Dissertations / Theses on the topic 'Reductive failure'
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1
Kitto, Kirsty, and Kirsty Kitto@flinders edu au. "Modelling and Generating Complex Emergent Behaviour." Flinders University. School of Chemistry, Physics and Earth Sciences, 2006. http://catalogue.flinders.edu.au./local/adt/public/adt-SFU20060626.132947.
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Despite a general recognition of the importance of complex systems, there is a dearth of general models capable of describing their dynamics. This is attributed to a complexity scale; the models are attempting to describe systems at different parts of the scale and are hence not compatible. We require new models capable of describing complex behaviour at different points of the complexity scale. This work identifies, and proceeds to examine systems at the high end of the complexity scale, those which have not to date been well understood by our current modelling
methodology. It is shown that many such models exhibit what might be termed contextual dependency, and that it is precisely this feature which is not well understood by our current modelling methodology. A particular problem is
discussed; our apparent inability to generate systems which display high end complexity, exhibited by for example
the general failure of strong ALife. A new model, Process Physics, that has been developed at Flinders University is discussed, and arguments are presented that it exhibits high end complexity. The features of this model that
lead to its displaying such behaviour are discussed, and the generalisation of this model to a broader range of complex systems is attempted.
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Farrahi, Geeti. "Transition of Care Guideline for Reducing Heart Failure Hospital Readmission." ScholarWorks, 2018. https://scholarworks.waldenu.edu/dissertations/5331.
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Heart failure (HF) patients are among the populations with the highest rates of hospital readmission within 30 days of discharge. Because of the 2010 Health Care Reform legislation, healthcare organizations are subject to financial penalty when a patient population exhibits excess readmissions. A significant reason for readmission of HF patients is a gap in the transition of care from hospital to home. The purpose of this doctoral project was to develop a practice guideline of best practices for transitioning HF patients from hospital to home. The transitional care model and care transitions intervention provided the theoretical underpinnings for developing this project. The research question explored whether a transition-of-care guideline would reduce hospital readmission for the HF population. The methodology used to develop the clinical practice guideline was derived from a synthesis of scholarly literature and evidence-based transitional care quality initiatives. Seven interdisciplinary experts involved in HF transition of care used the Appraisal of Guidelines Research and Evaluation II instrument (AGREE II) to assess the development of the practice guideline. The scores of 6 AGREE II domains were summed and scaled to obtain a percentage of the maximum possible score for each domain. Scores showed that the clinical practice guideline was rigorous, high quality, effective in improving transition of care, and has the potential to reduce HF readmission. Positive social changes resulting from this practice guideline include an improvement in patient outcomes, a reduction in readmission rates, and a reduction in the associated financial burden to the hospital.
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Chen, Quan. "Risk Management of Cascading Failure in Composite Reliability of a Deregulated Power System with Microgrids." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/52980.
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Due to power system deregulations, transmission expansion not keeping up with the load growth, and higher frequency of natural hazards resulting from climate change, major blackouts are becoming more frequent and are spreading over larger regions, entailing higher losses and costs to the economy and the society of many countries in the world. Large-scale blackouts typically result from cascading failure originating from a local event, as typified by the 2003 U.S.-Canada blackout. Their mitigation in power system planning calls for the development of methods and algorithms that assess the risk of cascading failures due to relay over-tripping, short-circuits induced by overgrown vegetation, voltage sags, line and transformer overloading, transient instabilities, voltage collapse, to cite a few. How to control the economic losses of blackouts is gaining a lot of attention among power researchers.
In this research work, we develop new Monte Carlo methods and algorithms that assess and manage the risk of cascading failure in composite reliability of deregulated power systems. To reduce the large computational burden involved by the simulations, we make use of importance sampling techniques utilizing the Weibull distribution when modeling power generator outages. Another computing time reduction is achieved by applying importance sampling together with antithetic variates. It is shown that both methods noticeably reduce the number of samples that need to be investigated while maintaining the accuracy of the results at a desirable level.
With the advent of microgrids, the assessment of their benefits in power systems is becoming a prominent research topic. In this research work, we investigate their potential positive impact on power system reliability while performing an optimal coordination among three energy sources within microgrids, namely renewable energy conversion, energy storage and micro-turbine generation. This coordination is modeled when applying sequential Monte Carlo simulations, which seek the best placement and sizing of microgrids in composite reliability of a deregulated power system that minimize the risk of cascading failure leading to blackouts subject to fixed investment budget. The performance of the approach is evaluated on the Roy Billinton Test System (RBTS) and the IEEE Reliability Test System (RTS). Simulation results show that in both power systems, microgrids contribute to the improvement of system reliability and the decrease of the risk of cascading failure.Ph. D.
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Lyons, Kristopher Samuel. "Effect of HMG Co-A reductase inhibition on biological and ultrasound measures of endothelial function in human heart failure." Thesis, Queen's University Belfast, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602362.
