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Tesi sul tema "Reliability of mechanical systems"
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1
Stephenson, John Antony. "Design for reliability in mechanical systems". Thesis, University of Cambridge, 1996. https://www.repository.cam.ac.uk/handle/1810/251589.
Testo completo
2
Zhao, Jian-Hua. "The reliability optimization of mechanical systems using metaheuristic approach". Mémoire, École de technologie supérieure, 2005. http://espace.etsmtl.ca/326/1/ZHAO_Jian%2DHua.pdf.
Testo completoAbstract (sommario):
Le problème d'optimisation de fiabilité des systèmes mécaniques est un problème compliqué avec contraintes multicritères, dont la solution optimale est en générale un compromis. Le travail présenté dans ce mémoire se concentre sur l'optimisation de fiabilité des systèmes mécaniques en séries parallèles. Basée sur le ACSRAP (Ant Colony System for Redundancy Apportionment Problem), une nouvelle approche est présentée. Cette approche combine les caractéristiques de l'ACS avec des recherches locales. Donc il optimise la fiabilité globale du système tout en satisfaisant les contraintes en terme de coût, de poids et de volume. Les avantages sur la précision, l'efficacité, et la capacité de la nouvelle approche sont illustrés par les résultats de comparaison de là nouvelle technique avec ceux obtenues par d'autres approches. En outre, l'application de la technique sur une boite de transmission (Gear Train System) est aussi présenté pour montrer les procédures de l'application de la nouvelle technique sur les cas réels.
3
Campean, Ioan Felician. "Product reliability analysis and prediction : applications to mechanical systems". Thesis, Bucks New University, 1998. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.714448.
Testo completo
4
Pu, Jun. "Reliability and availability analysis of three-state device systems". Thesis, University of Ottawa (Canada), 1996. http://hdl.handle.net/10393/10384.
Testo completoAbstract (sommario):
This study presents the reliability and availability analysis of three-state device systems with common-cause failures. The effect of common-cause failures on different systems is discussed. Different configurations are compared in order to obtain higher standby system reliability. Mathematical expressions are developed for the system reliability, the mean time to failure, the steady state availability and the time dependent availability of cold standby system, warm standby system, series system and parallel system. For system with constant common-cause failure rates, the Markov State Space approach is used to perform reliability analysis. The Method of Stages approach is used to investigate systems with non-constant common cause failure rates. Selected plots demonstrate the effect of the varying common cause failure rate on system reliability mean time to failure, steady state availability and time dependent availability. This study clearly shows that the occurrence of common-cause failure has a negative effect on standby system reliability parameters. However the system reliability, the mean time to failure, the steady state availability and the time dependent availability increase as the number of standby devices in the three-state device standby system increases.
5
Anude, Okezie. "The analysis of redundant reliability systems with common-cause failures". Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/6847.
Testo completoAbstract (sommario):
The reliability and income analyses of newly developed $k-out-of-(n + m):G$ (or $n, m, k$) type redundant systems subject to a combination of common-cause failures and independent failures are presented. The global goal was to evaluate the impacts of the standby activation policy and the system repair times on such relevant system performance indices as the reliability, long-run availability, mean time to failure, variance of time to failure and net income. To facilitate this investigation several possible repair policies are developed. Results obtained using typical and practical values of basic system variables indicate that the governing standby activation policy as well as the system repair time distribution affect profoundly the values of the afore-mentioned system performance indices. In addition, newly developed mathematical relationships that would enable the net incomes of $k-out-of-(n + m):G$ type systems to be maximized by the adoption of certain system repair rates are presented.
6
Burnham, Michael Richard. "Three competing risk problems in the study of mechanical systems reliability". Thesis, University of Strathclyde, 2010. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=16853.
Testo completoAbstract (sommario):
This thesis considers three problems within the eld of competing risks modelling in reliability. The rst problem concerns the question of identi ability within certain subclasses of Doyen and Gaudoin's recently proposed generalised competing risks framework. Bedford and Lindqvist have shown identi ability for one such subclass - a two component series system in which, every time a component fails it is restored to a state "as good as new", while the other component is restored to a state "as bad as old". In this thesis two different subclasses are shown to be identifiable. The first is a generalisation of the Bedford and Lindqvist example for series systems with n components. The second is an n component series system in which each time a component fails it is restored to a state "as good as new". At the same time the remaining components are restored to a state "as good as new" with probability p (which may depend on both the component being restored and the component that failed), or to a state "as bad as old" with probability (1 - p). The second problem concerns the use of competing risks models to study opportunistic maintenance. Bedford and Alkali proposed the following model - the system exhibits a sequence of warning signals, the inter-arrival times of which are assumed to be independently distributed (but non-identical) exponential random variables. The hazard rate of the time to system failure is modelled as a piecewise exponential distribution, in which the hazard rate is constant between signals. A sequence of maintenance opportunities occurs according to a homogeneous Poisson process and the rst opportunity after the kth signal is used to preventatively maintain the system. In this thesis closed form expressions for the above model are calculated (subject to some minor technical restrictions) for the marginal distributions of the time to both preventative and corrective maintenance. Also, the sub-distribution of the time to corrective maintenance is calculated. The third problem concerns the estimation of the marginal distribution for one of two independent competing risks, when knowledge of which risk caused the system shut-down is unknown for some of the observations in the dataset. In this thesis a new estimator based on the Kaplan-Meier product limit estimator is developed for the above set-up. A re-distribution to the right algorithm is also developed and this is shown to be equivalent to the new estimator. The new estimator is also shown to be consistent.
7
Crk, Vladimir 1958. "Component and system reliability assessment from degradation data". Diss., The University of Arizona, 1998. http://hdl.handle.net/10150/282820.
Testo completoAbstract (sommario):
Reliability estimation of highly reliable components, subsystems and systems has become very difficult using the traditional accelerated life tests. Therefore, there is a need to develop new models that will determine the reliability of such components, systems or subsystems, one of which is modeling a long term performance degradation. The proposed method is more general than any of the existing ones. It can be applied to any system, subsystem or component whose degradation over time can be identified and measured. It is assumed that the performance degradation is caused by a number, d, of independent degradation mechanisms and each of them is separately modeled by a unique nonlinear, monotonically increasing or decreasing curve as a function of time. The parameters of a degradation model are partitioned into a subset of parameters which are constant for all units and a subset of parameters that vary among units, or a subset of random parameters. To accelerate the degradation processes, random samples of identical units are exposed to stress levels which are higher than use stress levels. To capture the variability among units exposed to the same stress level, the parameters of the degradation model for each unit are estimated first and then the population parameters for a given stress level are estimated. The random parameters are assumed to be multivariate normally distributed, correlated and stress dependent. The multivariate multiple linear regression is applied to the stress dependent parameters and the parameter values at use stress levels are determined. Then, the times to failure are obtained from the degradation model for given degradation mechanisms by extrapolation to the critical level of degradation at which the system, subsystem, or component is considered to be in a failure state. Since the reliability function can not be obtained in a closed form the bootstrap simulation methodology is applied to estimate the system's reliability and the mean life for a single and multiple degradation mechanisms. Two algorithms are developed to obtain the point estimates and confidence intervals for the system's reliability and mean life.
8
Azarkhail, Mohammadreza. "Agent autonomy approach to physics-based reliability modeling of structures and mechanical systems". College Park, Md.: University of Maryland, 2007. http://hdl.handle.net/1903/7680.
