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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Die bonding of diode lasers /

Fritz, Mark A. Cassidy, Daniel Thomas. January 2004 (has links)
Thesis (Ph.D.)--McMaster University, 2004. / Advisor: Daniel T. Cassidy. Includes bibliographical references (p. 124-127).
42

Stitch weld effect on solar collector efficiency factor

Lo, Andy Ka-Ming January 1985 (has links)
The thermal effects of stitch welding the coolant conduits of a water-cooled flat plate solar collector to its absorber plate have been studied. A physical model of the heat transfer process from the plate to the fluid flowing inside the tube has been presented. The heat transfer coefficient based on the difference between bond temperature and fluid bulk mean temperature is an important factor in determining the collector efficiency factor F'. The upper and lower limits of the actual value of F' have been predicted by considering two extreme boundary conditions to which the fluid is subjected. For a thick and conductive tube wall, F' does not depend on spot size and spot spacing, and tends to an upper limit of 0.883. For a thin and non-conductive tube wall, the boundary condition comprises of a series of step changes in both the axial and circumferential directions of the heat flux. In this case, the heat transfer coefficient and hence F' approach their lower limits which are determined by the welding spot configuration. It was also found that F' increases with the following parameters: the spot angle; the percentage of tube length being welded; and the number of spots among which the welding is being distributed. Furthermore, the temperature distribution inside the fluid has also been computed for this case. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate
43

Elastohydrodynamic Analysis of a Rotary Lip Seal Using Flow Factors

Rocke, Ann H. 30 July 2004 (has links)
An elastohydrodynamic analysis of a rotary lip seal is performed numerically, incorporating both the fluid mechanics of the lubricating film and the elastic deformation of the lip, by solving the Reynolds equation with flow factors. Asperities on the lip surface dominate the behavior of the flow field in the lubricating film and the elastic deformation of the lip. Since previous analyses treated those asperities deterministically, they required very large computation times. The present approach is much less computationally intensive because the asperities are treated statistically. Since cavitation and asperity orientation play important roles, these are taken into account in the computation of the flow factors. An asperity distortion analysis is introduced to obtain a more realistic model of the complex variations in the asperity distribution on the surface of the seal. Results of the analysis show how the operating parameters of the seal and the characteristics of the asperities affect such seal characteristics as the thickness of the lubricating film, reverse pumping rate, power dissipation and load carrying capacity.
44

Multi-scale multi-physics model and hybrid computational framework for predicting dynamics of hydraulic rod seals

Thatte, Azam 25 October 2010 (has links)
Rod seals are one of the most critical components of hydraulic systems. However, the fundamental physics of seal behavior is still poorly understood and the seal designers have virtually no analytical tools with which to predict the behavior of potential seal designs. In pursuit of a comprehensive physics based seal analysis/ design tool, in this work, a multi-scale multi-physics (MSMP) seal model is developed. The model solves the transient problem involving macro-scale viscoelastic deformation mechanics, macro-scale contact, micro-scale two phase fluid mechanics in the sealing zone, micro-scale asperity contact mechanics and micro-scale deformation mechanics of the sealing edge in a strongly coupled manner. The model takes into account surface roughness, mixed lubrication, cavitation and two phase flow, transient squeeze film effects and the dynamic operation as well as the effect of macro/micro/nano scale viscoelasticity. A hybrid finite element-finite volume-statistical computational framework is developed to solve the highly coupled multi-physics interactions of the MSMP model simultaneously. Surface characterization experiments are performed to extract the parameters like RMS roughness, asperity density, autocorrelation length and asperity radius needed by MSMP. To remove the high frequency noise without removing the high frequency real surface features, a wavelet transform based adaptive surface extraction method is implemented. Dynamic mechanical analysis (DMA) is performed to extract the macro-scale viscoelastic parameters of the seal. Through atomic force microscopy (AFM) experiments, the local micro/nano scale elastic moduli were found to be varying within two orders of magnitude higher than the bulk of the polymer. Significant differences in local stiffness, adhesion and the relaxation time scales of individual surface asperities were also observed. With the MSMP model, dynamic seal performance was analyzed. The results confirmed the mixed lubrication and the effect of surface roughness. Thicker fluid films during instroke and cavitation during the outstroke were found to be important for non-leakage. Seal behavior was a function of the complex dual dependence on the time varying sealed pressure and hydrodynamic effects. Viscoelasticity is seen to critically affect the leakage and friction characteristics. It produces thicker fluid films and produces a significant increase in Poiseuille component of flow during instroke. Ignoring viscoelasticity leads to under-prediction of the time required to reach the zero leakage state. Several high pressure - high frequency sealing applications were analyzed. In such applications, a new phenomenon of "secondary contact" was observed. Viscoelastic creep was seen to critically affect the contact pressure and hence the friction characteristics. In high frequency applications, viscoelasticity induced significant differences in Poiseuille flow and friction force from cycle to cycle. Cycle frequency was seen to play an important role in governing visco-elastohydrodynamics and the leakage of such seals. The seals need to be designed by considering the relationship between relaxation time scales of the polymer and the cycle frequencies. Study also revealed the presence of characteristics like "critical temperature" and "critical frequency". Using the multi-physics modeling capability of MSMP framework, several novel seal designs using smart materials like piezo-ceramic embedded polymers are proposed and analyzed. The MSMP computational framework developed here has a great potential to be used as a stand-alone seal design and analysis software in academic and industrial research.
45