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Heart failure (HF) is a clinical syndrome in which neurohormonal activation and cardiac remodelling occur in response to an index pathological event. Functional measures and biological markers of blood vessel function have been shown to be altered in HF, and abnormalities of microvascular function have been demonstrated in a variety of vascular beds. Treatment of HF involves medications which target abnormalities in the neurohormonal systems that regulate cardiovascular function, however the role of HMG Co-A reductase inhibitors (statins) in HF is unclear. Some observational and mechanistic studies have suggested benefit, however, results of prospective intervention trails have been disappointing. This thesis reports the vascular and biological abnormalities detectable in HF patients with systolic dysfunction compared to controls, and the vasular and biological effect of treatment with simvastatin in HF patients with systolic dysfunction. Treatment with simvastatin resulted in a significant reduction in Co Q IO levels in HF patients but not in coQ10ILDL ratio. There was a non-significant trend toward reduction in NT-proBNP levels. Other biomarkers studied were unchanged by treatment At baseline, differences between HF patients and controls were apparent in brachial artery flow mediated dilatation and doppler waveforms obtained from the retrobulbar circulation. No such differences were apparent in brachial artery waveforms. Treatment with simvastatin did not result in any change in doppler waveforms obtained from the retrobulbar circulation or brachial artery. Abnormalities in vascular function in HF are widespread and can be detected by novel wavelet analysis of doppler waveforms obtained from the retrobulbar circulation. 4 weeks of treatment with simvastatin did not produce improvements in measures of vascular function suggesting a lack of additional benefit over and above baseline treatment in this population at least over a short treatment period. Further research is required to see if longer periods of treatment may be effective .
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Sano, Takahiro. "Biomechanics of Fixation of Distal Radius Fractures: Comparison between Volar Plate Fixator (VPF) and Non-Bridging External Fixator (NBX)." Scholarly Repository, 2008. http://scholarlyrepository.miami.edu/oa_theses/121.
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Fracture of the distal radius is one of the most frequent injuries, and it represents about 20% of all adults taken into emergency rooms. A number of studies suggest various methods to reduce the dislocation and to secure fragments of the distal radius. In this study, the Non-Bridging External Wrist Fixator System (NBX), a pre-market-released product manufactured by NUTEK Inc. was biomechanically assessed by comparing with the Universal Distal Radius System (Volar Plate Fixator: VPF), a market-released product manufactured by Stryker Co. The comparison was performed in several parameters, which were wrist motion, radial tilt angle, radial length, volar tilt angle, stiffness, and failure load. Five pairs of fresh human cadaver arms were used for this study. The wrists were tested to obtain x-ray images for 1 normal and 2 injury conditions (intact, fractured, and fixed), 2 load conditions (gravity only and torque applied), and 4 postural conditions (volar flexion, dorsiflexion, ulnar deviation, and radial deviation). These tests yielded 24 (3×2×4) x-ray images for each wrist, and the images were analyzed to obtain the data for each parameter. Although the results were not statistically significant in some conditions, NBX fixation limited wrist motion more than VPF fixation. This result can be explained not only by the difference in the ability of fixation, but also by the difference in the surgical trauma (NBX is less invasive than VPF). Furthermore, in the measurement of radial tilt angle, radial length, and volar tilt angle, NBX was more effective than VPF to reduce and secure the bone fragments of the distal radius. In destructive test, the NBX is less strong than VPF. However, NBX is strong enough to sustain the expected forces of daily activity.
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Zhang, Di. "Analysis and Design of Paralleled Three-Phase Voltage Source Converters with Interleaving." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/27579.
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Three-phase voltage source converters(VSCs) have become the converter of choice in many ac medium and high power applications due to their many advantages, including low harmonics, high power factor, and high efficiency. Modular VSCs have also been a popular choice as building blocks to achieve even higher power, primarily through converter paralleling. In addition to high power ratings, paralleling converters can also provide system redundancy through the so-called (N+1) configuration for improved availability, as well as allow easy implementation of converter power management. Interleaving can further improve the benefit of paralleling VSCs by reducing system harmonic currents, which potentially can increase system power density. There are many challenges to implement interleaving in paralleled VSCs system due to the complicated relationships in a three-phase power converter system. In addition, to maximize the benefit of interleaving, current knowledge of symmetric interleaving is not enough. More insightful understanding of this PWM technology is necessary before implement interleaving in a real paralleled VSCs system.
In this dissertation, a systematic methodology to analyze and design a paralleled three-phase voltage source converters with interleaving is developed. All the analysis and proposed control methods are investigated with the goal of maximizing the benefit of interleaving based on system requirement.