Testo completoAbstract (sommario):
Thesis (Ph. D.) -- University of Maryland, College Park, 2007.Thesis research directed by: Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
9
Wei, Frank L. (Frank Lili) 1977. "Effects of mechanical properties on the reliability of Cu/low-k metallization systems". Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/42026.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (leaves 211-217).
Cu and low-dielectric-constant (k) metallization schemes are critical for improved performance of integrated circuits. However, low elastic moduli, a characteristic of the low-k materials, lead to significant reliability degradation in Cu-interconnects. A thorough understanding of the effects of mechanical properties on electromigration induced failures is required for accurate reliability assessments. During electromigration inside Cu-interconnects, a change in atomic concentration correlates with a change in stress through the effective bulk modulus of the materials system, B, which decreases as the moduli of low-k materials used as inter-level dielectrics (ILDs) decrease. This property is at the core of discussions on electromigration-induced failures by all mechanisms. B is computed using finite element modeling analyses, using experimentally determined mechanical properties of the individual constituents. Characterization techniques include nanoindentation, cantilever deflection, and pressurized membrane deflection for elastic properties measurements, and chevron-notched double-cantilever pull structures for adhesion measurements. The dominant diffusion path in Cu-interconnects is the interface between Cu and the capping layer, which is currently a Si3N4-based film. We performed experiments on Cu-interconnect segments to investigate the kinetics of electromigration. A steady resistance increase over time prior to open-circuit failure, a result of void growth, correlates with the electromigration drift velocity. Diffusive measurements made in this fashion are more fundamental than lifetime measurements alone, and correlate with the combined effects of the electron wind and the back stress forces during electromigration induced void growth.
(cont.)Using this method, the electromigration activation energy was determined to be 0.80±0.06eV. We conducted experiments using Cu-interconnects with different lengths to study line length effects. Although a reliability improvement is observed as the segment length decreases, there is no deterministic current-density line-length product, jL, for which all segments are immortal. This is because small, slit-like voids forming directly below vias will cause open-failures in Cu-interconnects. Therefore, the probabilistic jLcrit values obtained from via-above type nterconnects approximate the thresholds for void nucleation. The fact that jLcrit,nuc monotonically decreases with B results from an energy balance between the strain energy released and surface energy cost for void nucleation and the critical stress required for void nucleation is proportional to B. We also performed electromigration experiments using Cu/low-k interconnect trees to investigate the effects of active atomic sinks and reservoirs on interconnect reliability. In all cases, failures were due to void growth. Kinetic parameters were extracted to be ... Quantitative analysis demonstrates that the reliability of the failing segments is modulated by the evolution of stress in the whole interconnect tree. During this process, not only the diffusive parameters but also B play critical roles. However, as B decreases, the positive effects of reservoirs on reliability are diminished, while the negative effects of sinks on reliability are amplified.
(cont.) Through comprehensive failure analyses, we also successfully identified the mechanism of electromigration-induced extrusions in Cu/low-k interconnects to be nearmode-I interfacial fracture between the Si3N4-based capping layer and the metallization/ILD layer below. The critical stress required for extrusion is found to depend not only on B but also on the layout and dimensions of the interconnects. As B decreases, sparsely packed, wide interconnects are most prone to extrusion-induced failures. Altogether, this research accounts for the effects of mechanical properties on all mechanisms of failure due to electromigration. The results provide an improved experimental basis for accurate circuit-level, layout-specific reliability assessments.
by Frank LiLi Wei.
Ph.D.
10
Singh, Naveen Chandra Lall Pradeep. "Thermo-mechanical reliability models for life prediction of area array electronics in extreme environments". Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Spring/master's/SINGH_NAVEEN_54.pdf.
Testo completo
11
Er, Kim Hua. "Analysis of the reliability disparity and reliability growth analysis of a combat system using AMSAA extended reliability growth models". Thesis, Monterey, California. Naval Postgraduate School, 2005. http://hdl.handle.net/10945/1788.
Testo completoAbstract (sommario):
The first part of this thesis aims to identify and analyze what aspects of the MIL-HDBK-217 prediction model are causing the large variation between prediction and field reliability. The key findings of the literature research suggest that the main reason for the inaccuracy in prediction is because of the constant failure rate assumption used in MIL-HDBK-217 is usually not applicable. Secondly, even if the constant failure rate assumption is applicable, the disparity may still exist in the presence of design and quality related problems in new systems. A possible solution is to apply reliability growth testing (RGT) to new systems during the development phase in an attempt to remove these design deficiencies so that the system's reliability will grow and approach the predicted value. In view of the importance of RGT in minimizing the disparity, this thesis provides a detailed application of the AMSAA Extended Reliability Growth Models to the reliability growth analysis of a combat system. It shows how program managers can analyze test data using commercial software to estimate the system demonstrated reliability and the increased in reliability due to delayed fixes.
12
Abou, Jaoudé Abdo. "Advanced Analytical Model for the Prognostic of Industrial Systems Subject to Fatigue". Phd thesis, Aix-Marseille Université, 2012. http://tel.archives-ouvertes.fr/tel-00874624.
Testo completoAbstract (sommario):
This thesis is dedicated to the prognostic evaluation of dynamic systems. The work presented here aims at developing an advanced tool to treat the prognostic evaluation in linear and nonlinear deterministic context in a first part as well as in the stochastic context in a second part. Our purpose is to prepare a general prognostic tool that can be capable of well predicting the RUL of a system based on an analytical damage accumulation law in either a deterministic or a stochastic context.
13
Trille, Christophe. "Reliability analysis for subsea pipeline cathodic protection systems". Thesis, Cranfield University, 1996. http://dspace.lib.cranfield.ac.uk/handle/1826/12142.
Testo completoAbstract (sommario):
Subsea pipelines, as the main transportation means for oil and gas produced offshore, are a key element of the production system. Cathodic protection systems (CPS) are used in combination with surface coatings to protect the pipeline from external corrosion. Although cases of pipeline failure due to external corrosion remain rare, such failures can have catastrophic effects in terms of human lives, environment degradation and financial losses. The offshore industry was led to the use of risk analysis techniques subsequent to major disasters, such as Piper Alpha and Alexander Kjelland. These accidents made the development and use of risk analysis techniques of highly significant interest, and reliability analysis is presently becoming a more important management tool in that field for determining reliability of components such as pipelines, subsea valves and offshore structures. This research is based on an analysis of subsea pipeline cathodic protection systems and on a model of the electrochemical potentials at the pipeline surface. This potential model uses finite element modelling techniques, and integrates probabilistic modules for taking into account uncertainties on input parameters. Uncertainties are used to calculate standard deviations on the potential values. Based on the potentials and potential variances obtained, several parameters characteristic of the cathodic protection system reliability, such as probability of failure and time to failure, are calculated. The model developed proved suitable for simulating any pipeline, under any environmental and operational conditions. It was used as a reliability prediction tool, and to assess the effects of some parameters on the cathodic protection system reliability.
14
Becker, Kaitlyn P. (Kaitlyn Patricia). "Reliability of torque and temperature feedback for an autonomous glass monitoring system". Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/54197.
Testo completoAbstract (sommario):
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 30).