Advanced CMP processes for special substrates and for device manufacturing in MEMS applications /

Kulawski, Martin. January 1900 (has links) (PDF)
Thesis (doctoral)--VTT Micronova, 2006. / Includes bibliographical references. Also available on the World Wide Web.
46

Bond strength of cementitious borehole plugs in welded tuff.

Akgun, Haluk, 1959- January 1990 (has links)
This study includes a systematic investigation of the bond strength of cementitious borehole plugs in welded tuff. Analytical and numerical analysis of borehole plug-rock stress transfer mechanics is performed. The interface strength and deformation are studied as a function of Young's modulus ratio of plug and rock, plug length and rock cylinder outside-to-inside radius ratio. The tensile stresses in and near an axially loaded plug are analyzed. The frictional interface strength of an axially loaded borehole plug, the effect of axial stress and lateral external stress, and thermal effects are also analyzed. Implications for plug design are discussed. Push-out tests are used to determine the bond strength by applying an axial load to the cement plugs. A total of 130 push-out tests are performed as a function of borehole size, plug length, temperature, and degree of saturation of the tuff cylinder. The use of four different borehole radii enables evaluation of size effects. A well-defined exponential strength decrease with increasing plug diameter results.
47

A new generation of high temperature oxygen sensors

Spirig, John Vincent, January 2007 (has links)
Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 164-176).
48

Development of Model for Solid Oxide Fuel Cell Compressive Seals

Green, Christopher K. 14 November 2007 (has links)
Fuel cells represent a promising energy alternative to the traditional combustion of fossil fuels. In particular, solid oxide fuel cells (SOFCs) have been of interest due to their high energy densities and potential for stationary power applications. One of the key obstacles precluding the maturation and commercialization of planar SOFCs has been the absence of a robust sealant. A leakage computational model has been developed and refined in conjunction with leakage experiments and material characterization tests at Oak Ridge National Laboratory to predict leakage in a single interface metal-metal compressive seal assembly as well as multi-interface mica compressive seal assemblies. The composite model is applied as a predictive tool for assessing how certain parameters (i.e., temperature, applied compressive stress, surface finish, and elastic thermo physical properties) affect seal leakage rates.
49

Process Improvement of Surface Preparation of Structuraly Bonded Helicopter Detail Parts / Process Improvement of Surface Preparation of Structurally Bonded Helicopter Detail Parts

