (2D), finite element (FE) shell supported on axially distributed linear springs. The structural model is coupled to a unique model of the gas film governed by modified Reynolds equation with the evolution of gas flow circumferential velocity, a function of the side end pressure. Predicted direct stiffness and damping increase as the pressure raises, while the difference in cross-coupled stiffnesses, directly related to rotor-bearing system stability, decreases. Prediction also shows that side end pressurization delays the threshold speed of instability. Dynamic response measurements are conducted on a rigid rotor supported on GFBs. Rotor speed-up tests first demonstrate the beneficial effect of side end pressurization on delaying the onset speed of rotor subsynchronous motions. The test data are in agreement with predictions of threshold speed of instability and whirl frequency ratio, thus validating the model of GFBs with side end pressurization. Rotor speed coastdown tests at a low pressure of 0.35 bar evidence nearly uniform normalized rotor motion amplitudes and phase angles with small and moderately large imbalance masses, thus implying a linear rotor response behavior. A finite element rotordynamic model integrates the linearized GFB force coefficients to predict the synchronous responses of the test rotor. A comparison of predictions to test data demonstrates an excellent agreement and successfully validates the rotordynamic model.

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Pitch and heave are limiting motions when driving at high speed on water. The installation ofa T-foil is an effective solution that reduces these motions. Commercial T-foils are available,but today none of them are non-magnetic. This thesis studies the possibility to design anon-magnetic T-foil that can carry the considerable loads that such a constructionexperiences. The T-foil is designed for vessels such as the Visby Class corvette. Vortex lattice theory is used to calculate the pressure distribution acting on the construction atdifferent load cases. Required laminate thickness is determined by iteration using a linearfinite element model of the fin. The conclusion is that it is possible to manufacture a non-magnetic T-foil of the required size.A critical area in the construction is the T-joint between the vertical strut and the horizontalfoil. Future investigations should include laboratory tests of the T-joint as well as moredetailed hydrodynamic analysis for more accurate input parameters of the T-foil. / NR 20140804

The purpose of this work is to determine experimentally the depression of the neutron density by a detecting foil. The depression factor is known as the "self-shading" of the foil.

Apart from being a support, the three substrates had their own roles in the growth of CNTs. Bamboo charcoal also acted as a catalyst provider. Au-coated silicon wafer participated in the formation of the silica/CNT composite nanowires. Copper foil itself was a catalyst. The silicate, the Au/Si droplet, and the copper particles were the catalysts for the growth of CNTs in these three substrates, respectively. The formation of the CNTs followed the vapor-liquid-solid (VLS) route which involved the decomposition of ethanol vapor into carbon, carbon dissolution inside the liquid catalyst and precipitation to form CNTs. / CNTs could be grown in a very wide temperature range (700-1400°C), but specific substrate for a particular temperature range was needed. The structures of the CNTs varied with the CVD processing conditions. The forms and the amount of catalytic material entering the interior of the CNTs depended on the characteristics of the catalyst for that process / The products formed on different substrates had their own characteristic features . Hollow or silicate filled CNTs with silicate droplet tips were formed on the surface of bamboo charcoal. Their diameter was in hundreds of nanometers and the length was about several microns. CNT-coated silica core-shell structures were obtained on Au-coated silicon wafer. The graphitic carbon shell was formed in thickness about 145 nm for the sample prepared at 1185°C, but amorphous carbon shell was produced in thickness more than 300 nm for the sample prepared at 1236°e. Lastly, CNTs with bamboo-like structure were synthesized on the copper foil substrate. The CNTs were getting thicker from 70 nm to 170 nm when temperature was increased from 700°C to 1000°C. The yield increased with temperature and annealing time if the sample was annealed for less than 30 min. / We report the growth of carbon nanotubes (CNTs) on different types of substrates with or without catalytic materials by using different approaches. The roles of the substrates and the catalysts in the formation of the CNTs are studied . We also characterized and identified the structural properties of the CNTs products. In this work, three types of substrates had been used, namely biomorphic bamboo charcoal , Au-coated silicon wafer, and copper foil. The CNTs were grown on different substrates by chemical vapor deposition (CVD) method at temperature range between 700°C and 1400°C. Ethanol vapor was used as the carbon source, while tetraethyl orthosilicate (TEOS) vapor was also applied to the process for bamboo charcoal. / Zhu, Jiangtao = 碳納米管在不同類型基底上的生長 / 朱江濤. / Adviser: D. H. L. Ng. / Source: Dissertation Abstracts International, Volume: 72-11, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Zhu, Jiangtao = Tan na mi guan zai bu tong lei xing ji di shang de sheng chang / Zhu Jiangtao.

Continuous and pulse selective laser sintering and laser powder deposition were used to find a solution to the manufacturing of micro-foil lattice structured components. A full factorial test matrix was used for each process to determine the processes capability to produce continuous tracks for joining the micro-foil materials. The samples were evaluated for dimensional profiles, distortion, and cycle times, to develop selection criteria for implementation of the processes into industry. The selective laser sintering processes were able to join the micro-foil materials into lattice structures with continuous tracks. The laser powder deposition processes were not able to properly join the micro-foil materials into lattice structures. The end results showed that micro-foil lattice structures can be produced using continuous and pulse selective laser sintering.

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Compliant Air Foil Bearings are used in a wide variety of applications. The versatility, ease of manufacture, and low cost of foil bearings are a few of the reasons foil bearing have been so thoroughly researched. Miniaturization of gas foil bearings has been explored using silicon parts with marginal success. An approach utilizing a well known micro-fabrication technique called LIGA (German acronym meaning Lithography, Electroplating, and Molding) is suggested as an alternative method. X-ray LIGA and UV-LIGA were explored and elastic foundations 200?m and 1mm in depth were made for an impulse turbine test setup. The main difference in between the two methods is resolution and depth that each is capable of producing. In addition, precision machine forming was used to create a top foil for the foil bearing. The predicted performance of the bearing was investigated through the orbit simulation method. A parametric study based on preload, as well as loss factor, was conducted in which the rotor speed was varied and the responses were used to create cascade plots. Both the response and cascade plots are useful to determine the onset of instability and the maximum operating speed of the foil bearing manufactured through LIGA. The unique features of the gas foil bearing introduced provide great promise in terms of its application considering the high stable operating speed is just above 1000 krpm.