Automated pipe turners used in glassblowing studios are limited in their application by the duration a blown glass piece can be left unattended. An autonomous monitoring system can increase the usefulness of pipe turners in small studio and hobby settings, enabling glassblowers to work more independently. An initial feasibility study for an autonomous system has been performed by using two parameters, temperature measured by an IR thermometer and torque measured via the current drawn by a dc motor, to monitor glass blown objects during their production. The intended use of the system is for a glassblowing-pipe turning machine designed to keep a blown glass object centered about its axis of rotation and to keep the object heated within a set temperature range. Temperature data was collected with a handheld IR thermometer for static and rotating samples with varying color additives and optic qualities. Some variation and noise was present in the temperature data, but the results were consistent enough to be readily implemented in an automated monitoring system. Torque feedback was monitored by recording the variation in current drawn by a dc motor that was mounted in a drive system to turn a glassblowing pipe. When a pipe carrying a misaligned piece was inserted in the drive system the data showed a recognizable oscillation corresponding to the varying torque due to gravitational forces on the rotating blown glass piece. This confirms that using the current drawn by the motor as alignment feedback will be feasible in an autonomous pipe turner.
(cont.) This work can now be extended to modify the drive system that was used for testing to allow control of the axial position of the pipe and to integrate a digital micro controller which will be programmed to use the temperature and torque feedback to control the drive system.
by Kaitlyn P. Becker.
S.B.
15
Krishnan, Ganesh. "Thermo-mechanical reliability of ultra-thin low-loss system-on-package substrates". Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26474.
Testo completoAbstract (sommario):
Thesis (M. S.)--Materials Science and Engineering, Georgia Institute of Technology, 2009.Committee Chair: Tummala, Rao; Committee Member: Pucha, Raghuram V.; Committee Member: Wong, C.P. Part of the SMARTech Electronic Thesis and Dissertation Collection.
16
Warburton, Daren. "Development of a generic methodology for probabilistically predicting the reliability of offshore mechanical components at the design stage". Thesis, Cranfield University, 2000. http://dspace.lib.cranfield.ac.uk/handle/1826/11302.
Testo completoAbstract (sommario):
The continuously developing requirements of the offshore oil and gas Operators are placing more stringent demands on the designers to produce optimised solutions, with reduced development schedules, and application of new technologies for extreme environmental and operational conditions. The compounding uncertainty of service conditions and in the design capabilities is causing the designer to over-design, conduct extensive pre-service testing and introduce design redundancy. As such, designers have been forced to turn to reliability techniques in order to quantify the life of their designs. This has extended as far as needing to integrate reliability concepts, tools and methodologies into the design process. In recent times, the industry has attempted to apply conventional reliability tools within the design process, in terms of failure identification and reliability quantification. However, the use of historical reliability data has shown to be a particular downfall. As such, there has been a drive to predict the reliability of mechanical components based on their underlying degradation and failure processes and mechanisms. Consequently, this research is initially concerned with the development of a methodology, including an assessment of existing methods, that could be used to more readily understand the underlying failure characteristics of a mechanical component in terms of material, geometrical, environmental and operational characteristics. A particular underlying mechanism has been chosen and mathematical models were developed that simulate its physical behaviour and its degradation characteristics. Additionally, due to the potential uncertainty in the models and limited understanding of the characteristics of the underlying mechanism, the model was simulated within a probabilistic framework, fundamentally by application of the stress strength interference modelling approach. Finally, the model and its parameters were assessed to determine how uncertain governing parameters could appear to lead to variations in the reliability of the actuator.
17
Sundaramurthi, Ranjitprakash. "Human Reliability Modeling for Next Generation System Codes". The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1324411548.
Testo completo
18
Mitseas, Ioannis. "An efficient stochastic dynamics framework for response determination, reliability assessment, and performance-based design of nonlinear structural systems". Thesis, University of Liverpool, 2015. http://livrepository.liverpool.ac.uk/2010745/.
Testo completoAbstract (sommario):
An approximate analytical technique for determining the survival probability and first-passage probability density function (PDF) of nonlinear multi-degree-of-freedom (MDOF) structural systems subject to an evolutionary stochastic excitation vector is developed. The proposed technique can be construed as a two-stage approach. First, relying on statistical linearization and utilizing a dimension reduction approach the nonlinear n-degree-of-freedom system is decoupled and cast into (n) effective single-degree-of-freedom (SDOF) linear time-varying (LTV) oscillators corresponding to each and every DOF of the original MDOF system. Second, utilizing the effective SDOF LTV oscillator time-varying stiffness and damping elements in conjunction with a stochastic averaging treatment of the problem, the MDOF system survival probability and first-passage PDF are efficiently determined. Applications regarding MDOF structural systems exhibiting highly nonlinear behavior subject to stochastic excitations possessing separable as well as non-separable evolutionary power spectra (EPS) are included. Furthermore, a computationally efficient methodology for conducting fragility analysis of nonlinear/hysteretic MDOF structural systems is developed. Specifically, fragility surfaces are estimated for nonlinear/hysteretic MDOF structural systems subject to evolutionary stochastic earthquake excitations. An approximate nonlinear stochastic dynamics formulation which consist the core of the developed methodology, allows for the efficient computation of structural system fragilities in a straightforward manner while it keeps the computational cost for the corresponding analyses at a minimum level. Nonlinear MDOF structural systems exhibiting a hysteretic restoring force-displacement Bouc-Wen feature, serve as numerical examples for demonstrating the efficiency of the proposed methodology. Comparisons with pertinent Monte Carlo simulations are included as well demonstrating the satisfactory level of the exhibited accuracy. Appended to the above, a novel integrated approach for structural system optimal design considering life cycle cost (LCC) is developed. Specifically, a performance-based multi-objective design optimization framework for nonlinear/hysteretic MDOF structural systems subject to non-stationary stochastic excitations is formulated. The developed approach encompasses an efficient analytical nonlinear stochastic dynamics approach for the determination of the response EPS as well as the non-stationary inter-story drift ratio (IDR) amplitude PDFs, circumventing computationally intensive numerical integrations of the nonlinear equations of motion. It is notable that the proposed framework complies with the most contemporary performance-based earthquake engineering (PBEE) provisions proposed by the Pacific Earthquake Engineering Research (PEER) center. Although the herein developed framework is tailored specifically for earthquake engineering related applications, it can be readily modified to account for other hazard kinds as well. Nonlinear building structures comprising the versatile Bouc-Wen (hysteretic) model serve as numerical applications for demonstrating the efficiency of the developed methodology.
19
Hawbaker, Benjamin F. (Benjamin Forrest). "Analyzing the effects of component reliability on naval Integrated Power System quality of service". Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44844.
Testo completoAbstract (sommario):
Thesis (Nav. E.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and, (S.M.)--Massachusetts Institute of Technology, System Design and Management Program, 2008.Includes bibliographical references (leaves 66-68).