Tafoya, Keirsten Breann 12 1900 (has links)
The objective of this study was to increase the bond strength at the surface interface of a thin stainless-steel panel for structural bonding on a helicopter. To achieve this objective, six activation methods for applying the coating to the panel in the surface preparation process are presented and explored. Adhesion and roughness tests were conducted to determine which method consistently initiates the etch and improves the bond at the surface. Based on the test results, three methods proved to be effective in initiating the etch. Of the three effective methods, only one method exhibited significantly improved bond strength at the surface interface as well as consistently initiated the etch in solution. The applicability of this method is discussed, and recommendations are presented for further study.
50

Avaliação do desempenho acústico de um sistema de construção modular: estudo de caso

Ribeiro, Rodrigo Scoczynski 30 March 2015 (has links)
O objetivo deste trabalho é avaliar o desempenho acústico de um sistema construtivo modular e industrializado por meio do método simplificado de campo indicado pelas normas ABNT NBR 15575-4:2013 e ISO 10052:2004, analisando as vedações verticais internas e externas quanto ao isolamento ao ruído aéreo e as comparando com análises já realizadas em outras edificações de trabalhos conhecidos. A indústria de construção civil, em todo o mundo, encontra-se em um momento dedicado à busca e implementação de estratégias de modernização do setor, a fim de se reduzir os custos e minimizar os desperdícios, investido em construções sustentáveis. Há uma necessidade de estudos baseados nos parâmetros da norma NBR 15575-4:2013 para a devida caracterização das tecnologias construtivas que surgem e ainda são consideradas novidade para o setor. A norma implica em uma série de exigências e recomendações, como por exemplo, o conforto acústico, que será abordado nesse trabalho. A metodologia utilizada foi baseada no método simplificado orientado pela ISO 10052:2004. Foram analisadas duas edificações de 40,0m2 cada. Uma delas é um sobrado, e a outra uma casa térrea. Foram feitas as medições de níveis de pressão sonora nos cômodos e nas fachadas, e as medições do tempo de reverberação dos cômodos. Depois de realizadas as medições foram feitas as análises pelo teste “t” de student. Em comparação com os padrões de outros países, percebeu-se que a norma ABNT NBR 15.575-4:2013 possui valores brandos, e que mesmo assim, as atuais técnicas construtivas brasileiras, em sua maior parte, não conseguem atingi-los. Através dos resultados encontrados, percebeu-se uma eficiência quanto ao isolamento ao ruído aéreo nas edificações modulares e industrializadas quando comparados às edificações de outras técnicas construtivas. Conclui-se, então, que o sobrado e a edificação térrea estão de acordo com os níveis de desempenho estabelecidos pelo norma ABNT NBR 15.575-4:2013. / The objective of this study is evaluate the modular and industrialized building system’s acoustic performance through the simplified field method indicated by ABNT NBR 15575-4:2013 and ISO 10052: 2004, analyzing the internal and external vertical seals for air noise insulation and comparing with previous analyzes in other approaches. The world construction industry is in a dedicated time to the pursuit and implementation of sector modernization strategies in order to reduce costs and minimize waste, invested in sustainable buildings. It’s is necessary studies based on the parameters of NBR 15575-4: 2013 for the proper characterization of building technologies that emerge and are still new to the sector. The standard implies a series of requirements and recommendations, such as the acoustic comfort, which will be addressed in this work. The methodology used was based on the simplified method guided by ISO 10052: 2004. Two buildings were analyzed, with 40,0m2 each. One of them is a two-story house, and the other is a ground floor building. Measurements of sound pressure levels were made in the rooms and on the frontages, and measurements of the reverberation time of rooms. After the measurements were made analyzes with test "t" student. Compared to the standards of other countries, it was realized that the ABNT NBR 15575-4: 2013 has soft values, and that even so, the current Brazilian construction techniques, for the most part, can not reach them. Through these results, it was noticed an efficiency about the isolation airnoise in modular and industrialized buildings compared to buildings of other construction techniques. It follows, then, that the floor and the ground floor building comply with the performance levels established by ABNT NBR 15575-4: 2013.

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