The dissertation is divided into five sections. Firstly, a complete analysis studying the impact of interleaving on harmonic currents in ac and dc side passive components for paralleled VSCs is presented. The analysis performed considers the effects of modulation index, pulse-width-modulation (PWM) schemes, interleaving angle and displacement angle. Based on the analysis the method to optimize interleaving angle is proposed. Secondly, the control methods for the common mode (CM) circulating current of paralleled three-phase VSCs with discontinuous space-vector modulation (DPWM) and interleaving are proposed. With the control methods, DPWM and interleaving, which is a desirable combination, but not considered possible, can be implemented together. In addition, the total flux of integrated inter-phase inductor to limit circulating current can be minimized. Thirdly, a 15 kW three phase ac-dc rectifier is built with SiC devices. With the technologies presented in this dissertation, the specific power density can be pushed more than 2kW/lb. Fourthly, the converter system with low switching frequency is studied. Special issues such as beat phenomenon and system unbalance due to non-triplen carrier ratio is explained and solved by control methods. Other than that, an improved asymmetric space vector modulation is proposed, which can significantly reduce output current total harmonic distortion (THD) for single and interleaved VSCs system. Finally, the method to protect a system with paralleled VSCs under the occurrence of internal faults is studied. After the internal fault is detected and isolated, the paralleled VSCs system can continue work. So system reliability can be increased.Ph. D.
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Weiss, Dorothea. "PRIMUM NON NOCERE : Medicine's Culture of Dealing with and Denial of the Occurrence of Medical Harm." Thesis, Linköpings universitet, Centrum för tillämpad etik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-154396.
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The hippocratic principle "primum non nocere" (above all do no harm) has always been and still is the strong foundation of medical conduct. For a long time healthcare professionals created the image of infallibility of medicine. Even within the "closed" hierarchies mistakes and malpractice were never openly discussed. This paper first investigates reasons for medical mistakes and introduces the legislation when malpractice occurs. Secondly ethical questions concerning medical mistakes are discussed through the lens of Beauchamp and Childress' principles of biomedical ethics (nonmaleficence, beneficence, respect for autonomy, justice). Thirdly, an ethically defensible strategy to deal with failure and malpractice is proposed. This proposal stresses how to improve the patient-physician communication by involving patients' experiences in order to increase patient safety and lower costs in the healthcare system. In regard to tackling medical harm there is the strong recommendation to follow four directives: open disclosure and explanation, adequate restorative and/or compensatory actions, fair and square apologies and information about strategies to avoid recurrence.
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Bredin, Fredrik. "Passive volume reduction heart surgery using the Acorn cor cap cardiac support device /." Stockholm : Karolinska institutet, 2007. http://diss.kib.ki.se/2007/978-91-7357-284-2/.
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Hommerding, João Daniel. "Aplicação e comparação de metodologias de projetos em grupos para resolução de problemas." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2011. http://hdl.handle.net/10183/31408.
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Faz-se necessária, no ambiente industrial atual, a participação ativa dos colaboradores, proporcionando melhorias de processo / produto e correção de problemas. A utilização de metodologias de projetos em grupo para resolução de problemas, tais como os Círculos de Controle de Qualidade (CCQs), criados há mais de 40 anos, resulta na motivação dos colaboradores, por meio da melhoria do ambiente de trabalho e, consequentemente, de processos e de custo. Um dos objetivos deste estudo é verificar resultados que justifiquem, ou não, a continuidade da utilização do CCQ em uma empresa multinacional com unidade fabril no Brasil. Outro objetivo é comparar a metodologia CCQ com a metodologia Seis Sigma por meio da aplicação de um projeto piloto Seis Sigma nesta mesma empresa. Os resultados sugerem a continuidade do uso da metodologia CCQ na empresa analisada para resolução de problemas de baixa e média complexidades, com adoção de pequenas adequações fornecidas pela análise da metodologia Seis Sigma, além da adoção da metodologia Seis Sigma para condução de projetos de resolução de problemas complexos.It is necessary in the current industrial environment, the active participation of employees, providing improvements in product / process and problem correction. The use of methodologies of group projects to solve problems, such as QCC (Quality Control Circle), established over 40 years, results in employee motivation by improving the work environment and, consequently, processes and costs. One purpose of this study is to verify results that would justify, or not, the continuing of the use of the QCC in a multinational company with manufacturing unit in Brazil. Another purpose is to compare the QCC methodology with the Six Sigma methodology by implementing a Six Sigma pilot project in the same company. The results suggest the continuing use of the QCC methodology in the analyzed company to solve problems of low and intermediate complexity, with the adoption of small adjustments provided by the analysis of Six Sigma beyond the adoption of Six Sigma methodology to conduct projects to solve complex problems.
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Madonsela, Alex Thulani. "A structured approach for the reduction of mean time to repair of blast furnace D, ArcelorMittal, South Africa, Vanderbijlpark / Madonsela A.T." Thesis, North-West University, 2011. http://hdl.handle.net/10394/7311.
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Organizations are expected by their shareholders to continually deliver above
industry returns on capital invested and to remain competitive in the industry of
choice through productivity, safety and quality. The maintenance function is a key
area in which competitiveness through efficiencies and world–class performance can
be attained by focusing on the prevention and reduction of long and costly
equipment repair times.
The question is: how can the mean time to repair of equipment already installed in
the plant be reduced?
To answer the above question correctly and comprehensively, the research explored
mixed methods in finding answers. Quantitative methodology using a survey was
used for data collection. Observations and interviews were held with maintenance
personnel to uncover information that couldn’t have been obtained by means of a
survey.