The Integrated Power System (IPS) is a key enabling technology for future naval vessels and their advanced weapon systems. While conventional warship designs utilize separate power systems for propulsion and shipboard electrical service, the IPS combines these functions. This allows greater optimization of engineering plant design and operations and leads to significant potential lifecycle cost savings through reduced fuel consumption and maintenance. Traditionally the focus of power system design has been survivability, with the assumption that service continuity was inherently provided. A new probabilistic metric, Quality of Service (QOS), now allows the power continuity and quality delivered to loads to be addressed explicitly during the design of IPS vessels. This metric is based both on the reliability of the power system components and the system architecture employed. This thesis describes and implements a method for modeling and evaluating the effects of component reliability on the QOS performance delivered by a current generation IPS architecture. First a representative "ship" is created, based largely on the U.S. Navy's ZUMWALT class destroyer (DDG-1000), including electrical loads, an operating profile, and Integrated Fight Through Power system architecture. This simulated ship is then run through a reliability analysis model employing Monte Carlo Simulation techniques to evaluate the QOS performance of the power system. By treating the reliability of power system components as a variable, the model gives insight into the role component reliability plays within the given system architecture. A method is then proposed for extending this analysis to comparative studies between future IPS architectures or components, with the ultimate goal of allowing research and development efforts to better focus precious funding and resources on areas with the greatest potential for high-value improvement.
by Benjamin F. Hawbaker.
S.M.
Nav.E.
20
O'Connor, Andrew N. "A general cause based methodology for analysis of dependent failures in system risk and reliability assessments". Thesis, University of Maryland, College Park, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3587283.
Testo completoAbstract (sommario):
Traditional parametric Common Cause Failure (CCF) models quantify the soft dependencies between component failures through the use of empirical ratio relationships. Furthermore CCF modeling has been essentially restricted to identical components in redundant formations. While this has been advantageous in allowing the prediction of system reliability with little or no data, it has been prohibitive in other applications such as modeling the characteristics of a system design or including the characteristics of failure when assessing the risk significance of a failure or degraded performance event (known as an event assessment).
This dissertation extends the traditional definition of CCF to model soft dependencies between like and non-like components. It does this through the explicit modeling of soft dependencies between systems (coupling factors) such as sharing a maintenance team or sharing a manufacturer. By modeling the soft dependencies explicitly these relationships can be individually quantified based on the specific design of the system and allows for more accurate event assessment given knowledge of the failure cause.
Since the most data informed model in use is the Alpha Factor Model (AFM), it has been used as the baseline for the proposed solutions. This dissertation analyzes the US Nuclear Regulatory Commission's Common Cause Failure Database event data to determine the suitability of the data and failure taxonomy for use in the proposed cause-based models. Recognizing that CCF events are characterized by full or partial presence of "root cause" and "coupling factor" a refined failure taxonomy is proposed which provides a direct link between the failure cause category and the coupling factors.
This dissertation proposes two CCF models (a) Partial Alpha Factor Model (PAFM) that accounts for the relevant coupling factors based on system design and provide event assessment with knowledge of the failure cause, and (b)General Dependency Model (GDM),which uses Bayesian Network to model the soft dependencies between components. This is done through the introduction of three parameters for each failure cause that relate to component fragility, failure cause rate, and failure cause propagation probability.
21
Trayhorn, Benjamin. "Power plant system reliability analysis : applications to insurance risk selection and pricing". Thesis, Cranfield University, 2012. http://dspace.lib.cranfield.ac.uk/handle/1826/7906.
Testo completoAbstract (sommario):
Within the Speciality Engineering Insurance Field the use of engineering opinion is the main component in risk analysis for underwriting decision making. The use of risk analysis tools to quantify the risk associated with perils such as mechanical breakdown is limited. A reliability model for the risk analysis of mechanical breakdown risk for the power generation sector, PowerRAT, has been developed and its performance evaluated against historic claim data. It has proven to closely forecast actual losses over a portfolio of power plants, and differentiate between power plant type; conventional steam, simple and combined cycle gas turbine plants. Differentiation based on the factors of equipment type and policy terms has been demonstrated. A review of existing survey report methodology has shown highly variable quality of reports with significant missing information on which to make underwriting decisions. A best practice survey report contents has been proposed in order to provide a consistent level of information for comparison with other risks. The development cycle of PowerRAT has led to a proposed framework for the development of future risk assessment tools for insurance. This is built on four main areas: risk identification, data analysis, calculation methodology and insurance factors.
22
Azad, Saeed. "Combined Design and Control Optimization of Stochastic Dynamic Systems". University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1602153122063302.
Testo completo
23
Basudhar, Anirban. "Computational Optimal Design and Uncertainty Quantification of Complex Systems Using Explicit Decision Boundaries". Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/201491.
Testo completoAbstract (sommario):
This dissertation presents a sampling-based method that can be used for uncertainty quantification and deterministic or probabilistic optimization. The objective is to simultaneously address several difficulties faced by classical techniques based on response values and their gradients. In particular, this research addresses issues with discontinuous and binary (pass or fail) responses, and multiple failure modes. All methods in this research are developed with the aim of addressing problems that have limited data due to high cost of computation or experiment, e.g. vehicle crashworthiness, fluid-structure interaction etc.The core idea of this research is to construct an explicit boundary separating allowable and unallowable behaviors, based on classification information of responses instead of their actual values. As a result, the proposed method is naturally suited to handle discontinuities and binary states. A machine learning technique referred to as support vector machines (SVMs) is used to construct the explicit boundaries. SVM boundaries can be highly nonlinear, which allows one to use a single SVM for representing multiple failure modes.One of the major concerns in the design and uncertainty quantification communities is to reduce computational costs. To address this issue, several adaptive sampling methods have been developed as part of this dissertation. Specific sampling methods have been developed for reliability assessment, deterministic optimization, and reliability-based design optimization. Adaptive sampling allows the construction of accurate SVMs with limited samples. However, like any approximation method, construction of SVM is subject to errors. A new method to quantify the prediction error of SVMs, based on probabilistic support vector machines (PSVMs) is also developed. It is used to provide a relatively conservative probability of failure to mitigate some of the adverse effects of an inaccurate SVM. In the context of reliability assessment, the proposed method is presented for uncertainties represented by random variables as well as spatially varying random fields.In order to validate the developed methods, analytical problems with known solutions are used. In addition, the approach is applied to some application problems, such as structural impact and tolerance optimization, to demonstrate its strengths in the context of discontinuous responses and multiple failure modes.
24
Ren, Xuchun. "Novel computational methods for stochastic design optimization of high-dimensional complex systems". Diss., University of Iowa, 2015. https://ir.uiowa.edu/etd/1738.
Testo completoAbstract (sommario):
The primary objective of this study is to develop new computational methods for robust design optimization (RDO) and reliability-based design optimization (RBDO) of high-dimensional, complex engineering systems. Four major research directions, all anchored in polynomial dimensional decomposition (PDD), have been defined to meet the objective. They involve: (1) development of new sensitivity analysis methods for RDO and RBDO; (2) development of novel optimization methods for solving RDO problems; (3) development of novel optimization methods for solving RBDO problems; and (4) development of a novel scheme and formulation to solve stochastic design optimization problems with both distributional and structural design parameters.
