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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.
1

Methods for reliability based design optimization of structural components

Dersjö, Tomas January 2012 (has links)
Cost and quality are key properties of a product, possibly even the two most important. Onedefinition of quality is fitness for purpose. Load-bearing products, i.e. structural components,loose their fitness for purpose if they fail. Thus, the ability to withstand failure is a fundamentalmeasure of quality for structural components. Reliability based design optimization(RBDO) is an approach for development of structural components which aims to minimizethe cost while constraining the probability of failure. However, the computational effort ofan RBDO applied to large-scale engineering problems has prohibited it from employment inindustrial applications. This thesis presents methods for computationally efficient RBDO.A review of the work presented on RBDO algorithms reveals that three constituentsof an RBDO algorithm has rendered significant attention; i ) the solution strategy for andnumerical treatment of the probabilistic constraints, ii ) the surrogate model, and iii) theexperiment design. A surrogate model is ”a model of a model”, i.e. a computationally cheapapproximation of a physics-based but computationally expensive computer model. It is fittedto responses from the physics-motivated model obtained via a thought-through combinationof experiments called an experiment design.In Paper A, the general algorithm for RBDO employed in this work, including the sequentialapproximation procedure used to treat the probabilistic constraints, is laid out. A singleconstraint approximation point (CAP) is used to save computational effort with acceptablelosses in accuracy. The approach is used to optimize a truck component and incorporatesthe effect that production related design variables like machining and shot peening have onfatigue life.The focus in Paper B is on experiment design. An algorithm employed to construct anovel experiment design for problems with multiple constraints is presented. It is based onan initial screening and uses the specific problem structure to combine one-factor-at-a-timeexperiments to a several-factors-at-a-time experiment design which reduces computationaleffort.In Paper C, a surrogate model tailored for RBDO is introduced. It is motivated by appliedsolid mechanics considerations and the use of the first order reliability method to evaluate theprobabilistic constraint. An optimal CAP is furthermore deduced from the surrogate model.In Paper D, the paradigm to use sets of experiments rather than one experiment at atime is challenged. A new procedure called experiments on demand (EoD) is presented. TheEoD procedure utilizes the core of RBDO to quantify the demand for new experiments andaugments it by a D-optimality criterion for added robustness and numerical stability. / QC 20120229
2

Approximate interval estimates for mechanical reliability

Yang, Wen-Huei. January 1990 (has links) (PDF)
Thesis (M.S. in Operations Research)--Naval Postgraduate School, September 1990. / Thesis Advisor(s): Woods, W.M. Second Reader: Bailey, Michael. "September 1990." Description based on title screen as viewed on December 15, 2009. DTIC Identifier(s): Intervals, Estimates, Parametric Analysis. Author(s) subject terms: Reliability, Confidence Limit, Parametric, Normal, Unknown Means and Variances. Includes bibliographical references (p. 53-54). Also available in print.
3

Reliability the life cycle driver : an examination of reliability management culture and practices /

Masiello, Gregory L. January 2002 (has links) (PDF)
Thesis (M.S.)--Naval Postgraduate School, 2002. / Thesis advisor(s): Donald R. Eaton, Lee Edwards. Includes bibliographical references (p. 101-104). Also available online.
4

Reliability analysis of the 4.5 roller bearing /

Muller, Cole. January 2003 (has links) (PDF)
Thesis (M.S. in Applied Science (Operations Research))--Naval Postgraduate School, June 2003. / Thesis advisor(s): David H. Olwell, Samuel E. Buttrey. Includes bibliographical references (p. 65). Also available online.
5

A univariate decomposition method for higher-order reliability analysis and design optimization

Wei, Dong. January 2006 (has links)
Thesis (Ph.D.)--University of Iowa, 2006. / Supervisor: Sharif Rahman. Includes bibliographical references (leaves 221-230).
6

Customer-centered reliability measures for flexible multistate reliability models /

Brunelle, Russell Dedric. January 1998 (has links)
Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographical references (p. [133]-162).
7

System dependability analysis and evaluation /

Yang, Joseph Sang-chin. January 1994 (has links)
Report (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Abstract. Includes bibliographical references (leaves 82-89). Also available via the Internet.
8

An application of fault tree analysis to operational testing

Rankin, Gordon Lee 08 1900 (has links)
No description available.
9

Negative bias temperature instability (NBTI) experiment

Schuster, Christopher Mark. 06 1900 (has links)
The phenomenon known as Negative Bias Temperature Instability (NBTI) impacts the operational characteristics of Complementary Metal Oxide Semiconductor (CMOS) devices, and tends to have a stronger effect on p-channel devices. This instability is observed with an applied "on" biasing during normal operation and can be accelerated with thermal stress. A normal applied electrical bias on CMOS transistors can lead to the generation of interface states at the junction of the gate oxide and the transistor channel. The hydrogen that normally passivates the interface states can diffuse away from the interface. As a result, the threshold voltage and transconductance will change. These interface states can be measured to determine the susceptibility to NBTI of the devices. For this purpose, a charge pumping experiment and other On-the-Fly techniques at certain temperatures can provide the interface state density and other valuable data. NBTI can impact current technological fabrication processes, such as those provided to the government from IBM. This paper explains this testing of current submicron transistor technology that will be used for military applications. / US Navy (USN) author.
10

Reliability of an electric motor system

Tang, Chao ran 27 August 2012 (has links)
M. Ing. / The design of electric motor systems as we know it today, is very important and has a direct influence on the reliability of the system. In this dissertation, recommendations in design are given to obtain a reliable electric motor system. This dissertation covers a literature review of reliability engineering, and this is then applied to an electric motor system in order to determine the reliability of the system. This dissertation is divided into five parts: Problem definition, theory and literature survey, economics of reliability engineering, analysis and synthesis of an electrical motor system, conclusions and recommendations. Part I describes the environment of an electric motor system and presents some fundamental concepts of reliability engineering. It emphasizes the importance of reliability analysis in the design of electric motor systems. Part II describes some theory and literature about reliability. It emphasizes some existing reliability analysis methods for development of electric motor systems. The reliability prediction method is very useful for analysis of electric motor systems. The author emphasizes that economics of reliability engineering should be taken into account in the design process in Part III. The analysis of life cycle costs is very important. Life cycle costs (LCC) usually consist of the initial investment, preventive maintenance costs, repair costs and the costs for production losses and outages due to failures and disturbances. Life cycle costing methodology is useful in analyzing the design, reliability and maintenance during trade off of technical systems and equipments. Part IV focuses a specific electric motor system. Some existing reliability analysis methods are used to analyse reliability of electric motor systems. It is highlighted how to improve the reliability of electric motor systems. Some economics considerations are also presented in this section. The main conclusion reached in this dissertation is that failure data feedback, and accurate records are very important for reliability engineering. The author makes some recommendations for reliability of an electric motor system in design. This dissertation may contain direct information from sources indicated generally by. This is however generally contextualized within the main aim of the research. This is the result of specific communication obstacles.

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