The survey was limited to equipment performance measures, human factors,
environmental factors, planning, spare parts, maintainability, procedures and
training. To test consistency and accuracy of representation of the total population
under study, a reliability test was done by using Cronbach’s alpha coefficient. To
determine whether there are any differences between groups, an ANOVA test was
used. Cohen’s d–value was used to determine practically significant differences
between one set of data with another and correlation analysis was used to determine
the relationships between the variables.
The approach designed and delivered by this research flowed from the existing body
of knowledge, case studies and survey findings. The approach adopts some of the
elements of the failure mode and effects analysis (FMEA) procedure and differs from
other work that has been done by others by taking into account the competency and
experience of maintenance personnel and assigning to them factors which are used
to compute anew MTTR of the equipment. The cost of implementing the
recommended corrective actions for realising the new MTTR is determined and
evaluated against an improved equipment availability that will be achieved as a
result of the recommended corrective actions assuming that the failure rate of the
equipment remains constant. This evaluation step imbedded within the approach is
valuable for the maintenance function and management for decision making in
ensuring that resources at the organization’s disposal are used productively.
Validation and test results of the approach showed that the MTTR of equipment
installed in the plant can be reduced. The results also indicated that through the use
of the designed approach a regular pattern of repair or replacement times can be
followed well in advance and that it is practical, user friendly and it also delivers on
its objective of offering a structure for analysis and decision making aimed at
reducing the MTTR.
Included with this dissertation is feedback information that can be included in a
maintenance job card feedback section to capture information about factors that can
be improved to lower the MTTR as part of a continuous improvement process.
Included also is a spare part development and management procedure that can be
used by the maintenance function.
Recommendations on training of maintenance personnel on the maintainability of
equipment, the FMEA procedure and maintenance procedures are highlighted.
Information that flowed from this approach will be valuable for continuous plant
performance improvement and during the design, installation and operation stages of a blast furnace.Thesis (M.Ing. (Development and Management Engineering))--North-West University, Potchefstroom Campus, 2012.
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Silva, Flávia Costa da. "Percurso da noção de drogas: por uma problematização do proibicionismo." Universidade Federal de Santa Maria, 2010. http://repositorio.ufsm.br/handle/1/6932.
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This present work, inserted in the research line called formation, knowledge and professional development linked to the post graduation program in Education at the Santa Maria Federal University, aims to understand the conceptions about drugs among a group of academical
students who are in a period of training for teachers. The analysis is guided by the perspective of Michel Foucault about the conformation of the discursive and no discursive practices. Also is made a brief comment about the concept that permeates educational practices on drugs. With the
purpose of contributing for emergency of education practices founded in a no prohibitionist point of
view, was introduced the experience of harm reduction program on the municipal office of health in Santa Maria developed during the period between july 2002 and march 2009.A presente dissertação de mestrado está inserida na linha de pesquisa Formação, Saberes e Desenvolvimento Profissional do Programa de Pós-graduação em Educação da Universidade Federal de Santa Maria UFSM. Teve como objetivo compreender que concepções sobre drogas circulavam entre um grupo de estudantes universitários em formação docente. Os dados foram analisados a partir da perspectiva foucaultiana sobre a conformação das práticas discursivas ao não-discursivo. Também foi realizado um breve comentário sobre noções proibicionistas que permeiam as práticas educacionais sobre drogas. Com o propósito de contribuir para a emergência de práticas educacionais pautadas em pressupostos não proibicionistas do uso de drogas, foi apresentada a experiência do Programa de Redução de Danos da Secretaria Municipal de Saúde de Santa Maria/RS durante o período que compreende julho de 2002 a março de 2009.
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Li, Miaozhen. "Using an APN-Led Transitional Care Program to Reduce 30-Day Hospital Readmissions." ScholarWorks, 2017. https://scholarworks.waldenu.edu/dissertations/4005.
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Heart failure (HF) is a serious public health problem associated with high mortality rates, hospital readmissions, and health care costs. Transitional care has emerged as a disease management model used to reduce readmissions for hospital-discharged patients with HF. However, the efficacy of an advanced practice nurse (APN)-led transitional care program (TCP) in readmission reduction is under debate. The practice question for this project examined the extent to which an APN-led TCP was effective in reducing 30-day all-cause readmissions for hospital-discharged HF patients. The logic model was the framework guiding this program evaluation. An analysis of quality improvement HF data from September 2015 to August 2016 was reviewed for one hospital in southern California. The APN-led TCP included 47 patients and had 7 patients with 30-day readmissions. The physicians' group included 298 patients and had 53 patients with 30-day readmissions. The results of chi-square analysis revealed a nonsignificant association between 30-day readmissions and post-discharge care providers [Ï? 2 (1, N = 345) = 0.236, p = 0.627], and the HF 30-day readmission rates were the same between two groups. The APN-led TCP served a large proportion of Medi-Cal patients (48.94%) who had less primary care access, while the majority of patients in the physicians' group were Medicare (51%) who had primary care providers. This project highlights the positive social changes that advanced practice nurses affect via their critical leadership and clinical roles in increasing care access for the low-income population. Further studies on payer sources and readmissions are recommended on the efficacy of APN-led TCP in readmission reduction.