The major achievements are as follows. Firstly, three new computational methods were developed for calculating design sensitivities of statistical moments and reliability of high-dimensional complex systems subject to random inputs. The first method represents a novel integration of PDD of a multivariate stochastic response function and score functions, leading to analytical expressions of design sensitivities of the first two moments. The second and third methods, relevant to probability distribution or reliability analysis, exploit two distinct combinations built on PDD: the PDD-SPA method, entailing the saddlepoint approximation (SPA) and score functions; and the PDD-MCS method, utilizing the embedded Monte Carlo simulation (MCS) of the PDD approximation and score functions. For all three methods developed, both the statistical moments or failure probabilities and their design sensitivities are both determined concurrently from a single stochastic analysis or simulation. Secondly, four new methods were developed for RDO of complex engineering systems. The methods involve PDD of a high-dimensional stochastic response for statistical moment analysis, a novel integration of PDD and score functions for calculating the second-moment sensitivities with respect to the design variables, and standard gradient-based optimization algorithms. The methods, depending on how statistical moment and sensitivity analyses are dovetailed with an optimization algorithm, encompass direct, single-step, sequential, and multi-point single-step design processes. Thirdly, two new methods were developed for RBDO of complex engineering systems. The methods involve an adaptive-sparse polynomial dimensional decomposition (AS-PDD) of a high-dimensional stochastic response for reliability analysis, a novel integration of AS-PDD and score functions for calculating the sensitivities of the failure probability with respect to design variables, and standard gradient-based optimization algorithms, resulting in a multi-point, single-step design process. The two methods, depending on how the failure probability and its design sensitivities are evaluated, exploit two distinct combinations built on AS-PDD: the AS-PDD-SPA method, entailing SPA and score functions; and the AS-PDD-MCS method, utilizing the embedded MCS of the AS-PDD approximation and score functions. In addition, a new method, named as the augmented PDD method, was developed for RDO and RBDO subject to mixed design variables, comprising both distributional and structural design variables. The method comprises a new augmented PDD of a high-dimensional stochastic response for statistical moment and reliability analyses; an integration of the augmented PDD, score functions, and finite-difference approximation for calculating the sensitivities of the first two moments and the failure probability with respect to distributional and structural design variables; and standard gradient-based optimization algorithms, leading to a multi-point, single-step design process.
The innovative formulations of statistical moment and reliability analysis, design sensitivity analysis, and optimization algorithms have achieved not only highly accurate but also computationally efficient design solutions. Therefore, these new methods are capable of performing industrial-scale design optimization with numerous design variables.
25
Simon, Derek. "Static Balancing of the Cal Poly Wind Turbine Rotor". DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/837.
Testo completoAbstract (sommario):
The balancing of a wind turbine rotor is a crucial step affecting the machine’s performance, reliability, and safety, as it directly impacts the dynamic loads on the entire structure.
A rotor can be balanced either statically or dynamically. A method of rotor balancing was developed that achieves both the simplicity of static balancing and the accuracy of dynamic balancing. This method is best suited, but not limited, to hollow composite blades of any size. The method starts by quantifying the mass and center of gravity of each blade. A dynamic calculation is performed to determine the theoretical shaking force on the rotor shaft at the design operating speed. This force is converted to a net counterbalance mass required for each blade. Despite the most careful methodology, there may still be large errors associated with these measurements and calculations. Therefore, this new method includes a physical verification of each blade’s individual balance against all other blades on the rotor, with the ability to quantify the discrepancy between blades, and make all balance adjustments in situ. The balance weights are aluminum plugs of varying lengths inserted into the root of each blade with a threaded steel rod running through the middle. The balance adjustment is thus not visible from outside. The weight of the plug and rod represent the coarse counterbalance of each blade, based on the dynamic calculations. The threaded steel rod acts as a fine adjustment on the blades’ mass moment when traveled along the plug. A dedicated blade-balance apparatus, designed and constructed in-house, is used to verify and fine-tune each individual blade and compare it to all other blades on the rotor. The resulting blade assembly is verified on a full rotor static balancing apparatus. The full rotor apparatus measures the steady state tilt of the rotor when balanced on a point. Next, the rotors' tilt is related to its overall level of imbalance with quantifiable error. Most error comes from the fact that the hub, comparable in mass to the blades, creates a false righting moment of the assembly not present in operation. The fully assembled rotor is tested, pre and post balance, in operation on the turbine at a series of predetermined speeds. This is accomplished with a 3-axis accelerometer mounted on the main turbine shaft bearing and a control system which regulates and records turbine speed at 100 Hz
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Vasiliauskas, Gediminas. "Girdimosios informacijos kokybės triukšmingoje aplinkoje tyrimai". Master's thesis, Lithuanian Academic Libraries Network (LABT), 2009. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2008~D_20090114_155102-81586.
Testo completoAbstract (sommario):
Darbo apimtis 69 puslapiai, 14 lentelių, 26 paveikslai, panaudotas 31 literatūros šaltinis, 4 priedai. Darbo tikslas yra ištirti sistemos „žmogus-mašina-aplinka“ elementų informacinį patikimumą ir išsiaiškinti garsinių signalų sklidimo triukšminga aplinka trukdžius bei įvertinti garsinės informacijos tokioje aplinkoje, kokybę. Darbe nagrinėjamas sistemos „žmogus-mašina-aplinka“ informacinis patikimumas ir jo neatitiktys situacijai, sukeliančios nepaprastuosius įvykius. Literatūros apžvalgoje didelis dėmesys skiriamas girdimosios informacijos kokybės pokyčių analizei esant triukšmui, aptariama klausos apsaugos priemonių įtaka darbuotojo informaciniam komfortui. Teoriniuose tyrimuose daug dėmesio skiriama erdvinės girdos ir garso šaltinio lokalizacijos biologiniams aspektams, analizuojami garsinio signalo kokybinio vertinimo rodikliai. Tyrimų rezultatų analizė rodo jog didelę reikšmę informacijos sklidimui turi jos amplitudinė dažninė charakteristika, o žmogus gali iš aplinkos išskirti net tuos signalus, kurių kalbos interferencijos rodiklis (SIL) mažesnis už 5dBA. Taip pat nustatyta, jog informaciniai signalai informatyvūs, kai jų lygis vienoje iš 4 oktavinių juostų bent 5 dBA aukštesnis, o klausos apsaugos priemonių slopinimas ne didesnis kaip 20 dBA. Darbe gauti rezultatai gali būti panaudoti kaip priedas vertinant profesinę riziką darbo vietose.Work consists of 69 pages, 14 data tables, 26 illustrations, 4 attachments, 31 literature sources is used The purpose of this work is to investigate informational reliability of the “man-machine-environment” system and find out the difficulties of audible information spread in noisy environment and also estimate the quality of this information. „Man-machine-environment“system informational reliability is being analyzed in literature review section. An extensive attention intended for audible information quality in noise, influence of using hearing protectors also discussed. Finally spatial hearing and sound localization biological aspects reviewed, qualitative indexes of audible signal analyzed. Research analysis showed that significant account for audible information propagation has its amplitude frequentative characteristic but man can dissociate even these audible signals, of which speech interference level (SIL) is poor, or less than 5 dBA. Also determined that informational signals are informative when their level is at least 5 dBA higher in one of four octave bands and when hearing protector suppression is less than 20 dBA. Results can be used as extra information for professional risk assessment.
27
Gupta, Jatin. "Application of Hazard and Operability (HAZOP) Methodology to Safety-Related Scientific Software". The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1398983873.
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Vromans, Michiel Johannes Cornelius Maria. "Reliability of railway systems". [Rotterdam]: Erasmus Research Institute of Management (ERIM), Erasmus University Rotterdam ; Rotterdam : Erasmus University Rotterdam [Host], 2005. http://hdl.handle.net/1765/6773.
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29
Tarokh, M. J. "Systems reliability performance modelling". Thesis, University of Bradford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.715427.
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30
Hoang, Lan H. (Lan Hoang). "Improving mechanical reliability of integrated circuits". Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/41344.
Testo completo
31
Yang, Wen-Huei. "Approximate interval estimates for mechanical reliability". Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA241071.