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Sánchez, Martínez Sergio. "Multi-feature machine learning analysis for an improved characterization of the cardiac mechanics." Doctoral thesis, Universitat Pompeu Fabra, 2018. http://hdl.handle.net/10803/663748.
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This thesis focuses on the development of machine learning tools to better characterize the cardiac anatomy and function in the context of heart failure, and in particular their extension to consider multiple parameters that help identifying the pathophysiological aspects underlying disease. This advanced and personalized characterization may eventually allow assigning patients to clinically-meaningful phenogroups with a uniform treatment response and/or disease prognosis. Specifically, the thesis copes with the technical difficulties that multivariate analyses imply, paying special attention to properly combine different descriptors that might be of different nature (e.g., patterns, continuous, or categorical variables) and to reduce the complexity of large amounts of data up to a meaningful representation. To this end, we implemented an unsupervised dimensionality reduction technique (Multiple Kernel Learning), which highlights the main characteristics of complex, high-dimensional data into fewer dimensions. For our computational analysis to be useful for the clinical community, it should remain fully interpretable. We made special emphasis in allowing the user to be aware of how the input to the learning process models the obtained output, through the use of multi-scale kernel regression techniques among others.Esta tesis se centra en el desarrollo de herramientas de aprendizaje automático para mejorar la caracterización de la anatomía y la función cardíaca en el contexto de insuficiencia cardíaca, y, en particular, su extensión para considerar múltiples parámetros que ayuden a identificar los aspectos pato-fisiológicos subyacentes a la enfermedad. Esta caracterización avanzada y personalizada podría en última instancia permitir asignar pacientes a fenogrupos clínicamente relevantes, que demuestren una respuesta uniforme a un determinado tratamiento, o un mismo pronóstico. Específicamente, esta tesis lidia con las dificultades técnicas que implican los análisis multi-variable, prestando especial atención a combinar de forma apropiada diferentes descriptores que pueden ser de diferente naturaleza (por ejemplo, patrones, o variables continuas o categóricas), y reducir la complejidad de grandes cantidades de datos mediante una representación significativa. Con este fin, implementamos una técnica no supervisada de reducción de dimensionalidad (Multiple Kernel Learning), que destaca las principales características de datos complejos y de alta dimensión utilizando un número reducido de dimensiones. Para que nuestro análisis computacional sea útil para la comunidad clínica debería ser enteramente interpretable. Por eso, hemos hecho especial hincapié en permitir que el usuario sea consciente de cómo los datos entrantes al algoritmo de aprendizaje modelan el resultado obtenido mediante el uso de técnicas de regresión kernel multi-escala, entre otras.
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Hsieh, I.-Ju, and 謝易儒. "Manifold-Learning Dimensionality Reduction for Business Failure Prediction." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/49046426209803885689.
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碩士嶺東科技大學
資訊管理與應用研究所
100
In this study, eight manifold learning methods are chosen to investigate to the effects of dimensionality reduction on performance of business failure classification. The sample in this study includes 884 Chinese companies listed in Shanghai or Shenzhen stock exchange market during 1996 to 2005, in which sample contains 268 financial distress companies and 616 health companies. The empirical results show that using different dimensionality reduction methods leads to a significant impact on performance of classification model. Among eight methods, the diffusion maps, stochastic proximity embedding and kernel principal component analysis methods reveal better performance on an average of 80%. Meanwhile, another three dimensionality reduction methods including isometric feature mapping, local linear embedding and Laplacian eigenmaps which are used frequently by machine learning researcher show poor performance of 59%-69%.
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楊振瀛. "LCD source driver IC testing:fault coverage improvement and early failure rate reduction." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/31327419960775416952.
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Kao, Kow-Chin, and 高國欽. "Optimal preventive maintenance policy for leased equipment by using failure rate reduction." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/86767373642832435763.
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博士國立臺灣科技大學
工業管理系
98
Due to rapid technological innovations, increased complexity of equipment, and the cost of professional technicians required maintaining equipment, it is not economical for manufacturers or businesses to own certain equipment. Therefore, there is a trend toward leasing instead of buying equipment and professional equipment leasing patterns emerged. The rights and obligations are bounded by a lease contract. The lessee (the manufacturer or business) shall have the obligation to afford the rent from the lessor (equipment owner) to obtain the right equipment for use. The leased equipment was bundled with maintenance and offered by the lessor in the leased contract. And, the lessor may incur a penalty when repair time exceeds a specified time limit. The lessor can employ preventive maintenance (PM) actions to reduce the number of possible failures to lower the repair and penalty cost within the lease period. This study proposes a maintenance scheme for leased equipment by using failure rate reduction method and rectifies failures with minimal repairs. Under the proposed maintenance scheme, the lessor incurs minimal repair costs, penalty costs and preventive maintenance costs. This study derives an optimal preventive maintenance (PM) policy that minimizes expected total cost in accordance with the maintenance scheme. An efficient algorithm is developed to derive the optimal PM policy and a closed-form solution is obtained for the case where the lifetime distribution of the equipment is Weibull. The proposed maintenance scheme is then compared with various failure rate reduction schemes through numerical examples to verify the performance of the optimal PM policy under the Weibull distribution.
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Kao, Kuang-Chuan, and 高廣權. "The Study of Aviation Gas Turbine Reduction Gearbox on Failure Investigation Analysis." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/26456556037199373889.
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碩士國立成功大學
工學院工程管理專班
97
The aircraft accident investigation or failure isolation has been studied for a long time. It is not only for issue of flight safety, but also a basis for aviation safety improvement. Some researchers argued that a majority proportion of causing accidents is due to the Human Factors, however, the mechanical related issue is also negligible for the flight safety. This thesis mainly focuses on the machinery malfunction of an aircraft gas turbine engine to analyze its root cause of flight accidents for future correction. The failure investigation adopts the gas turbine engine’s reduction gearbox malfunction to discuss and isolate the failure with a systematic way. In undertaking this complex problem, the Fishbone Diagram is used by collecting all the possible abnormal elements at the moment of a failure occurred and to analyze the preliminary findings. The Fishbone Diagram will then be transferred into the System Diagram accordingly. Working with the system operation of Fault Tree Analysis (FTA), it is able to evaluate all the listed possibilities to find out the relationship among each factor. The impact of each listed factor to a failure, however, is not equivalent. Thus, the experts of the engine maintenance will be consulted to evaluate the possibility of each fact to a failure. When the failure and root causes are shown in FTA, the Analytic Hierarchy Process (AHP) is used to evaluate the relative weight of each factor as a major evaluation method in the study. A questionnaire is also used to present the comments from the experts in this field. Besides, the Expert Choice program is used to calculate the relative weight of each factor. The result will indicate the relative possibility of each failure occurred. It is suggested that decision maker could correct these root causes in accordance with the highlighted items step by step. A benefit to improve will be achieved.
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Hsieh, Wen Jung, and 解文榮. "Periodical Preventive-Maintenance Policy for Leased Equipment using Fixed Failure Rate Reduction─Weibull Case." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/78864098563160622746.
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碩士國立臺灣科技大學
工業管理系
93
With intense competition among business, enterprises need to save capital expenditure. Equipment leasing will be an cost-effective method for high-cost equipment. The corrective and preventive maintenance for leased equipment is also outsourced to specialized maintenance firms. However, before leasing equipment, lessor and lessee must sign a lease contract to specify the privilege and obligation of both sides, which includes the ways of corrective and preventive maintenance of the equipment. In order to assist lessor to determine the terms of corrective and preventive maintenance of equipment after equipment leasing, this thesis develops a mathematical model to derive the optimal periodical preventive maintenance policy for leased equipment with Weibull life-time. Within a lease period, any equipment failures are rectified by minimal repair. To reduce equipment failures, additional preventive maintenance actions using fixed failure rate reduction method are carried out periodically during the lease period. The structural properties of the optimal policy are investigated, the optimal number of preventive maintenance actions and the corresponding maintenance degrees are jointly determined. Finally, the cost reduction by providing preventive maintenance is evaluated through numerical examples.
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Lee, Chia-chu, and 李家駒. "Optimal Number of Leased Periods and Maintenance Policy for Leased Equipment Using Failure Rate Reduction－Weibull Case." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/80332720489191960356.
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碩士國立臺灣科技大學
工業管理系
99
Due to professional services come of age, enterprises become only to put the resources into their core activities so that professional equipment leasing turn into a business trend. The rights and obligations are bounded by a lease contract. The rules of corrective and preventive maintenance are usually included in the lease contract and offered by the lesor, such as lessor must be responsible for repair of failure equipment and incurred a penalty cost to compensate for shutdown damage of lessee. Hence, lessor usually implements preventive maintenance actions to reduce the failure times of equipment as less as possible to reduce the penalty cost. Therefore, the choice between implementing preventive maintenance and incurring penalty is a key point of establishing lease contract and maintenance policy. This thesis constructs mathematical profit model for leased equipment with Weibull life-time by using failure rate reduction method and rectifies failures with minimal repairs and derives optimal maintenance policy and number of lease that maximize expected total profit.
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Chiu, Chuan-Wen, and 邱詮文. "Comparisons of Group and Individual Preventive Maintenance Policies for Two Leased Devices under Failure Rate Reduction Method." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/67ma3u.
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碩士國立臺灣科技大學
工業管理系
105
This thesis compares the performance of group and individual preventive maintenance policies for two leased devices. Failures are repaired by the lesser (the owner of the device) within the lease period and a penalty may occur to the lesser when the time required to perform a repair exceeds a tolerance limit. In order to reduce the total cost, the lesser may provide preventive maintenance service to reduce the number of failures. When the lesser provides preventive maintenance, the failure rate of the device can be reduced and it will also incur a setup cost and a maintenance cost. The failure of each device can be rectified by minimal repair and it occurs a cost of minimal repair. According to the above maintenance scheme, this thesis will construct the cost models of group and individual preventive maintenance policies. In addition, the numerical examples are given to illustrate the effect of each parameter on the optimal preventive maintenance policy.