Testo completoAbstract (sommario):
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.
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Lewin, Susanne. "Mechanical Reliability of Aged Lead-Free Solders". Thesis, KTH, Materialvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-98372.
Testo completoAbstract (sommario):
The usage of lead-free solder joints in electronic packaging is of greatest concern to the electronic industry due to the health and environmental hazards arising with the use of lead. As a consequence, lead is legally prohibited in the European Union and the industry is aiming to produce lead-free products. The reliability of solder joints is an important issue as the failure could destroy the whole function of a product. SnAgCu is a commonly used alloy for lead-free solders. Compared to solders containing lead, tin-rich solders react more rapidly with the copper substrate. The reaction results in formation of brittle intermetallic compounds and in poor mechanical reliability. The formation can be slowed down by the addition of nickel in the under bump metallization. In this project the objective was to evaluate the mechanical reliability of solder joints in high temperature applications. An alloy of nickel and phosphorus was plated on copper plates by electroless plating. The plates were joined together using SnAgCu solder. The samples were then thermally aged at 180°C for different durations (100, 200, 300, 400 and 500 hours). Tensile tests were performed on the samples. The result from the tensile test showed a decrease in mechanical strength with increasing aging duration. The fracture path shifted from being in the bulk solder to being at the interfaced.
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Cairns, Darran. "The mechanical reliability of silica optical fibres". Thesis, University of Birmingham, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395341.
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Adsul, Raveena Dnyaneshwar. "Reliability Assessment of Electro-mechanical Linear Actuator". Thesis, KTH, Skolan för industriell teknik och management (ITM), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-301632.
Testo completoAbstract (sommario):
Syftet med denna avhandling var att uppskatta livslängden och tillförlitligheten för det elektromekaniska linjära ställdonet genom att använda metoder för sannolikhet och statistik, med fokus på att fastställa svagare områden som kan förbättras för att inkludera dessa förbättringar i kommande generation. Bedömningen gjordes kvantitativt och kvalitativt. FMEA valdes för den kvalitativa analysen. För den kvantitativa analysen bedömdes Weibull-distribution vara den mest lämpliga för att skatta komponenternas felfrekvens. För detta valdes form- och skalparametrar enligt B. Bertsche. [1] Övergripande systemtillförlitlighet uppskattades utifrån den Boolean-teorin, där en känslighetsanalys utfördes med utgång från systemet fortsatta funktion. Det inkluderade utvärdering av komponenternas relativa betydelse för den övergripande tillförlitligheten, och att utföra känslighetsanalys med avseende på systemkomponenternas fördelningsparametrar. Baserat på den information som erhållits från kvalitativ och kvantitativ analys, erhölls underhållsaktiviteter för det elektromekaniska ställdonet under servicetiden. För att föreslå lämpliga tillförlitlighetstester var det nödvändigt att först fastställa storlek och testlängd för kommande prov. Flera testmetoder och respektive provstorleksuppskattning och urvalstester för testlängd studerades. Resultatet från FMEA ser totalt sett lovande ut. Det finns en möjlighet att några mindre fel uppstår i smörj-, kyl- och övervakningssystemet, som kan tas om hand genom att följa föreslagna underhållsaktiviteter. Ingen komponent sticker särskilt ut i tillförlitlighetsanalysen, med tanke på att säkerhetsfaktorerna för växlar överskrider minimigränsen och axlar som är konstruerade för oändlig livslängd. Individuellt verkar de utvalda lagren inte påverka det övergripande systemets tillförlitlighet. Men eftersom komponenterna anses vara i serie verkar den kombinerade tillförlitligheten hos lagren dominera hela systemets tillförlitlighet. Eftersom de tre fallstudierna genomförs för att förstå systemets beteende när det gäller tillförlitlighet, gäller ovanstående resultat för de två första fallstudierna där redskapen var säkra. I fallstudie tre påverkades systemets tillförlitlighet av både växlar och lager. Känslighetsanalysen följde samma mönster som det ses i tillförlitlighetsanalys. För fallstudie 1 och 2 - lager är signifikanta och i fallstudie 3 - rack och kugghjul 2 var mer signifikanta än lager. För tillförlitlighetsprovning har censureringsmetoder av Typ 1 och Typ 2 visat sig vara lämpliga. För uppskattning av testprov erhölls att generaliseringen av felmetoden med hjälp av Larsens nomogram var idealisk för tidiga förutsägelser.The purpose of this thesis was to estimate the life and reliability of an electromechanical linear actuator by using methods of probability and statistics. It was essential to determine weaker areas subject to improvement and include these improvements in the design to next generations. The assessment was carried out quantitatively and qualitatively. Failure mode effects analysis was the method opted for the qualitative analysis. For the quantitative analysis, Weibull distribution was found to be the most suitable to present the failure rate of components. For the same, the shape and scale parameters were selected as suggested by B. Bertsche. [1] Overall system reliability was estimated on the basis of Boolean theory. Sensitivity analysis was carried out by using survival signature method. It included evaluating the relative importance of the components with respect to overall reliability and carrying out sensitivity analysis with respect to the distribution parameters of the system components. Based on the information obtained from qualitative and quantitative analysis, maintenance activities were derived for the electro-mechanical actuator for the period of service time. To suggest the suitable reliability tests, it was necessary to first determine the test sample size and test duration. Several test methods and respective sample size estimation and test duration selection methods were studied. In performed failure mode and effects analysis, overall the system looks promising. There is a possibility of some minor possible failures to occur in lubrication, cooling and monitoring system, which could be taken care of by following suggested maintenance activities. No component in particular stand out in the reliability analysis, given that the safety factors of gears exceed the minimum limit and shafts designed for infinite lifetime. Individually the selected bearings seem to not affect the overall system’s reliability. However, since the components are considered to be in series, the combined reliability of the bearings seem to dominate the whole system’s reliability. As the three case studies are conducted to understand the system’s behaviour in terms of reliability, above result is applicable for the first two case studies where gears are found to be safe. In case of case study three, the system’s reliability is found to be affected by both gears and bearings. The results of sensitivity analysis followed the same pattern as reliability analysis. For case study 1 and 2 - bearings were significant and in case of case study 3 - rack and gear 2 were more significant than bearings. For reliability testing, Type 1 and Type 2 censoring methods both are found to be suitable. For test sample estimation, generalisation of failures method using Larsen’s nomogram was found ideal for early predictions.
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LEE, SEUNG JOO. "RELIABILITY-BASED OPTIMAL STRUCTURAL AND MECHANICAL DESIGN". Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184136.