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Chen, Yi-Jhong, and 陳逸仲. "The Optimal Maintenance Policy Proportion and Used Period for the Repairable Warranty Equipment Using Failure-Rate-Reduction Method." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/23560644649851459436.
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碩士華梵大學
工業工程與經營資訊學系碩士班
97
Following the change of the times, the quality and reliability of equipment for the demand of consumers have been promoted; the manufacture brings up the warranty period in order to meet the quality and reliability demand of equipment for consumer. They always considered the perfect preventive maintenance in the literature, but did not meet the practical needs and discuss the optimal used period after the warranty period. Therefore we define the time interval as warranty period and the time interval as the outside of warranty period. The manufacturers provide free preventive maintenance and repair policy when the equipment used in the warranty period; the cost was paid by consumer for the same degree of preventive maintenance, when the equipment was used in the outside of warranty period. In our study, the preventive maintenance caused the fixed failure rate reduction. Each implementation of preventive maintenance reduced the failure rate that there is the imperfect preventive maintenance of limited proportion. In our model the proportion of maintenance was divided into a fixed maintenance proportion and decreasing maintenance proportion. We obtained the optimal number of maintenance, the optimal proportion of maintenance degree and the cost of preventive maintenance for fixed maintenance proportion model, and the optimal number of maintenance, the optimal proportion of maintenance degree and the cost of preventive maintenance for decreasing maintenance proportion model. We also used the decision-making model to find the optimal number of preventive maintenance and the preventive maintenance cost for fixed maintenance proportion model, and the optimal number of preventive maintenance and the preventive maintenance cost for decreasing maintenance proportion model when the equipment is used in the outside of the warranty period. In the final, numerical and sensitivity analysis verify the results.
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LO, CHI-HSING, and 羅濟鑫. "A Study of the Failure Rate Reduction for Mechanical Car-Parking Systems－A Case of Multi-Circulating Type Device." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/ky2654.
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碩士國立臺灣科技大學
工業管理系
95
Faced with a time of decreasing profit margins, enterprises must now redirect their focus from “manufacturing” toward the higher value added areas of “research & development” and “marketing & service.” For sustainable operation, not only does the emerging industry of information science and technology need to make adjustments, but also the industry of traditional machine manufacturing. This research uses the case study method on a multi-circulating type device from a case company that manufactures mechanical car-parking systems. The failure rate of the multi-circulating type device after field operation for a long period of time is higher than a new device because of stepping into wear-out failure period, resulting in decreased customer satisfaction. Not only did the higher failure rate directly affect after-service quality but also resulted in the product receiving negative feedback from clients, in addition to influence to sales performance. Therefore, “reducing the failure rate” is the key factor in developing an effective solution for improving the company’s service performance and for enhancing the added value of their mechanical car-parking system after services. Maintenance-related data as well as related domestic and foreign literatures were collected to conduct a failure mode analysis on the multi-circulating type device. Results from the analysis suggest that simultaneously executing managerial “continuous improvement” and technical “organizational learning” would be the most effective solution in improving failure rate. Meanwhile, recording the variation of equipment failure rate and verifying with reliability theory is a practical way determines a suitable strategy for the enterprise. This strategy can then be applied to other products with similar characteristics.
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Mirhosseini, SomayehSadat. "The Effects of Nuclear Radiation on Aging Reinforced Concrete Structures in Nuclear Power Plants." Thesis, 2010. http://hdl.handle.net/10012/5452.
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In this thesis we look at one of the aging mechanisms that may have affected current aged Nuclear Power Plants (NPPs). Irradiation as an age-related degradation mechanism is studied for Reinforced Concrete (RC) in NPPs. This problem can be important for aged reactor buildings, radwaste buildings, spent nuclear fuel, research reactors, or accelerators that experience high levels of radiation close to existing thresholds. Mechanical properties of concrete are the most important parameters affected by radiation in NPPs. Compressive strength of concrete is reduced between 80 and 35 \% for radiation fluences between $2\times 10^{19}$ and $2\times 10^{21} n/cm^2$. Tensile strength reduction is more significant than compressive strength. It is reduced between 20 and 80 \% for a radiation fluence equal to $5\times 10^{19}$. We chose three radiation levels $2\times 10^{19}$, $2\times 10^{20}$, $2\times 10^{20}$ based on experimental results as the critical levels of radiation that RC structures in NPPs may be exposed to.
Structures susceptible to the problem are mostly RC walls; so the RC panel is chosen as an appropriate representative scale element for the analysis. The effect of radiation on mechanical properties of concrete is considered to analyze degraded scale elements. Material properties, geometry, and loading scenarios of scale elements are selected to be close to actual quantities in existing nuclear power plant. Elements are analyzed under six types of loading combination of shear and axial loading conditions. A nonlinear finite element program, Membrane-2000, based on the Modified Compression Field Theory (MCFT) is used to solve scale elements numerically. Element behaviors are studied considering the factors influence ultimate strength capacity, failure mode, and structural ductility index of members. The results show that ultimate shear capacity of the elements subjected to combinations of shear and tension loading are reduced significantly for highly reinforced elements ($1.35<\rho<1.88$) in $2\times 10^{21} n/cm^2$ radiation. RC panels under shear-biaxial and uniaxial compression also show significant strength capacity reduction in radiation levels $2\times 10^{20} n/cm^2$ and $2\times 10^{21} n/cm^2$, respectively. Failure modes of the elements change from yielding of steel to shear failure by increasing level of degradation for the elements with reinforcement ratio between 0.9 and 1.88. Ductility of the RC panels is reduced significantly in the critical levels of radiation. Ductility of the elements became less than the allowable ductility value by increasing level of radiation.
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Singh, Inderjeet 1978. "Risk-averse periodic preventive maintenance optimization." Thesis, 2011. http://hdl.handle.net/2152/ETD-UT-2011-08-4203.
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We consider a class of periodic preventive maintenance (PM) optimization problems, for a single piece of equipment that deteriorates with time or use, and can be repaired upon failure, through corrective maintenance (CM). We develop analytical and simulation-based optimization models that seek an optimal periodic PM policy, which minimizes the sum of the expected total cost of PMs and the risk-averse cost of CMs, over a finite planning horizon. In the simulation-based models, we assume that both types of maintenance actions are imperfect, whereas our analytical models consider imperfect PMs with minimal CMs. The effectiveness of maintenance actions is modeled using age reduction factors. For a repairable unit of equipment, its virtual age, and not its calendar age, determines the associated failure rate. Therefore, two sets of parameters, one describing the effectiveness of maintenance actions, and the other that defines the underlying failure rate of a piece of equipment, are critical to our models. Under a given maintenance policy, the two sets of parameters and a virtual-age-based age-reduction model, completely define the failure process of a piece of equipment. In practice, the true failure rate, and exact quality of the maintenance actions, cannot be determined, and are often estimated from the equipment failure history.
We use a Bayesian approach to parameter estimation, under which a random-walk-based Gibbs sampler provides posterior estimates for the parameters of interest. Our posterior estimates for a few datasets from the literature, are consistent with published results. Furthermore, our computational results successfully demonstrate that our Gibbs sampler is arguably the obvious choice over a general rejection sampling-based parameter estimation method, for this class of problems. We present a general simulation-based periodic PM optimization model, which uses the posterior estimates to simulate the number of operational equipment failures, under a given periodic PM policy. Optimal periodic PM policies, under the classical maximum likelihood (ML) and Bayesian estimates are obtained for a few datasets. Limitations of the ML approach are revealed for a dataset from the literature, in which the use of ML estimates of the parameters, in the maintenance optimization model, fails to capture a trivial optimal PM policy.
Finally, we introduce a single-stage and a two-stage formulation of the risk-averse periodic PM optimization model, with imperfect PMs and minimal CMs. Such models apply to a class of complex equipment with many parts, operational failures of which are addressed by replacing or repairing a few parts, thereby not affecting the failure rate of the equipment under consideration. For general values of PM age reduction factors, we provide sufficient conditions to establish the convexity of the first and second moments of the number of failures, and the risk-averse expected total maintenance cost, over a finite planning horizon. For increasing Weibull rates and a general class of increasing and convex failure rates, we show that these convexity results are independent of the PM age reduction factors. In general, the optimal periodic PM policy under the single-stage model is no better than the optimal two-stage policy. But if PMs are assumed perfect, then we establish that the single-stage and the two-stage optimization models are equivalent.text
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Mahlangu, Jethro Padya. "Guidelines for successful implementation of total productive maintenance in a chemical plant / Jethro Padya Mahlangu." Thesis, 2014. http://hdl.handle.net/10394/15382.
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With the world economy becoming unpredictable, it has become a necessity for businesses to relook at the way they do business. The world has become competitive and companies that aim to become profitable have seen the need to find ways to improve efficiencies and increase productivity to stay relevant. There has been an adoption of strategies that are aimed at improving the efficiencies in companies such as Total Productive Maintenance (TPM). The strategy is aimed at improving equipment efficiencies and increase productivity through the transfer of certain skills from maintenance personnel to operators. The aim is that the operators perform some of the activities that the maintenance people used to do and they do the more complex tasks. By transferring these skills to operators there is constant cleaning, inspections and lubricating of equipment. This frees up time for maintenance people to do planning and other jobs that require time and higher skills levels. The implementation of these activities allows companies to tap into unused capacity that was always hidden by breakdowns and unplanned stops. The process however requires commitment from management and all stakeholders involved in the organisation. There are prescribed implementation processes that can be followed or companies can follow their own processes but the fundamentals of involving people from the onset must be followed. The involvement of stakeholders creates commitment at all levels and in order to sustain this initiative people must be committed to it. The inclusion of the activities transferred from maintenance people to operators, will reinforce the knowledge and habits required from operators and perhaps sustain the initiative.MBA, North-West University, Potchefstroom Campus, 2015