Testo completoAbstract (sommario):
Structural reliability technology provides analytical tools for management of uncertainty in all relevant design factors in structural and mechanical systems. Generally, the goal of analysis is to compute probabilities of failure in structural components or system having single or multiple failure mode. Alternately, modern optimization methods provide efficient numerical algorithms for locating optima, particularly in large-scale systems having prescribed deterministic constraints. Optimization procedure can accommodate random variables either directly in its objective function or as one of the primary constraints. The combination of elementary optimization and probabilistic design techniques is the subject of this study. Presented herein is a general strategy for optimization when the design factors are random variables and some or all of the constraints are probability statements. A literature review has indicated that optimization technology in a reliability context has not been fully explored for the general case of nonlinear performance functions and nonnormal variates associated multiple failure modes. This research focuses upon development of the theory to address this general problem. Because analysis algorithms are complicated, a computer code, program RELOPT, is constructed to automate the analysis. The objective function to be minimized is arbitrary, but would generally be the total expected lifetime costs including all initial costs as well as all costs associated with failure. Uncertainty is assumed to be possible in all design factors (including the factors to be determined), and they are modeled as random variables. In general, all of the constraints can be probability statements. The generalized reduce gradient (GRG) method was used for optimization calculations. Options for point probability calculations are first order reliability analysis using the Rackwitz-Fiessler (R-F) or advanced reliability analysis using Wu/FPI. For system reliability analysis either the first order Cornell's bounds or the second order Ditlevsen's bounds can be specified. Several examples are presented to illustrate the full range of capabilities of RELOPT. The program is validated by checking with independent and exact solutions. An example is provided which demonstrates that the cost of running RELOPT can be substantial as the size of the problem increases.
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Mwanga, Alifas Yeko. "Reliability modelling of complex systems". Thesis, Pretoria : [s.n.], 2006. http://upetd.up.ac.za/thesis/available/etd-12142006-121528.
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Lenz, Malte, e Johan Rhodin. "Reliability calculations for complex systems". Thesis, Linköpings universitet, Reglerteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-69952.
Testo completoAbstract (sommario):
Functionality for efficient computation of properties of system lifetimes was developed, based on the Mathematica framework. The model of these systems consists of a system structure and the components independent lifetime distributions. The components are assumed to be non-repairable. In this work a very general implementation was created, allowing a large number of lifetime distributions from Mathematica for all the component distributions. All system structures with a monotone increasing structure function can be used. Special effort has been made to compute fast results when using the exponential distribution for component distributions. Standby systems have also been modeled in similar generality. Both warm and cold standby components are supported. During development, a large collection of examples were also used to test functionality and efficiency. A number of these examples are presented. The implementation was evaluated on large real world system examples, and was found to be efficient. New results are presented for standby systems, especially for the case of mixed warm and cold standby components.
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Cui, L. "Reliability analysis of repairable systems". Thesis, Swansea University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636331.
Testo completoAbstract (sommario):
In this thesis five repairable systems are considered for which the formulations of steady-state availability and downtime distribution are presented. The components in the reliability configurations, standby, series systems and R-out-of-N systems, are assumed identical. A finite number of spares, M, is available to install into the system to replace failed items and repair action returns the failed items to a good-as-new state. There is only one server who has to undertake both replacement and repair, the replacement action has priority over repair action. Throughout this thesis the replacement times and repair times are assumed to have general probability distributions. In chapter two, warm waiting is added; the working times of components and lifetimes of warm waiting spares are assumed to have exponential distributions. In chapters 3 and 5, the working times are also distributed exponentially. In chapters 4 and 6 the working system lifetimes are allowed to have general distributions. The stochastic models considered in this thesis are studied using the supplementary variable method. A lot of the equations can be solved by intuitive probabilistic arguments: this makes our results and their processes simple and beautiful. Numerical examples are shown in all chapters, except chapters one and seven. The calculations and simulation were done by using FORTRAN, and many subroutine programs come from the NAG software library.
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Toutounjee, Mohamad Mazhar. "The reliability of memory systems". Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47278.
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40
Terrier, Viktor. "North European Power Systems Reliability". Thesis, KTH, Elkraftteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-202581.
Testo completoAbstract (sommario):
The North European power system (Sweden, Finland, Norway, Denmark, Estonia, Latvia and Lithuania) is facing changes in its electricity production. The increasing share of intermittent power sources, such as wind power, makes the production less predictable. The decommissioning of large plants, for environmental or market reasons, leads to a decrease of production capacity while the demand can increase, which is detrimental to the power system reliability. Investments in interconnections and new power plants can be made to strengthen the system. Evaluating the reliability becomes essential to determine the investments that have to be made. For this purpose, a model of the power system is built. The power system is divided into areas, where the demand, interconnections between areas, and intermittent generation are represented by Cumulative Distribution Functions (CDF); while conventional generation plants follow a two-state behaviour. Imports from outside the system are set equal to their installed capacity, with considering that the neighbouring countries can always provide enough power. The model is set up by using only publicly available data. The model is used for generating numerous possible states of the system in a Monte Carlo simulation, to estimate two reliability indices: the risk (LOLP) and the size (EPNS) of a power deficit. As a power deficit is a rare event, an excessively large number of samples is required to estimate the reliability of the system with a sufficient confidence level. Hence, a pre-simulation, called importance sampling, is run beforehand in order to improve the efficiency of the simulation. Four simulations are run on the colder months (January, February, March, November, December) to test the reliability of the current system (2015) and of three future scenarios (2020, 2025 and 2030). The tests point out that the current weakest areas (Finland and Southern Sweden) are also the ones that will face nuclear decommissioning in years to come, and highlight that the investments in interconnections and wind power considered in the scenarios are not sufficient to maintain the current reliability levels. If today’s reliability levels are considered necessary, then possible solutions include more flexible demand, higher production and/or more interconnections.Det nordeuropeiska elsystemet (Sverige, Finland, Norge, Danmark, Estland, Lettland och Litauen) står inför förändringar i sin elproduktion. Den ökande andelen intermittenta kraftkällor, såsom vindkraft, gör produktionen mindre förutsägbar. Avvecklingen av stora anläggningar, av miljö- eller marknadsskäl, leder till en minskning av produktionskapaciteten, medan efterfrågan kan öka, vilket är till nackdel för kraftsystemets tillförlitlighet. Investeringar i sammankopplingar och i nya kraftverk kan göras för att stärka systemet. Utvärdering av tillförlitligheten blir nödvändigt för att bestämma vilka investeringar som behövs. För detta ändamål byggs en modell av kraftsystemet. Kraftsystemet är uppdelat i områden, där efterfrågan, sammankopplingar mellan områden, och intermittent produktion representeras av fördelningsfunktioner; medan konventionella kraftverk antas ha ett två-tillståndsbeteende. Import från länder utanför systemet antas lika med deras installerade kapaciteter, med tanke på att grannländerna alltid kan ge tillräckligt med ström. Modellen bygger på allmänt tillgängliga uppgifter. Modellen används för att generera ett stort antal möjliga tillstånd av systemet i en Monte Carlo-simulering för att uppskatta två tillförlitlighetsindex: risken (LOLP) och storleken (EPNS) av en effektbrist. Eftersom effektbrist är en sällsynt händelse, krävs ett mycket stort antal tester av olika tillstånd i systemet för att uppskatta tillförlitligheten med en tillräcklig konfidensnivå. Därför utnyttjas en för-simulering, kallad ”Importance Sampling”, vilken körs i förväg i syfte att förbättra effektiviteten i simuleringen. Fyra simuleringar körs för de kallare månaderna (januari, februari, mars, november, december) för att testa tillförlitligheten i nuvarande systemet (2015) samt för tre framtidsscenarier (2020, 2025 och 2030). Testerna visar att de nuvarande svagaste områdena (Finland och södra Sverige) också är de som kommer att ställas inför en kärnkraftsavveckling under de kommande åren. De indikerar även att planerade investeringar i sammankopplingar och vindkraft i scenarierna inte är tillräckliga för att bibehålla de nuvarande tillförlitlighetsnivåerna. Om dagens tillförlitlighetsnivåer antas nödvändiga, så inkluderar möjliga lösningar mer flexibel efterfrågan, ökad produktion och/eller fler sammankopplingar.
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Lau, Siu Lik. "Reliability of optical crossconnect systems /". View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202004%20LAUS.
Testo completoAbstract (sommario):
Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.Includes bibliographical references (leaves 73-76). Also available in electronic version. Access restricted to campus users.
42
La, Band Rachel A. "Systems reliability for phased missions". Thesis, Loughborough University, 2005. https://dspace.lboro.ac.uk/2134/34438.
Testo completoAbstract (sommario):
The concept of a phased mission has been introduced as a sequential set of objectives that operate over different time intervals. During each phase of the mission, the system may alter such that the logic model, system configuration, or system failure characteristics may change to accomplish a required objective. A new fault tree method has been proposed to enable the probability of failure in each phase to be determined in addition to the whole mission unreliability. Phase changes are assumed to be instantaneous, and component failure rates are assumed to be constant through the mission. For any phase, the method combines the causes of success of previous phases with the causes of failure for the phase being considered to allow both qualitative and quantitative analysis of both phase and mission failure. A new set of Boolean laws is introduced to combine component success and failure events through multiple phases so that the expression for each phase failure can be reduced into minimal form.
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Iacopino, G. "Reliability analysis of mechanical components containing random flaws". Thesis, Cranfield University, 2006. http://dspace.lib.cranfield.ac.uk/handle/1826/1787.
Testo completoAbstract (sommario):
The goal of structural reliability is to assure that a structure adequately performs its intended function when operating under specified environmental conditions. The major source of unreliability is the variability that characterizes engineering structures subjected to inherent randomness in material properties, loading and geometrical parameters. A sensible approach to structural reliability must be able to evaluate and control the effects of this variability, quantifying the uncertainties in the design variables and measuring their impact on the strength of the final product. The objective of this research is to assess the role that uncertainties in material microstructure, in particular concerning the presence of defects such as pores, inclusions and through-thickness cracks, have in the failure of engineering structures. For this purpose, a computational procedure, based on the coupled use of Finite Element Analysis and Monte Carlo simulation, is proposed to evaluate the failure probability of complex mechanical components containing random flaws. The proposed methodology is particularly suited for the structural design of ceramic components, whose strength properties are significantly affected by the presence of microstructural defects. Material flaws are modelled by a population of volume-embedded micro-cracks characterized by different geometrical features and size distributions. For each population the number of flaws is assumed to follow a homogenous Poisson process and flaws are sampled with a uniform spatial distribution and a random orientation. The interaction of a crack with the stress field produced in the component by the applied load is determined through a mixed-mode fracture criterion. Several solutions have been compared in this respect. The study conducted clearly shows how the application of a traditional deterministic approach may lead to incorrect conclusions. Due to the stochastic nature of the flaw distribution, failure of a component may not be initiated at the point of highest nominal stress. The whole component volume contributes to the total probability of failure and therefore the entire stress field must be considered. Moreover, the sensitivity analysis carried out indicates that the parameters controlling the failure process are strictly dependent on loading conditions. In particular, a significant difference in behaviour between uniform and non-uniform stress states was identified. A new failure criterion for brittle materials is also proposed. The criterion is based on the maximum admissible individual probability of failure and is applicable to biaxial stress conditions.
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Touzé, Patrick A. "Applications of fuzzy logic to mechanical reliability analysis". Thesis, Virginia Tech, 1993. http://hdl.handle.net/10919/41583.
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Touz'e, Patrick A. "Applications of fuzzy logic to mechanical reliability analysis /". This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-03142009-040345/.
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46
Jenab, Kouroush. "Stochastic and fuzzy analyses in reliability design". Thesis, University of Ottawa (Canada), 2005. http://hdl.handle.net/10393/29222.
Testo completoAbstract (sommario):
The risk analysis process involving information acquisition, modeling, analysis, and decision steps results in the product design improvement. To perform product risk assessment, this study addresses stochastic and fuzzy analyses in reliability design. Using decision-making techniques and the flow-graph concept, the main objective of this study is to develop analytical models with time varying input data, and/or fuzzy input data for reliability techniques. The models (i.e., Graph-based failure effects analysis, Group-based failure effects analysis, Imprecise-chance Markov chains, Fuzzy and stochastic fault tree analysis, Binary k-out-of-n system with self-loop units, Reversible multi-state k-out-of-n:G/F/Load sharing system, and Imprecise-chance reliability estimation) incorporate the stochastic self-healing mechanisms represented by self-loop graph, and/or conflict resolution approach. Stochastic models developed in this study compute Time-To-Event/State data made up of probability of the system failure, and mean and standard deviation of time to an event/state. To identify, prioritize and eliminate potential failures in the system, the fuzzy models presented in this study introduce aggregated/compensated approaches for mitigating conflict of input data. The applications of the stochastic and fuzzy models are demonstrated through practical examples. Using typical, practical, and extreme values of the basic parameters of the models and performing sensitivity analysis, the end results demonstrate the robustness of and conflict resolution capability of the models.
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Pennisi, Frank Joseph. "Design of a high reliability transport mechanism". Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/35982.
Testo completo
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Torng, Tony Yi. "Reliability analysis of maintained structural system vulnerable to fatigue and fracture". Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184955.
Testo completoAbstract (sommario):
Metallic structures dominated by tensile loads are vulnerable to fatigue and fracture. Fatigue is produced by oscillatory loads. Quasi-static brittle or ductile fracture can result from a "large" load in the random sequence. Moreover, a fatigue or fracture failure in a member of a redundant structure produces impulsive redistributed loads to the intact members. These transient loads could produce a sequence of failures resulting in progressive collapse of the system. Fatigue and fracture design factors are subject to considerable uncertainty. Therefore, a probabilistic approach, which includes a system reliability assessment, is appropriate for design purposes. But system reliability can be improved by a maintenance program of periodic inspection with repair and/or replacement of damaged members. However, a maintenance program can be expensive. The ultimate goal of the engineer is to specify a design, inspection, and repair strategy to minimize life cycle costs. The fatigue/fracture reliability and maintainability (FRM) process for redundant structure can be a complicated random process. The structural model considered series, parallel, and parallel/series systems of elements. Applied to the system are fatigue loads including mean stress, an extreme load, as well as impulsive loads in parallel member systems. The failure modes are fatigue, brittle and ductile fracture. A refined fatigue model is employed which includes both the crack initiation and propagation phases. The FRM process cannot be solved easily using recently developed advanced structural reliability techniques. A "hybrid" simulation method which combines modified importance sampling (MIS) with inflated stress extrapolation (ISE) is proposed. MIS and ISE methods are developed and demonstrated using numerous examples which include series, parallel and series/parallel systems. Not only reasonable estimates of the probability of system failure but also an estimate of the distribution of time to system failure can be obtained. The time to failure distribution can be used to estimate the reliability function, hazard function, conditional reliability given survival at any time, etc. The demonstration cases illustrate how reliability of a system having given material properties is influenced by the number of series and parallel elements, stress level, mean stress, and various inspection/repair policies.
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Mathiesen, Eric Martinus. "Component reliability database for weapons systems". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA280485.
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Malada, Awelani. "Stochastic reliability modelling for complex systems". Thesis, Pretoria : [s.n.], 2006. http://upetd.up.ac.za/thesis/available/etd-10182006-170927.
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